Spontaneous activity and pacemaker property of neurons in the cardiac ganglion of an isopod, Ligia exotica

1. 1. The Ligia cardiac ganglion which is composed of six similar-sized neurons has been studied electrophysiologically. 2. 2. Intracellular recordings from the ganglion cells show periodic burst activity with conspicuous pacemaker potentials between bursts. 3. 3. All of the ganglion cells burst almost simultaneously and produce compound action potentials in the ganglionic trunk and the ganglionic nerve branches. 4. 4. The burst discharge is not always initiated in the same cell, but changes during spontaneous activity. 5. 5. When isolated, any of the ganglion cells could produce periodic burst activity with pacemaker potentials. 6. 6. Intracellular stimulation applied to one of the ganglion cells changed the burst interval and reset the burst rhythm of all ganglion cells. 7. 7. In Ligia heart, all ganglion cells have the pacemaker activity and may be mononeurons to the heart. These are compared to the properties of neurogenic hearts of some other crustaceans and Limulus.