Exogenous neuromodulation of spinal neurons induces beta-band coherence during self-sustained discharge of hind limb motor unit populations

• Published in: Journal of applied physiology (1985) 2019-10, Vol.127 (4), p.1034-1041
• Main Authors: Thompson, Christopher K, Johnson, Michael D, Negro, Francesco, Mcpherson, Laura Miller, Farina, Dario, Heckman, Charles J
• Format: Article
• Language: English
• Subjects: Animals; Cats; Female; Hindlimb - physiology; Male; Motor Neurons - physiology; Muscle, Skeletal - physiology; Spine - physiology
• ISSN: 8750-7587; 1522-1601
• DOI: 10.1152/japplphysiol.00110.2019

The spontaneous or self-sustained discharge of spinal motoneurons can be observed in both animals and humans. Although the origins of this self-sustained discharge are not fully known, it can be generated by activation of persistent inward currents intrinsic to the motoneuron. If self-sustained discharge is generated exclusively through this intrinsic mechanism, the discharge of individual motor units will be relatively independent of one another. Alternatively, if increased activation of premotor circuits underlies this prolonged discharge of spinal motoneurons, we would expect correlated activity among motoneurons. Our aim is to assess potential synaptic drive by quantifying coherence during self-sustained discharge of spinal motoneurons. Electromyographic activity was collected from 20 decerebrate animals using a 64-channel electrode grid placed on the isolated soleus muscle before and following intrathecal administration of methoxamine, a selective α -noradrenergic agonist. Sustained muscle activity was recorded and decomposed into the discharge times of ~10-30 concurrently active individual motor units. Consistent with previous reports, the self-sustained discharge of motor units occurred at low mean discharge rates with low-interspike variability. Before methoxamine administration, significant low-frequency coherence (