Neuroethological evaluation of audiogenic seizures in hemidetelencephalated rats

Wistar-derived male rats were tested for audiogenic seizure (AS) susceptibility, and classified into sensitive (S) and resistant (R) groups. Rats from group R underwent unilateral ablation of the telencephalon, or were detelencephalated (HD), or sham-lesioned, and were tested for audiogenic susceptibility one month and one year after surgery. It was found that previously AS-resistant, HD-operated animals developed generalized tonic-clonic convulsions upon high intensity (110.8 dB) acoustic stimulation, with higher severity and shorter latencies than the susceptible, non-operated control animals. Sham-lesioned R animals maintained their previous resistance to AS. HD-lesioned R animals also presented asymmetric motor patterns, such as gyrating and barrel-rolling behavior, always oriented towards the side contralateral to the lesion. HD-lesioned S animals presented an increase in the severity of seizures, as well as a shortening of the latencies of the running (procursive) and convulsive phases of the seizures. This effect was more marked one year after surgery. Contralateral barrel-rolling behavior was also observed in these animals. The fact that seizure severity increases and latency decreases with time after lesion seems to indicate a role for denervation hypersensitivity and other cerebral plasticity phenomena in explaining the effects of HD lesions on AS. The fundamental neural structures involved appear to be those related to sensorimotor coordinating systems (substantia nigra/pontine-mesencephalic reticular formation and substantia nigra/superior colliculus), the acoustic pathways (inferior colliculus) and their projections to the superior colliculus and reticular formation.