Rotation produced by electrolytic lesions of the superior cerebellar peduncle in rats modifying other forms of circling behavior

Abstract

Unilateral electrolytic lesions were made at two different levels in the brain stems of rats. The caudally placed lesions frequently involved the superior cerebellar peduncle in the pons at the level ol the locus coeruleus. Mild damage to the peduncle at this level produced no visible effect on motor activity, moderate damage resulted in a body tilt toward the side of the lesion, plus ataxia, and severe damage resulted in the addition of ipsiversive rotation. This spontaneous ipsiversive turning was capable of inhibiting the apomorphine- and dexamphetamine-induced contraversive circling seen in rats with unilateral electrolytic lessions of the adjacent locus coeruleus. The more rostrally placed lesions often injured the ascending fibers of the superior cerebellar peduncle at and rostral to their decusation, and resulted in contraversive rotation without body tilt or ataxia. Such spontaneous rotation seemed capable of inhibiting the ipsiversive circling response to apomorphine and dexamphetamine seen in rats with damage to the adjacent dorsal noradrenergic bundle area. Unilateral damage to the superior cerebellar peduncle in rats produces circling behavior, and the direction of this depends on the level of injury. Such turning can modify the rotational effects of lesions in adjacent brain stem structures.