Roles of the substantia innominata in generalization and expression of limbic seizures in rats

Rats were kindled at the amygdala (AM) and substantia innominata (SI). Subsequently, the effects of unilateral injection of local anesthetic procaine into the SI (ipsilateral to the kindled site) were examined. In AM-kindled rats, intra-SI procaine caused immediate contralateral hemiparesis lasting about 30 min. When the kindled AM was stimulated, animals with the contralateral hemiparesis showed ipsilateral hemiconvulsive seizures. Similarly, intra-SI procaine in SI-kindled animals caused the immediate and transient hemiparesis, and produced ipsilateral hemiconvulsive seizures upon the SI stimulation. The data suggest: (1) functional disruption of the SI leads to the direct suppression of the ipsilateral cortical motor mechanism responsible for contralateral hemiconvuslive seizures; (2) the kindled AM can gain access to the contralateral cortical motor mechanism through the pathways independent of the primary connections between the SI and the ipsilateral cerebral cortex. They are possibly SI-mediated ictal linkage between the kindled AM and the contralateral cortical motor mechanism, and extra-SI accession of the kindled AM to the contralateral cortical motor mechanism.