Neural coupling mechanisms of cardiac output and haemolymph distribution in myogenic hearts

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Liolophura japonica is belonging to the most primitive molluscan taxa, Archiogastropoda. As in almost all studies on the circulatory system, species in Gastropoda, Bivalvia and Cephalopoda have been employed, this study using the chiton Liolophula is, to our knowledge, the first major study on the cardiovascular system of the chiton.1. (1) Heart beats occurred myogenically. The heart received both exciatory and inhibitory nerves from both the lateral and visceral nerve cords.(2) The pericardium showed rhythmic hearts, and received both excitatory and inhibitory nerves from both the lateral and visceral nerve cords. Slow depolarizing potentials preceded spike and plateau potetials of the pericardium. This indicates that pericardial beats occured myogenically.(3) Methysergide antagonized effects of stimulation of excitatory nerves on the heart. Serotonin-like immunoreactive neural processes were observed in the heart and pericardium. These results indicate that excitatory cardiac nerves … More may be serotonergic.(4) Effects of stimulation of inhibitory cardiac nerves on the heart were blocked by mechylxylocholine. Inhibirory nerves may be cholinergic. Peptides such as CARP (catch relaxing peptide) and FMRF amide depressed cardiac and pericardial actions. CARP-and FMRF amide-like immunoreactive neural processes were observed in both the pericardium and the heart. We cannot exclude the possibility that the inhibitory cardiac nerve involves axons containing the peptides or axons containing both co-existing peptide and ACh.2.In the gastropod Aplysia kurodai and A.californica an abdominal ganglionic neuron L7 makes synaptic contact with branchial ganglionic neurons. Excitatory effects of L7 on the gill muscle were depressed by a newly identified neuron in the abdominal ganglion.3.In the embryo of the gastropod Pleurobranchaea, serotonin-like immunoreactive cells first appeared in the trochophore. A larval serotonergic cell cluster appeared in the cerebral commissure in the veliger. The cluster disappeared at metamorphosis from veliger to the juveneile.4.In the silkworm Bombyx mori, the heart shows myogenic beats. A neuron responsible for triggering antidromically conducted heart beat was identified in the frontal ganglion. Less