Ž . Comparative Biochemistry and Physiology Part A 130 2001 341351 Early development of the serotonergic and dopaminergic ž / nervous system in Spisula solidissima surf clam larvae Jill A. Kreiling a,b,1 , Kathryn Jessen-Eller a,1 , Jessica Miller a , Richard F. Seegal c , Carol L. Reinisch a,  a Marine Biological Laboratory, 7 MBL St., Woods Hole, MA 02540, USA b Department of Obstetrics and Gynecology, Brown Uni  ersity School of Medicine, Women and Infants Hospital, 101 Dudley St., Pro idence, RI 02905, USA c Wadsworth Center, New York State Department of Health and School of Public Health, Uni  ersity at Albany, Box 509, Albany, NY 12201-0509, USA Received 18 August 2000; received in revised form 19 June 2001; accepted 26 June 2001 Abstract We have defined the development of the serotonergic and dopaminergic components of the central nervous system in Ž . the early Spisula solidissima surf clam embryo using HPLC and immunocytochemistry. HPLC analysis reveals norepinephrine, dopamine, and serotonin are present at 24 h post-fertilization. Immunocytochemistry shows that the serotonergic nervous system emerges during the late trochophore stage with the development of a single serotonergic cell, CA1, in the cerebralapical ganglion. After 48 h, a second serotonergic cell forms, CA2, which is connected to CA1 by two serotonergic processes, and a single serotonergic cell emerges in the visceral ganglion, V1. At 72 h, a new serotonergic cell body develops in the cerebralapical ganglion, CA3. After 96 h, the cerebralapical ganglion and visceral ganglion are connected by a serotonergic process. Expression of the dopamine receptor, D begins by 24 h with 2, a generalized expression in the region of the developing gut. D expression in the gut ceases by 48 h. At 48 h, a network 2 of fibers forms dorsolateral to the mouth. By 72 h, D expressing projections emerge from this network.  2001 Elsevier 2 Science Inc. All rights reserved. Keywords: Apical ganglion; Cerebral ganglion; Dopamine; Embryo; Neural development; Serotonin; Spisula solidissima; Visceral ganglion 1. Introduction Molluscs comprise one of the largest phyla of living organisms, with over 55 000 living species Ž . currently known Ruppert and Barnes, 1994 . With the exception of the cephalopods, most ma-  Corresponding author. Tel.: 1-508-289-7517; fax: 1- 508-540-6902. Ž . E-mail address: creinisc@mbl.edu C.L. Reinisch . 1 Equal contributions were made by both authors. rine molluscs exhibit a triphasic life cycle, includ- ing an embryonic, a larval and an adult stage. While the adult nervous system has been well characterized in many species, the presence of a larval nervous system has only recently been de- scribed. The development of the serotonergic and dopaminergic components of the larval molluscan nervous system has been extensively studied in several species of gastropods, including represen- Ž tatives of the vetigastropod Barlow and Truman, . Ž 1992 , caenogastropods Dickinson et al., 1999; 1095-643301$ - see front matter  2001 Elsevier Science Inc. All rights reserved. Ž . PII: S 1 0 9 5 - 6 4 3 3 01 00394-4