Department of Pharmacology, University of Washington, Seattle, Washington 98195, USA.
J Neurosci. 2012 Sep 5;32(36):12325-36. doi: 10.1523/JNEUROSCI.2053-12.2012.
Repeated stress releases dynorphins and causes subsequent activation of κ-opioid receptors (KORs) in limbic brain regions. The serotonergic dorsal raphe nucleus (DRN) has previously been found to be an important site of action for the dysphoric effects of dynorphin-κ-opioid receptor system activation during stress-evoked behaviors, and KOR-induced activation of p38α mitogen-activated protein kinase (MAPK) in serotonergic neurons was found to be a critical mediator of the aversive properties of stress. Yet, how dynorphins and KORs functionally regulate the excitability of serotonergic DRN neurons both in adaptive and pathological stress states is poorly understood. Here we report that acute KOR activation by the selective agonist U69,593 [(+)-(5α,7α,8β)-N-methyl-N-[7-(1-pyrrolidinyl)-1-oxaspiro[4.5]dec-8-yl]benzeneacetamide] inhibits serotonergic neuronal excitability within the DRN through both presynaptic inhibition of excitatory synaptic transmission and postsynaptic activation of G-protein-gated inwardly rectifying potassium channels (GIRKs) electrophysiologically recorded in brain slices. C57BL/6 mice subjected to repeated swim, stress sessions had significantly reduced KOR-mediated GIRK currents recorded in serotonergic neurons in DRN postsynaptically, without significantly affecting presynaptic KOR-mediated regulation of excitatory transmission. This effect was blocked by genetic excision of p38α MAPK selectively from serotonergic neurons. An increase in phospho-immunoreactivity suggests that this functional dysregulation may be a consequence of tyrosine phosphorylation of GIRK (K(IR)3.1) channels. These data elucidate a mechanism for stress-induced dysregulation of the excitability of neurons in the DRN and identify a functional target of stress-induced p38α MAPK activation that may underlie some of the negative effects of pathological stress exposure.
反复的应激会释放强啡肽，并导致随后在边缘脑区中κ-阿片受体（KOR）的激活。先前已经发现，在应激诱发行为期间强啡肽-KOR 系统激活引起的不愉快效应中，5-羟色胺能背侧中缝核（DRN）是一个重要的作用部位，并且在 5-羟色胺能神经元中 KOR 诱导的 p38α 丝裂原活化蛋白激酶（MAPK）的激活被发现是应激的厌恶性特性的关键介质。然而，强啡肽和 KOR 如何在适应性和病理性应激状态下调节 5-羟色胺能 DRN 神经元的兴奋性仍知之甚少。在这里，我们报告选择性激动剂 U69,593[（+）-（5α，7α，8β）-N-甲基-N-[7-（1-吡咯烷基）-1-氧螺[4.5]癸-8-基]苯乙酰胺]对急性 KOR 的激活通过抑制兴奋性突触传递的突触前抑制和在脑片中电生理记录的 G 蛋白门控内向整流钾通道（GIRK）的突触后激活来抑制 DRN 内的 5-羟色胺能神经元兴奋性。在重复游泳应激后，C57BL/6 小鼠的 5-羟色胺能神经元中的 KOR 介导的 GIRK 电流明显减少，而对突触前 KOR 介导的兴奋性传递的调节没有明显影响。这种作用被选择性地从 5-羟色胺能神经元中敲除 p38α MAPK 所阻断。磷酸化免疫反应性的增加表明，这种功能失调可能是 GIRK（K（IR）3.1）通道酪氨酸磷酸化的结果。这些数据阐明了应激诱导的 DRN 神经元兴奋性失调的机制，并确定了应激诱导的 p38α MAPK 激活的功能靶点，这可能是病理性应激暴露的一些负面影响的基础。
