Comparison of receptive field expansion produced by GABAB and GABAA receptor antagonists in raccoon primary somatosensory cortex

Recordings were made from 62 neurons in the forepaw representation of primary somatosensory cortex in anesthetized raccoons. Microiontophoretic administration of a specific GABAB receptor antagonist, CGP 55845, produced receptive field expansion in 74% of 46 neurons, in which it was tested first. The mean receptive field area was approximately doubled, with increases ranging from 12 to 500%. The GABAB receptor agonist baclofen reduced the receptive field in most (11 of 16) neurons, but increased the size in 4 neurons. Comparison of the effects of GABAB and GABAA antagonists in the same cells showed that GABAA receptor blockade produced greater expansion than GABAB blockade (144% vs 114%, respectively). Simultaneous administration of the two antagonists produced additional expansion in 16 of 25 neurons. There was no evidence of separate skin regions being masked by the two GABA receptor subtypes, as the larger expansion usually included the skin that was unmasked by the less effective drug. These results indicate that both GABAB and GABAA receptors play a role in shaping the normal receptive fields in somatosensory cortex.