Characterizing spinal interneuronal activity during air-stepping in sub-chronic spinal cats

Nicholas Au Yong

doi:10.17918/00000458

While the neuronal constituents of the locomotor CPG have not been identified, they likely include lumbar interneurons within the intermediate zone (Lamina IV-VII), previously shown to be active during locomotor behavior. Two different organizational schemes have been proposed for the locomotor center that governs stepping and other rhythmic behaviors. These include models based on spatially segmented modules or a system of longitudinal networks. In this project, the activity of spinal interneurons was examined using multichannel electrode arrays during air-stepping in sub-chronic spinal cats. Single-unit and population activity of spinal interneurons were examined in two separate studies. In the first aim, we examined if the spatial organization of the single-unit lumbar interneuronal activity patterns was consistent with either of these two organizational schemes. While the preferred phases of lumbar interneurons, calculated with circular statistics, from both sides of the spinal cord were distributed over the entire step cycle, we found that the preferred phases of units with respect to the ipsilateral step cycle largely fell within the first and last third of the step cycle. In contrast, preferred phases of contralateral units fell within the middle third of the step cycle. In the second aim, we investigated if the spatial-temporal dynamics of spinal interneuronal activity was consistent with the proposed organizational schemes for rythmogenicity. Segmental interneuronal activity, studied via multiunit activity (MUA), was found to be modulated with respect to the ipsilateral step cycle during air-stepping with maximal activity occurring near the ipsilateral swing-stance transition period. Furthermore, examination of population activity throughout the rostrocaudal extent showed no differences in their phasic dynamics between segmental levels, suggesting that the spinal interneurons targeted in this study may operate as part of a distributed network. Together, findings from both of these aims suggest that the interneurons examined in this study operate as part of a longitudinally distributed network within the lumbar cord. Furthermore, these results show that interneurons within lamina V, VI, and the top of lamina VII are not activated according to their rostrocaudal positions as would be expected from spatially organized spinal modules or a travelling wave mechanism.

Characterizing spinal interneuronal activity during air-stepping in sub-chronic spinal cats

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Characterizing spinal interneuronal activity during air-stepping in sub-chronic spinal cats

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