Maznychenko A. Changes in the activity of spinal neuronal networks induced by the fatigue and inflammation in skeletal muscles

In the study, peculiarities of spatial distribution of Fos-immunoreactive and NADPH-diaphorase-reactive neurons in the grey matter of the spinal cord activated by the muscle fatigue, acute muscle pain, and acute and chronic muscle inflammation we elucidated in rats and cats; the dynamics of modulation of monosynaptic reflexes in animals induced by signals from hindlimb muscle afferents under conditions of acute and chronic myositis was also examined. Immunohistochemical studies demonstrated that electrical, mechanical, or chemical stimulation of skeletal muscles induces intense expression of с-Fos protein in spinal neurons characterized by rather specific patterns. Spatial and quantitative distribution of the neurons, involved in the transmission of high- or low-threshold afferent signals is described. The data of a histochemical research demonstrate that changes in the number of NADPH-diaphorase reactive neurons occur only during high-intensity and long-lasting activation of nociceptive inputs; the respective effects are related to plastic changes in these neurons. Increases in the amplitude of monosynaptic reflexes of the hindlimb muscles and decreases in the intensity of segmental inhibition were revealed after acute and chronic myositis in high-spinalized animals. Comparative studies of the spatial distribution of Fos-immunoreactive spinal neurons activated by muscle fatigue, acute muscle pain, and acute and chronic muscle inflammation in animals show that certain changes in the intensity of spinal inhibition, activation of NO-generating neurons, and glia activation develop under these conditions. The observed changes in neuronal and glial activation are suggestive of the plasticity in segmental circuitries developing in response to the action of nociceptive inputs these can be important mechanisms in initiating of the adaptive intersegmental reflexes in the spinal cord. Such changes lead to increase in the intensity of pain and disorders of motor behavior during muscle fatigue or inflammation of skeletal muscles.