Spinal 5-HT or NA uptake inhibition potentiates supraspinal morphine antinociception in rats

Spinal injection of the specific uptake inhibitor of 5-hydroxytryptamine (5-HT), citalopram, or of noradrenaline (NA), desipramine, potentiated the antinociception following intracerebroventricular injection of morphine in rats tested on the hot plate. Combined spinal injection of citalopram and desipramine caused a synergistic potentiation. The unselective and less potent inhibitor of both 5-HT and NA uptake, amitriptyline, did not cause potentiation. The results support the suggested involvement of both 5-HT and NA pathways in supraspinal morphine antinociception.