[Investigation of c-fos expression and NADPH-diaphorase activity in the spine cord and brain in the development of the neck muscle weakness in rats].

The distribution of c-fos expression as a marker of neuronal activation and NADPH-diaphorase reactivity were examined in the cervical spinal cord, limbic structures and hypothalamus in anaesthetized rats after fatigue induced by intermittent high-rate (100 s(-1)) electrical stimulation of the dorsal neck muscles (mm. trapezius and splenius). In comparison to the control or sham-stimulated animals fatiguing stimulation induced significant increase in ipsilaterally in the C -C4 spinal segments and the contralateral central (Ce), medial (Me) nuclei, paraventricular nucleus of hypothalamus (Pa) and ventrolateral periaqueductal gray (VLPAG). In spinal cord the highest mean number of Fos-immunoreactive (Fos-ir) neurons per section was found in layers 1,4 and 5 (5.8 +/- 0.9, 13.1 +/- 0.9 and 11.1 +/- 0.7, P < 0.05) of the dorsal horn. The order of intensity of c-fos expression in different regions of the brain was as following sequence: Pa > VLPAG > Ce (447.7 +/- 23.5, 196.3 +/- 12.7, 104.6 +/- 12.3, respectively). About 50 % of double-labeled (Fos-ir and NADPH-diaphorase reactive) cells were found in Pa nucleus. Received data show that limbic structures, hypothalamus and VLPAG are involved in activation after neck muscle fatigue and might contribute to nociceptive processing and generation of the autonomic and affective components of the muscle pain.