IMPACT OF SPONTANEOUS SYNAPTIC ACTIVITY ON THE RESTING PROPERTIES OF CAT
NEOCORTICAL PYRAMIDAL NEURONS IN VIVO.
Denis Par‚, Eric Shink, H‚lŠne Gaudreau, Alain Destexhe, and Eric J. Lang.
D‚partement de Physiologie, Facult‚ de M‚decine, Universit‚ Laval, Qu‚bec,
(QUE), CANADA, G1K 7P4. Department of Physiology and Neuroscience, New York
University Medical Center, 550 First Avenue, New York, NY 10016, USA
APStracts 4:329N, 1997.
ABSTRACT
The frequency of spontaneous synaptic events in vitro is probably lower than
in vivo due to the reduced synaptic connectivity present in cortical slices
and the lower temperature used during in vitro experiments._ Since this
reduction in background synaptic activity could modify the integrative
properties of cortical neurons, we compared the impact of spontaneous synaptic events on the resting properties of intracellularly-recorded pyramidal neurons in vivo and in vitro by blocking synaptic transmission with tetrodotoxin
(TTX). The amount of synaptic activity was much lower in brain slices (at
34C) as the standard deviation of the intracellular signal was 10-17 times
lower in vitro than in vivo. Rins measured in vivo during relatively quiescent
epochs ('control Rins') could be reduced by up to 70% during periods of
intense spontaneous activity. Further, the 'control Rins' were increased by
30-70% following TTX application in vivo, approaching in vitro values. In
contrast, TTX produced negligible Rin changes in vitro (4%). These results
indicate that, compared to the in vitro situation, the background synaptic
activity present in intact networks dramatically reduces the electrical
compactness of cortical neurons and modifies their integrative properties. The
impact of the spontaneous synaptic bombardment should be taken into account
when extrapolating in vitro findings to the intact brain.
Received 15 July 1997; accepted in final form 14 November 1997.
APS Manuscript Number J591-7.
Article publication pending J. Neurophysiol.
ISSN 1080-4757 Copyright 1997 The American Physiological Society.
Published in APStracts on 12 December 1997