Charara A, Smith Y, Parent A
Centre de Recherche en Neurobiologie, Hôpital de l'Enfant-Jésus and Université Laval, Québec, Canada.
J Comp Neurol. 1996 Jan 8;364(2):254-66. doi: 10.1002/(SICI)1096-9861(19960108)364:2<254::AID-CNE5>3.0.CO;2-4.
To verify the possibility that the pedunculopontine nucleus is a source of glutamatergic terminals in contact with midbrain dopaminergic neurons in the squirrel monkey, we used the anterograde transport of Phaseolus vulgaris-leucoagglutinin in combination with preembedding immunohistochemistry for tyrosine hydroxylase and for calbindin D-28k and postembedding immunocytochemistry for glutamate and for gamma-aminobutyric acid. Following tracer injections in the pedunculopontine nucleus, numerous anterogradely labeled fibers emerged from the injection sites to innervate densely the pars compacta of the substantia nigra and ventral tegmental area. The major type of labeled fibers were thin with multiple collaterals and varicosities that established intimate contacts with midbrain dopaminergic neurons. At the electron microscopic level, the anterogradely labeled boutons were medium sized (maximum diameter between 0.9 microns and 2.5 microns) and contained numerous round vesicles and mitochondria. Postembedding immunocytochemistry revealed that 40-60% of anterogradely labeled terminals were enriched in glutamate and formed asymmetric synapses with dendritic shafts of substantia nigra and ventral tegmental area neurons. In triple-immunostained sections, some of the postsynaptic targets to these terminals were found to be dopaminergic. In addition, 30-40% of the anterogradely labeled terminals in both regions displayed immunoreactivity for gamma-aminobutyric acid and, in some cases, formed symmetric synapses with dendritic shafts. In conclusion, our results provide the first ultrastructural evidence for the existence of synaptic contacts between glutamate-enriched terminals from the pedunculopontine nucleus and midbrain dopaminergic neurons in primates. Our results also show that the pedunculopontine nucleus is a potential source of gamma-aminobutyric acid input to this region. These findings suggest that the pedunculopontine nucleus may play an important role in the modulation of the activity of midbrain dopaminergic cells by releasing glutamate or gamma-aminobutyric acid as neurotransmitter.
为了验证脚桥核是松鼠猴中与中脑多巴胺能神经元接触的谷氨酸能终末的来源这一可能性，我们采用菜豆白细胞凝集素的顺行运输，结合酪氨酸羟化酶、钙结合蛋白D - 28k的包埋前免疫组织化学，以及谷氨酸和γ-氨基丁酸的包埋后免疫细胞化学。在脚桥核注射示踪剂后，大量顺行标记的纤维从注射部位发出，密集地支配黑质致密部和腹侧被盖区。标记纤维的主要类型较细，有多个分支和膨体，与中脑多巴胺能神经元形成紧密接触。在电子显微镜水平上，顺行标记的终扣中等大小（最大直径在0.9微米至2.5微米之间），含有大量圆形囊泡和线粒体。包埋后免疫细胞化学显示，40% - 60%的顺行标记终末富含谷氨酸，并与黑质和腹侧被盖区神经元的树突干形成不对称突触。在三重免疫染色切片中，发现这些终末的一些突触后靶点是多巴胺能的。此外，两个区域中30% - 40%的顺行标记终末显示γ-氨基丁酸免疫反应性，在某些情况下，与树突干形成对称突触）。总之，我们的结果提供了首个超微结构证据，证明灵长类动物中脚桥核富含谷氨酸的终末与中脑多巴胺能神经元之间存在突触联系。我们的结果还表明，脚桥核是该区域γ-氨基丁酸输入的潜在来源。这些发现提示，脚桥核可能通过释放谷氨酸或γ-氨基丁酸作为神经递质，在调节中脑多巴胺能细胞的活动中发挥重要作用。
