| sexually dimorphic areas in the brain of whiptail lizards. | the whiptail lizard species cnemidophorus inornatus exhibits sexually dimorphic mating behaviors. we report that complementary sexual dimorphisms exist in two hypothalamic regions in male and female c. inornatus. the anterior hypothalamus-preoptic area (ah-poa), which is involved in male-typical mounting and intromission behaviors, is larger in males. the ventromedial hypothalamus (vmh), which controls female-typical receptivity, is larger in females. the all-female whiptail lizard cnemidophorus ... | 1990 | 2285854 |
| neural control of male-like pseudocopulatory behavior in the all-female lizard, cnemidophorus uniparens: effects of intracranial implantation of dihydrotestosterone. | dihydrotestosterone was implanted directly into the brain of ovariectomized all-female cnemidophorus uniparens. only implants located in the anterior hypothalamus-preoptic area (ah-poa) induced male-like pseudocopulatory behavior. implants in other brain regions, including the ventromedial hypothalamus (vmh), failed to elicit mounting and intromission behavior. implants in the vmh also failed to elicit female-like receptive behavior. radioimmunoassay revealed no significant difference in circula ... | 1987 | 3610057 |
| reptilian sex steroid receptors: amplification, sequence and expression analysis. | sex steroid hormones secreted by the gonads play a central role in the reproduction of all vertebrates. in addition to direct effects on gametogenesis, sex steroid hormones are important in sexual development, brain organization, and sexual behavior. the actions of sex steroid hormones are mediated primarily by ligand-dependent transcription factors, or receptors which bind to specific sequences of the dna and alter the transcription rates of nearby genes. we have used the polymerase chain react ... | 1995 | 7495707 |
| cloning and in situ hybridization analysis of estrogen receptor, progesterone receptor, and androgen receptor expression in the brain of whiptail lizards (cnemidophorus uniparens and c. inornatus). | gonadal steroid hormones act upon specific areas of the vertebrate brain to affect the reproductive physiology and behavior of the animal. steroid receptors are members of a superfamily of ligand-dependent transcription factors that mediate the effects of steroid hormones by modulating gene expression in the cells containing the receptors. the neuroanatomical distributions of steroid receptor-containing cells have been described for several species by using steroid autoradiography, immunocytoche ... | 1994 | 7814669 |
| progesterone inhibits female-typical receptive behavior and decreases hypothalamic estrogen and progesterone receptor messenger ribonucleic acid levels in whiptail lizards (genus cnemidophorus). | female-typical sexual behavior in tetrapods is mediated primarily by estrogen and progesterone acting through intracellular receptors at specific sites in the mediobasal hypothalamus. progesterone exerts both faciliatory and inhibitory actions on female sexual behavior and in well-studied rodent models, the inhibitory actions are exerted through downregulation of progesterone and estrogen receptors. this study examined progesterone effects on both female-typical sexual behavior and hypothalamic ... | 1996 | 8797022 |
| molecular cloning and characterization of reptilian estrogen receptor cdnas. | cdnas encoding alligator (caiman), caiman crocodilus and whiptail lizard, cnemidophorus uniparens estrogen receptors (ers) were cloned and sequenced. this is the first report of full-length cdna sequences for reptilian ers, to our knowledge. the full-length alligator (caiman) er cdna (1764 bp, 587 amino acid residues) shows 68% amino acid homology with the full-length whiptail lizard er cdna (1746 bp, 581 amino acid residues). the respective ligand binding e domains have 87 and 83% amino acid ho ... | 2001 | 11604222 |
| regulation of pseudosexual behavior in the parthenogenetic whiptail lizard, cnemidophorus uniparens. | neuroendocrine mechanisms underlying complementary behaviors like male-typical mounting and female-typical receptivity are most often studied independently in males and females, respectively. cnemidophorus uniparens is a unisexual lizard species consisting only of females that alternately express male- and female-like pseudosexual behavior across the ovarian cycle. intact, postovulatory (postov), and ovariectomized (ovx), androgen-implanted animals [ovx plus testosterone (t)] exhibit male-like m ... | 2008 | 18483155 |
| steroidogenic enzyme gene expression in the brain of the parthenogenetic whiptail lizard, cnemidophorus uniparens. | the steroidogenic enzyme cyp17 is responsible for catalyzing the production of androgenic precursors, while cyp19 converts testosterone to estradiol. de novo neurosteroidogenesis in specific brain regions influences steroid hormone dependent behaviors. in the all-female lizard species cnemidophorus uniparens, individuals alternately display both male-like mounting and female-like receptivity. mounting is associated with high circulating concentrations of progesterone following ovulation (postov) ... | 2009 | 19084508 |
| ovarian and adrenal function in the parthenogenetic whiptail lizard cnemidophorus uniparens in the field and laboratory. | the purpose of this study was to document circulating concentrations of corticosterone in the plasma in relation to the ovarian follicular cycle in animals in the field and to examine the effects of captivity and laboratory manipulations on plasma corticosterone in the parthenogenetic whiptail lizard cnemidophorus uniparens. in nature, circulating concentrations of corticosterone are highest in previtellogenic individuals when concentrations of progesterone are basal and estradiol-17 beta is und ... | 2008 | 2583474 |
| disruption of gestation and egg shelling in deluteinized oviparous whiptail lizards cnemidophorus uniparens (reptilia: teiidae). | | 1997 | 499745 |
| behavioral facilitation of reproduction in sexual and unisexual whiptail lizards. | all-female, parthenogenetic species afford a unique test of hypotheses regarding the nature and evolution of sexuality. mating behavior accomplishes the transfer of gametes and stimulates the coordination of reproductive activity of the male and female. cnemidophorus uniparens, a parthenogenetic species, is believed to have resulted from the hybridization of two extant gonochoristic species, cnemidophorus inornatus and cnemidophorus gularis. c. uniparens regularly and reliably perform behaviors ... | 1986 | 3467325 |
| evolutionary changes in dopaminergic modulation of courtship behavior in cnemidophorus whiptail lizards. | preoptic dopamine release is integral to the display of copulatory behaviors in male mammals and birds. however, while the anatomical distributions of the dopamine synthesizing enzyme tyrosine hydroxylase are similar among vertebrates, evolutionary changes in the functional role of dopamine are poorly understood. in this study, we tested whether a dopamine d1 receptor agonist would facilitate the display of courtship and copulatory behaviors in two related cnemidophorine lizards (cnemidophorus i ... | 2001 | 11716577 |
| androgenic regulation of steroid hormone receptor mrnas in the brain of whiptail lizards. | sex and species differences in androgenic regulation of steroid hormone receptor mrnas were examined in the diencephalon of two species of whiptail lizards: cnemidophorus inornatus is a sexual species and the direct evolutionary ancestor to cnemidophorus uniparens, an all-female parthenogenetic species. lizards were gonadectomized and treated with different doses of either aromatizable testosterone or nonaromatizable dihydrotestosterone. the relative abundances of androgen-, oestrogen-, and prog ... | 2000 | 10849204 |
| the effects of intracranial implantation of estrogen on receptivity in sexually and asexually reproducing female whiptail lizards, cnemidophorus inornatus and cnemidophorus uniparens. | the ventromedial hypothalamus (vmh) is an important site in the neuroendocrine control of sexual receptivity in mammals. this study was conducted to determine if the vmh was also involved in estrogen induction of receptivity in whiptail lizards. estradiol benzoate (eb) was implanted into the vmh of ovariectomized cnemidophorus inornatus, a sexually reproducing species, and c. uniparens, a parthenogenetic species which displays "pseudosexual" behaviors similar to the sexual behaviors typical of b ... | 1991 | 1937427 |
| natural hybridization between parthenogenetic and bisexual lizards: detection of uniparental source of skin grafting. | skin graft evidence is used to directly identify the unisexual parent of natural hybrids produced between the bisexual species cnemidophorus inornatus and the unisexual cnemidophorus neomexicanus. reciprocal grafts transplanted among there suspected hybrids between cnemidophorus inornatus and cnemidophorus neomexicanus are rejected as well as grafts from the hybrids to c. neomexicanus, indicating that the hybrids are each genetically different from each other and that c. neomexicanus has the abi ... | 1976 | 778325 |
| making males from females: the effects of aromatase inhibitors on a parthenogenetic species of whiptail lizard. | the parthenogenetic whiptail lizard cnemidophorus uniparens provides a good model for the study of sex determination and sexual differentiation because genetic variation is minimal and all unmanipulated embryos will develop as females. thus any deviation from the established course of development can be identified as a treatment effect. previous work has shown that early prenatal treatment with cgs16949a, a nonsteroidal aromatase inhibitor, causes hatchlings to develop as males. the present stud ... | 1995 | 8536943 |
| species differences in estrogen receptor and progesterone receptor-mrna expression in the brain of sexual and unisexual whiptail lizards. | circulating concentrations of gonadal steroid hormones and reproductive behavior in female vertebrates vary as a function of ovarian state. steroids secreted by the ovary, specifically estrogen and progesterone, influence the expression of behaviors associated with reproduction by intracellular sex steroid receptors located in specific regions of the brain. using in situ hybridization, we analyzed estrogen receptor and progesterone receptor messenger rna expression in several brain regions of ov ... | 1995 | 7496397 |
| species differences in behavioral and neural sensitivity to estrogen in whiptail lizards: correlation with hormone receptor messenger ribonucleic acid expression. | cnemidophorus uniparens is a unisexual species of whiptail lizard of hybrid origin whereas c. inornatus is a sexual species and the maternal ancestor of c. uniparens. together they represent an excellent model system for investigating the evolution of hormone-brain-behavior relationships. normal circulating estradiol (e) concentrations in c. uniparens are approximately 5-fold lower than those of female c. inornatus in a similar reproductive state. experiments were performed to determine whether ... | 1995 | 7659192 |
| electrolytic lesions to the ventromedial hypothalamus abolish receptivity in female whiptail lizards, cnemidophorus uniparens. | lesions to the ventromedial hypothalamus (vmh) inhibit receptive sexual behavior in the whiptail lizard, cnemidophorus uniparens, an all-female species. all lesions to the vmh that effectively abolished receptivity specifically damaged the dorsal lateral vmh, an area containing high concentrations of estrogen receptor in this species. these data further emphasize conservation of the vmh as a brain area critical to the expression of female sexual behavior in vertebrates. | 1995 | 7663980 |
| regulation of estrogen receptor and progesterone receptor messenger ribonucleic acid by estrogen in the brain of the whiptail lizard (cnemidophorus uniparens). | receptive behavior in females vertebrates is controlled by hormones, principally estrogen, secreted by the ovary. estrogen influences behavior by interacting with a specific estrogen binding protein, or receptor, located in target cells in certain hypothalamic nuclei. to better understand the molecular mechanisms involved in the control of receptive behavior in whiptail lizards, we investigated the effects of exogenous estrogen on the regulation of estrogen receptor and progesterone receptor exp ... | 1995 | 7767324 |
| the bisexual brain: sex behavior differences and sex differences in parthenogenetic and sexual lizards. | the parthenogenetic lizard cnemidophorus uniparens alternates in the display of male-like and female-like sexual behavior, providing a unique opportunity for determining the neuronal circuits subserving gender-typical sexual behavior within a single sex. here we report a 6-fold greater [14c]2-fluoro-2-deoxyglucose uptake in the medial preoptic area of c. uniparens displaying male-like behavior in comparison with c. uniparens displaying female-like receptivity. the ventromedial nucleus of the hyp ... | 1994 | 7850465 |
| putative aromatase inhibitor induces male sex determination in a female unisexual lizard and in a turtle with temperature-dependent sex determination. | treatment of developing embryos of two diverse species of reptiles with fadrozole (a potent and specific nonsteroidal inhibitor of aromatase activity in mammals) resulted in the induction of male sex determination. in the first experiment, males were produced in an all-female parthenogenic species of lizard (cnemidophorus uniparens). in the second experiment, male sex determination was induced in a turtle (trachemys scripta) with temperature-dependent sex determination. the results support the h ... | 1994 | 8046299 |
| the effects of sex steroid treatments on sexual differentiation in a unisexual lizard, cnemidophorus uniparens (teiidae). | cnemidophorus uniparens is a parthenogenetic unisexual species of lizard in which each individual develops as a female, making it a unique animal model for the study of sexual differentiation. in one study, administration of exogenous testosterone before and/or after hatching influenced the development of the gonads, the accessory reproductive ducts, the renal sex segment of the mesonephric kidney, and the femoral glands, a secondary sex character. testosterone treatment also affected the cross- ... | 1986 | 3959084 |
| sex steroid hormones during the ovarian cycle of an all-female, parthenogenetic lizard and their correlation with pseudosexual behavior. | cnemidophorus uniparens is a unisexual lizard that reproduces by parthenogenesis. individuals of this species display male-like and female-like copulatory behaviors during different phases of the ovarian cycle suggesting that these pseudocopulatory behaviors are hormonally activated. to learn more about both the endocrinology of parthenogenesis and the possible hormonal activation of male-like copulatory behavior in female individuals, we (1) characterized changes in plasma levels of the sex ste ... | 1985 | 4065527 |
| intraclonal histocompatibility in a parthenogenetic lizard: evidence of genetic homogeneity. | a total of 175 skin grafts were transplanted among 20 individuals belonging to two separate populations of the parthenogenetic lizard cnemidophorus uniparens. of these, 98.8 percent were permanently accepted, which indicates that all individuals of each population may be genetically identical. these results further suggest that large populations or the entire species may consist of one clone derived from a single individual. | 1976 | 779030 |
| successive clutches induced by surgical excision of post-ovulatory oocytes in the lizard cnemidophorus uniparens. | 19 animals had eggs excised from the oviducts soon after ovulation. number of clutches was nearly tripled in excised animals as compared to controls. an influence of eggs in the oviduct on number of clutches is suggested and may indicate a neuronal link between oviduct and hypothalamus. | 1976 | 1278326 |
| reproduction and the mechanism of meiotic restitution in the parthenogenetic lizard cnemidophorus uniparens. | | 1971 | 5542237 |
| molecular characterization and brain distribution of the progesterone receptor in whiptail lizards. | progesterone and its nuclear receptor are critical in modulating reproductive physiology and behavior in female and male vertebrates. whiptail lizards (genus cnemidophorus) are an excellent model system in which to study the evolution of sexual behavior, as both the ancestral and descendent species exist. male-typical sexual behavior is mediated by progesterone in both the ancestral species and the descendant all-female species, although the molecular characterization and distribution of the pro ... | 2011 | 21185292 |
| neuronal nitric oxide synthase as a substrate for the evolution of pseudosexual behaviour in a parthenogenetic whiptail lizard. | the evolution of neuroendocrine mechanisms governing sex-typical behaviour is poorly understood. an outstanding animal model is the whiptail lizard (cnemidophorus) because both the ancestral and descendent species still exist. the ancestral little striped whiptail, cnemidophorus inornatus, consists of males and females, which exhibit sex-specific mating behaviours. the descendent desert grassland whiptail, cnemidophorus uniparens, consists only of females that alternately exhibit both female-lik ... | 2011 | 21126273 |
| testosterone stimulates mounting behavior and arginine vasotocin expression in the brain of both sexual and unisexual whiptail lizards. | in nonmammalian vertebrates the abundance of arginine vasotocin (avt) neurons in the brain is sexually dimorphic, a pattern that is modulated by testicular androgen. this peptide is thought to be involved in the control of male-typical mounting behaviors. the all-female desert-grasslands whiptail (cnemidophorus uniparens) reproduces by obligate parthenogenesis and in nature no males exist, but eggs treated with aromatase inhibitor hatch into individuals (called virago c. uniparens) having testes ... | 2007 | 18391518 |
| serotonergic modulation of male-like pseudocopulatory behavior in the parthenogenetic whiptail lizard, cnemidophorus uniparens. | hormone-neurotransmitter interactions form an important link through which hormones influence a variety of behavioral processes. typically, sexual behavior is dimorphic with males mounting receptive females. in the all-female lizard species cnemidophorus uniparens, individuals display both male-like pseudocopulation and female-like receptivity. these respective behavioral states are correlated with high circulating concentrations of progesterone following ovulation and of estrogen preceding it. ... | 2006 | 16793042 |
| the nitric oxide synthase inhibitor l-name suppresses androgen-induced male-like pseudocopulatory behavior in whiptail lizards. | the synthesis of nitric oxide by the enzyme nitric oxide synthase (nos) is involved in the androgen-dependent gating of male-typical copulatory behavior, both centrally, particularly in the preoptic area, and peripherally, notably through its role in penile erection. in the all-female whiptail lizard species cnemidophorus uniparens, individuals display copulatory behaviors indistinguishable from males of similar species if gonadectomized and treated with testosterone. in this experiment, androge ... | 2005 | 16023092 |
| tracing the evolution of brain and behavior using two related species of whiptail lizards: cnemidophorus uniparens and cnemidophorus inornatus. | cnemidophorus whiptail lizards offer a unique opportunity to study behavioral and neural evolution because unlike most genera, ancestral and descendant species are still extant, and comparisons between species provide a window into correlated changes in biological organization through speciation. this review focuses on the all-female or parthenogenetic species cnemidophorus uniparens (descendant species), which evolved through several hybridization events involving the sexually reproducing speci ... | 2004 | 14752207 |
| teratoma in desert grassland whiptail lizards (cnemidophorus uniparens). | the clinical, gross necropsy, and histopathology findings in two unrelated desert grassland whiptail lizards (cnemidophorus uniparens) with teratoma are described. the desert grassland whiptail is a parthenogenic lizard species with a polyploid chromosomal complement. the chromosome composition of the teratomas from these lizards was not determined. | 2001 | 12790431 |
| "sexual" behavior in parthenogenetic lizards (cnemidophorus). | all-female, parthenogenetic species afford a unique test of hypotheses regarding the nature and evolution of sexuality. basic data on the behavior of parthenogens are lacking, however. we have discovered, from observations of captive cnemidophorus uniparens, c. velox, and c. tesselatus, behavior patterns remarkably similar to the courtship and copulatory behavior of closely related sexual species. briefly, in separately housed pairs, one lizard was repeatedly seen to mount and ride its cagemate ... | 1980 | 16592761 |
| refractoriness in female lizard reproduction: a probable circannual clock. | postreproductive cnemidophorus uniparens maintained under free-running conditions of constant darkness for 7 months became reproductive at the same time as controls exposed to a long photoperiod. this lizard exhibits a pause in reproductive activity (refractory period) commencing in late summer in nature and terminating in mid-december in captivity. both groups terminated refractoriness and started reproducing simultaneously in december despite maintenance of the experimental group in darkness s ... | 1977 | 17783251 |