Electrophysiological evidence for kappa-agonist activity of dynorphin in rat brain.

Dynorphin (1-13) and the mu-agonist, FK 33,824, have been applied microiontophoretically to single neurones in the hippocampus of the rat. Whereas FK 33,824 predominantly caused an increase in neuronal firing rates, dynorphin (1-13) decreased activity. Both effects were blocked by the opiate antagonist naloxone, whereas the effects induced by GABA and glutamate were not. This action of dynorphin (1-13) is comparable to that of other kappa-agonists in this brain region and suggests that dynorphin (1-13) may be a ligand for the kappa opiate receptor.