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The Journal of Neurophysiology Vol. 82 No. 5 November 1999, pp. 2029-2038
Copyright ©1999 by the American Physiological Society
Biophysics Sector and Istituto Nazionale di Fisica della Materia Unit, International School for Advanced Studies (SISSA), 34014 Trieste, Italy
Beato, M. and
A. Nistri.
Interaction Between Disinhibited Bursting and Fictive Locomotor
Patterns in the Rat Isolated Spinal Cord. J. Neurophysiol. 82: 2029-2038, 1999. Using a transverse
barrier that allowed discrete application of neurochemicals to certain
lumbar regions of the rat isolated spinal cord, we studied the
intersegmental organization of rhythmic patterns recorded
extracellularly from ventral roots and intracellularly from single
motoneurons. Fictive locomotor patterns were elicited by serotonin
(5-HT) and/or N-methyl-D-aspartate (NMDA) or
high K+ solution applied to the rostral or caudal lumbar
region of the cord. Neither 4-aminopyridine nor Mg2+-free
solution shared this property. Coapplication of strychnine and
bicuculline (blockers of fast synaptic inhibition) to the caudal part
elicited slow bursting in the whole cord. These bursts could trigger
episodes of fictive locomotion patterns in the rostral roots. When the
rostral region was exposed to 5-HT and/or NMDA (during continuous
application of strychnine and bicuculline caudally) a standard
locomotor-like pattern was generated during each interburst interval
and was surprisingly expressed with its typical pattern alternation
even in the caudal area despite the local presence of strychnine and
bicuculline. Midsagittal splitting of the caudal region did not change
this alternating pattern, indicating that it was driven by rostral
regions above the surgical cut. Discrete changes in the concentrations
of NMDA rostrally modulated the burst amplitude recorded in the same
region after caudal application of strychnine and bicuculline. The
period of fictive locomotor patterns changed bimodally depending on the
temporal relation with disinhibited bursts, indicating a tight
interaction between these two rhythmic activities. These results are
interpreted on the basis of a model that assumes a modular arrangement
for the locomotor central pattern generator, made up by a series of
unit burst generators with serial and crossed connections.
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