Genes controlling polyunsaturated fatty acid synthesis are developmentally regulated in broiler chicks.

1. The objective of this study was to characterise the regulation of the pathways that synthesise long-chain polyunsaturated fatty acids (PUFA) on developing adipose deposits in broiler embryos and chicks. Subcutaneous adipose depots were harvested from embryos and embryonic d E13, E15 and E17. Subcutaneous, abdominal and crop (neck) adipose, as well as liver, were collected at 7 and 14 d post-hatch. 2. Targeted RNA sequencing was used to quantify expression of 6 elongation of very long-chain fatty acid (ELOVL) genes, two isoforms of stearoyl-CoA desaturase (SCD and SCD5), and three fatty acid desaturases (FADS1, FADS2, and FADS6) in each depot and in the liver. Expression levels of marker genes for fatty acid oxidation and adipogenesis (peroxisome proliferator-activated receptor gamma (PPARG)) were quantified. Fatty acid composition of subcutaneous adipose was analysed using gas chromatograph-mass spectrometry (GC/MS). 3. Genes in the PUFA synthetic pathway were differentially expressed across developmental ages and between depots. These include elongase and desaturase genes, that have not previously been characterised in chicken. Correlation analyses identified subsets of co-regulated genes and fatty acids and highlighted relationships that may influence adipose metabolism and development. 4. It was concluded that PUFA synthesis is an active and dynamically regulated pathway in developing adipose deposits in the broiler chick. These data highlighted potential novel roles for specific elongase and desaturase genes in adipose deposition and metabolism.

Vomeronasal organ: critical role in mediating sexual behavior of the male hamster.

Sexual behavior in male hamsters is totally abolished by bilateral removal of the olfactory bulbs. This operation eliminates sensory input from both the olfactory and the vomeronasal systems. We previously demonstrated that peripheral destruction of the olfactory receptors caused anosmia but did not impair male hamster mating behavior. Here we demonstrate that peripheral deafferentation of the vomeronasal system produces severe sexual behavior deficits in approximately one-third of the treated animals. Combined deafferentation of both the vomeronasal and the olfactory systems eliminates copulation in 100 percent of the animals. This is the first experimental demonstration of a functional role for the vomeronasal organ in a mammalian species.

Medial nucleus of the amygdala mediates chemosensory control of male hamster sexual behavior.

Bilateral lesions restricted to the medial nucleus of the amygdala eliminate mating behavior in the male hamster and severely diminish the male's sniffing and licking investigation of the female hamster's anogenital region. The results suggest that olfactory and vomeronasal sensory information critical to male mating behavior is processed in the medial nucleus, which is an androgen-binding brain area. Thus the medial nucleus may act as a relay through which chemosensory information influences activity in the medial preoptic-anterior hypothalamic junction and the bed nucleus of the stria terminals, areas important in the mediation of male sexual behavior.

Differential effects of photoperiodic history on the responses of gonadotrophins and prolactin to intermediate daylengths in the male Syrian hamster.

The effect of photoperiodic history on the neuroendocrine response to intermediate daylengths (11-13.5 hr of light) was investigated in the male Syrian hamster. The duration of the nocturnal peak of pineal melatonin content was inversely proportional to photoperiod and independent of photoperiodic history. Serum levels of prolactin were lower in animals exposed to shorter photoperiods. Photoperiodic history had little effect on the response of serum prolactin to intermediate daylengths. Serum luteinizing hormone (LH) concentrations were also lower in shorter photoperiods, but in addition were sensitive to the direction of photoperiodic change, so that a single photoperiod could be interpreted as either stimulatory or inhibitory to LH secretion. This effect of photoperiodic history was expressed at intermediate photoperiods with 12-13.5 hr of light. The sensitivity of serum follicle-stimulating hormone (FSH) levels to photoperiodic history was masked by an early onset of photorefractoriness. Testicular size and serum testosterone levels revealed weaker effects of photoperiodic history; these were attributed to the dissociation between gonadotrophin and prolactin secretion induced by intermediate daylengths. The contrasting effects of photoperiodic history on the secretion of LH and prolactin may represent the expression of multiple photoperiodic time-measuring systems.

Photoperiodic influences on sexual behavior in male Syrian hamsters.

The effect of photoperiodic conditions on sexual behavior was investigated in male Syrian hamsters that were either gonadally intact, or castrated and treated with low doses of testosterone throughout the experiment. Hamsters were exposed to long (LD 16:8) or short (LD 8:16) days for 7 weeks; for the next 8 weeks, either they were exposed to an intermediate daylength (LD 12:12), or daylength conditions remained unchanged. Sexual behavior was affected by photoperiod conditions in both gonadally intact animals and testosterone-treated castrates, but to different degrees. Intact males exposed to short days for 15 weeks exhibited gonadal regression, and their copulatory performance was impaired. The percentage of animals that intromitted or ejaculated was significantly reduced. Additional measures of sexual performance among the copulating males were also affected. In contrast, among the castrates with testosterone clamped at low but stable levels, the proportion of males that mounted, intromitted, or ejaculated was not affected by photoperiod. However, among the males that continued to copulate, sexual performance changes were present in the short-day castrates that resembled those displayed by the intact males. We infer that these behavioral effects in both hormonal conditions reflect primarily a difficulty in the attainment of intromission. Gonadal regression alone cannot easily account for the behavioral deficits of the intact males, because circulating testosterone levels at the end of the experiment were not significantly different between the gonadally intact hamsters and the castrated, testosterone-treated hamsters exposed continuously to short days. Males transferred from either long or short days to the intermediate-daylength condition responded behaviorally to this photoperiod as if it were a short day, that is, their ejaculatory frequency declined. We conclude that male hamsters exposed to photoinhibitory daylengths exhibit deficits in their sexual behavior, not only because endogenous levels of testosterone decrease, but also because the substrates on which this hormone acts become less responsive. We hypothesize that under physiological conditions, the episodic secretion of testosterone imposes constraints on the maintenance or restoration of copulation, and that the potent behavioral effects achieved by constant-release implants of testosterone may mask the presence of photoperiodically induced alterations in the hamster's sensitivity to this gonadal hormone.

Neurons of origin and fiber trajectory of amygdalofugal projections to the medial preoptic area in Syrian hamsters.

The amygdaloid neurons of origin and the trajectory of amygdaloid fibers to the medial preoptic area of the adult male Syrian hamster were identified by using horseradish peroxidase (HRP) histochemistry. After iontophoresis of HRP into the medial preoptic area, retrogradely labeled amygdaloid neurons were located in the dorsal and caudal parts of the medial amygdaloid nucleus and throughout the amygdalohippocampal area. No amygdaloid neurons were labeled after HRP applications confined to the most rostral portion of the medial preoptic area (anterior to the body of the anterior commissure). Following more caudal medial preoptic area injections (body of the anterior commissure to the suprachiasmatic nucleus) the distribution of retrogradely labeled cells in the medial amygdaloid nucleus and the amygdalohippocampal area revealed no topographic organization of the amygdalopreoptic connections. When amygdaloid neurons were labeled, the amygdalohippocampal area contained two to five times as many HRP-filled cells as the medial amygdaloid nucleus. Retrogradely transported HRP could be followed from the medial preoptic area to the amygdala through fibers in the dorsomedial quadrant of the stria terminalis. In addition, electrolytic lesions of the stria terminalis prior to iontophoresis of HRP into the medial preoptic area prevented retrograde transport to neurons in both the dorsocaudal medial amygdaloid nucleus and the amygdalohippocampal area. These results confirm earlier observations describing the location of autoradiographically labeled efferents from the medial amygdaloid nucleus to the medial preoptic area and provide new information about the restricted region within the medial amygdaloid nucleus from which these projections arise. They also suggest that, unlike the projections from the medial amygdaloid nucleus to the bed nucleus of the stria terminalis, the efferents to the medial preoptic area travel entirely in the stria terminalis.

Effects of photoperiod duration and melatonin signal characteristics on the reproductive system of male Syrian hamsters.

Three experiments tested effects of photoperiod and the pineal hormone melatonin (MEL) on reproductive function among male Syrian-hamsters. In Experiment 1, hamsters were exposed for 32 weeks to 1 of 4 short photoperiods which varied in duration (11.5 L; 10 L; 8 L; 6 L). A fifth group was shifted from 11.5 L to 6 L after 6 weeks. Shorter photoperiods were associated with more rapid regression of the testes, but all groups eventually regressed to the same extent. In contrast, the temporal profile of testicular recrudescence, expressed as males became photorefractory, was not significantly different between groups. A decrease in photoperiod from 11.5 L to 6 L after 6 weeks did not delay the onset of recrudescence. The 11.5 L group was subdivided at week 32 and transferred to either 13 L or 16 L for the next 8 weeks to break photorefractoriness. Upon subsequent exposure to 8 L, both subgroups regressed their testes in similar fashion over weeks 40-52, indicating that the two long photoperiods were equally effective in breaking photorefractoriness. Nevertheless, FSH and prolactin were more consistently suppressed in the 16 L group following the switch to 8 L. Experiment 2 tested whether differing durations of MEL, administered s.c. each night for 9 weeks, elicit graded rates of reproductive regression in pinealectomized males. Testicular regression was more rapid in the group receiving MEL for 12 h than it was in the group receiving MEL for 8.5 h, thus supporting the hypothesis that the faster rates of testicular regression in the shorter photoperiods of Experiment 1 were due to their concomitant longer durations of nightly MEL secretion. Experiment 3 tested the hypothesis that rates of testicular regression in males receiving exogenous MEL would be affected by their prior photoperiodic history. Males were exposed to 18 L or 14 L for 7 weeks, then pinealectomized and administered 9.5 h MEL infusions s.c. each night for 9 weeks. In contrast to predictions, photoperiodic history had only transitory effects on MEL-induced testicular regression. Although the differences in MEL duration that accompany different short photoperiods have reproductive consequences (Experiment 1), the extent to which MEL duration expands during the transition from stimulatory to inhibitory photoperiods appears to be a less significant variable (Experiment 3).

The effect of signal frequency on the gonadal response of male Syrian hamsters to programmed melatonin infusions.

The aim of this study was to investigate which characteristics of the nocturnal melatonin signal, in addition to its duration, convey photoperiodic information to the reproductive axis. To achieve control over the pattern of circulating melatonin, male Syrian hamsters held under stimulatory long daylengths (16h light:8h dark) were pinealectomized to remove the principal source of circulating endogenous hormone and then fitted with chronic subcutaneous cannulae through which programmed infusions of melatonin solution or vehicle could be delivered. Experiment 1 tested whether long intervals between successive melatonin signals impaired the photoperiodic response. Animals which received a short day-like melatonin infusion of 10 h duration once every 24 h (T = 24) for 6 weeks underwent gonadal atrophy. When the same number of signals (42) was delivered at a frequency of once every 32 h (T = 32), they were ineffective and animals remained gonadally active. Two infusion patterns were used to determine if the loss of response to 10 h signals given at T = 32 h was a consequence of the frequency per se or the long interval between signals (22 h). In the first, a 'chimaeric' signal which combined a long duration i.e. short day-like 18 h melatonin signal with a short day-like melatonin-free interval of 14 h (combined signal T = 32 h) was able to induce significant, but only partial, gonadal atrophy. Second, when the 22-h interval between 10-h melatonin signals was interrupted by a short (2 h) melatonin pulse, significant but partial gonadal regression again occurred. Moreover, the response depended upon the timing of the 2 h pulse. When this fell early in the melatonin-free interval, leaving a large portion of it intact, it had no effect on gonadal condition. In contrast, a pulse delivered in the middle of the interval, which divided it up into two short day-like segments of 10 h each, was partially effective in restoring a short day response. The second experiment tested whether melatonin signals delivered at a high frequency would induce a photoperiodic response. A 10 h infusion delivered once every 24 h caused gonadal atrophy. The same melatonin infusion delivered at a periodicity of 20 h (T = 20) was also very potent as a short day stimulus. However, when 10-h signals were delivered at the higher frequencies of once every 18 or 16 h, they were less effective. Only a minority of animals exhibited gonadal atrophy and overall the group means were not significantly different from those of saline-infused controls, but were significantly greater than those of the 24 and 20 h groups. These data demonstrate that the photoperiodic response to the melatonin signal is sensitive to the frequency at which the signal is received. However, there is no evidence for a circadian basis to this sensitivity, nor a dependence upon the relationship between the endocrine stimulus and the light-dark cycle, insofar as signals encountered at a non-circadian period of 20 h are very effective. Moreover, the effectiveness of signals encountered at longer periodicities can be modified by manipulation of the uninterrupted duration of the interval free of melatonin, demonstrating a role in photoperiodic time measurement for the duration of the interval between signals.

Occlusion of the melatonin-free interval blocks the short day gonadal response of the male Syrian hamster to programmed melatonin infusions of necessary duration and amplitude.

Abstract Photoperiodic control of the neuroendocrine axis is mediated by changes in the duration of the nocturnal melatonin signal. This study tested the hypothesis that reading of the signal depends upon the presence of a period free of melatonin between successive signals. Adult male Syrian hamsters were pinealectomized and received chronic subcutaneous infusions of melatonin or saline for 6 weeks. Animals which received saline had large testes. Those which received a single daily infusion which lasted for 10 h (50 ng/h) followed by 14 h without infusion underwent gonadal atrophy. Other animals received a compound melatonin signal in which the melatonin-free interval was occluded by a continuous infusion (25 ng/h). Superimposed upon this was a 10 h phasic increase in infusion rate such that the maximum rate of infusion was equivalent to that observed in controls (25 ng/h increase, 50 ng/h peak rate), or the increase in rate over the baseline was the same as in controls (50 ng/h increase, 75 ng/h peak rate). In neither group did the animals undergo gonadal regression. Analysis of iodomelatonin binding sites by in vitro autoradiography failed to reveal any systematic difference between animals which did and did not respond to melatonin and so the absence of a response could not be attributed to loss of receptors. These data demonstrate that the photoperiodic system cannot identify the melatonin signal solely upon the features of nocturnal peak height or amplitude of the peak over baseline. They are consistent with the hypothesis that the melatonin-free interval plays a significant role in photoperiodic time measurement.

Stria terminalis lesions alter the temporal pattern of copulatory behavior in the male golden hamster.

The mating behavior of a group of male golden hamsters was observed before and after bilateral electrolytic lesions or knife cuts interrupting the stria terminalis (ST). Whereas males with bilateral lesions of the medial nucleus of the amygdala had previously been observed to stop mating, a majority of hamsters with bilateral ST destruction, whether by electrolytic lesions or knife cuts, continued to display mounts, intromissions, and ejaculations during tests over a two month postoperative period. ST-lesioned males did, however, display a distinctly altered pattern of copulation over the course of postoperative testing, consisting of an increase in mount latency during the first week, an increase in the inter-intromission interval during the second week, and an increase in the number of intromissions preceding ejaculation during the third and subsequent weekly tests. Males with bilateral lesions of the caudal amygdala, which damaged the amygdaloid exit of the ST, displayed alterations in copulatory behavior similar to those seen after bilateral ST destruction at a more rostral level.

MPOA and BNST lesions in male Syrian hamsters: differential effects on copulatory and chemoinvestigatory behaviors.

Electrolytic lesions were made in the medial preoptic area (MPOA) and bed nucleus of the stria terminalis (BNST) to evaluate their participation in the neural regulation of copulatory and chemoinvestigatory behaviors in male hamsters. Damage to either the MPOA or the BNST caused severe deficits in copulatory performance in a subset of the animals in each group. In the MPOA group all males displaying severe deficits had lesions which included a small central region of the caudal MPOA. In the BNST group, animals with severe copulatory deficits all had large lesions which covered most of both the medial and lateral parts of the nucleus. In contrast, MPOA and BNST lesions differentially affected chemoinvestigatory behaviors. MPOA lesions did not affect any of the males' anogenital investigation rates or attraction to female odors, even though some of these hamsters had stopped mating completely. Males with BNST lesions, on the other hand, all displayed significant reductions in their chemoinvestigatory responding even though the majority of them continued to mate normally. We suggest that the MPOA and BNST may in part regulate male sexual behavior by differentially responding to 'attractant' and 'mounting' substances within female hamster vaginal secretion.

Olfactory and vomeronasal deafferentation of male hamsters: histological and behavioral analyses.

Deafferentation of the vomeronasal system by cutting the vomeronasal nerves severely impaired mating behavior in 44% of male hamsters over a 1--2 month period of postoperative testing, but the remaining males mated normally after the surgery. Damage to the main olfactory bulbs, concomitant to vomeronasal nerve cuts, did not account for this behavioral difference. Subsequent deafferentation of olfactory system by intranasal infusion of zinc sulfate solution (5 g ZnSO4--7H2O in 95 ml 0.5% NaCl) had no effect on intromission or ejaculation latencies of sham vomeronasal cut males but eliminated mating behavior 2 days after treatment in males with bilateral vomeronasal nerve cuts. Some of these males recovered the behavior in 1--3 weeks of post zinc sulfate testing. Histological analyses of the olfactory mucosa in 7 males on day 2 after zinc sulfate showed that 89--97% of the mucosa had been destroyed in 6 out of 7 of the males and 78% in the seventh. We conclude that destruction of the vomeronasal system irreparably reduces arousal necessary for mating in some hamsters but in other males sufficient arousal for this behavior to occur is mediated through the olfactory system, presumably in conjunction with other sensory inputs. Subsequent removal of the olfactory input in these animals eliminates the behavior.

Effect of photoperiod on neural estrogen and progestin receptor immunoreactivity in female Syrian hamsters.

This study explored the possibility that reduced behavioral responsiveness to estradiol and progesterone in female Syrian hamsters exposed to a short photoperiod is associated with a reduction in the concentration of neural steroid receptors. The effects of long and short photoperiod (LP; SP) exposure on steroid receptor immunoreactivity were examined in the ventromedial hypothalamus (VMH), medial tuberal region (mTu), medial preoptic area (mPOA), medial nucleus of the amygdala (mAMYG), and the arcuate nucleus (ARC) of ovariectomized hamsters. In Experiment 1, exposure to SP for ten weeks attenuated the lordosis response following sequential treatment with estradiol and progesterone. In a separate group of animals not given hormones, SP decreased the staining intensity of estrogen receptor immunoreactive (ERIR) cells in the mPOA while increasing the number of detectable ERIR cells in part of the mAMYG. In Experiment 2, SP diminished the lordosis response as it did in Experiment 1. One week later, the same females were administered estradiol systemically to induce progestin receptors (PR). Animals housed in SP showed significantly reduced progestin receptor immunoreactivity (PRIR) in the VMH, mTu, mPOA, mAMYG, and ARC. Experiment 3 examined whether the results of Experiment 2 might have been influenced by photoperiodic effects on peripheral metabolism of estradiol. Among hamsters housed in LP or SP, PRs were induced by estradiol implanted unilaterally in the medial basal hypothalamus, thus bypassing possible photoperiodic effects on peripheral estradiol availability. This treatment resulted in significantly fewer cells with detectable PRIR in the VMH and mPOA of SP females, suggesting that the photoperiodic influences on PR induction observed in Experiment 2 do not depend on alterations in the peripheral availability of estradiol.

Development of olfactory bulb organization in precocial and altricial rodents.

The structural organization of the olfactory bulbs of spiny mice, Norway rats and Mongolian gerbils was followed over the course of their development. The pups of all 3 species normally begin to approach the odor of their dams at a time when their olfactory bulbs are at a similar stage of development. The data suggest that there may be a common aspect of olfactory bulb development that underlies the onset of olfactory guided approach behavior in rodents.

Photoperiodic and pineal influences on estrogen-stimulated behaviors in female Syrian hamsters.

Three experiments investigated the effects of short photoperiod exposure on the estrogenic facilitation of locomotor activity and lordosis. In Experiment 1, ovariectomized female hamsters were administered exogenous estrogen to stimulate locomotor activity in running wheels. Estrogen was effective in the long photoperiod group but did not stimulate running-wheel activity in the short photoperiod group. In Experiment 2, the role of the pineal gland in mediating photoperiodic influences on female hamster behavior was examined. Both estrogen-induced locomotor activity and estrogen+progesterone-stimulated lordosis behavior were significantly reduced in short photoperiod females. Both these photoperiodic effects were absent in pinealectomized hamsters. Sham-pinealectomized, short photoperiod females expressed behavioral deficits; pinealectomized hamsters in the short photoperiod did not. Experiment 3 investigated lordosis only and used hormone injections rather than silastic implants to administer estrogen. The photoperiodic and pineal effects observed in Experiment 2 were replicated in Experiment 3. Additionally, the suppression of lordosis responsiveness by short photoperiod exposure was estrogen dose dependent. Photoperiodic effects were present when 2 micrograms estradiol cypionate was used but absent when higher estrogen doses were used. These findings are discussed in the context of other results that suggested photoperiodic effects on hamster lordosis were pineal independent.

Effects of acute ovariectomy on the lordosis response of female rats.

The sexual receptivity of intact females with 4- or 5-day estrous cycles was compared to that of other females which had been ovariectomized at particular times during their cycles. The quality and frequency of lordosis responding were more degraded the earlier during the cycle ovariectomy was performed. This effect was more pronounced in 4-day than in 5-day cyclic females. Because exogenous progesterone was administered to all ovariectomized females, these behavioral deficits were attributed to removal of ovarian estradiol. Ovariectomy 6 hr before the critical period for luteinizing hormone release significantly shortened the duration of behavioral estrus, even though it had no effect when lordosis was tested at the time intact estrous females are maximally receptive. These findings are consistent with the hypothesis that the continual availability of estradiol throughout the 18--24 hr interval perior to the onset of behavioral estrus is essential for optimal conditioning of sexual receptivity to occur under physiological conditions. The relevance of triggering and maintenance functions of estradiol to these results is discussed.

Pinealectomy prevents short photoperiod inhibition of male hamster sexual behavior.

The role of the pineal gland in mediating photoperiodic influences on copulatory behavior (CB) of male hamsters (Mesocricetus auratus) was assessed in the presence and absence of testosterone (T). The results demonstrate that the pineal gland is necessary for short photoperiod exposure to alter CB. Sexually experienced males were exposed to either long (14L:10D; LP) or short (8L:16D; SP) photoperiods for 13 weeks; after the first 2 weeks of exposure, all animals were castrated and then either pinealectomized (PINX) or sham operated (SHAM PINX). CB tests over an 8-week period following surgery indicated that copulatory impairments developed in all animals, but deficits occurred more rapidly among short photoperiod males with intact pineal glands (SP-SHAM PINX), compared to pinealectomized males housed in either the long (LP-PINX) or short photoperiod (SP-PINX). LP-PINX and SP-PINX animals were not statistically different on any of the CB measures examined. Nine weeks after castration (11 weeks of photoperiod exposure), all hamsters were given a T-filled Silastic capsule to restore CB. Restoration of sexual behavior was less rapid and less complete among SP-SHAM PINX hamsters. Additionally, males in this group took longer to initiate copulation relative to the pinealectomized hamsters. These findings are compared to other reports suggesting that photoperiodic effects on the sexual behavior of female hamsters do not require an intact pineal gland.

Short photoperiods affect male hamster sociosexual behaviors in the presence and absence of testosterone.

Male hamsters were exposed to long (LD 14:10) or short (LD 8:16) photoperiods (LP; SP) to evaluate the effects of these environmental conditions on sociosexual behaviors. In Experiment 1, gonadally intact males in SP exhibited deficits in sexual behavior, reflected both in performance as well as initiation measures. Some aspects of the males' chemoinvestigation of females or their odors were also significantly different between LP and SP hamsters. In Experiment 2, castration resulted in the development of copulatory impairments, but they occurred more rapidly among males in SP conditions. Subsequent testosterone (T) replacement restored mounts, intromissions and ejaculations on tests given 2 and 4 weeks after T, but this happened more quickly in the LP group. SP males were still slower than LP males to initiate mounts and intromissions on their second test. These influences of photoperiod are discussed in the context of steroid-independent and steroid-dependent effects on behavior and the role of impaired processing of chemosensory information is evaluated.

Male hamster sociosexual behaviors: effects of testosterone and its metabolites.

Male hamsters were tested for copulatory behavior (CB) with receptive females, for investigatory responses to the females' ano-genital region (A/G), and for attraction to female hamster vaginal secretion (FHVS). After castration, the males received Silastic capsules containing one of two doses of testosterone (T), 5 alpha-dihydrotestosterone (DHT), estradiol (E2) or DHT + E2, and the maintenance of their copulatory and chemoinvestigatory responsiveness was assessed during weekly tests for the next month. The major findings were: (1) T thresholds for the maintenance of CB were lower than they were for the maintenance of A/G behavior and FHVS attraction; (2) DHT + E2 or DHT alone were more effective in maintaining A/G and FHVS attraction than was E2 alone; (3) DHT + E2 or DHT alone maintained ejaculatory behavior in some animals but E2 did not; (4) the posttreatment maintenance of normal ejaculation latencies and intromissions to ejaculation shown by intact and T-treated males was not demonstrated by males receiving DHT or DHT + E2. These results are consistent with the hypothesis that copulatory and chemoinvestigatory behaviors may be subserved by distinct neuroendocrine mechanisms in male hamsters.

Influence of daylength on male hamster sexual behavior: masking effects of testosterone.

Exposure of male hamsters to short photoperiods for 6-8 weeks cause deficits in sexual behavior with receptive females. The present experiment tested the hypothesis that short photoperiodic effects on behavior could be masked in the presence of chronic and stable levels of testosterone. Males were castrated and administered Silastic capsules of testosterone while housed in long (16L:8D) or short (8L:16D) photoperiodic conditions for 7 weeks. Sexual behavior tests at this time indicated that the short photoperiod males copulated less well, but group differences were not robust. Testosterone capsules were then removed and half the animals in both 16L:8D and 8L:16D were transferred to the opposite photoperiod. Sexual behavior was tested 18 days later as the effects of this functional castration developed. These tests indicate that photoperiodic effects were much more obvious in the absence of testosterone than they were during week 7 tests when testosterone was still present. The behavior of the males that were transferred from one photoperiod to the other demonstrated that exposure to the short photoperiod for only 18 days was not sufficient to generate short photoperiod-like sexual behavior deficits. In contrast, exposure to the long photoperiod for 18 days was sufficient to reverse short photoperiodic effects that had already developed.