Allen G V, Hopkins D A
Department of Anatomy, Dalhousie University, Halifax, Nova Scotia, Canada.
J Comp Neurol. 1990 Nov 8;301(2):214-31. doi: 10.1002/cne.903010206.
The anterograde and retrograde transport of horseradish peroxidase conjugated to wheat germ agglutinin (WGA-HRP) was used to study the anatomical organization of descending projections from the mamillary body (MB) to the mesencephalon and pons at light and electron microscopic levels. Injections of WGA-HRP into the medial mamillary nucleus resulted in dense anterograde and retrograde labeling in the ventral tegmental nucleus, while injections in the lateral mamillary nucleus resulted in dense anterograde labeling in the dorsal tegmental nucleus pars dorsalis and dense anterograde and retrograde labeling in the pars ventralis of the dorsal tegmental nucleus. Anterogradely labeled fibers in the mamillotegmental tract diverged from the principal mamillary tract in an extensive dorsocaudally oriented swath of axons which extended to the dorsal and ventral tegmental nuclei, and numerous axons turned sharply ventrally and rostrally to terminate topographically in the dorsomedial nucleus reticularis tegmenti pontis and rostromedial pontine nuclei. The anterograde labeling in these two precerebellar relay nuclei was distributed near the midline such that projections from the lateral mamillary nucleus terminated mainly dorsomedial to the terminal fields of projections from the medial mamillary nucleus. In the dorsal and ventral tegmental nuclei, labeled axon terminals contained round synaptic vesicles and formed asymmetric synaptic junctions primarily with small diameter dendrites and to a lesser extent with neuronal somata. A few labeled terminals contained pleomorphic vesicles and formed symmetric synaptic junctions with dendrites and neuronal somata. Labeled axon terminals were also frequently found in synaptic contact with retrogradely labeled dendrites and neuronal somata in the dorsal and ventral tegmental nuclei. These findings indicate that neurons in the dorsal and ventral tegmental nuclei are reciprocally connected with MB projection neurons. In the nucleus reticularis tegmenti pontis and medial pontine nuclei, labeled axon terminals contained round synaptic vesicles and formed asymmetric synaptic junctions primarily with small diameter dendrites. The present study demonstrates that projections from the medial and lateral nuclei of the MB are topographically organized in the mesencephalon and pons. The synaptic morphology of mamillotegmental projections suggests that they may have excitatory influences primarily on the distal dendrites of neurons in these brain regions.
运用与小麦胚凝集素结合的辣根过氧化物酶（WGA-HRP）的顺行和逆行运输，在光镜和电镜水平研究从乳头体（MB）到中脑和脑桥的下行投射的解剖结构。将WGA-HRP注入内侧乳头核，导致腹侧被盖核出现密集的顺行和逆行标记；而注入外侧乳头核，则导致背侧被盖核背侧部出现密集的顺行标记，以及背侧被盖核腹侧部出现密集的顺行和逆行标记。乳头被盖束中的顺行标记纤维在一条广泛的背尾向轴突束中与主要乳头束分开，该轴突束延伸至背侧和腹侧被盖核，许多轴突急剧转向腹侧和头侧，以拓扑方式终止于脑桥被盖网状核背内侧核和脑桥嘴内侧核。这两个小脑前中继核中的顺行标记分布在中线附近，使得来自外侧乳头核的投射主要终止于来自内侧乳头核投射终末场的背内侧。在背侧和腹侧被盖核中，标记的轴突终末含有圆形突触小泡，主要与小直径树突形成不对称突触连接，在较小程度上与神经元胞体形成突触连接。少数标记终末含有多形性小泡，与树突和神经元胞体形成对称突触连接。在背侧和腹侧被盖核中，还经常发现标记的轴突终末与逆行标记的树突和神经元胞体形成突触接触。这些发现表明，背侧和腹侧被盖核中的神经元与乳头体投射神经元相互连接。在脑桥被盖网状核和脑桥内侧核中，标记的轴突终末含有圆形突触小泡，主要与小直径树突形成不对称突触连接。本研究表明，乳头体内侧核和外侧核的投射在中脑和脑桥中呈拓扑组织。乳头被盖投射的突触形态表明，它们可能主要对这些脑区神经元的远端树突具有兴奋性影响。
