Short-term irradiation of rat hind limb with polychromatic polarized light at 400-2000 nm produces a long-term inhibition of baseline afferent traffic in n. saphenus, while nonpolarized light produces biphasic changes in baseline activity: transient activation is followed by long-term inhibition of discharges in the nerve. Subcutaneous injection of sodium nitroprusside (10 microg/ml) with subsequent irradiation of the hind limb with polarized light significantly increased afferent activity in the sciatic nerve and n. saphenus, which attests to involvement of nitric oxide in activation of cutaneous nerve terminals during irradiation with polarized light.

Subcutaneous injection of L-NAME inhibited afferent impulse activity in n. ischiadicus and n. saphenus and abolished the increase in this activity induced by stimulation of mechanoreceptors after skin irradiation with polarized light with various spectral characteristics. Subsequent subcutaneous injection of sodium nitroprusside restored the pattern of afferent impulse activity in these nerves during repeated skin irradiation with polarized light.

Experiments were performed on rats anesthetized with urethane and nembutal. Intrathecal administration of a nitric oxide inhibitor L-NAME (60 mg) into the cerebrospinal fluid of the thoracic spinal cord was followed by a 40-45% decrease in tonic activity of efferent fibers of the abdominal aortic nerves. L-NAME reduced a reflex increase in the rate of efferent impulses, which was induced by tetanic stimulation of afferent C-fibers in the mesenteric nerve. Administration of L-arginine into the cerebrospinal fluid of the spinal cord (80 mg/20 ml) was accompanied a long-term increase in tonic activity of efferent fibers of the abdominal aortic nerves (by 15-20%). These changes reflect a prolonged activating effect of L-arginine on sympathetic structures.