title: Motoneuron intrinsic properties, but not their receptive fields, recover in chronic spinal injury.
abstract: Proper movement execution relies on precise input processing by spinal motoneurons (MNs). Spinal MNs are activated by limb joint rotations. Typically, their movement-related receptive fields (MRRFs) are sharply focused and joint-specific. After acute spinal transection MRRFs become wide, but their manifestation is not apparent, as intrinsic excitability, primarily resulting from the loss of persistent inward currents (PICs), dramatically decreases. PICs undergo a remarkable recovery with time after injury. Here we investigate whether MRRFs undergo a recovery that parallels that of the PIC. Using the chronic spinal cat in acute terminal decerebrate preparations, we found that MRRFs remain expanded 1 month after spinal transaction, whereas PICs recovered to >80% of their preinjury amplitudes. These recovered PICs substantially amplified the expanded inputs underlying the MRRFs. As a result, we show that single joint rotations lead to the activation of muscles across the entire limb. These results provide a potential mechanism for the propagation of spasms throughout the limb.
authors.affiliation: Department of Physiology, Center for Comparative Medicine, Department of Physical Medicine and Rehabilitation, and Department of Physical Therapy and Human Movement Sciences, Northwestern University Feinberg School of Medicine, Chicago, Illinois 60611.
authors.forename: Michael D
authors.initials: MD
authors.lastname: Johnson
authors.forename: Elma
authors.initials: E
authors.lastname: Kajtaz
authors.forename: Charlette M
authors.initials: CM
authors.lastname: Cain
authors.forename: C J
authors.initials: CJ
authors.lastname: Heckman
mesh_terms: D000818:Animals; D002415:Cats; D004558:Electric Stimulation; D004576:Electromyography; D055724:Electrophysiological Phenomena / Q000502:physiology; D005260:Female; D006614:Hindlimb / Q000294:innervation / Q000502:physiology; D008297:Male; D009046:Motor Neurons / Q000502:physiology*; D018408:Patch-Clamp Techniques; D011984:Sensory Receptor Cells / Q000502:physiology*; D013119:Spinal Cord Injuries / Q000503:physiopathology*