Behavioral characteristics, associative learning capabilities, and dynamic association mapping in an animal model of cerebellar degeneration.

Young adult heterozygous Lurcher mice constitute an excellent model for studying the role of the cerebellar cortex in motor performance-including the acquisition of new motor abilities-because of the early postnatal degeneration of almost all of their Purkinje and granular cells. Wild-type and Lurcher mice were classically conditioned for eyelid responses using a delay paradigm with or without an electrolytic lesion in the interpositus nucleus. Although the late component of electrically evoked blink reflexes was smaller in amplitude and had a longer latency in Lurcher mice than that in controls, the two groups of animals presented similar acquisition curves for eyeblink conditioning. The lesion of the interpositus nucleus affected both groups of animals equally for the generation of reflex and conditioned eyelid responses. Furthermore, we recorded the multiunitary activity at the red and interpositus nuclei during the same type of associative learning. In both nuclei, the neural firing activity lagged the beginning of the conditioned response (determined by orbicularis oculi muscle response). Although red nucleus neurons and muscle activities presented a clear functional coupling (strong correlation and low asymmetry) across conditioning, the coupling between interpositus neurons and either red nucleus neurons or muscle activities was slightly significant (weak correlation and high asymmetry). Lurcher mice presented a nonlinear coupling (high asymmetry) between red nucleus neurons and muscle activities, with an evident compensatory adjustment in the correlation of firing between interpositus and red nuclei neurons (a coupling with low asymmetry), aimed probably at compensating the absence of cerebellar cortical neurons.