Force‐sensitive afferents recruited during stance encode sensory depression in the contralateral swinging limb during locomotion

Abstract

Afferent feedback alters muscle activity during locomotion and must be tightly controlled. As primary afferent depolarization-induced presynaptic inhibition (PAD-PSI) regulates afferent signaling, we investigated hind limb PAD-PSI during locomotion in an in vitro rat spinal cord-hind limb preparation. We compared the relation of PAD-PSI, measured as dorsal root potentials (DRPs), to observed ipsilateral and contralateral limb endpoint forces. Afferents activated during stance-phase force strongly and proportionately influenced DRP magnitude in the swinging limb. Responses increased with locomotor frequency. Electrical stimulation of contralateral afferents also preferentially evoked DRPs in the opposite limb during swing (flexion). Nerve lesioning in conjunction with kinematic results support a prominent contribution from toe Golgi tendon organ afferents. Thus, force-dependent afferent feedback during stance binds interlimb sensorimotor state to a proportional PAD-PSI in the swinging limb, presumably to optimize interlimb coordination. These results complement known actions of ipsilateral afferents on PAD-PSI during locomotion.

Nanomolar Oxytocin Synergizes with Weak Electrical Afferent Stimulation to Activate the Locomotor CPG of the Rat Spinal Cord In Vitro

“…Thus, there are no data on the effects of oxytocin in integrating afferent inputs into the CPG. The role of primary afferents in modulating the locomotor pattern is linked to the existence of sensory feedbacks evoked during gait to physiologically control, at a pre-synaptic level, incoming inputs to the spinal cord [34] , and to convey facilitatory signals to the CPG via multisegmental sacrocaudal afferents [35] , even with nociceptive content [36] .…”

Electrical Stimulation Able to Trigger Locomotor Spinal Circuits Also Induces Dorsal Horn Activity

“…Here, dorsal cells phasically depolarize during each ipsilateral VR burst . Earlier reports have shown a role of (electrically induced) contralateral afferent activity in the generation of DRPs in the opposite limb during hindpaw swing . Similarly, literature has shown that, during FL, the sensory inflow to the swing limb can be increased by presynaptic inhibition based on forces generated by the (contralateral) stance limb .…”

Molecular, genetic, cellular, and network functions in the spinal cord and brainstem

“…Hochman focused on presynaptic inhibition (PSI) recorded as a primary afferent depolarization (PAD) in the neonatal rat spinal cord with hindlimb attached. In this preparation that expresses actual locomotor movements of its hindlimbs, it is possible to monitor (1) the PAD with suction electrodes attached to dorsal roots and (2) motor neuron action potentials with suction electrodes attached to ventral roots.…”

“…The goal of this report is to highlight four spinal cord and brainstem themes discussed by speakers at the 2012 conference and authors of the present volume: neurogenetics, circuits, plasticity, and translational impacts. This report will discuss the contents of the summaries of the oral presentations of the conference and published data presented by speakers during the oral sessions . Space limitations prevent detailed descriptions of every important result, however.…”

“…This report will discuss the contents of the summaries of the oral presentations of the conference 4 and published data presented by speakers during the oral sessions. [51][52][53][54][55][56][57][58][59][60][61][62][63][64][65][66][67] Space limitations prevent detailed descriptions of every important result, however.…”