gamma-aminobutyric acid B receptors are negatively coupled to adenylate cyclase in brain, and in the cerebellum these receptors may be associated with granule cells.

Baclofen and gamma-aminobutyric acid (GABA) are shown to inhibit basal adenylate cyclase activity in brain of rat. The response is mediated through the GABAB receptor, and the rank order of potency for agonists is (-)-baclofen (EC50 = 4 microM) greater than GABA (EC50 = 17 microM) greater than muscimol greater than (+)-baclofen. GABAA agonists are not effective inhibitors of cyclase activity. The response is bicuculline-insensitive, and diazepam does not modify the GABA or (-)-baclofen inhibition of adenylate cyclase. Studies with neurologically mutant mice correlated a loss in GABAB receptor-mediated inhibition of cyclase with a loss in cerebellar granule cells. Thus, the GABAB receptor is negatively coupled to adenylate cyclase in various brain areas, and, in the cerebellum, data suggest a granule cell localization of this activity.