Fig. 2. Electrical activities of acutely isolated SNc dopamine neurons. Spontaneous firing activities were recorded from the cell-attached current-clamp cells (A,Ba). Their firing activities were converted into the frequency-time graph (A,Bb). The [Ca²⁺]_c using fura-2 was measured from the same cells (A,Bc). (A) The spontaneous firing activities were completely blocked by 500 nM TTX. Note that the change in [Ca²⁺]_c was mirrored by the firing rate. (B) The spontaneous firing was initially blocked by a nonspecific Ca²⁺ channel antagonist, 100 µM CdCl₂. But it recovered after some time even in the presence of CdCl₂. Note the persistent decreased [Ca²⁺]_c level after a full recovery of the spontaneous electrical activities.