title: Systemic serotonin sulfate in opisthobranch mollusks.
abstract: Serotonin (5-hydroxytryptamine, 5-HT) is a ubiquitous modulatory neurotransmitter with roles as a neurohormone and neurotransmitter. However, few studies have been performed characterizing this molecule and its related metabolites in circulating fluids. Here, we demonstrate native 5-HT sulfate, but much lower levels of 5-HT, in hemolymph of the marine mollusk Pleurobranchaea californica. The metabolite 5-HT sulfate forms from 5-HT uptake and metabolism in central ganglia of Aplysia californica and in the visceral nerve and eye of Pleurobranchaea, but not in hemolymph itself. In addition, 5-hydroxyindole acetic acid (5-HIAA), while not detected in hemolymph, forms in higher quantities than does 5-HT sulfate in the eye and visceral nerve, and gamma-glu-5-HT is also observed in this area but never in hemolymph. As systemic 5-HT sulfate appears not to originate from the optic region or from systemic 5-HT, 5-HT sulfate likely derives from the nervous system. Circulating 5-HT sulfate is at least 10-fold higher during the light portion of a 12 : 12-h light/dark cycle than during the dark portion (p < 0.0007), but there is no obvious trend for free systemic tryptophan (Trp) (p > 0.3) in Pleurobranchaea. 5-HT in mollusks is associated with general arousal state; thus, diurnal systemic changes in a 5-HT catabolite may reflect a regulatory role for indole catabolism in behavioral rhythms.
authors.affiliation: Department of Chemistry, University of Illinois, Urbana, Illinois 61801, USA.
authors.forename: Jeffrey N
authors.initials: JN
authors.lastname: Stuart
authors.forename: Jason D
authors.initials: JD
authors.lastname: Ebaugh
authors.forename: Ashley L
authors.initials: AL
authors.lastname: Copes
authors.forename: Nathan G
authors.initials: NG
authors.lastname: Hatcher
authors.forename: Rhanor
authors.initials: R
authors.lastname: Gillette
authors.forename: Jonathan V
authors.initials: JV
authors.lastname: Sweedler
mesh_terms: D006916:5-Hydroxytryptophan / Q000378:metabolism; D000818:Animals; D001048:Aplysia / Q000378:metabolism*; D001143:Arousal / Q000502:physiology; D002940:Circadian Rhythm / Q000502:physiology; D017952:Ganglia, Invertebrate / Q000737:chemistry / Q000378:metabolism; D006458:Hemolymph / Q000737:chemistry / Q000378:metabolism; D006897:Hydroxyindoleacetic Acid / Q000032:analysis / Q000378:metabolism; D008974:Mollusca / Q000378:metabolism*; D009928:Organ Specificity / Q000502:physiology; D017440:Photoperiod; D012701:Serotonin / Q000031:analogs & derivatives / Q000032:analysis / Q000378:metabolism*; D014364:Tryptophan / Q000032:analysis / Q000378:metabolism
chemical_list: C033396:5-hydroxytryptamine O-sulfate; D012701:Serotonin; D006897:Hydroxyindoleacetic Acid; D014364:Tryptophan; D006916:5-Hydroxytryptophan