Development of the vagal taste system of goldfish.

Goldfish are among a group of fishes which possess a highly developed sense of taste. Many species of the cyprinid (minnow) and catostomid (sucker) families possess specialized food-handling structures in the oropharynx (e.g. the palatal organ and branchial arches) which are covered with taste buds innervated by fibers of the glossopharyngeal and vagal nerves. The central termination for these gustatory afferents is an enlarged lobe on the dorsal surface of the hindbrain (vagal lobe). The vagal lobe is a highly organized, laminated structure consisting of an outer sensory zone, a central fiber zone, and an inner zone of vagal motor neurons (Morita et al., 1983). Gustatory afferents from the oropharyngeal epithelium travel into the vagal lobe through the fiber zone to terminate topographically in restricted portions of the sensory zone (Morita and Finger, 1985). Interneurons in the sensory layers project radially inward to the motor zone, connecting sensory input from a given portion of the sensory epithelium with motor neurons projecting to muscles in that same region of the oropharynx (Finger, 1988). This results in a highly ordered neural system organized in radial ‘modules’ that are topographically related to the sensory epithelium. While general development of the goldfish has been studied previously, and taste bud development in zebrafish (Hansen et al., 2002), little is known of the development of the central connections of the vagal nerve and of the vagal lobe in cyprinids. Our lab is investigating the development of the goldfish vagal taste system, and the relationships of peripheral and central developmental mechanisms.