A crustacean serotonin receptor: Cloning and distribution in the thoracic ganglia of crayfish and freshwater prawn

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Abstract
Serotonin (5‐HT) is involved in regulating important aspects of behavior and a variety of systemic physiological functions in both vertebrates and invertebrates. These functions are mediated through binding to 5‐HT receptors, of which approximately 13 have been characterized in mammals. In crustaceans, important model systems for the study of the neural basis of behaviors, 5‐HT is also linked with higher‐order behaviors, associated with different 5‐HT receptors that have been identified at the physiological and pharmacological levels. However, no crustacean 5‐HT receptors have been identified at the molecular level. We have cloned a putative 5‐HT1 receptor (5‐HT1crust) from crayfish, prawn, and spiny lobster and have raised antibodies that recognize this protein in all three organisms. 5‐HT1crust immunoreactivity (5‐HT1crustir) was observed surrounding the somata of specific groups of neurons and as punctate staining within the neuropil in all thoracic ganglia of crayfish and prawn. In the crayfish, 5‐HT1crustir was also found in boutons surrounding the first and second nerves of each ganglion and on the 5‐HT cells of T1–4. In the prawn, 5‐HT1crustir was also found in axons that project across the ganglia and along the connectives. We found examples of colocalization of 5‐HT1crust with 5‐HT, consistent with the short‐term modulatory role of 5‐HT, as well as cases of serotonergic staining in the absence of a 5‐HT1crust signal, which might imply that other 5‐HT receptors are found at these locations. We also observed receptors that did not possess counterpart 5‐HT staining, suggesting that these may also mediate long‐term neurohormonal functions of serotonin. J. Comp. Neurol. 473:526–537, 2004.