Effect of intraperitoneal administration of WIN on DR 5-HT neurons. A, Effect of WIN on 5-HT neuronal firing activity. WIN (0.05–2.0 mg/kg, i.p.) was administered 23, 5, and 0.75 h before electrophysiological recordings. Coapplication of RIM (1 mg/kg, i.p.) 10 min before WIN (0.2 mg/kg, i.p.) blocked the increase in spontaneous 5-HT single-unit firing activity. B, Effect of WIN on the number of spontaneously active 5-HT neurons. The number of spontaneously active neurons was calculated as the number of recorded 5-HT neurons per electrode descent in each treatment group. Values at the base of each column in A denote the number of 5-HT neurons recorded. Bars represent mean ± SEM values. **p < 0.01 versus vehicle.