Changes in the control of gonadotrophin secretion by neurotransmitters during sexual development in rats

Abstract

Gonadotrophin hormone releasing hormone (GnRH) is the primary messenger involved in sexual maturation and the onset of puberty. The activity of these neurons are controlled by several neurotransmitters systems. The onset of puberty implies changes from a prepubertal type of gonadotrophin secretion, characterized by a low activity of GnRH neurons, to an adult pattern of secretion with phasic and synchronous activation of GnRH neurons resulting in an increase in the amplitute and frequency of GnRH pulses. Neurotransmitter systems are involved in these changes of GnRH secretion during the onset of puberty by quantitative and qualitative modifications in the effect on GnRH secretion. Serotonin (5-HT), GABA and catecholamines (CA) have qualitative differences in the effects on GnRH and LH secretion in early prepubertal than in late prepubertal and adult female rats. The administration of 5-hydroxytryptophan a precursor of serotonin (5-HT) which increases 5-HT hypothalamic levels induces GnRH and LH release in early prepubertal female rats, these effects dissapear in late prepubertal stage having an inhibitory action in adult female rats. GABAergic system also stimulates GnRH and LH secretion in early prepubertal female rats and has an inhibitory action on this axis in late prepubertal period and in adult female rats. On the contrary the inhibition of catecholamines synthesis by alpha-methyl-p-tyrosine induced an increase of LH secretion in early prepubertal female rats and inhibitory effect in late prepubertal and adult stage. These effects indicate tha CA has an inhibitory effects on GnRH-LH secretion in early prepubertal female rats changing to an stimulatory action in the late puberty and adult rats. These qualitative modifications were observed only in female rats and are probably connected with the hypothalamic differentiation into a female type of gonadotrophin control. Opiadergic and excitatory amino acid systems have quantitative differences on GnRH-LH secretion during prepubertal and peripubertal and adult stages. Opiates has an high inhibitory tone in early prepubertal rats that is decreasing during sexual maturation to reach puberty. On the contrary EAA increases its stimulatory activity on GnRH-LH secretion during sexual maturation by increasing the hypothalamic release of aspartate and glutamate, the excitatory amino acids involved in GnRH release, and the sensibility of NMDA receptors to these amino acids. In conclusion sexual maturation and the onset of puberty in the female rats involve qualitative and quantitative modifications in the effects of neurotrasmitters system on GnRH secretion.

Postnatal development and gender‐dependent expression of TIP39 in the rat brain

“…Areas that contain TIP39 neurons are involved in sexual (Coolen et al, 2004;Holstege et al, 2003) and maternal functions (Li et al, 1999;Lin et al, 1998), suggesting that TIP39 may be as well. Nociception (Hamm and Knisely, 1988), hearing (Geal-Dor et al, 1993), endocrine functions (Eden, 1979;Moguilevsky and Wuttke, 2001) and clearly sexual functions (Lamming, 1994), undergo profound postnatal development in the rat. Bearing in mind that TIP39's homologue, PTHrP, has well-established effects on the development of many tissues (Kronenberg et al, 1998) and that TIP39 can affect the proliferation of some cell types in vitro (Misiano et al, 2003), the transient expression of TIP39 during postnatal development suggests that this peptide may be involved in developmental aspects of the above mentioned brain functions.…”

Serotonin stimulates GnRH secretion through the c-Src-PLC γ1 pathway in GT1–7 hypothalamic cells

“…Following earlier reports that implicated serotonin in the development and migration of GnRH neurons (Pronina et al 2003), a great deal of attention has become focused on the role of serotonin in GnRH release (Moguilevsky & Wuttke 2001, Wada et al 2006. The demonstration of synaptic contacts between the serotoninergic system and the GnRH neurons suggested that serotonin could act directly on GnRH release.…”

“…The secretion of GnRH is modulated by neurotransmitters (Moguilevsky & Wuttke 2001), catecholamines (Becu-Villalobos & Libertun 1995), and neuropeptides (Woller et al 1992). Within the hypothalamus, the auto-regulatory control of GnRH neural activity is integrated with other hormonal inputs to provide a more complex control system.…”

Reversal of the hypothalamo-pituitary–adrenal response to oestrogens around puberty

“…No such studies have been done in prepubertal females. However, a review by Moguilevsky & Wuttke (2001) discusses evidence showing that catecholaminergic effects on the HPG axis display qualitative changes over the pubertal period. First, GABAergic systems have a stimulatory effect before puberty, which becomes inhibitory by adulthood.…”