POSSIBLE INTERACTION BETWEEN THE INFERIOR COLLICULUS AND THE SUBSTANTIA-NIGRA IN AUDIOGENIC-SEIZURES IN WISTAR RATS

Male Wistar rats were tested for sensitivity to audiogenic seizures (AS; 110 dB), using an audiogenic severity index (SI). Sensitive (S) animals were subjected to bilateral lesion of the inferior colliculus (IC) and/or the lateral lemniscus (LL). Resistant (R) animals were subjected to bilateral lesions of the IC, unilateral sequential lesions of the substantia nigra reticulata (SN) and/or IC (contralateral to one another), and unilateral thalamic and sham lesions. Bilateral lesions of the IC and LL abolish AS in S rats. Lesion of the SN resulted in more pronounced sensitivity to AS than unilateral lesion of IC, in R rats. When the SN lesion was contralateral to a previous IC lesion, the effect was not only an increase in the SI, but also a reversal of the asymmetry generated by IC lesion. Although the behavioral effects resulting from IC lesions are due to alterations in the primary structures involved in the origin of AS, unilateral SN lesions can alter critical substrates of sensorimotor integration involved in the control and expression of AS.