Corticospinal tract transection prevents operantly conditioned H-reflex increase in rats.
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 (i.e., up-condition) or decrease (i.e., down-condition) the soleus H-reflex. Earlier work showed that corticospinal tract transection prevents acquisition and maintenance of H-reflex down-conditioning while transection of other major spinal cord tracts does not. This study explores the effects on acquisition of up-conditioning of the right soleus H-reflex of mid-thoracic transection of: the right lateral column (LC, five rats) (containing the rubrospinal, vestibulospinal, and reticulospinal tracts); the entire dorsal column (DC, six rats) [containing the main corticospinal tract (CST) and the dorsal ascending tract (DA)]; the CST alone (five rats); or the DA alone (seven rats). After initial (i.e., control) H-reflex amplitude was determined, the rat was exposed for 50 days to the up-conditioning mode in which reward was given when the H-reflex was above a criterion value. H-reflex amplitude at the end of up-conditioning was compared to initial H-reflex amplitude. An increase > or =20% was defined as successful up-conditioning. In intact rats, H-reflex amplitude at the end of up-conditioning averaged 164% (+/-10%, SE), and 81% were successful. In the present study, LC and DA rats were similar to intact rats in final H-reflex amplitude and percent successful. In contrast, results for DC and CST rats were significantly different from those of intact rats. In the six DC rats, final H-reflex amplitude averaged 105% (+/-3)% of control and none was successful; and in the five CST rats, final H-reflex amplitude averaged 94% (+/-3)% and none was successful. The results indicate that the main CST, located in the dorsal column, is essential for H-reflex up-conditioning as it is for down-conditioning, while the dorsal column ascending tract and the ipsilateral lateral column (containing the main rubrospinal, vestibulospinal, and reticulospinal tracts) do not appear to be essential.
Chen
Xiang Yang
XY
Laboratory of Nervous System Disorders, Wadsworth Center, New York State Department of Health and State University of New York, PO Box 509, Albany, New York 12201-0509, USA. chenx@wadsworth.org
Carp
Jonathan S
JS
Chen
Lu
L
Wolpaw
Jonathan R
JR
D000818:Animals; D001835:Body Weight / Q000502:physiology; D003216:Conditioning, Operant / Q000502:physiology*; D003714:Denervation; D005260:Female; D006181:H-Reflex / Q000502:physiology*; D009044:Motor Cortex / Q000503:physiopathology*; D018482:Muscle, Skeletal / Q000294:innervation / Q000503:physiopathology; D009473:Neuronal Plasticity / Q000502:physiology*; D011712:Pyramidal Tracts / Q000293:injuries / Q000473:pathology / Q000503:physiopathology*; D051381:Rats; D020127:Recovery of Function / Q000502:physiology*; D013119:Spinal Cord Injuries / Q000473:pathology / Q000503:physiopathology*