Pickel V M, Colago E E
Department of Neurology and Neuroscience, Cornell University Medical College, New York, New York 10021, USA.
Synapse. 1999 Aug;33(2):141-52. doi: 10.1002/(SICI)1098-2396(199908)33:2<141::AID-SYN4>3.0.CO;2-X.
Opioids acting at mu-opioid receptors (MORs) within the nucleus of the solitary tract (NTS) potently modulate autonomic functions that are also known to be influenced by inputs from the central nucleus of the amygdala (CEA). In addition, many of the physiological effects of MOR agonists have been attributed to interactions with neurons that contain gamma-aminobutyric acid (GABA), one of the neurotransmitters present in CEA-derived terminals and their targets in the medial NTS. Together, these observations suggest that MORs are present at pre- or postsynaptic sites within the CEA to NTS circuitry. To test this hypothesis, we combined anterograde transport of biotinylated dextran amine (BDA) with immunogold-silver localization of an antipeptide antiserum against the MOR in the NTS of adult rats. In animals receiving bilateral CEA injections of BDA, anterogradely labeled axons were seen throughout the rostrocaudal NTS. Electron microscopy of the medial NTS at rostral and intermediate levels showed anterograde BDA-labeling in many small unmyelinated axons and axon terminals, none of which contained detectable MOR. The BDA-labeled axon terminals formed mainly symmetric, inhibitory-type synapses with somata and dendrites. Over half of the somatic and approximately 10% of the dendritic targets showed nonsynaptic plasmalemmal immunogold labeling for MOR. The BDA-labeled axon terminals were also frequently apposed by other small axons that contained MORs. These results suggest that within the medial NTS, MOR agonists modulate the postsynaptic inhibition produced by CEA afferents and also play a role in the presynaptic release of other neurotransmitters.
作用于孤束核（NTS）内μ-阿片受体（MORs）的阿片类药物可有效调节自主功能，而这些自主功能也已知会受到杏仁核中央核（CEA）输入的影响。此外，MOR激动剂的许多生理效应都归因于与含有γ-氨基丁酸（GABA）的神经元的相互作用，GABA是CEA衍生终末及其在内侧NTS中的靶点所存在的神经递质之一。这些观察结果共同表明，MORs存在于CEA至NTS神经回路的突触前或突触后部位。为了验证这一假设，我们将生物素化葡聚糖胺（BDA）的顺行运输与针对成年大鼠NTS中MOR的抗肽抗血清的免疫金银定位相结合。在接受双侧CEA注射BDA的动物中，在整个NTS的头尾方向都可见到顺行标记的轴突。对吻侧和中间水平的内侧NTS进行电子显微镜观察发现，许多小的无髓鞘轴突和轴突终末中有顺行BDA标记，但均未检测到MOR。BDA标记的轴突终末主要与胞体和树突形成对称的抑制性突触。超过一半的胞体和大约10%的树突靶点显示有MOR的非突触质膜免疫金标记。BDA标记的轴突终末也经常与含有MORs的其他小轴突相邻。这些结果表明，在内侧NTS内，MOR激动剂可调节CEA传入纤维产生的突触后抑制，并且在其他神经递质的突触前释放中也起作用。
