Behavioral Functions Of Neuropeptides

神经肽甘丙肽位于海马中，与大鼠隔海马通路中的乙酰胆碱共存，与蓝斑中的去甲肾上腺素共存，并抑制谷氨酸、乙酰胆碱和去甲肾上腺素的释放。甘丙肽在阿尔茨海默病的基底前脑中过度表达。本实验室致力于研究甘丙肽抑制作用的行为伴随物。我们过去的实验表明，甘丙肽给药大鼠损害性能的几个学习和记忆任务。去年，我们的甘丙肽研究项目集中在甘丙肽过表达转基因小鼠的行为表型，由西雅图的华盛顿大学的Robert Steiner和同事产生，以及一种新的甘丙肽受体GAL-R1敲除小鼠，由澳大利亚悉尼Garvan医学研究所的Tiina Iismaa和同事产生。 博士后研究员Andrew Holmes，Craige Wrenn，Jeff Kinney和几名学生志愿者完成了一系列关于GAL-tg中认知和情感行为的表型研究，以及GAL-R1无效突变体，杂合子及其野生型对照同窝仔（WT）的第一个行为表型。与WT同窝对照组相比，GAL-tg在Morris水迷宫探针试验、食物偏好社会传递中的嗅觉记忆和痕量恐惧条件反射上表现出性能缺陷。Holmes、Wrenn和Kinney博士在两组小鼠中复制了这些发现。视觉，嗅觉，伤害感受，进食和运动功能的测量的对照实验表明，GAL-tg与WT没有显著差异，从而避免了认知缺陷的潜在人为解释。开始初步研究以测试集中施用甘丙肽拮抗剂拯救GAL-tg中的记忆缺陷的能力。 我们的研究结果表明，更具挑战性的记忆任务对小鼠中甘丙肽过表达更敏感。这些结果与当前的理论一致，即神经肽是在高神经元放电条件下释放的神经调质，其向突触后神经元传递高度选择性的信息。甘丙肽过表达小鼠的认知缺陷可能与甘丙肽过表达阿尔茨海默病患者的认知缺陷有关。这个翻译项目将继续评估甘丙肽受体拮抗剂在啮齿动物中改善记忆丧失的能力，这种记忆丧失可能是由甘丙肽过度表达引起的。 博士Holmes进一步分析了GAL-tg系在与人类焦虑相关的任务中的行为表型。在高架十字迷宫、明/暗探索、旷场中心时间或旷场运动的基线评分中未检测到基因型差异。GAL-tg显示出对苯二氮卓类药物在光/暗探索时的预期抗焦虑反应。然而，GAL-tg未能显示对育亨宾的致焦虑反应，表明过量甘丙肽仅在高应激条件下具有抗焦虑作用。 GAL-R1无效突变体和杂合子显示正常的一般健康状况，家庭笼行为，神经反射和运动功能。在两组独立的小鼠中，已经检测到几种学习和记忆任务的不可预测的损伤。一种假设是，当GAL-R1受体突变时，甘丙肽水平会增加。Wrenn博士与亚利桑那大学的加里温克教授合作进行了放射免疫测定，以验证这一假设。最初的数据并不支持这一解释。GAL-R1受体在认知过程中的作用正在通过药理学挑战进一步探索。Holmes博士还在分析GAL-R1在焦虑相关任务上的表现。 甘丙肽脑室注射损害大鼠的获得和工作记忆。Kinney博士完成了一系列实验，以测试甘丙肽是否也会损害记忆巩固。在Morris水任务中，在每日训练课程之前5分钟、之后1分钟、之后30分钟、之后3小时和之后18小时微量注射甘丙肽。在训练之前和之后的时间点，直到构成巩固期的3小时时间点，探测试验的性能缺陷是相同的。巩固完成后，在18小时时间点未检测到性能缺陷。预处理与腺苷酸环化酶激活剂forskolin防止甘丙肽诱导的抑制，表明通过cAMP突触后细胞内信号级联的机制。

The neuropeptide galanin is localized in the hippocampus, coexists with acetylcholine in the rat septohippocampal pathway, coexists with norepinephrine in the locus coeruleus, and inhibits the release of glutamate, acetylcholine, and norepinephrine. Galanin is overexpressed in the basal forebrain in Alzheimer's disease. Our laboratory is engaged in investigating the behavioral concomittants of the inhibitory effects of galanin. Our past experiments revealed that galanin administration to rats impairs performance on several learning and memory tasks. Last year, our galanin research program focused behavioral phenotyping of galanin overexpressing transgenic mice, generated by Robert Steiner and coworkers at the University of Washington in Seattle, and a new galanin receptor GAL-R1 knockout mouse, generated by Tiina Iismaa and coworkers at the Garvan Medical Research Institute in Sydney, Australia. Postdoctoral fellows Andrew Holmes, Craige Wrenn, Jeff Kinney, and several student volunteers completed a series of phenotyping studies on cognitive and emotional behaviors in the GAL-tg, and the first behavioral phenotyping on GAL-R1 null mutants, heterozygotes, and their wild type control littermates (WT). GAL-tg showed performance deficits on the Morris water maze probe trial, on olfactory memory in social transmission of food preference, and on trace fear conditioning, as compared to WT littermate controls. Drs. Holmes, Wrenn, and Kinney replicated these findings in two cohorts of mice. Controls experiments on measures of vision, olfaction, nociception, feeding, and motor functions showed that GAL-tg were not significantly different from WT, thus avoiding a potential artifactual interpretation of the cognitive deficits. Preliminary studies were initiated to test the ability of a centrally administered galanin antagonist to rescue the memory deficits in GAL-tg. Our findings indicate that more challenging memory tasks are more sensitive to galanin overexpression in mice. These results are consistent with the current theory that neuropeptides are neuromodulators released under conditions of high neuronal firing, that convey highly selective information to postsynaptic neurons. Cognitive deficits in galanin overexpressing mice may be relevant to cognitive deficits in galanin overexpressing patients suffering from Alzheimer's disease. This translational project will proceed to evaluate galanin receptor antagonists in rodents, for their ability to ameliorate memory loss that may be caused by galanin overexpression in Alzheimer's patients. Dr. Holmes further analyzed behavioral phenotypes of the GAL-tg line in tasks relevant to human anxiety. No genotype differences were detected in baseline scores on the elevated plus maze, light/dark exploration, open field center time, or open field locomotion. GAL-tg showed the expected anxiolytic response to a benzodiazepine on light/dark exploration. However, GAL-tg failed to show an anxiogenic response to yohimbine, indicating an anxiolytic action of excess galanin only under conditions of high stress. GAL-R1 null mutants and heterozygotes displayed normal general health, home cage behaviors, neurological reflexes, and motor functions. Unpredicted impairments on several learning and memory tasks have been detected in two independent groups of mice. One hypothesis is that galanin peptide levels increase when the GAL-R1 receptor is mutated. Radioimmunoassays were conducted by Dr. Wrenn, in collaboration with Professor Gary Wenk at the University of Arizona, to test this hypothesis. Initial data do not support this explanation. The role of the GAL-R1 receptor in cognitive processes is being further explored with pharmacological challenges. Dr. Holmes is also analyzing the GAL-R1 on anxiety-related tasks. Galanin administered intraventricularly to rats impairs acquisition and working memory. Dr. Kinney completed a series of experiments to test whether galanin also impairs memory consolidation. Galanin was microinjected 5 minutes before, 1 minute after, 30 minutes after, 3 hours after, and 18 hours after daily training sessions in the Morris water task. Performance deficits on the probe trial were identical at time time points before and after training, up to the 3 hour time point, which constitutes the consolidation period. No performance deficits were detected at the 18 hour time point, after consolidation is complete. Pretreatment with the adenylate cyclase activator forskolin prevented the galanin-induced inhibition, suggesting a mechanism through the cAMP postsynaptic intracellular signalling cascade.