Figure 1. Time course for the thermal withdrawal latencies (top: cutoff 20 s) during (0-90 min) and after (90-120 min) intrathecal infusion (0.1 micro liter/min) of equianalgesic doses of remifentanil, remifentanil + glycine, and alfentanil and for the supraspinal side effects (bottom: supraspinal index cutoff = 8). Each point represents the mean and SEM of 5-8 animals.