THE EFFECT OF CERTAIN ANALGESIC DRUGS ON SYNAPTIC TRANSMISSION AS OBSERVED IN THE PERFUSED SUPERIOR CERVICAL GANGLION OF THE CAT

1. In the perfused superior cervical ganglion of the cat the administration of morphine does not affect the size of the contraction of the nictitating membrane produced by pre-ganglionic stimulation, injection of acetylcholine or of KCI when the pre-ganglionic fibres are normally functional, but after degenerative section of the cervical sympathetic nerve, morphine in large doses potentiates the contraction elicited by injections of acetylcholine and of KCI. 2. Pethidine and amidone strongly depress the responses of the membrane to pre-ganglionic stimulation and to injections of acetylcholine or KCI. Both drugs have a similar depressant action on responses to acetylcholine and KCI after denervation of the ganglia. In these actions, 1-amidone is the most powerful and pethidine the least powerful, while dl-amidone is intermediate between the other two substances. 3. Of the three analgesics tested, none have the power to excite a response of the nictitating membrane when injected into the ganglion. 4. The effects of morphine, amidone and pethidine on the responses of the frog rectus abdominis muscle to acetylcholine are analogous to their effects on the responses of the denervated superior cervical ganglion to acetylcholine.