GABAergic inhibition in the rat pontine nuclei is exclusively extrinsic: evidence from an in situ hybridization study for GAD(67) mRNA

As clearly indicated by our electrophysiological work, GABAergic inhibition plays a powerful role in the pontine nuclei (PN), the major link between c erebral cortex and the cerebellum. Using the technique of in situ hybridiza tion for the mRNA encoding for the gamma-aminobutyric acid (GABA)-synthesiz ing isoenzyme glutamic acid decarboxylase(67) (GAD(67)), we demonstrate her e the total absence of potentially GABAergic neurons from the rat PN. This negative finding supports the notion that GABA-ergic inhibition in the PN o f rats, unlike that of higher mammals, is exclusively based on extrapontine GABAergic afferents.