SLEEP AND WAKE ALTERATIONS IN AFRICAN TRYPANOSOMIASIS: FUNCTIONAL AND HISTOPATHOLOGICAL STUDY

Human African trypanosomiasis (HAT), also called sleeping sickness, is a neglected, severe neuroinflammatory disease caused by the protozoan Trypanosoma brucei (T.b.), and is characterized by alterations of the sleep pattern and sleep-wake cycle. The first, hemolymphatic stage of the disease evolves into the second, meningoencephalitic stage when T.b. cross the blood-brain barrier (BBB) and invade the brain parenchyma. Pathogenetic mechanisms of brain dysfunction caused by the infection, as well as knowledge of disease stage timing and evolution, are of high relevance also from the translational point of view given their diagnostic and therapeutic implications. The present doctoral studies on African trypanosomiasis have been articulated in 4 steps. The first investigation focused on orexin, a neuropeptide which plays a key role in wakefulness and in stabilizing sleep-wake transitions, as well as melanin concentrating hormone (MCH), which plays a role in sleep regulation, in rats and mice infected with T.b. brucei. Immunocytochemical study of orexin and MCH revealed a decrease, at an advanced stage of infection, of hypothalamic cells expressing either peptides; orexin level in the cerebrospinal fluid was not, however, significantly affected, and thus cannot provide a disease biomarker. Interestingly, day/night activity (as shown by Fos expression) of orexin-containing neurons was found to be deregulated in infected animals. Further steps of the project focused on search for functional changes which could reflect T.b. passage across the BBB, and these were investigated in the above rat model. The timing of parasite neuroinvasion and T-cell recruitment in the brain parenchyma was determined in multiple labeling immunocytochemical investigations. This part of the study revealed a prevalence of both parasite and T-cell entry through the posterior hypothalamus, suggesting regional differences in BBB permeability due to inflammatory signaling during the infection, and a potential vulnerability of hypothalamic sleep-wake regulatory cell groups to these events. Sleep-wake stages, core body temperature and rest-activity during 24 h were then continuously monitored in infected rats with telemetric recording and compared to baseline data. Extensive analyses of such data revealed that sleep structure alterations start early after the infection and precede parasite neuroinvasion, and showed then the onset and progression of distinct changes of wake and sleep states, as well as of body temperature and rest-activity rhythms. Furthermore, analyses of the hypnograms and actograms of the infected animals showed that rest-activity changes can provide reliable measurements of sleep-wake alterations. This paved the way to the last part of the project, pursued in collaboration with the University of Yaoundé 1 (Cameroon), in which hypnograms and actigraphic recordings of HAT patients have been analyzed. It has thus been determined that actigraphy can provides a useful tool for disease severity monitoring, opening novel perspectives for the clinical evaluation of patients with a non-invasive technique.