Fig. 6.

Block of inhibition by bicuculline evokes equivalent enhancement of whole-cell electrophysiological and voltage-sensitive dye responses. A, Time series of optical responses to stimulation of a layer 4 barrel under control conditions (top) or after application of 10 μm bicuculline to block GABA_A receptors (below). The same stimulation strength evoked a larger response with a longer duration in the presence of bicuculline. Scale bar, 100 μm. B, The effect of bicuculline on the response measured by voltage-sensitive dye in a region (60 × 60 μm) surrounding a whole-cell recording (black box inA). C, The effect of bicuculline on the responses measured with whole-cell recording. Thesetraces are averages of the same 16 consecutive sweeps as for the voltage-sensitive dye measurements in A andB. There is a close correspondence of the changes in amplitude and time course of responses with those of the voltage-sensitive dye. D, Consecutive individual sweeps of the whole-cell recordings under control conditions (left) and after application of bicuculline (right). No action potentials are evoked in control conditions, whereas several are evoked by each stimulus when inhibition is blocked. The responses to consecutive stimuli are similar.