EFFECT OF OPIATES ON TRANSMITTER RELEASE FROM VISUALIZED HYPOGASTRIC BOUTONS INNERVATING THE RAT PELVIC GANGLIA

1 The effect of opiates on neurotransmission between visualized hypoga stric nerve boutons and postganglionic cell bodies has been examined u sing extracellular recording of nerve bouton impulses (NBIs) and excit atory postsynaptic currents (e.p.s.cs). 2 Morphine (10 to 40 mu M) did not affect neurotransmission in the ganglia. Dynorphin-A (4 mu M) and U50488H (1 mu M) decreased quantal transmitter release and naloxone ( 10 mu M) reversed these effects. 3 Morphine (10 mu M), dynorphin-A (4 mu M) and U50488H (1 mu M) did not affect either the time course or co nsistency with which the NBI was recorded. 4 Dynorphin-A (1 to 4 mu M) and U50488H (1 mu M) decreased the average amplitude of e.p.s.cs by i ncreasing the number of failures to release quanta from single or smal l groups of 2 to 4 boutons during continuous nerve stimulation at 0.1 Hz. 5 The decrease in quantal release induced by dynorphin-A and U5048 8H in 0.2 to 0.5 mM [Ca2+](o) was readily reversed by increasing the e xtracellular calcium ion concentration to 1 mM. 6 It was concluded tha t kappa-opioid receptors are located on the boutons of the hypogastric nerve and when activated by kappa-opioid receptor agonists reduce qua ntal release without affecting the NBI.