Department of Psychology, University of Toronto, Toronto, ON, Canada.
Eur J Neurosci. 2013 Sep;38(5):2774-85. doi: 10.1111/ejn.12279. Epub 2013 Jun 17.
M5 muscarinic acetylcholine receptors expressed on ventral tegmental dopamine (DA) neurons are needed for opioid activation of DA outputs. Here, the M5 receptor gene was bilaterally transfected into neurons in the ventral tegmental area (VTA) or the adjacent rostromedial tegmental nucleus (RMTg) in mice by means of a Herpes simplex viral vector (HSV) to increase the effect of endogenous acetylcholine. Three days after HSV-M5 gene infusion in VTA sites, morphine-induced locomotion more than doubled at two doses, while saline-induced locomotion was unaffected. When the HSV-M5 gene was infused into the adjacent RMTg, morphine-induced locomotion was strongly inhibited. The sharp boundary between these opposing effects was found where tyrosine hydroxylase (TH) and cholinesterase labelling decreases (-4.00 mm posterior to bregma). The same HSV-M5 gene transfections in M5 knockout mice induced even stronger inhibitory behavioural effects in RMTg but more variability in VTA sites due to stereotypy. The VTA sites where HSV-M5 increased morphine-induced locomotion receive direct inputs from many RMTg GAD-positive neurons, and from pontine ChAT-positive neurons, as shown by cholera-toxin B retrograde tracing. Therefore, morphine-induced locomotion was decreased by M5 receptor gene expression in RMTg GABA neurons that directly inhibit VTA DA neurons. Conversely, enhancing M5 receptor gene expression on VTA DA neurons increased morphine-induced locomotion via cholinergic inputs.
M5 毒蕈碱型乙酰胆碱受体在腹侧被盖区多巴胺（DA）神经元上的表达对于阿片类药物激活 DA 输出是必需的。在这里，通过单纯疱疹病毒载体（HSV）将 M5 受体基因双侧转染到小鼠腹侧被盖区（VTA）或相邻的穹隆柱腹侧核（RMTg）的神经元中，以增加内源性乙酰胆碱的作用。在 VTA 部位注射 HSV-M5 基因后 3 天，吗啡诱导的运动在两个剂量下增加了一倍以上，而生理盐水诱导的运动不受影响。当 HSV-M5 基因注入相邻的 RMTg 时，吗啡诱导的运动受到强烈抑制。在酪氨酸羟化酶（TH）和胆碱酯酶标记减少的位置（前囟后-4.00 毫米）发现了这些相反效应之间的明显边界。在 M5 基因敲除小鼠中，相同的 HSV-M5 基因转染在 RMTg 中引起了更强的抑制性行为效应，但由于刻板行为，在 VTA 部位的变异性更大。HSV-M5 增加吗啡诱导的运动的 VTA 部位直接接收来自许多 RMTg GAD 阳性神经元和来自脑桥 ChAT 阳性神经元的输入，正如霍乱毒素 B 逆行追踪所显示的那样。因此，M5 受体基因在 RMTg GABA 神经元中的表达抑制了直接抑制 VTA DA 神经元的吗啡诱导的运动。相反，增强 VTA DA 神经元上的 M5 受体基因表达通过胆碱能输入增加了吗啡诱导的运动。
