BILATERAL CONTROL OF HINDLIMB SCRATCHING IN THE SPINAL TURTLE - CONTRALATERAL SPINAL CIRCUITRY CONTRIBUTES TO THE NORMAL IPSILATERAL MOTOR PATTERN OF FICTIVE ROSTRAL SCRATCHING

In a spinal turtle, unilateral stimulation in the rostral scratch rece ptive field elicited rhythmic fictive rostral scratching in ipsilatera l hindlimb motor neurons; contralateral hip motor activity was also rh ythmic and out-of-phase with ipsilateral hip motor activity, When left and right rostral scratch receptive fields were stimulated simultaneo usly, bilateral rhythmic fictive rostral scratching was produced; left hindlimb scratching was out-of-phase with right hindlimb scratching, Thus, spinal circuits coordinate interlimb phase during bilateral fict ive scratching. We examined the contributions of contralateral spinal circuitry to the normal pattern of right hindlimb fictive rostral scra tching by removing the left halves of the D7 segment and the hindlimb enlargement (D8-S2 segments), After left-hemicord removal, stimulation in the right rostral scratch receptive field usually elicited a varia tion of rostral scratching with rhythmic right hip flexor activity and no right hip extensor activity; thus, right hip flexor rhythm generat ion does not require left hindlimb enlargement circuitry, Normal right hindlimb rostral scratching with rhythmic alternation between hip fle xor and extensor activities was rarely observed; thus, contralateral s pinal circuitry contributes to the production of normal ipsilateral fi ctive rostral scratching, After left-hemicord removal, stimulation in the left rostral scratch receptive field elicited rhythmic right hip e xtensor activity; thus, contralateral spinal circuitry can generate a hip extensor rhythm during ipsilateral rostral scratch receptive field stimulation. Our observations and those of Berkowitz and Stein (1994a ,b) support the concept that an ipsilateral hindlimb's normal rostral scratch motor pattern is generated by a modular central pattern genera tor that is bilaterally distributed in the spinal cord.