Acute muscle inflammation enhances the monosynaptic reflexes and c‐fos expression in the feline spinal cord

Abstract

The aim of this research was to study the changes of the motor reflex activity (monosynaptic reflex (MSR) of the flexor and extensor muscles) and Fos immunoreactivity in lumbo-sacral spinal cord after acute induced myositis of m. gastrocnemius-soleus (GS). The experiments were carried out on ischaemic decerebrated, spinalized in C1 cats. After infiltration of the GS muscle with carrageenan (2%) MSRs of flexors and extensors showed a significant increase in amplitude +127+/-24.5% and +155+/-28.5%, respectively, p<0.05. The exposed effect was initiated within 30 min and achieved a maximum 2.8h after the intramuscular injections of carrageenan. After analysis of dynamics of the MSRs, animals were perfused and c-fos expression in the spinal segments L6-S1 was evaluated. In comparison to sham-operated animals, the number of Fos-immunoreactive (Fos-ir) cells was noticeably increased in the lumbar cord of cats with carrageenan-induced myositis. The labeled cells were concentrated in the ipsilateral laminae I/II, neck of the dorsal horn (V/VI) and intermediate zone (VII), however, clear predominance of their concentration was found in the deep laminae. The effect of muscle inflammation was also expressed as a significant decline in the number of NADPH-d-reactive cells (p<0.05) in ipsilateral laminae I/II of L6/L7. The results show that the input from acutely inflamed muscles may induce an increase of the reflex responsiveness of flexors and extensors which is not mediated via the gamma-spindle-loop and which coincides with a significant increase in c-fos expression in the deep laminae of the lumbar spinal cord.

Changes in the levels of activity of spinal neurons after long-lasting vibrational stimulation of the shin muscles in rats

“…Such modifications correlate with the data on the role of recurrent proprioceptive influences in the maintenance of the muscle function upon excessive loadings [7]. At the same time, inflammation of the skeletal muscles [6] is accompanied by a considerable enhancement of the influences from group Ia afferents and of Fos immunoreactivity, i.e., manifestations that can be correlated with a specific complex of symptoms typical of myositis.…”

“…Estimation of the expression of c-Fos, a "fast-response" protein, is at present effectively used for identification of the neurons, which are components of the pathways related to realization of definite specific functions [1]. Modern studies of neuronal activity using this immunohistochemical technique of visualization of c-Fos in spinal neurons upon selective activation of intrafusal muscle fibers were stimulated by the existence of the data obtained in immunohistochemical [2,3] and electrophysiological studies of the role of proprioceptive impulsation from the skeletal muscles [4][5][6]. As was noted, the development of fatigue in such muscles is accompanied by some decrease in the intensity of impulsation of Ia fibers and parallel suppression of the activity of homonymous motoneurons.…”

Monosynaptic reflexes, c-fos expression, and NADPH-diaphorase activity in the cat spinal cord: Changes induced by chronic muscle inflammation

“…The obtained data indicate that substantial changes in the segmental reflex mechanisms can be triggered during chronic muscle inflammation. Recently, non-reciprocal excitation of both flexor and extensor motoneurons after acute carrageenan-induced muscle inflammation has been shown [8]. A reduction of the bilateral withdrawal thresholds and increased hyperalgesia after FCA-induced muscle inflammation were also demonstrated [28].…”

“…Mechanical or chemical activation of primary Aδ and C muscle afferents induces c-fos expression in spinal neurons [4][5][6][7]. It was recently shown that the development of carrageenaninduced acute experimental myositis was followed by a significant increase in the efficacy of the Ia input to spinal motoneurons, which was accompanied by a strong enhancement of c-fos expression in the dorsal and ventral horns of the spinal gray [8].…”

“…gastrocnemiussoleus (GS). We combined an electrophysiological approach with an immunohistochemical study of c-fos expression (as a marker of neuronal activation) and histochemical detection of NADPH-diaphorase (HADPH-d) reactivity in the same preparation; this was compared with the dynamics of the MSR amplitudes in the case of chronic adjuvant-induced or acute carrageenan-induced muscle inflammation [8]. A preliminary report has been published recently [22].…”