Synaptic responses and electrical properties of cells in brain slices of the mouse anteroventral cochlear nucleus

Intracellular recordings were made from cells in brain slices of the anteroventral cochlear nucleus. Responses to electrical stimulation of the stump of the auditory nerve were: (1) all-or-none, following the stimulus with no delay, and insensitive to the removal of extracellular Ca2+, probably representing the firing of directly stimulated auditory nerve fibers, or (2) graded, excitatory postsynaptic potentials, with synaptic delays of about 0.7 msec, which were often followed by graded, inhibitory synaptic potentials with synaptic delays of 1.2 msec or longer. The excitatory and inhibitory synaptic potentials were abolished by the removal of extracellular Ca2+. The result that delays of inhibitory synaptic responses were at least 2 times as long as those of excitatory ones indicates that probably an additional synapse was interposed. Responses to intracellularly injected current pulses show that cells in the anteroventral cochlear nucleus have one of two types of electrical characteristics. Type I properties are characterized by linear current-voltage relationships in the subthreshold voltage range and large, regularly firing action potentials in the suprathreshold range. Type II properties are characterized by nonlinear current-voltage relationships; suprathreshold depolarization elicits only one or two small action potentials. Type II characteristics are particularly well suited for maintaining the information contained in the timing and patterns of firing of the auditory nerve fibers.