Role of the Midline Brainstem in Feline Amygdaloid Kindling

Summary: Purpose: To study the role played by the midline brainstem in feline amygdaloid kindling in general and the formation of transhemispheric positive transfer effect (PTE) in particular. Methods: Eight adult male cats with either anterior or posterior midline brainstem bisection underwent primary and secondary site kindling and primary site retest. Results: Stage 4 seizure pattern was altered with either absence of contralateral circling in the anterior group or emergence of ipsilateral circling in the posterior group. Electroclinical manifestation of the tonic phase was absent in the posterior but not the anterior group. Kindled convulsive pattern remained asymmetrical with contralateral dominance in the anterior but not the posterior group. Intermittent truncation of the secondary clonic phase of the kindled seizure occurred in both groups. PTE was reduced whereas the negative transfer effect was preserved in both groups. Conclusions: The anterior half of the midline brainstem participates in stage 4 contralateral circling. Both the anterior and posterior halves of the midline brainstem participate in the mechanisms of repetitive circling during stage 4 and the stable maintenance of the kindled stage 6 seizure. The anterior and posterior halves of the midline brainstem participate in symmetrical patterning and electroclinical tonic expression of the kindled seizure, respectively. The midline brainstem, extending from the midbrain to the pons with some posterior emphasis, participates in the mechanisms of PTE formation. The findings indicate the importance of the brainstem for electroclinical ictal processes and a transhemispheric positive transfer effect associated with temporal limbic epileptogenesis.