Repetitive audiogenic seizures cause an increased acoustic response in inferior colliculus neurons and additional convulsive behaviors in the genetically-epilepsy prone rat

Abstract

Previous studies indicate that daily repetition of audiogenic seizures (AGS) leads to audiogenic ‘kindling’ with increased seizure duration and additional seizural behaviors. The present study examined the neuronal correlates of this phenomenon. Extracellular single neuron firing and concomitant convulsive behaviors associated with 14 repetitive AGS were evaluated in the genetically epilepsy-prone rat severe seizure strain (GEPR-9). An increase in the number of acoustically-evoked action potentials in neurons of the central nucleus of inferior colliculus OW was observed by the second day of AGS repetition, and peaked at day four. The ICc responses remained at similar enhanced level through day 14. ICc neuronal responses were completely absent for approximately two min post-ictally after a single AGS in all animals, but 80% of the animals undergoing repetitive AGS consistently exhibited neuronal firing in this post-ictal period. Post-tonic clonus and an increased duration of post-ictal behavioral depression were also observed with repetitive AGS. The increased ICc neuronal firing was observed prior to the appearance of the post-tonic clonus component of repetitive AGS. This suggests that the ICc neuronal firing increase may subserve, at least, the initial increase in AGS severity. However, changes in neuronal firing in nuclei of the neuronal network for AGS efferent to the ICc may be responsible for the increased AGS severity that occurs after the fourth day of AGS repetition.