The effect of midbrain collicular knife cuts on audiogenic seizure severity in the genetically epilepsy-prone rat

Previous studies showed that the inferior colliculus (IC) and the pontine reticular nucleus (RPO) are involved in the initiation and propagation of seizure activity in genetically epilepsy-prone rats (GEPR-9s), respectively. Bilateral knife cuts in the coronal plane were made in the midbrain to determine what effect the disruption of efferent fibers of the IC would have on seizure activity. In addition, some lesions were injected with horseradish peroxidase (HRP) to trace the interrupted fibers and identify the neurons of origin. Consistent with previous results, lesions that involved the central nucleus of the IC or the lateral lemniscus blocked audiogenic seizures. Seizures were also blocked with lesions located between the external and central nuclei of the IC. In contrast, lesions located between the IC and superior colliculus and those within the superior colliculus reduced the audiogenic response score, but did not completely block audiogenic seizures. In the cases with intercollicular lesions, HRP-labeled axons were observed to arise from neurons in both the external nucleus and dorsal cortex of the IC, but not the central nucleus, and they entered the deep layers of the superior colliculus. These results indicate that the projection from the central nucleus to the external nucleus of the IC is important for the propagation of seizure activity in GEPR-9s. Also, these data show that projections from the IC to the superior colliculus play a role in seizure propagation.(ABSTRACT TRUNCATED AT 250 WORDS)