Figure 2.

Single morphine exposure produces a prolonged change on the firing activities of the VTA DA neurons. Rats received morphine (20 mg/kg, s.c.) or saline. The firing activities were recorded at 24, 72 and 120 hours after morphine treatment. Naïve rats were used to indicate the basal activity. A: firing rate. B: bursting. C: CV of ISIs. D: cells/track. *P < 0.05, **P < 0.01, compared to saline control. Independent group t-test.