Postural control skills and quadrupedal locomotor pattern in infant rolling mice, a neurological mutant, were observed in the following situations: hindlimb support when suspended, rope descent, narrow path traverse, quadrupedal locomotion on an inclined comdor, and swimming behavior when entirely submerged. Until the second week of age, rolling mice developed primitive responses similar to, or somewhat slower than, their unaffected littermates, but failed to show mature adaptive and coordinated movements from Days 16-18 onward in hinblimb support and rope descent tests. The gait was broadbased and they frequently lurched, rolled over on the side in the narrow-path and incline situations. Also, swimming behavior was extremely clumsy with varying degrees of disturbed rhythm and inconsistent movement of hindlimb paddling. These findings might result from an immature development of hindlimb muscle tonus control system and distortion of smooth and orderly sequence of hindlimb muscular contractions which characterize skillful quadrupedal locomotion.
A new autosomal recessive mutant called Rolling mouse Nagoya (gene symbol roP), which is a new allele of tottering locus, was found among descendants of a cross between the SIII and C57BL/6JNa strains (Oda, 1973(Oda, , 1981)). The mutation apparently occurred in the SIII line. Motor deficits associated with this mutation were falling over sideways and an abnormal rhythm of the cyclic movements of the hindlimbs when walking (Ohno, 1979), despite no clinical sign of trunk tremor during movement or at rest. These deficits could be observed most readily in the second postnatal week. The trait is now maintained in a C3Hf/Nga background by the cross-intercross matings due to an infertile characteristic in the SIII strain that was selected for its high rate of suckling death.
The cerebella of 2-week-old or older rolling mice were reduced significantly in size, especially in the anterior lobe (Nakane, 1976;Nakane, Oda, & Kameyama, 1976). On