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D Crews

Publications and source records attributed to D Crews.

At least 19 recordsLinked to original sources
PubMed2006

Testosterone induction of male-typical sexual behavior is associated with increased preoptic NADPH diaphorase and citrulline production in female whiptail lizards.

In rodents, male-typical copulatory behavior is generally dependent on gonadal sex steroids such as testosterone, and it is thought that the mechanism by which the hormone gates the behavior involves the gaseous neurotransmitter nitric oxide. According to one model, testosterone induces an up-regulation of nitric oxide synthase (NOS) in the preoptic area, increasing nitric oxide synthesis following exposure to a sexual stimulus. Nitric oxide in turn, possibly through its effect on catecholamine turnover, influences the way the stimulus is processed and enables the appropriate copulatory behavioral response. In whiptail lizards (genus Cnemidophorus), administration of male-typical levels of testosterone to females induces the display of male-like copulatory responses to receptive females, and we hypothesized that this radical change in behavioral phenotype would be accompanied by a large change in the expression of NOS in the preoptic area. As well as comparing NOS expression using NADPH diaphorase histochemistry between testosterone-treated females and controls, we examined citrulline immunoreactivity (a marker of recent nitric oxide production) in the two groups, following a sexual stimulus and following a nonsexual stimulus. Substantially more NADPH diaphorase-stained cells were observed in the testosterone-treated animals. Citrulline immunoreactivity was greater in testosterone-implanted animals than in blank-implanted animals, but only following exposure to a sexual stimulus. This is the first demonstration that not only is NOS up-regulated by testosterone, but NOS thus up-regulated is activated during male-typical copulatory behavior.

Androgens↗
PubMed2006

Reproductive tradeoffs and yolk steroids in female leopard geckos, Eublepharis macularius.

Life history theory predicts tradeoffs among reproductive traits, but the physiological mechanisms underlying such tradeoffs remain unclear. Here we examine reproductive tradeoffs and their association with yolk steroids in an oviparous lizard. Female leopard geckos lay two eggs in a clutch, produce multiple clutches in a breeding season, and reproduce for several years. We detected a significant tradeoff between egg size and the number of clutches laid by females during their first two breeding seasons. Total reproductive effort was strongly condition-dependent in the first season, but much less so in the second season. Although these and other tradeoffs were unmistakable, they were not associated with levels of androstenedione, oestradiol, or testosterone in egg yolk. Female condition and egg size, however, were inversely related to dihydrotestosterone (DHT) levels in egg yolk. Finally, steroid levels in egg yolk were not directly related to steroid levels in the maternal circulation when follicles were developing, indicating that steroid transfer to eggs is regulated. These findings suggest that maternal allocation of DHT could mitigate tradeoffs that lead to poor offspring quality (i.e. poor female condition) and small offspring size (i.e. small egg size).

Androstenedione↗
PubMed2005

The distributions of the duplicate oestrogen receptors ER-beta a and ER-beta b in the forebrain of the Atlantic croaker (Micropogonias undulatus): evidence for subfunctionalization after gene duplication.

Teleost fishes have three distinct oestrogen receptor (ER) subtypes: ER-alpha, ER-beta a (or ER-gamma) and ER-beta b. ER-beta a and ER-beta b arose from a duplication of an ancestral ER-beta gene early in the teleost lineage. Here, we describe the distribution of the three ER mRNAs in the hypothalamus and cerebellum of the Atlantic croaker to address two issues: the specific functions of multiple ERs in the neuroendocrine system and the evolution and fate of duplicated genes. ER-alpha was detected in nuclei of the preoptic area (POA) and hypothalamus previously shown to possess ER-alphas in teleosts. AcER-beta b, but not ER-beta a, labelling was detected in the magnocellular neurons of the POA, nucleus posterior tuberis, the nucleus recessus posterior and cerebellum. By contrast, acER-beta a, but not ER-beta b, was detected in the dorsal anterior parvocellular POA and suprachiasmatic nucleus. Both ER-betas were found in posterior parvocellular and ventral anterior POA nuclei, the ventral hypothalamus, and periventricular dorsal hypothalamus. The differences we observed in ER subtype mRNA distribution within well-characterized brain nuclei suggest that ER-beta a and ER-beta b have distinct functions in the neuroendocrine control of reproduction and behaviour, and provide evidence that the teleost ER-beta paralogues have partitioned functions of the ancestral ER-beta gene they shared with tetrapods.

Animals↗
PubMed2004

Tyrosine hydroxylase expression is affected by sexual vigor and social environment in male Cnemidophorus inornatus.

Although the distribution of catecholamine-synthesizing cells has been described for a variety of taxa, less is known about the functional significance of particular populations in nonmammalian species, especially reptiles. To understand the role of these populations in the display of social behaviors in lizards, we studied the interactive effects of sexual vigor (sexually vigorous vs. sluggish) and social condition (housing in isolation vs. with females) on the number and somal areas of cells expressing tyrosine hydroxylase (TH), a rate-limiting enzyme in catecholamine synthesis, in male whiptail lizards, Cnemidophorus inornatus. We found that, regardless of social condition, sexually vigorous males had more TH-immunoreactive (TH-ir) cells in the dorsal hypothalamus (DH) relative to sluggish males. Sexually vigorous males also had more TH-ir cells in the substantia nigra pars compacta (SNpc), but this difference was significant only among males housed with females. Sexually vigorous males that had been housed with females had smaller TH-ir cells in the preoptic area (POA) than vigorous males housed in isolation. On the other hand, no significant differences were found in the anterior hypothalamus. These results highlight the regional heterogeneity in the plasticity of TH expression and suggest that, just as in other species, the DH, SNpc, and POA might be involved in the expression of social behaviors and in behavioral plasticity following social experiences in lizards.

Animals↗
PubMed2004

Cytochrome oxidase activity in the preoptic area correlates with differences in sexual behavior of intact and castrated male leopard geckos (Eublepharis macularius).

Although the utility of analyzing behavioral experience effects on neural cytochrome oxidase (CO) activity is well recognized, the behavioral correlates of endogenous differences in CO activity have rarely been explored. In male leopard geckos (Eublepharis macularius), the incubation temperature experienced during embryogenesis (IncT) and age affect CO activity in the preoptic area (POA), an area that modulates copulatory behavior. In this study, the authors assessed whether differences in POA CO activity correlate with differences in sexual behavior in intact and castrated geckos. Males with IncT- and age-dependent increases in POA CO activity mounted females with shorter latencies while intact and after castration and ejaculated more frequently after castration. The authors discuss the predictive value of CO activity and propose similar parallels in other species.

Age Factors↗
PubMed2004

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 species Cnemidophorus inornatus (ancestral species). Data compiled over more than 2 decades include behavioral, endocrine, and neural differences between these two related species of whiptail lizards. For example, unlike females of the ancestral species, individuals of the descendant species display male-like mounting behavior (pseudocopulatory behavior) after ovulation. Pseudocopulatory behavior in the parthenogen is triggered by the progesterone surge after ovulation, and the behavioral capacity to respond to progesterone appears to be an ancestral trait that was inherited from C. inornatus males through the hybridization events. Interestingly, the regulation of sex steroid hormone receptor mRNA in brain areas critical for the expression of sociosexual behaviors differs between females of the two species and suggests that evolutionary changes in the regulation of gene expression could be a proximate mechanism that underlies the evolution of a novel social behavior in the parthenogen. Finally, because the sexual species is diploid, whereas the parthenogen is triploid, differences between the species could directly assess the effect of ploidy. The behavioral and neuroendocrinological data are pertinent for considering this possibility.

Animal Husbandry↗
PubMed2002

Vasoactive intestinal polypeptide contacts on gonadotropin-releasing hormone neurones increase following puberty in female rats.

Successful reproduction requires precise temporal coordination among various endocrine and behavioural events. The circadian system regulates daily temporal organization in behaviour and physiology, including neuroendocrine rhythms. The main circadian pacemaker in mammals is located in the suprachiasmatic nuclei (SCN) of the anterior hypothalamus. The SCN sends direct efferents to the reproductive axis via monosynaptic projections to gonadotropin-releasing hormone (GnRH) neurones. This communication generates circadian endocrine rhythms as well as the preovulatory luteinizing hormone (LH) surge necessary for successful ovulation. One SCN peptide thought to be important for the regulation of oestrous cycles is vasoactive intestinal polypeptide (VIP). VIP neurones from the SCN contact GnRH cells, and these cells are preferentially activated during an LH surge in rats. Unlike adult rats, prepubertal females do not exhibit oestrous cycles, nor do they exhibit an LH surge in response to oestradiol positive-feedback. The present study was undertaken to determine the extent to which the development of a 'mature' reproductive axis in female rats is associated with modifications in VIP contacts on GnRH neurones. The brains of diestrus adult (approximately 60 days of age) and prepubertal (21 days of age) female rats were examined using double-label fluorescence immunohistochemistry for VIP and GnRH, with light and confocal microscopy. Although the total number of GnRH-immunoreactive neurones did not differ between adult and prepubertal females, adults had a significant increase in the percentage of GnRH cells receiving VIP contacts compared to juveniles. These data suggest that the development of reproductive hormone rhythms and oestrous cyclicity may be, in part, due to modifications of VIP input to the GnRH system.

Animals↗
PubMed2002

Variation in reproductive behaviour within a sex: neural systems and endocrine activation.

Intrasexual variation in reproductive behaviour, morphology and physiology is taxonomically widespread in vertebrates, and is as biologically and ecologically significant as the differences between the sexes. In this review, we examine the diverse patterns of intrasexual variation in reproductive behaviours within vertebrates. By illustrating the genetic, cellular, hormonal and/or neural mechanisms underlying behavioural variation in a number of species, another level of complexity is added to studies of brain organization and function. Such information increases our understanding of the unique and conserved mechanisms underlying sex and individual differences in behaviour in vertebrates as a whole. Here, we show that intrasexual variation in behaviour may be discrete or continuous in nature. Moreover, this variation may be due to polymorphism at a single genetic locus or many loci, or may even be the result of phenotypic plasticity. Phenotypic plasticity simply refers to cases where a single genotype (or individual) can produce (or display) different phenotypes. Defined in this way, plasticity subsumes many different types of behavioural variation. For example, some behavioural phenotypes are established by environmental factors during early ontogeny, others are the result of developmental transitions from one phenotype early in life to another later in life, and still other strategies are facultative with different behaviours displayed in different social contexts.

Animals↗
PubMed2001

Role of steroidogenic factor 1 and aromatase in temperature-dependent sex determination in the red-eared slider turtle.

Red-eared slider turtles are genetically bipotential for sex determination. In this species, as in many other reptiles, incubation temperature of the egg determines gonadal sex. At higher incubation temperatures females are produced and increasing temperature appears to increase estrogen production in the embryonic brain. Treatment of eggs incubating at a male-producing temperature with exogenous estrogen causes ovaries to form. At a female-biased incubation temperature, prevention of estrogen biosynthesis or administration of nonaromatizable androgens results in the development of testes. In mammals, steroidogenic factor 1 (SF-1) regulates most genes required for estrogen biosynthesis, including aromatase. In both mammals and red-eared sliders, SF-1 is differentially expressed in males and females during gonadogenesis. We have examined both SF-1 gene expression and aromatase activity in embryos incubating at different temperatures and after manipulation to change the course of gonadal development. Our findings indicate a central role for SF-1 in enacting the effect of estrogen. Estrogen treatment directly or indirectly downregulates SF-1 and, ultimately, causes development of females. The inhibition of estrogen results in upregulation of SF-1 and male hatchlings. Thus, SF-1 may lie at the center of one molecular crossroad in male versus female differentiation of the red-eared slider.

Animals↗
PubMed2001

Distribution of androgen and estrogen receptor mRNA in the brain and reproductive tissues of the leopard gecko, Eublepharis macularius.

Incubation temperature during embryonic development determines gonadal sex in the leopard gecko, Eublepharis macularius. In addition, both incubation temperature and gonadal sex influence behavioral responses to androgen and estrogen treatments in adulthood. Although these findings suggest that temperature and sex steroids act upon a common neural substrate to influence behavior, it is unclear where temperature and hormone effects are integrated. To begin to address this question, we identified areas of the leopard gecko brain that express androgen receptor (AR) and estrogen receptor (ER) mRNA. We gonadectomized adult female and male geckos from an incubation temperature that produces a female-biased sex ratio and another temperature that produces a male-biased sex ratio. Females and males from both temperatures were then treated with equivalent levels of various sex steroids. Region-specific patterns of AR mRNA expression and ER mRNA expression were observed upon hybridization of radiolabeled (35S) cRNA probes to thin sections of reproductive tissues (male hemipenes and female oviduct) and brain. Labeling for AR mRNA was very intense in the epithelium, but not within the body, of the male hemipenes. In contrast, expression of ER mRNA was prominent in most of the oviduct but not in the luminal epithelium. Within the brain, labeling for AR mRNA was conspicuous in the anterior olfactory nucleus, the lateral septum, the medial preoptic area, the periventricular preoptic area, the external nucleus of the amygdala, the anterior hypothalamus, the ventromedial hypothalamus, the premammillary nucleus, and the caudal portion of the periventricular nucleus of the hypothalamus. Expression of ER mRNA was sparse in the septum and was prominent in the ventromedial hypothalamus, the caudal portion of the periventricular nucleus of the hypothalamus, and a group of cells near the torus semicircularis. Many of these brain regions have been implicated in the regulation of hormone-dependent, sex-typical reproductive and agonistic behaviors in other vertebrates. Consequently, these nuclei are likely to control such behaviors in the leopard gecko and also are candidate neural substrates for mediating temperature effects on behavior.

Amino Acid Sequence↗
PubMed2001

Effects of medial and dorsal cortex lesions on spatial memory in lizards.

In mammals and birds, the hippocampus is a major learning and memory center that plays a prominent role in spatial memory, the use of distal cues to guide navigation. The role of reptilian hippocampal homologues, the medial and dorsal cortex, in spatial memory has not been thoroughly investigated. The medial and dorsal cortex of reptiles is known to play a role in learning both tasks that are hippocampally dependent and tasks that are not hippocampally dependent in mammals and birds. In order to examine the specific role of the medial and dorsal cortex in spatial memory, we trained medial cortex, dorsal cortex, and sham lesioned Cnemidophorus inornatus lizards to locate the one heated rock of four identical rocks spaced evenly around the perimeter of a circular, sand filled, arena in a cool room. We used probe trials to examine the strategies used by lizards to locate the goal. Medial cortex lesions and dorsal cortex lesions slowed acquisition and altered the strategies used to locate the goal. However, none of the lizards adopted a spatial strategy to locate the goal suggesting that the dorsal cortex and medial cortex are involved in using non-spatial strategies for navigation.

Animals↗
PubMed2001

Control of attractivity and receptivity in female red-sided garter snakes.

Female red-sided garter snakes emerge from their hibernacula in the spring attractive and receptive to males. Attractivity is communicated by a pheromone released through the female's skin and is a consequence of ovarian recrudescence the previous summer. Receptivity, on the other hand, is stimulated by ovarian estrogen secretion during emergence itself. Mating renders females both unattractive and unreceptive. Another "mating" pheromone of male origin is important in making females unattractive after mating. To investigate the role of cloacal stimulation in the loss of attractivity and receptivity we injected a local anesthetic (lidocaine or tetracaine) in the cloacal region of females before mating. This does not prevent mating, although it blocks neural transmission of copulatory sensory stimuli. The time course of transition from attractive and receptive states was then observed. Females treated with local anesthetic as well as control females were unattractive within 15 min of mating. However, when retested 2-3 and 24 h after mating, a significantly higher proportion of treated females regained their attractivity, while mated control females remained unattractive. This restorative effect was transient, though, as treated females retested 48 h after mating were as unattractive as the controls. Both anesthetized and control females were unreceptive when tested following mating and did not regain receptivity with time. Last, the mating-induced surge in circulating concentrations of prostaglandin was diminished in females that received a local anesthetic prior to mating. Taken together these results indicate that the loss of attractivity and receptivity following mating in the red-sided garter snake is due to combined effects of a mating pheromone and a physiological, neurally mediated response to the sensation of stimuli associated with the act of mating.

Animals↗
PubMed2001

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 inornatus and Cnemidophorus uniparens). Cnemidophorus lizards offer a unique system to study evolutionary changes in functionality because ancestral (e.g., C. inornatus) and descendant (e.g., C. uniparens) species can be studied in parallel. Cnemidophorus uniparens is an all-female, parthenogenetic species and is the triploid descendant of the sexual and diploid species C. inornatus. Here we report that in castrated male C. inornatus and ovariectomized C. uniparens a dopamine D1 agonist increased the proportion of individuals mounting and decreased the latency to mount. Moreover, there was a species difference in sensitivity to the agonist: Mounting was elicited at a lower dose in C. uniparens than in C. inornatus. One possible explanation for this heightened sensitivity in the triploid parthenogen is that, by virtue of the increased ploidy, the parthenogen has elevated levels of D1 receptor in limbic brain areas modulating courtship behavior.

Animals↗
PubMed2001

Estradiol and incubation temperature modulate regulation of steroidogenic factor 1 in the developing gonad of the red-eared slider turtle.

Red-eared slider turtles are genetically bipotential for sex determination, with incubation temperature of the egg determining gonadal sex. At higher incubation temperatures, females are produced, possibly due to increased biosynthesis of estrogen. Exogenous estrogen causes the formation of ovaries, and prevention of estrogen biosynthesis results in the development of testes. In mammals, steroidogenic factor 1 (SF-1) regulates most genes required for estrogen biosynthesis from cholesterol. In mammals as well as red-eared slider turtles, SF-1 is differentially expressed in males and females during gonadogenesis. To examine a possible role for SF-1 in temperature-dependent sex determination, we assayed its expression in red-eared slider turtles after treatments that alter sex development during gonadogenesis of the wild-type organism. We examined gonadal SF-1 expression in embryos 1) incubating at three different temperatures, 2) after treating eggs with estrogen at a male-producing temperature, and 3) after inhibition of estrogen biosynthesis at a female-producing temperature. Our findings suggest that both temperature and estrogen lie upstream of SF-1 in a sex-determining regulatory hierarchy in red-eared slider turtles and that estrogen directly or indirectly modulates the regulation of SF-1 expression.

Animals↗
PubMed2000

Identification of a third distinct estrogen receptor and reclassification of estrogen receptors in teleosts.

This paper describes three distinct estrogen receptor (ER) subtypes: ERalpha, ERbeta, and a unique type, ERgamma, cloned from a teleost fish, the Atlantic croaker Micropogonias undulatus; the first identification of a third type of classical ER in vertebrate species. Phylogenetic analysis shows that ERgamma arose through gene duplication from ERbeta early in the teleost lineage and indicates that ERgamma is present in other teleosts, although it has not been recognized as such. The Atlantic croaker ERgamma shows amino acid differences in regions important for ligand binding and receptor activation that are conserved in all other ERgammas. The three ER subtypes are genetically distinct and have different distribution patterns in Atlantic croaker tissues. In addition, ERbeta and ERgamma fusion proteins can each bind estradiol-17beta with high affinity. The presence of three functional ERs in one species expands the role of ER multiplicity in estrogen signaling systems and provides a unique opportunity to investigate the dynamics and mechanisms of ER evolution.

Amino Acid Sequence↗
PubMed2000

Sex steroid levels across the reproductive cycle of female leopard geckos, Eublepharis macularius, from different incubation temperatures.

Incubation temperature during embryonic development determines gonadal sex in many reptiles, including the leopard gecko (Eublepharis macularius). In this study, we examined the hormonal and behavioral changes that occur during the reproductive cycle of female leopard geckos from four (i.e., 26, 30, 32.5, and 34 degrees C) incubation temperatures. Controlling for reproductive status, plasma levels of dihydrotestosterone (DHT), testosterone (T), and progesterone (P) varied with incubation temperature but estradiol 17-beta (E2) levels did not. Controlling for the effects of incubation temperature, DHT and T levels were low when females were previtellogenic, increased slightly during early vitellogenesis, increased dramatically during late vitellogenesis (i.e., prior to ovulation), and then decreased to previtellogenic levels after ovulation. In contrast, E2 levels increased gradually from the previtellogenic stage to the early vitellogenic stage, peaked during late vitellogenesis, and decreased to previtellogenic levels after ovulation. Levels of P increased from the previtellogenic stage to the early vitellogenic stage, remained elevated during late vitellogenesis, and then decreased after ovulation. Moreover, we determined that females were not sexually receptive when previtellogenic, were somewhat receptive during early vitellogenesis (approximately 20% receptive), were most receptive during late vitellogenesis (approximately 80% receptive), and were again unreceptive after ovulation. Incubation temperature did not influence receptivity. Overall, these data show that hormone levels and behavior change coordinately during the reproductive cycle. Although incubation temperature has persistent effects on endocrine physiology in adult female leopard geckos, these effects are modest compared to hormonal changes across the reproductive cycle.

Animals↗