Effect of ethylketocyclazocine on acetylcholine release in guinea-pig brain slices

The effect of ethylketocyclazocine (EKC) on 3H-Choline (Ch) efflux and on endogenous acetylcholine (ACh) release from guinea-pig brain slices was studied. The drug inhibited the 3H-Ch efflux at a low concentration (0.1 mumol/l) in thalamus slices, while only at high concentrations (30-100 mumol/l) did EKC induce deep inhibition in the caudate nucleus and slight reduction in the cerebral cortex. Dynorphin (1-13) and morphine (Mo) inhibited the ACh release from thalamus slices as well. Naloxone (Nx) was more effective in antagonizing Mo than EKC. The experiments carried out with the endogenous ACh bioassay technique confirmed the above results. Mr 2266 and Mr 1452, both proposed as preferential k antagonists, per se enhanced 3H-Ch efflux from thalamus slices, while the dextrorotatory isomer Mr 1453, devoid of opioid properties, did not share such action. The role of k-opioid receptors in cholinergic system modulation in the guinea-pig brain is discussed.