Epileptiform activity induced by magnesium-free solution in slices of rat amygdala: Antagonism by N-methyl-d-aspartate receptor antagonists

The effects of the N-methyl-d-aspartate (NMDA) receptor antagonists, d-2-amino-5-phosphonovalerate (d-APV) and phencyclidine (PCP), were studied in vitro on epileptiform activity induced in magnesium-free solution in neurons of the basolateral amygdala of the rat, using intracellular recording techniques. Twenty to 30 min after switching to magnesium-free medium, spontaneous interictal-like events were observed in 33 out of 37 amygdala slices. The spontaneous interictal-like events consisted of an initial burst followed by a number of afterdischarges. Superfusion with d-APV, a competitive NMDA receptor antagonist, reversibly reduced the duration of the spontaneous interictal-like event in a dose-dependent manner. The frequency of spontaneous interictal-like events was also reduced. The IC₅₀, estimated from the graph of the concentration-response relationship, was approximately 10 μM which is close to the IC₅₀ for the binding of d-AVP to the NMDA receptor in other regions of the brain. The effect of phencyclidine, a noncompetitive NMDA receptor antagonist, was similar to that of d-APV. These results suggest that activation of NMDA receptors plays an intrinsic role in the induction or propagation of epileptiform activity seen in magnesium-free solution in the neurons of the amygdala.