Publications

vasoactive intestinal polypeptide and non-adrenergic, non-cholinergic inhibition in lower oesophageal sphincter of opossum.	1. field stimulation or vasoactive intestinal polypeptide (vip) relaxed lower oesophageal sphincter (los) from north american opossum. pretreatment with carbachol in cl-ion-containing or cl-ion-free krebs solution or with 10(-3) m 9-aminoacridine abolished or markedly reduced relaxation due to vip applied exogenously but not that elicited by field stimulation of non-adrenergic, non-cholinergic nerves. 2. inhibitory junction potentials (7.5 +/- 1.2 mv, n = 5) could be recorded in los strips with ...	1989	2720302
developmental plasticity of the rubrospinal tract in the north american opossum.	we have shown previously that rubral axons can grow caudal to a lesion of their pathway at thoracic levels of the spinal cord in the developing opossum, didelphis virginiana. in the present report we expand on that observation and present evidence which suggests that the critical period for plasticity of the rubrospinal tract ends earlier at cervical than at thoracic levels. in addition, we show that most rubrospinal neurons die as a result of axotomy during early stages of the critical period. ...	1989	2465321
the cardiac, oxyntic and pyloric glands in the developing opossum (didelphis virginiana).	in the opossum the fundic area of the gastric mucosa develops first, and oxyntic glands show early division into gastric pits and glandular components which then grow simultaneously. at 40 d postnatum the oxyntic glands are longer than the gastric pits but in the pyloric glands the pits still are longer than the glands and it is not until the 73rd postnatal day, that pyloric glands are longer than their pits. development of the cardiac glands is delayed even more and the length of the gland does ...	1989	2610381
comparative biochemistry of hepatic arylsulfatases from north and south american opossums.	1. the virginia opossum (didelphis virginiana) possessed an arylsulfatase which had a relative molecular weight of 130 +/- 12 kda, displayed anomalous kinetics, hydrolysed aa2s, and exhibited other properties of arylsulfatase a. no arylsulfatase b was found. 2. the arylsulfatase present in the gray short-tailed opossum (monodelphis domestica) had a relative molecular weight of 56 +/- 4 kda, exhibited linear kinetics, was inhibited by chloride, and possessed other characteristics of arylsulfatase ...	1989	2574650
the brainstem origin of enkephalin- and substance-p-like immunoreactive axons in the spinal cord of the north american opossum.	we have used the retrograde transport of true blue (tb) in conjunction with immunofluorescence to determine if any of the enkephalin (enk)- or substance p (sp)-immunoreactive axons in the spinal cord of the north american opossum originate within the brainstem. neurons containing enk-like immunoreactivity and tb after injections of the latter into the second or third cervical segment of the spinal cord were found within the locus coeruleus proper, the locus coeruleus pars alpha, the raphe magnus ...	1989	2480173
comparative enzymatic study of hplc-fractionated crotalus venoms.	1. ten venoms of the genus crotalus (crotalus adamanteus, crotalus atrox, crotalus durissus durissus, crotalus horridus horridus, crotalus lepidus, crotalus polystictus, crotalus molossus molossus, crotalus pusillus, crotalus scutulatus scutulatus, venom b, and crotalus viridis lutosus) were fractionated using hplc anion and cation exchange chromatography. 2. hplc venom fractions were tested for hemorrhagic, hemolytic, and proteolytic activities. 3. crude virginia opossum (didelphis virginiana) ...	1989	2680253
the early development of major projections to the dorsal striatum in the north american opossum.	we have employed immunocytochemical and axonal transport techniques to study the development of major projections to the dorsal striatum of the north american opossum. the opossum is born in a very immature state, 12-13 days after conception, and climbs into an external pouch where it remains attached to a nipple for several months. its immaturity at birth and its protracted postnatal development make the opossum a good model for developmental studies. although tyrosine hydroxylase-like immunore ...	1989	2472908
characterization of serotonin-1b receptors negatively coupled to adenylate cyclase in ok cells, a renal epithelial cell line from the opossum.	we have previously reported the presence of a 5-ht1 (serotonin)-like receptor coupled in an inhibitory manner to adenylate cyclase in the opossum kidney cell line, which is derived from the kidney of a north american opossum. pharmacological data from binding and cyclic amp production studies indicate that this receptor does not have characteristics of a 5-ht1a, 5-ht1c or 5-ht1d receptor, but is similar to 5-ht1b receptors found in rodent tissues. many serotonergic drugs, including 5-methoxy-3-( ...	1989	2542534
opossum kidney contains a functional receptor for the escherichia coli heat-stable enterotoxin.	the escherichia coli heat-stable enterotoxin (st1 or sta) binds to specific receptors on mammalian intestinal brush border membranes, and stimulates guanylate cyclase in those membranes. we have found a similar signal transduction system in brush border membranes prepared from kidney cortex of the american opossum (didelphis virginiana, and in a cell line (ok cell) derived from that tissue. activation of guanylate cyclase by st1 is therefore not limited to intestinal cells. furthermore, since it ...	1989	2564275
immunohistochemical study of the developing endocrine pancreas of the opossum (didelphis virginiana).	cells immunoreactive for insulin, glucagon, somatostatin, bovine pancreatic polypeptide and 5-hydroxytryptamine are found in the pancreas of the newborn opossum and of all later stages examined. all immunoreactive cell types are present in primary and secondary islets and within elements of the exocrine pancreas. cells immunoreactive for glucagon, bovine pancreatic polypeptide, somatostatin and 5-hydroxytryptamine generally are confined to the periphery of secondary (intralobular) islets, wherea ...	1989	2665414
fatal lungworm infection in an opossum.	a 3-mo-old male, feral opossum (didelphis virginiana) was presented to the university of tennessee college of veterinary medicine (usa) for evaluation of prolonged dyspnea. the animal died shortly after examination and a necropsy was performed. the cause of death was attributed to a verminous pneumonia, associated with numerous intrabronchial and intrabronchiolar nematodes, subsequently identified as didelphostrongylus hayesi.	1989	2716108
host associations of ticks (acari: ixodidae) parasitizing medium-sized mammals in a lyme disease endemic area of southern new york.	ticks of eight medium-sized mammal species were studied in an area of endemic lyme disease in westchester county, n.y., from 1 april 1984 to 31 march 1985. most (81%) of the 266 total mammal captures were raccoon, procyon lotor (l.) (47%), opossum, didelphis virginiana (kerr) (19%), and striped skunk, mephitis mephitis schreber (15%); these host species accounted for 91% of the 1,519 ticks collected. although the total number of ticks was rather evenly distributed among these mammals, species co ...	1989	2724317
a cyto-architectonic description of the thalamus of the tammar wallaby, macropus eugenii.	very few studies are available on the cyto-architectural features of the thalamus of metatherian mammals. most of these studies describe the thalamus of a polyprotodont metatherian, the north american opossum, didelphis virginiana. studies on diprotodont metatherians are fewer still. there are two descriptions of the thalamus of the australian possum trichosurus vulpecula. the only part of the thalamus that has been described in the wallabies is the lateral geniculate nucleus. hence, there was a ...	1989	2765853
studies on the energy metabolism of opossum didelphis virginiana erythrocytes--iv. red cells have low adenosine deaminase activity and high levels of deoxyadenosine nucleotides.	alkaline extracts of adult opossum red cells were used to determine triphosphates of adenosine, deoxyadenosine and guanosine by anion exchange hplc. mean (nm/g hg) atp content of erythrocytes was 3713 and that of datp 1913 (n = 12). sonicates of red cells deaminated adenosine (ado) at a rate of 1.55 nm/mg hg/h and deoxyadenosine (dado) at 1.82 nm/mg hg/h. datp synthesis from provided dado was one order of magnitude greater in opossum than in human erythrocytes at both low and high dado and pi co ...	1989	2784528
oral vaccination of raccoons (procyon lotor) with an attenuated (sad-b19) rabies virus vaccine.	unlike previous reports to the contrary, raccoons (procyon lotor) were successfully vaccinated against rabies with a liquid sad-b19 attenuated virus vaccine administered per os and given in vaccine-laden baits. there was neither evidence of vaccine-induced rabies in raccoons nor in a limited safety trial with opossums (didelphis virginiana) given sad-b19. protection from lethal street rabies virus infection was not absolute: only three of nine raccoons given 1 x 10(6.0) tcid/ml were protected ve ...	1989	2810555
laminar and non-laminar patterns of acetylcholinesterase activity in the marsupial lateral geniculate nucleus.	acetylcholinesterase (ache) distribution in the dorsal lateral geniculate nucleus (lgd) of 3 polyprotodont and 3 diprotodont marsupials has been compared with the cytoarchitecture and, as appropriate, with retinal terminal bands (rtbs) as demonstrated by tracers injected into the vitreous body. in this series those polyprotodont marsupials showing only partial segregation of retinal input (virginia opossum and tasmanian devil), display the least cell laminar differentiation. in them ache stainin ...	1989	2731033
receptors and cgmp signalling mechanism for e. coli enterotoxin in opossum kidney.	receptors for the heat-stable enterotoxin produced by escherichia coli were found in the kidney and intestine of the north american opossum and in cultured renal cell lines. the enterotoxin markedly increased guanosine 3',5'-cyclic monophosphate (cgmp) production in slices of kidney cortex and medulla, in suspensions of intestinal mucosa, and in the opossum kidney (ok) and rat kangaroo kidney (ptk-2) cell lines. in contrast, atrial natriuretic factor elicited much smaller increases in cgmp level ...	1988	2847547
studies on the energy metabolism of opossum didelphis virginiana erythrocytes--ii. comparative aspects of 2-deoxy-d-glucose catabolism in opossum and human red cells in vitro.	1. g-6-p, f-6-p, f-1, 6-p, dhap and ga-3-p in opossum erythrocytes were found at levels above those reported in human red cells. 2. about 1% of the radioactivity provided as [1-14c] dog to red cells of both species was recovered as 14co2 in 1 hr. 3. unlike [1-14c] dog, radiochromatography of extracts of cells incubated dog revealed two diffusible radiolabelled compounds in the supernatant of cell suspensions. 4. the catabolism of dog was quantitatively and qualitatively similar in opossum and hu ...	1988	2896089
studies on the energy metabolism of opossum didelphis virginiana erythrocytes--iii. metabolic depletion with 2-deoxyglucose markedly accelerates methemoglobin reduction in opossum but not in human erythrocytes.	1. glucose-depleted, nitrite-treated erythrocytes reduce ferriheme in vitro in an environment 100 mm to 2-deoxy-d-glucose at a rate of 2.4 microm/ml cells/hr (opossum) and 0.37 microm/ml cells/hr (human). 2. during the process of methemoglobin reduction the breakdown of adenine ribonucleotides is more rapid in opossum (0.9 microm/g hg/hr) than in human (0.36 microm/g hg/hr) erythrocytes. 3. radiolabelled ribose from [u-14c] atp is catabolized exclusively to [14c] lactate in opossum, and to [14c] ...	1988	2896090
catecholaminergic innervation of the spinal cord in the north american opossum, didelphis virginiana.	axons presumed to contain catecholamines were visualized in the spinal cord of the spinal cord of the north american opossum using antibodies to tyrosine hydroxylase (th) by an indirect antibody peroxidase-antiperoxidase (pap) technique. axons showing th-like immunoreactivity (th-ir) coursed primarily in the dorsal part of the lateral funiculus, although they were also present more ventrally. an occasional th-ir axon was seen in the dorsal funiculus. within the gray matter, th-ir axons were dist ...	1988	2906810
proteolytic, hemorrhagic and hemolytic activities of snake venoms.	proteolytic, hemorrhagic and hemolytic activities were tested on 47 different venoms from the crotalidae, viperidae, elapidae, and hydrophiidae families. antihemorrhagic activity of crude opossum (didelphis virginiana) and woodrat (neotoma micropus) serum was tested against the venoms that presented hemorrhagic activity. all venoms showed proteolytic activity when non-specific substrates such as hide powder and collagen were used. members of the crotalidae family had the highest hide powder, chy ...	1988	3059584
a cytoarchitectonic atlas of the medial geniculate body of the opossum, didelphys virginiana, with a comment on the posterior intralaminar nuclei of the thalamus.	the organization of the medial geniculate body and adjacent posterior thalamus of the virginia opossum was studied in nissl-, golgi-, reduced silver, and myelin-stained preparations. our chief goals were to define the cytoarchitectonic subdivisions and boundaries in nissl preparations and to reconcile these with those observed with the golgi method and in experimental material, to present these results in an atlas of nissl-stained sections, and to compare the chief nuclear groups in the opossum ...	1988	2464620
structure, processing and evolution of the neurohypophysial hormone-neurophysin precursors.	neurohypophysial hormones and neurophysins are derived from common precursors processed during the axonal transport from the hypothalamus to the neurohypophysis. two neurohormones, an oxytocin-like and a vasopressin-like, on one hand, two neurophysins, termed vldv-and msel-neurophysins according to residues in positions 2, 3, 6 and 7, on the other, are usually found in vertebrate species. in contrast to placental mammals that have oxytocin and arginine vasopressin, marsupials have undergone a pe ...	1988	3147712
trichinella spiralis in an agricultural ecosystem. iii. epidemiological investigations of trichinella spiralis in resident wild and feral animals.	as part of a larger epidemiological study examining the transmission of trichinella spiralis in an agricultural ecosystem, resident wild and feral animals were trapped to determine the extent of their involvement in the natural, on-farm cycling of the parasite among swine. during a 21-mo-study, seven of 15 skunks (mephitis mephitis), one of three opossums (didelphis virginiana), two of two feral domestic cats and a raccoon (procyon lotor) were found to be infected, while five shrews (blarina bre ...	1988	3193554
differential distribution of the p1 and p2 protamine gene sequences in eutherian and marsupial mammals and a monotreme.	at the protein level, the p1 protamine is the predominant form of mammalian protamine, present in all mammalian spermatozoa analyzed to date. an additional variant, the p2 protamine, has been detected only in spermatozoa of the mouse, hamster and human. southern blot analysis of a group of restriction enzyme-digested mammalian dnas has revealed the presence of sequences homologous to the p1 and p2 mouse protamine genes in diverse species. in agreement with protein studies, nucleotide sequences h ...	1988	3209180
localization of g6pd and hprt to different arms of the x chromosome of the north american marsupial (didelphis virginiana) by in situ hybridization and deletion mapping: evolutionary significance.	we have mapped hprt and g6pd loci on the x chromosome in the american opossum, didelphis virginiana, by in situ hybridization to cells derived from two females by using genomic opossum dna as probes. the localizations (g6pd to xp13 and hprt to xq21), indicating that the two genes are separated by the centromere, were confirmed by results of hybridization to x chromosomes with deletions that include the hprt locus and opossum-mouse cell hybrids containing the relevant fragment of the opossum x ch ...	1988	3243545
experimental cryptosporidium parvum infections in opossums (didelphis virginiana).	five nursing opossums (didelphis virginiana) were each inoculated with 5 x 10(6) cryptosporidium parvum oocysts of calf origin. following inoculation, endogenous stages of c. parvum were observed in the ileum, cecum, and colon of these opossums. two of three noninoculated pouch mates acquired infections during the study based on examinations of feces and tissue sections of all eight opossums. mild diarrhea was observed in four of seven opossums harboring c. parvum, although none died as a result ...	1988	3352085
valvular endocarditis associated with experimental erysipelothrix rhusiopathiae infection in the opossum (didelphis virginiana).	intravenous inoculation of a wild type isolate of erysipelothrix rhusiopathiae in opossums resulted in valvular endocarditis in all infected animals. opossums were inoculated once a week for 3 weeks. lesions became visible with cardiac ultrasound by week four post-inoculation. opossums remained clinically normal throughout the experiment, and preinfection body weight was maintained. other lesions of chronic erysipelas including skin necrosis and arthritis were not found in infected opossums.	1988	3374091
characterization of erysipelothrix rhusiopathiae isolated from an opossum (didelphis virginiana) with septicemia.	erysipelothrix rhusiopathiae was isolated from a wild-caught opossum (didelphis virginiana). the opossum was quarantined in isolation and removed from contact with other animals. after a 2-mo period it was found dead in its cage, and presented for postmortem examination. pure cultures of erysipelothrix rhusiopathiae (slu isolate) were recovered from heart blood, liver, spleen and lungs. to compare pathogenicity, an experimental infection was attempted in cf1 mice with a single dose of 1.5 x 10(7 ...	1988	3411715
the origin of projections from the medullary reticular formation to the spinal cord, the diencephalon and the cerebellum at different stages of development in the north american opossum: studies using single and double labeling techniques.	we have employed the retrograde transport of horseradish peroxidase alone or conjugated to wheat germ agglutinin, to label neurons within the medullary reticular formation which project to the spinal cord, the diencephalon and the cerebellum at different stages of development in the north american opossum. at selected ages, the fluorescent markers fast blue and diamidino yellow were also used in double-labeling experiments to determine if single neurons innervate both the spinal cord and diencep ...	1988	3393288
the early development of subcortical projections to presumptive somatic sensory-motor areas of neocortex in the north american opossum.	we have studied the early development of subcortical projections to presumptive somatic sensory-motor areas of neocortex in the north american opossum didelphis virginiana. the opossum is born in a very immature state, 12-13 days after conception, and climbs into an external pouch where it is available for experimental manipulation. using the retrograde transport of wheat germ agglutinin conjugated to horseradish peroxidase, we have obtained evidence that axons from the dorsal raphe and superior ...	1988	2459990
organization of forebrain projections from the medullary reticular formation in the north american opossum. evidence for connectional heterogeneity.	we have employed axonal transport techniques to study the organization of projections from the medullary reticular formation (rf) to the forebrain of the north american opossum. the results of retrograde transport studies using large injections of horseradish peroxidase (hrp), wheat germ agglutinin conjugated to hrp (wga-hrp), and fluorescent markers suggest that all nuclei of the medullary rf project to the forebrain although the parvocellular reticular nucleus makes only a very small contribut ...	1988	2450621
evidence for developmental plasticity of the rubrospinal tract. studies using the north american opossum.	using axonal tracing techniques we have shown that rubral axons are capable of growing around lesions of the rubrospinal tract during early stages of development in the north american opossum and that a critical period for such growth exists. the opossum was employed for study because it is born in a very immature state 12-13 days after conception and the entire development of its rubrospinal tract occurs postnatally.	1988	3378179
seasonal energetics of opossums (didelphis virginiana) in ohio.	1. female opossums acclimatized to each of the four seasons were not significantly different (p greater than 0.05) in oxygen consumption at a ta of 0 degrees c; the overall average was 0.66 +/- 0.1 ml o2/g-hr. 2. body weight decreased by 27% from autumn to spring; pelage density increased in winter, but thermal conductance changed very little between seasons. 3. respirometry revealed no evidence of thermoregulatory adjustments in opossums acclimatized to winter in ohio.	1988	2901314
sex determination in marsupials: evidence for a marsupial-eutherian dichotomy.	in this paper, we review briefly the current state of knowledge about sexual differentiation in eutherian mammals, and then describe the situation in detail in two marsupial species: the north american opossum and the tammar wallaby. the conventional explanation for the genesis of all male somatic sexual dimorphisms in mammals is that they are a consequence of the systemic action of testicular hormones. in the absence of testes, the embryo will develop a female phenotype. we present evidence for ...	1988	2907802
development of the optic nerve of the opossum (didelphis virginiana).	the development of the optic nerve of a marsupial, the north american opossum, was examined in 24 animals from postnatal days 5 to 78 (p5-p78): gestation is 13 days. the estimated number of axons increased from 24,000 at p5, to 267,000 at p27, approximately 2.7 times the mean number in the adult. following p27, axon numbers decreased rapidly to 140,000 at p40, then decreased more slowly, attaining adult values between p50 and p59. thus, the opossum is similar to placental mammals examined in evi ...	1988	3233732
dual duplication of neurohypophysial hormones in an australian marsupial: mesotocin, oxytocin, lysine vasopressin and arginine vasopressin in a single gland of the northern bandicoot (isoodon macrourus).	neurohypophysial hormones of an australian marsupial, the northern bandicoot (isoodon macrourus), have been identified by their retention times in high-pressure reverse-phase liquid chromatography using two solvent systems and by their molar pressor or uterotonic activities. two pressor peptides, arginine vasopressin and lysipressin, and two uterotonic peptides, mesotocin and oxytocin, have been characterized. because mesotocin and arginine vasopressin have been identified in three other austral ...	1988	3395337
evolutionary and developmental aspects of two hemoglobin beta-chain genes (epsilon m and beta m) of opossum.	a series of gene duplications that began in a stem species of mammalia and led to five developmentally regulated hemoglobin beta-chain loci (epsilon, gamma, eta, delta, and beta) in a common ancestor of eutherian orders artiodactyla, rodentia, lagomorpha, and primates had important consequences in mammalian evolution. findings reported here indicate that two progenitors of the five linked genes existed by the time of the eutherian (placental mammal)-metatherian (marsupial mammal) split and that ...	1988	3375246
dna methylation stabilizes x chromosome inactivation in eutherians but not in marsupials: evidence for multistep maintenance of mammalian x dosage compensation.	in marsupials and eutherian mammals, x chromosome dosage compensation is achieved by inactivating one x chromosome in female cells; however, in marsupials, the inactive x chromosomes is always paternal, and some genes on the chromosome are partially expressed. to define the role of dna methylation in maintenance of x chromosome inactivity, we examined loci for glucose-6-phosphate dehydrogenase and hypoxanthine phosphoribosyltransferase in a north american marsupial, the opossum didelphis virgini ...	1987	3476942
x-linked gene expression in the virginia opossum: differences between the paternally derived gpd and pgk-a loci.	expression of x-linked glucose-6-phosphate dehydrogenase (g6pd) and phosphoglycerate kinase-a (pgk-a) in the virginia opossum (didelphis virginiana) was studied electrophoretically in animals from natural populations and those produced through controlled laboratory crosses. blood from most of the wild animals exhibited a common single-banded phenotype for both enzymes. rare variant animals, regardless of sex, exhibited single-banded phenotypes different in mobility from the common mobility class ...	1987	3557111
distribution of fibre types in thirty-seven muscles of didelphis virginiana.	the proportions of type i and ii fibers were determined in 37 muscles of didelphis virginiana, representing 9 body regions. there was a distinct cranial/caudal gradation in the distribution of type ii fibers throughout the trunk musculature. muscles of the fore- and hind-limbs showed a gradation of type ii fiber across the width of the muscle, being more prominent at the surface. the type ii fibers in the tip of the tail showed peculiar staining properties in which the core of each fiber stained ...	1987	2960253
development of brainstem and cerebellar projections to the diencephalon with notes on thalamocortical projections: studies in the north american opossum.	the north american opossum is born in a very immature state, 12 days after conception, and climbs into an external pouch where it remains attached to a nipple for an extended period of time. we have taken advantage of the opossum's embryology to study the development of brainstem and cerebellar projections to the diencephalon as well as the timing of diencephalic projections to somatosensory motor areas of neocortex. the techniques employed included immunocytochemistry for serotonin, the retrogr ...	1987	3038968
development of the basilar pons in the north american opossum: dendrogenesis and maturation of afferent and efferent connections.	the present study provides data on temporal factors that may play a role in the development of precerebellar-cerebellar circuits in the north american opossum. in this study the basilar pons and cerebellum are analyzed from birth, 12-13 days after conception, to approximately postnatal day (pd) 80 at which time the brainstem and cerebellum have a mature histological appearance. in nissl preparations, the basilar pons was first seen at pd 7 as a small cluster of tightly packed cells. analysis of ...	1987	2441628
lyme disease ecology in wisconsin: distribution and host preferences of ixodes dammini, and prevalence of antibody to borrelia burgdorferi in small mammals.	lyme disease recently has been recognized in wisconsin. trapping studies were conducted at four geographically separate and ecologically distinct regions in wisconsin to elucidate the distribution and host preferences of ixodes dammini on small and medium sized mammals, and the occurrence of antibodies to borrelia burgdorferi in these wild mammals. peak i. dammini larval activity occurred from june-september. nymphs were most active from may-august. white-footed mice (peromyscus leucopus) and ch ...	1987	3605501
pathogenesis of sarcocystis falcatula in the budgerigar. i. early pulmonary schizogony.	sarcocystis falcatula is a protozoan parasite which obligatorily alternates its definitive host, the opossum (didelphis virginiana), and a uniquely wide range of avian intermediate hosts. the disease produced by this coccidian parasite in intermediate hosts was studied in the budgerigar bird (melopsittacus undulatus). the ultrastructure of pulmonary sporozoites, meronts and merozoites of this sarcocystis species is described. early schizogony occurs progressively in pulmonary capillary and in ve ...	1987	3099083
pathogenesis of sarcocystis falcatula in the budgerigar. ii. pulmonary pathology.	sarcocystis falcatula is a protozoan parasite which obligatorily alternates its definitive host, the opossum (didelphis virginiana), and a uniquely wide range of avian intermediate hosts. the disease produced by this coccidian parasite in intermediate hosts was studied in the budgerigar bird (melopsittacus undulatus). early schizogony occurs in pulmonary endothelial cells, resulting in endothelial cell hypertrophy, capillary obstruction preceding endothelial lysis, acute endophlebitis, and chron ...	1987	3099084
an immunohistochemical survey of gastric proteinase (pepsinogen and prochymosin)-containing cells in the stomach of the developing opossum (didelphis virginiana).	cells immunoreactive to antisera of bovine pepsinogen and prochymosin are seen in the oxyntic glands but not the pyloric or cardiac glands of the opossum. immunoreactivities to pepsinogen and prochymosin occur within the same cell and are restricted to an undifferentiated cell type prior to weaning. the undifferentiated cells producing these gastric proteinases decrease in number until just prior to weaning and disappear with the appearance of chief cells. thereafter, immunoreactivities to both ...	1987	3128513
molecular studies of marsupial x chromosomes reveal limited sequence homology of mammalian x-linked genes.	to explore the extent to which the x chromosome has been conserved during mammalian evolution, we compared six loci that are x-linked in the human genome with the corresponding genes of the north american marsupial, the virginia opossum (didelphis virginiana). our analysis shows that in the opossum genome there are sequences highly homologous to those of human cdnas for housekeeping genes, glucose-6-phosphoribosyltransferase (hprt), phosphoglycerate kinase a (pgk1), and alpha-galactosidase a (gl ...	1987	2822568
origin of mammalian thalamocortical projections. i. telencephalic projections of the medial geniculate body in the opossum (didelphis virginiana).	telencephalic projections from the medial geniculate nucleus (mg) in opossum were traced with tritiated leucine autoradiography and by horseradish peroxidase and fluorescent dye retrograde labeling techniques. the results show that the opossum's mg contains two separate populations of neurons-one in the anterior two-thirds of mg projecting to auditory neocortex, the other occupying the entire caudal one-third of mg and projecting mostly to lateral amygdala and putamen. because the subcortical pr ...	1986	2420841
receptive field properties and latencies of cells in the lateral geniculate nucleus of the north american opossum (didelphis virginiana).	relay cells in the lateral geniculate nucleus (lgn) of the north american opossum were classified as types 1, 2, and 3 on the basis of their receptive field properties and afferent latencies to optic nerve (on) and optic chiasm (ox) stimulation and antidromic latencies to stimulation of cortex. type 1 and type 3 cells gave transient responses and type 2 cells gave sustained responses to appropriate standing contrast in the receptive field center. the differences in response pattern were quantifi ...	1986	3097274
the adult organization and development of the rubrospinal tract. an experimental study using the orthograde transport of wga-hrp in the north-american opossum.	we have employed the orthograde transport of wheat germ agglutinin conjugated to horseradish peroxidase to study the organization of rubrospinal connections in adult and pouch young opossums. our results suggest that: in the adult opossum rubrospinal axons are distributed more widely than suggested by previous studies; rubrospinal projections are formed postnatally in the opossum, but much earlier than corticospinal connections; rubrospinal axons do not grow synchronously, as a massive bundle fo ...	1986	3779426
development of projections from somatic motor-sensory areas of neocortex to the diencephalon and brainstem in the north american opossum.	the development of projections from somatic motor-sensory areas of neocortex to the diencephalon and brainstem was studied by using the orthograde transport of wheat germ agglutinin conjugated to horseradish peroxidase (wga-hrp) in a series of pouch-young opossums. the opossum was chosen for study because it is born in a very immature state, 12 days after conception, and has a protracted postnatal development. cortical axons form a cerebral peduncle by at least postnatal day (pd) 10, a medullary ...	1986	2431011
the development and migration of large multipolar neurons into the cochlear nucleus of the north american opossum.	we have studied the maturation of the inferior colliculus and cochlear nuclei of the north american opossum with particular emphasis on the large multipolar neurons of the cochlear nucleus. these neurons include the principal and giant cells of the dorsal cochlear nucleus (dcn) and the large neurons of the ventral cochlear nucleus (vcn), all of which can be labelled by horseradish peroxidase (hrp) injections into the contralateral inferior colliculus (ic). the size of these neurons, their charac ...	1986	3722450
a plastic cage for restraint of the opossum (didelphis virginiana).		1986	3773475
mechanical factors in the evolution of the mammalian secondary palate: a theoretical analysis.	the secondary palate of mammals is a bony shelf that closes the ventral aspect of the rostrum. the rostrum, therefore, approximates to a tapered semicylindrical tube that is theoretically a mechanically efficient structure for resisting the forces of biting, including the more prolonged bouts of mastication typical of mammals. certain mammal-like reptiles illustrate stages in the development of the palate in which the shelves projecting medially from each premaxilla and maxilla do not meet in th ...	1986	3746918
isolation of antihemorrhagic factors in opossum (didelphis virginiana) serum using a monoclonal antibody immunoadsorbent.	the antihemorrhagic factor in opossum (didelphis virginiana) serum isolated by sephadex g-200 gel filtration and deae a-50 ion exchange chromatography was used as antigen to immunize balb/c mice. hybrid cell lines secreting monoclonal antibodies against antihemorrhagic factor were produced by fusion of sp2/0 myeloma cells with spleen cells of the immunized mice. the ascites fluid was produced in balb/c mice. the monoclonal antibody in the ascites fluid was partially purified by deae a-50 ion exc ...	1986	3750345
the sensory innervation of the nasal glabrous skin in the short-nosed bandicoot (isoodon macrourus) and the opossum (didelphis virginiana).	the glabrous skin at the anterior end of the snout of the short-nosed bandicoot and the american opossum was investigated by electron microscopy. in both species of animals, this region was lined by skin with broad epidermal pegs, innervated by three types of intraepidermal nerves. these were intraepidermal nerves which penetrated the epidermis up to the level of the stratum spinosum or the stratum granulosum, intraepidermal nerves in the basal layer of the epidermis partially surrounded by schw ...	1985	3870723
olfactory aposematism : association of food toxicity with naturally occurring odor.	visual and acoustic cues may serve as aposematic signals that warn predators of poisonous foods. olfactory aposematism, the use of innocuous odors as warning signals for toxic foods, is another possible means of alerting an animal that a potential food item is unpalatable. although it has been suggested that olfactory aposematism might be the principle mode of warning utilized by plants in their defense against herbivores, experimental evidence is lacking. this study demonstrates that the opossu ...	1985	24310390
quantitative distribution of enteroendocrine cells in the gastrointestinal tract of the adult opossum, didelphis virginiana.	the distribution and quantification of enteroendocrine cells exhibiting immunoreactivities to nine peptides and one amine were examined in the gastrointestinal mucosa of the adult opossum using specific immunocytochemical methods. in the stomach, 90% of the enteroendocrine cells are confined to the pyloric glands and this region contained 73% of the gastrin-containing cells, 60% of the somatostatin-containing cells and 9% of cells reactive for 5-ht. enteroendocrine cells showing immunoreactiviti ...	1985	4077699
electrical properties of smooth muscle cell membrane of opossum esophagus.	the electrical properties of the circular smooth muscle layer from the north american opossum esophagus (body) were studied in vitro by microelectrode recording techniques, both at rest and during stimulation of intramural inhibitory nerves. all observations were made at 37 degrees c in an abe-tomita partitioned bath on muscle strips dissected 2 cm orad of the lower esophageal sphincter. at rest, the potential of the smooth muscle cell membrane was -49 +/- 4 mv (mean +/- se); the length constant ...	1985	3976893
the synthesis and metabolism of gonadal steroids in pouch young of the opossum, didelphis virginiana.	we have measured steroid hormone biosynthesis from pregnenolone in ovaries and testes, aromatization of testosterone in gonads and peripheral tissues, and 5 alpha-reduction of testosterone in peripheral tissues of developing opossum pouch young. sex of the newborn opossums is discernible grossly with development of the pouch in females and the scrotum in males approximately 10 days after birth. differentiated endocrine function of ovaries and testes was demonstrable as soon as development of the ...	1985	3971901
the allantois of the north american opossum (didelphis virginiana) with preliminary observations on the yolk sac endoderm and trophectoderm.	during the middle of prenatal day 10, the opossum allantois forms as a ventral outgrowth of the hindgut. by day 11 it appears as a large, fluid filled sac and by the middle of day 12 (just prior to birth) it reaches its maximal development. the simple squamous epithelium lining the allantois consists of only one cell type that often contains numerous filaments in the apical cytoplasm. at the luminal surface, the apices of the cells are united by junctional complexes and desmosomes are present be ...	1985	3977085
placentation in the opossum, didelphis virginiana.	for the first 9 days of gestation, opossum embryos float in uterine secretions, separated from maternal tissues by a shell membrane. each embryo is part of the wall of its hollow embryonic sphere. by the 10th day of development, the embryo becomes enveloped by both the amnion and yolk-sac. the yolk-sac consists of vascular and non-vascular portions and, together with the surrounding trophectoderm (trophoblast), forms the yolk-sac placenta of the opossum: the allantois does not contribute to form ...	1985	4061035
the nonmammalian-mammalian transition through neurohypophysial peptides.	neurohypophysial hormones are particularly proper evolutionary tracers. whereas eutherian mammals have oxytocin and virtually always arginine vasopressin, nonmammalian tetrapods possess instead mesotocin and vasotocin. the transitions of mesotocin-oxytocin and vasotocin-vasopressin involved in the passage of reptiles-mammals seem to have occurred independently. australian marsupials are endowed with mesotocin but american marsupials have either oxytocin (south-american opossums) or both oxytocin ...	1985	3831965
corticospinal development in the north-american opossum: evidence for a sequence in the growth of cortical axons in the spinal cord and for transient projections.	the course and distribution of corticospinal axons have been traced in a series of pouch young and adult opossums using wheat germ agglutinin conjugated to horseradish peroxidase (wga-hrp). cortical axons enter the spinal cord approx. 28 days after birth (40 days after conception) and, at that time, are limited to those portions of the dorsal and lateral funiculi which contain them in the adult animal. shortly thereafter, cortical axons are also found in regions of presumptive white matter where ...	1985	4075107
cortical projections to superficial laminae of the dorsal horn and to the ventral horn of the spinal cord in the north american opossum. studies using the orthograde transport of wga-hrp.	the orthograde transport of horseradish peroxidase conjugated to wheat germ agglutinin (wga-hrp) has been used to study the distribution of corticospinal axons in adult and pouch-young opossums. as predicted from the results of degeneration and autoradiographic experiments, injections of wga-hrp into limb areas of somatic motor-sensory cortex labeled axons in the dorsal and lateral funiculi of the cervical and upper thoracic spinal cord which could be traced to dense terminal zones in laminae ii ...	1985	3839153
serotonergic innervation of the forebrain in the north american opossum.	the forebrain distribution of axons showing serotonin-like immunoreactivity was studied in the north american opossum. serotonergic innervation of the hypothalamus was extensive, particularly within the ventromedial nucleus, the periventricular nucleus and the rostral supraoptic nucleus. serotonergic axons were also present within the fields of forel and zona incerta, but they tended to avoid parts of the subthalamic nucleus. in the thalamus serotonergic innervation was dense within the midline ...	1985	3910165
the development of commissural connections of somatic motor-sensory areas of neocortex in the north american opossum.	the north american opossum does not have a corpus callosum; neocortical commissural axons are contained entirely within the anterior commissure. we have used axonal transport techniques to study the origin and distribution of commissural axons from somatic motor-sensory cortex in developing and adult opossums. neocortical axons grow into the anterior commissure by postnatal day (pnd) 12, the contralateral external capsule by approximately pnd 19, the area deep to the contralateral homotypic cort ...	1985	3838629
tactile cutaneous representation in cerebellar granule cell layer of the opossum, didelphis virginiana.	recent studies of the albino rat revealed extensive cutaneous somatosensory projections to the granule cell (gc) layer of the cerebellar hemispheres and the caudal vermis. these projections are organized asomatotopically in patchy mosaics. to determine whether similar projections exist in a marsupial, we explored the gc layer of the cerebellar cortex of anesthetized virginia opossums using in-depth microelectrode micromapping and juxtathreshold cutaneous natural stimulation techniques. we found: ...	1985	3843070
beta-like ganglion cells in the retina of the north american opossum.	injection of horseradish peroxidase into the severed optic tract or nerve of the opossum retrogradely filled retinal ganglion cells. an abundance of well-labeled ganglion cells had dendritic morphology closely resembling that of beta-type ganglion cells in the cat retina. this finding suggests that an x-like functional class of ganglion cells is prominent in the retina of the opossum.	1985	3921195
brucella abortus in wildlife on selected cattle farms in alabama.	two studies of brucellosis in wildlife on farms where the brucellosis infection prevalence in cattle was known are reported. on a research farm, 233 feral animals of 22 mammalian species and 12 of seven avian species were trapped during three time periods. sixty were studied before cattle were introduced, 128 were studied while 501 cattle infected with brucella abortus were calving and aborting, and 60 specimens were collected 20 mo after the last infected cow calved. selected tissues from 229 w ...	1985	3923213
experimental studies of st. louis encephalitis virus in vertebrates.	serologically negative birds and mammals of species, known from other studies to be exposed naturally to st. louis encephalitis (sle) virus in memphis, tennessee, and other selected species were inoculated experimentally with strains of sle virus to determine their potential as natural hosts. mosquitoes (culex sp.) were allowed to feed on some of the inoculated vertebrate species, held for 14 days, and tested for sle infection. the cardinals (richmondena cardinalis), robins (turdus migratorius), ...	1985	3999258
experimental la crosse virus infection of red fox (vulpes fulva), raccoon (procyon lotor), opossum (didelphis virginiana), and woodchuck (marmota monax).	susceptibility to infection, resulting viremia and antibody responses, and potential to provide infectious blood meals for aedes triseriatus were determined and compared for the red fox (vulpes fulva), raccoon (procyon lotor), and opossum (didelphis virginiana) exposed to la crosse (lac) virus transmitted by mosquitoes, ae. triseriatus. woodchucks (marmota monax) were infected with lac virus by needle and syringe. all 5 red foxes became viremic following the bite of a single lac virus-infected f ...	1985	4003669
responses of opossum and rat hippocampal ca1 cells to paired stimulus volleys.	short-term synaptic plasticity was studied in the in vitro hippocampus of the north american opossum (didelphis virginiana) and rat (rattus norvegicus). conditioning and test stimulus pulses were delivered to fibers in stratum radiatum, and intracellular and extracellular recordings were obtained from area ca1 pyramidal cells. in rat, the amplitude of the population spike in response to the second (test) of two stimulus impulses is suppressed at short inter-pulse-intervals (ipi's). in opossum, t ...	1985	4052826
the distribution of photoreceptors, dopaminergic amacrine cells and ganglion cells in the retina of the north american opossum (didelphis virginiana).	quantitative light microscopic techniques have been applied to photoreceptors, ganglion cells and dopaminergic amacrine cells in the retina of the north american opossum didelphis virginiana. this marsupial has a retina with a central areal specialization where ganglion cells reach a maximum density of 2900/mm2 and cone photoreceptors are concentrated. however, the retina is very much rod dominated and there is a ring of peak rod density approximately 2 mm around the area centralis (a.c.). at th ...	1985	4072000
a pharmacological study of oesophageal muscularis mucosae from the cat, dog and american opossum (didelphis virginiana). addendum.		1985	2411325
the distribution of glutamic acid decarboxylase immunoreactivity in the diencephalon of the opossum and rabbit.	we have examined the distribution of neurons and terminals immunoreactive for glutamic acid decarboxylase (gad) in the thalamus and adjacent structures of the opossum (didelphis virginiana) and the rabbit and have compared this distribution with the distributions we described previously for the cat and bushbaby (galago senegalensis). the significance of these experiments depends, first, on the fact that gad is the synthetic enzyme for gaba, and therefore that gad immunoreactivity is a marker for ...	1984	6090511
cerebellar cortical efferent fibers in the north american opossum, didelphis virginiana. i. the anterior lobe.	the distribution of cerebellar corticonuclear and corticovestibular fibers from the anterior lobe of the north american opossum, didelphis virginiana, was studied using the fink and heimer ('67) technique. corticonuclear fibers from medial areas of anterior lobe project into the medial cerebellar nucleus (nm) in a topographically organized manner. fibers from lobules ii and iii enter rostral and rostrodorsal nm, while those from lobules iv and v terminate in progressively more caudal parts of th ...	1984	6480900
motor units of the primary ankle extensor muscles of the opossum (didelphis virginiana): functional properties and fiber types.	motor units of the medial gastrocnemius (mg) and the single lateral gastrocnemius/soleus (lg/s) muscles of the opossum (didelphis virginiana) were found to have uniformly slow contraction times relative to homologous muscles of the cat. though a broad range of peak tetanic tensions was found among motor units from both muscles, most of the motor units were quite large relative to tension of the whole muscle. comparison of the relative sizes of motor units showed that those of lg/s are significan ...	1984	6481810
a double-labelling study of reticular collaterals to the spinal cord and cerebellum of the north american opossum.	injections of horseradish peroxidase into either the spinal cord or cerebellum label neurons in the gigantocellular and lateral reticular nuclei of the north american opossum. in order to determine if neurons which project to the spinal cord and cerebellum are intermingled in these two nuclei and if single neurons provide collaterals to both areas, we have employed fluorescent markers in double-labelling experiments. our results show that reticular neurons innervating either the spinal cord or c ...	1984	6205332
a study of overlap and collateralization of bulbar reticular and raphe neurons which project to the spinal cord and diencephalon of the north american opossum.	labeled neurons were found in most reticular and raphe nuclei of the opossum's medulla after horseradish peroxidase (hrp) injections into either the spinal cord or diencephalon. the labeling produced by spinal injections differed somewhat from that produced by diencephalic ones, but hrp-positive neurons were found in what appeared to be comparable areas. in order to study the intermingling of bulbospinal and bulbodiencephalic neurons more directly, we used fluorescent markers (true blue, nuclear ...	1984	6205718
a pharmacological study of oesophageal muscularis mucosae from the cat, dog and american opossum (didelphis virginiana).	strips of muscularis mucosae from the oesophagi of cat, dog and opossum have been studied to determine their responses to drugs to electrical field stimulation. all tissues were contracted by acetylcholine, histamine and, with the exception of strips of muscularis mucosae from the opossum proximal oesophagus, noradrenaline. the effects of acetylcholine and histamine were competitively antagonized by atropine (50 nm) and mepyramine (50 nm) and were abolished by atropine (1 microm) and mepyramine ...	1984	6207883
the purification and characterization of an antihemorrhagic factor in woodrat (neotoma micropus) serum.	a protein antihemorrhagic factor was purified from the serum of the southern plains woodrat (neotoma micropus) by gel filtration and ion exchange chromatography. the homogeneity of the purified factor was measured by disc electrophoresis in polyacrylamide gel. the factor had an isoelectric ph of 4.1, a molecular weight of 54,000, and migrated with alpha-globulins in disc electrophoresis. the factor failed to form a precipitate with crude western diamondback rattlesnake (crotalus atrox) venom and ...	1984	6372164
description of sarcocystis falcatula stiles, 1893, a parasite of birds and opossums.	sarcocystis falcatula stiles, 1893 is re-described. intermediate hosts of the parasite which was earlier described as sarcocystis debonei vogelsang, 1929 are species of passeriform, psittaciform, and columbiform birds. in these birds, muscle zoites are 6.88 x 2.19 (4.8-8.4 x 1.2-3.6) micron and are enclosed in a cyst wall with regular protrusions, 1-5 micron long. the convoluted primary wall has multiple thin areas in the osmiophilic layer. microtubules originate in the ground substance and exte ...	1984	6439855
developmental sequence in the origin of descending spinal pathways. studies using retrograde transport techniques in the north american opossum (didelphis virginiana).	the origin of descending pathways to thoracic and cervical levels of the spinal cord has been investigated with retrograde tracing techniques in a series of pouch young and adult opossums. the opossum was chosen because it is born in a very immature state, 12-13 days after conception, and has a protracted development in an external pouch. a few neurons in the pontine reticular formation and nucleus coeruleus were labeled by horseradish peroxidase (hrp) injections of the thoracic cord as early as ...	1984	6478250
metaphase synchronization and chromosome preparation from the ok opossum cell line having a potentially isolatable x chromosome.	as part of a study on x chromosomes, metaphase cell synchrony and chromosome isolation methods were developed for the opossum (didelphis virginiana) kidney epithelial cell line (ok). the cell synchrony yielded large amounts of metaphase cells using a relatively simple method in which a key feature was a calcium- and magnesium-free balanced salt wash. a neutral ph chromosome isolation method was developed for the kidney epithelial cells, because they were somewhat difficult to disrupt fully by ot ...	1984	6394469
cerebellar cortical efferent fibers in the north american opossum, didelphis virginiana. ii. the posterior vermis.	the projection pattern of corticonuclear and corticovestibular fibers from vermis lobules vi-x of the north american opossum, didelphis virginiana, was studied using a modification of the fink and heimer ('67) technique. the evidence suggests that corticovestibular projections in opossum are ipsilateral and exit the cerebellum via the juxtarestiform body. lobules vi and vii contribute few, if any, corticovestibular projections. corticovestibular fibers from lobule viii are sparse to moderate and ...	1984	6480901
studies on the energy metabolism of opossum (didelphis virginiana) erythrocytes. i. utilization of carbohydrates and purine nucleosides.	opossum erythrocytes filtered through cellulose columns were used to estimate their permeability to d-glucose and optimum inorganic phosphate requirement for d-glucose utilization at ph 7.4 and 8.1. d-glucose readily penetrated opossum red cells; there was no measurable difference whether plasma or electrolyte solution served as the suspending medium. optimum extracellular inorganic phosphate concentration for glucose utilization as indicated by red cell lactate production was ph-dependent, with ...	1984	6429161
collateral innervation of the inferior colliculus in the north american opossum: a study using fluorescent markers in a double-labeling paradigm.	the innervation of the opossum inferior colliculus was investigated using the retrograde transport of fluorescent markers in a double-labeling paradigm. true blue was injected into one inferior colliculus while nuclear yellow was placed into the other. many single-labeled neurons were found in all of the brainstem and cortical areas previously labeled by comparable injections of hrp. when the two injections of fluorescent markers were bilaterally symmetrical within the inferior colliculi, double ...	1984	6733522
why so many mammalian spermatozoa--a clue from marsupials?	mammals generally ejaculate many more spermatozoa than seem to be needed for fertilization. this apparent profligacy has not been explained, but observations made in marsupials may shed light on it. the virginia opossum, didelphis virginiana, inseminates only about three million spermatozoa, a very low number. as a corollary, relatively few (ca. 13 x 10(6] are stored in each cauda epididymidis. however, some 5% of the spermatozoa that the opossum ejaculates populate the oviduct about 12 h later ...	1984	6145161
the neuronal types and the distribution of 5-hydroxytryptamine and enkephalin-like immunoreactive fibers in the dorsal cochlear nucleus of the north american opossum.	the opossum dorsal cochlear nucleus is divided into four layers distinguishable either on the basis of differential distribution of neuron types or by neuropil organization. we have used nissl, golgi and protargol stained preparations to examine these components. four types of neurons (excluding granule cells) are seen. the principal neurons have large cell bodies arranged in a sheet defining layer ii, their apical dendrites extend dorsally to form an elaborate arbor in layer i and their basal d ...	1984	6372948
a simple technique for blood collection in the opossum (didelphis virginiana).	the left and right brachiocephalic veins were used for rapid collection of 5-10 ml blood samples in adult opossums. these vessels were also used to collect 0.5-1 ml blood samples in 120-day-old opossums. the animals were anaesthetized with 30 mg/kg of ketamine hydrochloride given intramuscularly prior to blood collection.	1984	10628788
scanning electron microscopic observations on the 9-day opossum (didelphis virginiana) embryo.	all three germ layers are present in the opossum embryo by the 9th prenatal day. the embryo proper is part of, and continuous with, the remainder of the chorionic wall. the wall of the yolk sac-chorion away from the embryo consists only of an outer covering of ectoderm and an inner layer of endoderm. ectodermal cells covering the neural folds have dome-shaped apices and often show large, bleb-like expansions. microvilli are short and few in number. the apical surfaces of ectodermal cells that ov ...	1984	6516775
two multigene families for marsupial neurohypophysial hormones? identification of oxytocin, mesotocin, lysipressin and arginine vasopressin in the north american opossum (didelphis virginiana).	oxytocin, mesotocin ([ile8]-oxytocin), lysipressin ([lys8]-vasopressin) and arginine vasopressin have been identified in the north american opossum (didelphis virginiana) by amino acid composition and high pressure liquid chromatography. the same peptides with the exception of mesotocin have previously been found in two south american opossums (didelphis marsupialis and philander opossum). although a dual heterozygocity could also explain the simultaneous presence of oxytocin/mesotocin on one ha ...	1984	6477584
ultrastructural observations on the shell membrane of the north american opossum (didelphis virginiana).	each developing opossum embryo is surrounded by a shell membrane which completely separates embryonic and maternal tissues. during the eighth and ninth prenatal days, the embryos together with their limiting shell membranes float freely within the uterine lumen, surrounded only by the secretions of the uterus. the shell membrane is transparent, nonelastic, tough, and capable of extreme deformation. it consists of a mat of interwoven fibers which vary in external diameter, are electron dense, and ...	1983	6650866
morphological observations on the parathyroid of the opossum (didelphis virginiana).	parathyroid iii of the opossum, didelphis virginiana, lies on the medial surface of the internal carotid artery at its origin just above the bifurcation of the common carotid artery. it is limited externally by a capsule and is subdivided into lobule-like structures by connective tissue septae. the parenchyma consists solely of chief (principal) cells, arranged in irregular cords and clumps supported by a delicate vascular connective tissue. ultrastructurally, the chief cells are polyhedral in s ...	1983	6862174
origin and topography of thalamocaudate projections in the opossum.	the origins of the thalamocadaute projections in the north american opossum include the intralaminar nuclei (parafascicular complex, the paracentral, centralis and central lateral nuclei) and the intermedial dorsal, medial dorsal and interanterior dorsal nuclei. of these, portions of the intralaminar nuclei exhibit rudimentary elements of a topographically organized projection. however, it is obvious that the patterns observed here are much less specific than those reported in other mammalian sp ...	1983	6856198
a developmental study of substance-p, somatostatin, enkephalin, and serotonin immunoreactive elements in the spinal cord of the north american opossum.		1983	6187780
luteal and follicular populations in the ovary of the opossum (didelphis virginiana) after ovulation.	the maximum diameters of all luteal and antral follicular structures were measured in opossum ovaries on days 3, 7 and 11 after oestrus, and follicles were classed as developing or atretic. ovarian weights and luteal diameters were equivalent in comparisons of pregnant and non-pregnant animals on each day. the number of cl (range 45-85) per animal per cycle indicated a very high ovulation rate for a mammal. luteinized follicles (1-4 per ovary) were identified in all day-3 ovaries. ovarian weight ...	1983	6822974
structure of the paws in didelphis virginiana.	the paws of didelphis virginiana show several unusual features. they possess dermatoglyphs on the foot pads, have opposable first digits and the pads show a peculiar vascular arrangement. the hallux lacks a claw. the degree of innervation and the number and size of pacinian corpuscles indicates that the paws of the opossum are finely sensitive to pressure and vibration.	1983	6660547