[Intensification of c-fos expression in the spinal cord initiated by the signals from fatigue skeletal muscles]

Immunohistochemical studies of c-fos expression in the lumbar and neck segments of spinal cord after fatiguing stimulation of the mm. gastrocnemius-soleus or m. trapezius and m. splenius, were carried out on the anaesthetized (chloral-hydrate 400 mg/kg, i.p.) rats. The patterns of the Fos-immunoreactive neurons distribution in the grey matter of spinal cord in the L4 and L5 segments, as well as the C2 and C3 were similar. The highest number of marked cells was registered in the dorsal horn in the first, fourth and fifth layers of grey matter, i.e. within the areas of termination of high-threshold muscle afferents of group III and IV. It is assumed, that the types of afferents could be activated by muscle fatigue-induced metabolites. The signals incoming to the spinal cord could be involved into the presynaptic inhibition of muscle spindle volleys than resulted in the impairment of motor output performance. This mechanism is substantial for limitation of the force of muscles contraction and prevention the injury of the muscles under the excessive physical loading.