Gamma-aminobutyric acid pathways in the cerebellum studied by retrograde and anterograde transport of glutamic acid decarboxylase antibody after in vivo injections.

Injections of characterized antibody against glutamic acid decarboxylase (GAD), the enzyme responsible for the synthesis of gamma-aminobutyric acid (GABA), were made into the cerebellum. Small cortical injections of anti-GAD antibody produced labeled stellate, basket, Purkinje, and Golgi cells and their processes at the injection site. Anterograde transport of GAD antigen-antibody complexes in Purkinje cell axons caused intense labelling of terminals in deep cerebellar and several vestibular nuclei. Small groups of mossy fiber rosettes labeled and produced retrograde labeling and GAD immunoreactivity in a small number of pleomorphic neurons in the deep cerebellar nuclei. Injections into the dentate nucleus produced retrograde labeling in Purkinje cell bodies and anterograde label in a small number of mossy fiber rosettes. All projections conformed to previously reported topographic distributions of corticonuclear and nucleocortical cerebellar pathways. These findings confirm the GABA content of most Purkinje cell-deep nuclei connections and provide new evidence for a GABA component in part of the nucleocortical pathway in the cerebellum. Immunocytochemical controls for specificity were conducted by injections of preimmune rabbit serum as a substitute for GAD antibody. Only nonspecific labeling was obtained in these cases. Colchicine caused a cumulative enhancement of GAD immunoreactivity in all cases. The present studies indicate that the method of in vivo antibody injections can be utilized to study chemically specific connections in nervous tissue.