Anatomical and electrophysiological study of multitransmitter neuron R14 of Aplysia.

This study provides detailed information on the Aplysia neuron R14, including its endogenous electrical activity and extensive axonal projections to a variety of vascular and vascular-related tissues. With the aid of intracellular recording techniques, R14 was found to display in vitro variable spontaneous patterns of silent, beating, or bursting activity. Electrophysiological tracing and intracellular cobalt staining revealed the peripheral processes and target tissues of R14. The white-colored axons of R14 exit the parietovisceral ganglion in the genito-pericardial, spermathecal, branchial, and vulvar nerves. These processes extended 20 mm or more into peripheral tissues: the pericardial wall and lumen, digestive gland sheath, aortae, arteries, and veins. R14 axons also project to the right bag cell cluster. Its extensive axonal projections to tissues associated with the cardiovascular system verify physiological studies that show that R14 plays a role in cardiovascular regulation. This neuron appears to have a wide influence over several aspects of circulation in contrast to individual neurons of the R3-13 group, each of which projects to limited numbers of vascular and vascular-related tissues. R14 also uniquely innervates digestive tissues, thus suggesting that it may act as a nexus between influences on digestive and renal physiology such as ion/water regulation, in addition to modulating cardiovascular homeostasis.