Inglefield J R, Sieghart W, Kellogg C K
Department of Neurobiology and Anatomy, University of Rochester, NY 14627.
J Chem Neuroanat. 1994 Oct;7(4):243-52. doi: 10.1016/0891-0618(94)90016-7.
This study examined both the function of the GABAA receptor complex and the expression of its alpha 1, alpha 2 and alpha 3 subunits within the hypothalamus as compared to that of the cerebral cortex. A large number of different GABAA receptor subunit combinations potentially exist in various brain regions which, presumably, would intimate differing receptor structure and function. Here, we present evidence that the average functional characteristics of GABAA receptors within the rat hypothalamus are considerably different from those of the cerebral cortex. We assessed two neurochemical measures of GABAA receptor function: namely, chloride-facilitation of [3H]flunitrazepam binding and GABA-mediated 36chloride uptake. [3H]Flunitrazepam binding in the rat cortex was facilitated by increasing concentrations (12.5-500 mM) of chloride, and this facilitation was responsive to 15 min restraint. Yet, hypothalamic [3H]flunitrazepam binding was not responsive to increasing chloride-concentration in either the basal or restraint conditions. Also, maximal facilitation of GABA-mediated 36chloride uptake was significantly blunted in the hypothalamus relative to cortex (7.4 +/- 0.9 versus 35.8 +/- 1.5 nmoles/mg protein, respectively). While in vitro addition of 10 microM diazepam shifted GABA-mediated 36chloride uptake curves of the cortex to the left, diazepam addition appeared to be without effect in the hypothalamus. However, the blunted maximal facilitation of GABA on hypothalamic 36chloride uptake made accurate determination of the EC50 for the diazepam-potentiation difficult. In addition to these functional disparities between the regions, differences in subunit expression were also apparent. Distributions of alpha 1, alpha 2 and alpha 3 subunit immunoreactivities within cingulate, parietal and temporal cortices and 8 major hypothalamic regions were assessed. Staining of the alpha 1 subunit was prevalent throughout the hypothalamus and cortex, and dense in both regions. However, the alpha 2 and alpha 3 subunits, while of intermediate density in cortex, were of low density or absent (alpha 3) in the hypothalamus. The alpha 2-immunoreactivity was restricted to cell bodies of the arcuate nucleus, dorsomedial nucleus and overlying dorsal area and to neuropil staining of the median eminence. Thus, functional responsiveness of the GABAA receptor differs in the hypothalamus relative to the cortex and this would seem related to the presence of different receptor alpha subunits in homogenate preparations of the two regions.
本研究检测了与大脑皮层相比，下丘脑内GABAA受体复合物的功能及其α1、α2和α3亚基的表达。大量不同的GABAA受体亚基组合可能存在于不同脑区，据推测，这意味着不同的受体结构和功能。在此，我们提供证据表明，大鼠下丘脑内GABAA受体的平均功能特性与大脑皮层的有显著差异。我们评估了GABAA受体功能的两种神经化学指标：即[3H]氟硝西泮结合的氯化物促进作用和GABA介导的36氯化物摄取。大鼠皮层中[3H]氟硝西泮的结合可被氯化物浓度增加（12.5 - 500 mM）所促进，且这种促进作用对15分钟的束缚有反应。然而，下丘脑内[3H]氟硝西泮的结合在基础状态或束缚状态下对氯化物浓度的增加均无反应。此外，相对于皮层，下丘脑内GABA介导的36氯化物摄取的最大促进作用明显减弱（分别为7.4±0.9与35.8±1.5纳摩尔/毫克蛋白）。虽然体外添加10微摩尔/升地西泮可使皮层的GABA介导的36氯化物摄取曲线向左移动，但地西泮添加在下丘脑似乎没有作用。然而，GABA对下丘脑36氯化物摄取的最大促进作用减弱使得准确测定地西泮增强作用的半数有效浓度（EC50）变得困难。除了这些区域间的功能差异外，亚基表达的差异也很明显。评估了扣带回、顶叶和颞叶皮层以及8个主要下丘脑区域内α1、α2和α3亚基免疫反应性的分布。α1亚基的染色在下丘脑和皮层中普遍存在，且在两个区域都很密集。然而，α2和α3亚基虽然在皮层中密度中等，但在下丘脑中密度较低或不存在（α3）。α2免疫反应性仅限于弓状核、背内侧核及其上方背侧区域的细胞体以及正中隆起的神经毡染色。因此，下丘脑内GABAA受体的功能反应性相对于皮层有所不同，这似乎与这两个区域匀浆制剂中不同受体α亚基的存在有关。
