The effects of reversible inactivation of the red nucleus on learning-related and auditory-evoked unit activity in the pontine nuclei of classically conditioned rabbits.

The pontine nuclei carry auditory conditioned stimulus information to the cerebellum during classical conditioning of the nictitating membrane response in rabbits. In well-trained animals learning-related as well as stimulus-evoked unit activity can be recorded throughout the pontine nuclei but particularly in the lateral and dorsolateral pons. Recent work in our laboratory has provided evidence that the learning-related unit activity in the pons is dependent on the interpositus nucleus and that the pons is not a site of essential plasticity for the learned response. In the present study we considered the question of whether learning-related unit activity might be projected from the interpositus nucleus to the pons through the red nucleus, a primary output target of the interpositus and a structure known to be essential for expression of the learned response. Multiple unit recordings were taken from lateral and dorsolateral pontine locations in well-trained rabbits before and during cooling of the red nucleus. Analysis of pooled data for all recording locations within the lateral and dorsolateral pons indicated that reversible inactivation of red nucleus abolished both stimulus-evoked and learning-related unit activity. However, we also found discrete recording locations where stimulus-evoked and learning-related unit activity were attenuated but not abolished by red nucleus cooling.