Extrinsic Inhibition of the Inferior Colliculus during Audiogenic Seizures: Effects of Unilateral Dorsal Nucleus of the Lateral Lemniscus Lesions in Young Rats

In this study, a model of generalized epilepsy was used to investigate the role of extrinsic inhibition of the inferior colliculus (IC) during audiogenic seizures (AGS). There is evidence to suggest that a deficiency of inhibition within the IC plays a major role in AGS; however, the importance of extrinsic inhibition of the IC is not as well understood. To investigate this, neurotoxin lesions of dorsal nucleus of the lateral lemniscus (DNLL) were made, therefore eliminating the main source of extrinsic inhibition to the IC. Long-Evans rats (N = 18) were primed for AGS susceptibility via acoustic insult on post-natal day (pnd) 18, tested for susceptibility on pnd 32, and then subjected to a series of inductions on seven occasions over 14 days beginning on pnd 35. Seizure-susceptible rats were divided into three groups (n = 6). One group received a neurotoxic injection in the DNLL, a second group was prepared for surgery, but did not receive the injection, and a third group experienced no aspects of the surgical procedure. Subjects then followed a post-surgery induction schedule to evaluate differences across three measures: latency to enter a wild-running phase, latency to enter clonus, and duration of the seizure. The hypotheses that subjects in the lesion group would have a shorter latency to enter a wild running phase in post-surgery inductions (p = .5289) and would exhibit a shorter latency to enter clonus in post inductions (p = .1713) were not supported by the data. The hypothesis that subjects in the lesion group would exhibit longer AGS post-surgery approached statistical significance (p = 0.0584); however, rats in the lesion group exhibited shorter AGS than controls. While a lack of intrinsic inhibition of the IC plays an important role in AGS, the data from this study suggest that a lack of extrinsic inhibition to the IC does not have a significant role in inhibiting the initiation and propagation of AGS activity in rats, but may aid in decreasing the duration of clonic seizures.