Effects of lidocaine injection in the interpositus nucleus and red nucleus on conditioned behavioral and neuronal responses.

The role of the cerebellum and the red nucleus in the conditioned eyeblink response was assessed, using a combination of reversible lesions and multiple-unit extracellular recording in the awake, behaving rabbit. Lesion, recording, and stimulation experiments have indicated that both of these structures are involved in the performance of learned skeletal muscle responses. The present study sought to distinguish the relative contributions of the interpositus nucleus and the red nucleus to the expression of the learned response by recording behavior-related multiple unit activity in one structure while reversibly inactivating the other via injections of local anesthetic. Results indicate that inactivating either the interpositus or the red nucleus temporarily abolishes the learned eyeblink response. Injection of lidocaine into the interpositus also abolishes the neuronal unit model of the conditioned response in the red nucleus, while injection into the red nucleus does not affect the model in the interpositus. These results are consistent with the hypothesis that the red nucleus acts as a relay for motor commands from the cerebellum, and that the plasticity that generates conditioned responses occurs in the cerebellum or an afferent structure.