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The Journal of Neurophysiology Vol. 82 No. 5 November 1999, pp. 2262-2270
Copyright ©1999 by the American Physiological Society
1Department of Biomedical Engineering,
Bikson, Marom,
Rahul S. Ghai,
Scott C. Baraban, and
Dominique M. Durand.
Modulation of Burst Frequency, Duration, and Amplitude in the
Zero-Ca2+ Model of Epileptiform Activity. J. Neurophysiol. 82: 2262-2270, 1999. Incubation of hippocampal slices in zero-Ca2+ medium blocks
synaptic transmission and results in spontaneous burst discharges. This
seizure-like activity is characterized by negative shifts (bursts) in
the extracellular field potential and a K+ wave that
propagates across the hippocampus. To isolate factors related to
seizure initiation, propagation, and termination, a number of
pharmacological agents were tested. K+ influx and efflux
mechanisms where blocked with cesium, barium, tetraethylammonium (TEA),
and 4-aminopyridine (4-AP). The effect of the gap junction blockers,
heptanol and octanol, on zero-Ca2+ bursting was evaluated.
Neuronal excitability was modulated with tetrodotoxin (TTX), charge
screening, and applied electric fields. Glial cell function was
examined with a metabolism antagonist (fluroacetate). Neuronal
hyperpolarization by cation screening or applied fields decreased burst
frequency but did not affect burst amplitude or duration. Heptanol
attenuated burst amplitude and duration at low concentration (0.2 mM),
and blocked bursting at higher concentration (0.5 mM).
CsCl2 (1 mM) had no effect, whereas high concentrations (1 mM) of BaCl2 blocked bursting. TEA (25 mM) and low
concentration of BaCl2 (300 µM) resulted in a two- to
sixfold increase in burst duration. Fluroacetate also blocked burst
activity but only during prolonged application (>3 h). Our results
demonstrate that burst frequency, amplitude, and duration can be
independently modulated and suggest that neuronal excitability plays a
central role in burst initiation, whereas potassium dynamics establish
burst amplitude and duration.
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