Benson D L, Huntsman M M, Jones E G
Department of Anatomy and Neurobiology, University of California at Irvine 92717.
Cereb Cortex. 1994 Jan-Feb;4(1):40-51. doi: 10.1093/cercor/4.1.40.
Tachykinin-immunoreactive neurons are a subgroup of the GABA neuronal population in layer IVC of monkey primary visual cortex. Following brief periods of monocular deprivation in adult monkeys, immunoreactivity for both GABA and tachykinins is dramatically reduced in layer IV cells that lie within the deprived ocular dominance columns of this cortical area. The present study shows that these activity-dependent changes are associated with changes in mRNA levels but over different time courses. Radioactive antisense riboprobes derived from monkey-specific cDNAs were used to localize glutamic acid decarboxylase (GAD) and beta-preprotachykinin (beta PPT) mRNAs by in situ hybridization histochemistry. GAD and beta PPT mRNAs decreased in deprived ocular dominance columns of adult monkeys when neural activity was abolished in one eye by intraocular injections of tetrodotoxin (TTX). beta PPT mRNA levels fell within 5 d of deprivation and thus appeared to parallel the fall in immunodetectable tachykinin levels. By contrast, reduced GAD mRNA levels were detectable only after 15 d of deprivation and long after the fall in immunoreactive GAD and GABA levels has maximized. These results suggest that tachykinin gene expression is regulated by transcriptional mechanisms as part of the first response to reduced neural activity whereas the initial downregulation of immunoreactive GAD and GABA depends on posttranscriptional mechanisms. Following a more prolonged period of deprivation, a secondary mechanism for GAD regulation appears to be engaged at the level of gene transcription or possibly by changes in mRNA stability.
速激肽免疫反应性神经元是猴初级视皮层IVC层中GABA神经元群体的一个亚群。成年猴经历短暂的单眼剥夺后，位于该皮层区域被剥夺眼优势柱内的IV层细胞中，GABA和速激肽的免疫反应性显著降低。本研究表明，这些依赖于活动的变化与mRNA水平的变化相关，但时间进程不同。通过原位杂交组织化学，使用源自猴特异性cDNA的放射性反义核糖探针来定位谷氨酸脱羧酶（GAD）和β-前速激肽原（βPPT）mRNA。当通过眼内注射河豚毒素（TTX）使一只眼睛的神经活动被消除时，成年猴被剥夺眼优势柱中的GAD和βPPT mRNA减少。βPPT mRNA水平在剥夺后5天内下降，因此似乎与免疫可检测的速激肽水平下降平行。相比之下，仅在剥夺15天后且在免疫反应性GAD和GABA水平下降达到最大值很久之后，才检测到GAD mRNA水平降低。这些结果表明，速激肽基因表达受转录机制调控，作为对神经活动减少的第一反应的一部分，而免疫反应性GAD和GABA的初始下调依赖于转录后机制。在更长时间的剥夺后，GAD调节的第二种机制似乎在基因转录水平或可能通过mRNA稳定性的变化起作用。
