Fig. 3.

Onset of the DA-induced calcium rise precedes the onset of membrane potential (V_m) oscillations. A: time course of the voltage (top) and free Ca²⁺ concentration ([Ca²⁺]_in; bottom) change during DA application; 10⁻⁴ M DA has reached the bath solution at the 50 s time point. Each dendrite [region of interest (ROI)] is indicated by different color; the data points from one of the neurites are fit with a sigmoid function (plotted as a red solid line). Note that in the time period highlighted with the vertical light gray bar, [Ca²⁺] started rising before emergence of bursting. Voltage oscillations initially are slower and accelerate as the DA concentration reaches steady state. B1: complete time course of AB oscillations and intracellular calcium measurements as DA is added and washed out. As DA was washed out of the bath solution, the voltage oscillations and calcium signal returned back to their pre-DA levels within 10–15 min. B2: summary of the changes in the average calcium levels under different conditions: physiological saline (140 ± 8 nM), TTX (67 ± 3 nM), 10⁻⁴ M DA (193 ± 17 nM), and washout of DA. The neuron was oscillating in saline and in the presence of DA and quiescent in TTX and after DA (wash). C: preincubation with intracellular calcium channel blockers (Ry+Xe) abolishes the DA-evoked rise in [Ca²⁺]_in and oscillations in the AB neuron. C1: the AB neuron was preincubated with Ry+Xe for 30–60 min before DA application. Intracellular [Ca²⁺] did not change upon DA application; the neuron depolarized, because of DA's effects on other currents, but did not oscillate. C2: there was no significant difference in mean [Ca²⁺] under different conditions: 82 ± 11 nM before DA (in Ry+Xe) and 87 ± 17 nM in the presence of DA and Ry+Xe (P > 0.05, n = 10 ROIs).