Regulation of Cholinergic Transmission in Adrenal Medulla

Abstract

Enkephalin-like peptides co-exist in splanchnic axons with acetylcholine (ACh) (7); therefore, when nerve impulses release these peptides together with ACh, the enkephalin-like peptides could interact with regulatory sites of ACh receptors and modify the responses that are elicited by this amine. Since we are testing this hypothesis in this presentation we have termed the ACh receptor of chromaffin cells “the receptor for the primary transmitter” and the peptide receptor will be referred to as the “co-transmitter receptor.” It appears that in various cholinergic axons a variety of neuropeptides may be stored with ACh (3). The co-existence of polypeptides and amine transmitters has generated great interest and much speculation. Among others, the following trends of thinking have emerged: 1) at the postsynaptic receptors, the sensitivity of recognition sites for primary transmitters is continuously modified by a number of factors, including the amount of co-transmitter that is released from the nerve terminals together with the primary transmitter (5,6) and 2) it appears that the co-existence of a primary transmitter with a given co-transmitter is not obligatory. For instance, ACh co-exists with enkephalin-like peptides in splanchnic axon but in other axons it is associated with VIP (3).