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The Journal of Neurophysiology Vol. 83 No. 4 April 2000, pp. 2463-2467
Copyright ©2000 by the American Physiological Society
RAPID COMMUNICATION
Department of Neurology and Department of Physiology and Pharmacology, State University of New York Health Science Center at Brooklyn, Brooklyn, New York 11203
Galoyan, Samvel M. and
Lisa R. Merlin.
Long-Lasting Potentiation of Epileptiform Bursts by Group I
mGluRs Is NMDA Receptor Independent. J. Neurophysiol. 83: 2463-2467, 2000. In CA3 pyramidal cells of guinea pig
hippocampal slices, picrotoxin (50 µM) elicited spontaneous,
rhythmically recurring epileptiform bursts 285-435 ms in duration. The
addition of (S)-3,5-dihydroxyphenylglycine (DHPG, 50 µM, 90 min
application), a selective group I metabotropic glutamate receptor
(mGluR) agonist, resulted in a rapid-onset transient increase in burst
frequency. This was followed by a slowly progressive increase in burst
duration, with bursts reaching 1.5-3.8 s in duration at 90 min of DHPG
application. The potentiation of epileptiform burst duration persisted
at least 2 h after agonist removal. To determine whether
N-methyl-D-aspartate (NMDA) receptor activation participates in the mGluR-induced potentiation of
epileptiform bursts, experiments were carried out in the presence of
D-2-amino-5-phosphonovaleric acid (APV, 50-100 µM), an
NMDA receptor antagonist. Application of DHPG in the presence of APV
resulted in a significantly enhanced transient increase in burst
frequency. Nevertheless, when compared with the control described
above, there was no significant alteration in the rate of development
of the burst prolongation nor its persistence after washout. In other
experiments, application of APV in the presence of fully developed
mGluR-induced potentiated bursts (after 90 min washout of DHPG)
resulted in no significant change in either burst frequency or
duration. The data reveal that both induction and maintenance of group
I mGluR-mediated potentiation of epileptiform discharges are NMDA
receptor-independent processes, suggesting that epileptogenesis, when
induced by group I mGluR activation, may occur and be sustained in the
absence of NMDA receptor activation.
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