Contrasting effects of flexor group II afferents during fictive locomotion

Abstract

This study examined the reflex actions of hindlimb flexor muscle nerves on fictive locomotion produced by stimulating the midbrain locomotor region in decerebrate, paralysed, adult cats. Electrical stimulation (typically 100-200 ms trains of 10-20 shocks) of flexor nerves was delivered at particular times during the step cycle and the effects on motoneuron activity recorded in electroneurograms from selected hindlimb nerves were examined. The effects of flexor nerve stimulation depended on the nerve being stimulated. Thus stimulation of the 'tibialis anterior' (TA) nerve at 5 times threshold (5T) terminated ongoing flexor activity and reset the locomotor rhythm to extension. In the same preparation, similar stimulation of the ' extensor digitorum longus' (EDL) nerve prolonged the flexion phase and enhanced the activity of hip knee and ankle flexor motoneurons. Enhancement of ongoing flexor motoneuron activity by EDL nerve stimulation was not seen with less than 2T stimulation intensity. When stimulation wasdelivered during extension, the effects of TA and EDL nerve stimulation were weak and variable. There was also some variability in the effects of 5T TA and EDL stimulation delivered during flexi n. The opposite effects of TA and EDL group II stimulation suggest that the reflex effects of flexor group II afferents differentiate into (at least) two classes during fictive locomotion; one promoting extension and another promoting flexion. (Abstract shortened by UMI.)