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Localization and quantification of 5‐hydroxytryptophan and serotonin in the central nervous systems of Tritonia and Aplysia
Author(s) -
Fickbohm David J.,
LynnBullock, Christina P.,
Spitzer Nadja,
Caldwell Heather K.,
Katz Paul S.
Publication year - 2001
Publication title -
journal of comparative neurology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.855
H-Index - 209
eISSN - 1096-9861
pISSN - 0021-9967
DOI - 10.1002/cne.1272
Subject(s) - aplysia , biology , immunolabeling , serotonin , dopamine , neuroscience , neurotransmitter , lucifer yellow , biocytin , neuron , anatomy , central nervous system , microbiology and biotechnology , immunohistochemistry , biochemistry , receptor , intracellular , immunology , gap junction
Serotonin (5‐hydroxytryptamine, 5‐HT) plays a central role in several behaviors in marine molluscs and other species. In an effort to better understand the regulation of 5‐HT synthesis, we used high performance liquid chromatography (HPLC) with electrochemical detection and immunohistochemistry to measure and map the distribution of the immediate precursor of 5‐HT, 5‐hydroxytryptophan (5‐HTP), in two model opisthobranch molluscs, the nudibranch Tritonia diomedea and the anaspid Aplysia californica . HPLC measurements showed that 5‐HTP is present at approximately the same level as the 5‐HT metabolite, 5‐hydroxyindolacetic acid (5‐HIAA) but is more than 100 times lower in concentration than either 5‐HT or dopamine in the same tissue. Specific 5‐HTP immunoreactivity was colocalized with serotonin in both species. The overall intensity of 5‐HTP immunoreactivity in individual ganglia agreed with HPLC measurements for those ganglia. The intensity of 5‐HTP immunolabeling varied between cell types and was correlated with the intensity of 5‐HT immunolabeling. In particular, differences in staining intensity were consistently seen among the three dorsal swim interneurons of the Tritonia swim central pattern generator circuit. Some nonserotonergic neurons also displayed low levels of 5‐HTP immunolabeling that were above background levels. Together, these results support the notion that production of 5‐HTP is a rate‐limiting step in serotonin synthesis and suggest that there may be additional regulation that allows 5‐HTP to accumulate to varying levels. J. Comp. Neurol. 437:91–105, 2001. © 2001 Wiley‐Liss, Inc.