흰쥐 치아이랑(dentate gyrus) 과립세포들의 발생과 세포자연사는 일생을 통하여 계속 진행된다는 것이 알려져 있다. 본 연구는 허혈에 의한 성체 흰쥐 치아이랑의 세포자연사(apoptosis)와 신경발생(neurogenesis)의 연관성을 알아보기 위하여 수행되었다. TUNEL 실험에서 허혈로 초래된 세포자연사는 치아이랑의 과립세포층 (granular zone)에서 주로 발생하였으며, proliferating cell nuclear antigen (PCNA)와 synapsin-α를 이용한 면역세포학적 실험에서 신경발생은 주로 치아이랑의 과립세포하층(subgranular zone)에서 일어나며, 세포자연사에 비하여 늦게 진행되는 것이 관찰되었다. 또한 세포자연사와 신경발생에 관련된 Bcl-2 발현의 증가는 치아이랑 과립세포하층에서의 신경발생 시기와 일치하였으나 과립세포층의 세포자연사의 시기와는 일치하지 않았다. 이는 허혈이 치아이랑의 과립세포층에서의 세포자연사와 과립세포하층에서의 신경발생을 동시에 촉진함을 의미한다. 한편, NR2A와 NR2B의 anti-sense probe를 이용한 in situ hybridization에서는 허혈로 인한 NMDA 수용체의 유의한 감소가 치아이랑에서 관찰되었다. 이는 허혈이 치아이랑 과립세포들의 NMDA 수용체의 숫적 감소를 야기함으로서 치아이랑 과립세포하층에서의 신경발생을 촉진시킬 수 있는 가능성을 제시하고 있다.
It has been known that granule neurons of the dentate gyrus (DG) are born in adulthood as well as during development. Apoptotic cell death also occurs normally throughout the life of the rat brain. The present study was designed to determine the effect of transient global ischemia on the apoptosis and/or neurogenesis of granule cells in the dentate gyrus. TUNEL study revealed that the ischemia produced an significant increase in apoptosis mainly in the granular zone (GZ) of the DG. The percentage of TUNEL-positive cells in the DG was maximal (37.3±2.5%) 8 hr after ischemia and declined thereafter. However, immunocytochemical studies showed that there was an increase in neurogenesis mainly in the subgranular zone (SGZ) although the induction of neurogenesis took longer than the apoptosis. As a neurogenesis marker, proliferating cell nuclear antigen (PCNA)-positive cells, possibly progenitor cells, were significantly increased by 34.1±2.2% (n = 3, p⁄0.05) mainly in the dentate SGZ 4 days after ischemia. In addition, the gradual increase in Bcl-2 expression was only paralleled with the neurogenesis in the SGZ, but not with the apoptosis in the GZ of the DG. The expression level of Bcl-2 in the SGZ was increased significantly (optical density 43.7±3.4; n = 3, p⁄0.05) 4 days after the ischemic insult. Furthermore, the ischemia-induced neurogenesis in the SGZ was also indirectly supported by the observation that the expression of synapsin-α was significantly increased (176%; n = 3 p⁄0.05) in the CA3 region 4 days after the ischemia. Taken together, these results strongly suggest that the transient global ischemia induces the apoptosis in the GZ, whereas the cell proliferation in the SCZ of the DG. In situ hybridization using the antisense probes to the NR2A and NR2B subunits of NMDA receptors revealed that the ischemia produced a more profound effect on the mRNA expression of NR2A (61.9% reduction) than NR2B (20.5% reduction). Thus, we also suggest a possibility that ischemia could induce the neurogenesis in the SGZ of the DG through downregulation of the number of functional NMDA receptors.
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