Anatomical correlates of return of locomotor function after partial spinal cord lesions in cats.

We trained cats to walk on a moving treadmill belt, then subjected them to partial transverse sections of the thoracic spinal cord. Afterwards, we observed their ability to walk on the treadmill, over a period of several weeks, using gait analysis techniques to describe the resultant deficits. The extent of the lesions was verified histologically, and the identity of the spared descending axons from the brain stem was demonstrated by retrograde labeling with horseradish peroxidase. We found that significant sparing or recovery of hindlimb locomotor function is closely linked to sparing of axons in at least one ventrolateral quadrant of the cord. The essential elements probably belong to vestibulospinal and reticulospinal systems.

Stepping by chronic spinal cats.

We investigated the consequences of spinal cord transection in adult cat. All became capable of stepping upon a treadmill. Two of six animals stepped in the first postoperative testing session, 1 week after surgery. It took up to 6 weeks for the others to start stepping. None of the cats became capable of hindquarter support within 2 months after surgery. There was permanent loss of fore-hindlimb coordination and increased variability in the duration of each step cycle and its components. Coordination between the hindlimbs was also impaired, as signaled by increased variability in the time between foot contacts with the belt. These changes may be due to the loss of timing signals coming down from supraspinal levels to the segmental step generators or - alternatively - to decreased excitability of segmental motoneurons leading to less precise execution of stepping commands from the hypothetical pattern generators.

Pulmonary arterial pulsus alternans secondary to primary pulmonary hypertension.

Pulsus alternans of the pulmonary artery without systemic pulsus alternans is uncommon and is associated with multiple diseases. Two cases of pulmonary hypertension with pulmonary arterial pulsus alternans and right-sided heart failure are described. Primary pulmonary hypertension was demonstrated at autopsy in both cases. These two case reports constitute another previously unreported cause for pulsus alternans in the pulmonary circuit.