Disruption of left-right reciprocal coupling in the spinal cord of larval lamprey abolishes brain-initiated locomotor activity.

In this study, contributions of left-right reciprocal coupling mediated by commissural interneurons in spinal locomotor networks to rhythmogenesis were examined in larval lamprey that had longitudinal midline lesions in the rostral spinal cord [8 --> 30% body length (BL), relative distance from the head] or caudal spinal cord (30 --> 50% BL). Motor activity was initiated from brain locomotor command systems in whole animals or in vitro brain/spinal cord preparations. After midline lesions in the caudal spinal cord in whole animals and in vitro preparations, left-right alternating burst activity could be initiated in rostral and usually caudal regions of spinal motor networks.

Changes in locomotor activity parameters with variations in cycle time in larval lamprey.

In larval lamprey, locomotor activity recorded from whole animals and in vitro brain/spinal cord preparations was analyzed to determine how two parameters of locomotor activity, burst proportion (BP; relative duration of motor burst activity) and intersegmental phase lag (phi; normalized delay of burst activity along one side of the body), vary with changes in cycle time (T). In individual animals, the slopes of BP and phi versus T were compared using linear regression analysis, followed by statistical analysis of the slopes to determine whether the parameters changed significantly with variations in cycle time. For locomotor muscle activity in whole animals, the BP values increased significantly with decreases in T (i.