Burst characteristics of dentate gyrus granule cells: Evidence for
endogenous and non-synaptic properties.
Pan, Enhui and Janet L. Stringer.
Department of Pharmacology and Division of Neuroscience, Baylor College of
Medicine, One Baylor Plaza, Houston TX 77030.
APStracts 2:0268N, 1995.
SUMMARY AND CONCLUSIONS
1. Hippocampal slices bathed in 8 mM potassium and 0-added calcium exhibited
spontaneous epileptiform activity in the dentate gyrus. Extracellular
recording revealed recurrent prolonged bursts of population spikes and an
associated negative DC shift. These episodes were very similar to the in vivo
phenomenon termed maximal dentate activation (MDA). Therefore, this in vitro
activity will be referred to as MDA-like activity, or events. 2. During the
MDA-like activity, the individual granule cells exhibited a sustained
depolarization that matched the duration of the negative extracellular DC
shift. At the beginning of the MDA-like activity there was a burst of action
potentials. Following the burst, most granule cells either continued to fire
action potentials regularly or in bursts. Some cells exhibited this initial
burst of activity and then a dramatic reduction in firing rate. This reduction
in rate was followed by a gradual increase in the amplitude and frequency of
the epileptiform activity recorded during the remainder of the MDA-like event.
3. Before and between MDA-like events, spontaneous cellular activity consisted
of single action potentials and bursts of action potentials on a depolarizing
envelope. In addition, depolarizing potentials, up to 13 mV, were recorded.
There were no extracellular field potentials associated with these
intracellularly recorded potentials. 4. In the 8 mM potassium, 0-added calcium
test solution, the membrane potential threshold for burst production was
significantly lower than in normal potassium and calcium medium. 5. The effect
of depolarizing and hyperpolarizing current injections on the amplitude and
frequency of the epileptiform activity was tested. Current injection had no
effect on the frequency of the epileptiform activity recorded during the MDA-
like events. However, the frequency of the cellular bursts between MDA-like
events was very sensitive to current injection. Depolarizing current increased
the frequency and hyperpolarizing current decreased the frequency of the
spontaneous activity. 6. This study has shown that in 8 mM potassium and 0-
added calcium the granule cells of the dentate gyrus are capable of generating
spontaneous bursts that appear to be mediated by endogenous mechanisms. In
addition, synchronized epileptiform discharges were recorded from the granule
cells at regular intervals that appear to be mediated by exogenous non-
synaptic mechanisms.
Received 7 July 1995; accepted in final form 24 August 1995.
APS Manuscript Number J430-5.
Article publication pending J. Neurophysiol.
ISSN 1080-4757 Copyright 1995 The American Physiological Society.
Published in APStracts on 23 September 1995.