Li H, Siegel R E, Schwartz R D
Department of Pharmacology, Duke University Medical Center, Durham, NC 27710.
Hippocampus. 1993 Oct;3(4):527-37. doi: 10.1002/hipo.450030412.
Inhibitory neurotransmission may play an important role in neuronal degeneration following transient cerebral ischemia. We studied the effect of transient forebrain ischemia on the GABAA receptor system in the gerbil hippocampus. Gerbils were subjected to 5 minutes of bilateral carotid occlusion and were sacrificed at various times over 4 days following reperfusion. There was a substantial loss of pyramidal cells in the CA1 area of the hippocampus 4 days following ischemia. No cell loss was detected in CA3 pyramidal cells of the hippocampus, granule cell layer of the dentate gyrus, and ventroposterior medial and ventroposterior lateral nuclei of the thalamus at any time following ischemia. Examination of brain slices by in situ hybridization histochemistry revealed that a change in expression of the GABAA receptor alpha 1 and beta 2 subunit mRNAs occurred in two phases following onset of reperfusion. The early phase (rapid) occurred within the first 4 hours following reperfusion. The expression of mRNAs significantly decreased (up to 25%) within 1 hour after occlusion in CA1 and CA3 pyramidal cell layers of the hippocampus and in the granule cell layer of the dentate gyrus. The expression of the mRNAs in these regions continued to decrease for 4 hours (up to 43%). In the second phase, which began between 4 and 12 hours following reperfusion, mRNA expression started to return to control levels in CA3 hippocampus and in the dentate. However, expression of both mRNAs continued to decline slowly in the CA1 pyramidal cell layer (up to 85%) over the next 3 days, concomitantly with degeneration of the CA1 pyramidal cells. Expression of mRNAs in the ventroposterior medial or ventroposterior lateral nuclei of the thalamus was similar to control values. To determine if a change in GABAA receptor distribution paralleled changes in receptor subunit mRNA expression, we also measured the binding of [35S]t-butylbicyclophosphorothionate to GABAA receptor chloride channels. The t-butylbicyclophosphorothionate [35S] binding decreased between 1 and 4 days after reperfusion in the dendritic fields of CA1 pyramidal cells (strata oriens, radiatum, and lacunosum-moleculare) but not in the pyramidal cell body layer. These results indicate that expression of GABAA receptor subunit mRNAs decrease well before CA1 pyramidal cell degeneration and loss of GABAA receptors. At present, it is not clear if an early loss of mRNA expression after an ischemic insult leads to a functional defect in GABAA receptors. If so, a loss of GABA neurotransmission may contribute to the development of neuronal degeneration following cerebral ischemia.(ABSTRACT TRUNCATED AT 400 WORDS)
抑制性神经传递可能在短暂性脑缺血后的神经元变性中起重要作用。我们研究了短暂性前脑缺血对沙鼠海马中GABAA受体系统的影响。对沙鼠进行5分钟的双侧颈动脉闭塞，并在再灌注后的4天内不同时间点处死。缺血后4天，海马CA1区的锥体细胞大量丢失。在缺血后的任何时间，海马CA3锥体细胞、齿状回颗粒细胞层以及丘脑腹后内侧核和腹后外侧核均未检测到细胞丢失。通过原位杂交组织化学检查脑切片发现，再灌注开始后，GABAA受体α1和β2亚基mRNA的表达变化分为两个阶段。早期阶段（快速）发生在再灌注后的前4小时内。海马CA1和CA3锥体细胞层以及齿状回颗粒细胞层在闭塞后1小时内，mRNA表达显著下降（高达25%）。这些区域的mRNA表达在接下来的4小时内持续下降（高达43%）。在第二阶段，开始于再灌注后的4至12小时之间，海马CA3区和齿状回的mRNA表达开始恢复到对照水平。然而，在接下来的3天里，CA1锥体细胞层中两种mRNA的表达继续缓慢下降（高达85%），与此同时CA1锥体细胞发生变性。丘脑腹后内侧核或腹后外侧核中mRNA的表达与对照值相似。为了确定GABAA受体分布的变化是否与受体亚基mRNA表达的变化平行，我们还测量了[35S]叔丁基双环磷硫代酸盐与GABAA受体氯离子通道的结合。再灌注后1至4天，CA1锥体细胞树突区域（原层、辐射层和分子层）中[35S]叔丁基双环磷硫代酸盐的结合减少，但在锥体细胞体层未减少。这些结果表明，GABAA受体亚基mRNA的表达在CA1锥体细胞变性和GABAA受体丢失之前就显著下降。目前尚不清楚缺血性损伤后mRNA表达的早期下降是否会导致GABAA受体功能缺陷。如果是这样，GABA神经传递的丧失可能会导致脑缺血后神经元变性的发展。（摘要截短至400字）
