Lopez H S, Burger B, Dickstein R, Desmond N L, Levy W B
Department of Neurological Surgery, University of Virginia Health Sciences Center, Charlottesville 22908.
Synapse. 1990;5(1):33-47. doi: 10.1002/syn.890050103.
This report further characterizes associative long-term synaptic modification of the ipsilateral and contralateral synapses formed by the bilateral entorhinal cortical (EC) projection to the dentate gyrus (DG). The experimental model is the anesthetized hooded rat. The quantitative results qualify this system as a model for studying the rules of associative synaptic modification formulated in terms of individual synapses. Bilateral DG microelectrodes recorded both ipsilateral and contralateral EC-DG responses before and after brief, high-frequency EC conditioning stimulation. The weak contralateral pathway received high-frequency conditioning before, during, or after similar conditioning of the strong, converging ipsilateral pathway. Statistical analyses revealed two types of significant, dissociated synaptic modifications, which depend on the relationship of the ipsilateral and contralateral afferents. First, contralateral EC-DG responses potentiated or depressed when the converging ipsilateral responses concurrently either potentiated or remained unchanged. Second, contralateral EC-DG responses potentiated, depressed, or showed no change when the collateral ipsilateral responses concurrently either potentiated or remained unchanged. Correlation and contingency table analyses indicated that changes in the contralateral synaptic responses are not well predicted by changes at either neighboring synapses of the converging ipsilateral pathway or at synapses of the collateral ipsilateral pathway. The contingencies of associated pre- and postsynaptic activation determined by the conditioning paradigm, however, accurately predicted the altered synaptic responses of both ipsilateral and contralateral EC-DG pathways. The results imply that associative synaptic modification in the EC-DG system is specific to individual synapses and requires both appropriate presynaptic and postsynaptic activation. Because this system provides suitable controls for nonspecific effects of conditioning stimulation and because modification of neighboring synapses is dissociable, the EC-DG system can be used to study further those rules of activity-dependent associative modification that are formulated in terms of individual synapses. The discussion briefly considers published rules of synaptic modification, pointing out several rules that are not consistent with the experimental observations and one that agrees with the present results.
本报告进一步阐述了双侧内嗅皮质（EC）投射至齿状回（DG）所形成的同侧和对侧突触的联合性长期突触修饰。实验模型为麻醉状态下的带帽大鼠。定量结果表明，该系统可作为一个模型，用于研究依据单个突触制定的联合性突触修饰规则。双侧DG微电极在短暂高频EC条件刺激前后记录同侧和对侧EC-DG反应。在对强的、汇聚性同侧通路进行类似条件刺激之前、期间或之后，对弱的对侧通路进行高频条件刺激。统计分析揭示了两种显著的、分离的突触修饰类型，这取决于同侧和对侧传入神经的关系。首先，当汇聚性同侧反应同时增强或保持不变时，对侧EC-DG反应增强或减弱。其次，当侧支同侧反应同时增强或保持不变时，对侧EC-DG反应增强、减弱或无变化。相关性分析和列联表分析表明，对侧突触反应的变化不能通过汇聚性同侧通路的相邻突触或侧支同侧通路的突触变化得到很好的预测。然而，由条件刺激范式确定的联合性突触前和突触后激活的偶然性，准确地预测了同侧和对侧EC-DG通路突触反应的改变。结果表明，EC-DG系统中的联合性突触修饰是单个突触特有的，并且需要适当的突触前和突触后激活。由于该系统为条件刺激的非特异性效应提供了合适的对照，并且相邻突触的修饰是可分离的，因此EC-DG系统可用于进一步研究那些依据单个突触制定的活动依赖性联合修饰规则。讨论简要考虑了已发表的突触修饰规则，指出了几条与实验观察结果不一致的规则以及一条与当前结果一致的规则。
