ASSOCIATIVE LTP OF AREA CA3 IN THE HIPPOCAMPUS IN VIVO

描述：(改编自申请人的摘要)：本项目的总体目标是评估阿片和NMDA受体在诱导海马区CA3区主要传入系统的联合长时程增强(LTP)中的作用。CA3区接受两种形式的LTP诱导传入：NMDA受体和阿片受体依赖。在CA3区的内侧穿支通路和连合投射中可观察到阿片受体依赖的LTP。初步研究表明，苔藓纤维投射到CA3区表现为联合LTP，但联合苔藓纤维LTP的诱导需要重复的突触活动，这是阿片受体激活所必需的。然而，联合苔藓纤维LTP也被NMDA受体拮抗剂阻断。同样，在内侧穿通通路-CA3突触的NMDA受体依赖性LTP的诱导可被阿片受体拮抗剂阻断，当它是由阿片能传入共同激活时。我们的主要假设是阿片受体和NMDA受体都通过这些不同的诱导过程在突触之间促进了联合LTP的诱导。具体目标1的研究将确定阿片和/或NMDA受体拮抗剂是否改变外侧穿支路径CA3突触上阿片受体依赖的LTP和NMDA受体依赖的内侧穿支路径CA3突触之间的联合LTP诱导，使用每个投射作为弱刺激(关联)或强刺激(条件化)途径。具体目标2的研究将确定阿片能传入的联合LTP是否通过频率依赖的阿片肽释放而具有频率依赖性，以及显示阿片受体依赖的LTP的传入的联合LTP是否对非阿片能突触的LTP的诱导产生频率依赖的限制。这将通过使用单脉冲联合范式来确定，在OIoid受体选择性拮抗剂存在的情况下，一条途径的低频刺激与另一条途径的高频刺激配对。具体目标3的研究将确定CA3传入之间联合相互作用的最佳时间参数是否对应于CA3传入的正常激活顺序，以及阿片肽是否参与了这一效应。这些数据将具有关于关联信息存储可能在CA3区域的传入系统之间正常发生的条件的含义。由于每条通路对LTP的联合诱导有不同的要求，内源性阿片肽可能会对LTP的联合诱导施加时间和频率依赖的限制。这可能表明，传入活动和阿片肽释放的顺序可能调节几乎所有发生在海马区CA3区投射之间的关联信息存储。

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.