Locomotion in exercised and nonexercised cats cordotomized at two or twelve weeks of age

Although the spinal cord contains the basic pattern-generating circuitry essential for locomotion, the recovery of this behavior was influenced by the animal's age at the time of cord transection and to a less obvious extent by subsequent training.

Abstract

The influences of an animal's age at the time of cord transection and the use of ambulatory training on the recovery of weight-supported locomotion were assessed with 21 cats spinalized (T12) at 2 or 12 weeks of age. The animals were assigned at random to an exercise (E) or to a nonexercise (NE) group, and exercise therapy consisted of assisting the cat to walk on a motorized treadmill for 30 min, five times per week. During a 4-month recovery period, spontaneous clonus and hyperactive cutaneous reflexes developed in all animals, but skeletoarticular disorders were more typical of the younger animals. Age at cord transection had an effect on the recovery of weight-supported walking, as locomotion in the 2-E and 2-NE animals rated significantly higher than in the 12-E or 12-NE groups. For the younger animals, training was not critical to the development of locomotion, but for the older ones it was important. EMG records from soleus and lateral gastrocnemius muscles of spinal cats that achieved weight-supported locomotion revealed that recruitment of these muscles was normal despite significant changes in fiber composition and muscle contractility. In contrast, kinematic analyses of the locomotor patterns revealed gait abnormalities, including an absence of the yield phase during stance and an uncoupling of knee and ankle actions. We conclude that although the spinal cord contains the basic pattern-generating circuitry essential for locomotion, the recovery of this behavior was influenced by the animal's age at the time of cord transection and to a less obvious extent by subsequent training.