Figure 1.

Cannabinoid receptor-mediated stimulation produced analgesia in the rat. (A) Electrode placements (n = 11) are shown with anterior–posterior coordinates (21) of the sections (interaural line = 0) to the right of each diagram. Note that the stimulation sites are located in the dorsal aspect of the PAG, and two lie outside the dorsal border of the PAG, an area from which SPA has been elicited in previous studies (22). (B) The analgesic effects of this stimulation were antagonized by SR141716A (P = 0.02). The long time course (approximately 20 hr) of SR141716A precluded following recovery on the test day. (C) Sample data from a single rat. After the establishment of a stable baseline of response, the threshold for SPA was determined. The current was raised in ascending steps until a level of stimulation (410 mA) that produced complete (10-sec tail-flick latency) analgesia was reached. After injection of SR141716A (100 μg/10 μl, i.c.v.), the stimulation no longer produced analgesia.