Development of early motor learning and topical motor skills in a model of cerebellar degeneration.

The development of motor learning and topical motor skills has been studied during the first month of life in neurodeficient Lurcher mutant mice derived from C3H strain. The examination of motor functions was conducted using four methods when animals were consecutively placed on: a horizontal wire, a rotating cylinder, a bridge and slanting ladder (on the rotating cylinder and slanting ladder in three different starting positions). A total of 150 animals were used, half being heterozygous mutants (+/Lc), the remaining consisting of their healthy littermates, homozygous wild-type mice (+/+). Some animals of both types were confronted with the tasks in four testing days without practice while the others were trained in all of these methods one time daily at the age of 3, 6, 9, 12, 15, 20, 25 and 30 days. The results of the research are expressed as a percentage of reaching criteria in the trained and untrained mice of both types (+/Lc, +/+), respectively on days 15, 20, 25, and 30. Because of their motor handicap, Lurcher mutants showed significantly worse results than normal mice in almost all of the tests. The most interesting observations of the study were obtained on the rotating cylinder and the slanting ladder tests where mainly untrained mutants were unable to cope promptly with the different starting position and failed. However, in 30-day-old Lurchers the effect of learning was relatively better in some tests when compared with the wild-type of mice. Experiments showed that, in spite of progressive cerebellar degeneration, the ability of motor learning in Lurcher mutants survived to a certain degree. The worsening of results after frequent training in both trained Lurchers and normal mice aged 20 days as compared with untrained ones is discussed within the context of the "overtraining reversal effect" and other possible hypotheses.