Release of met-enkephalin and its modulation through acetylcholine receptors in the rabbit superior colliculus. 
This report presents evidence for the depolarization-dependent release of met-enkephalin from the superior colliculus of the rabbit.  Collicular tissue was placed in superfusion chambers and met-enkephalin accumulation in the superfusate was measured by radioimmunoassay.  Exposure to high potassium concentrations (30 mM and 56 mM) increased met-enkephalin release.  This is the fourth transmitter shown to be released from collicular tissue.  Furthermore, we have obtained the first evidence that suggests that met-enkephalin release is susceptible to muscarinic modulation.  While the depolarization-dependent release of met-enkephalin was depressed in the presence of atropine (1 microM), hexamethonium (100 microM) did not block the increase of met-enkephalin release induced by high potassium.