Bilateral lesions of the interpositus nucleus completely prevent eyeblink conditioning in Purkinje cell-degeneration mutant mice

The authors have previously demonstrated that Purkinje cell-degeneration (p cd) mutant mice are impaired in eyeblink; conditioning (L. Chen et al., 199 6a). The present study addresses the following 3 questions: (a) whether pcd mice perceive the conditioned and unconditioned stimuli as well as the wil d-type mice, (b) whether pcd mice have a normal sensitization level, and (c ) whether the residual learning in pcd mice is cerebellum-dependent. Result s indicated that the pcd mice exhibited normal tone-induced responses in th e cochlear nucleus and normal sensitivity to heat-induced pain. They showed a similar level of sensitization as the wild-type mice and were completely unable to learn conditioned eyeblinks after bilateral lesions aimed at the anterior interpositus nucleus. Thus, pcd mice an partially impaired in eye blink conditioning because of a deficiency in learning mechanisms, and the residual learning in the pcd mice is mediated by the cerebellar nuclei.