Components Of Male Sexual Behavior Research Articles

The effect of septal lesion on sexual behavior, sperm count and testicular activity in Young male albino rats

The effect of septal lesion on sexual behavior, sperm count and testicular activity in Young male albino rats - IJCAP- Print ISSN No: - 2394-2118 Online ISSN No:- 2394-2126 Article DOI No:- 10.18231/2394-2126.2018.0015, Indian Journal of Clinical Anatomy and Physiology-Indian J Clin Anat Physiol

Age dynamics of changes in sexual behavior and androgen status of male rats caused by prenatal exposure to low dose dibutylphthalate

The aim of this work was to study the sexual maturation, testicular hormonal activity and sexual behavior of Wistar male rats, which were born to mothers treated intragastrically with di-n-butylphtha- late (DBP) for 15-21 days of their pregnancy, at a daily dose of 100 mg/kg b.w., that do not cause visible developmental morpho- logical abnormalities. Their sexual behaviour was analyzed via the proceptive reactions, the latent and refractory periods of time and number of mounts, intromissions and ejaculations at the presence of a receptive female. Female sexual behaviour was evaluated by lordosis responses of orchidectomized and activated with estradiol and progesterone males in the presence of a normal male. Prenatal administration of DBP induced an accelerated onset of puberty. In young mature males (6-month old), it was, unexpectedly (as for endocrine disruptors), discovered that was featured by hyperactive central (motivational) and peripheral (copulative and ejaculatory) components of male sexual behavior and a two-fold increase in the average levels of plasma testosterone. In 10-month old rats, we found both homosexual and enhanced lordotic behavior. In aging animals (18 months), hyperandrogenism had switched to quite the opposite condition: more than two-fold decrease in the levels of plasma testosterone, close to statistical significance; and a lessen- ing of male sexual behavior compared to controls. These findings show the presence of epigenetic alterations in the programming of the parts of the brain responsible for sexual differentiation (the hypermasculinization combined with feminization) and a regula- tion of testicular hormonopoeisis, as well as premature aging of the reproductive organs resulting from the prenatal influence of low dose DBP. Thereby we proposed the original concept of prenatally determined DBP syndrome. And, finally, the possible mechanism of these changes in the repro- ductive system are discussed. Key words: dibutylphthalate; prenatal effect; sexual behavior; tes- tosterone; male rats. For citation: Reznikov AG, Sachynska OV, Lymareva АA.

Steroid-independent male sexual behavior in B6D2F2 male mice

It is well established that male sexual behavior (MSB) is regulated by gonadal steroids; however, individual differences in MSB, independent of gonadal steroids, are prevalent across a wide range of species, and further investigation is necessary to advance our understanding of steroid-independent MSB. Studies utilizing B6D2F1 hybrid male mice in which a significant proportion retain MSB after long-term orchidectomy, identified as steroid-independent-maters (SI-maters), have begun to unravel the genetic underpinnings of steroid-independent MSB. A recent study demonstrated that steroid-independent MSB is a heritable behavioral phenotype that is mainly passed down from B6D2F1 hybrid SI-maters when crossed with C57BL6J female mice. To begin to uncover whether the strain of the dam plays a role in the inheritance of steroid-independent MSB, B6D2F1 hybrid females were crossed with B6D2F1 hybrid males. While the present study confirms the finding that steroid-independent MSB is a heritable behavioral phenotype and that SI-mater sires are more likely to pass down some components of MSB than SI-non-maters to their offspring, it also reveals that the B6D2F2 male offspring that were identified as SI-maters that displayed the full repertoire of steroid-independent MSB had the same probability of being sired from either a B6D2F1 SI-mater or SI-non-mater. These results, in conjunction with previous findings, indicate that the specific chromosomal loci pattern that codes for steroid-independent MSB in the B6D2F2 male offspring may result regardless of whether the father was a SI-mater or SI-non-mater, and that the maternal strain may be an important factor in the inheritance of steroid-independent MSB.

Rapid effects of 17β-estradiol on male copulatory behaviors are not elicited by the novel membrane active estrogenic compound STX.

Estrogens have been shown to rapidly promote male copulatory behaviors with a time-course that suggests rapid signaling events are involved. The present study tested the hypothesis that estrogen acts through a novel Gq protein-coupled membrane estrogen receptor (ER). Thus, either estradiol (E2), STX (a diphenylacrylamide compound that selectively activates a membrane ER pathway), or vehicle were administered acutely to castrated male rats that bore subcutaneous (sc) dihydrotestosterone implants to maintain genital sensitivity. Appetitive (level changes, genital investigation) and consummatory (mounts, intromissions, ejaculations) components of male sexual behavior were measured in a bilevel testing apparatus. Testing showed that E2 treatment promoted olfactory and mounting behaviors, but had no effect on motivation as measured by anticipatory level changes. STX treatment showed no effect on either component of male sexual behavior. These results support previous results that showed that E2 can rapidly affect male sexual behaviors but fail to support a role for the specific membrane-initiated pathway activated by STX.

Reproductive effects in male rats exposed to diuron

Diuron is a ureic herbicide considered to have very low toxicity. The present study evaluated several aspects of reproductive toxicity of diuron in adult male rats. Diuron was diluted in corn oil and administered by oral gavage to groups of 18–20 rats at doses of 0, 125 or 250 mg/kg per day for 30 days; the control group received only the corn oil vehicle. At the end of the treatment period, approximately half the animals from each group were assigned to one of two terminal assessment lines: (1) reproductive organ, liver and kidney weights; measurement of diuron concentrations in liver and kidney; plasma testosterone determinations; evaluation of daily sperm production per testis; sperm number and sperm transit time in the epididymis; or (2) sexual behavior assessment during cohabitation with a receptive female; fertility and pregnancy outcome after natural mating; testicular, epididymal, kidney and liver histopathology; sperm morphology. After 30 days of oral diuron treatment, there were no treatment-related changes in body weights, but dose-related diuron residues were detected in the liver of all treated rats and absolute and relative liver weights were increased in both groups. There were no statistically significant differences between the treated and control groups obtained in plasma testosterone concentrations, or in parameters of daily sperm production, sperm reserves in the epididymis, sperm morphology or measured components of male sexual behavior. On the other hand, the number of fetuses in the litters from diuron-treated rats was slightly smaller than litters from control rats. Therefore, although the results did not indicate that diuron exposure resulted in direct male reproductive toxicity in the rat, they suggest that additional studies should be undertaken to investigate the possible effects on fertility and reproductive performance.

Enhanced Sexual Behaviors and Androgen Receptor Immunoreactivity in the Male Progesterone Receptor Knockout Mouse

Reproductive and behavioral functions of progesterone receptors (PRs) in males were assessed by examining consequences of PR gene deletion. Basal hormone levels were measured in male progesterone receptor knockout (PRKO) mice and compared to wild-type (WT) counterparts. RIA of serum LH, testosterone, and progesterone levels revealed no significant differences. Levels of FSH were moderately but significantly lower and inhibin levels were higher in PRKOs; these differences were not accompanied by gross differences in testicular weight or morphology. PRKOs exhibited significant alterations in sexual behavior. In initial tests PRKOs exhibited reduced latency to mount, compared with WT. In second sessions, PRKOs again showed a significantly reduced latency to mount and increased likelihood of achieving ejaculation. RU486 treatment in WT produced increased mount and intromission frequency and decreased latency to intromission. In anxiety-related behavior tests, PRKO mice exhibited intermediate anxiety levels, compared with WT, suggesting that enhanced sexual behavior in PRKOs is not secondary to reduced anxiety. Immunohistochemical analysis revealed significantly enhanced androgen receptor expression in the medial preoptic nucleus and bed nucleus of the stria terminalis of PRKO. We conclude that testicular development and function and homeostatic regulation of the hypothalamic-pituitary testicular axis are altered to a lesser extent by PR gene deletion. In contrast, PR appears to play a substantial role in inhibiting the anticipatory/motivational components of male sexual behavior in the mouse. The biological significance of this inhibitory mechanism and the extent to which it is mediated by reduced androgen receptor expression remain to be clarified.

Effects of testosterone in the VMN on copulation, partner preference, and vocalizations in male rats

The present study tested whether testosterone propionate (TP) implanted in the ventromedial nucleus (VMN) of the hypothalamus could initiate performance, motivational, or sociosexual components of sexual behavior in castrated male rats. Twenty-seven intact male Long Evans rats were pretested for copulation, partner preference, and 50-kHz vocalization and were subsequently castrated. Approximately 3 weeks after castration, males were retested to confirm that these behaviors had declined, and groups were assigned. Groups 1 and 2 were implanted with bilateral stainless steel cannulae directed at the VMN that were either filled with TP (TVMN group) or remained empty (Blank group). A third group (TSC) was implanted subcutaneously with two 10-mm Silastic capsules filled with testosterone. Restoration of behavior was measured for 2 weeks after implants. We found that copulation and 50-kHz vocalization were not restored by TP in the VMN alone. However, partner preference returned to preoperative levels in both the TVMN and TSC groups, indicating that TP in the VMN was sufficient to restore sexual motivation. Following behavioral testing, prostate glands and seminal vesicles were weighed and confirmed that TP did not leak into the periphery in the TVMN group. Immunostaining for androgen receptors also verified that TP spread was confined to the immediate area surrounding the cannula tip. These results suggest that androgen activation at the VMN is sufficient to induce the motivational components of male sexual behavior, whereas activation of other brain sites is required for copulation and ultrasonic vocalization.

Sexual Partner Preference Requires a Functional Aromatase ( Cyp19) Gene in Male Mice

Sexual motivation, sexual partner preference, and sexual performance represent three different aspects of sexual behavior that are critical in determining the reproductive success of a species. Although the display of sexual behavior is under strict hormonal control in both sexes, the relative roles of androgen and estrogen receptors in activating the various components of male sexual behavior are still largely unknown. A recently developed mouse model that is deficient in estradiol due to targeted disruption of exons 1 and 2 of the Cyp19 gene (aromatase knockout (ArKO) mice) was used here to analyze the role of estradiol in the control of all three aspects of male sexual behavior. When tested in a Y-maze providing volatile olfactory cues, male ArKO mice did not show a preference for the odors from an estrous female over those from an intact male, whereas wild-type (WT) and heterozygous (HET) males clearly preferred to sniff estrous odors. When provided with visual and olfactory cues, male ArKO mice also failed to show a preference for an estrous female when given a choice between an estrous female and an empty arm. However, sexual partner preferences of male ArKO mice were not sex-reversed: they did not prefer to investigate an intact male over an estrous female or empty arm. Thus, male ArKO mice seemed to have general deficits in discriminating between conspecifics by using olfactory and visual cues. Male coital behavior was also severely impaired in male ArKO mice: they displayed significantly fewer mounts, intromissions, and ejaculations than WT and HET males. Latencies to first mount or intromission were also significantly longer in ArKO males compared to WT and HET males, in addition to them showing less interest in investigating olfactory and visual cues in a Y-maze, suggesting that they were sexually less motivated. However, three out of seven male ArKO mice were capable of siring litters provided they were housed with a female for a prolonged period of time. In conclusion, aromatization of testosterone to estradiol appears to be essential for sexual motivation and sexual partner preference. By contrast, estradiol may play only a limited role in the expression of male coital behaviors.

Role of the lateral septal noradrenergic system in the elaboration of male sexual behavior in rats

The study was aimed at investigating the possible involvement of noradrenergic mechanisms in the lateral septum (LS) for elaboration of male sexual behavior in rats. In this study, norepinephrine (NE), yohimbine (YOH), isoproterenol (ISOP), propranolol (PROP), saline (SAL) and dimethyl sulfoxide (DMSO) were injected bilaterally in the LS in six different groups of sexually active male rats, and various components of sex behavior were recorded. The application of NE (3 μg) and α 2-antagonist YOH (1 μg) produced a stimulation of most of the components of male sexual behavior, and there was increase in sexual arousal as well as performance. The microinfusion of nonspecific β-agonist ISOP (2 μg) also produced a stimulation of copulatory behavior whereas β-antagonist PROP (2 μg) produced an inhibition. The stimulation of male sexual behavior by YOH application at the LS could be due to an increased release of NE by its blocking effect on presynaptic α 2-receptors. These results suggest that the noradrenergic system in the LS has stimulatory effect upon male sexual behavior, probably acting through β-receptors.

Performance of appetitive or consummatory components of male sexual behavior is mediated by different brain areas: a 2-deoxyglucose autoradiographic study

The in vivo autoradiographic deoxyglucose method was used to identify the functional brain circuits that are involved in the performance of appetitive and consummatory components of male sexual behavior in Japanese quail ( Coturnix japonica). Two groups of castrated, testosterone-treated male quail were trained during 12 sessions to associate the view of a female behind a window with the opportunity to interact freely and to copulate with her. They developed, as a consequence, a social proximity response (staying close and looking through the window providing a view of the female) that has been used in previous experiments to measure appetitive sexual behavior. A third control group (also castrated and treated with testosterone) was allowed to view the female but not to copulate with her and therefore did not develop this proximity response. 2- 14C-deoxyglucose was then injected i.p. to these birds and they were allowed to either copulate freely with a female (consummatory sexual behavior group) or express the social proximity response (appetitive sexual behavior group). The control group was provided a view of the female but these birds, although they were exposed to the same stimuli as birds in the appetitive group, did not express the social proximity response because they had never learned the association with the opportunity to copulate. Birds were killed 45 min after the deoxyglucose injection and their brains were processed for autoradiography. Densitometric analyses of the autoradiograms revealed that the expression of appetitive or consummatory aspects of male sexual behavior was associated with significant increases by comparison with the control group in the deoxyglucose incorporation in the nucleus mesencephalicus lateralis, pars dorsalis and in the nucleus leminsci lateralis. In addition, an increase in the deoxyglucose incorporation was specifically observed in the paleostriatum primitivum, rostral preoptic area, nucleus intercollicularis, nucleus interpeduncularis and third nerve but a decrease was observed in the dorsomedial part of the hippocampus and in the nucleus nervi oculomotori in birds of the consummatory sexual behavior group by comparison with controls. By contrast, in the appetitive sexual behavior group, significant increases in deoxyglucose incorporation were observed in two telencephalic areas, the intermediate hyperstriatum ventrale and neostriatum caudolaterale by comparison with the controls, but decreases were detected in the stratum griseum et fibrosum superficiale of optic tectum by comparison with the consummatory behavior group. These studies demonstrate that the performance of appetitive or consummatory components of male sexual behavior affects in a specific manner the deoxyglucose uptake and accumulation in specific regions of the quail brain. Changes in metabolic activity were observed in steroid-sensitive areas, in auditory, visual and vocal brain regions, and in brain nuclei related to motor behavior but also in association telencephalic and limbic structures. These changes in oxidative metabolism overlap to some extent with metabolic changes as revealed by immunocytochemistry for the immediate early gene products Fos and Zenk, but many specific reactions are also detected indicating that these techniques are not necessarily redundant and, together, they can provide a more complete picture of the brain circuits that are implicated in the control and performance of complex behaviors.

Effects of Prenatal Morphine Exposure on Rat Heterotypical Sexual Behavior

Prenatal exposure to morphine inhibits ovarian steroid-dependent lordosis behavior in female rats, and enhances certain components of male sexual behavior in male rats. In the present study, the effects of mid to late gestational morphine exposure on male sexual behavior in females and on female sexual behavior in males were examined in adult offspring. Gonadectomized male rats were injected at weekly intervals with 30 or 60 μg estradiol benzoate and 1.0 mg progesterone and tested for female sexual behavior with stimulus males on 2 consecutive weekly tests. Ovariohysterectomized (OVX) females were injected with 500 μg testosterone propionate (TP) daily for 15 days and tested for male sexual behavior with stimulus females on the last day of TP injection and 1 week later, after TP withdrawal. Prenatal morphine exposure increased the expression of male sexual behaviors in female rats, but it did not increase lordosis behavior in male rats. Thus, exposure to morphine during gestation alters male and female sexual behavior in young adult animals. Because prenatal morphine exposure both defeminized and masculinized adult sexual behavior in female rats, it is possible that female brain development is more vulnerable to prenatal insult such as opiate exposure.

Effects of brain testosterone implants on appetitive and consummatory components of male sexual behavior in Japanese quail

Aromatization of testosterone (T) into an estrogen is necessary for the activation of consummatory and appetitive sexual behavior in male Japanese quail. T action within the medial preoptic nucleus (POM) is necessary and sufficient to activate consummatory behavior, and some evidence suggests that POM might be involved in the control of appetitive behavior, but other brain regions, such as the bed nucleus of the stria terminalis (BST), an area that contains a dense population of aromatase-immunoreactive neurons, are also likely to be involved. This study was performed to assess the effects of stereotaxic T implants targeting either the POM or the BST on the activation of both components of sexual behavior in castrated male quail. Appetitive sexual behavior was measured by an acquired social proximity response in which a male will approach a window providing visual access to a female after the window has been repeatedly paired with physical access to a female and the possibility to freely interact with her. Rhythmic cloacal sphincter movements that are produced by the male when given visual access to a female were used as another measure of appetitive sexual behavior that does not appear to depend on sexual learning. The experiments confirmed that copulation is necessary for males to develop the social proximity response that is used to measure the appetitive sexual behavior. T implants in the POM activated both components of sexual behavior, suggesting that these components cannot be completely dissociated. In contrast, T implants located within the BST did not affect either component, but because implants in the BST did not activate copulatory behavior, these results do not preclude a role for BST in the expression of a previously acquired appetitive sexual behavior.

Systemic and intracerebroventricular injections of vasotocin inhibit appetitive and consummatory components of male sexual behavior in Japanese quail.

The authors investigated the behavioral actions of vasotocin (VT) in castrated testosterone-treated male Japanese quail. The appetitive and consummatory components of sexual behavior as well as the occurrence frequency of crows were inhibited, in a dose-dependent manner, by injections of VT. The authors observed opposite effects after injection of the V1 receptor antagonist, dPTyr(Me)AVP. Lower doses of VT were more active after central than after systemic injection, and effects of systemic injections of VT were blocked by a central injection of dPTyr(Me)AVP. The behavioral inhibition was associated with a modified diuresis after systemic but not central injection. These results provide direct evidence that VT affects male sexual behavior in quail by a direct action on the brain independent of its peripheral action on diuresis.

Systemic and intracerebroventricular injections of vasotocin inhibit appetitive and consummatory components of male sexual behavior in Japanese quail.

The authors investigated the behavioral actions of vasotocin (VT) in castrated testosterone-treated male Japanese quail. The appetitive and consummatory components of sexual behavior as well as the occurrence frequency of crows were inhibited, in a dose-dependent manner, by injections of VT. The authors observed opposite effects after injection of the V1 receptor antagonist, dPTyr(Me)AVP. Lower doses of VT were more active after central than after systemic injection, and effects of systemic injections of VT were blocked by a central injection of dPTyr(Me)AVP. The behavioral inhibition was associated with a modified diuresis after systemic but not central injection. These results provide direct evidence that VT affects male sexual behavior in quail by a direct action on the brain independent of its peripheral action on diuresis.

Effects of Dopamine Agonists on Appetitive and Consummatory Male Sexual Behavior in Japanese Quail

The effects of pharmacological manipulations of dopaminergic transmission on appetitive and consummatory aspects of male sexual behavior were investigated in castrated male Japanese quail treated with exogenous testosterone. Appetitive male sexual behavior was assessed by measuring a learned social proximity response and consummatory behavior was assessed by measuring copulatory behavior per se. The nonselective dopamine receptor agonist, apomorphine, inhibited in a dose-dependent manner both components of male sexual behavior. Two indirect dopamine agonists were also tested. Nomifensine, a dopamine re-uptake inhibitor, decreased appetitive sexual behavior but increased the frequency of mount attempts, a measure of consummatory sexual behavior. Amfonelic acid, a compound that enhances dopaminergic tone by a complex mechanism, increased aspects of both appetitive and consummatory behaviors. These data suggest that, in quail, as in rodents, increases in dopaminergic tone facilitate both appetitive and consummatory aspects of male sexual behavior. Apomorphine may be inhibitory in quail because it acts primarily on D2-like receptors, unlike in rats, where it stimulates sexual behavior and acts primarily on D1-like receptors at low doses but interacts with D2-like receptors at higher doses. This is supported by the observation that stereotyped pecking, a behavior stimulated selectively in quail by D2 agonists, was increased by apomorphine but not by the two indirect agonists. The observed partial dissociation between the effects of these dopaminergic agonists on appetitive and consummatory sexual behaviors suggests that these two components of male sexual behavior may be controlled by the action of dopamine through different neuronal systems.

Differential Effects of D1 and D2 Dopamine-Receptor Agonists and Antagonists on Appetitive and Consummatory Aspects of Male Sexual Behavior in Japanese Quail

Balthazart, J., C. Castagna and G. F. Ball. Differential effects of D1 and D2 dopamine-receptor agonists and antagonists on appetitive and consummatory aspects of male sexual behavior in Japanese quail. Physiol Behav 62(3) 571-580, 1997.—Pharmacological studies in Japanese quail based on behavioral tests with a variety of dopaminergic compounds suggest that the activation of D2 dopamine receptors inhibits, and the activation of D1 dopamine receptors enhances, appetitive and consummatory components of male sexual behavior. This hypothesis was tested by studying the behavioral effects of specific D1 and D2 dopaminergic-receptor agonists and antagonists in castrated male Japanese quail chronically treated with exogenous testosterone (subcutaneous Silastic implants). The effects of 5 compounds were tested: 1 D1 (SKF38393) and 2 D2 (PPHT and quinpirole) agonists, and 1 D1 (SCH23390) and 1 D2 (Spiperone) antagonist. All compounds were tested at a low and a high dose (0.1 and 1 mg/kg, respectively, for all drugs, except spiperone where the doses were 2 and 10 mg/kg). A consistent effect of all drugs on consummatory sexual behavior was observed: it was stimulated by the D1 agonist and the D2 antagonist, but inhibited by the D1 antagonist and the D2 agonists. Far fewer effects of the treatments were detected on the measures of appetitive behavior. Measures of appetitive behavior were decreased by the 2 D2 agonists, but not affected by the other treatments. These data suggest that male copulatory behavior in quail is stimulated by dopamine acting on D1 receptors, but inhibited by activation of the D2 receptor subtype. The partial dissociation observed between the effects of the same treatments on appetitive and consummatory aspects of sexual behavior also suggests that these 2 behavioral systems may be controlled by the action of dopamine on different neuronal systems.

Are separable aromatase systems involved in hormonal regulation of the male brain?

In vitro study of testosterone (T) metabolism shows that formation of estradiol-17 beta (E2) is regionally specific within the preoptic area (POA) of the male ring dove. The POA is known to be involved in the formation of E2 required for specific components of male sexual behavior. Two sub-areas of high aromatase activity, anterior (aPOA) and posterior preoptic (pPOA) areas, have been identified. Aromatase activity is higher in aPOA than in pPOA. The aromatase activity within the aPOA is also more sensitive to the inductive effects of low circulating T, derived from subcutaneous silastic implants, than the enzyme activity in pPOA. Kinetic analysis of preoptic fractions indicates that a similar high-affinity enzyme occurs in both areas (apparent Km less than 14 nM), but the Vmax of aPOA enzyme activity is higher than pPOA. Cells containing estrogen receptors (ER) are localized in areas of high aromatase activity. There is overlap between immunostained cells in the aPOA and in samples containing inducible aromatase activity measured in vitro. Within the aPOA there is a higher density of ER cells in the nucleus preopticus medialis. The pPOA area also contains ER, notably in the nucleus interstitialis, but at a lower density. We conclude that the hormonal regulation of the male preoptic-anterior hypothalamic region, which is a target for the behavioral action of T, involves at least two inducible aromatase systems with associated estrogen receptor cells.

Clonidine Suppresses Copulatory Behavior and Erectile Reflexes in Male Rats: Lack of Effect of Naloxone Pretreatment

Adrenergic transmitters and opioid peptides are implicated in the regulation of male sexual behavior. In the present studies we examine a possible interaction between these two neurochemical systems in the regulation of components of male sexual behavior. In mating tests, clonidine (0.25 mg/kg, 6 min pretest) induced a profound deficit in intromissive and ejaculatory behavior whereas naloxone (5 mg/kg, 20 min pretest) evinced a facilitation of ejaculatory behavior, evidenced by decreases in the ejaculation latency in the initial copulatory series and by decreases in ejaculation latency and intercopulatory interval in the second copulatory series. Importantly, prior treatment with naloxone did not prevent or attenuate the copulatory suppression induced by clonidine. In ex copula penile reflex tests, clonidine (0.25 mg/kg, 6 min pretest) decreased the incidence of seminal emission and the number of penile responses (erections, cups and flips). Naloxone (5 mg/kg, 20 min pretest) was without effect on any of the parameters of penile reflex activity and, further, failed to prevent or attenuate the erectile suppression induced by clonidine. A final study evaluated the dose-response relationship of clonidine-induced erectile dysfunction. A similar degree of erectile dysfunction was observed after 0.005, 0.025 or 0.25 mg/kg clonidine, whereas 0.0005 mg/kg was without effect. Previous studies demonstrated a dose-dependent inhibition of mounting, intromissive and ejaculatory behavior, with 0.25 mg/kg selectively eliminating ejaculatory behavior in mating tests. These data demonstrate a dose-dependent inhibition of penile reflexes, with inhibition occurring at doses lower than those required to induce copulatory dysfunction. Further, we suggest that opioid receptors sensitive to naloxone blockade are not involved in the clonidine-induced suppression of copulatory or erectile function.

Sex differences in the inhibition by ATD of testosterone-activated mounting behavior in guinea pigs

Adult male and female guinea pigs from a genetically heterogeneous stock were gonadectomized and tested for mounting behavior before and during various treatments with testosterone cypionate (TC) alone or in combination with an aromatase inhibitor, 1,4,6-androstatriene-3,17-dione (ATD). ATD was implanted subdermally in Silastic capsules (either 1 or 2 in females; 2 or 3 in males). In females 2 capsules of ATD completely blocked the behavioral effects of TC, and 1 capsule was an effective blocker in 58% of the females. The blocking effect was reversed by injection of diethylstilbestrol. In males, there was no measurable effect of ATD on mounting activity even when 3 capsules were implanted. Moreover, the TC induction of higher components of male sexual behavior (intromission and ejaculation) was also not impaired by ATD. Results are interpreted as indicating that either the process of male sexual differentiation or the male genotype eliminates the requirement for aromatization in androgenic activation of sexual behavior.

Axon-sparing lesions of the hypothalamic paraventricular nucleus abolish gonadal responses to photoperiod in male Syrian hamsters.

Intrahypothalamic injections of the excitotoxin N-methyl-D,L-aspartic acid (NMA) that destroyed the parvocellular regions of the paraventricular nucleus (PVN) prevented gonadal regression in male hamsters (Mesocricetus auratus) kept in short days (LD 6:18). After 17 weeks in short days, these NMA-injected animals had large, functional gonads and displayed all components of male sexual behavior. These findings confirm that neurons of the PVN are part of the pathway that mediates photoperiodism in hamsters.