Stumbling corrective reaction during fictive locomotion in the cat.
An obstacle contacting the dorsal surface of a cat's hind foot during the swing phase of locomotion evokes a reflex (the stumbling corrective reaction) that lifts the foot and extends the ankle to avoid falling. We show that the same sequence of ipsilateral hindlimb motoneuron activity can be evoked in decerebrate cats during fictive locomotion. As recorded in the peripheral nerves, twice threshold intensity stimulation of the cutaneous superficial peroneal (SP) nerve during the flexion phase produced a very brief excitation of ankle flexors (e.g., tibialis anterior and peroneus longus) that was followed by an inhibition for the duration of the stimulus train (10-25 shocks, 200 Hz). Extensor digitorum longus was always, and hip flexor (sartorius) activity was sometimes, inhibited during SP stimulation. At the same time, knee flexor and the normally quiescent ankle extensor motoneurons were recruited (mean latencies 4 and 16 ms) with SP stimulation during fictive stumbling correction. After the stimulus train, ankle extensor activity fell silent, and there was an excitation of hip, knee, and ankle flexors. The ongoing flexion phase was often prolonged. Hip extensors were also recruited in some fictive stumbling trials. Only the SP nerve was effective in evoking stumbling correction. Delivered during extension, SP stimulus trains increased ongoing extensor motoneuron activity as well as increasing ipsilateral hip, knee, and ankle hindlimb flexor activity in the subsequent step cycle. The fictive stumbling corrective reflex seems functionally similar to that evoked in intact, awake animals and involves a fixed pattern of short-latency reflexes as well as actions evoked through the lumbar circuitry responsible for the generation of rhythmic alternating locomotion.
Quevedo
Jorge
J
Spinal Cord Research Centre and Department of Physiology, University of Manitoba, 730 William Ave., Winnipeg, Manitoba R3E3J7, Canada.
Stecina
Katinka
K
Gosgnach
Simon
S
McCrea
David A
DA
D000818:Animals; D002415:Cats; D003655:Decerebrate State / Q000503:physiopathology; D004307:Dose-Response Relationship, Radiation; D004558:Electric Stimulation / Q000379:methods; D004576:Electromyography / Q000379:methods; D007839:Functional Laterality / Q000502:physiology*; D008124:Locomotion / Q000502:physiology* / Q000528:radiation effects; D035002:Lower Extremity / Q000294:innervation* / Q000502:physiology*; D009046:Motor Neurons / Q000502:physiology* / Q000528:radiation effects; D009433:Neural Inhibition / Q000502:physiology / Q000528:radiation effects; D010543:Peroneal Nerve / Q000502:physiology / Q000528:radiation effects; D011930:Reaction Time / Q000502:physiology / Q000528:radiation effects; D012018:Reflex / Q000502:physiology*; D013997:Time Factors