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患儿中最常见的行为缺陷。开发有效的药物治疗干预这些残疾需要更清楚地了解胎儿乙醇诱导的学习缺陷的神经生物学基础，随后，确定治疗药物，其作用机制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期增强（LTP）和学习缺陷。我们还观察到胎儿乙醇后代齿状回中H3受体-效应偶联增加。鉴于突触前H3受体抑制谷氨酸释放；我们的研究结果表明，胎儿乙醇暴露增加了H3受体介导的谷氨酸释放抑制，而ABT-239减少了这种增强的抑制影响。我们假设：胎儿乙醇暴露可提高齿状回突触前组胺H3受体的功能。这种增强的抑制影响减少了贯穿通路-齿状颗粒细胞突触的谷氨酸释放，从而导致LTP缺陷和对齿状回功能损伤敏感的习得行为。为了验证这一假设，我们的具体目标将检验：1:[3H]-A349821（一种选择性H3受体拮抗剂）在齿状回中的结合，以定量测定对照组和胎儿酒精后代的H3受体密度（Aim 1A）。我们还将使用选择性H3受体激动剂甲氧美平（methimepip）进行甲氧美平置换[3H]- a349821结合研究，确定H3受体高亲和力和低亲和力激动剂结合位点的比例（Aim 1B），并通过测量甲氧美平刺激的[35S]- gtpgs结合（Aim 1C）来检测H3受体-效应器偶联。2：甲氧美平和ABT-239通过测量配对脉冲可塑性和微型突触后电流对谷氨酸和GABA释放的影响，以及这些药物对对照组和胎儿酒精暴露子代穿孔路径齿状颗粒细胞突触LTP的影响。3 .甲氧美平和ABT-239对对照组和胎儿乙醇暴露子代体内穿透通路-颗粒细胞突触成对脉冲可塑性和LTP的影响。4 .甲氧美平对单试验情境恐惧条件反射（Aim 4A）和空间导航（Aim 4B）的影响，以及甲氧美平和ABT-239对对照组和胎儿乙醇暴露子代径向臂迷宫（Aim 4C）空间模式分离变异的影响。我们预计这些研究将为胎儿乙醇暴露对谷氨酸神经传递和齿状回突触可塑性的组胺能调节的影响提供重要的新见解。此外，该结果可以为考虑将作为H3受体拮抗剂的药物作为治疗FASD患者学习缺陷的推定治疗剂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. PUBLIC HEALTH RELEVANCE: Despite public awareness campaigns warning of the dangers of drinking during pregnancy, it is estimated that between 2% and 5% of children born in the United States each year have fetal alcohol-associated functional brain damage that will lead to learning deficits over time. Currently, there are no evidence-based clinically useful pharmacotherapeutic interventions for these deficits. The long-term objective of our research program is understand the neurobiologic bases of fetal ethanol-induced learning deficits and subsequently, to identify therapeutic agents whose mechanisms of action would be predicted to have clinical utility in treating fetal alcohol-associated learning disabilities.