Characteristics of H- and M-waves recorded from rat forelimbs

The Hoffman reflex (H-reflex) is a useful tool for studying the functional aspects of the spinal cord without anesthesia and/or damage to the body. H-reflex studies are performed mainly in the hindlimbs. The purpose of the present study was to evaluate the characteristics of the H-reflex in the forelimbs and hindlimbs in rats anesthetized with ketamine–HCl. H- and M-waves were recorded from the interosseous muscles after electrical stimulation of the n. lateral plantar of the hindlimb and n. medialis of the forelimb. Hmax/Mmax values were significantly smaller in the forelimbs than in the hindlimbs. Furthermore, paired-pulse attenuation tended to be stronger in the forelimbs than in the hindlimbs. These findings suggest that control by descending and/or propriospinal pathways is stronger in the forelimbs than in the hindlimbs in rats.