The fine structure of nerve endings in the nucleus of the trapezoid body and the ventral cochlear nucleus

TLDR

Large calyciform axonal endings and typical boutons have been described in the ventral cochlear nucleus and nucleus of the trapezoid body by light microscopy. The study examined these endings ultrastructurally in chinchillas, rats, and a cat using osmium tetroxide–fixed electron microscopy. Calyces are elongated processes from myelinated axons forming multiple synapses with perikarya and dendrites, indicating high synaptic activity, while adjacent boutons—often smaller vesicle-bearing and likely centrifugal inhibitory fibers—provide additional contacts.

Abstract

Abstract Large, calyciform axonal endings, as well as typical terminal boutons, have been previously described in the ventral cochlear nucleus and the nucleus of the trapezoid body by light microscopists. In the present study, these endings were examined with the electron microscope in chinchillas, rats, and a cat after perfusion fixation with osmium tetroxide. The calyces were found to consist of elongated processes arising from myelinated axons and making multiple synaptic contacts with perikarya and dendrites. This finding suggests that an important property of calyces is the large amount of synaptic activity that they can bring to bear on a single post‐synaptic structure. Adjacent to the calyciform endings were variable numbers of boutons that made synaptic contacts with the same perikarya and dendrites. The majority of boutons contained smaller synaptic vesicles than those present in the calyces, implying both anatomical and functional differences between these two types of ending. It is suggested that many of these boutons in the ventral cochlear nucleus are endings of centrifugal, inhibitory fibers described by previous workers.