Effects of intrathecal L- and N-type calcium channel blockers on the antinociception evoked by opioid agonists in the rat tail flick test.

The effects of intrathecal administration of nimodipine or omega-conotoxin GVIA (L- and N-type calcium channel blockers, respectively) alone or followed by DAMGO, DADLE or bremazocine (mu-, delta- and kappa-opioid agonists, respectively) were studied on the rat tail flick test. The N- (16 to 64 pmoles), but not the L-type blocker (60 to 240 pmoles) produced a dose and time-dependent increase in the latency for the tail-flick reflex. DAMGO (30 to 120 pmoles) or bremazocine (190 to 560 pmoles), but not DADLE (50 to 200 pmoles), produced a dose-dependent increase in the latency for the tail-flick reflex. The effect of the highest dose of DAMGO was smaller, while the effects of DADLE and bremazocine were not changed after nimodipine (60 pmoles). The effects of DADLE were significantly potentiated, while the effects of DAMGO and bremazocine were not changed after omega-conotoxin GVIA (16 pmoles). The intrathecal administration of an N-type calcium channel blocker with a delta-opioid agonist seems to be the most effective combination to produce antinociception in the rat tail flick test.