Inter- and motor-neuronal functions of the cardio-inhibitory nerve in the heart of the isopod crustacean, Ligia exotica

1. 1. Innervation of the heart by the cardio-inhibitory nerve was electrophysiologically examined in Ligia exotica. 2. 2. Three kinds of cardio-regulatory impulses, one inhibitory and two acceleratory, were identified in each of the two anterior cardiac nerves. 3. 3. The inhibitory impulses induced inhibitory postsynaptic potentials (IPSPs) in all the six neurons comprising the cardiac ganglion and suppressed their spontaneous burst activities. 4. 4. The inhibitory impulses induced inhibitory junctional potentials (IJPs) in the myocardial cells and hyperpolarized their membrane potentials. 5. 5. We concluded that the cardio-inhibitory nerve innervates directly both the cardiac ganglion cells and the myocardial cells.