Fetal Ethanol Effects on Histaminergic Regulation of Neurotransmission

描述（由申请人提供）：学习障碍是胎儿酒精谱系障碍儿童中最常见的行为缺陷。开发有效的药物干预这些残疾需要更清楚地了解胎儿乙醇诱导的学习障碍的神经生物学基础，并随后确定其作用机制的治疗药物将被预测为具有临床实用性。我们已经观察到组胺H3受体拮抗剂ABT-239改善胎儿乙醇诱导的齿状回长时程增强（LTP）和学习缺陷。我们还观察到增加H3受体效应耦合在胎儿乙醇后代的齿状回。鉴于突触前H3受体抑制谷氨酸释放，我们的研究结果表明，胎儿乙醇暴露增加H3受体介导的抑制谷氨酸释放，ABT-239降低这种升高的抑制作用。我们假设：胎儿乙醇暴露提高突触前组胺H3受体在齿状回的功能。这种增强的抑制作用减少了穿通通路-齿状颗粒细胞突触的谷氨酸释放，这反过来又导致了LTP和对齿状回功能损伤敏感的学习行为的缺陷。为了验证这一假设，我们的具体目标将检查：1：结合[3 H]-A349821，一种选择性H3受体拮抗剂，在齿状回定量H3受体密度在对照组和胎儿酒精后代（目的1A）。我们还将使用选择性H3受体激动剂甲硫氨酸进行甲硫氨酸置换[3 H]-A349821结合研究，以确定H3受体的高亲和力和低亲和力激动剂结合位点的比例（Aim 1B），并通过测量甲硫氨酸刺激的[35 S]-GTPgS结合（Aim 1C）来检查H3受体-效应器偶联。第二章：通过测量成对脉冲可塑性和微型突触后电流，沿着这些药物对对照组和胎儿乙醇暴露后代中穿通路径齿状颗粒细胞突触LTP的影响，研究甲巯美匹和ABT-239对谷氨酸和GABA释放的影响。第三章：甲氧苄啶和ABT-239对对照和胎儿乙醇暴露后代体内穿通通路-颗粒细胞突触的成对脉冲可塑性和LTP的影响。第四章：在对照组和暴露于乙醇的胎儿后代中，甲巯咪唑对一次性情境恐惧条件反射（Aim 4A）和空间导航（Aim 4 B）的影响以及甲巯咪唑和ABT-239对放射臂迷宫（Aim 4C）的空间模式分离变体的影响。我们预计，这些研究将提供重要的新的见解胎儿乙醇暴露对组胺能调制的海马神经传递和突触可塑性的影响，在齿状回。此外，这些结果可以为考虑将作为H3受体拮抗剂的药物作为治疗FASD患者学习障碍的假定治疗药物提供临床前药理学依据。

DESCRIPTION (provided by applicant): Learning disabilities are the most common behavioral deficit observed in children with Fetal Alcohol Spectrum Disorder. The development of effective pharmacotherapeutic interventions for these disabilities requires a clearer understanding of the neurobiologic bases of fetal ethanol-induced learning deficits and subsequently, the identification of therapeutic agents whose mechanisms of action would be predicted to have clinical utility. We have observed that the histamine H3 receptor antagonist ABT-239 ameliorates fetal ethanol-induced deficits in dentate gyrus long-term potentiation (LTP) and learning. We have also observed increased H3 receptor-effector coupling in dentate gyrus of fetal ethanol offspring. Given that presynaptic H3 receptors inhibit glutamate release; our results suggest that fetal ethanol exposure increases H3 receptor-mediated inhibition of glutamate release, and that ABT-239 reduces this heightened inhibitory influence. We hypothesize that: Fetal ethanol exposure elevates presynaptic histamine H3 receptor function in dentate gyrus. This heightened inhibitory influence reduces glutamate release at the perforant path - dentate granule cell synapse which, in turn, contributes to deficits in LTP and learned behaviors sensitive to functional damage in the dentate gyrus. To test this hypothesis, our specific aims will examine: 1: The binding of [3H]-A349821, a selective H3 receptor antagonist, in dentate gyrus to quantitate H3 receptor density in control and fetal alcohol offspring (Aim 1A). We will also use the selective H3 receptor agonist methimepip to conduct methimepip-displacement of [3H]-A349821 binding studies to determine the proportion of high- and low-affinity agonist binding sites of the H3 receptor (Aim 1B) and examine H3 receptor-effector coupling by measuring methimepip-stimulated [35S]-GTPgS binding (Aim 1C). 2: The effects of methimepip and ABT-239 on glutamate and GABA release by measuring paired-pulse plasticity and miniature postsynaptic currents along with the effects of these agents on LTP at perforant path dentate granule cell synapses in control and fetal ethanol-exposed offspring. 3: The effects of methimepip and ABT-239 on paired-pulse plasticity and LTP at the perforant path - granule cell synapse in vivo in control and fetal ethanol-exposed offspring. 4: The effects of methimepip on one-trial contextual fear conditioning (Aim 4A) and spatial navigation (Aim 4B) and the effects of methimepip and ABT-239 on a spatial pattern-separation variant of the radial arm maze (Aim 4C) in control and fetal ethanol-exposed offspring. We anticipate that these studies will provide important new insights on the impact of fetal ethanol exposure on histaminergic modulation of glutamatergic neurotransmission and synaptic plasticity in the dentate gyrus. In addition, the results could provide a preclinical pharmacologic rationale for considering drugs that act as H3 receptor antagonists as putative therapeutic agents for the treatment of learning deficits in humans with FASD.