title: Corticospinal tract transection permanently abolishes H-reflex down-conditioning in rats.
abstract: Previous 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.
authors.affiliation: Laboratory of Nervous System Disorder, Wadsworth Center, New York State Department of Health and State University of New York, Albany, New York 12201-0509, USA. chenx@wadsworth.org
authors.forename: Xiang Yang
authors.initials: XY
authors.lastname: Chen
authors.forename: Yi
authors.initials: Y
authors.lastname: Chen
authors.forename: Lu
authors.initials: L
authors.lastname: Chen
authors.forename: Ann M
authors.initials: AM
authors.lastname: Tennissen
authors.forename: Jonathan R
authors.initials: JR
authors.lastname: Wolpaw
mesh_terms: D000818:Animals; D019771:Axotomy; D003216:Conditioning, Operant / Q000502:physiology; D004576:Electromyography; D005260:Female; D006181:H-Reflex / Q000502:physiology*; D009473:Neuronal Plasticity / Q000502:physiology*; D011712:Pyramidal Tracts / Q000503:physiopathology* / Q000601:surgery; D051381:Rats; D017207:Rats, Sprague-Dawley; D013119:Spinal Cord Injuries / Q000503:physiopathology*; D013997:Time Factors