慢性不可预见性应激中5-HT1B受体持续增强Temporoammonic-CA1兴奋性突触传递的机制研究

The biological basis of disturbed cognitive processing in major depressive disorders remains unknown. Antidepressant medications alter monoamine concentrations, particularly serotonin, but it remains uncertain which downstream molecular events affected by serotonin are critical to their therapeutic effects on cognitive function.. PRELIMINARY RESULTS: Endogenous serotonin induced by bath application of antidepressants selectively potentiates excitatory synapses formed by the temporo-ammonic pathway with CA1 pyramidal cells, without affecting nearby Schaffer collateral synapses. This potentiation is expressed postsynaptically by AMPA-type glutamate receptors, and required CaM-dependent protein kinase mediated phosphorylation of GluR1 subunits at the PKC/CaMKII Ser831 site. The effects of 5-HT1B receptor activation on TA-CA1 synaptic transmission are greatly altered in rats subjected to chronic unpredictable stress (CUS), a valid animal model of depression. In CUS animals, activation of 5-HT1B receptors induces a persistent potentiation on TA-CA1 (f)EPSPs. SPECIFIC AIMS: 1. Determine whether the malfunction of 5-HT1B on TA-CA1 synapses is involved in the etiology of depression. 2. Determine how potentiation of TA-CA1 synaptic transmission by 5-HT1B receptor is altered after chronic unpredictable stress. 3. Test the function of 5-HT1B receptor-mediated potentiation of TA-CA1 synaptic transmission on the dendritic integration of CA1 neurons and its alteration in depression. RESEARCH DESIGN: We will combine electrophysiological techniques, including glutamate uncaging, patch-clamp, with molecular biological techniques such as transfection with superecliptic pHluorin-GluR1, western blotting, and biotinylation assays, to investigate the actions of 5-HT1B receptors in hippocampal slices taken from control animals and animals subjected to CUS. OUTCOMES: The proposed project will help us to answer whether depression results, in part, from a dysregulation of the strength of excitatory synaptic transmission in brain regions involved in cognitive and emotional function and determine the key molecular event(s) involved in alterations of serotonin action on these excitatory synapses in depression. A better understanding of serotonin actions and their alteration by chronic stress will lead to improved antidepressant treatment strategies.

抑郁症的病理及抗抑郁药的作用机制，尤其是抗抑郁药物在突触间隙急性升高单胺类递质之后的事件，尚不清楚。预实验结果显示，内源性的5-HT通过激活5-HT1B受体，增强CaMKII和GluR1 Ser831的磷酸化,从而选择性地加强Temporoammonic-CA1（TA-CA1）突触的兴奋性突触传递。在慢性不可预见性应激抑郁症动物模型中，选择性地激动5-HT1B受体引起TA-CA1突触传递的持续性增强。本项目拟采用脑内药物微量注射、glutamate uncaging、PH-sensitive GluR1转染等方法对慢性应激导致的5-HT1B受体持续增强TA-CA1突触传递的机制、与抑郁行为产生的因果关系以及对CA1神经元树突信息整合的影响进行研究。本项目将以与记忆巩固相关的神经通路在慢性应激中的功能失调为契机，阐明导致这一改变的分子机制，为确立抑郁症治疗的新靶点提理论依据。

1. 我们发现五羟色胺通过激活5-HT1B受体增强了TA-CA1兴奋性突触传递，而不影响Schaffer collateral-CA1突触。这一效应通过突触后膜AMPA受体实现并依赖于钙调蛋白激酶对GluA1亚基的磷酸化。强直刺激引发的LTP和五羟色胺诱导的突触传递增强可以相互掩盖，提示其可能有共同机制。由TA-CA1介导的空间记忆的长时程巩固可以被5-HT1B受体拮抗剂增强。五羟色胺诱导的突触传递增强在鼠类抑郁症模型上发生了数量和质量的变化，这一作用可以被抗抑郁药物所恢复，并为抗抑郁效应所必需。这提示五羟色胺诱导的TA-CA1可能作为一个突触水平反应抑郁症的指标。.2.我们首次发现GABA的受体a6亚单位在海马GABA能中间神经元上有丰富表达。GABAA受体a6亚单位的选择性拮抗剂使海马CA1区椎体神经元中的mIPSC频率增高，而不影响其幅度。GABAA受体a6亚单位在慢性母婴分离应激所引起的抑郁症中表达下调，并能被抗抑郁药物反转。慢性母婴分离应激使海马CA1区椎体神经元中的mIPSC频率增高，而不影响其幅度。用病毒转染抑制该亚基的表达，能够引发抑郁行为。.3.应用双刺激在不同时间点分别刺激SC-CA1和TA-CA1。我们发现氯胺酮增强了CA1椎体神经元对来自TA和SC的两个阈下EPSPs的整合。HCN通道阻断剂ZD增加并掩盖氯胺酮的整合作用，提示HCN通道参与了氯胺酮对树突整合功能的调节。在HCN1基因敲除鼠中，氯胺酮不能促进整合，提示HCN通道对其CA1树突信息整合作用必不可少。 阻断后膜的HCN通道后，氯胺酮和ZD仍能增加SC-CA1 EPSCs和CA1神经元的树突整合作用，提示前膜的HCN通道参与了氯胺酮增强CA1区椎体神经元兴奋性突触传递和树突信息整合作用。