The epileptiform activity induced by 4-aminopyridine in rat amygdala slices: antagonism by non-N-methyl-d-aspartate receptor anatagonists

The effects of excitatory amino acid receptor antagonists kynuretic acid and 6-cyano-7-nitroquinoxaline-2,3-dione (CNQX) on epileptiform activity induced by 4-aminopyridine (4-AP) were studied in rat amygdala slices using intracellular recording techniques. Five to 10 min after switching to 4-AP-containing solution, spontaneous epileptiform bursts were observed in 35 out of 45 slices studied. The spontaneous epileptiform events consisted of an initial burst followed by a number of afterdischarges. Superfusion with kynuretic acid, a broad-spectrum excitatory amino acid receptor antagonist, reversibly reduced the duration of the spontaneous bursting discharges in a dose-dependent manner. The frequency of spontaneous bursting was also decreased. The IC₅₀, estimated from the graph of the concentration-response relationship, was approximately 130 μM. In addition, CNQX which is a specific non-N-methyl-d-aspartate (NMDA) receptor antagonist blocked the spontaneous and evoked epileptiform bursting. In 11 out of 15 neurons tested, there was a residual depolarizing component remained. This depolarizing component was reversibly blocked by specific NMDA receptor antagonist, d,l-2-amino-5-phosphonovaleate (d,l-APV). Relative to the CNQX-sensitive component, the d,l-APV-sensitive component is much smaller in amplitude and shorter in duration indicating that NMDA receptor plays only a minor role in this process. These data suggest that the generation of propagation of spontaneous epileptiform events induced by 4-AP in the neurons of basolateral amygdala is mediated by excitatory amino acids and that activation of non-NMDA receptors is of primary importance.