Induction of delayed synchronized bursts in hippocampal slices by weak sine-wave stimulation; role of the NMDA receptor.
Weak (20-50 microA) sine-wave stimulation at 60 Hz (SWS) of either the mossy fibers or the Schaffer collaterals promoted epileptiform synchronized bursts in the CA2/3 area of rat hippocampal slices in the absence of epileptogenic agents. Following brief SWSs (2-10 sec every 5 min), delayed synchronized bursts (DSBs) were triggered by weak test pulses in either pathway and transmitted to CA1. The long (2-10 sec) refractory periods which followed synchronized bursts in CA2/3 limited their rate of occurrence. Furthermore, SWS decreased the activity for several minutes in slices that exhibited frequent bursts. DSBs were reversibly blocked by perfusion with the N-methyl-D-aspartate (NMDA) specific antagonist DL-2-amino-5-phosphono-valeric acid (APV). The involvement of NMDA receptors was further suggested by the facilitation of CA2/3 synchronized bursts in medium with NMDA (5 microM) or lacking magnesium, and by iontophoresis of NMDA in the CA2/3 stratum radiatum. The findings that SWS-induced DSBs persisted for hours in undisturbed slices, and that bursts abolished by APV reappeared during washout in control solution, suggest long-term changes in the CA2/3 synaptic region.
Bawin
S M
SM
Department of Physiology, Loma Linda University, CA 92357.
Shahhal
I
I
Mahoney
M D
MD
Adey
W R
WR
D015763:2-Amino-5-phosphonovalerate; D000818:Animals; D001224:Aspartic Acid / Q000031:analogs & derivatives / Q000494:pharmacology; D004558:Electric Stimulation; D006624:Hippocampus / Q000187:drug effects / Q000378:metabolism / Q000503:physiopathology*; D066298:In Vitro Techniques; D008297:Male; D016202:N-Methylaspartate; D010406:Penicillins; D051381:Rats; D011919:Rats, Inbred Strains; D016194:Receptors, N-Methyl-D-Aspartate; D017981:Receptors, Neurotransmitter / Q000187:drug effects / Q000502:physiology*; D012640:Seizures / Q000139:chemically induced / Q000378:metabolism / Q000503:physiopathology*; D014633:Valine / Q000031:analogs & derivatives
D010406:Penicillins; D016194:Receptors, N-Methyl-D-Aspartate; D017981:Receptors, Neurotransmitter; D001224:Aspartic Acid; D016202:N-Methylaspartate; D015763:2-Amino-5-phosphonovalerate; D014633:Valine