A crucial role of the alpha-amino-3-hydroxy-5-methylisoxazole-4-propionic acid subtype of glutamate receptors in piriform and perirhinal cortex for the initiation and propagation of limbic motor seizures

The role of alpha-amino-3-hydroxy-5-methylisoxazole-4-propionic acid (AMPA) receptors in the initiation and propagation of limbic motor seizures in rats was examined by the intracerebral and systemic administration of 2,3-dihydroxy-6-nitro-7-sulfamoyl-benzo (f) quinoxaline (NBQX), a selective antagonist of the AMPA subtype of glutamate receptor. Limbic motor seizures were evoked focally by the application of the gamma-aminobutyric acid receptor antagonist, bicuculline, into area tempestas, an epileptogenic site in the deep anterior piriform cortex. Before eliciting seizures, NBQX was applied focally into either 1) area tempestas or 2) perirhinal or posterior piriform cortex ipsilateral to the area tempestas from which seizures were evoked. In addition, pretreatment with i.p. NBQX was evaluated for anticonvulsant actions against area tempestas-evoked clonic or systemically evoked tonic seizures. In all conditions, a dose-dependent decrease in the severity of seizures was obtained with NBQX. With focal intracerebral administration, a dose of 500 pmol of NBQX consistently protected against limbic motor seizures, with partial protection achieved with 100 pmol. After i.p. administration, 2.5 and 5.0 mg/kg significantly protected the rats from both limbic motor seizures and tonic extensor seizures. No overt disturbance of spontaneous behavior was associated with the anticonvulsant doses of NBQX. Moreover, both forebrain substrates of limbic motor seizures and hindbrain substrates of tonic extensor seizures were highly susceptible to disruption by NBQX. The results indicate that AMPA subtype of glutamate receptors are crucial mediators of seizure propagation via perirhinal and piriform cortics.