Reference: Biol. Bull., 148: 141-156. (February, 1975) HISTOFLUORESCENT LOCALIZATION OF SEROTONIN AND DOPAMINE IN THE NERVOUS SYSTEM AND GILL OF AIYTILUS EDULIS (BIVALVIA) l GEORGE B. STEFANO AND EDWARD AIELLO Department f Biological Sciences, Fordham University, Hnm.v, New York 10458 In bivalve molluscs there has been physiological evidence of neural control of ciliary activity (Koshtoyants, Buznikov and Manukhin, 1961 ; Aiello and Guideri, 1964, 1966; Takahashi and Murakami, 1968). There has also been histological evidence for the innervation of ciliated gill filaments (Splittstosser, 1913: Setna, 1930; Aiello and Guideri, 1965; Sweeney, 1968). Specifically, in Mytilns cdnlis. Aiello and Guideri (1965) have reported that nerve fibers from the branchial nerve enter individual gill filaments and run beneath the lateral cells. An electron mi-crographic description of this innervation has been given by Paparo (1972). Sweeney (1968) has reported the presence of nerves in the gill filament of Sphaerium sitlcatuni. Grave and Schmitt (1925) reported a bipolar nerve cell sys-tem beneath the ciliated epithelium of the gill in the bivalves Laiiipsilis, Anodonta and AI\a. It has also been established in Al . cdulis that transection of the branchial nerve depresses ciliary activity and this activity was increased by electrical stimulation in the intact animal or in the gill-nerve-visceral ganglion preparation (Aiello and Guideri, 1964, 1965; Takahashi and Murakami, 1968). Other experimenters have proposed the concept of local hormonal control employing acetylcholine (Bulbring, Burn and Shelly, 1953) or serotonin (Gos-selin. Moore and Milton, 1962). Acetylcholine has been found to be both a positive and a negative modulator of the frontal cilia and this effect is concen-tration dependent (Bulbring ct a!., 1953; Aiello and Paparo, 1974). However, acetylcholine esterase activity is largely localized in the nervous system (Bouf-fard, 1970) and the response of cilia on the gill to electrical stimulation of the branchial nerve is altered by the administration of physostigmine, a cholinesterase inhibitor (Aiello and Paparo, 1974). One might equally well, therefore, attribute to endogenous acetylcholine the role of neurotransmitter, with possible actions both on ciliated cells and on elements of the nervous system. Serotonin was also found to have a cilio-excitatory and metabolic stimulatory effect in several lamellibranch gills, and may be an endogenous regulator (Gosselin ct al., 1962; Schor, 1965; Sweeney, 1968; Aiello, 1970). Its precursors, trypto-phan and 5-hydroxytryptophan have been found in the gill of M. cdulis (Aiello, 1960, 1962; Gosselin ct al., 1962) , and the conversion of 5-hydroxytryptophan to serotonin and further breakdown products has been demonstrated ( Blaschko and Milton, 1960; Aiello. 1965). It is not known exactly where these substances are located but Sweeney (1968) has demonstrated the occurrence of serotonin 1 This work was supported in part by a grant from the U.S.P.H.S. (ND-07402). 141
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