Effects of selective spinal cord lesions on hind limb locomotion in birds.

In birds, a variety of subtotal thoracic spinal cord lesions were made to determine the spinal cord pathways essential for avian hind limb locomotion (bipedal walking). The various surgical disruptions included: section of the dorsal half of the cord, a hemisection, section of the dorsal cord and ventromedial funiculi, section of the dorsal cord ventrolateral funiculi, section of the entire thoracic cord except for one ventrolateral quadrant, section of the ventral half of the cord, and complete transection of the thoracic cord. The study compared the locomotion following these lesions in both chronic surviving and acutely decerebrated, brain stem-stimulated birds. Behavioral assessments and electromyographic recording techniques were used to evaluate locomotor activity. Our results showed that transectioning pathways within the dorsal cord did not hinder the activation and maintenance of self-supported walking in either preparation. However, sparing the spinal cord pathways within either the ventromedial or ventrolateral funiculi of the thoracic spinal cord was essential for the activation of self-supported walking in both preparations. When our findings are integrated with previous studies, medullary reticulospinal pathways (projecting through the ventral funiculi) are strongly implicated as a common descending projection for the activation of spinal cord locomotor networks and the initiation of locomotion. Similar findings have been found in quadrapedal mammals and, as a complement, birds may make an excellent model for the study of bipedal locomotion.