02272nas a2200241   4500008004100000022001400041245007000055210006800125260001200193300001400205490000800219520158400227653001301811653002001824653002501844653001501869653001801884100002301902700002101925700001501946700002101961856004801982       2001                        eng d  a0014-481900aMotor unit properties after operant conditioning of rat H-reflex.0 aMotor unit properties after operant conditioning of rat Hreflex  c10/2001  a382–3860 v1403 aOperant conditioning of the H-reflex produces plasticity at several sites in the spinal cord, including the motoneuron. This study assessed whether this spinal cord plasticity is accompanied by changes in motor unit contractile properties. Thirty-one adult male Sprague-Dawley rats implanted for chronic recording of triceps surae electromyographic activity and H-reflex elicitation were exposed for at least 40 days to HRup or HRdown training, in which reward occurred when the H-reflex was greater than (12 HRup rats) or less than (12 HRdown rats) a criterion value, or continued under the control mode in which the H-reflex was simply measured (7 HRcon rats). At the end of H-reflex data collection, rats were anesthetized and the contractile properties of 797 single triceps surae motor units activated by intraaxonal (or intramyelin) current injection were determined. Motor units were classified as S, FR, Fint, or FF on the basis of sag and fatigue properties. Maximum tetanic force and twitch contraction time were also measured. HRdown rats exhibited a significant increase in the fatigue index of fast-twitch motor units. This resulted in a significant decrease in the percentage of Fint motor units and a significant increase in that of FR motor units. HRup conditioning had no effect on fatigue index. Neither HRup nor HRdown conditioning affected maximum tetanic force or twitch contraction time. These data are consistent with the hypothesis that conditioning mode-specific change in motoneuron firing patterns causes activity-dependent change in muscle properties.10aH-Reflex10amotor unit type10aoperant conditioning10aplasticity10atriceps surae1 aCarp, Jonathan, S.1 aChen, Xiang Yang1 aSheikh, H.1 aWolpaw, Jonathan  uhttp://www.ncbi.nlm.nih.gov/pubmed/1168131402325nas a2200229   4500008004100000022001400041245009300055210006900148260001200217300001200229490000700241520165100248653001301899653001101912653002501923653001501948653001601963100002101979700002502000700002302025856004702048       1993                        eng d  a0014-481900aOperant conditioning of the primate H-reflex: factors affecting the magnitude of change.0 aOperant conditioning of the primate Hreflex factors affecting th  c12/1993  a31–390 v973 aPrimates can gradually increase or decrease H-reflex amplitude in one leg when reward depends on that amplitude. The magnitude of change varies greatly from animal to animal. This study sought to define the factors that control this magnitude. It evaluated the influence of animal age, muscle size (absolute and relative), background electromyographic activity (EMG) level, M response amplitude, initial H-reflex amplitude, performance intensity, and behavior of the contralateral leg. Fifty-four animals (Macaca nemestrina) underwent operant conditioning of the triceps surae H-reflex in one leg (the trained leg). Twenty-eight were rewarded for larger H-reflexes (HRup animals), and 26 were rewarded for smaller H-reflexes (HRdown animals). In the HRup animals, H-reflex amplitude in the trained leg rose to an average final value of 177% of its initial amplitude. Magnitude of increase varied widely across animals. Nine animals rose to 120-140%, 11 to 160-240%, three to 300% or more, and five remained within 20% of initial amplitude. In the HRdown animals, H-reflex amplitude in the trained leg decreased to an average of 69% of initial amplitude. Magnitude of decrease varied widely. Five animals decreased to 20-40%, seven to 40-60%, six to 60-80%, and eight remained within 20% of initial amplitude. Animal age, as assessed by weight, markedly affected HRdown conditioning, but not HRup conditioning. Heavy HRdown animals (> or = 6 kg) were more successful than light HRdown animals (< 6 kg). Thirteen of 14 heavy animals and only five of 12 light animals decreased to less than 80% of initial amplitude.(ABSTRACT TRUNCATED AT 250 WORDS)10aH-Reflex10amonkey10aoperant conditioning10aplasticity10aSpinal Cord1 aWolpaw, Jonathan1 aHerchenroder, P., A.1 aCarp, Jonathan, S.  uhttp://www.ncbi.nlm.nih.gov/pubmed/8131830