Effect of posture on the onset of fictive locomotion in the decerebrate rabbit preparation.

Spontaneous locomotor episodes were recorded from hindlimb muscle nerves of decerebrate curarized rabbit preparations. Changes in the static position of both hindfeet (from extended to flexed) or of the head (from horizontal to bent forward) were shown to elicit a shift of the first locomotor burst from flexion to extension. Interneurones whose activity was recorded in the lumbar spinal cord were active throughout the first locomotor burst only when the latter was an extensor burst. Such data show that proprioceptive inputs are able to determine the onset of central locomotor programmation. Neuronal interactions which, at the spinal level, could account for this effect, are discussed.