Differential roles of cerebellar cortex and deep cerebellar nuclei in learning and retention of a spatial task: studies in intact and cerebellectomized lurcher mutant mice.

Lurcher mutant mice (+/Lc) exhibit a massive loss of neurons in the cerebellar cortex and the inferior olivary nucleus, while deep cerebellar nuclei are essentially intact. To discriminate the relative participation of the cerebellar cortex and deep structures in learning and memory, 3 to 6-month-old +/Lc mice were subjected to a spatial learning task derived from the Morris water escape. They were able to learn to escape as well as their strain-matched controls (+/+). Seven days later, their scores showed that they had memorized the spatial environment but not as accurately as +/+ mice. Cerebellectomy before training did not significantly alter the escape learning capabilities of either group, whereas cerebellectomy performed after learning completely abolished retention in +/+, as well as in +/Lc, mice. These results suggest that the cerebellum, although not necessary for learning a spatial task, plays a crucial role in its retention, and that the storing structure of spatial information differs in +/+ and +/Lc mice.