Role of Sexual Differentiation of the Hypothalamus in the Differential Effect of the Serotoninergic System on LH in Prepubertal Male and Female Rats

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α-Methyl-p-tyrosine (α-MT), a competitive inhibitor of tyrosine hydroxylase, was used to block the synthesis of hypothalamic catecholamines in immature female rats of 14, 16 and 30 days of age and in castrated adults. The administration of α-MT (300 mg/kg body weight, free base) induced a significant decay in the hypothalamic content of norepinephrine (NE) and dopamine (DA) within the first 120 min. A second dose (150 mg/kg body weight), given 2 h after the first injection, did not further modify the low catecholamine levels observed 120 min after the first α-MT administration. The administration of 300 mg/kg body weight of α-MT induced a significant increase in LH concentrations in rats aged 14 and 16 days. On the contrary, after an α-MT injection, a significant LH decrease was observed in 30-day-old and in adult castrated rats. α-MT also increased FSH levels in prepubertal rats of 16 days of age, but no change occurred in 30-day-old and in adult rats. The administration of estrogen-progesterone (EP) to prepubertal rats of 16 days of age induced a significant decrease in serum LH levels as well as in the serotonin (5-HT) and 5-hydroxyindole-acetic acid (5-HIAA) concentrations in the anterior-preoptic hypothalamic area (AH-POA), but not in the medial basal hypothalamus. No modifications in the catecholamine content of these hypothalamic areas were observed in this age group after EP administration. On the contrary, in 30-day-old rats, EP induced a significant LH release as well as an increase in AH-POA concentrations of 5-HT, 5-HIAA and catecholamines. These data show that, during sexual development in the female rat, (1) the effect of catecholamines on LHRH-LH secretion changes from inhibition to stimulation, and (2) the modification in the feedback effects exerted by EP on LH is also accompanied by a changing effect of the ovarian hormones on catecholaminergic and serotoninergic systems. On this basis, the possibility exists that sexual maturation and the onset of puberty in the female rat involve the development of qualitatively different mechanisms of gonadotrophin control through changes in the ovarian hormones-neurotransmitters-LHRH interrelationships.

“…According to previous results [13][14][15], LHRH neurons would also change their responsiveness to 5-HT during sexual maturation in female rats. This change was not observed in males.…”

Section: Discussionmentioning

confidence: 57%

“…In immature female rats 5-hydroxytryptophan (5-HTP), a 5-HT precursor that increases hypothalamic concentra tions of this neurotransmitter, induces LH release at 16, 18 and 20 days of age; this effect is no longer observed in 26-day-old rats [13][14][15]. In immature female rats, 5-HT is likely to have an inhibitory' action on LH secretion [13].…”

mentioning

confidence: 99%

Sexual Maturation Modifies the Catecholaminergic Control of Gonadotrophin Secretion and the Effect of Ovarian Hormones on Hypothalamic Neurotransmitters in Female Rats

Moguilevsky

Arias²,

Szwarcfarb³

et al. 1990

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“…It has been previously demonstrated that the administration of 5-HTP induces LH release in prepubertal female rats [11][12][13], but not in male rats. These results demonstrate that in prepubertal rats there are sexual differences in the LH release response to 5-HTP.…”

Section: Discussionmentioning

confidence: 98%

“…On the other hand, 5-hydroxytryptophan (5-HTP) induces LH release in female prepubertal rats, but not in males [11]. We proposed that the sexual difference in the LH response to 5-HTP might be asso ciated with the regulatory action of serotonin on the cyclic hypothalamic control of gonadotrophin secretion [ 13].1 Supported by Grants from the Consejo Nacional de Investigaciones Científicas y Técnicas and from the University of Buenos Aires, Repú blica Argentina. Received: July 6, 1988 Accepted after revision: February 10, 1989 In adult male rats serotonin modifies FSH secretion when injected into the third ventricle of the brain having an inhibitory effect on this pituitary gonadotrophin [9].…”

mentioning

confidence: 99%

Effect of Serotoninergic System on FSH Secretion in Male and Female Rats: Evidence for Stimulatory and Inhibitory Actions

Justo¹,

Rossano²,

Szwarcfarb³

et al. 1989

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The present experiments were designed to assess the effect of the serotoninergic system on FSH secretion in prepubertal (16-, 18-, 20-, 26- and 30-day-old) and adult (60-day-old) male and female rats. The intraperitoneal administration of 5-hydroxytryptophan (5-HTP), a serotonin (5-HT) precursor, induced a significant increase of FSH levels in male rats at 16, 26, 30 and 60 days of age (p < 0.01) but not at 18 and 20 days. In the females, no modifications in FSH concentrations in prepubertal and adult rats were observed after 5-HΓP injection. These results indicate that there are sexual differences in the effect of the serotoninergic system on FSH secretion. Orchidectomy performed in prepubertal (30-day-old) and adult rats (60 days) besides increasing FSH levels, reversed the response of this hormone to 5-HTP administration, since in castrated rats the 5-HT precursor induced a significant decrease in serum FSH concentrations. The administration of 5-HTP to 30 day-old castrated rats treated with testosterone induced FSH release as it did in control animals of this age. In the adult castrated rats the administration of testosterone abolished the inhibitory effect of 5-HTP observed in castrated rats but did not invoke the stimulatory action of 5-HTP observed in the controls. This difference between prepubertal and adult rats appears to be related to a decrease in the sensitivity to testosterone of the central mechanism which controls FSH secretion. These results indicate that 5-HΓP stimulates FSH release in normal rats and inhibits FSH release in castrated rats, testosterone concentration being a relevant factor in determining the ‘type’ of effect produced. The hypothalamic concentrations of 5-HT and 5-hydroxy-indoleacetic acid (5-HIAA) are significantly higher at the ages at which 5-HTP induces FSH release than at other ages suggesting that hypothalamic turnover of these substances is related to the releasing effect of 5-HTP on FSH.

“…Nevertheless it is interesting to note in this respect that several neuroendocrine mechanisms of gonadotropin con trol change during sexual development. For instance 5-HTP in duces LH release in prepubertal but not in peripubertal or adult rats [10,11] and catecholamines inhibit gonadotropin secretion in prepubertal but stimulate these hormones in peripubertal and adult rats [12]. These modifications in the neuroendocrine control of gonadotropin secretion are related to the onset of sexual maturation [10][11][12].…”

Section: Discussionmentioning

confidence: 99%

Modulatory Effect of Testosterone on the Serotoninergic Control of Prolactin Secretion in Prepubertal Rats

Moguilevsky

Justo

et al. 1990

Self Cite

The administration of 5-hydroxytryptophan (5-HTP) induced a prolactin release in male and female prepubertal rats at 20 days of age. This response was significantly higher in male than in female rats. Neonatal androgenization of the females significantly increased the release of prolactin induced by 5-HTP treatment compared to the values observed in males; thus, the neonatal exposure to androgens seems to be responsible for the sexual differences in the prolactin response to 5-HTP. In a second series of experiments the effect of this serotoninergic precursor on prolactin release in prepubertal (16, 26, and 30 days of age), peripubertal (45-day-old) and adult male rats was studied. Castration significantly decreased the prolactin release response to 5-HTP in prepubertal rats. The administration of testosterone to castrated rats markedly increased the prolactin release response to 5-HTP. Neither castration nor testosterone administration modified the prolactin response to 5-HTP in peripubertal and adult rats. These results appear to indicate that testosterone modulates the serotoninergic control of prolactin secretion during the prepubertal stage. The control of prolactin levels could be one of the mechanisms by which testosterone participates in the sexual maturation.