African trypanosomiasis in the rat alters melatonin secretion and melatonin receptor binding in the suprachiasmatic nucleus.

Rats infected with Trypanosoma brucei brucei, a subspecies of the extracellular parasites that cause African sleeping sickness, were examined for disturbances in the circadian rhythms of melatonin secretion (evaluated by determination of the excretion of melatonin in the urine) and the binding of melatonin to its receptor in the suprachiasmatic nuclei of the anterior hypothalamus. In normal and infected rats, Cosinor analysis showed a significant nocturnal peak. The amplitude of this peak was, however, significantly decreased in the infected rats. The peak of melatonin receptor binding in the suprachiasmatic nuclei showed a 4-h phase advance in the infected rats, compared with the controls (0400 and 0800, respectively). These data point to a disturbance in the circadian rhythm of the melatonin-generating systems in the pathogenesis of African sleeping sickness.