Figure 4.

Effect of dopaminergic depletion on the responses of FSIs to cortical stimulations. A, Pairs of cortical stimulation (100 ms interval) were applied 20 times every 3 s. For each individual FSI, the stimulating current was adjusted by preliminary tests so that the spike response to the first pulse reached a probability close to 50%. The overlay of 20 consecutive traces, which were recorded from one FSI in a 6-OHDA-lesioned rat, is shown (left). Bar histograms (right) indicate that the stimulating current required for a response probability of 50% and the latency of the spike response to the first pulse were not significantly affected by dopaminergic depletion (open bars) compared with control (filled bars). Bar histograms indicate mean ± SEM, and the number of neurons studied is indicated inside bars. B, Examples of burst responses to series of 20 consecutive stimulations applied every 3 s at threshold and suprathreshold currents, which were evoked in one FSI recorded in a 6-OHDA-lesioned rat. C, Cumulative spike responses (mean ± SEM) of FSIs to four series of 20 consecutive stimulations at increasing currents. Dopaminergic depletion did not significantly affect FSI responses.