ULTRASTRUCTURE OF THE UNUSUAL ACCESSORY SUBMANDIBULAR-GLAND IN THE FRINGE-LIPPED BAT, TRACHOPS CIRRHOSUS

Background: The phyllostomid fringe-lipped bat, Trachops cirrhosus, is sui generis (in a family of ca, 138 species) in that it subsists in p art on tropical frogs, These amphibians frequently possess highly toxi c integument, We examined the salivary glands of this bat to determine if these glands could be the source of protective factors that permit consumption of seemingly unsavory prey The parotid and principal sali vary glands of this bat are similar to homologous glands in other phyl lostomids, but the accessory submandibular gland is unique0 Methods: T he accessory submandibular glands of live-trapped T. cirrhosus were fi xed and processed for transmission electron microscopy by conventional means. Results: The accessory submandibular gland consists of follicl es and ducts, The principal cells of the follicular walls have an abun dance of rough endoplasmic reticulum (RER), free ribosomes, and extens ive Golgi apparatuses. Typically, these cells have relatively few sero us secretory granules, The cells contain collections of peculiar lipid droplets, and some of their mitochondria have dense crystalloids with in expanded cristae, A layer of irregular, moderately dense bodies lie s immediately subjacent to the luminal plasmalemma; it is not clear if these structures are endocytotic or exocytotic. Clusters of mucous ce lls, some of which have a single, hugely distended RER cisterna, are e nsconced in the follicular walls; mucus from these cells reaches the l umen via intercellular canaliculi. Ducts progress from simple cuboidal to simple columnar epithelium. They lack basal striations, and their constituent cells contain relatively few mitochondria, Follicles and d ucts have numerous myoepithelial cells at their periphery, and both ar e heavily innervated by hypolemmal nerve terminals. Conclusions: The u nusual accessory submandibular gland in T. cirrhosus documents the ext reme modifications in gland histology and in cell ultrastructure that have occurred in mammalian families, The cells composing the follicle walls and ducts bear little similarity to typical acinar or duct cells , Duplication of the submandibular gland in some bat lineages might be the key innovation underlying such plasticity The heavy innervation o f both follicles and ducts also implies that these structures are sens itive to and capable of responding to various inputs, perhaps includin g dietary factors. (C) 1997 Wiley-Liss, Inc.