Fen. Lebeau et Be. Alger, TRANSIENT SUPPRESSION OF GABA(A)-RECEPTOR-MEDIATED IPSPS AFTER EPILEPTIFORM BURST DISCHARGES IN CA1 PYRAMIDAL CELLS, Journal of neurophysiology, 79(2), 1998, pp. 659-669
Epileptiform burst discharges were elicited in CA1 hippocampal pyramid
al cells in the slice preparation by perfusion with Mg2+-free saline.
Intracellular recordings revealed paroxysmal depolarization shifts (PD
Ss) that either occurred spontaneously or were evoked by stimulation o
f Schaffer collaterals. These bursts involved activation of N-methyl-D
-aspartate receptors because burst discharges were reduced or abolishe
d by DL-2-amino-5-phosphonovaleric acid. Bath application of carbachol
caused an increase in spontaneous activity that was predominantly due
to gamma-aminobutyric acid-A-receptor-mediated spontaneous inhibitory
postsynaptic potentials (sIPSPs). A marked reduction in sIPSPs (31%)
was observed after each epileptiform burst discharge, which subsequent
ly recovered to preburst levels after similar to 4-20 s. This sIPSP su
ppression was not associated with any change in postsynaptic membrane
conductance. A suppression of sIPSPs also was seen after burst dischar
ges evoked by brief (100-200 ms) depolarizing current pulses. N-ethylm
aleimide, which blocks pertussis-toxin-sensitive G proteins, significa
ntly reduced the suppression of sIPSPs seen after a burst response. Wh
en increases in intracellular Ca2+ were buffered by intracellular inje
ction of ethylene glycol bis(beta-aminoethyl)ether-N,N,N',N'-tetraacet
ic acid, the sIPSP suppression seen after a single spontaneous or evok
ed burst discharge was abolished. Although we cannot exclude other Ca2
+-dependent mechanisms, this suppression of sIPSPs shared many of the
characteristics of depolarization-induced suppression of inhibition (D
SI) in that it involved activation of G proteins and was dependent on
increases in intracellular calcium. These findings suggest that a DSI-
like process may be activated by the endogenous burst firing of CA1 py
ramidal neurons.