Figure 1. Effect of intracerebroventricular and intrathecal pertussis toxin on the tail-flick latency response (A) and analgesic effect of dexmedetomidine (B). Rats were pretreated with pertussis toxin (2.5 micro gram intracerebroventricular or 0.5 micro gram intrathecal) or vehicle administered either intracerebroventricularly or intrathecally and 7 days later the tail-flick latency was measured before (A) or after intraperitoneal dexmedetomidine 50 micro gram *symbol* kg sup -1 (B) by tail-flick test. Data are expressed as the absolute latency (A) or the percent of maximal possible analgesic effect (B) mean plus/minus SEM; the number of rats per group is shown in parentheses. *P < 0.05 compared to vehicle.