Immunohistochemical localization of GABA, GAD65, and the receptor subunits GABAAalpha1 and GABAB1 in the zebrafish cerebellum.

Gamma-aminobutyric acid (GABA) is the principal inhibitory neurotransmitter in the central nervous system. Its role is especially prominent in the cerebellum, where most neuron types are GABAergic. However, little is known about its function in the cerebellum of teleost fish, which is only partly homologous to its mammalian counterpart. Here, we investigated the expression and distribution of GABA, the GABA-synthesizing enzyme glutamic acid decarboxylase 65 (GAD65), and the receptor subunits GABA(Aalpha1) and GABA(B1) in the cerebellum of adult zebrafish. GABA and GAD65 presented a similar expression pattern that comprised the molecular layer, Purkinje cells and groups of presumed Golgi cells in the granular layer, both in the cerebellar corpus and valve. GABA(A) receptor subunits are principally found on fine radial fibers in the molecular layer, while GABA(B) receptor subunits localized prominently to the cell bodies of Purkinje cells in the ganglionic layer, and to their dendrites that span the molecular layer. These results are compared to the expression of the GABAergic system in the mammalian cerebellum.