Induction of audiogenic seizure susceptibility by focal infusion of excitant amino acid or bicuculline into the inferior colliculus of normal rats

N-Methyl-D-aspartate (NMDA) (10 to 20 nmol) or bicuculline (15 to 50 pmol) in 0.5 microliter was infused bilaterally into the inferior colliculus or the deep layers of superior colliculus (DLSC) in normal rats, and the response to high intensity acoustic stimulation was examined. Thirty-five percent of rats receiving NMDA infusions and 42% of animals receiving bicuculline infusions into the inferior colliculus exhibited sound-induced seizures exclusively that were behaviorally similar to audiogenic seizures displayed by genetically epilepsy-prone rats. Rats receiving microinjections into the DLSC did not display sound-specific seizures. A combined pattern of spontaneous and sound-induced seizures was seen in some rats with both drugs and loci of microinjection. These data and previous studies support a role for increased excitant amino acid action and decreased efficacy of GABA in the inferior colliculus as important mechanisms involved in genetic susceptibility to audiogenic seizures.