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.     

Coital stimuli controlling luteinizing hormone secretion and ovulation in the female ferret

A series of experiments focused on the masculine coital behaviors controlling pituitary luteinizing hormone (LH) secretion and reflex ovulation in the estrous female ferret. An initial experiment investigated which coital stimuli from the male are required to induce ovulation. It was found that corpus luteum formation, which served as an index of ovulation, occurred in estrous female ferrets only if the male achieved a penile intromission. Neck gripping, mounting, and pelvic thrusting behavior without intromission by the male failed to induce ovulation. A second experiment investigated the timing and magnitude of the coitus-induced LH surge associated with ovulation. Blood was obtained via jugular catheters from estrous females in various mating situations. Plasma LH concentrations were measured by a heterologous radioimmunoassay that was validated for use in the ferret. A significant surge in plasma LH occurred only when an intromission was achieved by the stud male. Plasma LH was significantly elevated 2.0 h after the introduction of the male, peak values were reached 6.0 h later, and this elevation lasted on average 5.7 hours (5/5 females). No LH rise occurred in 2/2 female ferrets in which only neck gripping, mounting, and pelvic thrusting, but no intromission, were allowed to occur. The ferret mating pattern and the resultant LH response differ from those seen in three other induced ovulators (cat, vole, and rabbit) in which the male's intromission latency and duration are much shorter than in the ferret, and in which a distinctive peak in plasma LH often occurs within 1 h after mating.     

Changes in the testicular binding of luteinizing hormone and plasma testosterone concentrations in the Djungarian hamster subjected to different photoperiods and temperatures and effects of long-term testosterone treatment on the binding

The effects of artificial photoperiod, temperature, and long-term testosterone treatment on testicular luteinizing hormone (LH) binding were studied in adult male Djungarian hamsters. In hamsters transferred to long-day (LD; 16 hr light, 8 hr dark) photoperiod 8 weeks after adaptation in short-day (SD; 8 hr light, 16 hr dark) photoperiod of 25 degrees C, testicular growth was associated with an increase in the total LH binding per two testes and a decrease in LH binding per unit testicular weight. Plasma testosterone levels reached a peak 47 days after transfer to LD and tended to decrease thereafter, while the testes continued growing. In contrast, when hamsters reared under LD conditions at 25 degrees C for 12 weeks were transferred to SD, testicular regression was associated with a decrease in plasma testosterone and the total LH binding per two testes and an increase in LH binding per unit testicular weight. A significant decrease in LH binding per unit weight compared to SD controls was observed in those hamsters exposed to SD with continuous testosterone treatment. The testosterone treatment tended to induce decrease in the total LH binding. Scatchard plot analyses of the binding suggested that changes in LH binding were due to changes in the number of binding sites. When sexually mature male hamsters were subjected for 8 weeks to two different ambient temperatures (7 degrees C and 25 degrees C) and photoperiods (LD and SD), the difference between the two temperature groups was statistically not significant regarding the weights of testes, epididymides, and prostates; plasma testosterone levels; and LH binding in either LD or SD group. These results suggest that photoperiod is a more important environmental factor than temperature for the regulation of testicular activity and LH receptors and that testosterone reduces the number of LH receptors per unit testicular weight in adult male Djungarian hamsters.     

Reciprocal relationships between pulsatile androgen secretion and the expression of mating behavior in adult male ferrets

The pulsatile secretion of androgen was similar over a 12-hr period in breeding male ferrets implanted with jugular catheters which either achieved an intromission with an estrous female or received no socio-sexual contact. This negative result contrasts with the previous demonstration (Carroll, Erskine, and Baum, 1987, Endocrinology 121, 1349-1359) of a significant, delayed rise in mean plasma androgen concentrations in breeding male ferrets 5-12 hr after mating. Males used in that previous study had lower initial mean plasma levels of androgen and smaller testis diameters than the present males. We therefore asked whether differences in circulating androgen levels, characteristic of males in different phases of the seasonal breeding cycle, might affect the expression of mating behavior. Castrated males given 0, 0.2, 2.0, or 5.0 mg/kg of testosterone propionate (TP) showed dose-related increases in the expression of different components of sexual behavior, including neck gripping, mounting, and intromitting. Surprisingly, intromissive performance was significantly better in intact breeding males than in castrates given even the highest dosage of TP. These results suggest that ferrets' mating performance may vary with seasonal variations in androgen availability, and that the ability of males to exhibit a postcoital increase in the testicular secretion of androgen may be limited to the beginning or end of the breeding season, when circulating levels of androgen are relatively low. Mating-induced increments in androgen secretion at these times may enhance subsequent reproductive success by facilitating males' intromissive capacity, which is required for the induction of ovulation and optimal sperm transport in female partners.     

Sexual dimorphism in the motor mounting pattern of the New Zealand white rabbit: steroid regulation of vigor and rhythmicity of pelvic thrusting

The motor mounting patterns of male and female New Zealand white rabbits were analyzed by means of an accelerometric technique and frequency analysis. Clear behavioral dimorphism was noted in the motor mounting pattern. Pelvic thrusting by males was periodic while that performed by females lacked rhythmicity. Thrusting in males was more vigorous than in females. Ovariectomy markedly decreased the incidence of mounting behavior. Testosterone propionate (TP, 5 mg daily for 1 month), restored mounting in all ovariectomized rabbits. TP stimulated the vigor of thrusting and induced a rhythmic mounting pattern in many cases similar to that displayed by intact male rabbits, i.e., thrusting frequency 13-16 per second. Estradiol benzoate (10 micrograms daily for 1 month), elicited mounting in three of the seven rabbits tested. Pelvic thrusting in these rabbits was often highly synchronous showing a frequency higher (18 to 21 thrusts per second) than that displayed by male rabbits. The results suggest the following conclusions: (a) the behavioral dimorphism in mounting observed in rabbits is due to variations in the secretion of sex steroids by the adult gonads rather than to differences in the organization of the neural substrate of mounting; (b) gonadal steroids influence directly or indirectly the neural structures involved in some characteristics of pelvic thrusting, i.e., rhythmicity and vigor.     

Effect of some antiestrogens and aromatase inhibitors on androgen induced sexual behavior in castrated male rats

The effect of antiestrogens (MER-25, ICI-46474, and cis-clomiphene) and aromatase inhibitors (5-α-androstanedione, metopirone, and aminoglutethimide) on androgen induced copulatory behavior was tested in sexually inexperienced castrated male tats. Daily injections of 1 mg testosterone (T) for 21 days induced sexual activity in most subjects (61% mounting). Daily pretreatment with MER-25 or cis-clomiphene at three dose levels did not block the behavioral response to T. ICI-46474 at the high dose level (1 mg/kg) elicited a significant depressory effect on the sexual behavior of the T treated castrated rats. A single injection of 6 mg testosterone propionate (TP) induced mounting behavior in 56% of the tested rats within 120 hr. Treatment with metopirone or 5 α-androstanedione (injections every 12 hr for 96 hr) did not inhibit the response to TP. By contrast, aminoglutethimide (5 or 15 mg every 12 hr for 96 hr) abolished the behavioral response to androgen.     

Androgen regulation of the motor copulatory pattern in the male New Zealand white rabbit

The effect of castration and testosterone propionate (TP) treatment on the motor copulatory pattern was studied by an accelerometric technique in five sexually experienced New Zealand white male rabbits. This technique permits the oscillographic recording of thrusting frequency, rhythmicity, and amplitude of the pelvic movements occurring during copulation. Castration resulted in a marked decrease in sexual activity in all rabbits. Mounting, including occasional intromissions, was retained by four of the rabbits for periods ranging from 2 to 15 weeks. Castration did not affect mount duration, but decreased strength and frequency of pelvic thrusting. Diminution in the frequency of pelvic thrusting was mainly due to intercalation of pauses within the mounting trains. The change in the rhythm of pelvic thrusting was related to the failure of most mounts performed by castrated rabbits to stimulate lordosis in the female. Testosterone propionate (TP, 10 mg daily for 15 days) restored mounting activity and increased strength and frequency of pelvic thrusting in all rabbits. It is concluded that TP, besides stimulating sexual motivation, regulates the vigor and rhythm of pelvic movements during copulation in the rabbit.     

Gonadal hormone-dependent and -independent regulation of immune function by photoperiod in Siberian hamsters

Siberian hamsters (Phodopus sungorus) exhibit changes in reproductive and immune function in response to seasonal variations in day length. Exposure to short days induces gonadal regression and inhibits testosterone secretion. In parallel, short days enhance immune function: increasing leukocyte numbers and attenuating cytokine and behavioral responses to infection. We examined whether photoperiodic changes in leukocyte phenotypes and sickness behaviors are dependent on concurrent photoperiodic changes in gonadal function. Male hamsters were gonadectomized or sham-gonadectomized and either exposed to short days (9 h light/day; SD) or kept in their natal long-day (15 h light/day; LD) photoperiod for 10-13 wk. Blood samples were obtained for leukocyte enumeration, and hamsters were challenged with bacterial LPS, which induced behavioral (anorexia, reductions in nest building) and somatic (weight loss) sickness responses. Among gonad-intact hamsters, exposure to SD increased total and CD62L+ lymphocytes and CD3+ T lymphocytes in blood and significantly attenuated LPS-induced sickness responses. Independent of photoperiod, castration alone increased total and CD62L+ lymphocyte and CD3+ T lymphocyte numbers and attenuated somatic and anorexic sickness responses. Among castrated hamsters, SD exposure increased lymphocyte numbers and suppressed sickness behaviors. In castrated hamsters, the magnitude of most immunological effects of SD were diminished relative to those evident in gonad-intact hamsters. The SD phenotype in several measures of immunity can be instated via elimination of gonadal hormones alone; however, photoperiodic effects on immune function persist even in castrated hamsters. Thus, photoperiod affects the immune system and neural-immune interactions underlying sickness behaviors via gonadal hormone-dependent and -independent mechanisms.     

Evidence that a decrease in testosterone negative feedback mediates the pubertal increase in luteinizing hormone pulse frequency in male ferrets

Neuroendocrine mechanisms regulating luteinizing hormone (LH) secretion during puberty were investigated in intact male ferrets and ferrets castrated at 8 wk of age that received s.c. implants of either empty or testosterone-filled Silastic capsules. To synchronize puberty onset among individuals, ferrets were exposed to short days between 8 and 16 wk of age, and then transferred to long days. Testis growth began in intact ferrets soon after photoperiod transition. Blood samples were obtained at 11, 15, 19, and 23 wk of age. LH pulse frequency was low in intact ferrets at 11 and 15 wk of age (less than or equal to 0.27 pulses/h), but rose to 0.94 pulses/h by 23 wk of age. No age-related increase in LH pulse frequency was observed in untreated castrated ferrets. LH pulses were rare in testosterone-treated castrated ferrets at 11 and 15 wk of age; but by 23 wk of age, frequency rose to 0.33 pulses/h. Thus, testis maturation in ferrets is accompanied by a dramatic increase in LH pulse frequency. No steroid-independent developmental increase in LH pulse frequency occurs in castrated ferrets. Furthermore, doses of testosterone that prevent LH secretion in young castrated ferrets do not as effectively suppress LH pulses in older ferrets. These data suggest that a decrease in the efficacy of testosterone negative feedback mediates the pubertal rise in LH pulse frequency in male ferrets.     

布氏田鼠社会行为对光周期的适应格局

对实验室内不同光周期条件下的布氏田鼠陌生成体—亚成体间社会行为模式的初步研究显示:不同光周期下成体对亚成体（特别是对雄性亚成体）的行为反应具性二型特征,长光照周期下（light:dark,14L:10D)成体与亚成体同性组合间的争斗较异性组合间的明显,容忍性低,其中成体雄对亚成体雄尤甚。短光照周期下（light:dark,10L:14D）成体雄对亚成体雄、成体雌对亚成体雌及亚成体雄的相容性均较成体雄对亚成体雌的容忍性低,尤成体雌对亚成体雄的排斥表现更为突出,其容忍性也较长光照条件下对应组的低。结果表明,不同光周期条件下布氏田鼠成体与亚成体间的社会行为模式不同。在自然条件下,这些行为模式是其对环境季节变化的一种有效适应,它影响种群中未成年个体存活、补充、扩散重组以及社群结构、种群空间格局季节变化,对该鼠的生存和繁殖有利。     

Inhibition of testosterone-induced sexual behavior in the castrated male rat by aromatase blockers

The effect of some aromatase inhibitors (aminoglutethimide, 1,4,6-androstatrien-3, 17-dione, and 4-hydroxy-androstenedione) on testosterone propionate (TP)-induced copulatory behavior was tested in sexually inexperienced castrated male rats. A single injection of 6 mg of TP induced mounting in 48% and ejaculatory pattern in 19% of the rats within 120 hr. Treatment with the aromatase inhibitors (injections every 12 hr for 108 hr) suppressed ejaculation in all but one rat and significantly reduced the number of rats mounting and intromitting. Concurrent administration of estradiol benzoate (EB, 1 or 3 μg every 12 hr) prevented the inhibitory effect of aromatase blockers. No inhibitory effect of the aromatization blockers was observed in rats in which sexual behavior was induced by dihydrotestosterone (1 mg/day) and EB (2.5 μg/day) for 20 days. The results support the concept that aromatization is an essential step for the induction of male sexual behavior by androgen in the rat.     

Peripubertal immune challenges attenuate reproductive development in male Siberian hamsters (Phodopus sungorus)

Differential allocation of energy to reproduction versus host defense is assumed to drive the seasonal antiphase relation between peak reproductive function and immunocompetence; however, evidence supporting this assumption is only correlational. These experiments tested whether photoperiod affects immune responses to antigens in peripubertal Siberian hamsters, whether such activation of the immune system exacts energetic and reproductive costs, and whether such costs vary seasonally. Male Siberian hamsters were raised from birth in long (LD) or short days (SD), which respectively initiate or inhibit the onset of puberty. To elicit a specific immune response, hamsters were injected with a novel antigen (keyhole limpet hemocyanin [KLH]) as juveniles. Reproductive development was attenuated and body temperature was elevated in LD hamsters relative to saline-injected control animals. In contrast, KLH treatments affected neither thermoregulation nor reproductive development in photoinhibited SD hamsters. In experiment 2, juvenile male hamsters were challenged with bacterial lipopolysaccharide (LPS) in order to elicit an innate immune response. Febrile and anorexic responses to LPS were greater in reproductively stimulated LD hamsters relative to reproductively inhibited SD hamsters. LPS treatments attenuated somatic and testicular development in LD hamsters, but did not significantly affect circulating testosterone concentrations. In contrast, LPS treatments were without effect on somatic and reproductive development in SD hamsters. These experiments indicate that photoperiod affects antigen-specific antibody production, febrile responses to LPS, and sickness behaviors in juvenile Siberian hamsters, and that peripubertal activation of the immune system exacts energetic and metabolic costs that can diminish the magnitude of somatic and reproductive maturation in LD. The data also underscore the importance of seasonally dependent life history factors in assessing physiological tradeoffs.     

Early androgen treatment and male and female sexual behavior in mice

To investigate the role of neonatal androgen stimulation in the development of the potential for masculine and feminine sexual behavior in the mouse, different groups of mice were hormonally manipulated early in life. One group of female mice was administered testosterone propionate (TP) within 24 hr of birth; a second group of females was given a control injection of oil on the day of birth; a third group of females received an injection of TP on the 10th day after birth. A group of males received a control injection of oil on the day of birth. All mice were gonadectomized at about 30 days of age. At 60 days of age, mice were injected with estrogen and progesterone and tested for sexual receptivity; several weeks later all mice were injected with TP and tested for male sexual behavior. Female behavior: Females given oil at birth and females given TP on the 10th day after birth showed high levels of sexual receptivity as adults following estrogen-progesterone treatment. Females given TP on the day of birth, and male mice, rarely exhibited lordosis following estrogen-progesterone treatment. Male behavior: Most mice, regardless of genetic sex or neonatal treatment, mounted in adulthood following administration of exogenous androgen. There was little difference in mounting frequency between groups, suggesting that exogenous or endogenous androgen stimulation of the neonatal mouse does not facilitate adult mounting behavior. These data for the mouse are in essential agreement with existing data for the rat, and indicate that sexual behavioral differentiation induced by androgen stimulation in infancy is best characterized as an inhibition of the potential to display feminine sexual behavior in adulthood.     

Pineal-dependent and -independent effects of photoperiod on immune function in Siberian hamsters (Phodopus sungorus)

Siberian hamsters (Phodopus sungorus) exhibit reproductive and immunological responses to photoperiod. Short (<10-h light/day) days induce gonadal atrophy, increase leukocyte concentrations, and attenuate thermoregulatory and behavioral responses to infection. Whereas hamster reproductive responses to photoperiod are dependent on pineal melatonin secretion, the role of the pineal in short-day induced changes in immune function is not fully understood. To examine this, adult hamsters were pinealectomized (PINx) or sham-PINx, and transferred to short days (9-h light/day; SD) or kept in their natal long-day (15-h light/day; LD) photoperiod. Intact and PINx hamsters housed in LD maintained large testes over the next 12 weeks; sham-PINx hamsters exhibited gonadal regression in SD, and PINx abolished this effect. Among pineal-intact hamsters, blood samples revealed increases in leukocyte, lymphocyte, CD62L+ lymphocyte, and T cell counts in SD relative to LD; PINx did not affect leukocyte numbers in LD hamsters, but abolished the SD increase in these measures. Hamsters were then treated with bacterial lipopolysaccharide (LPS), which induced thermoregulatory (fever), behavioral (anorexia, reductions in nest building), and somatic (weight loss) sickness responses in all groups. Among pineal-intact hamsters, febrile and behavioral responses to LPS were attenuated in SD relative to LD. PINx did not affect sickness responses to LPS in LD hamsters, but abolished the ameliorating effects of SD on behavioral responses to LPS. Surprisingly, PINx failed to abolish the effect of SD on fever. In common with the reproductive system, PINx induces the LD phenotype in most aspects of the immune system. The pineal gland is required for photoperiodic regulation of circulating leukocytes and neural-immune interactions that mediate select aspects of sickness behaviors.     

Modification of testicular and thyroid function by chronic exposure to short photoperiod: a comparison in four rodent species

Exposure of male Syrian hamsters (Mesocricetus auratus) for 10 weeks to short photoperiod (SP) providing 10 hr light: 14 hr darkness (10:14 LD) produced a significant reduction in the weights of the reproductive organs, plasma thyroxine (T4) levels and free T4 index (FT4I) compared to the values of animals exposed to long photoperiod (LP, 14:10 LD). C57bl male house mice (Mus musculus) kept in SP (10:14 LD) had reproductive organ weights equivalent to those of mice kept in long days (14:10 LD) and lower T3 uptake (T3U) values. Male gerbils (Meriones unguiculatus) exposed to 13 weeks of SP (10:14 LD) had lower body weights, testes and seminal vesicle weights and higher T3U values compared to LP (14:10 LD) controls. However, no effect was seen on plasma T4 and triiodothyronine (T3) values nor the FT4I and free T3 index (FT3I). White-footed male mice (Peromyscus leucopus) exposed to SP (8:16 LD) had significantly lower testes and seminal vesicle weights while plasma T4 and T3 levels were unaffected. Snell strain house mice (Mus musculus) exposed to SP (8:16 LD) had normal reproductive organ weights compared to the values of LP-exposed (16:8 LD) control animals. However, there was a significant depression in T3 and in the FT3I in the SP animals.     

Activation of sexual behavior by implantation of testosterone propionate and estradiol benzoate into the preoptic area of the male Japanese quail (Coturnix japonica)

Intracranial implantation of minute pellets of gonadal steroids was performed to determine neuroanatomical loci at which steroids activate sexual behavior in the Japanese quail (Coturnix japonica). In this species, systemic treatment of castrated males with either testosterone propionate (TP) or estradiol benzoate (EB) restores male-typical copulatory behavior (head grabbing, mounting, and cloacal contact movements). In addition, EB activates female-typical receptive behavior (crouching). Adult male castrated quail were implanted intracranially with 300-micrograms pellets containing TP, EB, or cholesterol (CHOL) and behavior was tested with intact males and females. Either TP or EB pellets in the preoptic area (POA) activated male-typical copulatory behavior. Mounting was specifically activated without concomitant activation of other steroid-sensitive sexual and courtship behaviors. TP and EB implants in adjacent nuclei containing receptors for these steroids and CHOL implants in POA had no effect on male-typical copulatory behavior. Eighteen percent of all males tested for female-typical receptivity crouched, but no specific effect of EB was seen at any site. The similarity of the POA sites for activation of mounting by TP and EB is consistent with the hypothesis that cells within the POA aromatize testosterone to estrogens, which directly stimulate the cellular processes leading to behavioral activation.     

The circadian rhythm of the sex-pheromone-mediated behavioral response in the turnip moth, Agrotis segetum, is not controlled at the peripheral level

The pheromone-mediated upwind flight of male turnip moths was observed in a flight tunnel at different times of day under conditions of a light-dark (LD) cycle, constant darkness (DD), and a shifted photoperiod. Under both LD and DD conditions, a significantly larger number of males flew to the pheromone during both the scotophase and the subjective scotophase than during the photophase and the subjective photophase for 2 consecutive days. When 1-day-old moths were transferred to a shifted LD cycle with lights turned off 4 h earlier, male behavioral responses to the pheromone advanced in time accordingly by 4 h. This showed that male behavioral responses to the pheromone are under the control of an endogenous oscillator. To further examine the level at which the circadian rhythm of the male behavioral response is regulated, the authors tested the olfactory responses of male antennal receptors to pheromone stimuli by means of electroantennograms (EAG) at different times of day. No significant variation in the sensitivity of the male antennal response to the pheromone was observed in terms of time of day. The results suggest that circadian regulation of the rhythmic behavioral response to pheromones in the male Agrotis occurs at the central nervous system level.     

Photoperiodic regulation of circulating leukocytes in juvenile Siberian hamsters: mediation by melatonin and testosterone

The reproductive system of Siberian hamsters (Phodopus sungorus) undergoes rapid phenotypic responses to changes in day length that occur around the time of weaning. The present experiments tested whether the immune system of Siberian hamsters is similarly photoperiodic early in life and whether photoperiodic changes in melatonin or gonadal hormone secretions mediate any such responses to day length. Circulating blood leukocyte concentrations (WBC) were measured in juvenile male Siberian hamsters that were gestated in long-days (LD), transferred to short-days (SD) on the day of birth, and subsequently either remained in SD or were transferred from SD to LD at 18 days of age (day 18). WBC values were comparable between LD and SD hamsters on day 18. Between day 18 and day 32, SD hamsters exhibited a 3-fold increase in WBC, whereas LD hamsters failed to undergo a significant increase in WBC during this interval. WBC of LD hamsters was significantly lower than that of SD hamsters on day 25 and on day 32. In LD housed males, peripheral injections of melatonin delivered so as to extend the nocturnal duration of elevated endogenous melatonin secretion (i.e., provided in late afternoon) on days 18-31 increased WBC as measured on day 32. Peripubertal (day 17) gonadectomy abolished the immunosuppressive effect of LD exposure on WBC, and treatment with silastic implants containing testosterone suppressed WBC independent of photoperiod treatment. These data indicate that juvenile Siberian hamsters are immunologically responsive to photoperiod and that the leukocyte responses to day length are the result of melatonin-mediated effects of photoperiod on testicular hormone secretion.     

光周期对雄性布氏田鼠种内个体气味辨别的影响

本文研究了成年雄性布氏田鼠对不同光照周期下(长光照: LD; 短光照: SD) 的陌生雌鼠和陌生雄鼠气味的行为表现。实验发现: 所有被试雄鼠对LD 雄鼠、雌鼠气味比SD 雄鼠、雌鼠气味有更多的社会探究行为。LD 雄鼠比SD 雄鼠对同性或异性陌生个体气味的嗅闻和挖掘行为要多, 而且差异显著。在探究LD 动情雌鼠气味源时, LD 雄鼠比SD 雄鼠表现出更多的嗅闻和挖掘行为; 在探究SD 动情雌鼠气味源时, LD 和SD 雄鼠的行为反应没有明显差别。所有被试雄鼠在LD 雄鼠气味源箱中的停留时间都显著多于在SD 雄鼠气味源箱中的停留时间。LD 雄鼠在LD 雌鼠气味源箱中的停留时间显著多于在SD 雌鼠气味源箱中的停留时间; 而SD 雄鼠在LD 和SD 雌鼠气味源箱中的进入频次和停留时间没有明显差别。同时, LD 雄鼠对LD 动情雌鼠的气味在嗅闻频次和嗅闻时间上多于非动情LD 雌鼠, 而对SD 动情和非动情雌鼠的气味没有表现出明显的偏好; SD 雄鼠对LD 和SD 动情雌鼠的嗅闻行为仅在频次上显著多于对非动情雌鼠的嗅闻, 而在时间上没有显著差别。结果表明: 布氏田鼠嗅觉通讯中的个体气味及其对气味进行辨别过程中的行为反应都随着光照周期的不同而发生变化。动物的个体气味带有季节性信息, 来源于长光照下的气味比短光照下的气味更具有性吸引; 短光照在一定程度上可能抑制了雌鼠的动情和雄鼠的性行为反应。其嗅觉通讯行为的适应意义可能在于: 减少秋季短日照环境下的繁殖活动, 提高雄性个体之间的社会容忍性以利于集群越冬。     

Sexual preferences of male hamsters (Mesocricetus auratus) for conspecifics in different endocrine conditions

The behavioral responses of sexually experienced male hamsters toward a pair of anesthetized conspecifics were investigated. Males spent significantly more time licking, sniffing, and mounting neonatally and adult castrated males than intact males. Adult castrated males receiving oil injections were preferred over castrates receiving exogenous testosterone propionate (TP). Ovariectomized females were preferred over intact males, adult castrated males, or spayed females receiving exogenous TP. It was concluded that the absence of an androgen-dependent factor(s) renders an animal more sexually attractive.