Stroh T, Kreienkamp H J, Beaudet A
Montreal Neurological Institute, McGill University, Montreal, Quebec H3A 2B4, Canada.
J Comp Neurol. 1999 Sep 13;412(1):69-82. doi: 10.1002/(sici)1096-9861(19990913)412:1<69::aid-cne5>3.0.co;2-v.
Somatostatin exerts its actions by means of a family of G protein-coupled receptors, five of which have so far been cloned. Whereas mRNAs for receptor subtypes sst(1)-sst(4) have been unequivocally localized in the brain, the data concerning the fifth subtype, sst(5), are contradictory. Moreover, whereas sst(1) and sst(2A) receptor proteins have been localized by immunohistochemistry, the distribution of sst(3)-sst(5) receptor proteins and/or subtype-specific binding remains to be determined in the central nervous system. In the present study, we investigated the distribution of immunoreactive sst(5) in adult rat brain and pituitary and demonstrated the presence of this receptor protein in the central nervous system by using an affinity-purified antibody generated against the C-terminus of the receptor. The specificity of the antibody for sst(5) was established by immunoblotting experiments on membranes prepared from cells transfected with cDNA encoding different somatotropin release inhibiting (SRIF) receptor subtypes as well as from anterior pituitary. In both systems, the antibody specifically recognized a band at approximately 50 kDa molecular mass, corresponding well to the reported size of the cloned receptor (48 kDa). Immunofluorescence in COS-7 cells transfected with individual SRIF receptor subtypes as well as in sections of rat pituitary demonstrated the antibody's applicability to the immunohistochemical detection of sst(5) receptors. In rat brain sections, sst(5) immunoreactivity was predominantly associated with neuronal perikarya and primary dendrites. Immunolabeling was most prominent in the olfactory tubercle, islands of Calleja, diagonal band of Broca, substantia innominata, and magnocellular preoptic nucleus of the basal forebrain as well as in the reticular nucleus of the thalamus. Other, less intensely labeled areas included the cerebral cortex, hippocampus, amygdala, preoptic area as well as the lateroanterior nucleus of the hypothalamus. The present findings provide the first characterization of the anatomic distribution of sst(5) receptors in the rat brain. They demonstrate a prominent expression of these receptors in the basal forebrain, suggesting that they may be involved in the mediation of somatostatin effects on the sleep-wake cycle through their association with cortically projecting subcortical systems.
生长抑素通过一类G蛋白偶联受体发挥其作用，目前已克隆出其中的五种。虽然受体亚型sst(1)-sst(4)的mRNA已明确在脑中定位，但关于第五种亚型sst(5)的数据却相互矛盾。此外，虽然sst(1)和sst(2A)受体蛋白已通过免疫组织化学定位，但sst(3)-sst(5)受体蛋白的分布和/或亚型特异性结合在中枢神经系统中仍有待确定。在本研究中，我们调查了成年大鼠脑和垂体中免疫反应性sst(5)的分布，并通过使用针对该受体C末端产生的亲和纯化抗体，证实了该受体蛋白在中枢神经系统中的存在。通过对用编码不同生长抑素释放抑制（SRIF）受体亚型的cDNA转染的细胞以及垂体前叶制备的膜进行免疫印迹实验，确定了该抗体对sst(5)的特异性。在这两个系统中，该抗体均特异性识别一条分子量约为50 kDa的条带，与报道的克隆受体大小（48 kDa）相符。在用单个SRIF受体亚型转染的COS-7细胞以及大鼠垂体切片中的免疫荧光显示了该抗体在sst(5)受体免疫组织化学检测中的适用性。在大鼠脑切片中，sst(5)免疫反应性主要与神经元胞体和初级树突相关。免疫标记在嗅结节、卡耶哈岛、布罗卡斜带、无名质、基底前脑的大细胞视前核以及丘脑网状核中最为明显。其他标记较弱的区域包括大脑皮层、海马体、杏仁核、视前区以及下丘脑的外侧前核。本研究结果首次对大鼠脑中sst(5)受体的解剖分布进行了表征。它们表明这些受体在基底前脑有显著表达，提示它们可能通过与投射到皮层的皮层下系统相关联，参与生长抑素对睡眠-觉醒周期的调节作用。
