Cervicolumbar Coordination in Mammalian Quadrupedal Locomotion: Role of Spinal Thoracic Circuitry and Limb Sensory Inputs
Journal of Neuroscience. 2012-01-18; 32(3): 953-965
DOI: 10.1523/jneurosci.4640-11.2012
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Juvin L(1), Le Gal JP, Simmers J, Morin D.
Author information:
(1)University Bordeaux, INCIA, UMR 5287, F-33000 Bordeaux, France.
Effective quadrupedal locomotion requires a close coordination between the
spatially distant central pattern generators (CPGs) controlling forelimb and
hindlimb movements. Using isolated preparations of the neonatal rat spinal cord,
we explore the role of intervening thoracic circuitry in cervicolumbar CPG
coordination and the contribution to this remote coupling of limb somatosensory
inputs. In preparations activated with bath-applied N-methyl-D,L-aspartate,
serotonin, and dopamine, the coordination between locomotor-related bursts
recorded in cervical and lumbar ventral roots was substantially weakened,
although not abolished, when the thoracic segments were selectively withheld from
neurochemical stimulation or were exposed to a low Ca(2+) solution to block
synaptic transmission. Moreover, cervicolumbar CPG coordination was reduced after
a thoracic midsagittal section, suggesting that cross-cord projections
participate in the anteroposterior coupling. In quiescent preparations, either
cyclic or tonic electrical stimulation of low-threshold afferent pathways in C8
or L2 dorsal roots (DRs) could elicit coordinated ventral root bursting at both
cervical and lumbar levels via an activation of the underlying CPG networks. When
lumbar rhythmogenesis was prevented by local synaptic transmission blockade, L2
DR stimulation could still drive left-right alternating cervical bursting in
preparations otherwise exposed to normal bathing medium. In contrast, when the
cervical generators were selectively blocked, C8 DR stimulation was unable to
activate the lumbar CPGs. Thus, in the newborn rat, anteroposterior limb
coordination relies on active burst generation within midcord thoracic circuitry
that additionally conveys ascending and weaker descending coupling influences of
distant limb proprioceptive inputs to the cervical and lumbar generators,
respectively.