The pain threshold Was observed after a microinjection of 6—hydr-oxydopamine,a specific neurotoxin of catecholamine,into the alpha part of thegigantocellular reticular nucleus of the rat.The result showed that the pain thre-shold,which was determined by potassium iontophoretic dolorimetry,significantlydecreased in the 6—hydroxydopamine—treated group on the second,fourth,eighthand sixteenth days after the injection as compared with that before the injectionor that in the control group.The data suggest that c...