Dopaminergic effects on tail-flick response in spinal rats.

R-Apomorphine (0.02-1.75 mumol/kg), administered by intrathecal infusion to spinalized rats, caused a dose-dependent increase in tail-flick latency. The effect of R-apomorphine was counteracted significantly by the dopaminergic receptors antagonists cis-flupenthixol (0.20-3.94 mumol/kg) and (+)-butaclamol (0.78 mumol/kg), but not by their enantiomers nor by phenoxybenzamine (29.40 mumol/kg) or methysergide (29.40 mumol/kg). The findings suggest that dopaminergic mechanisms play a role in the modulation of nociception in the spinal cord.