In rat isolated thalamic slices, intracellular recordings were made of responses to electrophoretically applied gamma-aminobutyric acid (GABA) in the absence and presence of sodium pentobarbitone (NaPb). 2. Responses to electrophoretically applied GABA were biphasic in the majority of neurones studied. They consisted of an early, negative-going and later, positive-going phase, when recorded close to reversal potential. 3. An increase in the GABA ejection current caused an enhancement of the late positive-going phase, along with a shift in the reversal potential of the whole response to a more positive value. These changes were accompanied by an increase in GABA-induced conductance (decrease in resistance) and an increase in the duration of the response. 4. Application of NaPb to the GABA response produced similar effects, namely an enhancement of the late positive-going phase, a shift in the reversal potential to a more positive value, an increase in conductance and an increase in duration. 5. GABA-mediated inhibitory postsynaptic potentials (i.p.s.ps) were evoked by electrical stimulation of the nucleus reticularis thalami. Application of NaPb caused an increase in the duration of the i.p.s.p. and a shift in its reversal potential to a more positive value.
