Phaclofen antagonizes baclofen-induced suppression of visually evoked responses in the cat's striate cortex.

The suppression of visually evoked responses (VER) in the cat's striate cortex by baclofen was reversibly antagonized by the phosphonic acid derivative of baclofen, phaclofen. The antagonistic effect of phaclofen was seen irrespective of whether it enhanced, suppressed or did not change VER on its own. The suppression of VER by gamma-aminobutyric acid (GABA) was not affected by phaclofen. Our findings support the notion (Kerr et al., Brain Research, 405 (1987) 150-154) that phaclofen is an effective baclofen antagonist in the central nervous system of mammals. Preliminary findings indicate that in spite of its possible action on GABAB receptors, phaclofen does not significantly alter functional properties of striate cortical neurons, in particular direction and orientation sensitivity.