Effect of GABAB receptor blockade on receptive fields of raccoon somatosensory cortical neurons during reorganization.

Single unit recordings were made in the fourth digit representation of raccoon somatosensory cortex after amputation of the fourth digit. The receptive fields of neurons in this "reorganized" cortex were studied before and after microiontophoretic application of a highly specific GABA(B) receptor antagonist, CGP 55845. When the recordings were performed early in the reorganization process, 3-5 weeks after amputation, CGP 55845 produced a greater expansion of the receptive field (184%) than at longer post-amputation intervals (17-34 weeks, 137% increase) or previously reported in intact animals (105%). Most of the receptive fields in these animals were restricted to either an adjacent digit or the palm and the expansion was adjacent to the predrug receptive field. However, in some cases block of GABA(B) receptors unmasked new responsive areas that were separated from the predrug field. In addition, GABA(B) receptor block often revealed higher threshold fields on an adjacent digit or palm. These results reinforce previous studies that used a GABA(A) receptor antagonist, and together they reveal the importance of GABAergic synapses in regulating the various inputs to cortical somatosensory neurons during reorganization.