Regulation of super(35)S-TBPS binding by bicuculline is region specific in rat brain

The allosteric regulation of specific super(35)S-TBPS binding to the convulsant site on the GABA sub(A) receptor/chloride (Cl super(-)) ionophore complex was studied in various brain regions in an attempt to characterize regional heterogeneity of the protein subunits forming the complex. Bicuculline methiodide (BIC), a GABA sub(A) antagonist, enhanced binding in cortex (CTX), substantia nigra (SN) and cerebellum (CBL), inhibited binding in inferior colliculus (IC) and did not affect binding in superior colliculus (SC). Similar results were found in CBL and IC using SR-95531, another GABA sub(A) antagonist. The levels of endogenous GABA in the different tissue samples could not account for the regional differences in binding. The findings provide a functional basis for regional heterogeneity of GABA sub(A) receptor.