Locomotor role of the reticulospinal-spinal commissural interneuronal system

The reticulospinal （RS） pathway is the main descending route in vertebrates for conveying locomotor command signals from higher motor centers to spinal interneuronal circuits. The RS pathway descends throughout the full length of the spinal cord （SC） and terminates mainly in laminae VII-VIII of the ventral horn, where commissural interneurons （CNs） are profuse. Most of lumbar CNs receiving excitatory RS inputs discharged rhythmically during the locomotor rhythm generation in decerebrate, paralyzed cats. The axons of such CNs ascended and/or descended in the contralateral white matter, giving off multiple axon collaterals. These collaterals terminated mainly in laminae VII-VIII. Such an arrangement suggests that CNs on the left and right sides are mutually connected at each SC level and thus participate in the generation of alternating left-right locomotor activity. Furthermore, since single RS axons innervate a large number of CNs at all SC levels, the activity of the CNs may be synchronously controlled by single RS neurons. Such an RS-CN organization may facilitate an integration of interlimb and/or limb-trunk locomotor rhythm activity, and thereby contribute to a smooth elaboration of locomotion.departmental bulletin pape