02272nas a2200253   4500008004100000022001400041245009400055210006900149260001200218300001600230490000700246520153000253653002401783653002601807653001501833653000801848653002301856100002101879700001301900700001301913700002301926700002101949856004801970       2006                        eng d  a0897-715100aCorticospinal tract transection permanently abolishes H-reflex down-conditioning in rats.0 aCorticospinal tract transection permanently abolishes Hreflex do  c11/2006  a1705–17120 v233 aPrevious studies have shown that corticospinal tract (CST) transection, but not transection of other major spinal cord tracts, prevents down-conditioning of the H-reflex, the electrical analog of the spinal stretch reflex. This study set out to determine whether the loss of the capacity for H-reflex down-conditioning caused by CST transection is permanent. Female Sprague-Dawley rats received CST, lateral column (LC), or dorsal column ascending tract (DA) transection at T8-9; 9-10 months later, they were exposed to the H-reflex down-conditioning protocol for 50 days. In the LC and DA rats, H-reflex size fell to 60 (+/- 9 SEM)% and 60 (+/- 19)%, respectively, of its initial size. This down-conditioning was comparable to that of normal rats. In contrast, H-reflex size in the CST rats rose to 170 (+/- 42)% of its initial size. A similar rise does not occur in rats exposed to down-conditioning shortly after CST transection. These results indicate that CST transection permanently eliminates the capacity for H-reflex down-conditioning and has gradual long-term effects on sensorimotor cortex function. They imply that H-reflex down-conditioning can be a reliable measure of CST function for long-term studies of the effects of spinal cord injury and/or for evaluations of the efficacy of experimental therapeutic procedures, such as those intended to promote CST regeneration. The results also suggest that the role of sensorimotor cortex in down-conditioning extends beyond generation of the essential CST activity.10acorticospinal tract10aH-reflex conditioning10aplasticity10arat10aspinal cord injury1 aChen, Xiang Yang1 aChen, Yi1 aChen, Lu1 aTennissen, Ann, M.1 aWolpaw, Jonathan  uhttp://www.ncbi.nlm.nih.gov/pubmed/17115915