Poster Z13 - Asynchronous Local Field Potentials Across Functional and Structural Spinal Networks and the Influence of Spinal Cord Injury

Introduction: Supraspinal structures have been characterized via local field potentials (LPFs), demonstrating a relationship between band-specific oscillatory activity associated with specific behavioral states, neural structures, and intrinsic processes. Oscillatory activity is often associated with synchrony but remain transient, lasting for no more than a few hundred of milliseconds, thus represent only a fraction of the neural activity. The bulk of activity present throughout is asynchronous, scale-free, activity. Growing evidence has demonstrated that asynchronous activity varies across brain behavioral and structural states which can represent covert network organization and information relay.
Since intraspinal LFPs remain largely unexplored, we explored their presence across structural and/or functional regions of the spinal cord and how these features may be altered by changes in ascending/descending pathways because of spinal cord injury (SCI). Our segment of focus was the below-lesion lumbar enlargement, which subserves as a hub for sensorimotor and autonomic functions and whose functional organization exhibits associations with distinct structural regions.

Materials and

Methods: All experiments were approved by the WUSTL IACUC and included a total of 15 Sprague Dawley rats, of which 5 were neurologically intact, 5 with SCI related neuropathic pain, and 5 with SCI without neuropathic pain. Moderate-to-severe SCI models were prepared via a T8/T9 vertebral laminectomy to perform a midline contusion with rodent spinal cord impactor (Infinite Horizon Impactor, IH-04000) delivering a force of 200 Kilodynes and 0 second dwell time. Animals with SCI were then allowed 6-8 weeks of recovery to account for spontaneous recovery of motor function and/or development of neuropathic pain. Animals were assessed for below-level neuropathic pain at least twice a week, beginning 1-week post-SCI leading up to the terminal experiments. Common signs denoting the development of neuropathic pain included, but were not limited to, mechanical allodynia and/or hyperalgesia in the dermatomes below the injury. Terminal electrophysiological experiments were conducted on all rats via a T13-L2 laminectomy and followed by a 32-channel dual shank microelectrode array (MEA, 16 channels per shank) implanted into the L5 dorsal root entry zone to target the globular portion of the hindpaw. Electrodes recorded throughout the dorsoventral extent of the spinal cords grey matter and recordings were gathered under periods of spontaneous activity absent of evoked sensory transmissions.

Results, Conclusions, and Discussions: Our preliminary results suggest that broad spectrum intraspinal LFP power is modulated by anatomically throughout the spinal cord. Neurologically intact rats and SCI lacking SCI-NP, had a consistent increase in power gradient from the dorsal horn, sensory-dominant region, to the ventral horn, motor-dominant regions. In contrast, rats with SCI-NP had a more variable gradient in power distribution that tended to increase in the intermediate gray matter associated with sensorimotor information integration. Regarding band limited LFPs traditionally associated with supraspinal activity, we noted a differential increase across depths in higher frequency bandwidths power in neurologically intact and rats with SCI-NP, while animals with SCI-NP demonstrated higher modulation power in lower frequencies bandwidths. These contrasting results may allude to the extent in which ascending/descending pathways contribute to asynchronous neural activity across local and distant spinal networks as a result to (dys-)function. In this study we characterized the presence of intraspinal LFPs and were able to correlate them with specific structural and functional regions of the spinal gray matter. In neurologically intact and SCI without SCI-NP, there is a consistent distribution of power that increases from the dorsal to the ventral depth of the cord. Animals with SCI-NP contrasted the other subjects by showing a higher power distribution in the gray matter’s intermediate zone which is highly associated with sensorimotor integration from. Rats that were neurologically intact and without SCI-NP showed consistent increases in power higher frequency broad bands, while SCI-NP rats showed increased power in lower frequency broad spectrums. These differences may reflect the changes in spinal reorganization post-SCI.

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