Abstract
GABA‐ergic characteristics of transcallosal (TC) responses were studied with specific antagonists of both GABA‐A and GABA‐B receptor subtypes. We used a paired‐pulse paradigm to get insight into the role of GABA in interhemispheric interactions between motor cortices. 3‐Amino‐2‐(4‐chlorophenyl)‐propylphosphonic acid (phaclofen) and 3‐aminopropyl‐diethoxymethyl‐phosphinic acid (CGP 35348) were used as GABA‐B antagonists and bicuculline methiodide (BMI) was used to block the GABA‐A receptor. Although both GABA‐A and GABA‐B antagonists increased spike discharge upon transcallosal stimulation, in both pyramidal tract and non‐pyramidal tract neurons, they had different effects on the responses to the first and second stimuli of paired‐pulse stimulation (200 msec interval). Although the inhibition seen with the second stimulus was greatly attenuated by antagonists of the GABA‐B receptor, it was maintained in the presence of the GABA‐A antagonist. These finding support a presynaptic regulation of callosal transmission by GABA‐B receptors in the callosal synapse of the cat motor cortex. © 2002 Wiley‐Liss, Inc.