OPIOIDS ACTING ON DELTA-RECEPTORS MODULATE CA2+ CURRENTS IN CULTURED POSTGANGLIONIC NEURONS OF AVIAN CILIARY GANGLIA

Opioid agonists inhibited Ba2+ currents in cultured postganglionic neu rones of 3-15-day-old embryonic avian ciliary ganglia. Leucine-enkepha lin (LENK, 10-20 mu M) inhibited transient Ba2+ currents by 50% and su stained currents by 21%. The delta-opioid receptor agonist, DPDPE (0.0 2-10 mu M), also inhibited Ba2+ currents, but kappa- (U50488H) and mu- (DAMGO) receptor agonists had no effect. Inhibition of Ba2+ currents showed profound desensitisation during prolonged application of agonis ts, being reduced to approximately 25% of the original response after 4 min superfusion with leucine-enkephalin (10-20 mu M).