Dysregulation of photic induction of Fos-related protein in the biological clock during experimental trypanosomiasis.

The mammalian suprachiasmatic nuclei of the hypothalamus (SCN) serve as pacemaker for circadian rhythms and the immediate-early gene c-fos is known to be induced by photic stimulation in the SCN of rodents. We studied the induction of Fos-related protein following a light pulse in rats infected with Trypanosoma brucei. This parasite causes in humans African sleeping sickness, a neuropsychiatric syndrome that involves changes of endogenous biological rhythms. Fos-like immunoreactivity after photic stimulation was dramatically reduced in the SCN of trypanosome- infected rats during the subjective night. These findings indicate that the photic entrainment of the biological clock may be altered during the infection.