The spino-reticulo-spinal loop can slow down the NMDA-activated spinal locomotor network in lamprey.

Lamprey spino-bulbar neurones modulate the activity of reticulospinal cells during locomotion. The aim of the present study was to investigate the effects of interrupting or increasing this feedback from the spinal cord on the fictive locomotor pattern. Double-bath experiments were performed on in vitro brain stem/spinal cord preparations. Fictive locomotion was induced by perfusing the spinal cord with 150 microM N-methyl-D-aspartate (NMDA). Blocking the synaptic transmission in the brain stem by exposing it to Mn2+ ions increased the locomotor rhythm. Conversely, stimulation of single reticulospinal neurones during the ipsilateral ventral root burst, when they were depolarized, increased the cycle duration by prolonging the ipsilateral motor burst. The spino-reticulo-spinal loop is an integral part of the locomotor network.