Effect of WIN 55,212-2 on the rate of spontaneous discharge of C-fiber nociceptors. (A) Representative examples of spontaneous discharge from separate nociceptors in tumor-bearing mice before (pre-injection) and at 15, 30, 45 and 60 min after intraplantar administration of vehicle, WIN 55,212-2, WIN 55,212-2 + AM281, and WIN 55,212-2 + AM630.(B) Mean (±SEM) rates of spontaneous activity in tumor-bearing mice before and at 15, 30, 45 and 60 min after intraplantar administration of vehicle, WIN 55,212-2, WIN 55,212-2 + AM281, and WIN 55,212-2 + AM630. Vehicle treatment did not alter the rate of spontaneous activity whereas treatment with WIN 55,212-2 produced a significant decrease in spontaneous activity throughout the post-injection testing period. Administration of AM281 or AM630 prevented the decrease in spontaneous activity produced by WIN 55,212-2. * p<.05, ** p≤.01, *** p≤.001 vs. WIN 55,212-2; ## p<.01, ### p≤.001 vs. pre-injection value.