Baclofen inhibits the spontaneous and visually evoked responses of neurones in the striate cortex of the cat.

The effects of iontophoretic application of gamma-aminobutyric acid (GABA) and beta-p-chlorophenyl-GABA (baclofen) on the activity of single neurones in the striate cortex of anaesthetized and paralysed cats were compared. Both compounds inhibited the spontaneous and the visually evoked responses of 92% of the neurones tested (n = 75) and they also eliminated the enhancement of the spontaneous and the evoked responses induced by the microiontophoretic application of glutamate. Bicuculline methiodide (BMI) antagonized the GABA-induced inhibition but did not significantly alter the effectiveness of baclofen for most neurones tested. The findings suggest that GABAB receptors are ubiquitous in the striate cortex of the cat. Evidence is presented to suggest that the GABAA and GABAB receptor subtypes differ in their distribution on some striate neurons.