RIORDAN, JR., T.J.; LINDSAY, S.M.*: Functional labeling of peripheral sensory cells in the spionid polychaete, Dipolydora quadrilobata

Our integrated investigation of chemoreception in deposit-feeding polychaetes has identified and described putative sensory structures on the feeding palps of several spionid polychaete species and shown that chemical cues bound to glass beads stimulate feeding in the spionid Dipolydora quadrilobata. Here, we present results from our most recent activity-dependent cell labeling experiments. Adapting an immunohistochemical method used to identify odor-activated neurons in spiny lobster and zebrafish, we immersed whole D. quadrilobata in artificial seawater (ASW) inside a small cover-slip perfusion chamber and exposed them to either the channel-permeant cation, Agmatine (1-amino-4-guanidobutane, AGB) in ASW, or AGB plus an amino acid mixture known to stimulate feeding behavior. An Anti-AGB antibody was used to detect activated cells in sections of fixed tissue. Bright-field images of sections were captured digitally from a light microscope equipped with a video camera. Palp cells labeled with AGB were identified by quanitifying the pixel intensity inside a cell of interest and comparing it to the pixel intensity of an adjacent unlabeled region. Labeled cells were grouped by region on the feeding palp: frontal, laterofrontal, lateral and abfrontal. Stimulation with amino acids in the presence of AGB resulted in significantly more labeled lateral and abfrontal cells compared to controls (AGB only). The number of labeled laterofrontal and frontal cells was not significantly different between treatment and controls. These results suggest that the lateral and abfrontal sensory cells function as chemoreceptors while the laterofrontal and frontal cells may function as mechanoreceptors, chemoreceptors, or both.