Effects of testosterone on neuronal nitric oxide synthase and tyrosine hydroxylase

Strong Binding of Phytochemicals to the Catalytic Domain of Tyrosine Hydroxylase as a Trojan Horse Decreases Dopamine in Dopaminergic Cells: Pharmaceutical Considerations in Schizophrenia and Parkinson's Disease

BACKGROUND

Imbalances in dopamine levels result in neurological and psychological disorders such as elevated dopamine in Parkinson's disease.

OBJECTIVE

Despite a considerable number of advertisements claiming Aloe-vera's effectiveness in PD treatment, it has hidden long-term disadvantages for healthy people and PD patients.

METHODS

In the present investigation, the impacts of Aloe-vera on dopaminergic cells were evaluated.

RESULTS

The results indicated that the focal adhesion kinase (FAK) enhancement was in line with the Bax/Bcl2 ratio decrement, reactive oxygen specious (ROS) production, and nonsignificant alteration in the sub-G1phase of the cell cycle. It led to glial cell-derived neurotrophic factor (GDNF) upregulation but did not significantly change the BDNF level involved in depression and motor impairment recovery. These events apparently resulted in the enhancement in dopaminergic cell viability and neurite length and attenuated PI+ cells. However, it also induced neuronal nitric oxide synthase (nNOS) overexpression and nitric oxide (NO) and lactate dehydrogenase (LDH) production. Notably, docking results of the catalytic domain in tyrosine hydroxylase (TH) with the Aloe-vera constituents showed strong binding of most Aloe-vera constituents with the catalytic domain of TH, even stronger than L-tyrosine as an original substrate. Following the docking results, Aloe-vera downregulated TH protein and attenuated dopamine.

CONCLUSION

It can be hypothesized that Aloe-vera improves PD symptoms through enhancement in antiapoptotic markers and neurotrophic factors, while it suppresses TH and dopamine in the form of a Trojan horse, later resulting in the future deterioration of the disease symptoms. The results provide cues to pharmaceutical companies to use the active components of Aloe-vera as putative agents in neurological and psychiatric disorders and diseases to decrease dopamine in patients with enhanced dopamine levels.

Irisin Improves High-Fat Diet-Induced Sexual Dysfunction in Obese Male Rats

INTRODUCTION

Obesity is known to cause sexual dysfunction including erectile dysfunction and poor semen quality. Lifestyle modifications such as exercise have increasingly been more recognized to lower the likelihood of having sexual dysfunction or infertility in obese men. In this context, as an exercise-mimetic hormone, irisin has a potential to improve obesity-related reproductive dysfunctions. We aimed to elucidate possible effects of irisin on high-fat diet (HFD)-induced reproductive dysfunction in obese male rats.

METHODS

Rats were divided into four groups: vehicle, irisin, obese, and obese + irisin. The rats in obese and obese+irisin groups were fed with HFD (60% kcal fat) pellets for 12 weeks to induce obesity, and then obesity-induced sexual dysfunction was confirmed by the sexual behavior test (SBT). Irisin and obese+irisin groups received irisin (100 ng/kg/day) infusion by an s.c. osmotic minipump for 4 weeks after HFD-induced obesity was formed.

RESULTS

Irisin did improve a number of measures of copulation, including penile erection, ejaculation, and sexual performance, and also improved sperm morphology and motility and decreased fat-induced testicular damage. It decreased serum leptin levels. On the other hand, irisin did not affect serum luteinizing hormone (LH), follicle-stimulating hormone (FSH), and testosterone. It also increased gene expression of tyrosine hydroxylase (TH) and adrenoceptor alpha 1A (ADRA1A) in the medial preoptic area (mPOA) and nucleus accumbens (NAc).

CONCLUSION

Irisin provided a marked enhancement of HFD-induced decrease in libido, potency, sexual performance, and erection in SBT. Taken together, our results emphasize that irisin has a restorative and improver role in HFD-induced reproductive dysfunctions in obese male rats.

Hypothalamic cellular and molecular plasticity linked to sexual experience in male rats and mice

Male sexual behavior is subject to learning, resulting in increased efficiency of experienced males compared to naive ones. The improvement in behavioral parameters is underpinned by cellular and molecular changes in the neural circuit controlling sexual behavior, particularly in the hypothalamic medial preoptic area. This review provides an update on the mechanisms related to the sexual experience in male rodents, emphasizing the differences between rats and mice.

Nitrergic perivascular innervation in health and diseases: Focus on vascular tone regulation

For a long time, the vascular tone was considered to be regulated exclusively by tonic innervation of vasoconstrictor adrenergic nerves. However, accumulating experimental evidence has revealed the existence of nerves mediating vasodilatation, including perivascular nitrergic nerves (PNN), in a wide variety of mammalian species. Functioning of nitrergic vasodilator nerves is evidenced in several territories, including cerebral, mesenteric, pulmonary, renal, penile, uterine and cutaneous arteries. Nitric oxide (NO) is the main neurogenic vasodilator in cerebral arteries and acts as a counter-regulatory mechanism for adrenergic vasoconstriction in other vascular territories. In the penis, NO relaxes the vascular and cavernous smooth muscles leading to penile erection. Furthermore, when interacting with other perivascular nerves, NO can act as a neuromodulator. PNN dysfunction is involved in the genesis and maintenance of vascular disorders associated with arterial and portal hypertension, diabetes, ageing, obesity, cirrhosis and hormonal changes. For example defective nitrergic function contributes to enhanced sympathetic neurotransmission, vasoconstriction and blood pressure in some animal models of hypertension. In diabetic animals and humans, dysfunctional nitrergic neurotransmission in the corpus cavernosum is associated with erectile dysfunction. However, in some vascular beds of hypertensive and diabetic animals, an increased PNN function has been described as a compensatory mechanism to the increased vascular resistance. The present review summarizes current understanding on the role of PNN in control of vascular tone, its alterations under different conditions and the associated mechanisms. The knowledge of these changes can serve to better understand the mechanisms involved in these disorders and help in planning new treatments.

Impact of diabetes on male sexual function in streptozotocin-induced diabetic rats: Protective role of soluble epoxide hydrolase inhibitor

Diabetes-induced male sexual dysfunction is associated with endothelial dysfunction. Inhibition of soluble epoxide hydrolase (sEH) is known to improve endothelial function in diabetes. Therefore, we hypothesized that sEH inhibitor (sEHI), [trans-4-{4-[3-(4-trifluoromethoxyphenyl)-ureido]cyclohexyloxy}benzoic acid] / t-TUCB can restore the male sexual function in diabetic rat. After one week of administration of diabetogenic agent STZ (52 mg/kg i.p) injection, diabetic rats were treated with t-TUCB (0.1 and 0.3 mg/kg, p.o) or vehicle for 8 weeks. The sexual behaviour parameters of the animals were evaluated at the end of dosing period. The levels of testosterone and glucose in serum, and sperm were quantified. Effect of treatment on weight of reproductive organs and histopathology of penile tissue was evaluated. Diabetes had a negative effect on male sexual function, weight of sexual organs and production of sperm with a parallel decrease in the level of testosterone. The sEHI, t-TUCB, significantly preserved the sexual function and minimized an increase in the level of blood glucose in diabetic rats. It also prevented a decrease in the level of testosterone and sperm in diabetic rats, in comparison to diabetic control rats. Further, diabetes induced distortion of corpus cavernosum was attenuated by t-TUCB. Based on our findings, sEHI may delay the development of sexual dysfunction in diabetes.

Neuronal nitric oxide synthase activity mediates Lycium barbarum polysaccharides-enhanced sexual performance without stimulating noncontact erection in rats

RATIONALE

Lycium barbarum polysaccharide (LBP) is known to promote reproductive functions. However, its role in noncontact erection (NCE) of penis initiated by brain regions including medial preoptic area (MPOA) and paraventricular nucleus (PVN) regions responsible for sexual behavior has not been investigated.

OBJECTIVES

Therefore, this study initially investigated the effects of LBP on male sexual function, and subsequently, the mechanistic insight was investigated through assessing the expression of neuronal nitric oxide synthase (nNOS) in the MPOA and PVN.

METHODS

The adult male rats were treated with 100 mg/kg of LBP or vehicle by oral gavage. Before and after 14 days of treatment, copulatory behavior and noncontact erection (NCE) were recorded. After the last behavioral test, the brain was isolated to measure nNOS expression in the MPOA and PVN.

RESULTS

Data showed that LBP treatment significantly increased both the frequencies of intromission as well as ejaculation, compared to the control group. Whereas, a reduced post-ejaculatory interval was observed compared to same group on day 0. Furthermore, the treatment led to an increased intromission ratio, inter-intromission interval, and the number of MPOA nNOS-immunoreactive cells (nNOS-ir). Additionally, a significantly positive correlation between ejaculation frequency and MPOA nNOS-ir cells was recorded. Of note, LBP treatment had no effects on NCE and PVN nNOS-ir expression.

CONCLUSION

These findings suggest that LBP enhances sexual behavior through increased nNOS expression in the MPOA in male rats.

Leaf-Methanolic Extract of Pseudopanax arboreus (Araliaceae) (L. F. Phillipson) Reverses Amitriptyline-Induced Sexual Dysfunction in Male Rats

The people of the Bayangi tribe (Manyu Division) of Cameroon have used the leaves of Pseudopanax arboreus (Araliaceae) traditionally for decades as an aphrodisiac. In order to scientifically investigate this folk claim, we evaluated the effects of the leaf-aqueous extract of P. arboreus on the sexual behavior of normal male rats. The present study was designed to assess the effects of the leaf-methanolic extract of P. arboreus on amitriptyline-induced sexual dysfunction in male rats. Sexually impaired male rats were randomly divided into 4 groups of 8 rats each. Group 1 received 10 ml/kg distilled water, while group 2 was given 6 mg/kg Viagra. Groups 3 and 4 received 46.5 and 93 mg/kg of the leaf-methanolic extract, respectively. Female rats were made receptive by ovariectomy and subsequent hormonal treatment. Sexual behavior parameters were monitored on days 1, 7, 14, and 21 by pairing each male to a receptive female. The extract-treated rats registered significant decrease in mount latency (ML) and intromission latency (IL); nonsignificant increase in mount frequency (MF), intromission frequency (IF), and penile licking (PL); significant decrease in postejaculatory interval (PEI); contrasting effects in ejaculation latency (EL); and mean intromission interval (MII). Both doses of the extract also provoked a significant increase in relative weight of testes, but had no significant effect on the plasma hormonal profile. These findings are similar to those obtained with normal male rats and show that the leaf-methanolic extract of P. arboreus could constitute a potential solution to male sexual impairment.

Co-localization patterns of neurotensin receptor 1 and tyrosine hydroxylase in brain regions involved in motivation and social behavior in male European starlings

Animals communicate in distinct social contexts to convey information specific to those contexts, such as sexual or agonistic motivation. In seasonally-breeding male songbirds, seasonal changes in day length and increases in testosterone stimulate sexually-motivated song directed at females for courtship and reproduction. Dopamine and testosterone may act in the same brain regions to stimulate sexually-motivated singing. The neuropeptide neurotensin, acting at the neurotensin receptor 1 (NTR1), can strongly influence dopamine transmission. The goal of this study was to gain insight into the degree to which seasonal changes in physiology modify interactions between neurotensin and dopamine to adjust context-appropriate communication. Male European starlings were examined in physiological conditions that stimulate season-typical forms of communication: late summer/early fall non-breeding condition (low testosterone; birds sing infrequently), late fall non-breeding condition (low testosterone; birds produce non-sexually motivated song), and spring breeding condition (high testosterone; males produce sexually-motivated song). Double fluorescent immunolabeling was performed to detect co-localization patterns between tyrosine hydroxylase (TH; the rate-limiting enzyme in dopamine synthesis) and NTR1 in brain regions implicated in motivation and song production (the ventral tegmental area, medial preoptic nucleus, periaqueductal gray, and lateral septum). Co-localization between TH and NTR1 was present in the ventral tegmental area for all physiological conditions, and the number of co-localized cells did not differ across conditions. Immunolabeling for TH and NTR1 was also present in the other examined regions, although no co-localization was seen. These results support the hypothesis that interactions between NTR1 and dopamine in the ventral tegmental area may modulate vocalizations, but suggest that testosterone- or photoperiod-induced changes in NTR1/TH co-localization do not underlie seasonally-appropriate adjustment of communication.

Neural Regulation of Paternal Behavior in Mammals: Sensory, Neuroendocrine, and Experiential Influences on the Paternal Brain

Across the animal kingdom, parents in many species devote extraordinary effort toward caring for offspring, often risking their lives and exhausting limited resources. Understanding how the brain orchestrates parental care, biasing effort over the many competing demands, is an important topic in social neuroscience. In mammals, maternal care is necessary for offspring survival and is largely mediated by changes in hormones and neuropeptides that fluctuate massively during pregnancy, parturition, and lactation (e.g., progesterone, estradiol, oxytocin, and prolactin). In the relatively small number of mammalian species in which parental care by fathers enhances offspring survival and development, males also undergo endocrine changes concurrent with birth of their offspring, but on a smaller scale than females. Thus, fathers additionally rely on sensory signals from their mates, environment, and/or offspring to orchestrate paternal behavior. Males can engage in a variety of infant-directed behaviors that range from infanticide to avoidance to care; in many species, males can display all three behaviors in their lifetime. The neural plasticity that underlies such stark changes in behavior is not well understood. In this chapter we summarize current data on the neural circuitry that has been proposed to underlie paternal care in mammals, as well as sensory, neuroendocrine, and experiential influences on paternal behavior and on the underlying circuitry. We highlight some of the gaps in our current knowledge of this system and propose future directions that will enable the development of a more comprehensive understanding of the proximate control of parenting by fathers.

Contributions of testosterone and territory ownership to sexually-motivated behaviors and mRNA expression in the medial preoptic area of male European starlings

Animals integrate social information with their internal endocrine state to control the timing of behavior, but how these signals are integrated in the brain is not understood. The medial preoptic area (mPOA) may play an integrative role in the control of courtship behavior, as it receives projections from multiple sensory systems, and is central to the hormonal control of courtship behavior across vertebrates. Additionally, data from many species implicate opioid and dopaminergic systems in the mPOA in the control of male courtship behavior. We used European starlings to test the hypothesis that testosterone (T) and social status (in the form of territory possession) interact to control the timing of courtship behavior by modulating steroid hormone-, opioid- and dopaminergic-related gene expression in the mPOA. We found that only males given both T and a nesting territory produced high rates of courtship behavior in response to a female. T treatment altered patterns of gene expression in the mPOA by increasing androgen receptor, aromatase, mu-opioid receptor and preproenkephalin mRNA and decreasing tyrosine hydroxylase mRNA expression. Territory possession did not alter mRNA expression in the mPOA, despite the finding that only birds with both T and a nesting territory produced courtship behavior. We propose that T prepares the mPOA to respond to the presence of a female with high rates of courtship song by altering gene expression, but that activity in the mPOA is under a continuous (i.e. tonic) inhibition until a male starling obtains a nesting territory.

Anatomy and physiology of genital organs - men

Male sexual functions involve a number of organs and structures in genitalia whose role is to produce fertilizing gametes and to allow female-partner insemination. The testes belong to the reproductive and endocrine systems as they synthesize spermatozoa and androgens, and are under finely regulated hormonal control by the hypothalamopituitary axis. Sexual responses are controlled by a complex and coordinated interplay of both the somatic and the autonomic nervous system in multiple components of the brain, spinal cord, and relevant peripheral organs. Erectile bodies are an essential element of the penis and engorgement of the penis with blood leads to penile tumescence. Blood engorgement is due to relaxation of smooth-muscle cells of erectile tissue and endothelium of the penile arteries. The penis gains additional rigidity when the ischiocavernosus muscles contract. Stimuli from peripheral and/or central origins activate particular spinal nuclei, causing penile erection. Ejaculation consists of two phases, emission and expulsion, which correspond, respectively, to secretion of the different components of the semen by sex glands and forceful expulsion of semen due to rhythmic contractions of the bulbospongiosus muscle. A spinal generator of ejaculation integrates genital stimuli and sexual cues and, when the excitatory threshold is reached, triggers ejaculation by orchestrating the activation of autonomic and somatic pathways commanding the peripheral events of ejaculation.

Sociosexual investigation in sexually experienced, hormonally manipulated male leopard geckos: relation with phosphorylated DARPP-32 in dopaminergic pathways

Dopaminergic activity is both associated with sociosexual exposure and modulated by sexual experience and hormonal state across vertebrate taxa. Mature leopard geckos, a reptile with temperature-dependent sex determination, have dopaminoceptive nuclei that are influenced by their embryonic environment and sensitive to adult hormonal manipulation. In this study, we exposed hormonally manipulated male leopard geckos from different incubation temperatures to conspecifics and measured their sociosexual investigation, as well as phosphorylated DARPP-32 at Threonine 34 (pDARPP-32) immunoreactivity as a marker for D1 dopamine receptor activity in the nucleus accumbens, striatum, and preoptic area. Social investigation time by males of different incubation temperatures was modulated in opposite directions by exogenous androgen treatment. Males exposed to novel stimuli spent a greater proportion of time investigating females of different incubation temperatures. The time spent investigating females was positively correlated to pDARPP-32 immunoreactivity in the preoptic area. This is the first study quantifying pDARPP-32 in a lizard species, and suggests the protein as a potential marker to measure differences in the dopaminergic pathway in a social setting with consideration of embryonic environment and hormonal state.

A review on plants used for improvement of sexual performance and virility

The use of plant or plant-based products to stimulate sexual desire and to enhance performance and enjoyment is almost as old as the human race itself. The present paper reviews the active, natural principles, and crude extracts of plants, which have been useful in sexual disorders, have potential for improving sexual behaviour and performance, and are helpful in spermatogenesis and reproduction. Review of refereed journals and scientific literature available in electronic databases and traditional literature available in India was extensively performed. The work reviews correlation of the evidence with traditional claims, elucidation, and evaluation of a plausible concept governing the usage of plants as aphrodisiac in total. Phytoconstituents with known structures have been classified in appropriate chemical groups and the active crude extracts have been tabulated. Data on their pharmacological activity, mechanism of action, and toxicity are reported. The present review provides an overview of the herbs and their active molecule with claims for improvement of sexual behaviour. A number of herbal drugs have been validated for their effect on sexual behavior and fertility and can therefore serve as basis for the identification of new chemical leads useful in sexual and erectile dysfunction.

Sexual experience affects reproductive behavior and preoptic androgen receptors in male mice

Reproductive behavior in male rodents is made up of anticipatory and consummatory elements which are regulated in the brain by sensory systems, reward circuits and hormone signaling. Gonadal steroids play a key role in the regulation of male sexual behavior via steroid receptors in the hypothalamus and preoptic area. Typical patterns of male reproductive behavior have been characterized, however these are not fixed but are modulated by adult experience. We assessed the effects of repeated sexual experience on male reproductive behavior of C57BL/6 mice; including measures of olfactory investigation of females, mounting, intromission and ejaculation. The effects of sexual experience on the number of cells expressing either androgen receptor (AR) or estrogen receptor alpha (ERα) in the primary brain nuclei regulating male sexual behavior was also measured. Sexually experienced male mice engaged in less sniffing of females before initiating sexual behavior and exhibited shorter latencies to mount and intromit, increased frequency of intromission, and increased duration of intromission relative to mounting. No changes in numbers of ERα-positive cells were observed, however sexually experienced males had increased numbers of AR-positive cells in the medial preoptic area (MPOA); the primary regulatory nucleus for male sexual behavior. These results indicate that sexual experience results in a qualitative change in male reproductive behavior in mice that is associated with increased testosterone sensitivity in the MPOA and that this nucleus may play a key integrative role in mediating the effects of sexual experience on male behavior.

Effect of aqueous extract of Arctium lappa L. (burdock) roots on the sexual behavior of male rats

BACKGROUND

Arctium lappa L. root has traditionally been recommended as an aphrodisiac agent. It is used to treat impotence and sterility in China, and Native Americans included the root in herbal preparations for women in labor. However, its use has not been scientifically validated. The present study therefore investigated the effects of aqueous extract of Arctium lappa L. roots on sexual behavior in normal male rats.

METHODS

Seventy-five albino male rats were randomly divided into five groups of 15 rats each. Rats in group 1 (control) were administered 10 mL/kg body weight distilled water (vehicle), group 2 received 60 mg/kg body weight sildenafil citrate (Viagra), while those in groups 3, 4, and 5 were given 300, 600, and 1,200 mg/kg body weight, respectively, of aqueous extract of Arctium lappa L. roots in the same volume. Female albino rats were made receptive by hormonal treatment. Sexual behavior parameters in male rats were monitored on days 3, 7 and 15 by pairing with receptive females (1:3). Male serum testosterone concentrations and potency were also determined.

RESULTS

Oral administration of Arctium lappa L. roots extract at 600 and 1,200 mg/kg body weight significantly increased the frequencies of mount, intromission, and ejaculation frequency (p < 0.05). The latencies of mount and intromission were significantly reduced and ejaculation latency was prolonged. Administration of the extract also reduced the post-ejaculatory interval. The standard drug (Viagra) was more effective than the extract. The extract significantly increased the frequencies of all components of penile reflexes as well as serum testosterone levels, compared with the distilled water controls.

CONCLUSIONS

The results of this study demonstrate that aqueous extract of Arctium lappa L. roots enhances sexual behavior in male rats. The aphrodisiac effects of the plant extract may be related to the presence of flavonoids, saponins, lignans and alkaloids, acting via a multitude of central and peripheral mechanisms. These results thus support the traditional use of Arctium lappa L. root extract for treating impotence and sterility.

Estrogenic regulation of dopaminergic neurons in the opportunistically breeding zebra finch

Steroid-induced changes in dopaminergic activity underlie many correlations between gonadal hormones and social behaviors. However, the effects of steroid hormones on the various behaviorally relevant dopamine cell groups remain unclear, and ecologically relevant species differences remain virtually unexplored. We examined the effects of estradiol (E2) manipulations on dopamine (DA) neurons of male and female zebra finches (Taeniopygia guttata), focusing on numbers of tyrosine hydroxylase-immunoreactive (TH-ir) cells in the A8-A15 cell groups, and on TH colocalization with Fos, conducted in the early A.M., in order to quantify basal transcriptional activity. TH is the rate-limiting enzyme for catecholamine synthesis, and specifically DA in the A8-A15 cell groups. In contrast to other examined birds and mammals, reducing E2 levels with the aromatase-inhibitor Letrozole failed to alter TH-ir neuron numbers within the ventral tegmental area (VTA; A10), while increasing neuron numbers in the central gray (CG; A11) and caudal midbrain A8 populations. Consistent with findings in other birds, but not mammals, we also found no effects of E2 manipulations (Letrozole or Letrozole plus E2 replacement) on TH-Fos colocalization in any location. In accordance with previous observations in both mammals and birds, E2 treatment decreased the number of TH-ir neurons in the A12 population of the tuberal hypothalamus, a cell group that inhibits the release of prolactin. In general, males and females exhibited similar TH-ir neuron numbers, although males exhibited significantly more TH-ir neurons in the A11 CG population than did females. These results suggest partial variability in E2 regulation of DA across species.

Sex, drugs and gluttony: how the brain controls motivated behaviors

Bart Hoebel has forged a view of an integrated neural network that mediates both natural rewards and drug use. He pioneered the use of microdialysis, and also effectively used electrical stimulation, lesions, microinjections, and immunohistochemistry. He found that feeding, stimulant drug administration, and electrical stimulation of the lateral hypothalamus (LH) all increased dopamine (DA) release in the nucleus accumbens (NAc). However, whereas DA in the NAc enhanced motivation, DA in the LH inhibited motivated behaviors. The Hull lab has pursued some of those ideas. We have suggested that serotonin (5-HT) in the perifornical LH inhibits sexual behavior by inhibiting orexin/hypocretin neurons (OX/HCRT), which would otherwise excite neurons in the mesocorticolimbic DA tract. We have shown that DA release in the medial preoptic area (MPOA) is very important for male sexual behavior, and that testosterone, glutamate, nitric oxide (NO) and previous sexual experience promote MPOA DA release and mating. Future research should follow Bart Hoebel's emphasis on neural systems and interactions among brain areas and neurotransmitters.

Nitric oxidergic cells related to ejaculation in gerbil forebrain contain androgen receptor and respond to testosterone

Two clusters of forebrain neurons-one in the posterodorsal preoptic nucleus (PdPN) and one in the lateral part of the posterodorsal medial amygdala (MeApd)-are activated at ejaculation in male rats and gerbils as seen with Fos immunocytochemistry. To understand the functions of these cells and how they respond synchronously, it may be useful to identify their neurotransmitters. Nitric oxide (NO) was of interest because its levels in the preoptic area affect ejaculation, and it could synchronize clustered neurons through paracrine/volume transmission. Thus, we determined whether the ejaculation-related cells produce NO by assessing Fos co-localization with NO synthase (NOS) in recently mated male gerbils. We also studied NOS-Fos co-localization in the medial part of the medial preoptic nucleus (MPNm), where half of the neurons that express Fos after mating reflect ejaculation. We also quantified NOS co-localization with androgen receptor (AR) and NOS sensitivity to androgens at these sites. Without quantification, we extended these analyses throughout the hypothalamus and amygdala. Many mating-activated PdPN, lateral MeApd, and MPNm cells contained NOS (32-54%), and many NOS neurons at these sites expressed Fos (34-51%) or AR (25-69%). PdPN and MPNm NOS cells were sensitive to testosterone but not its androgenic metabolite dihydrotestosterone. The overall distribution of NOS and NOS-AR cells was similar to that in rats. These data suggest that NO may help to synchronize the activation of PdPN and lateral MeApd neurons at ejaculation and that NOS in PdPN and MPNm cells is regulated by testosterone acting via estradiol or without undergoing metabolism.

Neuronal nitric oxide synthase as a substrate for the evolution of pseudosexual behaviour in a parthenogenetic whiptail lizard

The evolution of neuroendocrine mechanisms governing sex-typical behaviour is poorly understood. An outstanding animal model is the whiptail lizard (Cnemidophorus) because both the ancestral and descendent species still exist. The ancestral little striped whiptail, Cnemidophorus inornatus, consists of males and females, which exhibit sex-specific mating behaviours. The descendent desert grassland whiptail, Cnemidophorus uniparens, consists only of females that alternately exhibit both female-like and male-like pseudosexual behaviour. Castrated male C. inornatus will mount a conspecific in response to exogenous androgen, although some are also sensitive to progesterone. This polymorphism in progesterone sensitivity in the ancestral species may have been involved in evolution of progesterone-mediated male-typical behaviour in the descendant unisexual lizards. We tested whether progesterone activates a typically androgenic signalling pathway by investigating hormonal regulation of neuronal nitric oxide synthase (nNOS) using in situ hybridisation and NADPH diaphorase histochemistry, a stain for nNOS protein. NADPH diaphorase is widely distributed throughout the brain of both species, although only in the periventricular nucleus of the preoptic area (pvPOA) are there differences between mounting and non-mounting individuals. The number of cells expressing nNOS mRNA and NADPH diaphorase is higher in the pvPOA of individuals that mount in response to progesterone or androgen. Furthermore, the nNOS promoter has both androgen and progesterone response elements, and NADPH diaphorase colocalises with the progesterone receptor in the pvPOA. These data suggest that a polymorphism in progesterone sensitivity in the sexual ancestor reflects a differential regulation of nNOS and may account for the male-typical behaviour in unisexual whiptail lizards.

Neuropeptides and enzymes are targets for the action of endocrine disrupting chemicals in the vertebrate brain

Endocrine-disrupting chemicals (EDC) are molecules that interfere with endocrine signaling pathways and produce adverse consequences on animal and human physiology, such as infertility or behavioral alterations. Some EDC act through binding to androgen or/and estrogen receptors primarily operating through a genomic mechanism regulating gene expression. This mechanism of action may induce profound developmental adverse effects, and the major targets of the EDC action are the gene products, i.e., mRNAs inducing the synthesis of various peptidic molecules, which include neuropeptides and enzymes related to neurotransmitters syntheses. Available immunohistochemical data on some of the systems that are affected by EDC in lower and higher vertebrates are detailed in this review.

Estrous cycle influences the expression of neuronal nitric oxide synthase in the hypothalamus and limbic system of female mice

BACKGROUND

Nitric oxide plays an important role in the regulation of male and female sexual behavior in rodents, and the expression of the nitric oxide synthase (NOS) is influenced by testosterone in the male rat, and by estrogens in the female. We have here quantitatively investigated the distribution of nNOS immunoreactive (ir) neurons in the limbic hypothalamic region of intact female mice sacrificed during different phases of estrous cycle.

RESULTS

Changes were observed in the medial preoptic area (MPA) (significantly higher number in estrus) and in the arcuate nucleus (Arc) (significantly higher number in proestrus). In the ventrolateral part of the ventromedial nucleus (VMHvl) and in the bed nucleus of the stria terminalis (BST) no significant changes have been observed. In addition, by comparing males and females, we observed a stable sex dimorphism (males have a higher number of nNOS-ir cells in comparison to almost all the different phases of the estrous cycle) in the VMHvl and in the BST (when considering only the less intensely stained elements). In the MPA and in the Arc sex differences were detected only comparing some phases of the cycle.

CONCLUSION

These data demonstrate that, in mice, the expression of nNOS in some hypothalamic regions involved in the control of reproduction and characterized by a large number of estrogen receptors is under the control of gonadal hormones and may vary according to the rapid variations of hormonal levels that take place during the estrous cycle.

Estrous cycle influences the expression of neuronal nitric oxide synthase in the hypothalamus and limbic system of female mice

BACKGROUND

Nitric oxide plays an important role in the regulation of male and female sexual behavior in rodents, and the expression of the nitric oxide synthase (NOS) is influenced by testosterone in the male rat, and by estrogens in the female. We have here quantitatively investigated the distribution of nNOS immunoreactive (ir) neurons in the limbic hypothalamic region of intact female mice sacrificed during different phases of estrous cycle.

RESULTS

Changes were observed in the medial preoptic area (MPA) (significantly higher number in estrus) and in the arcuate nucleus (Arc) (significantly higher number in proestrus). In the ventrolateral part of the ventromedial nucleus (VMHvl) and in the bed nucleus of the stria terminalis (BST) no significant changes have been observed. In addition, by comparing males and females, we observed a stable sex dimorphism (males have a higher number of nNOS-ir cells in comparison to almost all the different phases of the estrous cycle) in the VMHvl and in the BST (when considering only the less intensely stained elements). In the MPA and in the Arc sex differences were detected only comparing some phases of the cycle.

CONCLUSION

These data demonstrate that, in mice, the expression of nNOS in some hypothalamic regions involved in the control of reproduction and characterized by a large number of estrogen receptors is under the control of gonadal hormones and may vary according to the rapid variations of hormonal levels that take place during the estrous cycle.

Correlation of nitric oxide (NO) activity and gonadal function in Japanese quail, Coturnix coturnix japonica following temporal phase relation of serotonergic and dopaminergic oscillations

Nitric oxide (NO), a highly reactive and short-lived radical, is considered to be an important trigger molecule for several physiological mechanisms including gonadotrophin releasing hormone (GnRH) secretion in mammals, although there is no such information in avian literature. On the other hand, specific temporal phase relation of circadian neural (serotonergic and dopaminergic) oscillations is reported to modulate reproductive activity in many avian species including Japanese quail. The present study was undertaken to investigate the correlation of NO activity and gonadal function of Japanese quail. In experiment I, the effect of serotonin and dopamine precursors, (5-hydroxytryptophan (5-HTP) and L-dihydroxyphenyalanine (L-DOPA) respectively; 5 mg per 100g body weight) administered at intervals of 8 or 12h over a period of 13 days, was studied on reproductive responses and NO activity. Measurements of body weight, cloacal gland size, testosterone concentration, spermatogenesis, nitrite-nitrate concentration in plasma, hypothalamus and testes, and NADPH-diaphorase (NADPH-d) activity in testes were made on the 2nd, 3rd, 6th and 11th days of treatment and 2nd and 30th day post-treatment. In experiment II, quail were divided into five groups including the control. One experimental group received 13 daily injections of 5-HTP and L-DOPA at intervals of 8h along with 0.1 ml of normal saline administered orally (8-hr+Veh), while another group of 8-hr quail received NO donor (sodium nitroprusside (SNP), 5 mg per 100 g body weight) orally (8-hr+SNP). The third experimental group received 5-HTP and L-DOPA at intervals of 12h along with normal saline (12-hr+Veh), while the fourth group of quail along with 5-HTP and L-DOPA at intervals of 12h also received the NOS inhibitor (N-nitro-L-arginine methyl ester, L-NAME, 25 microg per 100 g body weight) intraperitoneally (12-hr+L-NAME) for 13 days. This experiment was terminated after 21 days of the treatment. Results indicate that 5-HTP and L-DOPA administered 8h apart (8-hr) suppressed but if given 12h apart (12-hr) stimulated the reproductive system and NO activity compared to the control. These effects were apparent on the 6th day of injections and were maintained 30 days following the termination of the treatment. A significant decrease in nitrite and nitrate concentration and NADPH-d activity in reproductively inhibited 8-hr group and an increase in reproductively stimulated 12-hr quail was also evident. In contrast, these activities were stimulated in 8-hr+SNP quail and were suppressed in 12-hr+L-NAME group quail. It is concluded that activity of the reproductive system and NO activity waxes and wanes simultaneously in Japanese quail. Moreover, experimental modulation of gonadal activity (following changes in the phase relation of serotonergic and dopaminergic activity) or NO activity (following the administration of NO modulator or inhibitor) affects each other maintaining a parallel relation between the two systems. Further, it is interesting to note that the gonado-stimulatory effect of SNP overpowers the gonado-inhibitory effects of the 8-hr time interval and inhibitory effects of L-NAME mask the stimulatory effects of 12-hr temporal relation of 5-HTP and L-DOPA administration. These findings strongly suggest that reproductive effects may be induced via changes in NO activity, however the exact mechanism by which NO drives gonadal axis needs to be ascertained.

The effects of nitric oxide-cGMP pathway stimulation on dopamine in the medial preoptic area and copulation in DHT-treated castrated male rats

Dopamine (DA) in the medial preoptic area (MPOA) provides important facilitative influence on male rat copulation. We have shown that the nitric oxide-cGMP (NO-cGMP) pathway modulates MPOA DA levels and copulation. We have also shown that systemic estradiol (E(2)) maintains neuronal NO synthase (nNOS) immunoreactivity in the MPOA of castrates, as well as relatively normal DA levels. This effect of E(2) on nNOS probably accounts for at least some of the previously demonstrated behavioral facilitation by intra-MPOA E(2) administration in castrates. Therefore, we hypothesized that stimulation of the MPOA NO-cGMP pathway in dihydrotestosterone (DHT)-treated castrates should restore DA levels and copulatory behaviors. Reverse-dialysis of a NO donor, sodium nitroprusside (SNP), increased extracellular DA in the MPOA of DHT-treated castrates and restored the ability to copulate to ejaculation in half of the animals. A cGMP analog, 8-Br-cGMP, also increased extracellular DA, though not as robustly, but did not restore copulatory ability. The effectiveness of the NO donor in restoring copulation and MPOA DA levels is consistent with our hypothesis. However, the lack of behavioral effects of 8-Br-cGMP, despite its increase in MPOA DA, suggests that NO may have additional mediators in the MPOA in the regulation of copulation. Furthermore, the suboptimal copulation seen in the NO donor-treated animals suggests the importance of extra-MPOA systems in the regulation of copulation.

The effect of chronic antipsychotic treatment on sexual behaviour, hormones and organ size in the male rat

Antipsychotic drug-induced sexual dysfunction is an important and problematic side effect. We have investigated the effect of chronic antipsychotic treatment on sexual behaviour, sex hormones and genital organ size in the male rat. The following sexual functions were significantly impaired in both risperidone (2 mg/kg) and haloperidol (2 mg/kg) groups at 3 weeks: libido (assessed in mounting frequency and intromission), sexual arousability/motivation (in terms of latencies for mounting and intromission) and orgasm (in terms of latency for ejaculation). At 6 weeks, haloperidol also suppressed the 'hit ratio' (intromissions/mounts) as well as the above-mentioned parameters indicating erectile dysfunction. Risperidone had no significant effect on sexual function at 6 weeks. Compared with the control group, haloperidol and risperidone decreased the serum level of testosterone after 6 weeks but not after 3 weeks. The two drugs did not influence the serum level of leutenizing hormone (LH). At 3 weeks, the epididymis was significantly decreased below controls in both risperidone and haloperidol groups. At 6 weeks, the epididymis, seminal vesicle and prostate weights were significantly reduced in the haLoperidol group, but not in the risperidone group. The serum concentration of testosterone significantly correlated with sex organ weight, but not with sexual behaviours. These results suggest that sexual function, testosterone levels and genital tissue size in male rats were affected to different degrees by risperidone and haloperidol. These findings contribute to our understanding of antispsychotic drug-induced male sexual dysfunction.

Sexual behavior in male rodents

The hormonal factors and neural circuitry that control copulation are similar across rodent species, although there are differences in specific behavior patterns. Both estradiol (E) and dihydrotestosterone (DHT) contribute to the activation of mating, although E is more important for copulation and DHT for genital reflexes. Hormonal activation of the medial preoptic area (MPOA) is most effective, although implants in the medial amygdala (MeA) can also stimulate mounting in castrates. Chemosensory inputs from the main and accessory olfactory systems are the most important stimuli for mating in rodents, especially in hamsters, although genitosensory input also contributes. Dopamine agonists facilitate sexual behavior, and serotonin (5-HT) is generally inhibitory, though certain 5-HT receptor subtypes facilitate erection or ejaculation. Norepinephrine agonists and opiates have dose-dependent effects, with low doses facilitating and high doses inhibiting behavior.

Testosterone induction of male-typical sexual behavior is associated with increased preoptic NADPH diaphorase and citrulline production in female whiptail lizards

In rodents, male-typical copulatory behavior is generally dependent on gonadal sex steroids such as testosterone, and it is thought that the mechanism by which the hormone gates the behavior involves the gaseous neurotransmitter nitric oxide. According to one model, testosterone induces an up-regulation of nitric oxide synthase (NOS) in the preoptic area, increasing nitric oxide synthesis following exposure to a sexual stimulus. Nitric oxide in turn, possibly through its effect on catecholamine turnover, influences the way the stimulus is processed and enables the appropriate copulatory behavioral response. In whiptail lizards (genus Cnemidophorus), administration of male-typical levels of testosterone to females induces the display of male-like copulatory responses to receptive females, and we hypothesized that this radical change in behavioral phenotype would be accompanied by a large change in the expression of NOS in the preoptic area. As well as comparing NOS expression using NADPH diaphorase histochemistry between testosterone-treated females and controls, we examined citrulline immunoreactivity (a marker of recent nitric oxide production) in the two groups, following a sexual stimulus and following a nonsexual stimulus. Substantially more NADPH diaphorase-stained cells were observed in the testosterone-treated animals. Citrulline immunoreactivity was greater in testosterone-implanted animals than in blank-implanted animals, but only following exposure to a sexual stimulus. This is the first demonstration that not only is NOS up-regulated by testosterone, but NOS thus up-regulated is activated during male-typical copulatory behavior.

Getting his act together: roles of glutamate, nitric oxide, and dopamine in the medial preoptic area

Gonadal hormones have primarily slow, genomically mediated effects, but copulation requires rapid interactions with a partner. A major way in which hormones facilitate male sexual behavior is by increasing production of neurotransmitter receptors or of enzymes that regulate neurotransmitter synthesis or release. Dopamine is an important facilitative neurotransmitter, and the medial preoptic area (MPOA) is a critical integrative site for male sexual behavior. MPOA dopamine is released before and during mating and facilitates copulation, genital reflexes, and sexual motivation. Gonadal hormones regulate dopamine release in the MPOA of male rats in part by increasing nitric oxide synthase (NOS) in the MPOA; the resultant increase in production of nitric oxide (NO) increases both basal and female-stimulated dopamine release. Glutamate also increases dopamine release via increased production of NO. At least some of the glutamatergic inputs to the MPOA are from the medial amygdala (MeA) and bed nucleus of the stria terminalis (BNST), which mediate the female-stimulated increase in dopamine, which in turn enhances copulatory ability. Extracellular glutamate in the MPOA increases during copulation, especially during ejaculation, and increased glutamate facilitates copulation and genital reflexes. Previous sexual experience also facilitates copulation and confers resistance to impairment by various lesions, drugs, and stress. Experience enhances processing of sexual stimuli, and its effects require activation of glutamate NMDA receptors and NOS in the MPOA. Neuronal NOS is increased in the MPOA of experienced males. Therefore, glutamate, NO, and dopamine interact in the MPOA to facilitate mating and to enhance future sexual responsiveness.

The nitric oxide-guanosine 3',5'-cyclic monophosphate pathway regulates dopamine efflux in the medial preoptic area and copulation in male rats

Dopamine in the medial preoptic area (MPOA) plays a significant role in regulation of male copulation. One mediator of the MPOA dopamine level is nitric oxide. In the current study, we investigated the role of the nitric oxide-guanosine 3',5'-cyclic monophosphate (cGMP) pathway in the regulation of MPOA dopamine and copulation in male rats. The reverse-dialysis of a membrane-permeable analog, 8-Br-cGMP, increased, while a soluble guanylyl cyclase inhibitor, 1H-[1,2,4]oxadiazole[4,3-a]quinoxalin-1-one (ODQ), significantly reduced basal dopamine and its metabolite levels. ODQ successfully blocked a nitric oxide donor-induced increase in dopamine levels, while a neuronal nitric oxide synthase (nNOS) inhibitor was ineffective in blocking an 8-Br-cGMP-induced increase in dopamine, indicating that cGMP is "downstream" of nitric oxide. Furthermore, 8-Br-cGMP facilitated, while ODQ inhibited copulation. Given the steroid-sensitive nature of nNOS functions and the multiple roles nitric oxide plays in the MPOA, we propose that nitric oxide provides important integration of various neurochemical and neuroendocrine signals. The involvement of the central nitric oxide-cGMP pathway in the regulation of copulation also raises an interesting therapeutic possibility, as the manipulation of the same pathway in peripheral tissue is already utilized in treatment of male sexual dysfunction.

Effects of gonadal hormones on central nitric oxide producing systems

Nitric oxide-containing neurons are widely distributed within the CNS, including regions involved in the control of reproduction and sexual behavior. The expression of neuronal nitric oxide synthase is influenced by testosterone in male rat, and by estrogens in female. Moreover, nitric oxide synthase may co-localize with gonadal hormones' receptors. Gonadal hormones may influence nitric oxide synthase expression in adulthood as well as during the development. In fact, in mice knockout for estrogen receptor alpha, the nitric oxide synthase-expressing population is deeply reduced in specific regions. In physiological conditions, the female in mammalian species is exposed to short-term changes of gonadal hormones levels (estrous cycle). Our recent studies, performed in the rat vomeronasal system and in mouse hypothalamic and limbic systems reveal that, in rodents, the expression of nitric oxide synthase-producing elements within regions relevant for the control of sexual behavior is under the control of gonadal hormones. The expression of nitric oxide synthase may vary according to the rapid variations of hormonal levels that take place during the estrous cycle. This seems in accordance with the hypothesis that gonadal hormone activation of nitric oxide-cyclic guanosine-monophosphate pathway is important for lordosis behavior, as well as that this system is activated during mating behavior. Finally, comparative data available for other vertebrates suggest that class-specific and species-specific differences occur in the nitric oxide synthase system of hypothalamus and limbic structures. Therefore, particular caution is needed to generalize data obtained from studies in rodents.

Impaired male sexual behavior in activin receptor type II knockout mice

Integration of multiple hormonal and neuronal signaling pathways in the medial preoptic area (mPOA) is required for elicitation of male sexual behavior in most vertebrates. Perturbation of nitric oxide synthase (NOS) activity in the mPOA causes significant defects in male sexual behavior. Although activins and their signaling components are highly expressed throughout the brain, including the mPOA, their functional significance in the central nervous system (CNS) is unknown. Here, we demonstrate a neurophysiologic role for activin signaling in male reproductive behavior. Adult activin receptor type II null (Acvr2-/-) male mice display multiple reproductive behavioral deficits, including delayed initiation of copulation, reduced mount, and intromission frequencies, and increased mount, intromission, and ejaculation latencies. These behavioral defects in the adult mice are independent of gonadotropin-releasing hormone (GnRH) homeostasis or mating-induced changes in luteinizing hormone (LH) and testosterone levels. The impairment in behavior can be correlated to the nitric oxide content in the CNS because Acvr2-/- males have decreased NOS activity in the mPOA but not the rest of the hypothalamus or cortex. Olfactory acuity tests confirmed that Acvr2-/- mice have no defects in general odor or pheromone recognition. In addition, motor functions are not impaired and the mutants demonstrate normal neuromuscular coordination and balance. Furthermore, the penile histology in mutant mice appears normal, with no significant differences in the expression of penile differentiation marker genes compared with controls, suggesting the observed behavioral phenotypes are not due to structural defects in the penis. Our studies identify a previously unrecognized role of activin signaling in male sexual behavior and suggest that activins and/or related family members are upstream regulators of NOS activity within the mPOA of the forebrain.

Perinatal exposure to low levels of the environmental antiandrogen vinclozolin alters sex-differentiated social play and sexual behaviors in the rat

In this study we examined the effects of exposure to the antiandrogenic fungicide vinclozolin (Vz) on the development of two sex-differentiated behaviors that are organized by the perinatal actions of androgens. Pregnant Long-Evans rats were administered a daily oral dose of 0, 1.5, 3, 6, or 12 mg/kg Vz from the 14th day of gestation through postnatal day (PND)3. The social play behavior of juvenile offspring was examined on PND22 and again on PND34 during play sessions with a same-sex littermate. After they reached adulthood, the male offspring were examined with the ex copula penile reflex procedure to assess erectile function. Vz did not produce any gross maternal or neonatal toxicity, nor did it reduce the anogenital distance in male pups. We observed no effects of Vz on play behavior on PND22. However, the 12-mg/kg Vz dose significantly increased play behavior in the male offspring on PND34 compared with controls. The most dramatic increases were seen with the nape contact and pounce behavior components of play. The Vz effect was more pronounced in male than in female offspring. As adults, male offspring showed a significant reduction of erections at all dose levels during the ex copula penile reflex tests. The 12-mg/kg dose was also associated with an increase in seminal emissions. These effects demonstrate that perinatal Vz disrupts the development of androgen-mediated behavioral functions at exposure levels that do not produce obvious structural changes or weight reductions in androgen-sensitive reproductive organs.

Neuronal nitric oxide synthase and gonadal steroid interaction in the MPOA of male rats: Co-localization and testosterone-induced restoration of copulation and nNOS-immunoreactivity

Neuronal nitric oxide synthase (nNOS) in the medial preoptic area (MPOA) has been implicated in various physiological functions, including male rat copulation. Based on their apparent sensitivity to gonadal steroid manipulation, we hypothesized that nNOS cells contain steroid receptors, and the testosterone-induced restoration of nNOS-immunoreactivity in castrates should accompany the restoration of copulation. In Experiment 1, we investigated co-localization of nNOS with the androgen receptor (AR) and the estrogen receptor alpha (ERalpha) using immunocytochemistry. We found regionally specific co-localizations of nNOS-AR and nNOS-ERalpha. In Experiment 2, we investigated the relationship between MPOA nNOS-immunoreactivity (ir) and copulatory measures in the testosterone-induced restoration paradigm in castrates. The restoration of various copulatory measures was accompanied by an increase in optical density of nNOS-ir, but not in the number of nNOS-ir cells. These data provide additional evidence supporting the role of MPOA nitric oxide in male rat copulation.

Effects of testosterone metabolites on copulation, medial preoptic dopamine, and NOS-immunoreactivity in castrated male rats

The medial preoptic area (MPOA) is an important integrative site for male sexual behavior. Dopamine (DA) is released in the MPOA of male rats shortly before and during copulation. In a previous study, we identified 17beta-estradiol (E(2)) as the metabolite of testosterone (T) that maintains MPOA basal extracellular DA levels. However, the presence of dihydrotestosterone (DHT), an androgenic metabolite of T, is required for the female-induced increase in MPOA DA observed during copulation. Recently, we reported that assays of MPOA tissue DA content showed that castrates actually had more stored DA than did gonadally intact males. Therefore, the reduction in extracellular levels in castrates was not due to decreased availability of DA; most likely it was due to decreased release. Furthermore, T upregulates neuronal nitric oxide synthase (nNOS) in the MPOA. NO has been implicated in the regulation of DA release in the MPOA. It is not known, however, which metabolite(s) of T regulate(s) tissue stores of DA and/or nNOS in the MPOA of male rats. The present experiments were designed to test the following: (1) whether E(2), DHT, or the combination of the two influences MPOA DA tissue levels, an indication of stored DA, in male rat castrates; and (2) whether E(2), DHT, or the combination of the two influences NOS-ir in the MPOA of castrated male rats. The results indicate that E(2) up-regulates nNOS-ir in the MPOA and maintains tissue content of DA at levels similar to those in T-treated rats. DHT did not influence nNOS-ir, while attenuating the effect of castration on tissue DA content.

Treatment with tetrahydrobiopterin reduces blood pressure in male SHR by reducing testosterone synthesis

Treatment with tetrahydrobiopterin (BH(4)) reduces blood pressure in spontaneously hypertensive rats (SHR). In the present study, we tested the hypothesis that chronic BH(4) reduces blood pressure in male SHR by reducing testosterone biosynthesis mediated by increasing nitric oxide (NO). Male SHR, aged 17-18 wk, intact or castrated, were treated for 1 wk with BH(4) (20 mg.kg(-1).day(-1) ip). After 1 wk, mean arterial pressure (MAP), serum testosterone, and nitrate/nitrite excretion (NO(x)) were measured. MAP was significantly higher in intact males than castrated males (179 +/- 2 vs. 155 +/- 4 mmHg, P < 0.001). In intact males, BH(4) caused a 17% reduction in MAP (148 +/- 2 mmHg), had no effect on NO(x), and reduced serum testosterone by 85% (24.09 +/- 2.37 vs. 3.72 +/- 0.73 ng/dl; P < 0.001). In castrated males, BH(4) had no effect on MAP (152 +/- 5 mmHg) but increased NO(x) by 38%. When castrated males were supplemented with testosterone, MAP increased to the same level as in intact males (180 +/- 7 mmHg), and BH(4) had no effect on MAP (182 +/- 7 mmHg) or NO(x). NO has been shown to decrease testosterone biosynthesis. Chronic sodium nitrite (70 mg.kg(-1).day(-1) x 1 wk) decreased MAP in intact males (150 +/- 4 mmHg) but had no effect on serum testosterone (21.46 +/- 3.08 ng/dl). The data suggest that BH(4) reduces testosterone synthesis and thereby reduces MAP in male SHR, an androgen-dependent model of hypertension. The mechanism(s) by which BH(4) reduces serum testosterone levels are not clear, but the data do not support a role for NO as a mediator.

Distribution of nitric oxide synthase immunoreactivity in the mouse brain

Nitric oxide (NO) is a gaseous intercellular messenger with a wide range of neural functions. NO is synthesized by activation of different isoforms of nitric oxide synthases (NOS). At present NOS immunoreactivity has been described in mouse brain in restricted and definite areas and no detailed mapping studies have yet been reported for NOS immunoreactivity. We have studied the distribution of neuronal NOS-containing neurons in the brain of three months male mice, using a specific commercial polyclonal antibody against the neuronal isoform of nitric oxide synthase (nNOS). Neuronal cell bodies exhibiting nNOS immunoreactivity were found in several distinct nuclei throughout the brain. The neurons that were positively stained exhibited different intensities of reaction. In some brain areas (i.e., cortex, striatum, tegmental nuclei) neurons were intensely stained in a Golgi-like fashion. In other regions, immunoreactive cells are moderately stained (i.e., magnocellular nucleus of the posterior commissure, amygdaloid nucleus, interpeduncular nucleus, lateral periaqueductal gray) or weakly stained (i.e., vascular organ of the lamina terminalis, hippocampus, inferior colliculus, reticular nucleus). In the mouse, the NO-producing system appears well developed and widely diffused. In particular, nNOS immunoreactive neurons seem chiefly present in several sensory pathways like all the nuclei of the olfactory system, as well as in many regions of the lymbic system. These data suggest a widespread role for the NO system in the mouse nervous system.

Dopamine and serotonin: influences on male sexual behavior

Steroid hormones regulate sexual behavior primarily by slow, genomically mediated effects. These effects are realized, in part, by enhancing the processing of relevant sensory stimuli, altering the synthesis, release, and/or receptors for neurotransmitters in integrative areas, and increasing the responsiveness of appropriate motor outputs. Dopamine has facilitative effects on sexual motivation, copulatory proficiency, and genital reflexes. Dopamine in the nigrostriatal tract influences motor activity; in the mesolimbic tract it activates numerous motivated behaviors, including copulation; in the medial preoptic area (MPOA) it controls genital reflexes, copulatory patterns, and specifically sexual motivation. Testosterone increases nitric oxide synthase in the MPOA; nitric oxide increases basal and female-stimulated dopamine release, which in turn facilitates copulation and genital reflexes. Serotonin (5-HT) is primarily inhibitory, although stimulation of 5-HT(2C) receptors increases erections and inhibits ejaculation, whereas stimulation of 5-HT(1A) receptors has the opposite effects: facilitation of ejaculation and, in some circumstances, inhibition of erection. 5-HT is released in the anterior lateral hypothalamus at the time of ejaculation. Microinjections of selective serotonin reuptake inhibitors there delay the onset of copulation and delay ejaculation after copulation begins. One means for this inhibition is a decrease in dopamine release in the mesolimbic tract.

Cytochrome oxidase activity in the preoptic area correlates with differences in sexual behavior of intact and castrated male leopard geckos (Eublepharis macularius)

Although the utility of analyzing behavioral experience effects on neural cytochrome oxidase (CO) activity is well recognized, the behavioral correlates of endogenous differences in CO activity have rarely been explored. In male leopard geckos (Eublepharis macularius), the incubation temperature experienced during embryogenesis (IncT) and age affect CO activity in the preoptic area (POA), an area that modulates copulatory behavior. In this study, the authors assessed whether differences in POA CO activity correlate with differences in sexual behavior in intact and castrated geckos. Males with IncT- and age-dependent increases in POA CO activity mounted females with shorter latencies while intact and after castration and ejaculated more frequently after castration. The authors discuss the predictive value of CO activity and propose similar parallels in other species.