Effect of midbrain and pontine tegmental lesions on audiogenic seizures in genetically epilepsy-prone rats.

A bilateral mechanical lesion of the midbrain and pontine tegmentum was found to abolish completely the tonic components of sound-induced seizures in genetically epilepsy-prone rats (GEPR) that display tonic-clonic seizures. Correlations between varied lesions placements and effects on maximal audiogenic seizures provided evidence that damage to the nucleus reticularis pontis oralis (RPO) of the midbrain and pontine reticular formation (RF) was responsible for the seizure-attenuating effects. Moreover, electrolytic lesions of the pontine RF involving the RPO nucleus were found to abolish the tonic components of the maximal audiogenic seizure. Additionally, bilateral mechanical lesions involving the RPO nucleus were found to attenuate the clonic components of sound-induced seizures in GEPR that display only running seizures and clonus. These findings are consistent with previous studies showing that pontine tegmental lesions attenuate the tonic components of maximal electroshock- and pentylenetetrazol-induced seizures, and lend further support to the hypothesis that all generalized tonic seizures share a common neural substrate. The role of the brainstem RF in tonic versus clonic convulsions is discussed in light of the present findings.