Selective retention of the fluorescent dye DASPEI in a larval gastropod mollusc after paraformaldehyde fixation

In the vertebrates, the vital mitochondrial dye DASPEI (2-(4-dimethylaminostyryl)-N-ethylpyridinium iodide) has been used for the rapid visualization of several distinct classes of epidermal cells in vivo and in vitro: epidermal electroreceptors, mechanoreceptors, and chloride cells in teleosts, and mechanoreceptors in amphibians. I used DASPEI in an attempt to locate a different type of sensory cell, namely, the chemosensory neurons that mediate the initiation of metamorphosis in veliger larvae of the prosobranch gastropod Ilyanassa obsoleta. In vivo, bath-applied DASPEI stains entire larvae in a relatively non-specific fashion. After fixation in phosphate-buffered paraformaldehyde, most of the cells in these animals retained relatively little stain, with some exceptions. Significant DASPEI staining was maintained in approximately nine neurons in the apical ganglion, a temporary cephalic structure that is lost at metamorphosis. Little staining was observed in the rest of the larval central nervous system (CNS), nor could any peripheral sensory neurons be definitively identified. DASPEI was also retained by cells in other larval organs such as the velum and buccal mass, and in two acellular structures, the radula and operculum.