The calcium-dependent neuronal release of serotonin and its antagonism by lithium

The cilio-excitatory serotonergic innervation of lateral gill cilia of Mytilus edulis was studied in vivo. Peripheral serotonin release was dependent on the external calcium concentration. Serotonin release was inhibited by autodialyzing calcium from the tissue or by increasing the calcium concentration in the medium, as determined by measuring ciliary activity stroboscopically and by biochemical and radioassays of serotonin. Lithium also inhibited serotonin release when added to the external bathing medium. Concomitantly, altering calcium concentrations altered the degree of inhibition of serotonin release caused by lithium. The study demonstrates that the terminal release of the monoamine serotonin is a calcium-dependent mechanism. The pharmacological effects of lithium in this system appear to be interrelated with the calcium-dependent releasing mechanism.