[Action duality of nitrogen oxide (NO) in experimental African trypanosomiasis].

Abstract

Patients with human African trypanosomiasis present a major dysruption of the circadian rhythmicity of the sleep-wake cycle, which was also found in rats infected with Trypanosoma brucei brucei (T.b.b.). The alterations in the immune function and nervous system in African trypsanosomiasis led us to investigate the involvement of nitric oxide (NO), a key molecule in immune and neurophysiological mechanisms, in experimental trypanosomiasis. NO was measured in 35 Sprague Dawley rats using differential impulsional voltammetry with a carbon fiber coated with porphyrin-nickel and nafion, ex vivo in the blood and in vivo in the brain. The rats were anaesthetized with sodium chlorate. Infection was performed intraperitoneally (i.p.) with 0.2 ml of a T.b.b. cryostabilate (clone AnTat 1.1E). Blood was collected by an intracardiac puncture with immediate replacement of blood volume (1 ml) in 7 control rats and 8 rats infected since 15 days, before and after i.p. administration of L-ANA (L-arginine-p-nitro-anilide, 100 mg.kg-1, an inhibitor of NO synthase). Brain measures were done in 20 rats (8 controls, and 12 rats infected since 15 or 21 days), in the cortex (H, -0.5 mm; AP, -0.8 mm; L, 1.2 mm) and the lateral ventricle (H,-3.2 mm). In infected rats, blood NO was at 70% of control values (p < 0.001), and L-ANA suppressed the NO signal in all animals (p < 0.0001), demonstrating that the signal originated from NO. Cortical NO was higher than in the ventricle in both control (p < 0.0001) and infected rats (p < 0.001). NO was more elevated in both structures in 15-day-infected rats than in control rats (p < 0.0001), the difference being enhanced in 21-day-infected rats (p < 0.001). L-ANA suppressed the NO signal in 30 to 60 min. These data suggest that NO intervenes in the development of trypanosomiasis in different manners. It is increased in the brain, which remains unexplained, where it may be involved in blood-brain barrier permeation. Conversely, it is decreased in the blood, may be because of macrophage function impairment, which would explain why trypanosomes can multiply in the host.