Enkephalins presynaptically inhibit cholinergic transmission in sympathetic ganglia

Abstract

Recent biochemical and immnnohistochemical studies have shown that the opioid peptides, enkephalins, occur in nerve terminals and cell bodies in mammalian sympathetic ganglia^1–3. Opiates and enkephalins are thought to inhibit synaptic transmission in the peripheral nervous tissues as well as in the central nervous system^4–12. The mechanisms of the opiate actions, however, are not entirely clear; both pre- and postsynaptic sites of action have been proposed^7–9,11,12. As acetylcholine is known to be the major neurotransmitter in the autonomic ganglia and as the mechanism of synaptic transmission is well clarified¹³, analysis of the peptide action could be more easily but equally usefully carried out in the peripheral synapses than in central synapses. We now report that enkephalins presynaptically inhibit cholinergic transmission in sympathetic ganglia.