DORSAL COLUMN BUT NOT LATERAL COLUMN TRANSECTION PREVENTS DOWN CONDITIONING OF H-REFLEX IN RATS A.Xiang Yang Chen, Jonathan R. Wolpaw Xiang Yang Chen, Ph.D., Wadsworth Center, New York State Dept. of Health, P.O. Box 509, Empire State Plaza, Albany, New York 12201-0509, Phone: (518)486-4916,473-3631, Fax: (518)486-4910, E-mail: chenx@wadsworth.org
APStracts 4:0075N, 1997.
ABSTRACT
Operant conditioning of the H-reflex, the electrical analog of the spinal stretch reflex, in freely moving rats is a relatively simple model for studying long-term supraspinal control over spinal cord function. Motivated by food reward, rats can gradually increase or decrease the soleus H-reflex. This study is the first effort to determine which spinal cord pathways convey the descending influence from supraspinal structures that changes the H-reflex. In anesthetized Sprague-Dawley rats, the entire dorsal column (DC), which includes the main corticospinal tract, or the right lateral column (LC) was transected by electrocautery. Animals recovered quickly and the minimal transient effects of transection on the right soleus H-reflex disappeared within 16 days. Beginning at least 18 days after transection, 12 rats were exposed to the HRdown conditioning mode, in which reward was given when the H- reflex of the right soleus muscle was below a criterion value. In 7 LC rats exposed to the HRdown mode, the H-reflex fell to 71% ñ8% (mean ñ SEM) of its initial value. In 6 of the 7, conditioning was successful (i.e., decrease to ó80%). These results were comparable to those previously obtained from normal rats. In contrast, in 5 DC rats exposed to the HRdown mode, the H-reflex at the end of exposure was 106 ñ12% of its initial value. In none of these rats was HRdown conditioning successful. DC rats differed significantly from normal and LC rats in both final H-reflex values and number successful. In 5 DC and 3 LC rats continued under control conditions over 30-78 days, the H-reflex at the end of the period was 98% ñ4% and 100% ñ8%, respectively, of its initial value, indicating that DC or LC transection itself did not lead to gradual increase or decrease in the H-reflex. The results indicate that the dorsal column, containing the main corticospinal tract, is essential for HRdown conditioning, while the ipsilateral lateral column, containing the main rubrospinal, vestibulospinal, and reticulospinal tracts, is not essential. Combined with the known muscular specificity of conditioning, these results suggest that the main corticospinal tract is essential for HRdown conditioning. The dorsal column ascending tract might also be necessary. The respective roles of the descending and ascending tracts, and transection effects on HRup conditioning and on the maintenance of both HRup and HRdown conditioning after they have occurred, remain to be defined. 

Received 1997 March 24; accepted in final form 1997 May 20.
APS Manuscript Number J246-7.
Article publication pending J. Neurophysiol.
ISSN 1080-4757 Copyright 1997 The American Physiological Society.
Published in APStracts on 11 June 1997