Differential effects of inducible cerebellar granule cell and Purkinje cell ablation on motor coordination and motor learning in adult mice

The cerebellum regulates motor coordination and motor learning through highly organized circuits composed mainly of granule cells (GCs) and Purkinje cells (PCs). To investigate their distinct roles, we generated two lines of inducible transgenic mice in which either GCs or PCs could be selectively ablated in adulthood by administration of the progesterone receptor antagonist RU-486. This system combined a Cre recombinase-progesterone receptor fusion, in which Cre activity is induced in an RU-486-dependent manner, with a Cre-dependent diphtheria toxin A expression to achieve cell-type-specific ablation. High-dose RU-486 induced nearly complete loss of either GCs or PCs and resulted in severe ataxia. When partial ablation was induced by low-dose RU-486, different phenotypes emerged. Mice retaining about 20% of PCs were still able to improve motor coordination in the rotarod test and maintained performance in the balance beam test comparable to that of controls. In contrast, mice with about 30% of GCs remaining showed marked deficits, failing to improve across rotarod trials and exhibiting reduced latency to fall in the balance beam test. These results suggest that while both GCs and PCs are indispensable for motor coordination, a sufficient number of GCs is required for both motor coordination and motor learning. This inducible ablation model highlights the differential contributions of cerebellar neurons and provides a valuable tool to dissect circuit-specific functions in the adult brain.