Opioids & plasticity in regulation of serotonin release

描述(由申请人提供)：本项目的总体目标是 了解阿片类药物介导的生理和病理机制 5-羟色胺(5-羟色胺)释放神经回路的可塑性 哺乳动物的前脑，从而为理解和 治疗精神疾病，如抑郁症和毒瘾。这个 实验方法将行为测量与微透析相结合 自由行为大鼠的中枢神经系统。 我们认为Mu、Delta、kappa和ORL-1阿片类物质在脑内的作用不同。 调节5-羟色胺的释放。经逆行微渗析选择性输注 阿片受体激动剂注入中缝背核(DRN)，我们将测试 穆阿片和德尔塔阿片类药物产生增加的具体假设，以及卡帕-卡帕- ORL-1在5-羟色胺释放减少。我们进一步假设阿片类药物 5-羟色胺的区域选择性效应。初步数据显示，MU-和 Delta-阿片作用于DRN增加特定前脑5-羟色胺的释放 投影点。相反，kappa-阿片可能通过作用抑制5-羟色胺的释放 在大脑广泛区域的终末，包括DRN、中缝中缝 核团、伏隔核和背侧海马体。 阿片类药物引起5-羟色胺升高的假说 间接通过神经回路也将被检查。具体地说，穆阿片类药物 可能同时抑制GABA能和谷氨酸能传入DRN的5-羟色胺能神经元。 这一假说将通过使用选择性的GABA和谷氨酸来研究 受体拮抗剂用于表征抑制性和紧张性的活性 兴奋性对5-羟色胺神经元的影响。初步数据显示补药很强 γ-氨基丁酸与谷氨酸作用相对较弱的比较 DRN.我们建议进行实验，以进一步检验这一假设 Mu阿片类药物对5-羟色胺的作用可归因于直接抑制GABA和 谷氨酸神经元。因为，GABA基调占主导地位， 抑制这两种输入是5-羟色胺释放的增加。相比之下，卡帕-和 Orl-1-阿片类药物可能直接抑制5-羟色胺神经元。 长时间阿片类药物治疗可能导致突触强度的可塑性 中缝内的连接，从而影响5-羟色胺释放的调节。至 检验这一假设，阿片类药物依赖将由任何一种直接诱导 阿片类药物注入DRN 4天或皮下埋植阿片 吗啡药丸。根据我们之前的观察，我们将测试 阿片类药物通过增强5-羟色胺释放引起适应性的假说 GABA输入。同样，谷氨酸突触增强的可能性 将对变速器进行测试。通过测定戒断过程中5-羟色胺的变化， 我们将测试特定假设，即GABA的增强超过 谷氨酸的变化。这可能会导致更明显的净抑制效应 阿片类药物耐受后5-羟色胺释放减少 发展起来。进一步的实验将检验这一假设，即 延长ORL-1阿片类药物治疗后，5-羟色胺神经元数量增加。 最后，我们将检验以下假设：5-羟色胺的释放在 经常锻炼，这可能会减轻长时间运动的不良后果 阿片类药物治疗。最近的数据表明，5-羟色胺释放的增加 与跑步机相关的运动在有规律的运动后得到加强。至 研究锻炼在缓解行为抑郁方面的作用， 阿片依赖大鼠将定期在跑步机上锻炼。我们 假设有规律的锻炼会增加……的力量 谷氨酸与GABA在DRN内与5-羟色胺神经元的联系 这可能会使与延长时间相关的净抑制增强正常化 接触阿片类药物。

DESCRIPTION (provided by applicant): The overall objective of this project is to understand the physiological and pathological mechanisms of opioid-mediated plasticity in the neural circuitry controlling serotonin (5-HT) release in the mammalian forebrain, and thereby provide a sound basis for understanding and treatment of psychiatric disorders such as depression and drug addiction. The experimental approach combines behavioral measures with microdialysis in the CNS of freely behaving rats. We propose that mu, delta, kappa and ORL-1 opioids have different roles in regulation of 5-HT release. By reverse microdialysis infusion of selective opioid receptor agonists into the dorsal raphe nucleus (DRN) we will test the specific hypothesis that mu- and delta-opioids produce increases, and kappa- and ORL-1 decreases in 5-HT release. We further hypothesize that opioids have regionally selective effects on 5-HT. Preliminary data indicate that mu- and delta- opioids act in the DRN to increase 5-HT release in specific forebrain projection sites. In contrast, kappa-opioids may inhibit 5-HT release by acting on terminals in widespread areas of the brain including the DRN, median raphe nucleus, nucleus accumbens and dorsal hippocampus. The hypothesis that the increase in 5-HT elicited by mu-opioids is mediated indirectly by neural circuitry will also be examined. Specifically, mu-opioids may inhibit both GABAergic and glutamatergic inputs to 5-HT neurons in the DRN. This hypothesis will be investigated by using selective GABA and glutamate receptor antagonists to characterize the tonic activity of inhibitory and excitatory influences on 5-HT neurons. Preliminary data indicate a strong tonic influence of GABA compared with a relatively weak effect of glutamate in the DRN. We propose experiments to further examine the hypothesis that the effect of mu-opioids on 5-HT can be attributed to direct inhibition of both GABA and glutamate neurons. Because, GABA tone is predominant, the net effect of inhibiting both inputs is an increase in 5-HT release. In contrast, kappa- and ORL-1-opioids may directly inhibit 5-HT neurons. Prolonged opioid treatment may produce plasticity in the strength of synaptic connections in the raphe and thus affect the regulation of 5-HT release. To examine this hypothesis, opioid dependence will be induced by either direct infusion of opioids into the DRN for 4 days or by subcutaneous implantation of morphine pellets. Based on our previous observations, we will test the hypothesis that mu-opioids cause adaptations in 5-HT release by enhancement of GABA inputs. Similarly, the possibility of enhanced glutamate synaptic transmission will be tested. By determining changes in 5-HT during withdrawal, we will test the specific hypothesis that the enhancement in GABA exceeds the change in glutamate. This may result in a more pronounced net inhibitory effect of afferent inputs, thus decreased 5-HT release after tolerance to opioids develops. Further experiments will test the hypothesis that the excitability of 5-HT neurons is increased after prolonged treatment with ORL-1 opioids. Finally, we will test the hypothesis that 5-HT release is enhanced after regular exercise and this may ameliorate the adverse consequences of prolonged opioid treatment. Recent data suggest that the increase in 5-HT release associated with treadmill locomotion is enhanced after regular exercise. To examine the role of exercise in alleviating behavioral depression, opioid-dependent rats will be exercised regularly on a treadmill. We hypothesize that regular exercise results in an increase in the strength of glutamate relative to GABA connections with 5-HT neurons in the DRN, and that this may normalize the enhancement in net inhibitory associated with prolonged exposure to opioids.