Field potential mapping of neurons in the lumbar spinal cord activated following stimulation of the mesencephalic locomotor region

B. R. Noga, P. A. Fortier, D. J. Kriellaars, X. Dai, G. R. Detillieux, L. M. Jordan

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Abstract

The spinal neurons involved in the control of locomotion in mammals have not been identified, and a major step that is necessary for this purpose is to determine where these cells are likely to be located. The principal objective of this study was to localize lumbar spinal interneurons activated by stimulation of the mesencephalic locomotor region (MLR) of the cat. For this purpose, extracellular recordings of MLR-evoked cord dorsum and intraspinal field potentials were obtained from the lumbosacral enlargement during fictive locomotion in the precollicular-postmammillary decerebrate cat preparation. Potentials recorded from the dorsal surface of the cord between the third lumbar (L3) and first sacral (S1) segments typically showed four short-latency positive waves (P1-P4). These P-waves were largest between the L4-L6 segments. The amplitude of the P2-4 waves increased with the appearance of locomotion and displayed rhythmic modulation during the locomotor step cycle. Microelectrode recordings from the L4-L7 spinal segments during fictive locomotion revealed the presence of both positive and negative short- latency MLR-evoked intraspinal field potentials, and were used to construct isopotential maps of the evoked potentials. Positive field potentials were observed throughout the dorsal horn of the L4-L7 spinal segments with the largest amplitude potentials occurring in laminae III-VI. Negative field potentials were found in laminae VI-X of the lumbar cord. The shortest latency negative field potentials were observed in lamina VII and at the border between laminae VI and VII and were considered to be evoked monosynaptically from the arrival of the descending volley. Short-latency mono- and disynaptic negative field potentials were also observed in lamina VIII. Longer latency, tri- and polysynaptic field potentials were observed in laminae VII and VIII. Many of the longer latency negative waves observed in laminae VII and VIII followed shorter latency negative potentials recorded from the same location. Laminae VII and VIII negative field potentials were largest in the L5-6 and L4-5 spinal segments, respectively. Negative field potentials were also evoked in the motor nuclei of the L4-7 spinal segments. The segmental latencies for these potentials indicate that they were evoked di- and trisynaptically. Di- and trisynaptic negative field potentials were also observed near the central canal (in lamina X and the adjacent medial lamina VII) of the L5 and L6 segments. The MLR-evoked negative field potentials were modulated during fictive locomotion. These results suggest that stimulation of the MLR produces a descending volley that activates interneurons in the intermediate zone and ventral horn throughout the lumbosacral segments of the spinal cord, but predominantly between L4 and L6. We propose that the neurons giving rise to MLR-evoked cord dorsum and negative field potentials form part of the spinal circuitry responsible for the initiation and/or maintenance of locomotion.

Original languageEnglish (US)
Pages (from-to)2203-2217
Number of pages15
JournalJournal of Neuroscience
Volume15
Issue number3 II
StatePublished - Jan 1 1995
Externally publishedYes

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Keywords

  • fictive locomotion
  • field potentials
  • interneurons
  • mesencephalic locomotor region
  • spinal cord

ASJC Scopus subject areas

  • Neuroscience(all)

Cite this

Noga, B. R., Fortier, P. A., Kriellaars, D. J., Dai, X., Detillieux, G. R., & Jordan, L. M. (1995). Field potential mapping of neurons in the lumbar spinal cord activated following stimulation of the mesencephalic locomotor region. Journal of Neuroscience, 15(3 II), 2203-2217.