A Blocker of NO Synthase Intensifies c-fos Expression in Spinal Neurons of Rats Realizing Stereotypic Movements

Neurons with the presence of c-Fos protein, the product of expression of the “early’ c-fos gene, were detected in the cervical region of the spinal cord of rats performing stereotypic operant food-procuring movements by the forelimb. An immunohistochemical technique was used; the presence of c-Fos was interpreted as a correlate of the activated state of the respective neurons. Effects of suppression of the activity of neuronal NO synthase (nNOS) provided by systemic injections of a selective blocker of this enzyme, 7-nitroindazole (7-NI), were studied under the above conditions. In the absence of 7-NI, the main foci of Fos-immunoreactivity in the spinal segments C6 and C7 were observed in laminae 2i, 3, and 4 of the gray substance, while after injection of this blocker these were found in laminae 3, 4, and 6 and also in the motor nuclei (lamina 9). In animals that performed repetitive food-procuring movements and were preliminarily injected with 7-NI, significantly greater mean numbers of Fos-immunoreactive neurons were found in slices of the gray matter, as compared with the respective figures in rats with no suppression of nNOS activity (54.4 ± 0.7 cells in a 40 μm-thick slice ipsilaterally with respect to the working limb, as compared with 31.7 ± 1.1 cells, P < 0.05). Thus, expression of the c-fos gene in certain regions of the cervical part of the spinal cord increases significantly under conditions of 7-NI-induced suppression of NO production; this is observed in rats realizing repeated movements for a long time.