title: Neuromodulation of motor-evoked potentials during stepping in spinal rats.
abstract: The rat spinal cord isolated from supraspinal control via a complete low- to midthoracic spinal cord transection produces locomotor-like patterns in the hindlimbs when facilitated pharmacologically and/or by epidural electrical stimulation. To evaluate the role of epidural electrical stimulation in enabling motor control (eEmc) for locomotion and posture, we recorded potentials evoked by epidural spinal cord stimulation in selected hindlimb muscles during stepping and standing in adult spinal rats. We hypothesized that the temporal details of the phase-dependent modulation of these evoked potentials in selected hindlimb muscles while performing a motor task in the unanesthetized state would be predictive of the potential of the spinal circuitries to generate stepping. To test this hypothesis, we characterized soleus and tibialis anterior (TA) muscle responses as middle response (MR; 4-6 ms) or late responses (LRs; >7 ms) during stepping with eEmc. We then compared these responses to the stepping parameters with and without a serotoninergic agonist (quipazine) or a glycinergic blocker (strychnine). Quipazine inhibited the MRs induced by eEmc during nonweight-bearing standing but facilitated locomotion and increased the amplitude and number of LRs induced by eEmc during stepping. Strychnine facilitated stepping and reorganized the LRs pattern in the soleus. The LRs in the TA remained relatively stable at varying loads and speeds during locomotion, whereas the LRs in the soleus were strongly modulated by both of these variables. These data suggest that LRs facilitated electrically and/or pharmacologically are not time-locked to the stimulation pulse but are highly correlated to the stepping patterns of spinal rats.
authors.affiliation: Biomedical Engineering IDP, University of California, Los Angeles, California;
authors.forename: Parag
authors.initials: P
authors.lastname: Gad
authors.forename: Igor
authors.initials: I
authors.lastname: Lavrov
authors.forename: Prithvi
authors.initials: P
authors.lastname: Shah
authors.forename: Hui
authors.initials: H
authors.lastname: Zhong
authors.forename: Roland R
authors.initials: RR
authors.lastname: Roy
authors.forename: V Reggie
authors.initials: VR
authors.lastname: Edgerton
authors.forename: Yury
authors.initials: Y
authors.lastname: Gerasimenko
mesh_terms: D000767:Anesthesia, Epidural; D000818:Animals; D004558:Electric Stimulation; D019054:Evoked Potentials, Motor / Q000187:drug effects*; D005260:Female; D006614:Hindlimb / Q000294:innervation / Q000502:physiology; D018482:Muscle, Skeletal / Q000294:innervation / Q000502:physiology; D018377:Neurotransmitter Agents / Q000494:pharmacology*; D011187:Posture; D011814:Quipazine / Q000494:pharmacology*; D051381:Rats; D017207:Rats, Sprague-Dawley; D013116:Spinal Cord / Q000502:physiology*; D013331:Strychnine / Q000494:pharmacology*; D016138:Walking / Q000502:physiology*
chemical_list: D018377:Neurotransmitter Agents; D011814:Quipazine; D013331:Strychnine
keywords: EMG; evoked potentials; quipazine; spinal cord stimulation; strychnine