Vrang N, Larsen P J, Møller M, Mikkelsen J D
Institute of Medical Anatomy, University of Copenhagen, Denmark.
J Comp Neurol. 1995 Mar 20;353(4):585-603. doi: 10.1002/cne.903530409.
The suprachiasmatic nucleus (SCN) is a dominant pacemaker involved in the generation of circadian rhythms in mammals. Surprisingly, the expression of the many rhythms appears to be mediated via a limited efferent projection system of the pacemaker, of which the largest pathway terminates in the subparaventricular area and in the paraventricular nucleus of the hypothalamus. In order to investigate a possible topographical organization of this major outflow pathway of the SCN, microiontophoretic injections of the anterograde tracer Phaseolus vulgaris-leucoagglutinin (PHA-L) or the retrograde tracer cholera toxin subunit B (ChB) were centered in distinct subparts of the SCN (PHA-L) or in the subparaventricular area-paraventricular nucleus (ChB), respectively. PHA-L injections involving the entire SCN revealed not only a major projection to the subparaventricular area, but also one directed towards the medial and dorsal parvicellular subnuclei of the paraventricular nucleus. As opposed to injections involving the entire nucleus, injections of PHA-L centered in the dorsomedial subdivision of the SCN resulted in a relatively larger number of PHA-L-immunoreactive fibers in the parvicellular subdivisions of the PVN, whereas the terminal field in the subparaventricular area was less substantial. A topography of the SCN efferent output system was also revealed by the retrograde tracing with ChB. Injections of ChB in the dorsal part of the paraventricular hypothalamic nucleus, not involving the underlying subparaventricular area, gave rise to a population of retrogradely labeled cells in the dorsomedial part of the SCN. In contrast, ChB injections in the subparaventricular area resulted in labeling of neurons clustered in a more ventrolateral aspect of the SCN. The present data provide evidence for a topography in the major efferent projection system from the SCN, implying that different subparts of the rat SCN, presumably containing partly different potential neurotransmitter substances, may regulate different circadian rhythms.
视交叉上核（SCN）是参与哺乳动物昼夜节律产生的主要起搏器。令人惊讶的是，许多节律的表达似乎是通过起搏器有限的传出投射系统介导的，其中最大的通路终止于下丘脑室旁下区和室旁核。为了研究SCN这条主要传出通路可能的拓扑结构，分别将顺行示踪剂菜豆白细胞凝集素（PHA-L）或逆行示踪剂霍乱毒素B亚单位（ChB）通过微量离子电渗法注射到SCN的不同亚部分（PHA-L）或室旁下区-室旁核（ChB）。涉及整个SCN的PHA-L注射不仅显示出向室旁下区的主要投射，还显示出一条指向室旁核内侧和背侧小细胞亚核的投射。与涉及整个核的注射不同，将PHA-L注射到SCN背内侧亚区会导致室旁核小细胞亚区中PHA-L免疫反应性纤维数量相对较多，而室旁下区的终末区域则不那么明显。用ChB进行的逆行追踪也揭示了SCN传出输出系统的拓扑结构。将ChB注射到下丘脑室旁核的背侧部分，不涉及下方的室旁下区，会在SCN的背内侧部分产生一群逆行标记的细胞。相反，将ChB注射到室旁下区会导致SCN更腹外侧部分聚集的神经元被标记。目前的数据为SCN主要传出投射系统中的拓扑结构提供了证据，这意味着大鼠SCN的不同亚部分，可能含有部分不同的潜在神经递质物质，可能调节不同的昼夜节律。
