European Journal of Pharmacology, 62 (1980) 111-115 0 Elsevier/North-Holland Biomedical Press 111 DENERVATION PRODUCES SUPERSENSITIVITY OF A SEROTONERGICALLY INNERVATED STRUCTURE EDWARD J. CATAPANE, ERICA D. COLLINS, JUAN A. MARCANO and GEORGE B. STEFANO zyxwvutsrqponmlkjihgfe Department of Natural Sciences, Medgar Euers College, C.U.N.Y. Brooklyn, New York, U.S.A. (Received 20 November 1979, accepted 14 January 1980 E.J. CATAPANE, E.D. COLLINS, J.A. MARCANO and G.B. STEFANO, Deneruation produces supersensitivity of a serotonergically innervated structure, European J. Pharmacol. 62 (1980) 111-115. The lateral ciliated gill epithelium of Myths edulis was denervated physically and chemically with 5,6dihy- droxytryptamine. Lateral ciliary activity which is under excitatory serotonergic control displayed an increased response to superfusion with serotonin after both treatments, as compared to controls. Endogenous serotonin levels were reduced by these treatments. An increase in maximal cilioexcitatory response was also noted. Denervation Serotonergic innervation 5,6-Dihydroxytryptamine 1. Introduction 2. Materials and methods Supersensitivity following denervation of an organ has been extensively studied in peripheral cholinergically and adrenergically innervated organs (for a review see: Fleming et al., 1973; Langer, 1975). However the con- sequences of denervation have not been much studied in serotonergically innervated systems partly because of the difficulties associated with producing specific lesions of serotonergic systems and with quantifying physiological responses of the CNS due to serotonin. Specimens of M. edulis were collected at low tide from the shores of Long Island Sound at New Rochelle, N.Y. and maintained in the laboratory in a marine aquarium (Aquarium Systems) in artificial sea water (ASW) prepared from synthetic sea salts (Instant Ocean, Aquarium Systems, Eastlake, Ohio) dissolved in deionized distilled water kept at a specific gravity of 1.024 * 0.001, pH 7.2 ?r 0.2 at 17 f 1°C. M y tilus edulis, a marine bivalve mollusc, possesses a well-defined peripheral serotonergic system whose physiological activity can be accurately monitored and quantified. Its lateral ciliated gill epithelium is innervated by serotonergic motor neurons which constitute a part of the branchial nerve and are responsible for accelerating the beating rate of the cilia (Catapane et al., 1978). The purpose of the present investigations was to study the physiological effects of denervation with the serotonergically inner- vated gill of M. edulis used as test system. Lateral ciliary activity was determined by stroboscopic microscopy as described by Catapane et al. (1978). A binocular inverted microscope (Olympus C-400) was used in which a Grass PS22 photostimulator replaced the light source. Cilia of the lateral gill cells were routinely observed at a magnification of 200X. Their beating rate is measureable by synchronizing the flashing of the stroboscope with their beating rate. When synchronization is achieved the lateral ciliary wave gives the illusion of being motionless in a characteristic horseshoe-like configuration. Physically denervated gills were prepared