Neurochemical correlates of gamma-aminobutyrate (GABA) inhibition in cat visual cortex.

High affinity binding of [3H]gamma-aminobutyric acid (GABA) to neuronal membranes from different parts of cat visual cortex was tested for sensitivity to GABA(A) agonists isoguvacine and THIP, GABA(A) antagonist SR95531 and GABA(B) agonist baclofen. Some of the GABA(A)-binding sites were found to have a very low affinity for THIP, suggesting the presence and, possibly, uneven distribution of "non-synaptic" GABA(A) receptors in cat visual cortex. There were no differences in Km and Vmax values of high affinity uptake of GABA and in the potency of K(+)-stimulated release of GABA, between primary and association cortices. Consequently, the present results indicate that despite the anatomical and physiological differences between the primary and association feline visual cortices the neurochemical characteristics of GABAergic inhibition are very similar in the two regions.