Deletions of Rhythmic Motoneuron Activity During Fictive Locomotion and Scratch Provide Clues to the Organization of the Mammalian Central Pattern Generator

• Published in: Journal of neurophysiology 2005-08, Vol.94 (2), p.1120-1132
• Main Authors: Lafreniere-Roula, Myriam, McCrea, David A
• Format: Article
• Language: English
• Subjects: Animals; Cats; Decerebrate State; Electrophysiology; Evoked Potentials - physiology; Hindlimb - physiology; Laminectomy - methods; Locomotion - physiology; Models, Neurological; Motor Neurons - classification; Motor Neurons - physiology; Muscle, Skeletal - innervation; Muscle, Skeletal - physiology; Periodicity; Peripheral Nerves - physiology; Physical Stimulation; Reaction Time; Reflex - physiology; Skin - innervation; Time Factors
• ISSN: 0022-3077; 1522-1598
• DOI: 10.1152/jn.00216.2005

Spinal Cord Research Centre and Department of Physiology, University of Manitoba, Winnipeg, Manitoba, Canada Submitted 1 March 2005; accepted in final form 24 April 2005 We examined the features of spontaneous deletions of bursts of motoneuron activity that can occur within otherwise rhythmic alternating flexor and extensor activity during fictive locomotion and scratch in adult decerebrate cats. Deletions of activity were observed both in hindlimb flexor and extensor motoneuron pools during brain stem–stimulation-evoked fictive locomotion but only in extensors during fictive scratch. Paired intracellular motoneuron recordings showed that deletions reduced the depolarization of homonymous motoneurons in qualitatively similar ways. Differences occurred in the extent to which activity in synergist motoneuron pools operating at other joints within the limb was reduced during deletions. The timing of the rhythmic activity that followed a deletion was often at an integer multiple of the preexisting locomotor or scratch cycle period. This maintenance of cycle period was also seen during deletions in which there was a complete failure of motoneuron depolarization. The activity of antagonist motoneurons was usually sustained during deletions with some rhythmic modulation at intervals of the preexisting cycle period. We discuss an organization of the central pattern generator for locomotion and scratch that functions as a single rhythm generator with separate and multiple pattern formation modules for controlling the hyper- and depolarization of subsets of motoneurons within the limb. Address for reprint requests and other correspondence: D. A. McCrea, Spinal Cord Research Center, University of Manitoba, 730 William Avenue, Winnipeg, Manitoba R3E3J7, Canada (E-mail: dave{at}scrc.umanitoba.ca )