Pentobarbital Depressant Effects Are Independent of GABA Receptors in Auditory Thalamic Neurons

Pentobarbital, a general anesthetic, has received extensive study for its ability to potentiate inhibition at GABAA subtype of receptors for GABA. Using whole cell current-clamp techniques and bath applications, we determined the effects of pentobarbital and GABA receptor antagonists on the membrane properties and tonic or burst firing of medial geniculate neurons in thalamic slices. Pentobarbital (0.01–200 μM) induced depressant effects in 50 of 66 neurons (76%). Pentobarbital hyperpolarized neurons by a mean of 3 mV and decreased the number of action potentials in tonic firing, evoked by current pulse injection from near the resting potential. Pentobarbital also decreased burst firing or low threshold Ca2+-spikes, evoked by current pulse injection into neurons at potentials hyperpolarized from rest. The blockade of tonic and burst firing, as well as low threshold Ca2+-spikes, was surmountable by increasing the amplitude of input current. The GABAA receptor antagonists, bicuculline (100 μM) and picrotoxi...