Role of androgen in sexual reflexes of the male rat

Chronic treatment with glucocorticoids does not affect egg quality but increases cortisol deposition into egg albumen and elicits changes to the heterophil to lymphocyte ratio in a sex-dependent manner

During chronic stress, there is an initial increase in glucocorticoid (GC) levels, but they then return to low, albeit not baseline, levels. Recent studies have renewed interest in cortisol in that it may also have important roles in the stress response. The purpose of our study was to test the hypothesis that chronic treatment with low levels of either corticosterone or cortisol would alter HLR and immune organ morphometrics. Further, we wanted to determine if chronic treatment with either GC would elicit an increase in cortisol levels in egg albumen. To test our hypotheses, we implanted silastic capsules that contained corticosterone, cortisol, or empty capsules as controls (N = 5/sex/treatment). Blood serum, smears, body weights, and egg quality data were collected. Ducks were then euthanized and body weight, weights of spleens, livers, and the number of active follicles were recorded. Albumen GC levels were assessed using mass spectrometry. Data were analyzed using a 2- or 3-way ANOVA as appropriate and post-hoc with Fishers PLSD. No treatment elicited differences in egg quality measures or body weight compared to controls. Corticosterone treatment did elicit an increase in serum corticosterone (p < 0.05), but not cortisol, levels compared to controls in both sexes. Both cortisol and corticosterone treatments increased (p < 0.05) serum levels of cortisol compared to controls. Relative spleen weights were higher (p < 0.05) in hens following corticosterone but not cortisol treatment. No other organs showed any differences among the treatment groups. Both GCs elicited an increase (p < 0.001) in HLR in hens at all time-points over the 2-week treatment period compared to controls. Cortisol, not corticosterone, only elicited an increase in HLR for drakes (p < 0.05) compared to controls but only at day 1 after implants. Chronic treatment with cortisol, but not corticosterone, elicited an increase (p < 0.01) in egg albumen cortisol levels compared to other groups. Corticosterone was not detected in any albumen samples. Our results suggest that glucocorticoids elicit differential effects and although corticosterone has been stated to be the predominant GC in avian species, cortisol may provide critical information to further understand bird welfare.

Coenzyme Q10 enhances testicular functions and sexual behavior through regulating steroidogenic-related gene expression and inflammatory pathways of Japanese quail (Coturnix japonica) aganist cadmium

A progressively essential bird of high economic significance for meat production and commercial egg is the Japanese quail, and so more experiments are necessary to improve the productivity of these birds under stressful encounters. The current work was performed to define the influences of Coenzyme Q10 (CoQ10) on growth, sexual behavior, and testicular characteristics (size of the gonad, traits of spermatic features, levels of plasma testosterone, steroidogenic-related gene expression) of Japanese quail (Coturnix coturnix japonica) aganist cadmium (Cd) administration. Chicks of quail (n = 250), 14 days old of age were distributed into 4 groups: basal ration (Group 1), basal ration and CoQ10 at 100 mg/kg ration (Group 2), basal ration and Cd at 50 mg/kg ration (Group 3), and CoQ10 + Cd (Group 4). Several parameters relating to productive performance, such as weight of the body, weight gain, feed intake, and the conversion ratio of feed, were evaluated. Constant visual scanning of the quails was performed to observe their sexual behaviors. Sperm characteristics, plasma testosterone levels, and testicular inflammatory markers of interleukin-6 (IL-6) and tumor necrosis factor-α (TNF-α) were also determined. Oxidative-antioxidant redox status in the testes was evaluated by analyzing MDA level, GPx, and SOD activities. Steroidogenic-related gene expression in the testes (CYP17A1, StAR, 3β-HSD, and Cyp19) was also examined. In addition, testicular apoptosis was assessed by monitoring the alterations in the local expression of stress-induced (HSP70), proteins of anti-apoptotic marker (Bcl-2), and pro-apoptotic markers (caspase-3 and Bax). Cd administration hurts body performance, sexual behavior, and testicular efficiency parameters. Interestingly, CoQ10 supplementation improved reproductive performance. Moreover, it significantly increases the % of birds exhibiting sexual behavior and enhances testicular functions, which were damaged by Cd administration, by enhancing plasma testosterone level, antioxidative enzyme activity, and sperm quality traits while reducing the MDA and pro-inflammatory markers. Furthermore, downregulation of pro-apoptotic factor expression, though it increased the expression of the anti-apoptotic protein, was recorded. Correspondingly, CoQ10 revealed a marked upregulation in the expression of steroidogenic-related genes. Conclusion: It is established that the consumption of CoQ10 in the ration of Japanese quail, following a Cd adminstration, improves productive performance, sexual behavior, and several testicular function parameters as a potent antioxidant.

Pathobiology of ischiocavernosus and bulbospongiosus muscles in long-term diabetic male rats and its implication on erectile dysfunction

OBJECTIVE

To analyze pathobiology of ischiocavernosus (IC) and bulbospongiosus (BS) muscles in long-term diabetic male rats and its implication on erectile dysfunction (ED).

METHODS

Male rats were grouped into control and diabetic rats (received single injection of 60 mg/kg bw. of streptozotocin [STZ]). At 120th day, the animals were subjected to various analyses like serum hormone, penile reflex, electromyography of IC and BS muscles, after euthanasia IC and BS muscles were processed for morphological, histology, histometric analysis, immunostaining and immunoblotting synaptophysin, nNOS and NADPH diaphorase histochemistry.

RESULTS

Significant reduction in serum hormone level, penile reflex, reduced action potential or activity in both these muscles and wide range of histological alterations were observed in STZ rats. Muscles showed significant reduction in the diameter, volume and numerical density of the fiber in both muscles of STZ rats. Synaptophysin, nNOS and NADPH diaphorase were significantly reduced in diabetic animal IC and BS.

CONCLUSION

Severe neuromuscular circuitry alteration in IC and BS. Study concludes that degenerative changes in IC and BS may play a major role in ED in diabetic condition. Indicating diabetic-induced postsynaptic neuronal degeneration along with impaired motor action of the muscle and severe muscle degeneration affecting ED.

Adverse reproductive outcomes associated with fetal alcohol exposure: a systematic review

Fetal alcohol exposure results in well-characterised neurobehavioural deficits in offspring, which form the basis for diagnosing fetal alcohol spectrum disorder. However, there is increasing interest in the full range of health complications that can arise in children and adults with this disorder. We used a systematic review approach to locate all clinical and preclinical studies across a broad range of health outcomes in offspring exposed to prenatal alcohol. Our search encompassed four databases (PubMed, CINAHL, EMBASE and Web of Science) and titles/abstracts from retrieved studies were screened against strict inclusion/exclusion criteria. This review specifically evaluated studies reporting on reproductive outcomes in both males and females. A total of 23 studies were included, 5 clinical and 18 preclinical. Although there was a wide range in the quality of reporting across both clinical and preclinical studies, and variable results, trends emerged amongst the reproductive measures that were investigated. In females, most studies focussed on age at first menarche/puberty onset, with evidence for a significant delay in alcohol-exposed offspring. In males, offspring exposed to prenatal alcohol had altered testosterone levels, reduced testes and accessory gland weights and reduced sperm concentration and semen volume. However, further studies are required due to the paucity of clinical studies, the narrow scope of female reproductive outcomes examined and inconsistencies in outcomes across preclinical studies. We recommend that adolescents and individuals of reproductive age diagnosed with f-etal alcohol spectrum disorder be assessed for reproductive dysfunction to allow appropriate management of their reproductive health and fertility.

ICV galanin-like peptide stimulates non-contact erections but not touch-based erections in adult, sexually experienced male rats

Galanin-like peptide (GALP) is a neuropeptide transcribed only within the arcuate nucleus of the hypothalamus and is thought to be a mediator between energetics and reproductive function. Intracerebroventricular (ICV) injection of GALP is known to have effects on feeding, and to significantly increase gonadotropin releasing hormone- (GnRH-) mediated luteinizing hormone (LH) secretion. Furthermore, ICV GALP is known to stimulate fos production in the medial pre-optic area (mPOA) and to a lesser extent, the paraventricular nucleus (PVN). ICV injection of 5.0nmol GALP profoundly stimulates male rat sexual behavior. It is not known if GALP's effects on sex behavior are due to an increase in appetitive or mechanical (erectile) aspects of male sexual behavior. To determine this, sexually experienced male rats were cannulated in the lateral ventricle and injected with 5.0nmol GALP or vehicle. Immediately after injections, male rats were placed in an arena connected to a second arena via a tube with a fan. The second arena contained a steroid-primed female and her bedding. The male rat had olfactory but not visual or tactile contact with the female. We analyzed the amount of time the male rats spent investigating the air intake and the number of non-contact erections (NCEs) in a 30minute test. ICV GALP significantly (p<0.05) increased both the amount of time of olfactory investigations and NCEs compared to vehicle. In a second set of animals, we tested if ICV GALP could stimulate touch-based erections. GALP had no significant effect on touch-based erections compared to vehicle. These data suggest that GALP's activation of fos within the mPOA is indicative of its action to stimulate the appetitive aspects of male sexual behavior.

Nuclear expression of PG-21, SRC-1, and pCREB in regions of the lumbosacral spinal cord involved in pelvic innervation in young adult and aged rats

In rats, ageing results in dysfunctional patterns of micturition and diminished sexual reflexes that may reflect degenerative changes within spinal circuitry. In both sexes the dorsal lateral nucleus and the spinal nucleus of the bulbospongiosus, which lie in the L5-S1 spinal segments, contain motor neurons that innervate perineal muscles, and the external anal and urethral sphincters. Neurons in the sacral parasympathetic nucleus of these segments provide autonomic control of the bladder, cervix and penis and other lower urinary tract structures. Interneurons in the dorsal gray commissure and dorsal horn have also been implicated in lower urinary tract function. This study investigates the cellular localisation of PG-21 androgen receptors, steroid receptor co-activator one (SRC-1) and the phosphorylated form of c-AMP response element binding protein (pCREB) within these spinal nuclei. These are components of signalling pathways that mediate cellular responses to steroid hormones and neurotrophins. Nuclear expression of PG-21 androgen receptors, SRC-1 and pCREB in young and aged rats was quantified using immunohistochemistry. There was a reduction in the number of spinal neurons expressing these molecules in the aged males while in aged females, SRC-1 and pCREB expression was largely unchanged. This suggests that the observed age-related changes may be linked to declining testosterone levels. Acute testosterone therapy restored expression of PG-21 androgen receptor in aged and orchidectomised male rats, however levels of re-expression varied within different nuclei suggesting a more prolonged period of hormone replacement may be required for full restoration.

The effects of chronic administration of testosterone propionate with or without estradiol on the sexual behavior and plasma steroid levels of aged female rats

Low sexual desire concomitant with feelings of distress is reported in naturally and surgically menopausal women. A combination of estradiol (E2) and testosterone (T) restores sexual desire and interest in these women. The central mechanisms by which E2 and T act to restore desire are poorly understood. Here we examined the effect of chronic treatment with testosterone propionate (TP) administered by a sc SILASTIC brand capsule in aged ovary-intact female rats. Females were first treated with TP alone, followed by a second phase when TP was administered in combination with estradiol benzoate (EB; 10 μg) by sc injection 48 h prior to testing (EB+TP). Each phase consisted of 5 test days at 4-d intervals. Appetitive and consummatory female sexual behaviors were observed in bilevel chambers, and plasma E2 and T concentrations were measured with ELISA. Sexual solicitations and hops and darts were facilitated by the highest TP dose, and the lordosis quotient was increased by the two highest TP doses when administered alone, coinciding with an increase in plasma T, but those behavioral effects were not maintained across time. The lordosis quotient was inversely related to the TP dose in the EB+TP phase. These results suggest that the administration of TP by sc capsules to aged female rats facilitates appetitive and consummatory sexual behaviors; however, chronic treatment appears to be inhibitory. This is the first study to assess sexual behavior after SILASTIC brand implants of TP in the aged female rat. Additional research is needed to elucidate the mechanisms underlying the effects of T on female sexual function.

Trophic effects of brain-derived neurotrophic factor blockade in an androgen-sensitive neuromuscular system

In adult male rats, androgens are necessary for the maintenance of the motoneurons and their target muscles of the sexually dimorphic, steroid-sensitive spinal nucleus of the bulbocavernosus (SNB) neuromuscular system, regulating motoneuron and muscle morphology, function, and expression of trophic factors. Castration of males results in somal, dendritic, and muscle atrophy as well as increases in brain-derived neurotrophic factor (BDNF) in the target musculature. Because BDNF can have either facilitative or inhibitory effects in other systems, we examined SNB neuromuscular morphology after BDNF blockade using a fusion protein (tyrosine kinase receptor type B IgG). Blockade of BDNF in gonadally intact males resulted in hypertrophy of SNB motoneuron dendrites and target musculature, suggesting that normal levels of BDNF are inhibitory in SNB neuromuscular system. BDNF blockade in castrated males prevented SNB motoneuron atrophy and attenuated target muscle weight loss. This is the first demonstration that the highly androgen-sensitive SNB motoneuron dendrites and target muscles can be maintained in the absence of gonadal hormones and, furthermore, that blocking BDNF can have trophic effects on skeletal muscle. These results suggest that whereas BDNF is involved in the signaling cascade mediating the androgenic support of SNB neuromuscular morphology, its action can be inhibitory. Furthermore, the elevations in BDNF after castration may be responsible for the castration-induced atrophy in SNB motoneurons and target muscles, and the trophic effects of androgens may be mediated in part through a suppression of BDNF. These results may have relevance to therapeutic approaches to the treatment of neurodegenerative disease or myopathies.

Testosterone metabolites differentially maintain adult morphology in a sexually dimorphic neuromuscular system

The lumbar spinal cord of rats contains the sexually dimorphic, steroid-sensitive spinal nucleus of the bulbocavernosus (SNB). Androgens are necessary for the development of the SNB neuromuscular system, and in adulthood, continue to influence the morphology and function of the motoneurons and their target musculature. However, estrogens are also involved in the development of the SNB system, and are capable of maintaining function in adulthood. In this experiment, we assessed the ability of testosterone metabolites, estrogens and nonaromatizable androgens, to maintain neuromuscular morphology in adulthood. Motoneuron and muscle morphology was assessed in adult normal males, sham-castrated males, castrated males treated with testosterone, dihydrotestosterone, estradiol, or left untreated, and gonadally intact males treated with the 5alpha-reductase inhibitor finasteride or the aromatase inhibitor fadrozole. After 6 weeks of treatment, SNB motoneurons were retrogradely labeled with cholera toxin-HRP and reconstructed in three dimensions. Castration resulted in reductions in SNB target muscle size, soma size, and dendritic morphology. Testosterone treatment after castration maintained SNB soma size, dendritic morphology, and elevated target muscle size; dihydrotestosterone treatment also maintained SNB dendritic length, but was less effective than testosterone in maintaining both SNB soma size and target muscle weight. Treatment of intact males with finasteride or fadrozole did not alter the morphology of SNB motoneurons or their target muscles. In contrast, estradiol treatment was completely ineffective in preventing castration-induced atrophy of the SNB neuromuscular system. Together, these results suggest that the maintenance of adult motoneuron or muscle morphology is strictly mediated by androgens.

Exogenous testosterone reverses age-related atrophy in a spinal neuromuscular system

Aging is associated with a variety of pathologies, including motor dysfunctions and reductions in sexual behavior. In male rats, declines in sexual behavior during the aging process may be caused in part by the loss of the lumbar spinal cord motoneurons that innervate the penile musculature. Alternatively, declining sexual behavior may be caused by the precipitous reductions in circulating testosterone that occur during aging. In this paper, we report two experiments examining these issues. In Experiment 1, we counted motoneurons in the lumbar motor nuclei and measured several androgen-sensitive morphological properties of the penile muscles and their innervating motoneurons at several time points during the aging process. Motoneuron number in the lumbar nuclei did not change over time, even with very advanced age. In contrast, the penile muscles and their innervating motoneurons underwent profound atrophy, with muscle weight and motoneuron dendritic length declining to less than 50% of young adult levels. In Experiment 2, we treated aged animals with exogenous testosterone, and then examined their penile neuromuscular systems for morphological changes. Testosterone treatment, both acute and chronic, completely reversed age-related declines in the weight of the penile muscles and in the soma size and dendritic length of their innervating motoneurons. Together, these data suggest that reductions in male sexual behavior during the aging process are caused primarily by declines in testosterone levels rather than motoneuron loss. Furthermore, they raise the possibility that testosterone treatment could play an important role in maintaining neuronal connectivity in the aging body.

Effects of testosterone on sexual function in men: results of a meta-analysis

OBJECTIVES

The role of androgen decline in the sexual activity of adult males is controversial. To clarify whether sexual function would benefit from testosterone (T) treatment in men with partially or severely reduced serum T levels, we conducted a systematic review and meta-analysis of placebo-controlled studies published in the past 30 years. The aim of this study was to assess and compare the effects of T on the different domains of sexual life.

DATA SOURCE

A comprehensive search of all published randomized clinical trials was performed in MEDLINE, the Cochrane Library, EMBASE and Current Contents databases.

REVIEW METHODS

Guided by prespecified criteria, software-assisted data abstraction and quality assessed by two independent reviewers, a total of 17 randomized placebo-controlled trials were found to be eligible. For each domain of sexual function we calculated the standardized mean difference relative to T and reported the results of pooled estimates of T treatment using the random effect model of meta-analysis. Heterogeneity, reproducibility and consistency of the findings across studies were explored using sensitivity and meta-regression analysis.

RESULTS

Overall, 656 subjects were evaluated: 284 were randomized to T, 284 to placebo (P) and 88 treated in cross-over. The median study length was 3 months (range 1-36 months). Our meta-analysis showed that in men with an average T level at baseline below 12 nmol/l, T treatment moderately improved the number of nocturnal erections, sexual thoughts and motivation, number of successful intercourses, scores of erectile function and overall sexual satisfaction, whereas T had no effect on erectile function in eugonadal men compared to placebo. Heterogeneity was explored by grouping studies according to the characteristics of the study population. A cut-off value of 10 nmol/l for the mean T of the study population failed to predict the effect of treatment, whereas the presence of risk factors for vasculogenic erectile dysfunction (ED), comorbidities and shorter evaluation periods were associated with greater treatment effects in the studies performed in hypogonadal, but not in eugonadal, men. Meta-regression analysis showed that the effects of T on erectile function, but not libido, were inversely related to the mean baseline T concentration. The meta-analysis of available studies indicates that T treatment might be useful for improving vasculogenic ED in selected subjects with low or low-normal T levels. The evidence for a beneficial effect of T treatment on erectile function should be tempered with the caveats that the effect tends to decline over time, is progressively smaller with increasing baseline T levels, and long-term safety data are not available. The present meta-analysis highlights the need, and pitfalls, for large-scale, long-term, randomized controlled trials to formally investigate the efficacy of T replacement in symptomatic middle-aged and elderly men with reduced T levels and ED.

Neural control of erection

Penile erection is a vascular event controlled by the autonomic nervous system. The spinal cord contains the autonomic preganglionic neurons that innervate the penile erectile tissue and the pudendal motoneurons that innervate the perineal striated muscles. Sympathetic pathways are anti-erectile, sacral parasympathetic pathways are pro-erectile, and contraction of the perineal striated muscles upon activity of the pudendal nerves improves penile rigidity. Spinal neurons controlling erection are activated by information from peripheral and supraspinal origin. Both peripheral and supraspinal information is capable of either eliciting erection or modulating or inhibiting an erection already present. Sensory information from the genitals is a potent activator of pro-erectile spinal neurons and elicits reflexive erections. Some pre-motor neurons of the medulla, pons and diencephalon project directly onto spinal sympathetic, parasympathetic and pudendal motoneurons. They receive in turn sensory information from the genitals. These spinal projecting pathways release a variety of neurotransmitters, including biogenic amines (serotonin, dopamine, noradrenaline, and adrenaline) and peptides that, through interactions with many receptor subtypes, exert complex effects on the spinal network that controls penile erection. Some supraspinal structures (e.g. the paraventricular nucleus and the medial preoptic area of the hypothalamus, the medial amygdala), whose roles in erection have been demonstrated in animal models, may not project directly onto spinal pro-erectile neurons. They are nevertheless prone to regulate penile erection in more integrated and coordinated responses of the body, as those occurring during sexual behavior. The application of basic and clinical research data to treatment options for erectile dysfunction has recently proved successful. Pro-erectile effects of phosphodiesterase type 5 inhibitors, acting in the penis, and of melanocortin agonists, acting in the brain, illustrate these recent developments.

Estrogen alters excitability but not morphology of a sexually dimorphic neuromuscular system in adult rats

In rats, motoneurons of the spinal nucleus of the bulbocavernosus (SNB) innervate the bulbocavernosus (BC) muscle, which surrounds the base of the penis. The SNB/BC is a sexually dimorphic, steroid-sensitive neuromuscular system, which is critically important in male reproductive behavior. Androgens are necessary for the development, morphology, and function of the SNB/BC system. However, estradiol (E) is also necessary for the development of the SNB/BC system, and E is capable of maintaining BC EMG activity in adulthood. In this study, we used electrophysiological and anatomical methods to examine estrogenic effects on BC EMG activity. We used a modified H-reflex testing method to investigate polysynaptic reflex characteristics in intact males, castrates, and castrates treated short term with estradiol benzoate (EB). Measures of EMG activity, response latency, and spike count were altered in castrates, but maintained in EB-treated castrates to the levels of intact males. Furthermore, estrogenic effects were found in EMG activity that could be isolated to the periphery of the SNB/BC system. BC NMJ size and muscle fiber area have been demonstrated to be hormone sensitive, and we examined these for possible correlates of E's effects on BC EMG activity. BC muscles of intact males, castrates, and short-term EB-treated castrates were fixed and stained with zinc iodide and osmium tetroxide. NMJ size and muscle fiber area did not differ between groups. Together, these data suggest that E treatment results in changes in the neuromuscular periphery that maintain BC EMG activity, but this effect cannot be accounted for by changes in NMJ size or muscle fiber area.

Central nervous system agents in the treatment of erectile dysfunction: how do they work?

Drugs acting within the central nervous system (CNS) that reduce the sympathetic antierectile flow and enhance the parasympathetic proerectile flow to the penis may restore penile erection in cases of erectile dysfunction of both psychogenic and organic origin. The best characterized of such drugs is the dopaminergic agonist apomorphine, which acts on the hypothalamus and, perhaps, the autonomic nuclei in the spinal cord. Other drugs that target the CNS and have been registered and tested are the a(2)-adrenoceptor antagonists yohimbine and delequamine, the alpha-melanocyte-stimulating hormone agonist melanotan II, and the serotonin reuptake inhibitor trazodone. Androgens also may influence sexual behavior by acting within the CNS, notably by modifying the neurotransmitter system targeted by these drugs. Our knowledge of the mode of action of CNS drugs comes mainly from experiments on rodents. Consequently, explanations regarding the way they work in humans are only speculative.

Androgen-dependent nitric oxide release in rat penis correlates with levels of constitutive nitric oxide synthase isoenzymes

Androgens are known to influence penile erection and nitric oxide synthase (NOS) activity in cavernosal tissue homogenates. The present study was an assessment of the effects of castration and androgen replacement on the in vivo release of nitric oxide (NO), and of the simultaneously recorded intracavernosal pressure (ICP) changes elicited by electrostimulation of the cavernosal nerves (SCN) in the anesthetized rat. The extracellular levels of NO in the corpora were monitored electrochemically using porphyrin microsensors. The content of NOS isoenzymes in corporal homogenates was determined by immunoblotting. The responses of castrated rats with or without testosterone (T) implants were compared to those of intact animals. Castration virtually abolished both the NO and the ICP responses to SCN. There was a concomitant significant decrease in the content of both the neuronal (nNOS) and the endothelial (eNOS) isoenzymes in the cavernosal tissue. All these effects of castration were prevented by T replacement. The NO response to SCN was positively correlated with the levels of nNOS and eNOS, especially when the values of the two isoforms were added (r = 0.71, P < 0.001). These data suggest that the facilitatory action of androgens on penile erection involves the up-regulation of both constitutive NOS isoenzymes in the corpora cavernosa.

Regulation of noncontact erection in rats by gonadal steroids

Male rats exhibit erections in the presence of inaccessible estrous females, and we investigated which gonadal steroids regulate these noncontact erections (NCEs). Sexually experienced Wistar males (n >/= 8/group) were tested for NCE four times (every 3 days) before castration, after castration, and after receiving subcutaneous implants of 10-mm Silastic capsules that were empty or filled with crystalline testosterone propionate (TP), dihydrotestosterone (DHT), estradiol benzoate (EB), or DHT + EB (10 mm each). Before castration, males responded with NCE in approximately 50% of tests. No males had NCEs after castration, beginning 3 days after surgery. Also, no males responded after treatment with EB or empty capsules. After receiving implants of TP, DHT, or DHT + EB, 50% of males had NCEs, beginning with the first test 3 days after treatment. On every measure of NCE, males treated with DHT or DHT + EB were indistinguishable from each other and from TP-treated males. Among the sexual responses of male rats, NCE appears to be more sensitive than other behaviors to changes in gonadal condition. In its profile of response to gonadal steroids (testosterone+, dihydrotestosterone+, estradiol-), NCE is similar to reflexive erection, for which spinal systems are sufficient, and unlike copulation (T+, DHT-, E+), which depends on discrete areas of the brain. We nonetheless conclude that NCE depends on androgen-sensitive systems in the brain, but androgen-sensitive neurons in the lumbosacral spinal cord may also play a role.

Neuropeptide Y (NPY) levels in alcoholic and food restricted male rats: implications for site selective function

Neuropeptide Y (NPY) has been implicated in the control of ingestive, cardiovascular, and reproductive function. Blood pressure and sexual function were examined in Long-Evans rats receiving 6% ethanol-containing or calorically matched liquid diets, or rat chow ad lib. After 12 weeks of exposure, rats were sacrificed and plasma hormone levels and NPY content of microdissected brain regions were determined. Neither long-term alcohol ingestion nor caloric restriction were associated with major decrements in copulatory behavior. Long-term alcohol ingestion was associated with decrements in erectile function ex copula. Long-term alcohol ingestion was also associated with: (i) a moderate degree of hypertension; (ii) a failure to gain weight; (iii) decrements in circulating levels of LH, testosterone, and ACTH (but not progesterone); and (iv) increased corticosterone levels. Long-term alcohol ingesting and calorically-restricted rats exhibited alterations in daily feeding patterns. These physiological changes in response to long-term alcohol ingestion or caloric restriction were associated with neural site-selective differences in NPY content. Elevated NPY in the paraventricular nucleus was associated with voluntary (as in alcohol ingestion) or involuntary (as in caloric restriction) reductions in food intake. Differences in NPY in the suprachiasmatic and ventromedial nuclei were associated with the differences in feeding patterns. The decrements in hormone levels were associated with higher levels of NPY in the median eminence and in the arcuate nucleus.

Afferents originating from the dorsal penile nerve excite oxytocin cells in the hypothalamic paraventricular nucleus of the rat

Electrical stimulation of the dorsal penile nerve (DPN) produced orthodromic excitation in about half of oxytocin cells in the paraventricular nucleus (PVN). In contrast, less than 10% of vasopressin cells were excited. Tactile stimulation of the glans penis by a paintbrush produced excitation in 40% of oxytocin cells. Castration did not prevent activation of oxytocin cells. These results suggest that somatosensory information from the penis is transmitted to the PVN through the DPN and that such afferent input preferentially innervates oxytocin cells.

The inhibitory effects of propranolol on genital reflexes in male rats

We have previously reported that propranolol adversely affects sexual behavior in male rats. To elucidate whether the effects of propranolol might involve decrements in ability, we examined two components of sexual function ex copula--ejaculatory reflex capacity and erectile reflexes. In the first study, we examined the effects of various doses of (+/-)-propranolol (1.25-10 mg/kg) administered subcutaneously. Marked inhibition was observed, evidenced by increases in the latency to ex copula ejaculation and to initial erection and decrements in the number of seminal emissions and in the number of erectile reflexes. Analyses of dose-response relationships indicated that the degree of inhibition increased with increasing dose. In the second study, we evaluated the stereo-selectivity of the responses. Both (+)- and (-)-propranolol (1.25 mg/kg) significantly inhibited ejaculatory reflex potential, and although (+)- and (-)-propranolol significantly inhibited erectile reflexes, (-)-propranolol had a greater effect. The data are interpreted to indicate that a) propranolol-induced sexual dysfunction involves both motivational and ability aspects; and b) propranolol-induced inhibition of genital reflexes may be due, at least in part, to mechanisms other than beta-adrenoceptor blockade.

Prepubertal testosterone treatment of neonatally gonadectomized male rats: defeminization and masculinization of behavioral and endocrine function in adulthood

Testosterone (T) administered well after the neonatal "critical" period to females at a dose approximating male levels permanently defeminizes reproductive function (see companion publication). To obtain comparable data for the male, neonatally gonadectomized (NeoGx) males received T filled or empty Silastic capsules during days 15-30 of age and were studied in adulthood. Compared to controls, the T treatment resulted in reduced lordosis and proceptive behaviors, increased mounting and intromission behaviors without differences in penile reflexes or size, and reduced plasma FSH and LH surges. Twenty of twenty-three sham-NeoGx males, but only one NeoGx male, showed ejaculatory behavior despite equivalence in penile reflexes and size after detaching a frenulum when present on the penis. These results show that T can still act on neural substrates well beyond the neonatal period to defeminize and masculinize endocrine and behavioral function in the male rat. A comparison with effects in females indicates a sex difference, the male appearing to be more sensitive to these actions of T.

Sexual function in altered physiological states: comparison of effects of hypertension, diabetes, hyperprolactinemia, and others to "normal" aging in male rats

In this review, we examine the changes in sexual function that accompany deviations from "normal" physiological states. We propose that the changes one observes in many altered physiological states should not be viewed in isolation. We describe our paradigms for assessing sexual function, and proceed to evaluate how sexual function changes with hormonal deprivation and aging, in rat models for hypertension, in severe hyperprolactinemia, in streptozotocin-induced diabetes, after chronic alcohol intake, after chronic morphine administration, and after exposure to the heavy metal, cadmium. We will provide evidence for the involvement of adrenergic transmitters and two neuropeptides, neuropeptide Y and somatostatin, in the neuroendocrine regulation of sexual behavior. Finally, we compare and contrast the changes observed relative to the changes seen in "normal" aging in rats. The sequence of age-related changes in sexual function is distinct. The first change observed is a decrement in ex copula erectile reflexes. Next are decreases in ejaculatory threshold, followed shortly by increases in initiation and reinitiation of copulation after ejaculation. This is followed by a decrement in the number of males copulating to ejaculation. Finally, there is a failure to initiate the copulatory process. This sequelae is relatively common, being evident after castration, with hyperprolactinemia, and after exposure to cadmium. The data available for sexual function in hypertension is incomplete and modified by the etiology, but a suggestion for this sequelae is seen in SHR. In contrast, sexual dysfunction associated with chronic morphine administration appears to be due to an initial deficit in motivational aspects. Testosterone reverses sexual dysfunction associated with castration, but not with idiopathic sexual inactivity, nor with sexual dysfunction associated with aging, diabetes, or chronic morphine administration. Comparing sexual function in rat models for hypertension, diabetes and chronic ethanol leads to the conclusion that increases in blood pressure, like decreases in testosterone, cannot be the primary causal factor for sexual dysfunction. Age, hormonal history of the subject, and the age at castration influence changes in sexual function. Age-related sexual dysfunction appears to be contributed to by changes in adrenergic-neuropeptidergic, to include sympathetic, systems. Site-specific administration of NPY induces alterations in parameters of copulatory behavior which mimic those seen in aging and the retention of ejaculatory behavior with aging is associated with site-selective attenuation (or reversal) of age-associated changes in NPY content. Yohimbine enhances copulatory activity in castrated and aging rats, and attenuates or reverses the antisexual effects of clonidine, epinephrine and somatostatin.(ABSTRACT TRUNCATED AT 400 WORDS)

Placing erection in context: the reflexogenic-psychogenic dichotomy reconsidered

Penile erections are usually classified as arising from "reflexogenic" or "psychogenic" causes. In practice this dichotomy has translated, somewhat circularly, to a distinction between spinal vs. supraspinal mediation, pelvic vs. hypogastric neural mediation, and perineal somesthetic stimulation vs. stimulation of receptors innervated by the cranial nerves. Evidence for differential regulation of erection in different contexts is reviewed. Research ascribing a physiological role to the hypogastric nerves in psychogenic erection, exemplified by classic studies of cats and spinally injured men, is suggestive but not compelling. Somewhat stronger is evidence that erection in some contexts (e.g., nocturnal penile tumescence (NPT) in humans or touch-stimulated erection in rats) is more sensitive to androgen levels than in other contexts (e.g., visual erotic stimuli in men or copulation in rats). However, some of these differences may arise from the relative erectogenic strength of the stimuli, rather than from qualitative differences in androgen sensitivity of different contexts. More compelling is the possibility that conflicting interpretations of the role of dopamine in erection may stem in large part from differences among laboratories in the context in which erection is evoked. In light of the evidence reviewed, it seems unlikely that the conventional reflexogenic-psychogenic dichotomy should be retained, at least in its present form. As a first step, it may be worth considering that reflexive erections may not be limited to somesthetic perineal stimulation, but rather may also include stimuli received via the cranial nerves. Two alternatives to the standard reflexogenic-psychogenic dichotomy are proposed. The first is a minor revision in which two senses of psychogenic erection are distinguished: the weak, commonly used, sense would include erection resulting from any extrinsic nonsomesthetic stimulation, whether visual, auditory, or chemosensory. In this sense, reflexive erections and psychogenic erections may not be mutually exclusive. The strong sense of psychogenic erection would be limited to memory and fantasy. The origins of psychogenic erection in both senses need not be available to consciousness, which may account for apparently spontaneous erections. In the second alternative taxonomy, erectogenic stimuli are classified as contact (somesthetic) or noncontact, and their action in evoking erection is placed on a continuum of reflexivity. Erectile contexts could then be considered as orthogonal to the other two dimensions. Even without a change in taxonomy, the conduct and interpretation of research into erectile function may be expected to benefit from closer attention to differences and similarities between contexts and species, and to context-sensitive differences in the regulation of erection.

Cadmium-induced sexual dysfunction does not involve increased hepatic metabolism of testosterone nor increased circulating levels of corticosterone

Sexually experienced male rats were injected IP with 0, 0.3, 1.5, 3.0, or 6.0 mg/kg cadmium chloride. The highest dose was fatal within 48 h of injection. A dose-related deficit in erectile function was observed in ex copula tests 48 h after injection. Copulatory dysfunction was evident in mating tests 72 h after injection. Hepatic mixed function oxidase activity after 0.3 mg/kg injections was not different from controls, but was diminished by 50% in rats treated with 3.0 mg/kg. The higher cadmium doses (1.5 and 3.0 mg/kg) were associated with equivalent and marked reductions in circulating testosterone levels, and lesser decrements in circulating corticosterone levels. The rats treated with 1.5 or 3.0 mg/kg cadmium chloride lost weight (32 +/- 12 and 39 +/- 9 g, respectively). Relative decapsulated adrenal gland weights were markedly increased in rats treated with 3.0 mg/kg. These data indicate that exposure to cadmium is associated with alterations in sexual, hepatic, and adrenal function, with erectile dysfunction occurring at the lowest dose. The effects on copulatory behavior are especially striking because it requires some weeks for copulatory behavior to wane following castration.

Effects of castration and exogenous testosterone supplementation in an animal model of penile erection

The dependence of erectile behavior on androgen functioning is well established. Castration produces loss of both libido and potency in man and animals. The present study, using an animal model for potency, demonstrates the dependence of centrally induced erectile behavior on an intact androgen milieu. Castrated rats failed to produce an erection in response to apomorphine, an agent shown to produce erection in nearly all normal rats. Administration of exogenous testosterone propionate in dosages exceeding 60 micrograms./kg. produced a significant increase in erectile behavior. Yawning, an essentially parallel phenomenon to the stimulation of the erectile response, was also decreased following castration and responded similarly to increasing amounts of exogenous testosterone, demonstrating the influence of androgen functioning on the central nervous system. It was concluded that testosterone is a necessary prerequisite for the maintenance of a centrally induced erectile and yawning response. In an animal model of penile erection, testosterone increases the number of erections in a dose-dependent manner in castrated rats. The dependence of the erectile response on testosterone is, at least in part, centrally mediated.

Relative androgen sensitivity of the vascular and striated-muscle systems regulating penile erection in rats

In this study we sought to compare the androgen sensitivity of the penile vascular erectile system with that of the striated muscles that augment the vascular effectors. All males were castrated 2 weeks before the experiments. At the time of castration, all males were implanted SC with a 45-mm testosterone (T)-filled Silastic capsule to maintain reflexive erections in ex copula tests. Experimental males had the bulbospongiosus (bulbocavernosus and levator ani) and ischiocavernosus muscles removed, while control animals underwent sham muscle excision surgery. After two baseline penile reflex tests, the T capsules were removed, and the groups were compared for the rate of loss of penile responses over 5 weeks. After these tests were completed, the T capsules were reimplanted and the two groups were compared for the rate of restoration of penile reflexes. These tests were conducted at 6, 12, 24, 36, 48, 72, and 96 h after reimplantation of the T capsules. Our results demonstrated that the vascular effector mechanisms responsible for initiating erections are androgen sensitive. The effects of T withdrawal and replacement on erection latency and low intensity erections (E1s) were manifested at about the same rate in the vascular and striated muscle effector systems. In contrast, the restoration of moderate intensity erections (E2s) by T occurred at a faster rate in rats with intact penile muscles. This result suggests that T was acting on the striated muscle effector systems to augment penile erection during this time, presumably due to the bulbospongiosus muscle exerting greater force on the penile bulb.

Neurons in the paraventricular nucleus of the hypothalamus that project to the sexually dimorphic lower lumbar spinal cord concentrate 3H-estradiol in the male rat

The location and distribution of estradiol-concentrating neurons in the hypothalamus afferent to segments of lumbar spinal cord that contain the sexually dimorphic spinal nucleus of the bulbocavernosus (SNB) were determined by combining retrograde fluorescent tract tracing with steroid hormone autoradiography. Injections of Fluorogold were made into segments of L5-L6 of the spinal cord of adult male rats and 12 days later animals were castrated. One week following castration, males received injections of [3H]estradiol and were perfused. Their brains were then processed for steroid hormone autoradiography. Following exposure times of 11 to 12 months, autoradiograms were developed and the hypothalamus was analyzed for neurons that concentrate estradiol and project to the spinal cord. Numerous neurons in the hypothalamus projected to the spinal cord, specifically neurons in the paraventricular nucleus (PVN), the lateral hypothalamus and the dorsal area of the hypothalamus. Although many subnuclei of PVN, as well as lateral hypothalamus, contained Fluorogold labelled neurons and estradiol concentrating neurons, the majority of double labeled cells were found in the lateral parvocellular (LP) subnucleus of PVN. Approximately 30% of the neurons in the lp subnucleus that projected to spinal cord also concentrated estradiol. Up to one half of the estradiol-concentrating neurons in lp sent axons to the lower lumbar spinal cord. These results suggest that some of the effects of gonadal steroid hormones on SNB development, plasticity and function may in fact, be indirect, via steroid-sensitive afferents.

Erectile and copulatory dysfunction in chronically diabetic BB/WOR rats

The pituitary-testicular axis, penile reflexes, and copulatory behavior were studied in male BB diabetic rats from 10 to 40 wk of diabetes. Serum testosterone was diminished from 18 to 28 wk of diabetes, and the responses to human chorionic gonadotropin stimulation were blunted. Serum luteinizing hormone (LH) in diabetic rats did not differ from that of the control rats before or after LH-releasing hormone stimulation. Serum follicle-stimulating hormone and prolactin levels were also similar to controls. After 26 wk of diabetes, androgen-sensitive reproductive accessory organs were significantly reduced in size. This also was true for the androgen-sensitive bulbocavernosus and ischiocavernosus muscles. Penile reflexes in these animals from 20 to 32 wk of diabetes were consistently reduced in number and demonstrated prolonged latency. Copulatory behavior was evaluated in these animals at 25 and 28 wk of diabetes and revealed a reduced number of BB diabetic rats showing normal behavior at 25 wk of diabetes. At 28 wk of diabetes, mount latency, intromission latency, ejaculatory latency, and the postejaculatory interval were all prolonged compared with controls. In addition, the number of diabetic animals showing normal behavior was reduced compared with controls. These studies demonstrate that chronically BB diabetic rats develop diminished testosterone and erectile dysfunction that precedes ejaculatory dysfunction in a similar fashion as impotence in diabetic men. We suggest that further studies in this animal model may be critical to the better understanding and treatment of impotence in diabetic men.

Hormones and sexual behavior in relationship to aging in male rats

To determine if the age-related decline in male sex behavior is correlated with hormonal factors, a longitudinal study was conducted. Sexually experienced males were given mating tests every 2 months from 7 through 27 months of age. To study possible relationships between changes in behavior and alterations in hormone levels, blood samples were taken before and after these bimonthly tests. At 23 months, cross-sectional studies were also conducted comparing results to those obtained in 5-month-old males. Significant changes in mating behavior first appeared at 11 months; mount latency, intromission latency, ejaculation latency, postejaculatory interval, and intercopulatory interval were increased. Similarly, detectable decreases in testosterone (T) also occurred at this age. A significant decline in luteinizing hormone (LH) was not seen until 19 months. Correlational analyses revealed small (r less than or equal to -0.29) but significant negative correlations between T and parameters of mating behavior with age. When each age was examined separately, no significant correlations appeared. Plasma T was not predictive of behavioral performance. At 23 months, cross-sectional studies revealed deficits in mounting and penile reflex behavior but ejaculatory reflex capacity was unimpaired. At 28 months, males were decapitated. Only T levels showed a significant effect of age; estradiol, prolactin, and LH were unaffected when compared to 5-month-old males. The data suggest that although there are small and significant negative correlations between circulating testosterone and parameters of mating behavior with advancing age, it is unlikely that the observed decline in testosterone is the primary cause of the age-induced behavioral deficits. It is likely that the major causal factor(s) involves non-hormone-dependent changes within the CNS.

Sex differences in estrogen and androgen receptors in hamster brain

The present study was conducted to measure the levels of estrogen and androgen receptors (ER and AR, receptively) simultaneously in the anterior pituitary (AP), and various brain regions from adult male and proestrous female hamsters. Medial preoptic area (MPOA), medial basal hypothalamus (MBH), lateral hypothalamus (LH), medial forebrain bundle (MFB), and amygdala (AMG) were identified and removed from 200-microns frozen brain sections by the Palkovits punch-out technique. ER and AR were determined by the in vitro binding assay using [3H]-estradiol and [3H]-methyltrienolone as the binding ligands. In males, high levels of AR were found in the MPOA, MBH, and AP. In females, the MPOA, MBH, LH, and AP contained high levels of ER. The males exhibited significantly higher levels of AR than females in the MPOA, MBH, and LH, whereas the ER levels in these areas were higher in females. In males, ER and AR contents in the AP were higher, but the contents in the AMG were lower as compared to those of females. The calculated ER/AR ratio in MPOA, MBH, and LH were lowest in males. On the contrary, the ratio in these areas were highest in females. These data suggest that sex differences in response to estrogen and androgen may in part be due to sex differences in ER and AR contents in specific brain regions.

Multisensory regulation of maternal behavior and masculine sexual behavior: a revised view

Frank Beach's view of the multisensory regulation in Norway rats of copulation in males (12) and of pup retrieval in females (23) is critically analyzed and revised in terms of Lashley's influence, Beach's other work, and current neurobiological knowledge. Beach's view was that no single sensory stimulus is essential to elicit these behaviors, but that all relevant stimuli available summate in the neocortex; consequently, (a) sexual "arousal" is increased in males, leading to copulation, and (b) the "efficiency," or likelihood, of retrieval is increased in postpartum mothers. The revised view is based on a component analysis in which each of these behaviors consists of a chain of motoric responses elicited by somatosensory stimulation. Distal stimuli emanating from the female or pups induce proximity by provoking orientation, attention and arousal; the meaning of these stimuli is largely learned by conditioned associations during the initial executions of the behavior, although odors may have a prepotent influence for some individuals. Stimuli are integrated in a multisensory manner by both subcortical and neocortical mechanisms. Generalizations concerning the reproductive behavior of other mammalian species are suggested.

Testosterone dose-dependency of sexual and nonsexual behaviors in the gonadotropin-releasing hormone antagonist-treated male rat

The testosterone dose-dependency of several mating and nonmating behaviors was examined in the male rat, chemically castrated with a GnRH antagonist analog. Graded doses of testosterone enanthate (TE) were given to male rats to reinstate behaviors abolished by GnRH antagonist treatment. GnRH antagonist treatment alone markedly lowered serum LH, FSH and T concentrations and ventral prostate and testis weights. Open field behaviors were not significantly affected by GnRH antagonist treatment or castration. Scent-marking behavior was markedly suppressed by both castration and GnRH antagonist and restored by the lowest dose of TE (0.05 mg). All measures of male sexual behavior were impaired by GnRH antagonist treatment and castration and restored by the lowest dose of TE (0.05 mg). The doses of TE required to restore normal ventral prostate weights and testis weights were higher than those required to maintain scent marking and mating behaviors. No direct behavioral effects of the GnRH antagonist, other than those that can be explained by GnRH antagonist-induced suppression of testosterone were observed. The finding that sexual and nonsexual behaviors in the male rat have different testosterone requirements from those maintaining spermatogenesis and fertility may have significant implications for contraception.

A component analysis of the effects of DPAT on male rat sexual behavior

Male rat sexual behavior was examined in a variety of tests following a single acute IP injection of the serotonin1A (5-HT1A) receptor agonist 8-hydroxy-2-(di-n-propylamino)tetralin (DPAT). The objective was to determine the effects of 5-HT1A receptor stimulation on the components of sexual behavior (arousal/motivation, erection and ejaculation) using this prototypical 5-HT1A ligand. In the ex copula genital reflex test, DPAT dramatically inhibited ejaculation and the display of penile erections. When examined in the mating behavior test, DPAT caused a significant reduction in intromission frequency (IF), ejaculation latency (EL), intercopulatory intervals (ICI) and postejaculatory interval (PEI). The decrease in IF and EL indicated a lowering of the behavioral-ejaculatory threshold, while the reduction in ICI and PEI indicated a stimulation of two aspects of sexual arousal. Further tests, however, revealed complexities. Using the mounting test (with genital anesthesia) as an assessment of sexual arousal, no effect of DPAT was found. Collection and examination of the coagulated ejaculates resulting from mating (copulatory plugs) provided evidence of an impairment in ejaculation, as a result of DPAT treatment. The data suggests that 5-HT1A receptor stimulation lowers the behavioral-ejaculatory threshold despite inhibition of ejaculation in and ex copula; as well as stimulating specific aspects of sexual arousal. It remains to be determined whether the effects on arousal were either due to nonselectivity as currently believed or because 5-HT1A receptor stimulation affects alpha 2-adrenoceptor activity by some as yet undefined mechanism; and as a result modulates sexual arousal.

Intraspinal transplants of serotonergic neurons in the adult rat

Adult male Sprague-Dawley rats were made paraplegic by a complete transection of the spinal cord at lower thoracic level. One week later they were transplanted, below the level of the section, with a cell suspension prepared from the raphe region of 14-day embryos. After survival periods of 10 days to 1 year, the animals were sacrificed and the spinal cord processed for the immunocytochemical detection of 5-HT. Axons from grafted cells grew extensively into the grey matter of the host, and established axosomatic and axodendritic synapses in the anterior horn and intermediolateral column, similar to those of the intact animal. In addition, a group of transplanted animals was tested for sexual reflexes which are under the control of serotonin. It was found that ejaculation reflexes, which are absent in paraplegic rats, are restored in transplanted animals.

GABAergic regulation of penile reflexes and copulation in rats

In three experiments we investigated the role of the GABAergic system in regulating penile reflexes and copulation in rats. All males had the suspensory ligament of the penis removed 3 weeks before the experiments, thereby permitting the novel observation of penile body erections in addition to penile glans responses. In Experiments 1 and 2, rats were assigned to one of the following treatment groups: control (saline-injected); baclofen, a GABA-B receptor agonist (1 or 2 mg/kg); THIP, a GABA-A receptor agonist (5 mg/kg); or (+)bicuculline, a GABA-A receptor antagonist (0.25 mg/kg). Penile reflex tests began 20 min after SC injection. Baclofen treatment decreased the number of males responding with glans erections within the 30 min latency limit, and significantly reduced the number of glans erections displayed, in a dose-dependent manner. These results indicate that activation of GABA-B receptors inhibits penile reflexes outside the context of copulation (ex copula). Rats treated with baclofen also had a dose-dependent reduction in the ratio of clusters of glans erections to penile body erections, and a significant increase in the number of penile body erections observed prior to the first glans erection. These findings suggest that baclofen inhibited the mechanisms mediating penile glans responses more than those mediating penile body erections. Bicuculline was without effect in both experiments; THIP significantly increased erections in Experiment 2 but had no reliable effect in Experiment 1. Because baclofen inhibited penile responses in ex copula tests, Experiment 3 was designed to assess the effects of the same dosages of this agent on male copulatory behavior.(ABSTRACT TRUNCATED AT 250 WORDS)

Evidence for the reestablishment of copulatory behavior in castrated male rats with a brain-enhanced estradiol-chemical delivery system

We have developed a redox-chemical system for brain-enhanced drug delivery of estradiol based on an interconvertible dihydropyridine in equilibrium with pyridinium salt carrier. Estradiol, when combined with the carrier, readily crosses the blood-brain barrier and upon oxidation of the carrier is "locked" in the brain. The aim of this study was to evaluate the effects of an estradiol-chemical delivery system (E2-CDS) versus an equimolar dose of estradiol-17-valerate (E2-VAL) on copulatory behavior in orchidectomized rats. The data revealed that a single dose of E2-CDS was more efficacious than E2-VAL in stimulating mounting behavior (percent responding) and the effect was 100% through 5 weeks. E2-CDS increased intromission behavior more than E2-VAL through 28 days. Mount and intromission latencies were reduced by E2-CDS to a greater extent and for a longer time (28 days) than E2-VAL. Neither form of estradiol restored ejaculation parameters or penile reflexes. These data suggest that E2-CDS causes a potent and long-acting stimulation of proceptive and consummatory components of male sexual behavior, presumably acting through the local brain-release of estradiol.

Effects of a selective alpha 1-adrenoceptor agonist, methoxamine, on sexual behavior and penile reflexes

Methoxamine, an adrenergic agonist with selectivity for the alpha 1-adrenoceptor, when administered intraperitoneally 10 minutes prior to mating tests (1 to 5 mg/kg), effected reductions in the ejaculatory threshold, evidenced by a decrease in the number of intromissions preceding ejaculation. In mounting tests after penile anesthetization, a test which specifically assesses sexual motivation, 3 mg/kg methoxamine was without a stimulatory effect. Further, in penile reflex tests (ex copula) 1 mg/kg methoxamine was without effect, whereas 5 mg/kg decreased the number of erections, cups and flips per test, and increased the incidence of seminal emission. These data indicate a facilitation of the ejaculatory mechanism, both in and ex copula, coupled with an inhibition of erectile responses for moderate doses of methoxamine. Treatment of male rats with the alpha 2-adrenoceptor agonist clonidine (0.25 mg/kg, IP, five minutes pretest) drastically reduced the number of animals exhibiting intromissive and ejaculatory behavior in mating tests. This suppressive effect of clonidine was not prevented by prior treatment with methoxamine (3 mg/kg, 10 minutes pretest and five minutes preclonidine). Further, ST-91, a polar analog of clonidine which does not readily enter the central nervous system, was without effect on male sexual behavior. Since (1) the effects of methoxamine administration are not of similar quality or magnitude to those reported earlier after yohimbine, an alpha 2-adrenoceptor antagonist, (2) since concurrent stimulation of alpha 1- (by methoxamine) and alpha 2- (by clonidine) adrenoceptors is followed by a suppression of sexual behavior similar to that seen after clonidine alone.(ABSTRACT TRUNCATED AT 250 WORDS)

Alpha 2-adrenoceptor antagonists and male sexual behavior: II. Erectile and ejaculatory reflexes

Three alpha 2-adrenoceptor antagonists, yohimbine, idazoxan, and imiloxan, all shown to have stimulatory effects on sexual arousal/motivation, were studied to identify their possible effects on the other two major components of male copulatory behavior: erection and ejaculation. Genital reflex ex copula tests were used in order to assess these two responses without the confounding factors of mating behavior. Dose ranges were yohimbine: 0.25-4.0 mg/kg; idazoxan: 1.0-8.0 mg/kg; and imiloxan: 12.5-50.0 mg/kg. Lower doses of two of the drugs significantly enhanced the frequency of erections, while the third (yohimbine) showed a strong trend in that direction. At higher doses, all three alpha 2-antagonists produced significant reductions in the number of rats showing penile reflexes, including both erections and ejaculations. In those rats which did show penile reflexes, higher doses of yohimbine (4.0 mg/kg) inhibited the frequency of erections, while the higher dose of idazoxan showed a trend towards such inhibition. Thus, profound, largely inhibitory effects of these agents were demonstrated at dose ranges which have been shown to enhance sexual arousal. These data indicate that within the nervous system alpha 2-adrenoceptor antagonists can modulate erectile and ejaculatory mechanisms quite independently from effects on arousal/motivation.

Intermale social aggression in rats: suppression by medial hypothalamic lesions independently of enhanced defensiveness or decreased testicular testosterone

Medial hypothalamic lesions or sham lesions were made in castrated adult male rats with subcutaneous implants of testosterone-filled silastic capsules. Seven days following surgery all animals were given a test of defensiveness (reactivity) toward an experimenter. The following day, groups composed of one lesioned male rat, one sham-lesioned male rat, and one intact female rat were placed in large cages. Beginning two weeks later, unfamiliar intruders were introduced into each colony on a weekly basis and the aggressive behavior of the residents recorded. All 12 of the sham-lesioned animals but only 2 of 12 lesioned animals displayed substantial intermale social aggression toward intruders. Analysis of individual elements of intermale social aggression indicated that the lesioned animals were deficient in attack, bite, and piloerection but not in on-top behavior. The deficit in intermale social aggression was not correlated with defensiveness toward the experimenter or body weight of the lesioned animals. It is argued that the medial hypothalamus plays a role in the modulation of intermale social aggression which is independent of its role in modulating defensiveness or testosterone production. These results also demonstrate that intermale social aggression develops even when testosterone levels are held relatively constant by replacing testicular testosterone with an artificial testosterone source.

Testosterone removal in rats results in a decrease in social aggression and a loss of social dominance

Alpha male rats from mixed sex colony groups were tested for aggressiveness toward nonaggressive male intruders. Afterward, they were castrated and implanted with testosterone filled Silastic tubes, castrated and implanted with empty tubes, or sham castrated and implanted with empty tubes. There were significant declines in the aggressiveness (lateral attacks, bites, and piloerection but not on-top) of castrated rats without testosterone replacement but not in castrated rats with testosterone replacement. At a second operation, castrated animals had their testosterone capsules removed or had their empty capsules replaced with testosterone filled capsules. When tested for aggression toward nonaggressive intruders, those alpha males which had testosterone removed declined in aggressiveness while those which had it implanted returned to a level of aggressiveness close to that emitted by sham castrated control animals. Subordinate males became dominant when alpha males were castrated and not given testosterone replacement. In a final series of observations, sham castrated males were found to be more aggressive than castrated males when pitted against one another. It is argued that testosterone plays a primary role in intermale social aggression and that the decline in aggressiveness following castration is typically accompanied by a loss of social dominance.

Central effects of RDS-127: sexual behavior after intracerebroventricular administration and in vitro receptor binding studies

RDS-127, in a dose-related manner, induced seminal emission ex copula after intracerebroventricular (i.c.v.) administration. In mating tests initiated 6 min after i.c.v. administration, RDS-127 induced decreases in ejaculation latency and intromission frequency, with some rats ejaculating on the initial intromission. Additionally, penile reflexes were eliminated by 150 micrograms and 600 micrograms, but not by an intermediate dose. In in vitro radioligand binding studies, RDS-127 potently displaced [3H]DPAT binding to 5-HT1A sites in rat cortex (Ki = 14 +/- 4 nM) and was only moderately effective in displacing [3H]spiperone binding to dopaminergic D2 sites in rat striatum. RDS-127 was essentially ineffective at 5-HT1B sites labeled by [3H]5-HT in rat striatum (Ki = 13 000 +/- 4 000 nM). These data demonstrate that centrally administered RDS-127 mimics the previously reported alterations in sexual behavior after systemic treatment and that RDS-127 is a high affinity 5-HT1A agent with low affinity at the 5-HT1B binding site.

Stimulation of spinal serotonergic receptors facilitates seminal emission and suppresses penile erectile reflexes

Penile erection and ejaculation are produced by spinal reflexes subject to tonic control from the brain. This study examines the possible involvement of serotonergic transmission in the supraspinal modulation of such reflexes. The effects of two drugs which facilitate serotonergic transmission by different mechanisms, namely the direct receptor agonist, 5-methoxy-N,N'-dimethyltryptamine (5-MeODMT), and the reuptake inhibitor, zimelidine, were compared in intact and spinal rats. Results show that serotonergic stimulation in intact rats by either drug produces a dose-related increase in the incidence of seminal emission as well as a definite decrease of the display of erectile responses. In the spinal animals 5-MeODMT treatment reproduced both effects. By contrast, zimelidine, which needs functional nerve endings to exert its agonistic action, was ineffective in the spinal rats. This is interpreted to exclude a peripheral mechanism for the effects of the serotonin agonists on penile reflexes of intact animals and makes a strong case for a spinal site of action. We postulate the existence of serotonergic receptors located in the lower segments of the spinal cord which, when stimulated, trigger seminal emission and suppress erection.