Research Article: Cerebral inducible nitric oxide synthase protein expression in microglia, astrocytes and neurons in Trypanosoma brucei brucei-infected rats

Date Published: April 17, 2019

Publisher: Public Library of Science

Author(s): Raymond Cespuglio, Donia Amrouni, Elizabeth F. Raymond, Bernard Bouteille, Alain Buguet, Martin E. Rottenberg.


To study the anatomo-biochemical substrates of brain inflammatory processes, Wistar male rats were infected with Trypanosoma brucei brucei. With this reproducible animal model of human African trypanosomiasis, brain cells (astrocytes, microglial cells, neurons) expressing the inducible nitric oxide synthase (iNOS) enzyme were revealed. Immunohistochemistry was achieved for each control and infected animal through eight coronal brain sections taken along the caudorostral axis of the brain (brainstem, cerebellum, diencephalon and telencephalon). Specific markers of astrocytes (anti-glial fibrillary acidic protein), microglial cells (anti-integrin alpha M) or neurons (anti-Neuronal Nuclei) were employed. The iNOS staining was present in neurons, astrocytes and microglial cells, but not in oligodendrocytes. Stained astrocytes and microglial cells resided mainly near the third cavity in the rostral part of brainstem (periaqueductal gray), diencephalon (thalamus and hypothalamus) and basal telencephalon. Stained neurons were scarce in basal telencephalon, contrasting with numerous iNOS-positive neuroglial cells. Contrarily, in dorsal telencephalon (neocortex and hippocampus), iNOS-positive neurons were plentiful, contrasting with the marked paucity of labelled neuroglial (astrocytes and microglial) cells. The dual distribution between iNOS-labelled neuroglial cells and iNOS-labelled neurons is a feature that has never been described before. Functionalities attached to such a divergent distribution are discussed.

Partial Text

Protozoan parasites belonging to the genus Trypanosoma are the causative agents of diseases affecting humans and animals. Human African trypanosomiasis (HAT) [1, 2] is transmitted by hematophagous tsetse flies that inject Trypanosoma brucei (T. b.) gambiense or T. b. rhodesiense resulting in two clinical entities. In both diseases, two stages occur successively. The early hemolymphatic stage 1 corresponds to parasite proliferation in the blood, lymphatic system and vital organs. The blood-brain barrier (BBB) crossing and the invasion of the central nervous system (CNS) by the parasites [1–3] constitutes the meningoencephalitic stage 2. The neurological signs of the disease are predominant during this stage, resulting in a wide panel of sensory, motor and psychiatric disturbances, along with sleep-wake cycle disruptions, which gave its name to the illness [2]. In animals infected with T. b. brucei, similar clinical disturbances have been described [3, 4].

The present approach is first in achieving an original cartography of brain cells (neurons, astrocytes, microglia) expressing iNOS in rats infected with T. b. brucei. The iNOS-positive astrocytes and microglial cells exhibit a similar brain distribution in weak BBB areas (periaqueductal gray, surrounding the third cavity, basal telencephalon). The iNOS-positive neurons are distributed in different brain structures (dorsal part of the telencephalon), often located in areas that are poor or devoid of iNOS-positive astrocytes and microglial cells. Such distribution differences may serve different functionalities, i.e., a parasiticidal action for iNOS-positive microglial cells and astrocytes, versus protective and/or reparative roles for iNOS positive neurons. This aspect underlines the importance of animal models for diseases such as HAT, particularly in representing a general model for immune and reparation processes in the infected brain.