Van Bockstaele E J, Gracy K N, Pickel V M
Department of Neurology and Neuroscience, Cornell University Medical College, New York, New York 10021.
J Comp Neurol. 1995 Jan 2;351(1):117-33. doi: 10.1002/cne.903510111.
The endogenous opioid peptide dynorphin is enriched in neurons in the nucleus accumbens, for which coexistence and synaptic interactions with substance P have been postulated. We examined the immunogold-silver localization of dynorphin and immunoperoxidase labeling for substance P in single coronal sections through the core subregion of the nucleus accumbens of acrolein-fixed rat brain tissue. Dynorphin-immunoreactive somata were more prevalent than substance P-containing neurons throughout the region sampled for ultrastructural analysis. Dynorphin-labeled cells were spherical, contained unindented nuclei, and were closely apposed to other somata and dendrites, some of which also contained dynorphin immunoreactivity. The appositions were characterized by the absence of glial processes and contiguous contacts between the plasma membranes. Smooth endoplasmic reticulum and coated vesicles could also be identified in the cytoplasms on either side of the somatic or dendritic appositions. The dynorphin somata and dendrites received synaptic input from numerous unlabeled as well as dynorphin- and/or substance P-labeled axon terminals. Both types of terminals were morphologically similar in their content of small and large dense core vesicles and their formation of mainly symmetric synaptic specializations. In addition to dynorphin-immunoreactive targets, numerous dynorphin- and substance P-labeled terminals also formed synapses with unlabeled somata and dendrites. In some cases, terminals separately labeled for dynorphin and substance P converged on common targets with or without detectable dynorphin immunoreactivity. Terminals colocalizing both peptides were also found to synapse on unlabeled or dynorphin-labeled somata and dendrites. Additionally, presynaptic interactions were suggested by close appositions between dynorphin- and/or substance P-labeled terminals and other terminals that were unlabeled, dynorphin labeled, or substance P labeled. These results provide morphological data suggesting nonsynaptic communication between dynorphin-immunoreactive neurons and other neurons possibly mediated through receptive sites or second messengers associated with smooth endoplasmic reticulum in the nucleus accumbens. They also indicate that, in this region, 1) the activity of dynorphin neurons may be dependent on activation of autoreceptors for dynorphin as well as substance P and 2) additional neurons lacking dynorphin immunoreactivity are most likely inhibited (symmetric junctions) by terminals containing either one or both peptides. The findings may have implications for motor and analgesic responses to aversive tonic pain transmitted through dynorphin and substance P pathways within the nucleus accumbens.
内源性阿片肽强啡肽在伏隔核的神经元中含量丰富，据推测它与P物质共存并存在突触相互作用。我们通过丙烯醛固定的大鼠脑组织伏隔核核心亚区的单冠状切片，研究了强啡肽的免疫金银定位和P物质的免疫过氧化物酶标记。在整个用于超微结构分析的区域中，强啡肽免疫反应性胞体比含P物质的神经元更普遍。强啡肽标记的细胞呈球形，细胞核无凹陷，与其他胞体和树突紧密相邻，其中一些也含有强啡肽免疫反应性。这些相邻关系的特征是没有胶质细胞突起，且质膜之间有连续接触。在胞体或树突相邻部位两侧的细胞质中也可识别出滑面内质网和被膜小泡。强啡肽胞体和树突接受来自许多未标记以及强啡肽和/或P物质标记的轴突终末的突触输入。这两种类型的终末在其小而大的致密核心小泡含量以及主要形成对称突触特化方面在形态上相似。除了强啡肽免疫反应性靶点外，许多强啡肽和P物质标记的终末也与未标记的胞体和树突形成突触。在某些情况下，分别标记强啡肽和P物质的终末会汇聚到有或没有可检测到的强啡肽免疫反应性的共同靶点上。还发现共定位这两种肽的终末与未标记或强啡肽标记的胞体和树突形成突触。此外，强啡肽和/或P物质标记的终末与未标记、强啡肽标记或P物质标记的其他终末紧密相邻，提示存在突触前相互作用。这些结果提供了形态学数据，表明强啡肽免疫反应性神经元与其他神经元之间可能通过与伏隔核中滑面内质网相关的感受位点或第二信使介导非突触通讯。它们还表明，在该区域，1）强啡肽神经元的活动可能依赖于强啡肽以及P物质自身受体的激活，2）缺乏强啡肽免疫反应性的其他神经元很可能受到含有一种或两种肽的终末的抑制（对称连接）。这些发现可能对通过伏隔核内强啡肽和P物质途径传递的厌恶性紧张性疼痛的运动和镇痛反应有影响。
