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Biomedical subjects

D Crews

Publications and source records attributed to D Crews.

At least 181 records · Page 10Linked to original sources
PubMed1984

Hormonal independence of courtship behavior in the male garter snake.

Garter snakes exhibit a dissociated reproductive tactic in which gonadal activity is minimal at the time of mating, increasing only after the breeding season has ended. Experiments are presented demonstrating that neither short-term nor longterm castration affects courtship behavior in adult male red-sided garter snakes (Thamnophis sirtalis parietalis). So long as males have passed through a low-temperature dormancy period (hibernation), castration either shortly after emergence in the spring, or before entering winter dormancy in the fall, does not prevent the display of intense courtship behavior on emergence. Similarly, males castrated during mating activity the previous spring prior to the annual testicular growth phase actively courted females on emergence from hibernation. Males adrenalectomized and castrated during low-temperature dormancy also courted females on emergence. Hypophysectomy during or before low-temperature dormancy did not prevent males from displaying high-intensity courtship behavior on emergence from hibernation. Treatment with sex steroid hormones, as well as hypothalamic and pituitary hormones, and a variety of neural and metabolic affectors also fails to elicit courtship behavior in noncourting males during the summer. It was concluded that causal mechanisms controlling courtship behavior in the red-sided garter snake are fundamentally different, at least at the physiological level, from those mechanisms described for many laboratory and domesticated species.

Adrenal Glands↗
PubMed1984

Role of the amygdala in the reproductive and aggressive behavior of the lizard, Anolis carolinensis.

Thirteen male green anole lizards were lesioned in the ventromedial nucleus (VMN) of the posterior dorsal ventricular ridge ("amygdala") and/or the paleostriatum (PS) to determine the influence of these structures on assertion and challenge displays addressed to male intruders, or courtship displays and copulatory neckgrip directed toward females. Lesions that affected both VMN and PS reduced or eliminated both challenge and courtship displays as well as the neckgrip, a crucial component in courtship. Subjects with lesions limited to VMN had assertion and challenge left unimpaired but courtship was reduced and neckgrip eliminated in most subjects. A lesion restricted to PS caused a significant deficit in challenge while other measures were unaffected. These data indicate that the VMN is involved in reproductive function in the green anole lizard.

Aggression↗
PubMed1983

The relationship among ovarian condition, steroid hormones, and estrous behavior in Anolis carolinensis.

The lizard Anolis carolinensis ovulates a single egg alternately from each ovary every 14 days. The ovulated egg enters the ipsilateral oviduct, acquires a shell, and is oviposited 18 or 19 days later. Thus, there is only a single egg in one of the oviducts (one-egg condition) during most of the estrous cycle, but there is a 4-5 day period when a mature, shelled egg is in one oviduct while a recently ovulated egg is in the contralateral oviduct (two-egg condition). Analysis of ovarian follicular diameters indicates that the largest follicle in a single ovary exhibits a growth spurt about halfway through its 28-day vitellogenic growth phase. The corpus luteum, once formed from the ovulated follicle, exhibits a linear decrease in weight, becoming fully regressed just before oviposition of the egg in the ipsilateral oviduct. Plasma concentrations of estradiol-17 beta and progesterone are high in two-egg animals. After oviposition, plasma concentrations of progesterone are still high in one-egg animals whereas those of estradiol-17 beta are much lower. These ovarian and hormonal changes during the estrous cycle are discussed in relation to the probable sources of estradiol-17 beta and progesterone, the control of the alternating pattern of ovulation and oviposition, and the role of steroid hormones in female sexual receptivity in this species.

Animals↗
PubMed1983

Metabolic changes in male snakes, Thamnophis melanogaster, during a breeding period.

1. Daily basking periods were lengthened substantially during a breeding period in a natural population of the snake, Thamnophis melanogaster. 2. In the laboratory, oxygen consumption of male T. melanogaster significantly increased during a breeding period, compared to pre- and post-breeding levels in the same males. 3. In both laboratory and field males, serum lipid increased initially and then decreased during the breeding period. 4. Serum protein of laboratory males decreased significantly following the breeding period. 5. Serum glucose did not change significantly in laboratory males, but increased significantly during the breeding period in field males. 6. Changes in oxygen consumption and nutrient distribution may reflect changing energy demands attendant with gonadal recrudescence in this snake.

Animals↗
PubMed1982

Serum concentrations of calcium and vitamin D metabolites in prosimians.

The concentrations of total calcium, 25-hydroxyvitamin D [25-(OH)D] and 1,25-dihydroxyvitamin D3 [1,25-(OH)2D3] were measured in serum obtained from prosimians, the brown lemurs. The mean serum calcium level was 10.6 mg/dl in male and female lemurs. The mean serum mean 25-(OH)D concentration in serum from male and female lemurs was 27.1 and 31.0 ng/ml, respectively. The mean serum level of 1,25-(OH)2D3 in the female and male lemurs was 65.2 and 65.9 pg/ml, respectively. A small segment of the lemurs had hypercalcemia and elevated serum concentrations of 25-(OH)D or 1,25-(OH)2D3, suggesting the idea that the episodic ingestion of a large quantity of the calcium- and vitamin D-enriched diet normally provided ad libitum might cause hypercalcemia.

Animals↗
PubMed1981

Female sex pheromone in the skin and circulation of a garter snake.

Serums and extracts of tissues from the female garter snake (Thamnophis sirtalis parietalis) each act as a pheromone and elicit male courtship behavior when applied to the back of another male. Since pheromonal activity is present in yolk and liver tissue of untreated females and can be induced with estrogen treatment in the serums and livers of males, the pheromone may be associated with the circulating yolk lipoprotein, vitellogenin.

Animals↗
PubMed1981

Estrogen-sensitive progestin binding sites in the brain of the lizard, Anolis carolinensis.

Cytosol binding sites for the synthetic progestin [3H]R5020 have been identified in the brain and oviduct from untreated and estrogen primed ovariectomized female lizards (Anolis carolinensis). Competition of various unlabeled steroids at either 10 nM (brain) or 10 and 100 nM (oviduct) revealed that progestins were effective competitors whereas two glucocorticoids as well as testosterone and estradiol were ineffective. The apparent dissociation constant (Kd) of the receptor for [3H]R5020 in the hypothalamus and telencephalon of the brain was determined to be 0.7-0.8 nM. The concentration of binding sites in the hypothalamus was approximately twice as great as in the telencephalon. The dissociation constant of the binding site for [3H]R5020 in the oviduct was determined to be 1.4-1.7 nM. Although sucrose density gradient centrifugation of brain cytosols labeled with [3H]R5020 failed to reveal a discretely sedimenting peak of radioactivity, oviduct cytosol gradients contained two broad peaks of [3H]R5020 binding at 3-6S and 8-9S. The concentration of [3H]R5020 binding sites in both the oviduct and hypothalamus was found to increase after estrogen treatment. Scatchard analysis of oviduct cytosol [3H]R5020 binding showed that estrogen priming increased binding levels 3-fold. Single point assays with 0.4 nM [3H]R5020 demonstrated that estrogen priming increased binding by 55% in hypothalamus but did not alter binding in cytosol from the telencephalon sample. These results suggest that the [3H]R5020 binding sites identified in the brain and oviduct of the lizard A. carolinensis may correspond to cytoplasmic progestin receptors. Furthermore, the finding of an estrogen-induced increase in the concentration of these receptors in the hypothalamus and oviduct indicate that the capability of estrogen to modulate the concentration of progestin receptor is present in a representative of a vertebrate class whose progenitors gave rise to birds and mammals.

Animals↗
PubMed1981

Effects of prostaglandins on sexual receptivity in the female lizard, Anolis carolinensis.

Prostaglandins (PGs) have been implicated in the mediation of sexual behavior in vertebrates. In this study, the effects of administered PGs on sexual receptivity were examined in the ovariectomized female green anole lizard (Anolis carolinensis). Injection (ip) of 15 microgram PGF2 alpha failed to induce sexual receptivity in nonreceptive females which were either untreated or estrogen primed. On the other hand, PGF2 alpha treatment of sexually receptive estrogen-pretreated females inhibited sexual receptivity 1 h post injection. A dose of 7.5 microgram PGF2 alpha was as effective as 15 microgram in inhibiting sexual receptivity, while a dose of 1.5 microgram was near the minimum effective level. Treatment with 15 microgram PGE2 and, to a lesser extent, PGE1 also reduced sexual receptivity. In contrast, arginine-8-vasotocin, a neuropeptide capable of stimulating smooth muscle contractions in reptiles, did not decrease sexual receptivity. The inhibitory effects of PG treatment observed at 1 h were diminished by 3 h and were no longer present 6 and 24 h post injection, with females, again, being fully receptive. Inhibition of sexual receptivity occurs very rapidly after PGF2 alpha treatment. When tested 5 min post injection, all females treated with 15 microgram arginine-8-vasotocin were sexually receptive. The oviducts were not required for PGF2 alpha inhibition of sexual receptivity, as sexual receptivity was inhibited in oviductectomized females 1 h after the injection of 15 microgram PGF2 alpha. The inhibitory action of PGF2 alpha was also observed when sexually receptive females were injected intracranially rather than ip. Intracranial injection of 3.8 microgram PGF2 alpha inhibited sexual receptivity in females tested 1 h post injection. These results indicate that exogenous PGs, possibly acting centrally within the brain, inhibit sexual receptivity in female A. carolinensis, a species with a rapid mating-induced termination of sexual receptivity.

Animals↗
PubMed1980

"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 and appose the cloacal regions. Dissection or palpation revealed that, in each instance, the courted animal was reproductively active, having ovaries containing large, preovulatory follicles, while the courting animal was either reproductively inactive or postovulatory, having ovaries containing only small, undeveloped follicles. These observations are significant for the questions they raise. For example, is this behavior a nonfunctional vestige of the species' ancestry, or is this behavior necessary for successful reproduction in the species (e.g., by priming reproductive neuroendocrine mechanisms as has been demonstrated in sexual species)?

Journal Article↗
PubMed1980

Luteinizing hormone-releasing hormone and thyrotropin-releasing hormone induction of female sexual receptivity in the lizard, Anolis carolinensis.

Both luteinizing hormone-releasing hormone (LHRH) and thyrotropin-releasing hormone (TRH) induce sexual receptivity in ovariectomized, estrogen-primed female lizards (Anolis carolinensis). Ovariectomized females pretreated with three daily injections of a subthreshold dose (0.2 micrograms) of estradiol benzoate were administered either 500, 1,000 or 1,500 ng of LHRH, or 1,000 ng of TRH 48 h following the last estrogen pretreatment injection. Hormone-treated females exhibited significantly higher sexual receptivity scores than controls when tested 2, 4, 6 and 24 h post-injection. Female sexual receptivity scores in females that were administered 500 ng of LHRH or 1,000 ng of deamido TRH were, however, no different than control scores at these test times. The observed ability of LHRH to increase female sexual receptivity is consistent with previous results in birds and mammals. The ability of TRH to increase female sexual receptivity is a novel finding that may underscore differences in neuroendocrine regulation of vertebrate estrous behavior.

Animals↗
PubMed1979

3H-estradiol, 3H-testosterone and 3H-dihydrotestosterone localization in the brain of the lizard Anolis carolinensis: an autoradiographic study.

The presence and the neuroanatomical topography of sex hormone concentrating cells in the brain of the American chameleon, Anolis carolinensis have been demonstrated by these experiments. After 3H-estradiol administration large numbers of hormone concentrating cells were found in the amygdala, septum, medial preoptic area, anterior hypothalamic area, the ventromedial and periventricular nuclei of the hypothalamus, and anterior pituitary. In addition, labelled cells were found in the torus semicircularis, in and around the nucleus isthmus pars parvocellularis. A small number of labelled cells could also be found in the rostral pallium, motor nucleus of the fifth cranial nerve, the raphé nuclei, and the spinal cord. After 3H-testosterone or 3H-dihydrotestosterone administration the neuroanatomical pattern was very similar to that found after 3H-estradiol; however, fewer labelled cells were seen after the androgens were given. Two exceptions to the similarity of pattern were in a caudal part of the pallium and in the mesencephalic tegmental area. Hormone-concentrating cells were found after 3H-testosterone or 3H-dihydrotestosterone administration, while labelled cells in these two areas after 3H-estradiol administration were extremely rare. The pattern of hormone-concentrating cells was the same in male and female brains, for each of the hormones. The preoptic area, hypothalamus, and anterior pituitary have been demonstrated in reptiles to be involved in neuroendocrine regulation and in the control of sex behaviors. The presence and neuroanatomical pattern of sex steroid binding cells in the brains of a wide variety of vertebrates have been documented. Large numbers of hormone-concentrating cells were found in all of these species in the medial preoptic area, tuberal hypothalamus, specific limbic structures, the mesencephalon deep to the tectum, and the anterior pituitary. Most hormone-concentrating cells in the brain of A. carolinensis were found in these same brain regions, thus indicating a vertebrate-wide stable core of hormone-concentrating cells in neuroanatomically defined regions.

Amygdala↗