RELATIONSHIP BETWEEN 5-HYDROXYTRYPTAMINE AND NERVE STIMULATION OF CILIARY ACTIVITY

¹ Department of Pharmacology, New York Medical College, New York, New York

Mussels (Mytilus edulis) were injected with 1 mg of reserpine 1 to 5 days prior to testing for an increase in the rate of beating of cilia in the gill in response to electrical stimulation of the branchial nerve. Reserpine-treated mussels responded significantly less than saline injected controls and had significantly less 5-hydroxytryptamine (HT) in their gills. In both groups, ciliary beating was accelerated equally by exogenous HT. Bromolysergic acid diethylamide (BOL) diminished the effect of both exogenous HT and nerve stimulation. BOL block could be overcome by higher concentrations of HT but not by high concentrations of hydroxytryptophan (HTP), even though the endogenous concentration of HT was elevated more by incubation in HTP than in HT. It was concluded that the rate of diary beating is unrelated to the total concentration of gill HT, but may be dependent on the concentration of free HT, which in turn may be determined by branchial nerve activity.