Bali Balázs, Kovács Krisztina J
Laboratory of Molecular Neuroendocrinology, Institute of Experimental Medicine, P.O. Box 67, H-1450 Budapest, Hungary.
Eur J Neurosci. 2003 Sep;18(6):1518-26. doi: 10.1046/j.1460-9568.2003.02877.x.
To assess the functional impact of local inhibitory gamma-aminobutyric acid (GABA)ergic interneuron population on the cellular and transcriptional activity of parvocellular neurosecretory neurons in the hypothalamic paraventricular nucleus (PVH), we followed the expression of corticotropin-releasing hormone (CRH) and arginine vasopressin (AVP) genes along with the activation marker c-fos in response to the blockade of GABA-A receptors. First, we analysed the effect of the GABA-A receptor antagonist bicuculline methiodide (BMI) in organotypic cultures of hypothalamic slices. These preparations preserve the cytoarchitecture of CRH-synthesizing cell populations and elements of local interneuronal networks, while remote connections originating from limbic- and brainstem areas are missing. In vitro, BMI resulted in a selective induction of c-Fos immunoreactivity that was localized exclusively to the PVH and upregulated both CRH mRNA and AVP hnRNA levels. Local microinjection of BMI into the paraventricular region of freely moving rats increased the adrenocorticotropin secretion and activated PVH neurons ipsilateral to the injection. c-Fos immunoreactivity was distributed within the PVH and in the perinuclear region, where it appeared in GABAergic and also in non-GABAergic profiles. This treatment induced AVP hnRNA expression in the parvocellular compartment without any reliable stimulation of CRH transcription in the parvocellular- and AVP hnRNA levels in the magnocellular neurons. These results reveal an intrinsic GABAergic mechanism in the PVH microenvironment that by itself, without limbic contribution, impinges a tonic inhibitory influence on the parvocellular CRH neurons in vitro. In vivo, remote inputs are superimposed on the local circuit, allowing differential transcriptional regulation of CRH and AVP genes in the hypophysiotropic neurons.
为了评估局部抑制性γ-氨基丁酸（GABA）能中间神经元群体对下丘脑室旁核（PVH）中细小细胞神经分泌神经元的细胞和转录活性的功能影响，我们追踪了促肾上腺皮质激素释放激素（CRH）和精氨酸加压素（AVP）基因的表达以及激活标记物c-fos在GABA-A受体阻断后的反应。首先，我们分析了GABA-A受体拮抗剂甲磺酸荷包牡丹碱（BMI）在下丘脑切片器官型培养物中的作用。这些制剂保留了CRH合成细胞群体的细胞结构和局部中间神经元网络的元素，而来自边缘和脑干区域的远程连接则缺失。在体外，BMI导致c-Fos免疫反应性的选择性诱导，其仅定位于PVH，并上调CRH mRNA和AVP hnRNA水平。将BMI局部微量注射到自由活动大鼠的室旁区域会增加促肾上腺皮质激素分泌，并激活注射同侧的PVH神经元。c-Fos免疫反应性分布在PVH和核周区域，在GABA能和非GABA能细胞中均有出现。这种处理在细小细胞区室诱导了AVP hnRNA表达，而在细小细胞中对CRH转录没有任何可靠的刺激，在大细胞神经元中也没有刺激AVP hnRNA水平。这些结果揭示了PVH微环境中的一种内在GABA能机制，其本身在没有边缘系统贡献的情况下，在体外对细小细胞CRH神经元施加了一种紧张性抑制影响。在体内，远程输入叠加在局部回路之上，允许对促垂体神经元中的CRH和AVP基因进行差异转录调控。
