Moguilevsky J A, Wuttke W
Department of Physiology Buenos Aires Medical School, Argentina.
Exp Clin Endocrinol Diabetes. 2001;109(4):188-95. doi: 10.1055/s-2001-15105.
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.
促性腺激素释放激素（GnRH）是参与性成熟和青春期启动的主要信使。这些神经元的活动受多种神经递质系统控制。青春期的启动意味着从青春期前促性腺激素分泌类型的变化，其特征是GnRH神经元活性低，转变为成年分泌模式，GnRH神经元呈阶段性和同步激活，导致GnRH脉冲的幅度和频率增加。神经递质系统通过对GnRH分泌影响的定量和定性改变，参与青春期启动期间GnRH分泌的这些变化。血清素（5-HT）、γ-氨基丁酸（GABA）和儿茶酚胺（CA）对青春期前早期雌性大鼠GnRH和促黄体生成素（LH）分泌的影响与青春期后期和成年雌性大鼠存在质的差异。给予5-羟色氨酸（血清素（5-HT）的前体，可增加下丘脑5-HT水平）可诱导青春期前早期雌性大鼠释放GnRH和LH，这些作用在青春期后期消失，在成年雌性大鼠中具有抑制作用。GABA能系统在青春期前早期雌性大鼠中也刺激GnRH和LH分泌，在青春期后期和成年雌性大鼠中对该轴具有抑制作用。相反，α-甲基-对-酪氨酸抑制儿茶酚胺合成，在青春期前早期雌性大鼠中诱导LH分泌增加，在青春期后期和成年期具有抑制作用。这些作用表明，CA在青春期前早期雌性大鼠中对GnRH-LH分泌具有抑制作用，在青春期后期和成年大鼠中转变为刺激作用。这些质的改变仅在雌性大鼠中观察到，可能与下丘脑分化为雌性促性腺激素控制类型有关。阿片肽能和兴奋性氨基酸系统在青春期前、青春期前后和成年期对GnRH-LH分泌存在量的差异。阿片类物质在青春期前早期大鼠中具有高抑制性张力，在性成熟过程中降低直至青春期。相反，兴奋性氨基酸在性成熟过程中通过增加下丘脑天冬氨酸和谷氨酸（参与GnRH释放的兴奋性氨基酸）的释放以及NMDA受体对这些氨基酸的敏感性，增强其对GnRH-LH分泌的刺激活性。总之，雌性大鼠的性成熟和青春期启动涉及神经递质系统对GnRH分泌影响的质和量的改变。
