Functional ablation of deep cerebellar nuclei temporarily impairs learned coordination of forepaw and tongue movements

The role of the cerebellum in complex skilled movements was assessed by the use of functional ablation technique. Rats were trained to synchronize tongue and forepaw movements in a drinking box equipped with a retractable spout which was automatically withdrawn after every lick but could be returned by pressing and releasing a lever placed 4 cm below the spout. The animals learned to perform short presses synchronized with the lick cycle in such a way as to allow continuous drinking. The contribution of the neocerebellum to these lick-associated instrumental movements was estimated by intracranial injection of 2 ng of tetrodotoxin into the dentate and lateral part of interposed nuclei. Bilateral blockade of the mainly neocerebellar output interfered with learned synchronization of licking and bar pressing, but did not suppress licking from a stationary spout and only decreased the licking frequency by 10%. It is concluded that the tongue-forepaw synchronization is disrupted by elimination of the neocerebellar output but for a much shorter time (< 9 h) than the tetrodotoxin-induced inactivation of the lateral part of the caudate nucleus (72 h) reported earlier. The results confirm participation of cerebellar hemispheres in learned tongue-forepaw synchronization, but indicate at the same time that elimination of this link can be easily compensated. (C) 2000 Elsevier Science B.V. All rights reserved.