Identifying supraspinal influences on lumbosacral motor neuron excitability after spinal cord injury

Society for Neuroscience Chicago 2015 Motoneuron Excitability SCI and Plasticity

Identifying supraspinal influences on lumbosacral motor neuron excitability after spinal cord injury: Effects of galvanic vestibular stimulation and acoustic startle reflex on MMR amplitude in leg muscles

Abstract: In the presence of epidural stimulation, individuals with complete motor paralysis after spinal cord injury (SCI) have shown the ability to voluntarily execute movement in the lower limbs, suggesting descending connections may have existed since the time of injury that were not detected clinically. Currently these pathways cannot be determined due to a lack of sensitive and quantitative measures. The purpose of this study is to develop a tool capable of assessing the viability of descending supraspinal pathways in humans with SCI. Multi-segmental monosynaptic reflexes (MMR) were evoked via transcutaneous electrical stimulation over the lumbosacral enlargement while lying in a supine position (n=13, 4 AIS A, 2 AIS B, 4 AIS C, 3 AIS D). Electromyographic activity was recorded in bilateral rectus femoris, vastus lateralis, medial hamstrings, tibialis anterior, medial gastrocnemius, soleus, and adductor hallucis brevis. MMRs were conditioned by an auditory stimulus (30 ms tone of 90dB @ 700Hz) delivered using binaural headphones to elicit the acoustic startle reflex (ASR) for evaluation of the reticulospinal pathway. MMRs were conditioned with galvanic vestibular stimulation (GVS) (rectangular pulses, 300ms) directly over the mastoid processes for evaluation of the vestibulospinal pathway. Condition-test intervals (CTI) ranging from 60-300 ms were used. Conditioning of lower limb muscles varied depending on severity of injury. Preliminary results indicate conditioning is present in at least 1 muscle in 13/13 participants in both GVS and ASR conditions. With GVS conditioning, 1/13 participants had all muscles conditioned, whereas with ASR conditioning, 2/13 participants had all muscles conditioned. Facilitation was most robust at CTI’s of 140 ms and 190 ms with GVS conditioning and CTI’s of 90 ms and 110 ms in ASR conditioning. This method of evaluating descending translesion pathways in SCI population may have potential in more effectively diagnosing individuals after neurological injury.

Authors: A. MINK1,4, D. SAYENKO5, D. ATKINSON2,4, Y. GERASIMENKO5,6, S. HARKEMA3,4, *.. .. .1; 1Physiol. and Biophysics, 2Anatom. Sci. and Neurobio., 3Neurolog. Surgery, Univ. of Louisville, Louisville, KY; 4Neurosci. Collaborative Center, Frazier Rehab Inst., Louisville, KY; 5Dept. of Integrative Biol. and Physiol., UCLA, Los Angeles, CA; 6Pavlov Inst. of Physiol., St. Petersburg, Russian Federation

Support: Frazier Rehab Institute and Kentucky One Health Kentucky Spinal Cord & Head Injury Research Trust Grant no. 11-7 Helmsley Foundation Grant #2011PG-MED011 Commonwealth of Kentucky Challenge for Excellence Trust Fund National Institute of General Medical Sciences Grant 8 P30 GM-103507 Owsley Brown Frazier Chair in Neurological Rehabilitation Endowment Russian Foundation for Basic Research Grant 13-04-12030 ofi-m

Disclosures: A. Mink: None. D. Sayenko: None. D. Atkinson: None. Y. Gerasimenko: None. S. Harkema: None. …. .: None.

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