Neural Control of the Lateral Abdominal Arterial Valves in the Lobster <i>Homarus americanus</i>

Abstract

A dorsal abdominal artery in Homarus americanus runs the length of the abdomen, giving rise to one pair of large lateral arteries in each segment. These lateral arteries supply hemolymph to the abdominal muscles and the swimmerets. In addition, many small vessels leave the dorsal abdominal artery ventrolaterally to supply the gut and gonads. Bicuspid muscular valves are located at the junction of each segmental lateral artery with the dorsal abdominal artery, but not at the origin of the gut vessels. Nerves originating from the ventral abdominal ganglia travel along the lateral arteries to innervate the valves, providing both inhibitory and excitatory inputs. Inhibitory input produces hyperpolarizing inhibitory junctional potentials that relax the valve muscles, and in intact in situ perfused arteries causes increases in outflow from the affected lateral artery. Excitatory input produces depolarizing excitatory junctional potentials that close the valves and reduce perfusate outflow. The valve nerves also branch to innervate valves up to two segments anterior and one segment posterior. Application of exogenous {gamma}-aminobutyric acid hyperpolarizes valve muscle fibers. This and the hyperpolarizing effect of valve nerve stimulation are reversibly abolished by the application of picrotoxin (10-5 M). Acetylcholine (10-5 M), but not glutamate, causes depolarization and contraction of valves. The role of the valves in controlling the distribution of hemolymph flow is discussed.