Enhancement of footshock-induced analgesia by spinal 5,7-dihydroxytryptamine lesions

The analgesia induced by 30-s footshock (1 mA) is enhanced and attenuated by decreasing and increasing the extraneuronal availability of serotonin (5-HT), respectively. In the present work we have shown the effect to be mediated by spinal 5-HT systems as the response was increased by depletion of spinal but not brain 5-HT following injection of 5,7-dihydroxytryptamine into the spinal cord or raphe magnus. Injection of 5,7-DHT into the medial raphe which depleted brain but not spinal 5-HT was without effect.