Demonstration of denervation supersensitivity: a pharmacological approach.

1. Although the phenomenon of denervation supersensitivity has been extensively studied in peripheral cholinergically and adrenergically innervated organs, the consequences of denervation have not been studied in as much detail in serotonergically innervated s stems. This may be due in part to the difficulties associated with producing specific lesions of serotonergic systems and with quantifying physiological responses of the CNS due to serotonin. 2. Because the lateral ciliated cells of the gill of the bivalve mollusc, Mytilus edulis, are innervated by serotonergic motor neurons which are responsible for accelerating the beating rate of the cilia we used this as a model system with which to study the effects of denervation by physical transections of the branchial nerve and by pharmacological treatments with 5,6 dihydroxytryptamine. 3. Both treatments produced a supersensitive response of the ciliated cells to the superfusion of serotonin. Two mechanisms with different time courses may be responsible. 4. The initial faster acting component may be due to changes in re-uptake mechanisms for serotonin, while the later slowly developing component may be due to other causes, including a hyperplasia of postjunctional serotonin receptors.