Effects of male sex hormones on specific uptake and release of 3H-serotonin in the rat hypothalamus in vitro]

With the use of "isotopic method" a study was made of the main parameters of functional activity of serotoninergic elements of hypothalamus--the specific uptake and release of 5-OT. The animals used were sexually mature rats castrated on the first postnatal day. In sexually mature intact males the specific uptake of 3H-5-OT by serotoninergic structures of the anterior hypothalamus was significantly lower than in females. Castration of animals on the first day of life resulted in the increase of specific 5-OT uptake in sexually mature males up to that observed in females. There were no differences between the sexes in the rate of spontaneous release of 5-OT. However, response to K(+)-depolarization in the anterior hypothalamus of intact males was significantly lower than that in females. In the hypothalamus of males castrated neonatally the amplitude of the response to the effect of the depolarizing agent was increase up to the level observed in females. By the results obtained it is indicated that elimination of the effect of male hormones on the first postnatal day results in the increase of 5-OT uptake and release in the hypothalamus of sexually mature rat males.     

Changes in the pituitary and hypothalamic content of methionine-enkephalin during the estrous cycle of rats

Met-Enkephalin content of the anterior hypothalamic-preoptic area, medial basal hypothalamus, anterior pituitary, intermediate and posterior pituitary was measured using a specific radioimmunoassay. Met-Enkephalin content of the anterior hypothalamic-preoptic area, medial basal hypothalamus and anterior pituitary was very high on the morning of proestrus but decreased on the afternoon of proestrus and on estrus. The content of met-Enkephalin was more variable in the anterior pituitary than in the anterior hypothalamic-preoptic area and medial basal hypothalamus during the estrous cycle. The results suggest that the met-Enkephalin may be involved in regulating the hypothalamo-hypophyseal function during estrous cycle in the rat.     

Estrone sulfatase activity in rat brain and pituitary: effects of gonadectomy and the estrous cycle

Estrone sulfatase activity was characterized in microsomal preparations from rat brain and anterior pituitary. No differences in apparent Km were found in hypothalamic-preoptic area between male (7.5 microM) and female (7.4 microM) rats. Apparent Km's of anterior pituitaries from males (14.5 microM) and females (22.5 microM) were higher than those found in brain. Estrone sulfatase activity was equally inhibited by estradiol-17 beta-3-sulfate, dehydroepiandrosterone-3-sulfate and estrone-3-sulfate indicating a broad range of substrate specificity for this enzyme. Sulfatase activity in female anterior pituitary was found to be twice that of male. Sulfatase activity was distributed similarly in brain tissues between sexes with cerebellum greater than or equal to medial basal hypothalamus greater than preoptic area = cortex. Following gonadectomy, sulfatase activity in anterior pituitary of males was significantly greater than activity found in intact animals (P less than 0.05). This increase in activity, however, was unaffected by treatment with testosterone, dihydrotestosterone or estradiol-17 beta. Gonadectomy did not change sulfatase activity in brains of males or females or in pituitaries of females. However, sulfatase activity in pituitary glands of females changed significantly (P less than 0.05) with stages of the estrous cycle (metestrus less than diestrus less than proestrus less than estrus). These data indicate sulfatase activity in rat anterior pituitary gland may be controlled by gonadal factors while sulfatase activity in brain is regulated differently.     

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.     

Neuroanatomical distribution of aromatase mRNA in the rat brain: indications of regional regulation

Aromatase, the enzyme responsible for the conversion of testosterone to estradiol, is found in the rat brain and is present in regions of the preoptic area, hypothalamus, and limbic system. Gonadal steroid hormones regulate aromatase activity levels in many brain regions, but not all. Using in situ hybridization, we examined the distribution of aromatase mRNA in the adult male forebrain, as well as the levels of aromatase mRNA in the brains of males and females, and the regulation by gonadal steroid hormones. In the adult male, many heavily labelled cells were found in the encapsulated bed nucleus of the stria terminalis (BNST), the medial preoptic nucleus (MPN), the ventro-medial nucleus (VMN), the medial amygdala (mAMY) and the cortical amygdala (CoAMY). The regional distribution of aromatase mRNA was similar in males and females, but males tended to have a greater number of aromatase mRNA-expressing cells in each region compared to females. Aromatase mRNA levels in the BNST, MPN, VMN and mAMY tended to be lower in castrated males than in intact males, whereas aromatase mRNA levels were unaltered by castration in the CoAMY. Further analysis of individual cells expressing aromatase mRNA suggests that aromatase mRNA may be regulated by steroid hormones differentially in specific populations of cells in regions where enzyme activity levels are steroid-hormone-dependent.     

Hypothalamic receptors of sex hormones in the mechanism of the sexual differentiation of the brain in rats

Studies have been made on the content of receptors of estradiol (E2) and testosterone (T) in cytoplasmic and nuclear fractions of the hypothalamus of male and female rats during neonatal development, as well as in adult females after androgenization in neonatal period and adult males castrated within 3 days of postnatal life. It was shown that both E2 and T are present in the blood serum of male and female newborn rats. In female hypothalamus, only E2 receptors were found, whereas in males both types of receptors were revealed, their content being higher than in females. In adult animals subjected to changes in the level of sex hormones in the blood during early neonatal period, changes in concentration of the receptors in the hypothalamic centres of regulation of tonic and cyclic secretion of gonadotropins were found. The data obtained presumably reveal the role of receptors of sex hormones in sex differentiation of the brain.     

Effect of psychotropic drugs on 3,4-dihydroxyphenylacetic acid (DOPAC) content in the medial basal hypothalamus

The effect of different psychotropic drugs on 3,4-dihydroxyphenylacetic acid (DOPAC) levels in the medial basal hypothalamus has been studied by the use of a very sensitive radioenzymatic method. Apomorphine and haloperidol, which are known to respectively decrease and increase DOPAC levels in the caudate nucleus, fail to influence DOPAC level in the medial basal hypothalamus. Reserpine, which increases DOPAC level in the caudate nucleus, decreases it in the medial basal hypothalamus. Amphetamine decreases DOPAC level in the medial basal hypothalamus as it does in the caudate nucleus. These results suggest that DA metabolism in the medial basal hypothalamus is controlled by mechanisms different from those operating in other brain areas.     

The role of the basal hypothalamus in the regulation of reproductive behavior in the lizard, Anolis carolinensis: lesion studies

Bilateral radiofrequency lesions in the anterior and posterior basal hypothalamus decreased courtship and agonistic behaviors in both intact, sexually active, and castrated, androgen treated male Anolis carolinensis. Intact males receiving lesions in the anterior basal hypothalamus had atrophied testes, aspermia, and decreased epithelial cell height of the renal sex segment. Lesions of the posterior basal hypothalamus had no effect on testicular activity or the development of accessory organs. All animals demonstrating behavioral changes had lesion destruction in the ventromedial nucleus and the accompanying periventricular system. It is concluded that the basal hypothalamus in male A. carolinensis is involved both in the regulation of reproductive behavior and pituitary function.     

Sociality and oxytocin and vasopressin in the brain of male and female dominant and subordinate mandarin voles

The dominant–subordinate hierarchy in animals often needs to be established via agonistic encounters and consequently affects reproduction and survival. Differences in brain neuropeptides and sociality among dominant and subordinate males and females remain poorly understood. Here we explore neuropeptide levels and sociality during agonistic encounter tests in mandarin voles. We found that dominant mandarin voles engaged in higher levels of approaching, investigating, self-grooming and exploring behavior than subordinates. Dominant males habituated better to a stimulus vole than dominant females. Dominant males displayed significantly less oxytocin-immunoreactive neurons in the paraventricular nuclei and more vasopressin-immunoreactive neurons in the paraventricular nuclei, supraoptic nuclei, and the lateral and anterior hypothalamus than subordinates. Dominant females displayed significantly more vasopressin-immunoreactive neurons in the lateral hypothalamus and anterior hypothalamus than subordinates. Sex differences were found in the level of oxytocin and vasopressin. These results indicate that distinct parameters related to central nervous oxytocin and vasopressin are associated with behaviors during agonistic encounters in a sex-specific manner in mandarin voles.     

The medial basal hypothalamus and luteinizing hormone release in the rat: Where are the LH-RH neurons responsible for tonic gonadotropin secretion?

Careful review of the literature demonstrates conflicting results concerning the ability of the deafferented medial basal hypothalamus to support gonadotropin release in the rat and thus one may question the existence of LH-RH neurons in the medial basal hypothalamus. The direct search for the LH-RH perikarya in the rat hypothalamus has not settled the question of whether these releasing hormone neurons are located in the medial basal hypothalamus. Most investigators do agree that following complete hypothalamic deafferentation there is a reduction of the immunoassayable LH-RH in the medial basal hypothalamus; however, these results do not necessarily prove that LH-RH originates outside the hypothalamus. It is argued that the completely deafferented medial basal hypothalamus may be so altered by the deafferentation procedure that it may be inadequate as a means to study neuroendocrine function.     

Hypothalamo-amygdaloid connections of cat's brain]

Under study were the afferent connections of the cat's amygdala nuclei with the hypothalamus (Nauta's method) in parallel with studying geometrical parameters of the afferent fibre endings in these nuclei by the Golgi method. It has been shown that the medial hypothalamus gives the beginning to a small amount of fibres running to the medial group of the amygdala nuclei; dissipated solitary fibres run to the large- and small-cellular parts of the basal nucleus. A considerable amount of fibres run from the lateral hypothalamus to the amygdala, mainly to the medial group of its nuclei and the anterior amygdalar area, only solitary fibres were followed in the basal nuclei. We failed to observe degenerated fibres from the medial preoptical area to the amygdale. The geometry of branches of these fibre systems in the amygdala nuclei was established: they all terminate as a compact but rarely branching brush.     

Plasma growth hormone responses to microinfusion of noradrenergic agents into or electrical stimulation of the hypothalamus and amygdala in baboons

In nine baboons (Papio papio) guide cannulae and electrodes were stereotaxically implanted into the medial basal or lateral hypothalamus, the anterior hypothalamus or the dorsal amygdala. Plasma GH responses were measured after microinfusion (1 microliter) of the alpha2 adrenergic agonist, clonidine, or the beta adrenergic antagonist, propranolol, or electrical stimulation, in each of these sites. Clonidine, 100 nmol/microliter, infused into the medial basal or lateral hypothalamus elevated plasma GH levels by 5-30 ng/ml, 30-45 min post-infusion. Plasma GH responses to clonidine infused into the anterior hypothalamus or the dorsal amygdala were all less than 10 ng/ml. The prior, intravenous, administration of piperoxane, 1.0 mg/kg prevented GH responses to clonidine. Propranolol, 50 nmol/microliter, infused into the dorsal amygdala consistently increased plasma GH levels by 5-15 ng/ml. Electrical stimulation of the medial basal or lateral hypothalamus elevated plasma GH levels by 7-35 ng/ml, 15-45 min post stimulation. Electrical stimulation of anterior hypothalamus or dorsal amygdala did not alter plasma GH levels. The stimulation of alpha 2 adrenergic receptors in the medial basal or lateral hypothalamus of the baboons appears to facilitate GH release.     

Radioautographic study of the rat brain and pituitary after injection of 3H dexamethasone

The central nervous system and the pituitary of adrenalectomized male rats injected with 3H-dexamethasone were examined by radioautography. At 1 hr after the injection, radioactivity concentration was high in the medial basal hypothalamus, the pituitary and the pineal gland. In the hypothalamus, radioactive material was found to be selectively concentrated in neurons in the ventral part of nucleus arcuatus and in the infundibular region. In the anterior pituitary, a large proportion of cells showed silver grains both in the cytoplasm and over the cell nuclei. However, in a small number of cells, the radioactive material was associated with the cell nuclei. Less radioactivity was present in the intermediate and posterior lobes. The pineal gland contained more silver grains than did other regions of the brain. The results obtained in the present study suggest essentially an action of dexamethasone in the medial basal hypothalamus and at the level of the pituitary.     

Brain Organization in a Reptile Lacking Sex Chromosomes: Effects of Gonadectomy and Exogenous Testosterone

In mammals, males and females differ both genetically and hormonally, making it difficult to assess the relative contributions of genetic constitution and fetal environment in the process of sexual differentiation. Many reptiles lack sex chromosomes, relying instead on the temperature of incubation to determine sex. In the leopard gecko (Eublepharis macularius), an incubation temperature of 26°C produces all females, whereas 32.5°C results in mostly males. Incubation temperature is the primary determinant of differences both within and between the sexes in growth, physiology, and sociosexual behavior, as well as the volume and metabolic capacity of specific brain nuclei. To determine if incubation temperature organizes the brain directly rather than via gonadal sex hormones, the gonads of male and female leopard geckos from the two incubation temperatures were removed and, in some instances, animals were given exogenous testosterone. In vertebrates with sex chromosomes, the size of sexually dimorphic nuclei are sensitive to hormone levels in adulthood, but in all species studied to date, these changes are restricted to the male. Therefore, after behavior tests, morphometrics of certain limbic and nonlimbic brain areas were determined. Because nervous system tissue depends on oxidative metabolism for energy production and the level of cytochrome oxidase activity is coupled to the functional level of neuronal activity, cytochrome oxidase histochemistry also was performed on the same brains. Hormonal manipulation had little effect on the volume of the preoptic area or ventromedial hypothalamus in geckos from the all-female incubation temperature, but significantly influenced the volumes of these brain areas in males and females from the male-biased incubation temperature. A similar relationship was found for cytochrome oxidase activity of the anterior hypothalamus, amygdala, dorsal ventricular ridge, and septum. The only sex difference observed was found in the ventromedial hypothalamus; males showed no significant changes in cytochrome oxidase activity with hormonal manipulation, but females from both incubation temperatures were affected similarly. The results indicate that incubation temperature organizes the brain directly rather than via hormones arising from its sex-determining function. This is the first demonstration in a vertebrate that factors other than steroid hormones can modify the organization and functional activity of sexually differentiated brain areas.     

Region-specific regulation of cytochrome P450 aromatase messenger ribonucleic acid by androgen in brains of male rhesus monkeys

We demonstrated previously that testosterone regulates aromatase activity in the anterior/dorsolateral hypothalamus of male rhesus macaques. To determine the level of the androgen effect, we developed a ribonuclease protection assay to study the effects of testosterone or dihydrotestosterone (DHT) on aromatase (P450(AROM)) mRNA in selected brain areas. Adult male rhesus monkeys were treated with testosterone or DHT. Steroids in serum were quantified by RIA. Fourteen brain regions were analyzed for P450(AROM) mRNA. Significant elevations of its message over controls (P<0.05) were found in the medial preoptic area/anterior hypothalamus of both androgen treatment groups and the medial basal hypothalamus of the testosterone-treated males. Other brain areas were not affected by androgen treatment. We conclude that testosterone and DHT regulate P450(AROM) mRNA in brain regions that mediate reproductive behaviors and gonadotropin release. The P450(AROM) mRNA of other brain areas is not androgen dependent. Brain-derived estrogens may also be important for maintaining neural circuitry in brain areas not related to reproduction. The control of P450(AROM) mRNA in these areas may differ from what we report here, but it is equally important to understand the function of in situ estrogen formation in these areas.     

Aromatase inhibition abolishes courtship behaviours in the ring dove (Streptopelia risoria) and reduces androgen and progesterone receptors in the hypothalamus and anterior pituitary gland

The aim of this study was to determine in the ring dove, the effects of aromatase inhibition on the expression of aggressive courtship and nest-soliciting behaviours in relation to the distribution of cells containing immunoreactive androgen (AR) and progesterone (PR) receptor in the hypothalamus and pituitary gland. Isolated sexually experienced ring doves were transferred in opposite sex pairs to individual breeding cages, and then injected with the aromatase inhibitor, fadrozole (four males and four females), or saline vehicle (four males and four females) for 3 days at 12 hourly intervals. Saline-injected control males displayed aggressive courtship behaviours (bow-cooing and hop-charging) and nest-soliciting throughout the study, and control females displayed nest-soliciting. By day 3, fadrozole treatment resulted in the disappearance of all these behaviours and in a decrease or disappearance of AR and PR in the anterior pituitary gland, and in the nucleus preopticus paraventricularis magnocellularis (PPM), nucleus preopticus medialis (POM), nucleus hypothalami lateralis posterioris (PLH), and ventral, lateral and dorsal nucleus tuberalis in the hypothalamus (VTu, LTu, DTu). In the nucleus preopticus anterior (POA), fadrozole treatment decreased AR in both sexes and decreased PR in females but not in males. Cells containing co-localized nuclear AR and PR were found in all hypothalamic areas examined, and in the anterior pituitary gland. Fadrozole is suggested to reduce the local availability of estrogen required indirectly for the induction of AR, and except in cells containing PR in the male POA, for the direct induction of PR. It is suggested that aggressive courtship behaviour is terminated by “cross talk” between aromatase-independent PR and aromatase-dependent AR co-localized in neurons in the POA. Aromatase-independent PR may increase in the male POA in response to visual cues provided by a partner. Aromatase-dependent PR in the POM, and basal hypothalamus may play a role in the facilitatory effect of progesterone on estrogen-induced nest-orientated behaviours. (Mol Cell Biochem 276: 193–204, 2005)     

Central regulation of thyrotropin secretion in rats: methodological aspects, problems and some progress

The concept of the regulatory role of the hypothalamic and brain neurotransmitters in the secretion of the hypothalamic releasing hormones and corresponding anterior pituitary hormones has been generally accepted. The tuberoinfundibular portal vessels form an anatomical framework for regulating these hormones. Our present knowledge about the origin and course of the main aminergic and peptidergic bundles and their collaterals into the hypothalamus conforms with the accepted concept. The general methods in neuroendocrinology are well established. In our study, the unique TSH burst induced by a short cold-exposure has proved very useful, since it is mediated through the activation of TRH in the hypothalamus. When used together with the TSH-response caused by the exogenous TRH and with stereotaxic microinfusions of various chemicals into specific areas in the brain, the level of action of the pharmacological agents can be determined. Methodological pitfalls are, however, possible unless care is taken to avoid unspecific stress factors, general anaesthesia and intracerebral injections at unphysiological concentrations. The role of different neurotransmitters in the central TRH-TSH regulation has been clarified in recent years and the simple concepts of the early days elaborated accordingly. The cold-stimulated TSH secretion can be modified by several neurotransmitters. Noradrenaline is a stimulatory transmitter at high hypothalamic centers, but it may also retard TRH release into the portal vessels. It also seems possible that alpha 1- and alpha 2-receptors mediate opposite effects. Nigrostriatal (but not tuberoinfundibular) dopamine has only an inhibitory action on TRH release and/or synthesis. The importance of 5-HT is still controversial, partly because of the unspecificity of the experimental tools available. Evidently both stimulating and inhibiting components are involved. The role of different 5-HT receptors remains to be established. The function of GABA is complicated, too, the real GABAergic action being an inhibition of TRH release from the medial basal hypothalamus. Only histamine and some amino acids affect TRH-induced TSH secretion. Hence the anterior pituitary in the rat is not so important a locus as the hypothalamus in the action of neurotransmitters on the TRH-TSH regulation.     

Possible underlying mechanisms of sexual dimorphism in the immune response, fact and hypothesis

It is a confirmed fact that in females both the humoral and cell mediated immune response is more active than in males. A large amount of information supports the view that hormones of the endocrine system are intimately involved in this immunological dimorphism. Such hormones include the gonadal steroids, the adrenal glucocorticoids, growth hormone (GH) and prolactin (Prl) from the pituitary, thymic hormones, and substances generated by activated lymphocytes. It is suggested that a complex medley of these hormonal interactions effect both developing lymphocytes within the microenvironment and regulate adult effector cells. The most important of these hormonal interactions leading to immunological dimorphism are the effects elicited by estrogen (E) elaborated at elevated levels from the female ovary after puberty. Elevated E leads to basal GH secretion, increased Prl, and increased thymosin release, all of which are hypothesized to effect lymphocyte development and stimulate adult T- and B-cell function in females. Interactions of hormonal regulatory axes involving the hypothalamus, pituitary, gonads, adrenals, and thymus are also thought to be involved. Factors elaborated by activated immune cells including IL-1 and IL-2 may also play a role in down regulation of these responses. Finally, genetic components are also considered pertinent especially under conditions of pathological disequilibrium leading to autoimmune disease. While the benefits provided by immunological dimorphism are still not entirely clarified, since sex hormones are intimately involved in immunological regulation it is quite possible that the increased immune response in females allows them to compensate for the increased physiological stress which accompanies reproduction. The final outcome would thus be the assurance of reproductive success of the species.