Altered Neuronal Activity Rhythm and Glutamate Receptor Expression in the Suprachiasmatic Nuclei of Trypanosoma briucei-infected Rats

The parasites Trypanosoma brucei cause African trypanosomiasis (sleeping sickness), a severe neuropsychiatric disease with marked disturbances of sleep-wake alternation. The sites of brain lesions are not well characterized. The present experimental investigation is focused on the hypothalamic suprachiasmatic nuclei, which play a role of a biological clock entraining endogenous rhythms in the mammalian brain. The electrophysiological properties of these neurons were analyzed in slice preparations from trypanosome-infected rats. The neuronal spontaneous activity, which shows a circadian oscillation, was markedly altered in the infected animals, displaying a reduced firing rate and phase advance of its circadian peak. The direct retinal fibers, which play a pivotal role in entrainment of the circadian pacemaker, displayed a normal density and distribution in the suprachiasmatic nuclei of infected animals after intraocular tracer injections in vivo. At the postsynaptic level, immunohistochemistry and Western blotting revealed in the suprachiasmatic nuclei of infected rats a selective decrease of the expression of glutamate AMPA GluR2/3 and NMDAR1 receptor subunits that gate retinal afferents. These data disclose an impairment of the neuronal functions in the biological clock in African trypanosomiasis, and may serve to unravel functional and molecular mechanisms behind endogenous rhythm disturbances. Keywords: Brain slices, Circadian pacemaker, Circadian rhythm, Cytokines, Glutamate receptors, Interferon-[gamma], Nervous system