Treadmill locomotion and aversive effects induced by electrical stimulation of the mesencephalic locomotor region in the rat.

The effects of electrical stimulation of the "mesencephalic locomotor region" and adjacent dorsolateral tegmentum were assessed and compared in the same rats in freely moving conditions or when lightly anesthetized and suspended over a moving treadmill. In freely moving conditions, electrical brain stimulation (EBS) of this part of the mesencephalon elicited mainly aversive effects (escape reactions: violent running and explosive jumps), but also ipsiversive circling and "gnawing." On the treadmill, EBS induced flexions of hindlimbs followed by locomotion (stepping) or flexions only. In addition, it was found that locomotion and flexions on the treadmill were almost exclusively elicited by EBS of sites positive for escape reactions in freely moving conditions.