In vivo and in vitro studies on the effect of the serotoninergic system on luteinizing hormone and luteinizing hormone-releasing hormone secretion in prepubertal and peripubertal female rats

The differential sensitivity of the hypothalamic-hypophysial-ovarian axis to 5-hydroxytryptophan alters the secretion of estradiol

Serotonin [5-hydroxytryptamine (5-HT)] modulates ovarian function. The precursor of 5-HT, 5-hydroxytryptophan (5-HTP), has been used to treat depression. However, the effects of 5-HTP on ovarian and reproductive physiology remain unknown. In this research, we analysed the impact of 5-HTP on the monoaminergic system and its interactions with the reproductive axis and ovarian estradiol secretion when administered by distinct routes. Female rats 30 days of age were injected with 5-HTP i.p. (100 mg/kg), into the ovarian bursa (1.5 µg/40 µL) or into the median raphe nucleus (20 µg/2.5 µL) and were killed 60 or 120 min after injection. As controls, we used rats of the same age injected with vehicle (0.9% NaCl). Monoamine, gonadotrophin and steroid ovarian hormone concentrations were measured. The injection of 5-HTP either i.p. or directly into the ovarian bursa increased the concentrations of 5-HT and the metabolite 5-hydroxyindole-3-acetic acid in the ovary. For both routes of administration, the serum concentration of estradiol increased. After i.p. injection of 5-HTP, the concentrations of luteinizing hormone were decreased and follicle-stimulating hormone increased after 120 min. Micro-injection of 5-HTP into the median raphe nucleus increased the concentrations of 5-HT in the anterior hypothalamus and dopamine in the medial hypothalamus after 120 min. Our results suggest that the administration of 5-HTP either i.p. or directly into the ovarian bursa enhances ovarian estradiol secretion.

The effect of parachlorophenylalanine treatment on the activity of gonadal and lactotrophic axes in native Polish crested chickens stimulated to broodiness

Brooding behavior, a common characteristic of native breeds of the domestic chicken, is marked by elevated prolactin (PRL) levels, which is necessary for incubation and connected with changes in hypothalamic–pituitary–gonadal axis activity. Evidence indicates the serotoninergic system is a potent modulator of PRL secretion. The objective of this study is to investigate whether blocking serotonin synthesis with parachlorophenylalanine (PCPA) prevents incubation behavior in native Polish crested chickens. In addition, we examined the effect of PCPA on the gene expression of the gonadal and lactotrophic axes. Birds were stimulated to broodiness by artificial eggs in nests. At 34 wk of age (April: spring period), the hens were divided into 2 groups (14 hens in each group): control and PCPA-treated (50 mg/kg BW) group. After 5 wk of treatment, the artificial eggs were removed from the nests. Egg production, incubation activity, and levels of plasma ovarian steroids progesterone (P4), testosterone (T), estradiol (E2), and PRL were examined. At the end of the experiment (45 wk of age, June: summer period), ovarian characteristics and mRNA gene expression of gonadal (gonadotropin-releasing hormone [GnRH] I, luteinizing hormone [LH] ß, follicle-stimulating hormone [FSH] ß) and lactotrophic (vasoactive intestinal peptide [VIP], PRL) axes were measured by quantitative real-time PCR. Incubation activity was observed in the hens of both groups but with lower frequency in PCPA-treated birds. Moreover, the PCPA group had a higher cumulative egg production than the controls. During the first six and 8 wk of the experiment, levels of P4 and E2, respectively, were similar in both groups, but all concentrations increased in the PCPA-treated hens after this period. In addition, increased GnRH-I, LHß, and FSHß and decreased VIP mRNA expression was observed in the PCPA group compared with the controls. There were no differences in PRL mRNA expression, the PRL level, and ovarian morphometry between the 2 groups. These results indicate that blockage of serotonin synthesis by PCPA does not effectively prevent incubation in native Polish crested chickens. However, treatment with PCPA increased gonadal axis activity and improved reproductive performance.

Serum and follicular fluid levels of serotonin, kisspeptin, and brain-derived neurotrophic factor in patients undergoing in vitro fertilization: an observational study : Neurohormones in patients receiving IVF

OBJECTIVE

This study aimed to examine the effect of interactions between serotonin (5-HT), brain-derived neurotrophic factor (BDNF), and kisspeptin on the reproductive potential in women receiving in vitro fertilization (IVF).

METHODS

Paired serum and follicular fluid (FF) samples were obtained from 30 consecutive patients receiving IVF. Primary and secondary outcome measures were the rate of chemical/clinical pregnancy and the number of mature oocytes and embryos, respectively. Serum and FF 5-HT, BDNF, kisspeptin, and platelet-activating factor (PAF) levels were measured by enzyme-linked immunosorbent assay.

RESULTS

In response to ovarian hyperstimulation, serum 5-HT and kisspeptin levels significantly increased, whereas serum BDNF and PAF levels remained unchanged. These factors were detected in FF, but they were unrelated to serum levels. FF 5-HT and BDNF levels were positively correlated. Serum kisspeptin levels were negatively correlated with FF BDNF and serum and FF PAF levels. Women who were pregnant had significantly lower FF BDNF levels compared with women who were not pregnant (21.96±12.75 vs 47.63±52.90 µg/mL). Multivariate stepwise linear regression and logistic regression analyses showed that only 5-HT and kisspeptin improved IVF outcome.

CONCLUSIONS

This study indicates a role of serotoninergic mechanisms in success of IVF, but the contribution of interacting neuropeptides requires additional investigation.

Maternal exposure to fluoxetine during gestation and lactation does not alter plasma concentrations of testosterone, oestrogen or corticosterone in peripubertal offspring

Antidepressants are widely used around the world, primarily for the treatment of mood disorders, anxiety and pain syndromes. Women who use antidepressants often continue to use them during pregnancy. Selective serotonin reuptake inhibitors, including fluoxetine, are the main class of antidepressants prescribed to pregnant women. It is known that fluoxetine crosses the placental-blood barrier and is excreted in breast milk. Consequently, indirect exposure of the infant occurs. Knowing that fluoxetine alters the balance of neurotransmitters in the central nervous system, several studies have shown that maternal exposure to this drug leads to various adverse effects on the nervous, reproductive and cardiovascular systems of the offspring. The aim of the present study was to evaluate the effects of exposure to fluoxetine during gestation and lactation on parameters related to steroid hormones in prepubertal and pubertal male and female rats. The endpoints evaluated were date of puberty onset, plasma testosterone and oestrogen concentrations before and after puberty onset and corticosterone concentration before and after adrenocorticotrophin stimulus. None of the parameters was affected by fluoxetine exposure.

Fluoxetine treatment of prepubertal male rats uniformly diminishes sex hormone levels and, in a subpopulation of animals, negatively affects sperm quality

Fluoxetine (Flx) is a selective serotonin reuptake inhibitor that alters the male reproductive system when administered at the adult stage or after maternal exposure. In the present study we evaluated the effects of Flx administration on reproductive parameters during juvenile–peripubertal development when treated male rats reached adulthood. Groups of rats were treated daily with Flx (5 mg kg−1, i.p.) or saline (0.9% NaCl), or were left untreated. Rats were treated between 30 and 53 days of age and were killed at 65 days of age. Serotonin concentrations were determined in the hypothalamus, hypophysis and testis. Gonadotrophins, sex steroids and sperm quality (membrane integrity, sperm with functional mitochondria, sperm density, sperm motility and morphological abnormalities) were also evaluated. Flx did not affect bodyweight, but significantly diminished LH, FSH, progesterone and testosterone serum concentrations. After graphical analysis, a subgroup of rats was identified whose sperm quality parameters were greatly affected by Flx. In the present study we show that Flx administered to juvenile rats disrupts the hypothalamic–hypophyseal–testicular axis and its effects on sperm quality are not homogeneous in adults. In contrast, Flx altered concentrations of gonadotrophins and sexual steroids in all treated rats. These results suggest caution should be exercised in the prescription of Flx to prepubertal males.

Role of the serotonergic axis in the reproductive failure associated with aging broiler breeder roosters

Reproductive failure associated with aging is a well-known phenomenon. However, the mechanism by which this failure occurs in broiler breeder roosters is still unclear. A previous study conducted in our laboratory, comparing young and aging broiler breeder roosters, demonstrated an elevation in hypothalamic vasoactive intestinal peptide (VIP) and pituitary prolactin (PRL) gene expression accompanied by a deterioration of gonadal axis function. This resulted in a decrease in semen-quality variables as roosters aged. The objective of this study was to examine the involvement of the serotonergic axis in the age-associated reproductive failure in broiler breeder roosters. Cobb roosters aged 64 wk were divided into 3 groups (n = 20 each): parachlorophenylalanine (PCPA) administration, active immunization against chicken VIP, and controls. At 69 wk of age, each group was divided into 2 equal subgroups: 1 received ovine PRL and the other served as controls. Weekly semen volume, concentration and motility, and plasma testosterone, estradiol, and PRL concentrations were examined. At the end of the experiment, roosters were euthanized, testes were weighed, and hypothalamus and pituitary were removed to assay the expression of genes encoding hypothalamic GnRH-I, pituitary FSH, pituitary LH, hypothalamic VIP, and pituitary PRL. Both PCPA administration and active immunization against chicken VIP significantly increased testis weight, semen volume, sperm concentration, ejaculation grade, plasma testosterone level, and GnRH-I, FSH and LH gene expression compared with controls (P ≤ 0.05). In addition, a decrease in plasma estradiol and PRL concentrations and VIP and PRL gene expression was observed in PCPA- and VIP-immunized birds compared with controls (P ≤ 0.05). Administration of PRL in all groups decreased gonadal axis function and semen-quality variables (P ≤ 0.05). Collectively, these results suggest that the increasing expression levels of the serotonergic axis in aging broiler breeder roosters inhibit proper gonadal function and reproductive performance. This article establishes for the first time the inhibitory role of serotonin on reproduction in aging roosters.

Serotonin reuptake inhibitor citalopram inhibits GnRH synthesis and spermatogenesis in the male zebrafish

Selective serotonin reuptake inhibitors (SSRIs) are widely used antidepressants for the treatment of depression. However, SSRIs cause sexual side effects such as anorgasmia, erectile dysfunction, and diminished libido that are thought to be mediated through the serotonin (5-hydroxytryptamine, 5-HT) system. In vertebrates, gonadotropin-releasing hormone (GnRH) neurons play an important role in the control of reproduction. To elucidate the neuroendocrine mechanisms of SSRI-induced reproductive failure, we examined the neuronal association between 5-HT and GnRH (GnRH2 and GnRH3) systems in the male zebrafish. Double-label immunofluorescence and confocal laser microscopy followed by three-dimensional construction analysis showed close associations between 5-HT fibers with GnRH3 fibers and preoptic-GnRH3 cell bodies, but there was no association with GnRH2 cell bodies and fibers. Quantitative real-time PCR showed that short-term treatment (2 wk) with low to medium doses (4 and 40 μg/L, respectively) of citalopram significantly decreased mRNA levels of gnrh3, gonadotropins (lhb and fshb) and 5-HT-related genes (tph2 and sert) in the male zebrafish. In addition, short-term citalopram treatment significantly decreased the fluorescence density of 5-HT and GnRH3 fibers compared with controls. Short-term treatment with low, medium, and high (100 μg/L) citalopram doses had no effects on the profiles of different stages of spermatogenesis, while long-term (1 mo) citalopram treatment with medium and high doses significantly inhibited the different stages of spermatogenesis. These results show morphological and functional associations between the 5-HT and the hypophysiotropic GnHR3 system, which involve SSRI-induced reproductive failures.

Effects of systemic administration or intrabursal injection of serotonin on puberty, first ovulation and follicular development in rats

To elucidate the role of serotonin in the onset of puberty, the effects of both systemic and in-ovarian bursa administration of serotonin on the neuroendocrine mechanism that modulates the onset of puberty, follicular development and first ovulation were evaluated. Two experiments were carried out. For the first, 25 or 37.5 mg kg–1 of bodyweight of serotonin creatinine sulfate was administered by a subcutaneous route to 30-day-old female rats. In the second experiment, serotonin creatinine sulfate was administered directly into the ovarian bursa of 34-day-old female rats. Systemic administration of 25 or 37.5 mg kg–1 of serotonin creatinine sulfate induced a delay in the ages of vaginal opening and first vaginal oestrus, a decrease in the number of ovulating animals, and serum concentrations of FSH, LH, oestradiol and progesterone. An increase in the number of Class 3 (>500 μm) and atretic follicles was observed in the ovaries of these animals. The administration of serotonin creatinine sulfate in the ovarian bursa did not modify the onset of puberty and ovulation, but a reduced serum concentration of oestradiol was observed. Our results suggest that serotonin acts on the components of the hypothalamus–hypophysis–ovary axis by modulating follicular development, ovarian functions and the onset of puberty.

Tryptophan hydroxylase: a target for neuroendocrine disruption

Tryptophan hydroxylase (TPH), the rate-limiting enzyme in serotonin (5-HT) synthesis, performs an essential role in the maintenance of serotonergic functions in the central nervous system (CNS), including regulation of the neuroendocrine system controlling reproduction. The results of recent studies in a teleost model of neuroendocrine disruption, Atlantic croaker, indicated that hypothalamic TPH is a major site of interference of hypothalamic-pituitary-gonadal function by environmental stressors. The effects of exposure to two different types of environmental stressors, low dissolved oxygen (hypoxia) and a polychlorinated biphenyl mixture (Aroclor 1254), on the stimulatory brain serotonergic system controlling reproductive neuroendocrine function in Atlantic croaker are reviewed. Exposure to both stressors produced decreases in TPH activity, which were accompanied by a fall in hypothalamic 5-HT and gonadotropin-releasing hormone (GnRH I) content in the preoptic-anterior hypothalamic area and were associated with reduction in luteinizing hormone (LH) secretion and gonadal development. Pharmacological restoration of hypothalamic 5-HT levels after exposure to both stressors also restored neuroendocrine and reproductive functions, indicating that the serotonergic system is an important site for hypoxia- and Aroclor 1254-induced inhibition of reproductive neuroendocrine functions. The mechanisms underlying downregulation of TPH activity by these stressors remain unclear but may involve alterations in hypothalamic antioxidant status. In support of this hypothesis, treatment with an antioxidant, vitamin E, was found to reverse the inhibitory effects of Aroclor 1254 on TPH activity. The results suggest that TPH is a major target for neuroendocrine disruption by diverse environmental stressors.

Serum fluctuations of total and free tryptophan levels during the menstrual cycle are related to gonadotrophins and reflect brain serotonin utilization

BACKGROUND

Serotoninergic (5-HT) neurons are suggested to regulate estrous cycle in animal models. In the present study we evaluated whether a relationship exists between the serotoninergic precursors in the central nervous system and the gonadotrophin-ovarian cyclic function.

METHODS

We measured 5-HT precursors [free (FT) and total (TT) tryptophan] and LH, FSH and 17beta-estradiol (E2) levels in the serum of 15 fertile women with normal menstrual cycles during the follicular (cycle days 1-5, 7-11), mid-cycle (cycle days 14-16) and luteal (cycle days 17-19, 22-24) phases.

RESULTS

TT and FT were significantly increased in the 7-11 and 17-19 cycle days and were decreased at mid-cycle (P < 0.01), with a cyclic and opposite behaviour when compared to that of FSH and LH. Indeed, correlation analysis through the matrix of mean values showed that LH was negatively correlated to TT (r = -0.636) and FT (r = -0.574), as well as FSH (TT, r = -0.655; FT, r = -0.663), and that TT and FT were positively correlated to each other (r = 0.801; P < 0.001). Furthermore, whilst the two FT peaks reached approximately the same levels in the follicular and luteal phase, TT levels were approximately 30% higher in the luteal than in the follicular phase of the cycle: thus in the first (follicular) phase FT peak was relatively higher than that of TT, whereas the contrary occurred in the second (luteal) phase of the cycle.

CONCLUSIONS

Both TT and FT levels have cyclic variations throughout the menstrual cycle, being lowest at mid-cycle (14-16 cycle days), concomitant with the highest LH and FSH concentrations, and higher before and after mid-cycle phase, coinciding with the lowest circulating LH/FSH levels. Since TT and FT levels in the plasma have cyclic changes, our study: (i) suggests that a consumption of serum serotonin precursors takes place concomitant with gonadotrophin release during menstrual cycle; (ii) may represent an in vivo model to investigate this relationship in women in different physiopathological conditions.

In vivo and in vitro sex steroids stimulate seabream gonadotropin-releasing hormone content and release in the protandrous black porgy, Acanthopagrus schlegeli

The objective of the present study was to investigate the regulation of seabream gonadotropin-releasing hormone (sbGnRH) release using in vivo and in vitro approaches in the protandrous black porgy, Acanthopagrus schlegeli. Estradiol-17beta (E2), testosterone (T), and 11-ketotestosterone (11-KT) were found to significantly stimulate the increase of sbGnRH levels in pituitary of black porgy after 5-96 h of injection. An in vitro culture system using dispersed brain neurons was also developed to investigate the effects of various steroids on sbGnRH release. Different doses (10(-6) - 10(-12) M) of E2, T, 11-KT, and cortisol were applied during 6 h experiment. KCl stimulated sbGnRH release at a dose- and time-dependent manner. The concentration of sbGnRH increased 2-fold in the highest dose of KCl treatment compared to the control. Treatments with E2, T, 11-KT and cortisol significantly stimulated the release of sbGnRH from the cultured brain neurons. The concentration of sbGnRH in medium was increased by 2-, 1.9-, 2.1-, and 4.9-fold when treated with E2, T, 11-KT, and cortisol, respectively, as compared to the respective control. Cholesterol did not have any stimulatory effects in the release of sbGnRH. The results showed that sex steroids and cortisol had direct effect on brain neuronal cells stimulating the release of sbGnRH.

Interactions between serotoninergic and aminoacidergic pathways in the control of PRL secretion in prepubertal male rats

Prolactin secretion is controlled by the hypothalamus through different neurotransmitters which interact with multiple receptor subtypes. The discovery of different families of receptors for serotonin (5-HT1-5-HT7) and excitatory aminoacids (NMDA, KA, AMPA and metabotropic receptors) ilustrates the complexity of this regulation. Moreover, in the rat the role of different neurotransmitters changes during pubertal development. Present experiments were carried out to analyse the interactions between AMPA and serotoninergic receptors in the control of prolactin secretion in prepubertal male rats. For this purpose, 16 and 23-day old male rats were treated with 5-hydroxytryptophan (5-HTP, precursor of serotonin synthesis) plus fluoxetine (blocker of serotonin reuptake), 8-OH-DPAT (agonist of 5-HT1A receptors), DOI and alpha-Me-5-HT (agonists of 5-HT2 receptors), 1-phenylbiguanide (agonist of 5-HT3 receptors) alone or in combination with AMPA (agonist of AMPA receptors). The results obtained indicate that: (a) activation of 5-HT1A receptors stimulated PRL secretion on day 16 and inhibited it on day 23; activation of 5-HT2 receptors stimulated PRL secretion on days 16 and 23, whereas activation of 5-HT3 receptors inhibited PRL release only on day 23; (b) activation of AMPA receptors inhibited PRL secretion on day 23, but not on day 16 and (c) a cross-talk is apparent between 5-HT2 and AMPA receptors in the regulation of PRL secretion, the stimulatory effect of DOI being blocked by AMPA.

Protein- and tryptophan-restricted diets induce changes in rat gonadal hormone levels

The release of gonadotrophic hormones starts at puberty and, along with the subsequent estral cyclicity, is subject to hormonal feedback systems and to the action of diverse neuroactive substances such as gamma amino butyric acid and catecholamines. This study shows the effect of the administration during 40 days of protein-restricted and corn-based (tryptophan- and lysine-deficient) diets on the serotonin concentration in medial hypothalamic fragments as well as in follicle-stimulating luteinizing hormones, 17-beta-estradiol and progesterone serum levels, and estral cyclicity in 60- and 100-day-old rats (young, mature, and in gestation). In young rats, a delay in vaginal aperture development, and a lengthening of the estral cycle to a continuous anestral state was observed, mainly in the group fed corn. This group showed a 25% decrease in the serotonin concentration compared with the protein-restricted group, which exhibited an increase of 9% over the control group. Luteinizing hormone levels decreased in 16% and 13%, whereas follicle-stimulating hormone increased in 13% and 5% in the young animals of restricted groups, respectively, compared with the control group. Serum progesterone levels decreased only in young restricted versus control animals, and no differences were seen among adult and gestational rats. Serum levels of 17-beta-estradiol in restricted animals showed different concentration patterns, mainly in the corn group, which was higher at the 20th gestational day, falling drastically postpartum. The results obtained in this study show serotonin to be a very important factor in the release of gonadotrophic hormones and the start of puberty.

Changes in monoaminergic activity in the anterior, medium and posterior hypothalamus, gonadotropins levels and ovarian hormones during puberty of the female rat

The aim of present study is the analysis of monoamines concentrations changes in the anterior, medium and posterior hypothalamus, as well as changes in serum gonadotropins levels, ovarian steroids and follicular growth during the prepubertal development of the female rat. Noradrenergic activity in the anterior, medium and posterior hypothalamus reached highest level at day 13 after birth, followed by a subsequent decrease from day 15 to 19 and an increase on days 22 and 27 postnatal. At day 1, neural activity in the medium hypothalamus was higher than the activity in the anterior and posterior hypothalamus. Serotoninergic activity in three portions of the hypothalamus was higher throughout the prepubertal development. Follicle-stimulating hormone and luteinizing hormone serum levels increased between days 11 and 17 and decreased from day 19 to 36. The concentration of 17beta-estradiol was consistently low throughout the prepubertal development and increased at day 39 after birth. These results indicate that during the prepubertal development of the rat, the three regions of the hypothalamus show significant changes in the monoaminergic neural activity. There is an inverse relationship between the noradrenergic activity on the anterior and medium hypothalamus and serotoninergic activity in the posterior hypothalamus with ovarian steroids during sexual maturation. These changes may be linked to the development of the neuroendocrine processes that modulate gonadotropin secretion and ovarian function.

Disruption of neuroendocrine control of luteinizing hormone secretion by aroclor 1254 involves inhibition of hypothalamic tryptophan hydroxylase activity

Mechanisms governing the effect of polychlorinated biphenyl (PCB) toxicity on hypothalamic serotonergic function and the neuroendocrine system controlling LH secretion were investigated in Atlantic croaker (Micropogonias unulatus) exposed to the PCB mixture Aroclor 1254 (1 microg x g body weight(-1) x day(-1)) in the diet for 30 days. PCB treatment caused a decrease in hypothalamic 5-hydroxytryptamine (5-HT) concentrations and significant inhibition of hypothalamic tryptophan hydroxylase (TPH), the rate-limiting enzyme in 5-HT synthesis, but did not alter the activity of monoamine oxidase, the catabolic enzyme. Further, PCB treatment caused significant decreases in GnRH content in the preoptic-anterior hypothalamic area. Significant decreases in pituitary GnRH receptor concentrations and the LH response to the GnRH analogue (GnRHa) were also observed in PCB-exposed fish, possibly as a consequence of a decline in GnRH release. The possible association between impaired serotonergic and neuroendocrine functions after PCB treatment was explored using serotonergic drugs. Treatment of croaker with p-chlorophenylalanine, an irreversible TPH inhibitor, mimicked the effects of PCB on the GnRH system and the LH response to GnRHa. Bypassing the TPH-dependent hydroxylation step with the administration of 5-hydroxytryptophan restored 5-HT to control levels and prevented the deleterious effects of PCB on the neuroendocrine parameters. Moreover, slow-release GnRH implants prevented the PCB-induced decline in GnRH receptors and restored the LH response to GnRHa, suggesting that GnRH therapy can reverse PCB-induced disruption of LH secretion. These results demonstrate that TPH is one of the targets of PCB neurotoxicity and indicate that a decrease in 5-HT availability in PCB-exposed croaker results in disruption of the stimulatory 5-HT/GnRH pathway controlling LH secretion.

Interleukin-1 inhibits NMDA-stimulated GnRH secretion: associated effects on the release of hypothalamic inhibitory amino acid neurotransmitters

Immune system activation is often accompanied by alterations in the reproductive axis. Interleukin-1 (IL-1), a polypeptide cytokine, has been postulated as a chemical messenger between the immune and the neuroendocrine systems. Using superfused hypothalamic fragments explanted from intact male rats, we evaluated the effects of IL-1 (0. 5 and 5 nM) on basal and N-methyl-D-aspartate (NMDA)-stimulated release of gonadotropin-releasing hormone (GnRH), and the associated modifications in the output of inhibitory amino acid neurotransmitters involved in the control of GnRH secretion. IL-1 did not modify basal GnRH release, but markedly restrained the stimulatory effect of NMDA on GnRH secretion. gamma-Aminobutyric acid, glycine and taurine concentrations significantly increased in the superfusion medium only after pretreatment with the higher dose of IL-1 (p < 0.05). Our results indicate that this cytokine inhibits NMDA- stimulated GnRH release, affecting the activity and/or the release of hypothalamic excitatory and inhibitory amino acid neurotransmitters participating in the regulation of GnRH secretion.

Effects of a lesion in the dorsal raphe nuclei performed during the juvenile period of the female rat, on puberty

The present study examined the effect of thermic lesions on the dorsal raphe nuclei (DRN) of the female rat, performed at various ages during the prepubertal period (21, 24, or 27 days), on puberty, and at first ovulation. In comparison with sham-operated animals, the age of vaginal opening and first vaginal oestrus was delayed in rats with a DRN lesion performed at the end of the infantile period (day 21) (45.6+/-0.94 vs. 89.9+/-1.03, p < 0.05), whereas differences were not observed in animals with lesions performed during the juvenile period (day 24 or 27). The number of ova shed by ovulating animals was greater in those rats with lesions performed on day 24 or 27 (9.7+/-0.4 vs. 7.4+/-0.4; 9.5+/-0.5 vs. 7.7+/-0.4, p < 0.05). Ovarian follicular atresia in these animals was significantly lower than in control and sham-operated ones. On the day of first vaginal oestrus and 48 h after the lesion, the serotonin-hypothalamic concentration decreased in all lesioned animals. Present results support the idea of the participation of the serotoninergic system, arising from the DRN, in the neuroendocrine mechanisms regulating the onset of puberty and the first ovulation, with variations depending on animal maturity.

Role of serotoninergic receptors in gonadotropin secretion in male rats

Experimental data concerning the role of serotonin (5-HT) in the control of gonadotropins secretion remain controversial: different receptors subtypes should mediate the serotoninergic action. In the present work we analyzed in prepubertal and adult male rats the FSH and LH responses after administration of the following drugs: 5-hydroxy-L-tryptophan (5-HTP), precursor of 5-HT synthesis, the 5-HT1 receptor agonist 8-hydroxy-2-(di-n-propylamino) tetralin (8-OH-DPAT), the 5-HT2 receptor agonists alpha-methylserotonin maleate (alpha-CH3-HT) and (+/-)-DOI hydrochloride (DOI), the 5-HT3 agonists, quipazine-N-methyldimaleate (QUIP), 2 methyl-serotonin maleate (2-CH3-HT), trimethylserotonin iodide (5-HTQ) and 1-phenylbiguanide (PHE). We found that: a) FSH secretion in adult males was stimulated by 5-HTP, inhibited by 5-HT2 agonists and unaffected by 5-HT3 agonists; b) LH secretion in adult males was stimulated by 5-HTP and alpha-CH3-HT, while DOI and 5-HT3 agonists were ineffective; c) in prepubertal males, 5-HT2 and 5-HT3 agonists inhibited LH release. All these results taken together suggest that: (1) 5-HT2 and 5-HT3 receptors are involved in the control of gonadotropin secretion; (2) FSH and LH secretion are differently modulated by agonists of 5-HT2 and 5-HT3 receptors; (3) the 5-HT2 agonists alpha-CH3-HT and DOI elicit different responses; and (4) the responses obtained vary with animal age, since the inhibitory effect of 5-HT2 and 5-HT3 agonists on LH secretion was observed only in prepubertal males.

Amine neurotransmitter levels in male and female rats through developmental periods

Monoamines (MA) such as dopamine (DA), norepinephrine (NE), and 5-hydroxytryptamine (5-HT) are now generally regarded as widely distributed and essential endogenous mediators contributing to the integration of reproductive physiology. MA measured in the hypothalamus tissue of male and female rats aged 1 to 90 days showed its own characteristic development pattern. Significant differences were observed at 5, 15, and 90 days of age in NE mean levels and at all ages except for 3 days of age in 5-HT mean levels. In contrast, no sex differences were seen in DA mean levels.

Opioid tonus and luteinizing hormone secretion in anorexia nervosa: priming effect with serotonin precursor L-5-hydroxytryptophan during pulsatile gonadotropin-releasing hormone administration

In anorexia nervosa (AN) luteinizing hormone (LH) release is often impaired during opioid blockade. We investigated whether a restoration of the endogenous sex steroid milieu, together with a rise in central serotonergic tone, could increase LH responsiveness to Naloxone (NAL) in seven young women affected by AN. The spontaneous pulsatility of gonadotropins and their response to gonadotropin-releasing hormone (GnRH) and NAL challenges were tested before and after 13 days of pulsatile GnRH treatment and oral administration of L-5-hydroxytryptophan. Low and unpulsatile gonadotropin levels, responsive to GnRH, but not to NAL, were found before treatment. Pulsatile GnRH brought about a quasi-normal secretory pattern and 17 beta-estradiol increased to preovulatory levels in six of seven patients. On day 13 the lack of response to NAL administration was still present, however. A neuroendocrine disorder seems to be present in AN, which appears more complex than in other forms of hypothalamic amenorrhea.

Sexual differences in the effect of the GABAergic system on LH secretion and in the hypothalamic ontogenesis of GABAA receptors in prepubertal rats

The administration of aminooxyacetic acid (AOAA), which increases hypothalamic GABA concentrations, induced a significant increase in LH levels in female rats of 12, 16 and 18 days of age. This stimulatory effect of AOAA on serum LH levels was not observed at 21 and 25 days of age whereas a significant decrease in the LH concentrations by AOAA was found at 30 days of age. The neonatal androgenization of female rats abolished the effects of AOAA and no effects of AOAA were found in male rats at the different ages studied. The muscimol binding sites in medial basal and preoptic anterior hypothalamic areas showed a significant different sexual ontogenic pattern. Males rats castrated at birth showed a very similar ontogenic pattern of [3H]muscimol binding sites to female rats and significantly different to male control rats. It is concluded that there are sexual differences in the effect of GABAergic system on LHRH-LH secretion and in the development of hypothalamic GABAA receptors during sexual maturation. These differences are probably connected with the neonatal exposure to androgens that would induced changes in the composition and probably in the properties of GABAA receptor that in turn modified its effects on LHRH neurons.

Ontogenic changes in the hypothalamic levels of amino acid neurotransmitters in the female rat

In order to evaluate the participation of several amino acid neurotransmitters (AANT) in sexual maturation we measured the hypothalamic concentrations of aspartate (Asp), glutamate (Glu), homocysteic acid (HCA), glycine (Gly), taurine (Tau) and gamma-aminobutyric acid (GABA) in female rats at different ages of sexual development. Animals (15-, 20-, 25-, 30-, 35- and 40-day-old female rats, as well as adult diestrous rats, n = 8-10/group) were decapitated at noon; each brain was rapidly removed and frozen on dry ice. Preoptic area (POA) and mediobasal hypothalamic (MBH) needle punch samples were obtained from 500-600 microns thick coronal slices, homogenized and centrifuged. AANT concentrations were measured in the supernatants following derivatization with phenyl isothiocyanate and reverse-phase HPLC separation by UV detection. Significant (P < 0.05) changes in hypothalamic AANT concentrations can be summarized as follows: POA Glu, HCA and Gly levels rose transiently at day 20 and then increased steadily in 35- and 40-day-old rats. Asp concentrations rose in 35- and 40-day-old rats. Tau concentrations decreased markedly from day 30 onwards. GABA levels were lowest in 15-day-old rats, as compared to the other age groups. Asp, Glu, Gly and GABA concentrations were highest in adult diestrous rats. Changes in MBH AANT levels were not as relevant: only Gly concentrations rose significantly at day 40; Asp, Glu, HCA, Gly and GABA concentrations increased in adult diestrous rats and Tau concentrations were lower from day 35 onwards.(ABSTRACT TRUNCATED AT 250 WORDS)

Gonadotropin and prolactin secretion in prepubertal female rats treated with 8-hydroxy-2-(di-n-propylamino) tetralin

The effect of serotoninergic activation on gonadotropin and prolactin release were analysed in 16-day-old intact female rats. In the first experiment, females were decapitated 30 min after i.p. administration of 100 mg/kg of 5-hydroxytryptophan (5-HTP) or vehicle; in the second experiment the rats were decapitated 15 and 30 min after i.p. injection of vehicle or some doses (0.1, 1 and 10 mg/kg) of 8-hydroxy-2-(di-n-propylamino) tetralin (8-OH-DPAT), a selective agonist of the serotonin (5-HT)1A receptors. We found that: 1) serum follicle-stimulating hormone (FSH), luteinizing-hormone (LH) and prolactin concentrations increased after 5-HTP administration; 2) serum LH and prolactin concentrations and pituitary prolactin content increased after administration of 8-OH-DPAT. Our results indicate that in prepubertal rats, activation of serotoninergic system stimulated gonadotropin and prolactin release, and that 5-HT1A receptors are involved in this effect. In addition, the simultaneous increase in serum and pituitary prolactin content suggests that 8-OH-DPAT enhances prolactin synthesis.

Sexual maturation modifies the GABAergic control of gonadotrophin secretion in female rats

Administration of aminooxyacetic acid, (an inhibitor of gamma-aminobutyric acid (GABA)-transaminase which enhances the hypothalamic GABA content) increased luteinizing hormone (LH) and follicle stimulating hormone (FSH) levels in prepubertal rats (16 days of age), and decreased the levels of these pituitary hormones in peripubertal rats (30 days of age). Prepubertal and peripubertal female rats were administered with muscimol, a GABAA-antagonist, with baclofen, a GABAB agonist, and with bicuculline, a GABA-antagonist, and the serum concentrations of LH and FSH were determined. In prepubertal rats, muscimol increased both LH and FSH levels, while in peripubertals the GABAA agonist showed the opposite effect, i.e. both gonadotrophins were decreased after its administration. Baclofen lowered serum concentrations of LH and FSH at the different ages studied. Administration of bicuculline produced a decrease in LH and FSH concentrations in prepubertal rats, and an increase of these values in peripubertal rats. These results indicate that GABA exerts a stimulatory tone on gonadotrophin secretion in prepubertal rats and an inhibitory one in peripubertal animals. This effect is most probably mediated by GABAA receptors. It is suggested that the change in the effect on gonadotrophin secretion of the activation of GABAA receptors which takes place during sexual maturation in the female rats is related to the central mechanisms involved in the onset of puberty.