title: Excitatory synaptic potentials in spastic human motoneurons have a short rise-time.
abstract: This study assessed whether changes in size or time-course of excitatory postsynaptic potentials (EPSPs) in motoneurons innervating spastic muscle could induce a greater synaptic response, and thereby contribute to reflex hyperexcitability. We compared motor unit (MU) firing patterns elicited by tendon taps applied to both spastic and contralateral (nonspastic) biceps brachii muscle in hemiparetic stroke subjects. Based on recordings of 115 MUs, significantly shortened EPSP rise times were present on the spastic side, but with no significant differences in estimated EPSP amplitude. These changes may contribute to hyperexcitable reflex responses at short latency, but the EPSP amplitude changes appear insufficient to account for global differences in reflex excitability.
authors.affiliation: Sensory Motor Performance Program, Rehabilitation Institute of Chicago, 345 East Superior Street, Suite 1406, Chicago, Illinois 60611, USA. n-suresh@northwestern.edu
authors.forename: Nina L
authors.initials: NL
authors.lastname: Suresh
authors.forename: Michael D
authors.initials: MD
authors.lastname: Ellis
authors.forename: Jennifer
authors.initials: J
authors.lastname: Moore
authors.forename: Heather
authors.initials: H
authors.lastname: Heckman
authors.forename: William Zev
authors.initials: WZ
authors.lastname: Rymer
mesh_terms: D019706:Excitatory Postsynaptic Potentials / Q000502:physiology*; D006801:Humans; D008875:Middle Aged; D009046:Motor Neurons / Q000502:physiology*; D009128:Muscle Spasticity / Q000503:physiopathology*; D010291:Paresis / Q000175:diagnosis / Q000503:physiopathology*; D020521:Stroke / Q000175:diagnosis / Q000503:physiopathology*; D013710:Tendons / Q000294:innervation / Q000502:physiology