大鼠海马CA_3区的习得性长时程突触增强

THE LEARNING DEPENDENT LONG-TERM SYNA PTIC POTENTIATION IN THE RAT HIPPOCAMPAL CA_3 REGION

本实验应用慢性埋植电极技术以电生理学结合行为学的方法,观察大鼠条件性饮水反应的建立、消退和再建立过程中,其海马CA_3区突触效应的变化规律。以刺激内嗅区的穿通纤维(PP)诱发的单突触的群体锋电位(PS)及群体兴奋性突触后电位(EPSPs)为指标,经叠加处理分析,发现随着条件反应的建立,海马CA_3锥体细胞出现突触效应的长时程增强(LTP),它随行为反应的实验性消退而消退,而在随后再次建立条件反应时,又重新出现;且无论此LTP达最高水平还是它的完全消退均超前于条件性行为反应的水平。又在一个实验日训练作业结束时PS并未立即随之增大,在24h内它随时间而发展,但到第4小时已达最高水平,且条件反应率是与PS的水平相应的,对PS与EPSPs的斜率进行相关分析表明,PS的变化主要是突触传递功效的变化。上述结果表明,海马CA_3区随着行为训练有习得性LTP产生。从其发神变化特点及其与条件性行为的关系,提示此习得性LTP极其可能是本实验中学习和记忆的展经基础。

The purpose of this study is to investigate the changes of synaptic efficacy in the rat hippocampal CA_3 region during establishment, extinction and re-establishment of conditioned drink response by means of implanted electrodes and behavioral observation. The monosynaptic population excitatory postsynaptic potential (EPSPs) and population spike (PS) elicited by stimulating the perforant path were recorded. The results showed that the long-term potentiation (LTP) in the hippocampal CA_3 region appeared with the establishment of conditioned response, the LTP extinguished with experimental extinction of conditioned response and reappeared during the re-establishment of conditioned response. Moreover, both maximal level of LTP and its complete extinction preceded those of conditioned behavior, suggesting that the LTP was learning-dependent. In addition, the enhanced PS was not presented immediately after behavioral training, and developed Within subsequent 24h, with a maximum at the 4th hour. The magnitude of conditioned response depended on the level of LTP. A cross-correlation analysis of the slopes of PS and EPSPs indicated that the changes of PS were caused by alterations of synaptic transmission. These results suggest that the learning-dependent LTP might be one of the neuronal substrates underlying behavioral learning and memory.