GIANT TERMINALS IN THE DORSAL OCTAVOLATERALIS NUCLEUS OF LAMPREYS

The dorsal octavolateralis nucleus of lampreys is a primary nucleus fo r electroreceptive stimuli in the medulla. In Lampetra japonica, the r ostral and caudal thirds of this nucleus are exclusively occupied by g iant terminals, which become evident when the primary fibers of an ele ctrosensory nerve (recurrent branch of the anterior lateral line nerve ) are labeled with horseradish peroxidase. We studied the ultrastructu re of these terminals. They contain neurofilaments, mitochondria, micr otubules, and tubular membranous structures. Many synapses, all of the chemical type, are located around the neck region of the terminal swe llings. Many vesicular structures, which are clear, round, and uniform in size, and most of which are probably synaptic vesicles, are densel y clustered in a single large mass in the neck region of the terminals . Some of the tubular structures may serve as a membrane reservoir for the large number of synaptic vesicles required in the giant terminals . (C) 1993 Wiley-Liss, Inc.