Cardioacceleratory Neurons of the Isopod Crustacean, Ligia exotica: Visualization of Peripheral Projection onto the Heart Muscle

Abstract

Innervation of the heart muscle by the cardioacceleratory neurons was morphologically and electrophysiologically examined in the isopod crustacean, Ligia exotica. Intracellular injection of neurobiotin into the first and second cardioacceleratory neurons (CA1 and CA2) revealed their peripheral axonal projections. Inside the heart, the CA1 and CA2 axons ran along the trunk of the cardiac ganglion. Finely arborized branches with many varicosities arose from the axon and projected over the heart muscle. Stimulation of either the CA1 or CA2 axon caused an overall depolarization in the muscle of a quiescent heart. The amplitude of the depolarization increased with increasing stimulus frequency. During stimulation, the membrane resistance of the heart muscle decreased. In a beating heart, the cardioacceleratory nerve stimulation caused multiple effects on the heart muscle activity and the heartbeat. The results suggest that the cardioacceleratory neurons of Ligia exotica regulate the amplitude of the heartbeat (inotropic effect) and the heart tonus (tonotropic effect) via the synaptic contacts on the heart muscle, while the heartbeat frequency (chronotropic effect) is regulated via the synapses on the cardiac ganglion neurons.

Developmental Changes in Dopamine Modulation of the Heart in the Isopod Crustacean Ligia exotica: Reversal of Chronotropic Effect

“…gishi et al ., 2004). Contractile force of the Ligia cardiac muscle depends on the absolute value of the membrane potential change (Sakurai and Yamagishi, 1998;Yamagishi et al ., 2004), as reported in crustacean skeletal (Orkand, 1962;Atwood and Dorai Raj, 1964) and cardiac muscles (Brown, 1964;Holley and Delaleu, 1972). Hence, reinforcement of the myocardial plateau potential results in a positive inotropic effect (increase in contractile force) on the heart.…”

Dual Effects of Dopamine on the Adult Heart of the Isopod Crustacean Ligia exotica

“…This fact indicates that dopamine reinforces the plateau potential of the myocardium, as observed in the adult neurogenic heart (Yama- , 2004). Contractile force of the Ligia cardiac muscle depends on the absolute value of the membrane potential change (Sakurai and Yamagishi, 1998;Yamagishi et al ., 2004), as reported in crustacean skeletal (Orkand, 1962;Atwood and Dorai Raj, 1964) and cardiac muscles (Brown, 1964;Holley and Delaleu, 1972). Hence, reinforcement of the myocardial plateau potential results in a positive inotropic effect (increase in contractile force) on the heart.…”

Myocardial Depolarizing Response to Glutamate in the Myogenic Heart of the Branchiopod Crustacean Triops longicaudatus

“…Magnitude of contraction of crustacean skeletal and cardiac muscle depends on the absolute value of the potential change (Orkand, 1962: Atwood andDorai Raj, 1964;Brown, 1964;Holley and Delaleu, 1972). In the Ligia heart, reinforcement of the action potential plateau (plateau potential) of the myocardium induced by stimulation of the cardioacceleratory nerve results in an increase in the amplitude of the heartbeat (Sakurai and Yamagishi, 1998b). These facts lead to the conclusion that dopamine produces an inotropic effect on the heartbeat by reinforcing the myocardial plateau potential.…”