Neuronal NOS expression in rat's cuneate nuclei following passive forelimb movements and median nerve stimulation

Nitric oxide (NO) synthase (NOS) has been observed in the Cuneate Nuclei (CN), suggesting a role for NO in the modulation of their neurons' activity. The present study was undertaken to evaluate whether passive movement of forelimb as well as electric stimulation of medial nerve modulate the expression of neuronal isoform of NOS (nNOS) within CN. The experiments were carried out on 21 male Wistar rats, by using two different protocols. In the first group of rats the median nerve was stimulated with high frequency trains (phasic stimulation) or at constant frequency (tonic stimulation); as a control, in the third group, no stimulus was delivered. Moreover, in the second group of rats, we imposed to the animal's left forepaw circular paths at a roughly constant speed (continuous movement), or rapid flexions and extensions of the wrist (sudden movement); as a control, in the third group, no movement was imposed. After the experimental session, free-floating frontal sections of medulla oblongata were processed for nNOS or glutamate (GLU) immunohistochemistry. Phasic stimulation of the median nerve or sudden movements of the forelimb determines a significant decrement of the nNOS-positive neurons within the ipsilateral CN, whereas no effects were observed on GLU positive cells. We have also found a peculiar topographical distribution within IN of nNOS-positive neurons: positive cells were clustered at periphery of some "niches" having circular or elliptical form, with GLU positive cells at center.