Characterization of HRP-labeled globular bushy cells in the cat anteroventral cochlear nucleus.

We report on the anatomical and physiological features of globular bushy cells in the posterior division of the anteroventral cochlear nucleus based on the characteristics of 20 cells from this population. Each of these cells was recorded from and characterized intracellularly and/or extracellularly, injected with horseradish peroxidase, and studied at the light and/or electron microscopic level. Intracellular records from the vicinity of the globular bushy cell body displayed large, fast synaptic potentials, and in some instances a larger presumed action potential both in silence and during short tone stimulation. Intraaxonal recordings displayed large action potentials in addition to small, fast potentials, which evidence indicates may be the decrementally conducted subthreshold synaptic potentials. Both recording situations indicated that these auditory nerve inputs need not be suprathreshold. Bushy cells with high characteristic frequencies (CFs greater than 3 kHz) typically showed primary-like-with-notch responses to short tones at CF or on-type L responses if the sustained level of discharge after the notch was not as robust. Low-CF bushy cells phase-locked after a well-timed onset spike. Light microscopic anatomy revealed a typically oval cell body giving rise to one or two primary dendrites that branched profusely and an axon that gave off no collaterals within the cochlear nucleus before entering the trapezoid body. Electron microscopic analysis showed a high concentration of large, round, vesicle-containing terminals on the cell body and primary dendrite while the population of terminals on the initial segment and sparsely covered distal dendrites was made up mostly of flat and pleomorphic vesicle-containing terminals.