TY - JOUR T1 - Corticospinal tract transection reduces H-reflex circadian rhythm in rats. JF - Brain research Y1 - 2002 A1 - Xiang Yang Chen A1 - Lu Chen A1 - Jonathan Wolpaw A1 - Jakeman, Lyn B. KW - circadian rhythms KW - corticospinal tract KW - diurnal rhythm KW - H-Reflex KW - rat KW - spinal cord injury AB - In freely moving rats and monkeys, H-reflex amplitude displays a marked circadian variation without change in background motoneuron tone. In rats, the H-reflex is largest around noon and smallest around midnight. The present study evaluated in rats the effects on this rhythm of calibrated contusions of mid-thoracic spinal cord and mid-thoracic transection of specific spinal cord pathways. In 33 control rats, rhythm amplitude averaged 29.0(+/-2.6 S.E.)% of H-reflex amplitude. Contusion injuries at T8-9 that destroyed 53-88% of the white matter significantly reduced the rhythm to 18.9(+/-2.4)% of H-reflex amplitude. Transection of the ipsilateral lateral column, which contains the rubrospinal, vestibulospinal, and reticulospinal tracts, or bilateral transection of the dorsal column ascending tract did not affect rhythm amplitude or phase. In contrast, bilateral transection of the main corticospinal tract significantly reduced the rhythm to 14.7(+/-6.6)%. These results indicate that the H-reflex circadian rhythm depends in part on descending influence from the brain and that this influence is conveyed by the main corticospinal tract. VL - 942 UR - http://www.ncbi.nlm.nih.gov/pubmed/12031858 ER -