Extrahypothalamic serotonergic modification after masculinization induced by neonatal gonadal hormones

5-HT1A receptors of the prelimbic cortex mediate the hormonal impact on learned fear expression in high-anxious female rats

Hormones highly influence female behaviors. However, research on this topic has not usually considered the variable hormonal status. The prelimbic cortex (PrL) is commonly engaged in fear learning. Connections from and to this region are known to be critical in regulating anxiety, in which serotonin (5-HT) plays a fundamental role, particularly through changes in 5-HT1A receptors functioning. Also, hormone fluctuations can greatly influence anxiety in humans and anxiety-related behavior in rodents, and this influence involves the functioning of 5-HT brain systems. The present investigation sought to determine whether fluctuations in ovarian hormones relative to the estrous cycle would influence the expression of learned fear in female rats previously selected as low- (LA) or high-anxious (HA). Furthermore, we investigate the role of the 5-HT system of the PrL, particularly the 5-HT1A receptors, as a possible modulator of estrous cycle influence on the expression of learned fear through intra-PrL microinjections of 5-HT itself or the full 5-HT1A agonist 8-OH-DPAT (8-hydroxy-2-(di-n-propylamine)tetralin). Behavioral changes were assessed using the fear-potentiated startle (FPS) procedure. The results showed that fear intensity is associated with hormonal decay, being more accentuated during the estrus phase. This increase in fear levels was found to be negatively correlated with the expression of potentiated startle. In rats prone to anxiety and tested during the proestrus and estrus phases, 5-HT mechanisms of the PrL seem to play a regulatory role in the expression of learned fear. These results were not replicated in the LA rats. Similar but less intense results were found regarding the early and late diestrus. Our data indicate that future studies on this subject need to take into account the dissociation between low- and high-responsive females to understand how hormones affect emotional behavior.

Oestradiol modulation of serotonin reuptake transporter and serotonin metabolism in the brain of monkeys

Serotonin (5-hydroxytryptamine; 5-HT) is an important brain neurotransmitter that is implicated in mental and neurodegenerative diseases and is modulated by ovarian hormones. Nevertheless, the effect of oestrogens on 5-HT neurotransmission in the primate caudate nucleus, putamen and nucleus accumbens, which are major components of the basal ganglia, and the anterior cerebral cortex, mainly the frontal and cingulate gyrus, is not well documented. The present study evaluated 5-HT reuptake transporter (SERT) and 5-HT metabolism in these brain regions in response to 1-month treatment with 17β-oestradiol in short-term (1 month) ovariectomised (OVX) monkeys (Macaca fascicularis). SERT-specific binding was measured by autoradiography using the radioligand [³H]citalopram. Biogenic amine concentrations were quantified by high-performance liquid chromatography. 17β-Oestradiol increased SERT in the superior frontal cortex and in the anterior cingulate cortex, in the nucleus accumbens, and in subregions of the caudate nucleus of OVX monkeys. 17β-Oestradiol left [³H]citalopram-specific binding unchanged in the putamen, as well as the dorsal and medial raphe nucleus. 17β-Oestradiol treatment decreased striatal concentrations of the precursor of 5-HT, 5-hydroxytryptophan, and increased 5-HT, dopamine and 3-methoxytyramine concentrations in the nucleus accumbens, caudate nucleus and putamen, whereas the concentrations of the metabolites 5-hydroxyindoleacetic acid, 3,4-dihydroxyphenylacetic acid and homovanillic acid remained unchanged. No effect of 17β-oestradiol treatment was observed for biogenic amine concentrations in the cortical regions. A significant positive correlation was observed between [³H]citalopram-specific binding and 5-HT concentrations in the caudate nucleus, putamen and nucleus accumbens, suggesting their link. These results have translational value for women with low oestrogen, such as those in surgical menopause or perimenopause.

Prenatal treatment with picrotoxin promotes heterotypical sexual behavioral and neurochemical changes in male rat offspring

The effects of maternal prenatal exposure to picrotoxin (0.75 mg/kg S.C. days 16-19 of pregnancy) in male rat offspring were observed. Adult sexually experienced and inexperienced animals were evaluated for heterotypical sexual behavior, as well as the testosterone plasma levels and striatal neurotransmitters. In relation to sexual behavior and analysis of sexual organs, the results showed that animals treated with picrotoxin exhibited a more intense reproductive behavior, and this could be expressed by a significant decrease in the number of mounts and intromissions and increase in the numbers of ejaculation, showed that these males are most motivate for sexual behavior. Testosterone levels as well as weight for sexual organs did not differ from control group. The neurochemical analysis showed that picrotoxin did not alter DA, 5-HT, 5-HIAA and GABA in animals. The DOPAC/DA and HVA/DA relation showed that the treatment increased the DA system activity in animals sexually experienced, as well as promote a decrease in 5-HT/5-HIAA relation, that is known was an inhibitory neurotransmitter system, blockade a male sexual behavior. There are no alterations observed in GABA levels. It's could be explained by suggests that picrotoxin modification DA system activity through GABAergic system, permitting that DA system to be freely active and facilitate the heterotypical behavior of male rats. These results show that the maternal prenatal exposure to picrotoxin produced changes in the neurochemical and sexual behavior of the adult male rats. Also previous heterotypical experience leads to changes in biogenic amine concentrations in these animals.

Aging, estradiol and time of day differentially affect serotonin transporter binding in the central nervous system of female rats

Estrogen-related changes in serotonergic neuronal transmission, including changes in the number of serotonin transporter (SERT) binding sites, have been cited as a possible cause for changes in mood, memory and sleep that occur during the menopausal transition. However, both aging and estradiol regulate SERT binding sites in the brain. The goal of this experiment was to determine how aging and estrogen interact to regulate SERT levels in the forebrain of young and reproductively senescent female Sprague-Dawley rats using [3H]paroxetine. The density of specific [3H]paroxetine binding in various brain regions was compared in young (2-4 months) and reproductively senescent (10-12 months) female rats at three times of day. In most brain regions examined, estrogen and aging independently increased the number of [3H]paroxetine binding sites. The only region that displayed a reduction in [3H]paroxetine binding with age was the suprachiasmatic nucleus (SCN). Time of day influenced [3H]paroxetine binding in the SCN and the paraventricular thalamus (PVT), two regions known to be involved in the regulation of circadian rhythms. Aging and/or estrogen also altered the pattern of binding in these regions. Thus, based on the results of this study, we conclude that aging and estrogen both act to regulate SERT binding sites in the forebrain of female rats, and that this regulation is region specific.

Progesterone receptor gene and protein expression in the anterior preoptic area and hypothalamus of defeminized rats

Progesterone receptor (PR) plays an important role during sexual differentiation of the rat brain. The objective of the present study was to determine PR protein and gene expression pattern in preoptic-anterior hypothalamic area (POA-AHA) and hypothalamus (HYP), after estradiol or testosterone treatment during the postnatal critical period of sexual differentiation of the rat brain (defeminized animals). Three-day-old female rats were subcutaneously (s.c.) injected with a single dose of 17beta-estradiol (200 microg), or testosterone enanthate (200 microg), or vehicle (corn oil). POA-AHA and HYP were dissected 3 h, 24 h, and 14 days, as well as on the day of vaginal opening (VO) after treatments. Other animals, previously treated as above, were acutely injected with 17beta-estradiol (5 microg) on the day of VO; POA-AHA and HYP were obtained 3 h later. Total RNA was extracted and processed for semiquantitative RT-PCR and tissue slices were prepared for protein detection by immunohistochemistry. We observed that PR mRNA expression was increased in POA-AHA and HYP of the animals treated with estradiol or testosterone 3 hours after treatments, compared with the vehicle-treated control group. We also found a significant increase in PR mRNA and protein expression in POA-AHA and HYP on the day of VO in both estradiol and testosterone defeminized rats. Interestingly, the acute administration of estradiol on the day of VO (VO + E(2)) did not increase PR mRNA or protein expression in POA-AHA and HYP of either estradiol or testosterone defeminized animals, as opposed to the marked induction observed in the intact animals of the control group. The overall results suggest that estradiol and testosterone treatment during the postnatal critical period of sexual differentiation of the brain modifies the regulation of the PR mRNA and protein expression during early onset of maturity.

c-Fos gene expression pattern in the hypothalamus and the preoptic area of defeminized rats

The object of the present study was to determine the c-fos gene expression pattern in the hypothalamus (HYP) and the preoptic area (POA) after estradiol and testosterone priming during the critical period of sexual differentiation of the rat brain. Three-day-old female rats were injected s.c. with a single dose of 17beta-estradiol (200 microg), testosterone enantate (200 microg) or vehicle (corn oil). HYP and POA were dissected 2 h, 24 h and 14 days after treatments and on the day of vaginal opening (VO). Other animals, previously treated as above, were acutely injected with 17beta-estradiol (5 microg) on the day of VO; HYP and POA were obtained 3 h later. Total RNA was extracted and processed for semiquantitative RT-PCR. We observed that c-fos gene expression was markedly increased in POA of the animals treated with estradiol or testosterone 2 h after treatments, while a non-significant increase in c-fos gene expression was observed in the HYP of these animals. We found a significant increase in c-fos expression in HYP and POA on the day of VO in both estradiol and testosterone defeminized rats. Interestingly, the acute estradiol administration on the day of VO did not induce c-fos gene expression in either HYP or POA of defeminized animals, instead a diminution in its expression was observed in animals treated with testosterone in POA. The overall results suggest that estradiol and testosterone imprinting during critical postnatal period of sexual differentiation of the brain permanently modifies the regulation of c-fos gene expression.

Perinatal treatment with picrotoxin induces sexual, behavioral, and neuroendocrine changes in male rats

The effects of maternal exposure to picrotoxin (PT) during the prenatal and postnatal periods of sexual brain differentiation were studied. Behavioral (sexual behavior), physical (sexual maturation, body, and organ weights) and neurochemical (striatal and hypothalamic monoamine and respective metabolite levels) data were assessed in the offspring of PT-treated dams. The following results were obtained: 1) sexual maturation as measured by the day of testis descent and testis weight comparison was unchanged; 2) a decrease in male sexual behavior occurred, as well as a decrease in body, ductus deferens, and seminal vesicle weights and in plasma testosterone levels of adult male offspring; 3) striatal dopamine (DA) and homovanillic acid (HVA) levels were decreased and hypothalamic norepinephrine (NE) levels were increased. These results indicate that perinatal exposure to PT during the critical periods of male brain sexual differentiation has long-term effects on the reproductive physiology and behavior of male rats.

Reduced extracellular levels of serotonin in the amygdala of androgenized female rats

The object of this study was to evaluate the effect of androgenization on the extracellular concentrations of serotonin in the amygdala of otherwise intact female rats. One group of animals received one high dose of testosterone (1 mg, s.c.) within three hours after birth, one group received continuous administration of testosterone by means of silicone tubings (50 mm) for approximately 20 days starting at day 40, and one group received testosterone both in the neonatal period and from day 40 and onwards. Assessment of extracellular levels of serotonin in the amygdala was undertaken around day 60 using in vivo microdialysis with HPLC detection; the animals were awake and unrestrained during the microdialysis procedure. Dialysate serotonin concentrations did not differ between the three groups of androgenized animals; however, in all three groups, dialysate levels of serotonin were significantly lower than in controls receiving sesame oil neonatally and empty tubings at day 40. It is suggested that the effects of testosterone on sex-dependent behaviours such as aggression and sexual activity may be at least partly due to a reduction in brain serotonin function.

Effect of delta 9-tetrahydrocannabinol on short-term memory in the rat

We have reported that marihuana and its principal psycoactive compound, delta 9-tetrahydrocannabinol (delta 9-THC) produce alterations in several cerebral areas after acute treatment. Based on the involvement of 5-hydroxytryptamine (5-HT) on memory and learning and the reported effects of delta 9-THC on short-term memory, we designed an experiment to evaluate the memory performance and its possible relationship with serotonergic alterations after delta 9-THC administration. Male Wistar rats received an acute oral dose of THC (5 mg/kg). Short-Term memory was tested on a radial 8-arm maze with a 5 s delay, after 35 days of training. The animals were food deprived and adjusted for growth. 5-HT and its metabolite, 5-HIAA, levels were measured in cerebral cortex, dorsal hippocampus, ventral hippocampus, rostral neoestriatum and amygdala basal nucleus, by HPLC-ED. The experiment indicates an impairment of short-term memory in the radial maze test after delta 9-THC administration. The control group performed the test without errors, while the treated group made a significant number of errors (Z = 0.019, Mann-Whitney test). This behavioral effect did not seem to be related to serotonergic alterations, as the 5-HT turnover rate was not different between treated and control animals.

Injection of an aromatase inhibitor after the critical period of sexual differentiation

We have investigated the possible role of the second week of life in the differentiation of sexually dimorphic behaviours, dependent on the androgenic aromatization, and its possible relationship with the serotonergic systems. For this purpose, 5 mg/kg of a suspension of an aromatase inhibitor, LY43578, has been intraventricularly injected to males on day 12 of life. Studies have been made in adulthood on exploratory and motor activities, anxiety, sexual motivation, and sexual performance. Indoleamine levels in the hypothalamus and corpus striatum have been measured. Sexual behaviour, exploration, and serotonergic metabolism were not affected by the treatment. Sex partner preference and anxiety in the plus-maze showed a feminized tendency in the treated group that, however, did not reach statistical significance. From these results we have confirmed the restriction of the critical period of androgenic aromatization for the organization of reproductive and exploratory behaviour.