Immobility responses in Lurcher mutant mice.

Different facets of inhibition were examined in Lurcher mutant mice, characterized by degeneration of the cerebellum and associated brain regions. Lurcher mutants spent less time in an immobile floating posture than normal littermate controls of the same background strain. Lurcher mutants were more active than controls on a board set at the horizontal but not when it was inclined. The mutants did not differ from controls on the inclined grid or in the dorsal immobility response. Although impaired in an unstable platform motor coordination test, both mutants and controls were able to withhold responding with repeated trials. These results indicate that Lurcher mutants are defective in inhibitory mechanisms during swimming and locomotion but not during continuous restraint. Moreover, the mutants are able to improve with practice during a task requiring equilibrium that can be solved by the absence of movement, although terminal performance was not so high as that of controls.