Firing properties of chopper and delay neurons in the lateral superior olive of the rat |
| |
Authors: | T J Adam Dietrich W F Schwarz Paul G Finlayson |
| |
Institution: | (1) The Rotary Hearing Centre, Department of Surgery, Koerner Pavilion, F-153, 2211 Wesbrook Mall, U. B. C. Vancouver, B.C., Canada, V6 T 2B5 e-mail: rothearc@unixg.ubc.ca Tel.: +1-604-822-7133, Fax: +1-604-822-7240, CA |
| |
Abstract: | Neurons in the lateral superior olivary nucleus (LSO) respond to acoustic stimuli with the ”chopper response”, a regular
repetitive firing pattern with a short and precise latency. In the past, this pattern has been attributed to dendritic integration
of synaptic inputs. We investigated a possible contribution of intrinsic membrane properties using intracellular recording
techniques in a tissue slice preparation. We found two electrophysiological classes of neurons in the LSO. Chopper neurons
responded to depolarizing current pulses with a single onset spike at short, precise latency close to threshold and with repetitive,
regular, but accommodating discharges at greater current intensities. An emphasis of response onset and subsequent rate accommodation
resulted from the activation of a voltage- and time-dependent sustained outward rectification in a range depolarized from
rest. Responses to hyperpolarizing pulses were characterized by an inward rectification, which caused a depolarizing voltage
sag in a range negative to –65 mV. Peristimulus time histograms were multimodal, and discharge regularity was evident in narrow
unimodal interspike interval time histograms and low coefficients of variation. The accommodation time course was usually
fit best by two exponentials with time constants of τ1=3–8 ms and τ2=32–97 ms. Delay neurons responded with a regular repetitive firing to depolarization by current pulses. However, repetitive
spike discharge occurred with a prolonged, variable delay of 25–180 ms. High current intensities evoked an additional onset
spike with short, precise latency. Activation of a transient outward conductance in the depolarized voltage range caused an
early repolarization, which terminated as a depolarizing ramp, reaching spike threshold after the delay. Flat peristimulus
time histograms characterized the repetitive discharge in spite of narrow unimodal interspike interval time histograms and
low coefficients of variation. Intracellular neurobiotin injections revealed morphological differences between these classes.
Chopper neurons were large and fusiform, with a bipolar dendritic distribution oriented perpendicular to the curvature of
the LSO. Delay neurons were small and spherical, with highly branched tortuous dendritic arbours of bipolar origin and variable
orientation. Chopper and delay neurons are probably LSO principal cells and lateral olivocochlear efferent neurons, respectively.
Our findings suggest that the pattern of firing activity of LSO neurons to sound, in vivo, is determined to a large extent
by intrinsic membrane properties. Somato-dendritic integration of synaptic inputs are fundamental to the encoding of interaural
sound differences, but membrane non-linearities play an important role in determining postsynaptic response patterns.
Received: 3 December 1997 / Accepted: 28 July 1998 |
| |
Keywords: | Regularity Lateral superior olive Chopper Lateral olivocochlear system |
本文献已被 PubMed SpringerLink 等数据库收录! |
|