Corticospinal tract transection permanently abolishes H-reflex down-conditioning in rats.
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.
Chen
Xiang Yang
XY
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
Chen
Yi
Y
Chen
Lu
L
Tennissen
Ann M
AM
Wolpaw
Jonathan R
JR
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