Estradiol facilitates mounting behavior in male green anole lizards

Steroid hormones activate sexual behaviors across vertebrate species. In green anole lizards, testosterone is particularly important for the display of courtship and copulation by adult males. However, unlike a variety of other species, the role of its metabolite, estradiol, has been unclear. To evaluate its function and potential interaction with testosterone in the facilitation of reproductive behaviors, adult males were gonadectomized and given two treatments. The first consisted of either estradiol or its vehicle, and the second testosterone or a blank control. Parallel manipulations were done in the breeding and non-breeding seasons. Courtship and copulatory behaviors were more readily facilitated during the breeding than non-breeding season. As predicted based on previous experiments, testosterone increased the display of sexual behaviors. In addition, estradiol increased mount attempts. While this hormone did not influence the effects of subsequent testosterone exposure, the present data are consistent with the idea that it facilitates a component of reproduction in the green anole, as in species from other taxa.     

Neonatal androgen influences sexual motivation but not the masculine copulatory motor pattern in the rat

Masculine sexual responses displayed by female rats, were compared to those of males. Twenty-five percent of females mounted and 19% showed intromission behavior, but none of them displayed the ejaculation pattern. Masculine sexual behavior was displayed in all stages of the estrous cycle. Accelerometric and spectrum frequency analysis of electrical signals generated by pelvic movements during mounting and intromission showed that these patterns were identical in both sexes excepting that mount duration in females was longer than in males. Neonatal androgenization of females increased the display of intromission patterns. Treatment of ovariectomized rats, androgenized or not, with either estradiol benzoate or testosterone propionate stimulated masculine sexual behavior. The ejaculatory pattern was only displayed by neonatally androgenized females. Mounting and intromission motor patterns of females under steroid treatment, and ejaculations of neonatally androgenized females, were similar to those of males. The results show that the organization of the movements involved in masculine sexual behavior in rats are identical in both sexes, thus suggesting that the neural circuits controlling these behaviors could be identical. Neonatal or postpubertal androgen in the rat influences the frequency with which male-like responses are displayed, but not their temporal (frequency, rhythm) or dynamic (acceleration, vigour) characteristics.     

Estrogen reduces the excitability of the female rat medial amygdala afferents from the medial preoptic area but not those from the lateral septum

Electrical stimulation of the medial amygdala (AMY) elicited antidromic action potentials in neurons in the preoptic area (POA) and the lateral septum (LS) of 36 urethane-anesthetized ovariectomized female rats, which were either treated with estrogen o not treated. The extracellular potentials from the two sites showed similar characteristics, with the exception of the sensitivity to estrogen: they had latencies between 3 and 35 ms. Thresholds were as low as 100 A. The mean relative refractory period was 2.2 ms. The peak-to-peak amplitudes of the positive-negative biphasic potential ranged from 1.0 mV to 12.0 mV. Estrogen had site-specific effects on parameters of antidromic activation in the POA. Estrogen-treated rats had a significantly higher threshold (937 vs 664 A) and a longer refractory period (2.5 vs 2.1 ms) than the ovariectomized rats (P < 0.05 for each). The effects were absent in the LS. Selective cutting of the stria terminalis diminished the AMY-induced antidromic responses in the POA and LS. Electrical stimulation of the stria blocked the AMY-induced antidromic potentials by collision. Thus, estrogen-sensitive POA efferents as well as non-estrogen-sensitive LS efferents project to the AMY via the stria terminalis. Reductions in axonal excitability would inhibit neural conduction and transmission. Estrogen may therefore reduce the AMY inputs from the POA, without affecting those from the LS. Such alterations in the neural impulse flow may underlie estrogen-dependent neuroendocrine or behavioral regulation.     

Sexual behavior of the obese male Zucker rat

Obese male Zucker rats displayed inadequate sexual behavior at four months placed with ovariectomized lean females pretreated with estrogen and progesterone. Only one out of seven obese males ejaculated during the test sessions. Diet-restricting the obese males at five months of age did not improve their sexual behavior when tested at six months of age. At ten months of age none of the obese males ejaculated during the test sessions. Lean littermates ejaculated during the sessions at all ages tested. Obese males which do ejaculate are capable of inducing pseudopregnancy in intact lean females. These findings suggest that inadequate sexual behavior is one factor contributing to the reduced reproductive capacity of obese male Zucker rats.     

Dihydrotestosterone stimulates mounting behavior but not lordosis in female rats

The ability of androgens to stimulate masculine sexual behavior is thought to depend on the aromatization of such androgens to estrogens. In this scheme, reduced androgens such as dihydrotestosterone (DHT) which cannot be aromatized, are thought to exert major peripheral but little or no central nervous system influences on the display of masculine sexual behavior. Further, an early report that DHT can induce lordosis, an estrogen (E) dependent behavior, led to a notion that DHT may effect behavior through metabolic intermediates such as 5α-androstane-3β, 17β-diol (ADIOL) which then binds to estrogen receptors eliciting the E-dependent lordotic response. The present study reexamined and compared the relative effectiveness of a range of DHT dosages in stimulating a characteristic masculine (mounting) and feminine (lordosis) sexual behavior. Adult ovariectomized rats were randomly assigned to either 250 μg or 1 mg daily injections of DHT or DHTP. Other animals received OIL injections or crystalline DHT delivered by two different lengths (20 mm or 40 mm) of Silastic capsules. Animals were tested once weekly (for 5 weeks) for mounting behavior (20 minute test). Then animals were tested thrice (once weekly) for lordosis 4 hrs after the addition of 500 μg Progesterone (P). Finally, all females were tested for lordotic potential to respond to 10 μg EB plus P. 1 mg DHT or DHTP dosages and the 40 mm-Silastic condition significantly increased mounting behavior over that of lower dosages and OIL controls. A significant correlation existed between mounting frequency and circulating level of serum DHT. Treatment with DHTP was not different than DHT in eliciting mounting behavior. Lordosis was not enhanced by any treatment with DHT or DHTP over that of controls, although all females were capable of lordotically responding to EB. These data demonstrate that DHT can induce mounting behavior, but not lordosis, suggesting that whatever action DHT has may not occur via estrogen or estrogen receptors. A role for androgen and androgen receptors upon mounting behavior is discussed.     

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.     

Rostral midbrain lesions and copulatory behavior in male rats

Discrete electrolytic lesions were placed in the mesencephalic dorsal noradrenergic (DNE) bundle of 22 male Sprague-Dawley rats, and sham operations were performed on 14 control animals. Eight components of copulatory behavior were compared in 2 preoperative and 2 postoperative heterosexual mating tests. A significant postlesion decrease in the postejaculatory interval (PEI), number of intromissions, number of incomplete mounts and the ejaculation latency from the first intromission (ELI) occurred. Norepinephrine levels were significantly reduced in the hippocampus, amygdala and hypothalamus, but not in the preoptic area. The only statistically significant correlations between NE concentrations and behavior in the lesioned animals were negative (hippocampal NE with PEI and ELI). The results support the hypothesis that rostral midbrain lesions disinhibit some components of male rodent copulatory behavior, but suggest that a system or systems other than the DNE bundle may be responsible for this disinhibition.     

Effects of sex hormones on sleep patterns of male rats gonadectomized in adulthood and in the neonatal period

Sleep-wakefulness cycles were recorded following the administration of estrogen and progesterone to adult male rats castrated at birth or in adulthood. For the neonatal male castrates, two daily injections of estrogen followed by progesterone resulted in significant reductions in the percentages of time spent in both REM and NREM stages of sleep during the night following the progesterone injection. That response to female hormones was similar to the response previously reported for similarly treated gonadectomized female rats. The adult male castrates did not show the modification of sleep patterns in response to hormone treatment. The data represent evidence of sexual differentiation of the brain mechanisms regulating sleep that is comparable in certain respects to the differentiation of mechanisms regulating sexual behavior in rats.     

Electrical activity of the cat amygdala during sexual behavior

Recordings from inplanted electrodes in the amygdala of male and female cats were taken during coitus and the female postcoital after reaction. In the female there was a marked increase in the amplitude and duration of the 30–40 Hz activity during coitus and after-reaction. In the male there was no observable change.     

Activation of sexual reflexes of male rats by dihydrotestosterone but not estrogen

Previous studies have shown that withdrawal and administration of testosterone propionate (TP) has a quantitative influence on sexual reflexes which parallels changes in copulatory activity following castration and administration of TP. The present study involving castrated spinal male rats explored further this parallel, focusing on the effects on sexual reflexes of the administration of dihydrotestosterone propionate (DHTP) and estradiol benzoate (EB), both of which can activate sexual behavior in spinally intact castrated male rats, but only if given in very large doses for a prolonged period of time. A parallel effect on reflexes and behavior was not found inasmuch as DHTP activated sexual reflexes at a dose (200 microgram daily) considerably below that needed to activate behavior, and EB did not appreciably activate reflexes, even after prolonged treatment at levels (100-200 microgram) higher than necessary to activate behavior. The results, with EB in particular, point out that the display of intromissive and ejaculatory patterns in rats may not involve spinal neural mechanisms that are customarily associated with these behavioral patterns.     

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.     

Copulation affects body weight but not food intake or dietary self-selection in male rats

The mechanisms responsible for copulation-induced changes in body weight were investigated using adult male rats. Animals that copulated two or three times a week for 6 weeks gained less weight than sexually inactive controls. The reductions in body weight gain were not associated with changes in total caloric intake or the intake of specific nutrients. Adipose tissue lipoprotein lipase activity was not affected by sexual activity. Based upon these results and previous observations, we suggest that copulation-induced reductions in body weight may not be mediated solely by testicular testosterone.     

Patterns of motor and seminal vesicle activities during copulation in the male rat

The interaction between behavioral and visceral events during copulation was studied in nine intact adult male Wistar rats. The motor copulatory pattern was analyzed by an accelerometric technique and the seminal vesicle pressure (SVP) was recorded through a catheter chronically inserted into the right seminal vesicle. Mounting was associated with a small broad rise in SVP that often preceded the initiation of pelvic thrusting. Penile insertion resulted in a second sharp rise in SVP superimposed on the primary wave related to mounting. A steep rise in SVP occurred during the performance of the motor ejaculatory pattern after a variable period of intravaginal thrusting. This final rise was associated with ejaculation. Analysis of the temporal relationships between the SVP changes and copulatory behavior revealed that each of the three rises of SVP was related to distinct patterns of stimulation, suggesting that they were mediated by separate reflex arcs.     

Characterization of copulatory behavior in female mice: evidence for paced mating

In this study we characterized female mouse sexual behavior using a pacing paradigm similar to that used to evaluate sexual behavior in female rats. A pacing chamber was designed for use with mice and we compared the sexual behavior of female mice that were tested in both pacing and nonpacing paradigms and under different hormone conditions. We found that, like rats, female mice do pace their copulatory behavior by altering the temporal sequence of copulatory events. Female mice take longer to return to the male after an ejaculation, compared to either a mount or intromission. However, it is still unclear if female-paced mating serves the same functions as it does in female rats. More work is needed to confirm that paced mating induces hormonal changes needed for pregnancy as is the case in rats.     

Electrographic changes in the amygdala and hippocampus associated with biting attack

Squirrel monkeys had chronic electrodes implanted in various brain structures known to be involved in aggression. Changes in the electrical activity of these regions were monitored in sessions where the animals were restrained and biting either a pneumatic hose or food. It was found that whereas eating behavior was not consitently associated with desynchronization of the basolateral and corticomedial division of the amygdala and the hippocampus, hose-biting was associated with concurrent shifts from synchronization to desynchronization in these regions. The present findings are consistent with the interpretation of amygdaloid function as being that of a modulator of anatomically related regions. The data further suggest that portions of the amygdala are preferentially activated by aversive environmental conditions, and that such activation is functionally related to the occurrence of aggressive behavior.     

Lordosis behavior and mounting behavior in male rats: effects of castration and treatment with estradiol benzoate or testosterone propionate.

Male rats were selected for showing or not showing lordosis in response to manual stimulation. They were subsequently tested for mounting behavior with receptive females and for lordosis behavior in response to manual stimulation and to male mounting. Males showing lordosis as intacts displayed this behavior more readily following castration or castration and treatment with estradiol benzoate or testosterone propionate than males which did not show lordosis before castration. No group differences in mounting behavior could be detected under any of the endocrine conditions studied. It is suggested that the neural mechanisms mediated mounting and lordosis are dissociated and that individual differences in the occurrence of lordosis in male rats are due to differences in neural sensitivity to estrogen.     

Time-contingent change in infanticide and parental behavior induced by ejaculation in male mice

About 50% of sexually-naive male CF-1 mice (Mus musculus) commit infanticide (kill young). But, 80-90% of male mice commit infanticide between 1-4 days after mating. Between 12 and 50 days after mating infanticide is inhibited and most males (80-100%) behave parentally toward young (they build a nest, retrieve and groom the young, and hover over the young to keep them warm). Beginning at 60 days after mating, infanticide is again facilitated and parental behavior is inhibited (70-80% of males commit infanticide). The facilitation and inhibition of infanticide as a function of time after mating is mediated by the act of ejaculating rather than by mounting and intromitting during mating or by cohabiting with a female either before or after mating. The experience of committing infanticide either prior to mating or within the first 4 days after mating does not influence the facilitation of parental behavior that occurs 12 days after mating. But, repeated contact with young after males become parental serves to maintain parental behavior for an extended period of time. The age of the young (newborn-20 days old) utilized as stimulus animals does not influence these time-dependent changes in the behavior of male mice after ejaculation. This phenomenon is unique in that a response (infanticide) to a novel stimulus (young) is facilitated, then inhibited, and then facilitated again as a function of time between an event (ejaculation) and exposure to the novel stimulus.(ABSTRACT TRUNCATED AT 250 WORDS)     

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.     

Effects of pelvic nerve and pudendal nerve transection on mating behavior in the male rat

The role of the pelvic nerves in mediating erection in the male rat was investigated. The frequency and duration of erections and other criteria of mating behavior were studied in a group of animals in which the pelvic nerves were bilaterally transected. Compared with the performances of sham-operated animals, no differences were obtained in 4 postoperative mating tests. It is concluded that erection in the rat is not mediated by the pelvic nerves. The effects of bilateral transection of the pudendal nerves upon mating behavior and the temporal patterning of this behavior were studied in adult male rats. It appeared that erection, intromission and ejaculation were prevented, while mounting behavior and the temporal patterning of the mating behavior were not affected. The results indicate that erection in the rat is mediated by the pudendal nerves. Moreover it is concluded that by means of pudendal nerve transection sexual motivation in the rat can be studied without the possible interference of intromissions, for a prolonged period.     

Elicitation of ejaculation and penile reflexes in spinal male rats by peripheral electric shock

Mild electrical shock, applied bilaterally to the skin of the flank of spinal male rats occasionally evokes an ejaculatory complex consisting of seminal expulsion followed by penile erections and flips. The ejaculatory reaction appears to be inhibited by penile stimulation. The inhibitory effect of penile stimulation on ejaculation may represent a spinal mechanism responsible for the obligatory copulatory intromissions which precede ejaculation. The function of penile erections and flips, may be to pack and seal seminal plugs into the vaginocervical junction.