光刺激和多巴胺D2、D4受体介导的外侧缰-腹侧被盖区通路在调节早期帕金森病工作记忆障碍中的作用

The lateral habenula (LHb) regulates the activity of dopamine (DA) transmitter system of the ventral tegmental area (VTA), which plays an important role in cognitive functions. The VTA is divided into anterior VTA (aVTA), posterior VTA (pVTA) and tail of the VTA (tVTA or rostromedial tegmental nucleus, RMTg); and these sub-regions send projections to different brain regions. Two DA pathways can be distinguished in the VTA. The mesocortical pathway which originates from the aVTA and send projections to the prefrontal cortex but does not send collaterals to the nucleus accumbens, and the mesolimbic circuit, which originates from the pVTA, and projects mainly to the nucleus accumbens and amygdala but does not send axonal collaterals to the prefrontal cortex. In addition, GABA efferent of the RMTg projects to the VTA. Therefore, their activities are involved in cognition and motivational effects. Further, the LHb also receives DA afferent from the VTA, and expresses DA D2 and D4 receptors. The working memory impairments are a mostly encountered non-motor symptom of Parkinson’s disease (PD); however, the pathogenesis of the working memory impairments is poorly understood. On the basis of our previous studies, the present study aims to investigate: (1) the effects of the excitation or inhibition of the LHb by the light stimulation, and activation or blockade of D2 and D4 receptors by intra-LHb injection of D2 and D4 receptor agonist and antagonist in the regulation of the working memory impairments measured by the Morris water maze and T maze rewarded alternation tests in rats with partial bilateral lesions of the nigrostriatal pathway, and that these stimuli induce the changes in the firing activity of LHb, aVTA, pVTA and RMTg neurons by in vivo electrophysiological recordings; (2) that these stimuli induce the changes in the firing activity of aVTA and pVTA neurons after lesioning of the RMTg; (3) the effects of DA release in the limbic and limbic-related brain regions including the medial prefrontal cortex, hippocampus and amygdala after the excitation or inhibition of the LHb by the light stimulation, and activation or blockade of D2 and D4 receptors by intra-LHb injection of D2 and D4 receptor agonist and antagonist using in vivo microdialysis and neurochemistry, and (4) the changes in expression of D2 and D4 receptors in the presynaptic and postsynaptic membrane of the LHb. These studies will illustrate that light stimulation LHb, and D2 and D4 receptors in the LHb pass through LHb-VTA direct pathway and/or LHb-RMTg-VTA indirect pathway to regulate the activity of DA transmitter system of the aVTA and pVTA, and the effects of the two pathways in the regulation of the working memory impairments in early stage PD. In addition, these studies also help to bring understanding about the neurobiology of other cognitive impairments, psychiatric illnesses and addiction.

外侧缰（LHb）调节腹侧被盖区（VTA）多巴胺（DA）递质系统的活动，该系统在认知功能中具有重要作用；VTA包括前端（aVTA）、后端（pVTA）和尾端（RMTg）亚区。工作记忆障碍是帕金森病（PD）常见的表现，其发生机制不清。本项目以具有工作记忆障碍的早期PD模型大鼠为对象，研究：（1）光刺激LHb和D2、D4受体激活、阻断在调节大鼠工作记忆障碍中的作用；这些因素对LHb、aVTA、pVTA和RMTg神经元电活动的影响；（2）损毁RMTg后，上述因素对aVTA和pVTA神经元电活动的调节；（3）光刺激和D2、D4受体对认知相关脑区DA释放的影响；（4）LHb内D2、D4受体在突触前、后的表达变化。这些研究将阐明光刺激和D2、D4受体是通过LHb-VTA直接通路或/和LHb-RMTg-VTA间接通路影响aVTA和pVTA的DA递质系统活动，以及这两条通路在早期PD工作记忆障碍中的作用。

工作记忆障碍及抑郁是帕金森病（PD）常见的非运动症状，其发生机制不清。外侧缰（LHb）直接和间接通过吻内侧被盖核（RMTg）影响腹侧被盖区（VTA）多巴胺（DA）递质系统的活动，参与认知功能及抑郁的调节；LHb也接受来自VTA的DA能纤维投射，并表达D2和D4受体。然而，目前仍不清楚LHb内D2、D4受体在调节PD非运动症状中的作用。因此，本研究以黑质致密部（SNc）损毁的PD模型大鼠为研究对象，采用行为学、电生理学、在体微透析等方法，观察了LHb中D2、D4受体的激活或阻断对大鼠工作记忆、抑郁样行为、LHb神经元电活动及细胞外液中DA、GABA、谷氨酸（Glu）含量的影响；并进一步观察了损毁RMTg后，激活或阻断LHb的D4受体对LHb神经元电活动及递质释放的影响。结果如下：1）D2、D4受体激动剂和拮抗剂调节大鼠的工作记忆及抑郁样行为，并且在SNc假损毁组和SNc损毁组大鼠中，不同剂量的D2、D4受体激动剂和拮抗剂诱发不同的行为学效应。2）低剂量D4受体激动剂和拮抗剂调节SNc假损毁组大鼠LHb神经元的电活动及细胞外液递质含量，但不影响SNc损毁组神经元的电活动及递质释放；高剂量激动剂和拮抗剂调节两组大鼠神经元的电活动及递质释放，但显著性作用的时间在损毁组明显缩短。3）损毁RMTg后，在SNc假损毁组，不同剂量D4受体激动剂均兴奋LHb神经元，不同剂量拮抗剂均抑制神经元；在SNc损毁组，低剂量激动剂或拮抗剂不改变LHb神经元的电活动，高剂量激动剂或拮抗剂分别兴奋或抑制神经元。4）损毁RMTg后，低剂量激动剂和拮抗剂不改变两组大鼠LHb递质释放，高剂量激动剂或拮抗剂分别升高或降低了这些递质的含量。结果提示：激活或阻断LHb内D2、D4受体可以调节大鼠的工作记忆及抑郁样行为，不同剂量激动剂或拮抗剂所诱发的不同行为学效应与LHb神经元电活动和递质的改变有关，这些变化涉及到LHb内突触前、后膜D4受体；黑质–纹状体通路损毁导致了LHb内突触前、后膜D4受体表达或/和功能异常。本研究为了解LHb D2、D4受体在调节PD非运动症状中的作用提供了有力证据。