Excitant amino acids and audiogenic seizures in the genetically epilepsy-prone rat. I. Afferent seizure initiation pathway.

The afferent pathway involved in initiation of audiogenic seizures in the genetically epilepsy-prone rat was investigated by bilateral microinfusion of the excitant amino acid antagonist 2-amino-7-phosphonoheptanoate into the major brain stem and subcortical nuclei of the auditory system. This antagonist has been shown to possess anticonvulsant properties in other seizure models, and an excitant amino acid has been implicated as a putative neurotransmitter in several of these nuclei. Seizure severity was significantly reduced following infusion of this agent into the cochlear nucleus, superior olivary complex, inferior colliculus, and medial geniculate body. Many of these animals exhibited a complete blockade of seizures. The smallest effective dose in the cochlear nucleus and the medial geniculate body was 5 nmol per side. The smallest effective dose in the olive was 1 nmol, and in the inferior colliculus 0.1 nmol per side was protective. The onset of anticonvulsant effectiveness was earliest in the inferior colliculus. These findings showed that the inferior colliculus was the most sensitive auditory center to the anticonvulsant action of 2-amino-7-phosphonoheptanoate and that imbalance between inhibitory and excitatory transmission within this brain structure may be crucial in the initiation of audiogenic seizures in the genetically epilepsy-prone rat.