[Electrophysiological effects of opiates and endogenous peptides on central neurons]

The influence of micro-iontophoretically administered opiates and opiate peptides on the activity of single neurones in the central nervous system will be discussed. It will be shown that in single neurone studies in several different supraspinal regions opiates and opiate peptides have similar actions on individual neurones and both may excite or depress neuronal activity. The excitatory and inhibitory effects of these substances can be reversed by a necrotic antagonist and therefore may be mediated via an action at specific opiate receptors. Studies on spinal neurons indicate that the excitatory action of morphine and enkephalin may be due to an interaction with a cholinergic receptor or at least cholinoceptive neurones. Evidence will also be presented showing that responses of dorsal horn neurones to nowious peripheral stimuli may be selectively reduced by morphine and enkephalin administered into the substantia gelatinosa region or the spinal cord. The relevance of these observations to the pharmacological action of opiates and the possible physiological function of endogenous opiate peptides will be mentioned.