Spontaneous epileptiform discharges in hippocampal slices induced by 4-aminopyridine.
4-Aminopyridine (4-AP) induced 2 types of spontaneous field potentials (SFPs) in the hippocampal slice. Type I resembled spontaneous activity induced by other convulsants. They occurred at a rate of approximately 1 Hz, started in the CA2/CA3 region and spread at a velocity of 0.3 m/s to area CA1. Transsection experiments and laminar profiles indicated that they spread synaptically along the Schaffer collateral pathway. Synaptic blockade by low Ca2+/high Mg2+ or kynurenic acid reversibly abolished type I SFPs. Increasing [Ca2+]o lowered the rate and slightly increased the amplitude. Possibly, increased spontaneous transmitter release, and not disinhibition, is responsible for the generation of type I SFPs. Type II occurred at a rate of about 0.15 Hz and travelled in the same direction, but a factor 10 slower. They could not be blocked by separation of the CA1 and CA3 region; coupling remained until stratum moleculare was severed. Type II could not be suppressed by blockade of synaptic transmission. The laminar profile is similar in shape to that of type I but not identical. Increasing [Ca2+]o had the same but stronger effect as on type I. Type II SFPs depressed evoked population spikes up to a second and delayed the next type I SFP. The mechanisms involved remain largely speculative; further analysis is needed to help understand the epileptogenic action of 4-AP.
D015761:4-Aminopyridine; D000631:Aminopyridines / Q000494:pharmacology*; D000818:Animals; D005260:Female; D006624:Hippocampus / Q000187:drug effects* / Q000502:physiology; D066298:In Vitro Techniques; D008297:Male; D008564:Membrane Potentials / Q000187:drug effects; D051381:Rats; D011919:Rats, Inbred Strains; D012640:Seizures / Q000139:chemically induced* / Q000503:physiopathology
D000631:Aminopyridines; D015761:4-Aminopyridine