THE DEVELOPMENT OF QUADRUPEDAL LOCOMOTION IN THE KITTEN

The development of bipedal treadmill locomotion and overground locomot ion has previously been studied in the kitten; the development of quad rupedal treadmill locomotion has not. We evaluated and compared all th ree forms of locomotion in the normal kitten and present quantitative data comparing the development of quadrupedal treadmill and overground locomotion. Overground locomotion was studied from the day of birth t o 5 months of age and quadrupedal treadmill locomotion was studied in the same animals from 9 weeks to 5 months of age. Treadmill locomotion was initiated postweaning, since it could not be reliably elicited wi thout a food reward. Three locomotor characteristics (weight support, balance, and coordination between the forelimbs and the hindlimbs) wer e evaluated quantitatively. Kittens first consistently demonstrated ov erground steps with the ventral surface of their bodies supported abov e the walking surface throughout the entire step cycle during the seco nd and third postnatal weeks. By 4 weeks of age, overground locomotion consistently showed full weight support and midline positioning of th e hindquarters. Coordination between the forelimbs and the hindlimbs d eveloped differently in the two forms of quadrupedal locomotion evalua ted. During overground locomotion, the kittens initially used a single pattern in which only one limb was in swing at any time. As the kitte ns' weight support and trunk control improved, additional swing phase coordination patterns emerged and these patterns were correlated with the animals' ability to change speeds during locomotion. The consisten cy with which a dominant interlimb swing phase pattern was used at a p articular speed increased with age and, by 6 weeks, the frequency of e ach speed-related dominant pattern approached 100% during overground l ocomotion. At 6 weeks, interlimb coordination also was evident in the nearly consistent interlimb phase interval present between the forelim b's initiation of the first extension subphase and the ipsilateral hin dlimb's initiation of the flexion phase. The consistent patterns appea red to be fostered by maturation of weight support and balance. In con trast, the interlimb phase interval was inconsistent during quadrupeda l treadmill locomotion until 20 weeks of age. Moreover, the interlimb swing phase patterns used during quadrupedal treadmill locomotion diff ered from those used during overground locomotion. The differences in the developmental time course and patterns of interlimb coordination b etween overground and quadrupedal treadmill locomotion suggest that di fferent mechanisms regulate the control of interlimb coordination duri ng these two different forms of quadrupedal locomotion. (C) 1995 Acade mic Press, Inc.