Location of Spinal Cord Pathways That Control Hindlimb Movement Amplitude and Interlimb Coordination During Voluntary Swimming in Turtles

Abstract

Samara RF, Currie SN. Location of spinal cord pathways that control hindlimb movement amplitude and interlimb coordination during voluntary swimming in turtles. J Neurophysiol 99: 1953-1968, 2008. First published February 13, 2008 doi:10.1152/jn.01087.2007. We performed mechanical lesions of the midbody (D2-D3; second to third postcervical spinal segments) spinal cord in otherwise intact turtles to locate spinal cord pathways that 1) activate and control the amplitude of voluntary hindlimb swimming movements and 2) coordinate hindlimb swimming with the movement of other limbs. Preand postlesion turtles were held by a band clamp around the carapace just beneath the water surface in a clear Plexiglas tank and videotaped from below so that kinematic measurements could be made of voluntary forward swimming with motion analysis software. Movements of the forelimbs (wrists) and hindlimbs (knees and ankles) were tracked relative to stationary reference points on the plastron to obtain bilateral measurements of hip and forelimb angles as functions of time along with foot trajectories. We measured changes in limb movement amplitude, cycle period, and interlimb phase before and after spinal lesions. Our results indicate that locomotor command signals that activate and regulate the amplitude of voluntary hindlimb swimming travel primarily in the dorsolateral funiculus (DLF) at the D2-D3 level and cross over to drive contralateral hindlimb movements. This suggests that electrical stimulation of the D3 DLF, which was previously shown to evoke swimming movements in the contralateral hindlimb of low-spinal turtles, activated the same locomotor command pathways that the animal uses during voluntary behavior. We also show that forelimb-hindlimb coordination is maintained by longitudinal spinal pathways that are largely confined to the ventrolateral funiculus (VLF) and mediate phase coupling of ipsilateral limbs, presumably by interenlargement propriospinal fibers.

A Neural Basis for Motor Primitives in the Spinal Cord

“…Examination of both extracellular and intracellular recordings in turtle fictive and nonfictive preparations by Stein, Berkowitz, Currie, Hounsgaard, and others also show both shared and dedicated neurons recruited in fictive vertebrate motor patterns (Berkowitz, 2001(Berkowitz, , 2002(Berkowitz, , 2008Alaburda et al, 2005;Stein, 2005Stein, , 2008Berg et al, 2007;Samara and Currie, 2008). However, their data cannot or did not examine modularity in terms of premotor drive, or examine EMG and force patterns as we did here.…”

Cervical Spinal Stimulation at Different Levels Evoked Multisegmental Motor Responses in the Lower Limbs

“…Activation of the propriospinal pathway could not be ruled out in this experiment, a possibility that has been supported in previous reports [12]. Studies have emphasized the integrative function of the propriospinal pathways between upper and lower limbs [13]. However, as mentioned above either tracts carrying these signals is a speculative venture.…”

Whole-Body Responses: Neural Control and Implications for Rehabilitation and Fall Prevention

“…There are a number of neural mechanisms available to ensure appropriate coordination of the legs and arms during balance reactions. Based on the results of studies in the cat (Gernandt and Megirian 1961;others 1973, 1975;Skinner and others 1980) and, more recently, in the turtle (Samara and Currie 2008) and neonatal rat (Juvin and others 2005), it has been suggested that propriospinal pathways provide the necessary link between the lumbrosacral and cervical spinal segments responsible for controlling the lower and upper limbs, respectively. In humans, interlimb reflexes have been identified whereby electrical stimulation of the foot (Kearney and Chan 1979) or mechanical perturbation of the ankle (Kearney and Chan 1981) produces responses in the muscles of the arms.…”