Cellular mechanisms of HPA axis neuroadaptations in alcohol dependence

描述(申请人提供)：酒精中毒是一种慢性复发性障碍，特征是强迫性寻求酒精并失去对酒精摄入量的控制。众所周知，酒精中毒与下丘脑-垂体-肾上腺(HPA)轴和促肾上腺皮质激素释放激素(CRH)信号的持续失调有关，从而导致对应激的不适当反应，从而增加戒酒者的复发易感性。然而，戒酒者HPA轴对压力反应迟钝的细胞和分子机制尚未被发现。在大鼠中，急性束缚应激诱导下丘脑室旁核(PVN)小细胞神经分泌细胞(PNC)中CRH依赖性的N-甲基-D-天冬氨酸受体(NMDAR)功能抑制，从而使兴奋性输入的高频刺激(HFS)后的联合短期突触增强(STP)被揭穿。这代表了一种细胞机制，即应激诱导HPA轴的神经适应性反应。在慢性间歇性乙醇(CIE)诱导的大鼠酒精依赖模型上的初步结果表明，在没有急性应激的情况下，CIE大鼠的PNC可以诱导出STP。相反，在急性应激CIE大鼠的PNC中，STP受到损害。我们还证实了突触后NMDAR功能的长期增强与CIE大鼠PNC中NMDAR的GluN2B亚单位的表达增加有关。总之，初步结果强烈表明，CIE暴露改变了PNC的基础突触可塑性和应激诱导的突触可塑性，这可能是酒精依赖大鼠HPA轴对应激的激素反应明显迟钝的原因。因此，本研究的主要假设是CIE引起的STP损伤是由PVN内NMDAR功能和CRH信号的长期改变所介导的。我们还假设，恢复这种应激诱导的可塑性将恢复HPA轴对应激源的反应。为了验证这些假说，我们将结合行为、电生理、生化和药理学技术来确定：1)NMDAR信号改变在慢性乙醇暴露后应激诱导的PNC谷氨酸能突触可塑性中的作用，以及2)慢性Etoh暴露改变PVN长期戒断过程中PNC中CRH信号的机制。这些研究将有助于揭示酒精依赖中HPA轴对应激反应失调背后的细胞机制，这将有助于发现治疗应激诱导的强迫性酒精寻求的新的有效疗法。

DESCRIPTION (provided by applicant): Alcoholism is a chronic relapsing disorder characterized by compulsive ethanol-seeking and loss of control over alcohol intake. Alcoholism is known to be associated with a persistent dysregulation of the hypothalamic pituitary adrenal (HPA) axis and corticotropin-releasing hormone (CRH) signaling that leads to inappropriate responses to stress, thereby increasing relapse susceptibility in abstinent alcoholics. However, the cellular and molecular mechanisms responsible for the blunted HPA axis responses to stress in abstinent alcoholics have yet to be uncovered. In rats, acute restraint stress induces a CRH-dependent depression of N-methyl-D- aspartate receptor (NMDAR) function in parvocellular neurosecretory cells (PNCs) of the paraventricular nucleus of the hypothalamus (PVN) which allows for the unmasking of associative short-term synaptic potentiation (STP) following a burst of high-frequency stimulation (HFS) of excitatory inputs. This represents a cellular mechanism by which stress induces neuroadaptive responses of the HPA axis. Preliminary results in a rat model of alcohol dependence induced by chronic intermittent ethanol (CIE) exposure show that STP can be induced in PNCs of CIE rats without acute stress. By contrast, STP is impaired in PNCs from acutely stressed CIE rats. We also demonstrated long-lasting potentiation of postsynaptic NMDAR function associated with increased expression of the GluN2B subunit of NMDARs in PNCs of CIE rats. Altogether, preliminary results strongly suggest that CIE exposure modifies both basal and stress-induced synaptic plasticity in PNCs, which could be responsible for the characteristically blunted hormonal response of the HPA axis to stress in alcohol- dependent rats. Thus, the main hypothesis of this proposal is that CIE-induced impairment of STP is mediated by the long-lasting alterations in both NMDAR function and CRH signaling in the PVN. We also hypothesize that restoring this stress-induced plasticity will restore the HPA axis responsiveness to stressors. To test these hypotheses we will use a combination of behavioral, electrophysiological, biochemical and pharmacological techniques to determine: 1) the role of altered NMDAR signaling in stress-induced plasticity at glutamatergic synapses in PNCs after withdrawal from chronic EtOH exposure, and 2) the mechanisms by which chronic EtOH exposure alters CRH signaling in PNCs of the PVN during protracted withdrawal. These studies will help uncover the cellular mechanisms behind the dysregulation of the HPA axis response to stress in alcohol dependence, which will be useful in the discovery of new effective therapies for stress-induced compulsive alcohol seeking.