Fredette B J, Mugnaini E
Laboratory of Neuromorphology, University of Connecticut, Storrs 06269.
Anat Embryol (Berl). 1991;184(3):225-43. doi: 10.1007/BF01673258.
Immunocytochemical detection of glutamate decarboxylase (GAD), the predominant biosynthetic enzyme of gamma-aminobutyric acid (GABA), reveals the presence of a dense GABAergic innervation in all parts of the inferior olive. One brain center that provides a substantial projection to the inferior olive is the cerebellar nuclei, which contain many small GABAergic neurons. These neurons were tested as a source of GABAergic olivary afferents by combining retrograde tract tracing with GAD immunocytochemistry. As expected from previous studies, injections of wheat germ agglutinin-conjugated horseradish peroxidase (WGA-HRP) into the inferior olive retrogradely label many small neurons in the interposed and lateral cerebellar nuclei and the dorsal part of the lateral vestibular nucleus, and fewer neurons in the ventro-lateral region of the medial cerebellar nucleus. These projections are predominantly crossed and are topographically arranged. The vast majority, if not all, of these projection neurons are also GAD-positive. The relative contribution of this projection to the GABAergic innervation of the inferior olive was tested by lesion of the cerebellar nuclei, or the superior cerebellar peduncle. Within 10 days the lesion eliminates most GAD-immunoreactive boutons in the principal olive, the rostral lamella of the medial accessory olive, the ventrolateral outgrowth, and the lateral part of the dorsal accessory olive ventral fold. Thus, the effectiveness of this depletion demonstrates that the cerebellar nuclei provide most of the GABAergic innervation to regions of the inferior olive known to receive a cerebellar projection. Moreover, when the lateral vestibular nucleus is damaged, the dorsal fold of the dorsal accessory olive is depleted of GABAergic boutons. The synaptic relations that boutons of the GABAergic cerebello-olivary projection share with olivary neurons were investigated at the electron microscopic level by GAD-immunocytochemistry, anterograde degeneration of the cerebellar axons or anterograde transport of WGA-HRP. All of these methods confirm that GABAergic, cerebello-olivary axon terminals contain pleomorphic vesicles, and synapse on various portions of olivary neurons, and especially on dendritic spines within glomeruli, often in very close proximity to the gap junctions that characteristically couple the dendritic profiles. These results demonstrate four major points: that virtually all of the GABAergic, and presumably inhibitory, neurons of the cerebellar and dorsal lateral vestibular nuclei are projection neurons; that a large portion of the inferior olive receives GABAergic afferents from the cerebellar nuclei; that a portion of the dorsal accessory olive receives GABAergic afferents from the dorsal lateral vestibular nucleus; and that cerebello-olivary fibers often synapse near gap junctions, and therefore could influence electrical coupling of olivary neurons.
免疫细胞化学检测γ-氨基丁酸（GABA）的主要生物合成酶谷氨酸脱羧酶（GAD），结果显示在延髓橄榄核的所有部分均存在密集的GABA能神经支配。向延髓橄榄核发出大量投射的一个脑中心是小脑核，其中包含许多小型GABA能神经元。通过将逆行束路追踪与GAD免疫细胞化学相结合，对这些神经元作为GABA能橄榄传入神经的来源进行了检测。正如先前研究所预期的那样，将小麦胚芽凝集素结合辣根过氧化物酶（WGA-HRP）注入延髓橄榄核后，可逆行标记间位核、外侧小脑核以及外侧前庭核背侧部分的许多小型神经元，而内侧小脑核腹外侧区域的神经元标记较少。这些投射主要是交叉的且呈拓扑排列。这些投射神经元中的绝大多数（如果不是全部的话）也是GAD阳性。通过损伤小脑核或小脑上脚，测试了该投射对延髓橄榄核GABA能神经支配的相对贡献。在10天内，损伤消除了主橄榄核、内侧副橄榄核嘴侧薄片、腹外侧突出部以及背侧副橄榄核腹侧褶外侧部分的大多数GAD免疫反应性终扣。因此，这种消耗的有效性表明，小脑核为已知接受小脑投射的延髓橄榄核区域提供了大部分GABA能神经支配。此外，当外侧前庭核受损时，背侧副橄榄核的背侧褶会失去GABA能终扣。通过GAD免疫细胞化学、小脑轴突的顺行变性或WGA-HRP的顺行运输，在电子显微镜水平研究了GABA能小脑-橄榄投射的终扣与橄榄神经元的突触关系。所有这些方法均证实，GABA能小脑-橄榄轴突终末含有多形性囊泡，并与橄榄神经元的不同部分形成突触，尤其是与小球体内的树突棘形成突触，且常常非常靠近典型地连接树突轮廓的缝隙连接。这些结果证明了四个要点：小脑和背外侧前庭核中几乎所有的GABA能神经元（推测为抑制性神经元）都是投射神经元；大部分延髓橄榄核接受来自小脑核的GABA能传入神经；一部分背侧副橄榄核接受来自背外侧前庭核的GABA能传入神经；并且小脑-橄榄纤维常常在缝隙连接附近形成突触，因此可能影响橄榄神经元的电耦合。
