Effect of dopamine receptors on the ventrolateral orbital cortex induced antinociception

Objective To examine whether activation of D1-like and D2-like dopamine receptors are involved in the ventrolateral orbital cortex(VLO) induced antinociception.Methods A damaging thermal stimulation was applied on rats tail lightly anesthetized to evoke tail flick(TF) reflex.Using TF latency(TFL) as an index,the effect of microinjection of different drugs were observed in VLO.Results Microinjection of the D1-like dopamine receptors agonist SKF-38393(1.0、5.0 μg) in VLO didn′t change the baseline of TFL.But microinjection of the D2-like dopamine receptor agonist quinpirole(0.1-2.0 μg) into VLO produced dose-dependent antinociception.The order of the TFL increases in different treated groups were 0.1 μg group=0.5 μg group 1.0 μg group 1.5 μg group 2.0 μg group.This antinociception was antagonized by D2-like dopamine receptor antagonist raclopride(1.5 μg) in VLO at the same site of injection.Raclopride(1.5 μg) microinjected alone into the VLO had no effect on the TF reflex.Conclusion D2-like dopamine receptor activation may be involved in the VLO induced antinociception.