Figure 3. The effects of (-)-baclofen on postsynaptic responses evoked by carbachol.

A, a chart record of membrane potential and input resistance (downward voltage deflections to -0.3 nA, 300 ms current steps) with the black arrows and the black bar indicating the period of carbachol (CCh, 3 μm) and (-)-baclofen (10 μm) applications, respectively. Constant DC injection (lower bar) was used in the presence of (-)-baclofen to restore the cell membrane potential to control levels. At the peak of the carbachol-induced depolarization DC injection was adjusted (-DC) to bring the membrane potential in line with that prior to the carbachol application. The transient upward deflections at various time points throughout the chart record are spike frequency adaptation responses to +0.3 nA, 300 ms current steps in the presence and absence of carbachol and (-)-baclofen. The initial membrane potential of this neurone was -64 mV. The bar graph in B shows the peak depolarization induced by carbachol, or evoked by the EPSP_M, in the presence of baclofen (Bac) or baclofen + CGP 55845A (+ CGP) plotted as a percentage of that evoked in its absence.