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

Abstract

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.

Amino Acid Levels in the Hypothalamus and Response to N-Methyl-D-Aspartate and/or Dizocilpine Administration during Sexual Maturation in Female Rats

“…We have recently demonstrated that the administra tion of sexual steroid hormones to female rats induces different changes in the hypothalamic content of amino acid before or after sexual maturation [24], and we have also postulated the maturation of new intemeuronal cir cuits during sexual maturation [25][26][27]. In order to in vestigate the possibility that sexual maturation might be accompanied by changes in the endogenous amino acid concentration in the hypothalamus and in the response of these neurons to stimulation or blockade of the NMDA receptor, the endogenous amino acid concen tration and the effect of pharmacological manipulation of the NMDA receptor on amino acid content in cer tain hypothalamic areas were measured in the present study.…”

Changes in the Hypothalamic Interaction between Norepinephrine and Prostaglandin E₂ during Sexual Maturation in Female Rats

“…It is probable that this change is connected with the modifications in the effect of catecholamines on gonadotropin secretion during sexual development previously described [12] as well as with an increase of rxr adrenoreceptors probably induced by an 229 increase of E2 activity during the maturational period [17]. Experiments are now in progress in order to clarify these points.…”

“…the decrease in the inhibitory action of opiates on LHRH neurons [22], the increase in the LHRH release effect of excitatory amino acids [23], etc. For instance, catecholamines have a predominantly inhibito ry effect on gonadotropin secretion in prepubertal rats while stimulating these pituitary hormones in peripuber tal and adult rats [12]. In a similar way, the possibility arises that the lack of effect of NE on PGE2 in prepubertal rats represents the existence, during sexual maturation, of a different qualitative relationship among the neurotrans mitters involved in gonadotropin secretion.…”

“…In previous papers, we have demonstrated that the serotoninergic, catecholaminergic and GABAergic control of the LHRH-LH system is qualitatively different between prepubertal (younger than 21 days of age) and peripubertal female rats [11][12][13]. For instance, catecholamines exert a stimulatory effect of gonadotropin secretion in peripuber tal and adult female rats but have an inhibitory action in prepubertal female rats [ 12], We have proposed that sexual maturation and the onset of puberty involve the develop ment of new mechanisms of gonadotropin control different from those operating in immature rats.…”

Serotoninergic system blockage in the prepubertal rat inhibits spermatogenesis development

“…The effects of serotonin and other catecholamines, and neurotransmitters such as GABA, on the hypothalamus change during pubertal development (Moguilevsky et al 1990(Moguilevsky et al , 1991. Distinct and well-defined populations of germ cells interact with Sertoli cells in a cyclic pattern.…”