Cabot J B, Bushnell A, Alessi V, Mendell N R
Department of Neurobiology and Behavior, State University of New York at Stony Brook 11794-5230, USA.
J Comp Neurol. 1995 Jun 5;356(3):418-32. doi: 10.1002/cne.903560309.
Peripheral regulation of cardiovascular function is fundamentally influenced by central excitation and inhibition of sympathetic preganglionic neurons in thoracic spinal cord. This electron microscopy study investigated whether the gamma-aminobutyric acid (GABA)-ergic and glycinergic inhibitory innervation of sympathetic preganglionic neurons arises from mutually exclusive afferent populations. Sympathetic preganglionic neurons were retrogradely labeled with cholera beta subunit. GABAergic terminals were identified using strict quantitative statistical analyses as those boutons containing significantly elevated levels of GABA-like immunogold labeling (GABA+). Glycinergic terminals were classified as those boutons opposite postsynaptic gephyrin immunostaining containing background levels of GABA-like immunogold labeling (gephyrin+/GABA- association). Approximately 43% of the synaptic terminals that contacted sympathetic preganglionic somata and proximal dendrites and that were opposite gephyrin were GABA-; the remaining 57% were GABA+. Only two GABA+ boutons (4%) that synapsed on identified sympathetic preganglionic neuron (SPN) processes were not opposite gephyrin immunostaining (GABA+/gephyrin- association). GABA-/gephyrin+ associations were anticipated given prior anatomical, physiological, and pharmacological data. The observed nearly one-to-one correspondence between postsynaptic gephyrin immunoreactivity and GABA+ boutons was unexpected. Prior physiological and pharmacological experiments suggest that the postsynaptic effects of GABAergic inputs to sympathetic preganglionic neurons are mediated by activation of GABAA receptors. Those data, the present results, and other molecular, biochemical, and anatomical studies of gephyrin in the central nervous system (CNS) are consistent with two hypotheses: 1) Postsynaptic gephyrin is associated with GABAA receptors in the membranes of sympathetic preganglionic neurons, and 2) GABA+/gephyrin+ associations do not necessarily predict colocalization of GABA and glycine within single boutons synapsing on sympathetic preganglionic somata and dendrites.
心血管功能的外周调节从根本上受到胸段脊髓中交感神经节前神经元的中枢兴奋和抑制的影响。这项电子显微镜研究调查了交感神经节前神经元的γ-氨基丁酸（GABA）能和甘氨酸能抑制性神经支配是否来自相互排斥的传入群体。交感神经节前神经元用霍乱β亚基进行逆行标记。通过严格的定量统计分析，将含有显著升高水平的GABA样免疫金标记（GABA+）的终末确定为GABA能终末。甘氨酸能终末被分类为那些与突触后gephyrin免疫染色相对的终末，其含有背景水平的GABA样免疫金标记（gephyrin+/GABA-关联）。约43%与交感神经节前胞体和近端树突接触且与gephyrin相对的突触终末为GABA-；其余57%为GABA+。在已识别的交感神经节前神经元（SPN）突起上形成突触的GABA+终末中，只有两个（4%）与gephyrin免疫染色不相对（GABA+/gephyrin-关联）。鉴于先前的解剖学、生理学和药理学数据，GABA-/gephyrin+关联是预期的。观察到的突触后gephyrin免疫反应性与GABA+终末之间几乎一对一的对应关系是出乎意料的。先前的生理学和药理学实验表明，GABA能输入对交感神经节前神经元的突触后效应是由GABAA受体的激活介导的。这些数据、目前的结果以及中枢神经系统（CNS）中gephyrin的其他分子、生化和解剖学研究与两个假设一致：1）突触后gephyrin与交感神经节前神经元膜中的GABAA受体相关联，2）GABA+/gephyrin+关联不一定预示着在与交感神经节前胞体和树突形成突触的单个终末内GABA和甘氨酸的共定位。
