Catcholaminergic salivary glands in Gammarus pulex (Crustacea, Amphipoda): An electron microscopic and microspectrofluorometric study

The type of gland (salivary gland) described here for the amphipod Gammarus pulex belongs to the tegumental glands, which have different structural characteristics. The present type, called rosette gland, is common in some crustaceans and is located in the ventral half of the head. The functional unit is a lobule of gland cells with a central-draining duct. Ducts from groups of lobules conjoin and terminate on the body surface at different points around and in the mouth and mouth parts. With the fluorescence histochemical method of Falck and Hillarp, specific green fluorescence was discerned centrally in the lobules and was confined to the gland cells. The spectral characteristics of the fluorescence, as revealed by microspectrofluorometric analysis, indicated either a mixture of dopamine and a presumed new catechol compound or the presence of two tautomeric forms either of dopamine or of a new catechol compound. Evidence of new catechol compounds with similar spectral characteristics has previously been found in the sensory cells of some invertebrates. The fluorescence distribution within the lobule coincides with the presence, ultrastructurally, of large dense vesicles in the gland cells. These dense vesicles occur in the predominant cell type, also characterized by a smooth endoplasmic reticulum. The other cell type in the lobules differs ultrastructurally by possessing a rough endoplasmic reticulum and a different vesicle type. No innervation of the salivary gland was perceived.