Independent co-release of acetylcholine and somatostatin from cardiac vagal neurones in toad.

Vagal postganglionic neurones in toad (Bufo marinus) cause cardio-inhibition by releasing both acetylcholine and somatostatin. In isolated, electrically paced, toad atria, intracardiac neurones were stimulated by short bursts of high-voltage pulses applied during the atrial refractory period. Treatment with hemicholinium-3 (5 X 10(-4) M) for 5 h eliminated most of the acetylcholine-mediated cardio-inhibition but did not inhibit somatostatin-mediated transmission. It is concluded that somatostatin release does not depend on the simultaneous release of acetylcholine.