Ranson R N, Santer R M, Watson A H D
Cardiff School of Biosciences, Biomedical Sciences Buildings, Cardiff University, P.O. Box 911, Museum Avenue, Cardiff CF10 3US, Wales, UK.
Neuroscience. 2006 Sep 15;141(4):1935-49. doi: 10.1016/j.neuroscience.2006.05.015. Epub 2006 Jun 15.
Preganglionic neurones in the lumbosacral spinal cord give rise to nerves providing the parasympathetic and sympathetic innervation of pelvic organs. These neurones are modulated by neurotransmitters released both from descending supra-spinal pathways and spinal interneurones. Though serotonin has been identified as exerting a significant influence on these neurones, few studies have investigated the circuitry through which it achieves this particularly in relation to sympathetic preganglionic neurones. Using a combination of neuronal tracing and multiple immunolabeling procedures, the current study has shown that pelvic preganglionic neurones receive a sparse, and probably non-synaptic, axosomatic/proximal dendritic input from serotonin-immunoreactive terminals. This was in marked contrast to dopamine beta hydroxylase-immunoreactive terminals, which made multiple contacts. However, the demonstration of both serotonin, and dopamine beta hydroxylase immunoreactive terminals on both parasympathetic and sympathetic preganglionic neurones provides evidence for direct modulation of these cells by both serotonin and norepinephrine. Serotonin-containing terminals displaying conventional synaptic morphology were often seen to contact unlabeled somata and dendritic processes in regions surrounding the labeled preganglionic cells. It is possible that these unlabeled structures represent interneurones that might allow the serotonin containing axons to exert an indirect influence on pelvic preganglionic neurones. Since many spinal interneurones employ GABA as a primary fast acting neurotransmitter we examined the relationship between terminals that were immunoreactive for serotonin or GABA and labeled pelvic preganglionic neurones. These studies were unable to demonstrate any direct connections between serotonin and GABA terminals within the intermediolateral or sacral parasympathetic nuclei. Colocalization of serotonin and GABA was very rare but terminals immunoreactive for each were occasionally seen to contact the same unlabeled processes in close proximity. These results suggest that in the rat, the serotonin modulation of pelvic preganglionic neurones may primarily involve indirect connections via local interneurones.
腰骶脊髓中的节前神经元发出神经，为盆腔器官提供副交感神经和交感神经支配。这些神经元受到来自下行脊髓上通路和脊髓中间神经元释放的神经递质的调节。尽管血清素已被确定对这些神经元有重大影响，但很少有研究调查其实现这一作用的神经回路，特别是与交感节前神经元相关的回路。通过结合神经元追踪和多重免疫标记程序，本研究表明盆腔节前神经元从血清素免疫反应性终末接受稀疏的、可能是非突触性的轴体/近端树突输入。这与多巴胺β羟化酶免疫反应性终末形成多个接触形成了显著对比。然而，在副交感和交感节前神经元上同时存在血清素和多巴胺β羟化酶免疫反应性终末，这为血清素和去甲肾上腺素对这些细胞的直接调节提供了证据。显示传统突触形态的含血清素终末常可见于标记的节前细胞周围区域，与未标记的胞体和树突过程接触。这些未标记的结构可能代表中间神经元，它们可能使含血清素的轴突对盆腔节前神经元产生间接影响。由于许多脊髓中间神经元使用γ-氨基丁酸作为主要的快速作用神经递质，我们研究了血清素或γ-氨基丁酸免疫反应性终末与标记的盆腔节前神经元之间的关系。这些研究未能证明中间外侧核或骶副交感核内血清素和γ-氨基丁酸终末之间有任何直接联系。血清素和γ-氨基丁酸的共定位非常罕见，但偶尔可见各自免疫反应性终末接触紧邻的相同未标记过程。这些结果表明，在大鼠中，血清素对盆腔节前神经元的调节可能主要涉及通过局部中间神经元的间接联系。
