Membrane properties and discharge characteristics of guinea pig dorsal cochlear nucleus neurons studied in vitro

Abstract

Intracellular recordings were made from neurons of the guinea pig dorsal cochlear nucleus in an in vitro brain slice preparation. The membrane properties of the cells were studied, and the membrane potentials were manipulated by current injection to determine how intrinsic conductances might alter the cell discharge patterns. Eleven cells were marked with Lucifer yellow. Ten of these cells were identified as the large pyramidal cells of layer 2 of this nucleus, and 1 cell was identified as a "vertical" cell in layer 3. Two kinds of action potentials were observed: simple spikes and complex spikes. This report discusses only cells with simple spikes. Simple spiking cells (60/72 recorded cells; all stained cells were simple spiking cells) discharged in a regular fashion with depolarization, and had linear frequency-current relationships up to 2 nA with a mean slope of 116 Hz/nA. The discharge rate was approximately constant throughout the current pulse. Responses of simple spiking cells to depolarizing current steps superimposed on a steady-state membrane hyperpolarization were studied. When the membrane has been held hyperpolarized, small current pulses produce a long-latency regular train of action potentials. Larger current pulses superimposed on membrane hyperpolarization can produce a short-latency action potential followed by a long silent interval (i.e., a long first interspike interval), and finally a regular train of spikes. It is concluded that the membrane conductances of DCN pyramidal cells are capable of generating at least 3 discharge patterns (regular firing, long first spike latency, and long first interspike interval) depending on the state of the membrane potential prior to a depolarizing current step. These responses are similar to the "chopper," "buildup," and "pauser" discharge patterns reported for these cells in vivo in response to tone bursts. The modulation of the intrinsic membrane conductances by membrane polarization and the possible contribution of these conductances to the generation of DCN discharge patterns provide new insights into the mechanisms underlying the responses of DCN cells to acoustic stimuli.

Response patterns to sound associated with labeled globular/bushy cells in cat

“…Later studies of response physiology showed that a single morphological unit type can exhibit multiple temporal response patterns. This was best shown in the dorsal CN where fusiform cells exhibit a variety of PSTH patterns (descriptively labeled pauser, buildup and chopper) that depend upon the intracellular potential (Rhode and Smith, 1986b;Manis, 1990).…”

Coding interaural time differences at low best frequencies in the barn owl

“…Although brief EPSCs underlie the rapid synaptic potential changes seen in time coding neurons, the intrinsic electrical properties of these neurons also shape the synaptic response as well as the temporal firing pattern. Voltage sensitive K þ conductances determine the response properties of auditory neurons, and each cell type exhibits a distinct complement of outward K þ currents [3,67,77,123]. At least two K þ conductances underlie phase locked responses in auditory neurons: a low and a high threshold conductance [11,67,90,91,120].…”

“…Bushy and medial nucleus of the trapezoid body cells share similar brief active constants and potassium conductances with octopus cells [67,68,76,81], but instead encode the phase of the auditory stimulus [15,46,83]. Bushy and trapezoid body neurons do not sum many synaptic inputs, as octopus cells do.…”

Identification of cell types in brain slices of the inferior colliculus

“…This behavior is similar to the ªbuildupº response in the cochlear nucleus 42 that is caused by the A-type potassium current and also revealed by pre-hyperpolarization. 14,23 The sustained ®ring of one neuron is shown at two current levels (Fig. 4A).…”

“…Finally, the buildup±pauser pattern is seen in the fusiform cell both in vitro to current and in vivo to acoustic stimuli. 8,12,23,29,50 These cells in dorsal cochlear nucleus respond to frequencies above 2 kHz, where phase locking to pure tones is limited, and also project directly to the IC. 30 As in the cochlear nucleus, the distinct discharge patterns reported here in the IC may signify neurons with different functions.…”