TY - JOUR

T1 - Reciprocal Ia inhibition contributes to motoneuronal hyperpolarisation during the inactive phase of locomotion and scratching in the cat

AU - Geertsen, Svend Sparre

AU - Stecina, Katinka

AU - Meehan, Claire Francesca

AU - Nielsen, Jens Bo

AU - Hultborn, Hans

N1 - CURIS 2011 5200 007

PY - 2011

Y1 - 2011

N2 - Despite decades of research, the classical idea that "reciprocal inhibition" is involved in the hyperpolarisation of motoneurones in their inactive phase during rhythmic activity is still under debate. Here, we investigated the contribution of reciprocal Ia inhibition to the hyperpolarisation of motoneurones during fictive locomotion (evoked either by electrical stimulation of the brainstem or by L-DOPA administration following a spinal transection at the cervical level) and fictive scratching (evoked by stimulation of the pinna) in decerebrate cats. Simultaneous extracellular recordings of Ia inhibitory interneurones and intracellular recordings of lumbar motoneurones revealed the interneurones to be most active when their target motoneurones were hyperpolarised (i.e. in the inactive phase of the target motoneurones). To date, these results are the most direct evidence that Ia inhibitory interneurones contribute to the hyperpolarisation of motoneurones during rhythmic behaviours. We also estimated the amount of Ia inhibition as the amplitude of Ia IPSC in voltage-clamp mode. In both flexor and extensor motoneurones, Ia IPSCs were always larger in the inactive phase than in the active phase during locomotion (n = 14) and during scratch (n = 11). Results obtained from spinalised animals demonstrate that the spinal rhythm-generating network simultaneously drives the motoneurones of one muscle group and the Ia interneurones projecting to motoneurones of the antagonist muscles in parallel. Our results thus support the classical view of reciprocal inhibition as a basis for relaxation of antagonist muscles during flexion-extension movements.

AB - Despite decades of research, the classical idea that "reciprocal inhibition" is involved in the hyperpolarisation of motoneurones in their inactive phase during rhythmic activity is still under debate. Here, we investigated the contribution of reciprocal Ia inhibition to the hyperpolarisation of motoneurones during fictive locomotion (evoked either by electrical stimulation of the brainstem or by L-DOPA administration following a spinal transection at the cervical level) and fictive scratching (evoked by stimulation of the pinna) in decerebrate cats. Simultaneous extracellular recordings of Ia inhibitory interneurones and intracellular recordings of lumbar motoneurones revealed the interneurones to be most active when their target motoneurones were hyperpolarised (i.e. in the inactive phase of the target motoneurones). To date, these results are the most direct evidence that Ia inhibitory interneurones contribute to the hyperpolarisation of motoneurones during rhythmic behaviours. We also estimated the amount of Ia inhibition as the amplitude of Ia IPSC in voltage-clamp mode. In both flexor and extensor motoneurones, Ia IPSCs were always larger in the inactive phase than in the active phase during locomotion (n = 14) and during scratch (n = 11). Results obtained from spinalised animals demonstrate that the spinal rhythm-generating network simultaneously drives the motoneurones of one muscle group and the Ia interneurones projecting to motoneurones of the antagonist muscles in parallel. Our results thus support the classical view of reciprocal inhibition as a basis for relaxation of antagonist muscles during flexion-extension movements.

U2 - 10.1113/jphysiol.2010.199125

DO - 10.1113/jphysiol.2010.199125

M3 - Journal article

C2 - 21059756

VL - 589

SP - 119

EP - 134

JO - The Journal of Physiology

JF - The Journal of Physiology

SN - 0022-3751

IS - 1

ER -