INHIBITORY CONTROL OF EXCITABLE DENDRITES IN NEOCORTEX.
Kim, Han G., Michael Beierlein, and Barry W. Connors.
Department of Neuroscience, Brown University, Providence, RI 02912.
APStracts 2:0184N, 1995.
Summary and Conclusions
1. Many dendrites of pyramidal cells in mature neocortex express active Na -
and Ca 2- conductances. Dendrites are also the target of numerous inhibitory
synapses. We examined the interactions between the intrinsic excitability of
dendrites and synaptic inhibition using whole-cell recordings from the apical
dendrites of layer 5 pyramidal cells. Experiments were performed on slices of
somatosensory cortex from mature rats. Slices were bathed in the glutamate
receptor antagonists APV and DNQX, and maintained at 32-36 o C. 2. In
agreement with previous findings, intradendritic current injection evoked two
distinct types of dendritic firing. Type I dendrites generated monophasic fast
spikes, whereas type II dendrites showed more complex firing patterns,
consisting of fast and slow spike components. 3. Stimulation of cortical
layers 2/3 evoked fast IPSPs in all dendrites tested. IPSP reversal potentials
were bimodally distributed, with means of about -53 mV and -85 mV when
recorded with high [Cl - ]-filled electrodes. Interestingly, IPSP reversal
potentials were correlated with the type of dendritic spiking pattern. 4.
IPSPs were able to delay, completely block, or partially block spiking in
dendrites, depending on the relative timing between inhibition and dendritic
spiking. Slow, Ca 2- -dependent spike components could be blocked selectively
by IPSPs. Furthermore, inhibition could either phase-advance or phase-delay
repetitive patterns of dendritic spiking, depending upon the timing of the
IPSP.
Received 6 March 1995; accepted in final form 28 June 1995.
APS Manuscript Number J-143-5
Article publication pending J. Neurophysiol.
ISSN 1080-4757 Copyright 1995 The American Physiological Society.
Published in APStracts on 18 July 1995.