TY - JOUR

T1 - Bistable firing properties of soleus motor units in unrestrained rats

AU - EKEN, T.

AU - KIEHN, O.

PY - 1989/1/1

Y1 - 1989/1/1

N2 - EMG recordings from single motor units in the soleus muscle were performed in alert unrestrained rats. A cuff electrode around the tibial nerve and subcutaneously placed electrodes in the foot permitted stimulation of afferent fibres. The movements of the rat and the simultaneous EMG activity were displayed together on a video monitor. Most motor units were tonically active for extended periods during quiet standing. During tonic discharge, maintained shifts between stable low (8–12 Hz; quartiles) and high (16–22.8 Hz) frequency ranges were initiated by short‐lasting synaptic excitation of the motoneuron pool by stimulation of la afferents, or inhibition by stimulation of skin afferents. The shifts were not related to gross limb movements. This phenomenon is referred to as a bistable firing pattern. Bistable firing also occurred spontaneously during quiet standing. Typically the firing frequency shifted between a low (9–12.5 Hz) and a high (20–24.5 H) mode. During recordings of simultaneous activity in two units, spontaneous and stimulus‐induced frequency jumps causing maintained changes in firing frequency were regularly seen to occur in one unit, while the frequency in the second unit was unchanged or only phasically influenced. These results demonstrate for the first time a bistable firing pattern during postural activity in the intact animal. The firing pattern closely resembles the bistable behaviour described in spinal motoneurons in reduced preparations, where it is due to the presence of a plateau potential. This suggests that the bistable firing is unexplained by plateau potentials also in the intact animal.

AB - EMG recordings from single motor units in the soleus muscle were performed in alert unrestrained rats. A cuff electrode around the tibial nerve and subcutaneously placed electrodes in the foot permitted stimulation of afferent fibres. The movements of the rat and the simultaneous EMG activity were displayed together on a video monitor. Most motor units were tonically active for extended periods during quiet standing. During tonic discharge, maintained shifts between stable low (8–12 Hz; quartiles) and high (16–22.8 Hz) frequency ranges were initiated by short‐lasting synaptic excitation of the motoneuron pool by stimulation of la afferents, or inhibition by stimulation of skin afferents. The shifts were not related to gross limb movements. This phenomenon is referred to as a bistable firing pattern. Bistable firing also occurred spontaneously during quiet standing. Typically the firing frequency shifted between a low (9–12.5 Hz) and a high (20–24.5 H) mode. During recordings of simultaneous activity in two units, spontaneous and stimulus‐induced frequency jumps causing maintained changes in firing frequency were regularly seen to occur in one unit, while the frequency in the second unit was unchanged or only phasically influenced. These results demonstrate for the first time a bistable firing pattern during postural activity in the intact animal. The firing pattern closely resembles the bistable behaviour described in spinal motoneurons in reduced preparations, where it is due to the presence of a plateau potential. This suggests that the bistable firing is unexplained by plateau potentials also in the intact animal.

KW - bistability

KW - electromyogram

KW - motoneuron

KW - motor unit

KW - noradrenaline

KW - plateau potential

KW - rat

KW - serotonin

KW - soleus

KW - spinal cord

UR - http://www.scopus.com/inward/record.url?scp=0024319212&partnerID=8YFLogxK

U2 - 10.1111/j.1748-1716.1989.tb08679.x

DO - 10.1111/j.1748-1716.1989.tb08679.x

M3 - Journal article

C2 - 2750539

AN - SCOPUS:0024319212

VL - 136

SP - 383

EP - 394

JO - Acta Physiologica Scandinavica

JF - Acta Physiologica Scandinavica

SN - 0001-6772

IS - 3

ER -