Central generation of locomotion in the spinal dogfish.

After a transection of the spinal cord a dogfish performs continuous swimming movements with a phase lag between adjacent segments. It is shown that the intersegmental coordination remains after an extensive dorsal root transection as well as after curarization. In the former case the motor activity was recorded electromyographically in several segments along the body, in the latter case the intersegmental coordination was evaluated by recording the efferent activity in different ventral roots along the body. It was concluded that a spinal central network can account for the phase lag observed between successive segments during swimming. It was also shown that the efferent activity from parts of the spinal cord with no dorsal roots intact could be influenced by peripheral stimuli such as pressure on the pelvic fins; this result suggests that some afferent fibres reach the spinal cord via the ventral roots.