Autoradiographic localization of binding sites for the gamma-aminobutyric acid analogues 4,5,6,7-tetrahydroisoxazolo[5,4-c]pyridin-3-ol (THIP)isoguvacine and baclofen on cultured neurons of rat cerebellum and spinal cord.

By means of light microscopic autoradiography, binding sites for the gamma-aminobutyric acid (GABA) analogues, 4,5,6,7-tetrahydroisoxazolo[5,4-c]pyridin-3-ol ([7-3H]THIP), [3H]isoguvacine and [3H]baclofen were found on many cultured cerebellar and spinal neurons of fetal and newborn rats. The number of neurons labelled by [3H]THIP was considerably smaller than that by the other two radioligands. Unlabelled THIP, GABA and bicuculline methiodide inhibited binding of [3H]THIP and [3H]isoguvacine, whereas binding of [3H]baclofen was inhibited by unlabelled GABA and baclofen but not by bicuculline methiodide. Our results indicate that cultured cerebellar and spinal neurons possess both GABAA and GABAB binding sites and that [3H]THIP possibly binds to a subclass of GABAA receptors.