Interganglionic regulation of heartbeat in the cockle Clinocardium nuttallii

Abstract

1. 1. The response of the heart to stimulation of selected nerve pathways and ganglia was studied in the bivalve Clinocardium nuttallii Conrad. 2. 2. Output from the cerebral ganglion chiefly excited the heart, whereas that from the visceroparietal ganglion predominantly inhibited the heart. An inhibitory pathway from the cerebral ganglion and an excitatory pathway from the visceroparietal ganglion were also found. 3. 3. Fibers capable of evoking cardioregulatory activity passed between cerebral and visceroparietal ganglia. These interganglionic pathways were indicated by the fact that stimulating either or both ganglia with the connective between them intact produced excitation and then inhibition. 4. 4. Pathways through both ganglia of a bilateral pair conveyed impulses across the body and produced heart reactions similar to those evoked from a single ganglion of each pair. In addition a nerve pathway between cardioregulatory nerves was found; when all ganglia were excluded and the heart was severed between an auricle and the ventricle, stimulation of the connective on the side of the isolated auricle produced excitation or inhibition of the ventricle. 5. 5. In animals with intact nervous systems, excitation of the heart preceded foot extension, and inhibition of the heart accompanied foot retraction. These and other reactions suggest the extent of co-ordinated involvement of cerebral and visceroparietal ganglia in some aspects of bivalve activity. 6. 6. Possible cardioregulatory nerve pathways are diagrammed.