Figure 6.

Bath application of dopamine to preparations with intact modulatory inputs. A, Intracellular recordings of PD neuron activity in 10^-6m dopamine from three different preparations (1, 2, 3). B, C, Instantaneous cycle frequencies over time. Dopamine application increased cycle frequency regardless of peripheral spike initiation. The onset of the increase in cycle frequency was always earlier than the appearance of antidromic spikes, and there was no additional increase in cycle frequency after the onset of peripheral spiking. D, Mean cycle frequencies for eight preparations. Cycle frequency in dopamine was significantly increased compared with the control (p < 0.01, n = 8, paired t test).