Grofova I, Zhou M
Department of Anatomy, Michigan State University, East Lansing 48824-1316, USA.
J Comp Neurol. 1998 Jun 8;395(3):359-79.
The substantia nigra (SN) has long been known as an important source of afferents to the pedunculopontine tegmental nucleus (PPN). However, it has not been established which of the chemospecific cell populations receive this synaptic input. We sought to address this issue by a correlative light and electron microscopic approach that combines anterograde tracing of nigral efferents with pre-embedding choline acetyltransferase (ChAT) and/or glutamate (Glu) immunohistochemistry. Following large bilateral injections of Phaseolus vulgaris-leucoagglutinin (PHA-L) in the SN, the labeled nigrotegmental fibers were concentrated in a small area of the mesopontine tegmentum which contained very few ChAT-immunoreactive (ChAT-ir) cell bodies. However, strands of fine varicose fibers penetrated to adjacent regions of the PPN which harbored numerous cholinergic perikarya. The anterogradely labeled boutons were often seen in the proximity of ChAT-ir perikarya and dendrites, but the majority (82-93%) established symmetric synaptic junctions with noncholinergic profiles. In the pars dissipata of the PPN (PPNd), one-third of the labeled terminals synapsed onto noncholinergic perikarya and primary dendrites, while in the pars compacta of the PPN (PPNc) axosomatic synapses were rare. The possibility that the perikarya receiving a rich synaptic input from the SN are glutamatergic was tested in experiments combining anterograde transport of biotinylated tracers biocytin and dextran-amine (BDA) with glutamate immunohistochemistry. In double-labeled sections, Glu-ir perikarya within the terminal plexus of nigrotegmental fibers were surrounded by synaptic terminals. The PPNd also contained retrogradely BDA-labeled neurons which were contacted by anterogradely labeled terminals. These results indicate that although a small subpopulation of cholinergic neurons in the mesopontine tegmentum receive direct synaptic input from the SN, the primary target of nigrotegmental fibers are glutamatergic cells in the PPNd. Our results also provide ultrastructural evidence that some nigrotegmental fibers innervate pedunculonigral neurons.
长期以来，黑质（SN）一直被认为是脑桥脚被盖核（PPN）传入纤维的重要来源。然而，尚未确定哪些化学特异性细胞群接受这种突触输入。我们试图通过一种相关的光镜和电镜方法来解决这个问题，该方法将黑质传出纤维的顺行追踪与包埋前胆碱乙酰转移酶（ChAT）和/或谷氨酸（Glu）免疫组织化学相结合。在SN进行双侧大剂量注射菜豆白细胞凝集素（PHA-L）后，标记的黑质被盖纤维集中在中脑桥被盖的一个小区域，该区域含有极少的ChAT免疫反应性（ChAT-ir）细胞体。然而，细的曲张纤维束穿透到含有大量胆碱能核周体的PPN相邻区域。顺行标记的终扣常出现在ChAT-ir核周体和树突附近，但大多数（82%-93%）与非胆碱能形态形成对称突触连接。在PPN的分散部（PPNd），三分之一的标记终末与非胆碱能核周体和初级树突形成突触，而在PPN的致密部（PPNc），轴体突触很少见。在将生物素化示踪剂生物胞素和葡聚糖胺（BDA）的顺行运输与谷氨酸免疫组织化学相结合的实验中，测试了接受来自SN丰富突触输入的核周体是否为谷氨酸能的可能性。在双标记切片中，黑质被盖纤维终末丛内的Glu-ir核周体被突触终末包围。PPNd还含有逆行BDA标记的神经元，这些神经元与顺行标记的终末接触。这些结果表明，虽然中脑桥被盖中的一小部分胆碱能神经元接受来自SN的直接突触输入，但黑质被盖纤维的主要靶标是PPNd中的谷氨酸能细胞。我们的结果还提供了超微结构证据，表明一些黑质被盖纤维支配脑桥黑质神经元。
