ASSOCIATIVE LTP OF AREA CA3 IN THE HIPPOCAMPUS IN VIVO

描述：（改编自申请人摘要）：本项目的总体目标是评估阿片和NMDA受体在海马CA3区主要传入系统中诱导联想长期增强（LTP）的作用。CA3区接收的传入事件显示两种形式的LTP诱导：NMDA受体和阿片受体依赖性。阿片受体依赖的LTP在内侧穿通路径和连接到CA3区的投射中被观察到。我们的初步研究表明，苔藓纤维投射到CA3区显示联合LTP，但联合苔藓纤维LTP的诱导需要重复的突触活动，这是激活阿片受体所必需的。然而，联合苔藓纤维LTP也被NMDA受体拮抗剂阻断。同样，当阿片能传入事件共激活时，NMDA受体依赖性LTP在内侧穿透通路- ca3突触的诱导被阿片受体拮抗剂阻断。我们的主要假设是，阿片受体和NMDA受体都利用这些不同的诱导过程促进突触之间的关联性LTP诱导。具体目标1的研究将确定阿片受体和/或NMDA受体拮抗剂是否会改变阿片受体依赖的LTP诱导在侧穿通通路- ca3突触和NMDA受体依赖的内侧穿通通路- ca3突触之间的关联，使用每个投射作为弱刺激（相关）或强刺激（条件作用）途径。具体目标2的研究将确定阿片能传入事件中的关联性LTP是否通过频率依赖性阿片肽释放而具有频率依赖性，以及显示阿片受体依赖性LTP的传入事件中的关联性LTP是否对非阿片能突触的LTP诱导具有频率依赖性约束。这将通过使用单脉冲关联范式来确定，其中一个途径的低频刺激与另一个途径的高频刺激配对，存在类黄酮受体选择性拮抗剂。具体目标3中的研究将确定CA3传入事件之间关联相互作用的最佳时间参数是否符合CA3传入事件激活的正常序列，以及阿片肽是否有助于这种效应。这些数据将对在CA3区域的传入系统之间通常可能发生的关联信息存储的条件具有暗示意义。由于每种途径对LTP的关联诱导都有不同的要求，内源性阿片肽可能对LTP的关联诱导具有时间和频率依赖的限制。这表明传入活动和阿片肽释放的顺序可能调节海马CA3区的投射中发生的几乎所有关联信息存储。

DESCRIPTION: (Adapted From The Applicant's Abstract): The overall goal of this project is to evaluate the contribution of opioid and NMDA receptors in the induction of associative long term potentiation (LTP) in the major afferent systems of the CA3 region of the hippocampus. The CA3 region receives afferents displaying two forms of LTP induction: NMDA receptor and opioid receptor- dependent. Opioid receptor-dependent LTP is observed in medial perforant path and commissural projections to area CA3. Out initial studies show that mossy fiber projections to area CA3 display associative LTP, but associative mossy fiber LTP induction requires repetitive synaptic activity, which is necessary for the activation of opioid receptors. However, associative mossy fiber LTP also is blocked by NMDA receptor antagonists. Likewise, the induction of NMDA receptor-dependent LTP at medial perforant path-CA3 synapses is blocked by opioid receptor antagonists when it is induced by coactivation of opioidergic afferents. Our primary hypothesis is that both opioid and NMDA receptors contribute to associative LTP induction between synapses utilizing these different induction processes. The studies in specific aim 1 will determine if opioid and/or NMDA receptor antagonists alter associative LTP induction between the opioid receptor-dependent LTP at lateral perforant path-CA3 synapses and NMDA receptor-dependent medial perforant path-CA3 synapses using each projection as either the weakly stimulated (associated) or the strongly stimulated (conditioning) pathway. The studies in specific aim 2 will determine if associative LTP in opioidergic afferents is frequency-dependent by virtue of frequency-dependent opioid peptide release, and if associative LTP in afferents displaying opioid receptor-dependent LTP confer frequency-dependent constraints on LTP induction at non- opioidergic synapses. This will be determined by using a single- pulse associative paradigm, in which low frequency stimulation of one pathway is paired with high-frequency stimulation of another pathway in the presence of oioid receptor selective antagonists. The studies in specific aim 3 will determine if the optimal temporal parameters of associative interaction among CA3 afferents corresponds to the normal sequence of activation by CA3 afferents, and if opioid peptides contribute to this effect. These data will have implication regarding conditions in which associative information storage may normally occur among the afferent systems of the CA3 region. Because each pathway displays distinct requirements for associative LTP inductions, endogenous opioid peptides may confer both temporal and frequency-dependent constraints on the associative induction of LTP. This would suggest that the order of afferent activity and opioid peptide release may regulate virtually all associative information storage occurring among projections to the CA3 region of the hippocampus.