Alonso Fernández-Guasti

Sex differences in the distribution of androgen receptors in the human hypothalamus

The present study reports for the first time the distribution of androgen receptor immunoreactivity (AR‐ir) in the human hypothalamus of ten human subjects (five men and five women) ranging in age between 20 years and 39 years using the antibody PG21. Prolonged postmortem delay (72:00 hours) or fixation time (100 days) did not influence the AR‐ir. In men, intense nuclear AR‐ir was found in neurons of the horizontal limb of the diagonal band of Broca, in neurons of the lateromamillary nucleus (LMN), and in the medial mamillary nucleus (MMN). An intermediate nuclear staining was found in the diagonal band of Broca, sexually dimorphic nucleus of the preoptic area, paraventricular nucleus, suprachiasmatic nucleus, ventromedial nucleus, and infundibular nucleus, whereas weaker labeling was found in the bed nucleus of the stria terminalis, medial preoptic area, dorsal and ventral zones of the periventricular nucleus, supraoptic nucleus, and nucleus basalis of Meynert. In most brain areas, women revealed less staining than men. In the LMN and the MMN, a strong sex difference was found. Cytoplasmic labeling was observed in neurons of both sexes, although women showed a higher variability in the intensity of such staining. However, no sex differences in AR‐ir were observed in the bed nucleus of the stria terminalis, the nucleus basalis of Meynert, or the islands of Calleja. Species differences and similarities of the AR‐ir distribution are discussed. The present results suggest the participation of androgens in the regulation of various hypothalamic processes that are sexually dimorphic. J. Comp. Neurol. 425:422–435, 2000.

Antidepressant-like effect of different estrogenic compounds in the forced swimming test.

The present study evaluated the possible antidepressant-like action of the natural estrogen 17β-estradiol (E2, 2.5–10 μg/rat), the synthetic steroidal estrogen ethinyl-estradiol (EE2, 1.25–10.0 μg/rat), and the nonsteroidal synthetic estrogen, diethyl-stilbestrol (DES, 0.25–1.0 mg/rat) in ovariectomized adult female Wistar rats using the forced swimming test (FST). The behavioral profile induced by the estrogens was compared with that induced by the antidepressants fluoxetine (FLX, 2.5–10 mg/kg) and desipramine (DMI, 2.5–10 mg/kg). In addition, the temporal course of the antidepressant-like action of the estrogenic compounds was analyzed. FLX and DMI induced an antidepressant-like effect characterized by a reduced immobility and increased swimming for FLX and decreased immobility and increased climbing for DMI. Both E2 and EE2 produced a decrease in immobility and an increase in swimming, suggesting an antidepressant-like action. DES did not affect the responses in this animal model of depression at any dose tested. The time course analysis of the actions of E2 (10 μg/rat) and EE2 (5 μg/rat) showed that both compounds induced an antidepressant-like effect observed 1 h after their injection lasting for 2–3 days.

Anti-anxiety effects of progesterone and some of its reduced metabolites: an evaluation using the burying behavior test

In this study, pregnenolone sulfate, progesterone and some of its main reduced metabolites were tested for anxiolytic properties in rats using the burying behavior paradigm. All steroids were subcutaneously injected. Progesterone (0.5, 1.0, 2.0 and 4.0 mg/rat) and its 3 alpha-5 alpha-reduced metabolite (0.125, 0.250, 0.5 and 1.0 mg/rat) produced a clear dose-dependent anxiolytic response, without affecting the spontaneous ambulatory behavior. 5 alpha-Pregnanedione decreased burying behavior only at the highest dose (4.0 mg/rat). Pregnenolone sulfate (1.0, 2.0 and 4.0 mg/rat), 5 beta-pregnanedione and 3 beta- or 5 beta-pregnenolones were devoid of effects. The 3 beta-5 beta-reduced metabolite of progesterone (2.0 and 4.0 mg/rat) decreased motor activity, without altering the burying behavior. These results demonstrate that the 3 alpha-5 alpha metabolite of progesterone shows the highest anxiolytic potency in the burying behavior test, when compared with all steroids evaluated. The data are discussed in terms of the close structure-activity relationship requirements of steroids to stimulate the GABA/benzodiazepine receptor-chloride ionophore complex.

The actions of diazepam and serotonergic anxiolytics vary according to the gender and the estrous cycle phase

The anxiolytic effect of diazepam (0.5, 1.0 and 2.0 mg/kg), buspirone (2.5 and 5.0 mg/kg), indorenate (2.5 and 5.0 mg/kg) and ipsapirone (5.0 and 10.0 mg/kg) was evaluated in male and female rats during the proestrus and metestrus phases. The burying behavior test was used to measure the anxiety levels. In this test, increases in the behavior latency are interpreted as prolonged reactivity, while reductions in the burying behavior are considered to reflect anxiolytic states. Diazepam increases in burying behavior latency were consistently higher than those observed after serotonergic anxiolytics. Buspirone, at no dose tested, affected the burying behavior latency, while indorenate and ipsapirone had only minor effects. Male individuals were more sensitive than females to the actions of diazepam on burying behavior. The serotonergic anxiolytics produce similar responses in both sexes. Metestrus females were much less sensitive to the action of all anxiolytics on burying behavior latency than proestrus females. Proestrus females were highly sensitive to the actions of diazepam on burying latency as compared both with males and metestrus females. Data show that a larger gender and within females variation occurs after treatment with diazepam as compared with the serotonergic anxiolytics. The results are discussed considering the relationships between ovarian hormones and the GABA-benzodiazepinic and serotonergic systems.

GABAergic control of masculine sexual behavior

Drugs affecting the GABAergic transmission were injected into the medial preoptic anterior hypothalamic area (MPOA) and the masculine sexual behavior analyzed. Antagonizing GABAergic neurotransmission by (+) bicuculline methiodide (30 ng/cannula), or 3-mercaptopropionic acid (10 or 20 micrograms/cannula) resulted in a drastic shortening of the postejaculatory intervals and a shortening of the ejaculation latency. Injection of compounds causing an increase in GABAergic activity, muscimol (25 ng/cannula) or ethanolamine-O-sulphate (80 micrograms/cannula) depressed masculine sexual behavior. Systemic treatment or injection into the nucleus caudatus putamen of compounds affecting the GABAergic transmission did not cause any alteration in the mating pattern. It is suggested that the GABAergic neurotransmission is involved in inhibitory processes underlying the masculine sexual behavior.

Stimulation of 5-HT1A and 5-HT1B receptors in brain regions and its effects on male rat sexual behaviour

In the present series of experiments we compared the effect of injecting serotonin (40 micrograms/cannula), the 5-HT1A agonist, 8-hydroxy-2-(di-n-propylamino)tetralin (8-OH-DPAT) (5.0 micrograms/cannula), and the 5-HT1B/C agonist, trifluoromethyl-phenyl-piperazine (TFMPP) (1.0 micrograms/cannula), into the preoptic area, the nucleus accumbens and the nucleus raphe dorsalis. The dose injected was selected on the basis of dose-response curves. Injection of serotonin and TFMPP into the medial preoptic area and nucleus accumbens resulted in an inhibition of male sexual behaviour, as evidenced by an increase in the number of mounts and a prolongation of the ejaculation latency. Injection of 8-OH-DPAT into these brain areas facilitated copulatory behaviour as evidenced by a reduction in the number of mounts, intromissions and ejaculation latency. Administration of these compounds into the nucleus raphe dorsalis produced no effect, except for a prolongation of the intromission latency after serotonin. These results would suggest that at least some of the 5-HT1A receptors involved in the facilitation of male sexual behaviour are located postsynaptically in limbic brain areas that regulate male sexual behaviour. On the basis of the similarities between the inhibitory effects of serotonin and TFMPP, the present results further support the idea that endogenous serotonin acts via the stimulation of 5-HT1B receptors to inhibit male sexual behaviour.

Changes in burying behavior during the estrous cycle: Effect of estrogen and progesterone

This study demonstrates changes in cumulative burying behavior during various phases of the rat estrous cycle. Low levels of burying behavior were observed during late proestrus. Similar burying behavior levels among females tested in early proestrus, metestrus or diestrus and ovariectomized females were found. In ovariectomized females, treatment with estrogen (E) produced a slight, non-significant reduction in burying behavior. In contrast, progesterone (P) treatment resulted in a dose-dependent, statistically significant decrease in time spent burying. The combined treatment of E and P produced no effect. These data are discussed from the standpoint of the putative anxiolytic effect of P.

Anxiolytic-like actions of testosterone in the burying behavior test: role of androgen and GABA-benzodiazepine receptors

The first objective of the present study was to explore if several androgens, including testosterone propionate (TP) and its reduced metabolites, 5alpha-androstan-3alpha, 17beta-diol (3alpha-androstanediol) and 5alpha-androstan-3alpha-ol-17-one (androsterone), produce an anxiolytic-like effect in the burying behavior paradigm. Additionally, the possible participation of androgen or GABA(A)-benzodiazepine receptors in the anxiolytic-like effect of TP was analyzed. Orchidectomized male rats were treated with four injections of TP (0.25, 0.50, 1.0 mg/rat), 3alpha-androstanediol or androsterone (0.5 and 1.0 mg/rat), and the cumulative burying (denoting anxiety levels) and burying behavior latency (reflecting reactivity) evaluated. Besides, a single injection (0.5 mg/rat, -30 m) of each androgen was also tested in castrated rats. Repeated treatment with TP (0.5 and 1.0 mg/rat), but not a single injection of this androgen, produced an anxiolytic-like effect without changes on reactivity. Neither repeated- nor single-treatment with 3alpha-androstanediol nor androsterone produced a reduction of anxiety-like behavior. For the experiment studying the TP mechanism of action, this androgen (0.5 mg/rat, four injections) was combined with an antagonist for androgen receptors, flutamide (50 mg/kg, SC, 7 injections), or with a benzodiazepine antagonist, flumazenil (15 mg/kg, IP, -30 m). Flutamide, but not flumazenil, blocked the anxiolytic-like effects produced by TP. Results are discussed on the basis of interaction of these steroids with androgen receptors or GABA(A)-benzodiazepine receptors.

Reversal of sexual exhaustion by serotonergic and noradrenergic agents

The possible participation of the serotonergic and the noradrenergic systems in the control of the inhibitory state present during sexual satiation was studied from a pharmacological perspective. It was found that the 5-HT1A agonist 8-OH-DPAT and the alpha 2 adrenoceptor antagonist, yohimbine were effective in reversing the sexual inhibition resulting from sexual exhaustion. These findings show that the inhibition present during satiation is reversible and suggest that central mechanisms underlie it. The serotonergic as well as the noradrenergic systems, probably through their 5-HT1A and alpha 2 receptors, respectively, play a role in the establishment of this phenomenon. Additionally, the main features of the development of sexual exhaustion were reviewed. It was found that sexual exhaustion has two different expressions: a major proportion of the exhausted rats does not copulate and a third part of this population is able to execute one ejaculatory series from which they do not recover. The data are discussed in terms of the motivational and consummatory components of male sexual behaviour.

Suppression of lordosis behavior by the putative 5-HT receptor agonist 8-OH-DPAT in the rat

The administration of 8-hydroxy-2-(di-n-propylamino)tetralin (8-OH-DPAT), inhibited the lordosis induced by estradiol benzoate or estradiol benzoate plus progesterone in ovariectomized rats. There was no facilitation of lordosis by 8-OH-DPAT in animals pretreated with a threshold dose of estradiol benzoate. The results are consistent with the view that 8-OH-DPAT is an agonist at 5-HT receptors and provide further support for an inhibition role of central 5-HT in the mediation of lordosis behavior.