title: Does elimination of afferent input modify the changes in rat motoneurone properties that occur following chronic spinal cord transection?
abstract: The purpose of this study was to determine the effects of 6-8 weeks of chronic spinal cord isolation (SI, removal of descending, ascending and afferent inputs), compared with the same duration of spinal cord transection (ST, removal of descending input only) on hindlimb motoneurone biophysical properties. Adult female Sprague-Dawley rats were placed into three groups: (1) control (no removal of inputs), (2) ST and (3) SI. The electrophysiological properties from sciatic nerve motoneurones were recorded from deeply anaesthetized rats. Motoneurones in SI rats had significantly (P < 0.01) lower rheobase currents and higher spike afterhyperpolarization amplitudes and input resistances compared with motoneurones in control rats. A higher percentage (chi2, P = 0.01) of motoneurones in SI than control rats demonstrated frequency-current (f-I) relationships consistent with activation of persistent inward currents. Motoneurone steady state f-I slopes determined by increasing steps of 500 ms current pulses were significantly lower (P < 0.02) in SI than control rats. Motoneurone spike frequency adaptation measured using 30 s square-wave current injections (1.5-3.0 nA above the estimated rhythmic firing threshold), was similar for control and SI motoneurones. Changes in motoneurone properties following SI did not differ from ST. These findings indicate that the removal of afferent and ascending inputs along with descending inputs has little additional affect on motoneurone properties than removal of descending inputs alone. This study is the first to demonstrate that intact ascending and afferent input does not modify the effects of spinal transection on basic and rhythmic firing properties of rat hindlimb motoneurones.
authors.affiliation: Spinal Cord Research Centre, Department of Physiology, University of Manitoba, 730 William Avenue, 436 BMSB, Winnipeg, Manitoba, Canada R3E 3J7.
authors.forename: Duane C
authors.initials: DC
authors.lastname: Button
authors.forename: Jayne M
authors.initials: JM
authors.lastname: Kalmar
authors.forename: Kalan
authors.initials: K
authors.lastname: Gardiner
authors.forename: Tanguy
authors.initials: T
authors.lastname: Marqueste
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: Phillip F
authors.initials: PF
authors.lastname: Gardiner
mesh_terms: D000200:Action Potentials / Q000502:physiology; D000818:Animals; D004594:Electrophysiology; D005260:Female; D006614:Hindlimb / Q000294:innervation; D009046:Motor Neurons / Q000502:physiology*; D009475:Neurons, Afferent / Q000502:physiology*; D051381:Rats; D017207:Rats, Sprague-Dawley; D013116:Spinal Cord / Q000601:surgery; D013119:Spinal Cord Injuries / Q000503:physiopathology*