The GABAB antagonist phaclofen inhibits the late K-dependent IPSP in cat and rat thalamic and hippocampal neurones

Phaclofen (0.5–1 mM) reversibly inhibited the late, bicuculline resistant, K⁺ dependent IPSP recorded in projection cells of the cat and rat dorsal lateral geniculate nucleus and in rat hippocampal CA1 pyramidal neurones. At the same concentrations, phaclofen reversibly blocked the K⁺ dependent, bicuculline insensitive hyperpolarization evoked by GABA and baclofen but had no effect on the GABA_A IPSP. These results represent conclusive evidence that GABA_B receptors mediate the late K⁺ dependent IPSP in cortical and subcortical neurones.