title: Corticospinal tract transection prevents operantly conditioned H-reflex increase in rats.
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 (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.
authors.affiliation: 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
authors.forename: Xiang Yang
authors.initials: XY
authors.lastname: Chen
authors.forename: Jonathan S
authors.initials: JS
authors.lastname: Carp
authors.forename: Lu
authors.initials: L
authors.lastname: Chen
authors.forename: Jonathan R
authors.initials: JR
authors.lastname: Wolpaw
mesh_terms: 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*