Mikkelsen J D
Institute of Medical Anatomy B, University of Copenhagen, Denmark.
J Comp Neurol. 1990 Sep 22;299(4):493-508. doi: 10.1002/cne.902990409.
The lateral geniculate nucleus of the thalamus sends efferents to the hypothalamic suprachiasmatic nucleus, which is involved in generation and entrainment of several circadian rhythms. It seems reasonable to believe that the lateral geniculate conveys visual information about the length of the photoperiod to the circadian oscillator. In order to study in more detail the topographical relationship between the lateral geniculate and the suprachiasmatic nucleus, anterograde tracing with Phaseolus vulgaris leucoagglutinin (PHA-L) and retrograde tracing with wheatgerm agglutinin coupled to horseradish peroxidase (WGA-HRP) were performed in the gerbil. After iontophoretic injections of PHA-L in the lateral geniculate, a large number of PHA-L-immunoreactive fibers and nerve terminals were observed in the ventrolateral part of the suprachiasmatic nucleus. Nerve fibers were also present in the ventromedial and dorsolateral portions, particularly in the caudal half of the nucleus. PHA-L-immunoreactive nerve fibers continued outside the borders of the suprachiasmatic nucleus to the adjacent anterior hypothalamic, the periventricular, and the subparaventricular areas. A moderate number of fibers entered the lateral hypothalamic area and the tuber cinerum via the optic tract and chiasm. Moreover, the paraventricular nucleus, the supraoptic nucleus, the medial preoptic area, the lateral preoptic area, and the supramammillary nucleus contained a few labeled fibers. In all parts of the hypothalamus receiving an input from the lateral geniculate, fine beaded immunoreactive fibers with varicosities and nerve terminals were observed, some of which were found in close apposition to hypothalamic neurons. Only after labeling of neurons in the intergeniculate leaflet of the lateral geniculate nucleus, fibers were found in the hypothalamus. This topographical organization of the geniculohypothalamic pathway was supported by retrograde tracing after injections of WGA-HRP in the suprachiasmatic area. In these experiments, retrograde labeled neurons were observed in the intergeniculate leaflet and, in agreement with the anterograde studies, most of labeling was observed in the ipsilateral side. These results confirm that the suprachiasmatic nucleus receives a substantial input from the intergeniculate leaflet of the lateral geniculate. Moreover, the present data demonstrate that the suprachiasmatic nucleus is not the only nucleus that receives a direct visual input. Thus other hypothalamic areas might be influenced by a direct rhythmic neuronal input as well.
丘脑外侧膝状体核向参与多种昼夜节律产生和同步化的下丘脑视交叉上核发出传出纤维。有理由相信，外侧膝状体将有关光周期长度的视觉信息传递给昼夜节律振荡器。为了更详细地研究外侧膝状体与视交叉上核之间的拓扑关系，在沙鼠中进行了菜豆白细胞凝集素（PHA-L）顺行示踪和与辣根过氧化物酶偶联的小麦胚凝集素（WGA-HRP）逆行示踪。在外侧膝状体进行离子电渗法注射PHA-L后，在视交叉上核的腹外侧部分观察到大量PHA-L免疫反应性纤维和神经末梢。神经纤维也存在于腹内侧和背外侧部分，特别是在核的后半部分。PHA-L免疫反应性神经纤维在视交叉上核边界之外延伸至相邻的下丘脑前部、室周和室旁下区域。相当数量的纤维通过视束和视交叉进入下丘脑外侧区和灰结节。此外，室旁核、视上核、内侧视前区、外侧视前区和乳头体上核含有一些标记纤维。在接受外侧膝状体输入的下丘脑所有部位，均观察到有曲张的细珠状免疫反应性纤维和神经末梢，其中一些与下丘脑神经元紧密相邻。仅在外侧膝状体核间小叶的神经元被标记后，才在下丘脑中发现纤维。在视交叉上区注射WGA-HRP后的逆行示踪支持了膝状体-下丘脑通路的这种拓扑组织。在这些实验中，在核间小叶观察到逆行标记的神经元，并且与顺行研究一致，大多数标记出现在同侧。这些结果证实视交叉上核接受来自外侧膝状体核间小叶的大量输入。此外，目前的数据表明视交叉上核不是唯一接受直接视觉输入的核。因此，其他下丘脑区域也可能受到直接节律性神经元输入的影响。
