Effects of tyrosyl-arginine (kyotorphin), a new opioid dipeptide, on single neurons in the spinal dorsal horn of rabbits and the nucleus reticularis paragigantocellularis of rats.

The effects of a new endogenous opioid dipeptide (Tyr-Arg), kyotorphin, on single unit activities recorded from the lamina V type neurons in the spinal dorsal horn and the neurons in nucleus reticularis paragigantocellularis (NRPG) of the medulla oblongata were investigated in the rabbit and rat, respectively. Microelectrophoretically applied kyotorphin predominantly depressed the lamina V type neurons but excited the NRPG neurons. Such predominant effects were antagonized by naloxone. These results suggest that kyotorphin has qualitatively similar actions to those of enkephalins in both central regions examined.