Summary:
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-hidroxytryptophan 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 α -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 sensiti- bitity 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.
Key words:
Puberty - GnRH - neurotransmitters - sexual maturation
References
N -methyl-D,L-aspartate in cycling rats.
Endocrinology.
129
3254-3258
1991;
N -methyl-D-aspartate in adult female rats: studies on hypothalamic luteinizing hormone-releasing
hormone and neurotransmitter release.
Neuroendocrinology.
57
710-715
1993;
N -methyl-D-aspartate and on hypothalamic excitatory amino acid levels during sexual
maturation in female rats.
Endocrinology.
130
1365-1370
1992;
N -methyl-D-Aspartate and non N -methyl-D-aspartate receptors of the excitatory amino acids system on LH and FSH secretion.
Its effects on the hypothalamic luteinizing hormone releasing hormone during maturation
in male rats.
Brain Research.
707
139-145
1996;
N -methyl-D-aspartate acid type mediate the increase in luteinizing-hormone releasing
hormone release by excitatory amino acids in vitro.
Endocrinology.
126
414-420
1990;
N -methyl-D,L-aspartate elicits hypothalamic gonadotrophins releasing hormone release
in prepubertal male rhesus monkeys (Macaca mulatta). .
Endocrinolgy.
120
2289-2296
1987;
N -methy-asoartic acid lesions of the arcuate nucleus in adult C57BL/6J mice: a new
model for age related lenghening of estrus cycle.
Neuroendocrinology.
50
605-612
1989;
N -methyl-D-aspartate and/or dizocilpine administration during sexual maturation in
female rats.
Neuroendocrinology.
57
960-964
1993;
N -methyl-D,L aspartic acid in the male rat.
Brain Research.
184
425-437
1980;
γ -aminonobutiric acid (GABA in discrete nuclei of hypothalamus and sustancia nigra.
Brain Research.
125
109-121
1979;
