Effect of dalargin, a synthetic leu-enkephalin analogue on synaptic transmission in the Lorenzini ampullae of rays

Abstract

Effects of dalargin, a synthetic leu-enkephalin analogue and its antagonist naloxone on synaptic transmission in afferent synapses of ray electroreceptors were investigated using an isolated preparation of Lorenzini ampullae from Black sea rays. It was shown that dalargin (10−6–10−10 mole liter) both decreased background activity and evoked activity of an afferent fiber in a dose-dependent manner. Naloxone (10−5 mole/liter) also inhibited afferent impulsation and completely blocked responses of the Lorenzini ampullae to dalargin application. L-glutamate-induced excitatory responses were reduced in the presence of dalargin. It is suggested that the modulatory action of dalargin on glutamatergic synaptic transmission in the Lorenzini ampullae is exerted via specific opiate receptors.