GABAERGIC CONTROL OF LHRH NEURONAL FUNCTION

γ-氨基丁酸(GABA)是中枢神经系统中的主要抑制性神经递质，在控制下丘脑LHRH的分泌中起着重要作用。现在看来，通过GABA/A受体(GABA-AR)施加的GABA能控制是在LHRH神经元发育的早期建立的，并在LHRH神经元网络的整个自然历史中继续发挥作用。这种调节影响的一部分很可能是直接作用于LHRH神经元，因为它们表达组装功能性GABA-AR所需的所有受体亚单位。虽然最近的研究表明GABA-AR激活对LHRH神经元迁移具有调制作用，但这种作用是否直接作用于LHRH神经元尚不清楚。同样，对LHRH神经元上的GABA能神经支配对成年生殖功能控制的生理影响也一无所知。由于GABA影响的神经元回路的复杂性和GABA-AR系统的分子复杂性，通过传统的神经内分泌实验很难解决这些问题。最近以细胞特异性和时间受限的方式改变基因表达的遗传学方法的发展，以及参与GABA-AR介导的信号转导的一些关键成分的鉴定，为我们提供了一个独特的机会来揭示GABA能控制生殖功能的一些基本机制。在这项研究中，我们提出了一种遗传学和神经内分泌相结合的方法来确定GABA在LHRH神经元胚胎发育和成年期LHRH神经网络功能能力中的作用。1)GABA能直接兴奋性输入对LHRH神经元的迁移和发育起作用。2)成年LHRH神经元直接接受GABA-AR介导的信息输入是正常生殖周期所必需的LHRH神经元网络的调节成分。3)选择性破坏LHRH神经元中的GABA-ARβ/3亚单位导致下丘脑性腺功能低下；4)GABA释放的定点和时间特异性、可逆性激活足以扰乱非人类灵长类动物的月经周期，从而在实验环境中重现人类下丘脑闭经综合征。我们预计这些研究将有助于更好地理解人类综合征(如下丘脑闭经和特发性下丘脑性腺功能低下症)中生殖能力中枢丧失的细胞机制。

Gamma aminobutyric acid (GABA), the dominant inhibitory neurotransmitter in the central nervous system plays a prominent role in the control of hypothalamic LHRH secretion. It now appears that a GABAergic control exerted via GABA/A receptors (GABA-AR) is established during early LHRH neuronal development and continues to operate throughout the natural history of the LHRH neuronal network. It is likely that part of this regulatory influence is exerted directly on LHRH neurons, as they express all of the receptor subunits required for the assembly of functional GABA-AR. Although recent studies have demonstrated a modulatory effect of GABA-AR activation on LHRH neuronal migration, it is not known if such an effect is directly exerted on LHRH neurons. Likewise, nothing is known about the physiological impact that the GABAergic innervation on LHRH neurons may have on the control of adult reproductive function. Resolution of these issues by conventional neuroendocrine experimentation is difficult, because of the intricacy of the neuronal circuities affected by GABA and the molecular complexity of the GABA-AR system. The recent development of genetic approaches to modify the expression of genes in a cell-specific and temporally- restricted manner, and the identification of some of the key components involved in GABA-AR-mediated signaling, provide us with a unique opportunity to unravel some of the basic mechanisms underlying the GABAergic control of reproductive function. In this study, we propose a combination of genetic and neuroendocrine approaches to define the contribution of GABA to the embryonic development of LHRH neurons and to the functional competencies of the LHRH neuronal network during adulthood. To this end, the following aims are proposed to test the hypotheses that: 1) Direct GABAergic excitatory inputs play a role in the migration and developmental rate of LHRH neurons. 2) The direct GABA-AR-mediated input received by adult LHRH neurons is a regulatory component of the LHRH neuronal network required for normal reproductive cyclicity. 3) Selective disruption of the GABA-AR beta/3 subunit in LHRH neurons results in hypothalamic hypogonadism, and 4) A site- and time- specific, reversible activation of GABA release suffices to disrupt menstrual cyclicity in non-human primates, thus re-creating in an experimental setting the human syndrome of hypothalamic amenorrhea. We anticipate that these studies will lead to a better understanding of the cellular mechanisms underlying the central loss of reproductive competence in human syndromes such as hypothalamic amenorrhea and idiopathic hypothalamic hypogonadism.