In memory of our dear friend and colleague Professor Håkan Johansson, who passed away on 15 January, 2004. His co-authors will remember him with much affection and a great sense of loss.
Fatigue-related depression of the feline monosynaptic gastrocnemius–soleus reflex
Article first published online: 30 MAR 2004
The Journal of Physiology
Volume 556, Issue 1, pages 283–296, April 2004
How to Cite
Kalezic, I., Bugaychenko, L. A., Kostyukov, A. I., Pilyavskii, A. I., Ljubisavljevic, M., Windhorst, U. and Johansson, H. (2004), Fatigue-related depression of the feline monosynaptic gastrocnemius–soleus reflex. The Journal of Physiology, 556: 283–296. doi: 10.1113/jphysiol.2003.053249
- Issue published online: 30 MAR 2004
- Article first published online: 30 MAR 2004
- (Received 10 August 2003; accepted after revision 21 November 2003; first published online 28 November 2003)
In decerebrate cats, changes in the monosynaptic reflex (MSR) of gastrocnemius–soleus (G–S) motoneurones were studied after fatiguing stimulation (FST) of the G–S muscles. Monosynaptic reflexes were evoked by stimulation of Ia fibres in the G–S nerve and recorded from a filament of ventral root (VR) L7. FST (intermittent 40 s−1 stimulation for 10–12 min) was applied to the distal part of the cut VR S1. FST reduced MSR amplitudes to 0.64 ± 0.04 (mean ±s.e.m.) of the prefatigue values. The suppression remained stable for approximately 25 min and then MSR amplitudes gradually returned towards the normal. To test for the involvement of presynaptic and recurrent inhibition, MSRs were conditioned by stimulation of the nerve to the posterior biceps and semitendinosus (PBSt) muscles or a filament of VR L7, respectively. The intensity of presynaptic inhibition (reduction of the normalized value of MSR amplitude during conditioning) increased from 0.19 ± 0.02 in prefatigue to 0.44 ± 0.04 within a 5.3–18.2 min interval after FST, followed by a recovery. In contrast, the intensity of recurrent inhibition first diminished from 0.23 ± 0.02 in prefatigue to 0.15 ± 0.01 within 15.6–30.1 min after FST and then gradually recovered. Both primary afferent depolarization and the intensity of antidromic discharges in primary afferents increased with the presynaptic inhibition intensity. These results demonstrate a fatigue-related suppression of Ia excitation of synergistic motoneurones, probably arising from the activation of group III and IV afferents. The effects could in part be due to increased presynaptic inhibition, while recurrent inhibition plays a minor role.