Plasma testosterone levels and sexual performance of young obese male Zucker rats

The sexual behavior of obese male Zucker rats was studied at the age of 7, 8, 9, 10, 11, 14, and 16 weeks. Between 12–14 weeks of age, obese rats were treated with 400 μg testosterone propionate daily. Plasma testosterone levels were determined at the age of 10, 14, 16, and 20 weeks. Compared to lean rats, the sexual performance of the obese rats was abnormal at all ages. Plasma testosterone levels of obese rats were significantly lower at the age of 20 weeks but not at the age of 10 and 16 weeks, compared to those of their lean littermates. At the age of 14 weeks, after 2 weeks of testosterone treatment, plasma testosterone concentration rose to levels significantly higher than those of their lean littermates. However, there was no improvement in their sexual behavior following this period of hormone treatment. This study strongly suggests that obese male Zucker rats have abnormal reproductive function at all ages and that testosterone deficiency is not a primary cause of this abnormality.     

Naltrexone effects on male sexual behavior, corticosterone, and testosterone in stressed male rats

Chronic physical or psychological stress disrupts male reproductive function. Studies in our laboratory have shown that stress by immersion in cold water (ICW) and by electrical foot shocks (EFS) has inhibitory effects on male sexual behavior; these effects do not seem to be mediated by an increase in corticosterone, nor by a decrease in testosterone. On the other hand, it is known that endogenous opioids are released in the brain in response to these same stressors; consequently, they could be participating in the impairment of sexual behavior, as well as in the changes in corticosterone and testosterone caused by stress. The aim of this study was to analyze the effects of the opioid antagonist naltrexone (NTX) on male sexual behavior, corticosterone, and testosterone in both stressed sexually experienced and naive male rats. Sexually experienced adult male rats were assigned to one of the following groups (n = 10 each): 1) control group, males without sexual evaluation; 2) control group, rats injected ip with saline, non-stressed; 3) control group, rats injected with NTX (3 mg/kg) non-stressed; 4) rats injected ip with saline, and stressed by EFS; 5) rats injected ip with NTX (1.5 mg/kg) and stressed by EFS; 6) rats injected ip with saline and stressed by ICW; 7) rats injected ip with NTX (1.5 mg/kg) and stressed by ICW; 8) rats injected ip with NTX (3 mg/kg) and stressed by ICW. Naive males were assigned to the same control groups but only stressed by ICW and the NTX dose used was 3 mg/kg. Injections were given 30 min before stress sessions. Stress was applied on 20 consecutive days. Male sexual behavior was assessed 15 min after EFS or 30 min after ICW, on days 1, 4, 8, 12, 15, and 20. Trunk blood was collected at the end of the experiments on day 20 of stress. Corticosterone and testosterone were evaluated by HPLC.Mount, intromission and ejaculation latencies were longer in control saline naive males compared to control saline sexually experienced males on the first day. NTX administration to control naive males caused a decrease in mount, intromission, and ejaculation latencies, as well as an increase in ejaculatory frequency/30 min, compared to control-saline only on day 1. Stressed naive males showed higher mount, intromission and ejaculation latencies, compared to control and stressed sexually experienced males, as well as comparable increase in corticosterone and decrease in testosterone plasma levels. NTX administration before exposure to stress prevented the modifications caused by stress in sexual parameters. Sexual behavior in control sexually-active males injected with saline or NTX was not modified. Saline stressed males showed the previously reported alterations in sexual behavior, as well as an increase in corticosterone and a decrease in testosterone plasma levels. Stressed males injected with NTX before exposure to stress showed no alterations in male sexual behavior. NTX in control non-stressed males did not modify corticosterone plasma levels, but did cause a significant increase in plasma testosterone. The increase in corticosterone and the decrease in testosterone due to stress, were attenuated with the opioid antagonist, both in naive and sexually experienced males. Prevention of ICW stress effects was more effective with higher doses of NTX (3 mg/kg). These data suggest that endogenous opioids could be participating in the effects caused by stress on male sexual behavior, corticosterone, and testosterone.     

Evidence of incomplete behavioral sexual differentiation in obese male Zucker rats

Genetically obese male Zucker rats displayed lower rates of intromission behavior and ejaculated in significantly fewer tests than lean Zucker littermates. After castration and daily injections of a low dosage (5 micrograms/kg) or estradiol benzoate (EB) followed by progesterone (1 mg/kg), obese males displayed significantly higher lordosis quotients than lean controls. Continued daily administration of higher (10, 15 micrograms/kg) dosages of EB followed by progesterone caused significant reductions in lordotic responsiveness in obese males but not in lean controls. Thus, deficient masculine coital performance was correlated with altered receptive responsiveness to ovarian steroids in obese Zucker male rats. This suggests that the sexual differentiation of the developing brain may be deficient in obese Zucker males.     

Correlation of diurnal changes in hormones with sexual behavior and age in male rhesus macaques

—We designed this study to determine whether the sexual behavior of male monkeys changes on a diurnal schedule that coincides with changes in the levels of hormones such as luteinizing hormone (LH), testosterone, estradiol, and cortisol, and whether these differences vary with age. Old (n=8) and young (n=8) males were bled and given sexual behavior tests eight times at 0900 and eight times at 2100. The old and young males did not differ in mean serum levels of testosterone, estradiol, cortisol, or LH. Testosterone and LH levels were lower at 0900 than at 2100 (p<0.01), and estradiol and cortisol levels were higher at 0900 than at 2100 (p<0.01). The young males had higher percentages of tests with erections, mounts, intromissions, and ejaculations than the old males (p<0.01). The rates contacting, mounting, and intromitting were higher at 0900 than at 2100 (p<0.05). We failed to confirm previously obtained correlations between hormone levels and sexual performance. This failure led us to conclude that any significant correlation between sexual behavior and hormone levels must be regarded as tentative unless repeated in successive independent studies.     

Penile deafferentation and the effect of mating experience on sexual motivation in adult male rats

In the present study naive male rats were used, in which before or after housing for 5 days with receptive females penile deafferentation was performed by means of transection of the pudendal nerves. In subsequent mating tests the males were only able to exhibit mounting behavior. It appeared that the animals with mating experience prior to penile denervation, mounted significantly more than the animals that had been denervated before housing with the females. Furthermore the last group showed longer contact latencies, which were similar to those observed in denervated animals that had not been housed with females. It is concluded that the reinforcing value of copulatory performances upon sexual motivation in the rat is completely dependent upon the integrity of penile afferent innervation.     

Neonatal bonadal hormones: effect on maternal and sexual behavior in the male rat

Neonatal exposure of rats to androgen results in alteration of adult sex behavior and gonadotropin release. Other sexually dimorphic adult behaviors have also been shown to be dependent, either in part or in full, upon exposure to androgen neonatally. The present study was conducted to determine the effect of neonatal androgens in organizing the brain of the male rat (Long-Evans strain) with regard to maternal behavior. The results indicate that males neonatally exposed to androgen exhibit poor maternal behavior as adults when compared to males castrated at birth and males receiving gonadotropin antiserum in infancy. The males castrated at birth and males receiving gonadotropin antiserum in infancy, when primed with estrogen and progesterone, showed high levels of female sexual behavior when compared to controls. In terms of male sex behavior, the control groups performed slightly better than the males castrated at birth and males receiving antisera in infancy. The results suggest that the neonatal pituitary gland has an indirect role in the process of sexual differentiation.     

Effects of sex, litter size and periconceptional ewe nutrition on offspring behavioural and physiological response to isolation

Maternal periconceptional undernutrition alters fetal hypothalamic-pituitary-adrenal (HPA) axis development. However, the effects of this early nutritional insult on postnatal HPA axis function and stress-related behaviours are unknown. We investigated in sheep the effects of different periods of undernutrition, and of sex and litter size, on offspring behavioural and cortisol responses to isolation stress. We studied four nutritional groups: controls well nourished throughout pregnancy (n = 39), or ewes undernourished (UN, 10-15% body weight reduction) before mating (−60 to 0 d, n = 26), after mating (−2 to + 30 d, n = 20) or both (−60 to + 30 d, n = 36). At 4 and 18 months of age, offspring were isolated for 5 min, their behaviour video recorded, and plasma cortisol concentrations measured.Offspring of all undernourished groups demonstrated 50% fewer escape attempts than controls at 4 months of age, and offspring of UN−60 + 30 ewes had 20% lower plasma cortisol area under the curve in response to isolation at 18 months. Females had higher cortisol concentrations and vocalised more than males at 4 and 18 months, and were more active at 18 months. After isolation, UN−2 + 30 males had higher cortisol concentrations than UN−2 + 30 females whereas in all other groups males had lower concentrations than females. Singleton males made more escape attempts than females, whereas in twins females made more escape attempts than males.These findings suggest that maternal periconceptional undernutrition in sheep can suppress behavioural reactions and cortisol secretion in response to isolation stress in the offspring into adulthood, and that these effects differ between males and females.     

Effets de la restriction sociale et de l'absence d'experience sexuelle sur la maturation sexuelle de la souris male

On the day of birth, pups of Swiss strain mice were assigned to two groups: A (one male pup reared with mother alone, and B (3 male pups and 3 female pups with their mother). Animals were sacrificed at 1, 20, 40, 60 and 90 days. Pups of both groups were weaned on 20th day. At weaning, after removal of the mother, males of Group A stayed one per cage until sacrifice, while in Group B they stayed in cohabitation with females (3 males and 3 females per cage). In Group B, litters which appeared in the cages indicated the first fertile copulations occurred about 38–40 days. Males of Group A are sexual naîve males. Testosterone was measured by RIA. Compared to males of Group B, the testicular growth of Group A males was slower from 1 to 20 days, then more rapid from 20 to 60 days, and was prematurely stopped at this stage while it continued until Day 90 in males of Group B. From 1 to 40 days, testicular and plasma testosterone levels followed a similar pattern in the two groups. From 40 to 90 days testosterone level decreased significantly in the plasma and in the testis of animals of Group B, while it remained stable in Group A males. The results showed that, in mice, social deprivation as soon as birth and therefore lack of sexual experience, modify testicular growth as well as testosterone synthesis and secretion.     

The role of the dorsal nerves of the penis in the sexual behaviour of the male rhesus monkey

The effect of sectioning the dorsal nerves on the male monkey's sexual behaviour with oestrogen-treated females was examined in two experiments. In Experiment 1, first one and then both dorsal nerves were sectioned. In Experiment 2 progressively greater amounts of nerves were removed in a series of operations until none remained; the number of fibres removed at each operation was counted. Section of one dorsal nerve (Experiment 1) had no consistent effect on behaviour. Removal of more than half the total number of fibres caused ataxic thrusting and prolonged the time taken to ejaculation (Experiment 2). Total removal resulted in grossly abnormal thrusting and practically abolished ejaculation (Experiments 1 and 2). Intromission was less affected and continued to occur in the majority of mounts even after complete nerve section. Some males made an increased number of thrusts per intromission after partial nerve section, but markedly less when removal was complete. The mean mounting rate (i.e. the mean rate at which successive mounts occurred) was unaltered by partial section but decreased after total removal when overall levels of sexual activity declined; this occurred progressively after all the nerves had been removed. Pairing nerve-sectioned males, in which sexual activity had declined to low levels, with strange females could restore their sexual activity for a while. These results are compared with the effects on the male's behaviour of altering the hormonal condition of the female.     

Brain-spinal cord neural circuits controlling male sexual function and behavior

Men and women exhibit differences in sexual behavior. This indicates that neural circuits within the central nervous system (CNS) that control sexual behavior differ between the sexes, although differences in behavior are also influenced by sociocultural and hormonal factors. Sexual differentiation of the body and brain occurs during the embryonic and neonatal periods in humans and persists into adulthood with relatively low plasticity. Male sexual behavior is complex and depends on intrinsic and extrinsic factors, including olfactory, somatosensory and visceral cues. Many advances in our understanding of sexually dimorphic neural circuits have been achieved in animal models, but major issues are yet to be resolved. This review summarizes the sexually dimorphic nuclei controlling male sexual function in the rodent CNS and focuses on the interactions of the brain-spinal cord neural networks controlling male sexual behavior. Possible factors that relate findings from animal studies to human behavior are also discussed.     

Effects of dihydrotestosterone on sexual behavior of castrated male rhesus monkeys

The sexual and sex-related behavior of 10 adult male rhesus monkeys castrated three years earlier was studied in pair tests with receptive females. Their performance before and during treatment with 1 mg/kg dihydrotestosterone propionate (DHTP) was compared. Nine unoperated adult males served as controls. DHTP effectively rendered the performance level of the castrates comparable to that of the intact controls.     

Hyperprolactinemia and male sexual behavior: effects of steroid replacement with estrogen plus dihydrotestosterone

To determine if alterations in the availability of the active metabolites of testosterone (T) are involved in the inhibition of sexual activity in hyperprolactinemic animals, the effects of four ectopic pituitary grafts on copulatory behavior were examined in castrated male rats given subcutaneous implants of T or estradiol-17 beta (E2) plus 5 alpha-dihydrotestosterone (DHT). Two weeks after implantation of the steroid-filled capsules, half the animals of each group were given pituitary grafts and the remainder were sham-operated. Tests of copulatory behavior were performed prior to, and one, two, and three months following pituitary transplantation. Pituitary grafting caused significant inhibition of copulatory behavior in both T and E2 + DHT treated animals. PRL levels were significantly higher in E2 + DHT treated grafted males than in T treated grafted animals (2000 +/- 140 vs. 395 +/- 26 ng/ml), but did not differ between the corresponding control groups (61 +/- 8 vs. 73 +/- 6 ng/ml). The results of these experiments preclude the possible involvement of alterations in steroid secretion by the testes or modifications of the conversion of T to its active metabolites in the effects of hyperprolactinemia on copulatory behavior.     

Interactional effects of pudendal nerve section and social restriction on male rat sexual behavior

Transection of the pudendal nerve causing desensitization of the glans penis impaired the sexual behavior of male rats. Compared to intact males, fewer animals performed intromissions and ejaculations while no decrease in mounting frequency was observed. The total sexual activity as measured by number of mounts and intromissions was decreased and the copulatory efficiency as measured by the ratio of intromissions and total sexual activity was lowered. The impairment of the sexual activity following penile desensitization was more marked in inexperienced rats than in experienced ones. It was concluded that penile stimulation, although not a prerequisite for any specific component of the mating pattern, still is necessary for maintaining the behavior at a normal performance level.     

The effects of sexual experience and estrus on male-seeking motivated behavior in the female rat

Ovariectomized (OVX) female rats were trained to traverse a straight alley and return to a goal box where they had previously encountered a male rat, a female rat or an empty goal box. The time required to run the alley was used as an index of the subjects' motivation to re-engage the goal box target. Subjects were tested in both estrus and non-estrus, first sexually naïve and then again after sexual experience. Female rats ran most quickly for a male target, most slowly for an empty goal box, and at intermediate speeds for a female target. Sexual experience tended to slow run times for all but male targets. Estrus enhanced approach behavior for males and an empty goal box, but tended to slow the approach toward females, both before and after sexual experience. This latter finding was further investigated in a second experiment in which sexually naïve OVX females were tested during estrus and non-estrus in a locomotor activity apparatus, a runway with an empty goal box, and an open field. Estrus produced no changes in spontaneous locomotion either in the activity box or the open field, but decreased run times in the alley and increased the number of center-square entries in the open-field. Thus, estrus produces increases in sexual motivation that selectively enhance exploratory, presumably male-seeking behavior, but not simple spontaneous locomotion.     

Effect of insulin on the relationship of estrous behaviors to estradiol and LH surges in intact ewes

The objective of this study was to determine whether acute stress alters the frequency of spontaneous estrous behaviors and temporal relationships with preovulatory increases in peripheral plasma estradiol and LH. Follicular phases of intact ewes were synchronized with prostaglandin administered at progesterone pessary withdrawal (PW). Twelve ewes served as controls and 12 were acutely stressed (insulin 4 IU/kg given at 30 and 32 h after PW). Ewes being near to ram(s) 21.3 ± 1.9 h after PW was the first precopulatory behavioral sign and rams nosed the perineal region of ewes after a further 9.0 ± 2.0 h (P < 0.01), with ewes being nudged and mounted by rams 6.8 ± 2.3 h later still (P < 0.01). Insulin did not affect the frequency or timing (relative to PW) of each behavioral sign of estrus. However, within each animal, estradiol values were more than 2 pg/ml lower (P < 0.05) for 6 h following insulin, and the onset of the LH surge was delayed in insulin-treated ewes compared to controls (49.5 ± 3.3 versus 38.2 ± 2.6 h; P = 0.01). Consequently, the interval between the onset of being mounted and the LH surge was longer in insulin-treated ewes compared to controls (10.4 ± 3.0 versus 2.3 ± 0.7 h; P < 0.01). Maximum LH values were also 15 ng/ml lower after insulin (P < 0.01). Thus, acute stress did not alter the timing or frequencies of estrous behaviors but it did reduce estradiol concentrations and delayed the onset and magnitude of the LH surge.     

Influence of the presence of rams on the timing of ovulation and discharge of LH in ewes

The influence of the presence of the male on the ovulation process was investigated in ewes after oestrus control by progestagens (intravaginal fluorogestone acetate) and PMSG. Permanent contact with the rams throughout oestrus accelerates the ovulation and the appearance of the LH surge. The results suggest that the action of the presence of the male on ovulation is mediated by way of the ovulatory surge of LH.     

Anosmia differently affects the reproductive hormonal pattern in sexually experienced and inexperienced male rats

Effects of anosmia induced by surgical destruction of the olfactory epithelium were studied on testosterone (T), estradiol (E₂), 5α-dihydro-testosterone (DHT) and corticosterone secretion and hypothalamic T metabolism in male Wistar rats, part of which were sexually experienced and part of which were sexually inexperienced. Anosmia was followed by decreased T and E₂ plasma levels and increased DHT and corticosterone levels in experienced animals. In inexperienced rats, anosmia caused increased DHT levels. Experience decreased E₂ and increased corticosterone levels in anosmic rats, whereas in intact rats, experience caused increased T and DHT levels. Anosmia increased brain aromatization activity in experienced rats. Experience increased the formation of androstenediol in anosmic as well as in intact rats and caused a decrease in the formation of brain E₂ in intact rats. The results obtained suggest that odoriferous stimuli may influence T, E₂, DHT and corticosterone secretion and T aromatization provided such stimuli are associated with previous sexual experience.     

Changes in gonadotrophins and prolactin levels in isolated (seasonally or lactationally) anovular ewes associated with ovulation caused by the introduction of rams

The response of seasonally or lactationally anovular ewes to ram stimulation (teasing) was investigated in Ile-de-France (IF) and Prealpes (PA) ewes. In the first experiment (seasonally anovular IF and PA ewes) the possible role of prolactin (PRL) in the response to teasing was investigated by selective blockage of the secretion of PRL by CB 154 for 7 days before teasing. In the second experiment (lactationally anovular PA ewes) the role of PRL in the teasing response was investigated by studying ewes suckling one or two lambs, which presented differences in LH and PRL concentrations (p<0.025). In the first experiment, before teasing, basal concentration of LH and frequency of pulses were higher in PA than in IF ewes (p<0.001). The concentration of PRL was higher in IF ewes (p<0.001). Treatment by CB 154 did not affect the secretion of LH or FSH in either breed. Following the introduction of rams a rapid increase (<60 min) in concentration of LH, but not FSH, was observed, irrespective of breed or CB 154 treatment. In suckling ewes (Exp. 2) the frequency of pulses of LH was higher in ewes rearing one lamb than in ewes rearing twins (p=0.05). Stimulation by the rams resulted in a rapid increase (<40 min) in the pulsatile release of LH, irrespective of PRL concentration before teasing. In both experiments most ewes ovulated within 3 days of the start of the ram stimulation. It is concluded that PRL concentration does not affect the sensitivity of the brain to stimuli provided by rams. Analysis of hormonal patterns indicate also that hormonal events preceding ovulation are different from those observed in cyclic females.     

Sexual play and its functional significance in the domestic sheep (Ovis aries L.)

All the patterns of male sexual behavior were present from the first week of age in male and female lambs. The frequency of this sexual play increased considerably during the first month of life, and returned to a low level until early puberty. These behavioral changes could not be correlated with any hormonal changes. Rearing the lambs in the absence of adult females, in all-male groups or in physical isolation until weaning at 3 months of age, was without consequence for adult sexual behavior. However, despite the low level of sexual-like interactions during the pre and early pubertal period, i.e., between 3 and 6 months of age, the sexual segregation had a clear adverse effect on the development of the copulatory activity: the occurrence of the first copulation was delayed. However, after the first mating, the level of sexual activity was not affected by the treatment.     

Effects of stimulus female on sexual behavior of male rats given olfactory tubercle and corticomedial amygdaloid lesions

Lesions of the olfactory tubercle (OT) or corticomedial amygdala (CMA) damaging projections from the main or accessory olfactory bulbs, respectively, were made in male rats. When paired with ovariectomized females treated with estradiol benzoate (EB) and progesterone (Experiment 1) sexual behavior of lesioned males did not differ from sham and unoperated controls. During Experiment 2 males were paired with females chronically treated with EB only. Lesions of the OT did not affect mating while CMA lesions produced lengthened ejaculatory latencies (EL), longer mean interintromission intervals and more intromissions per ejaculation. Lesions of the CMA produced EL which were either within a normal range or noticeably extended with ejaculatory deficits becoming more exaggerated through three ejaculatory series. Low levels of soliciting by EB treated females seemed to precipitate ejaculatory deficits.