Behavioral alterations in long-term Toxoplasma gondii infection of C57BL/6 mice are associated with neuroinflammation and disruption of the blood brain barrier

Abstract

The Apicomplexa protozoan Toxoplasma gondii is a mandatory intracellular parasite and the causative agent of toxoplasmosis. This illness is of medical importance due to its high prevalence worldwide and may cause neurological alterations in immunocompromised persons. In chronically infected immunocompetent individuals, this parasite forms tissue cysts mainly in the brain. In addition, T. gondii infection has been related to mental illnesses such as schizophrenia, bipolar disorder, depression, obsessive-compulsive disorder, as well as mood, personality, and other behavioral changes. In the present study, we evaluated the kinetics of behavioral alterations in a model of chronic infection, assessing anxiety, depression and exploratory behavior, and their relationship with neuroinflammation and parasite cysts in brain tissue areas, blood-brain-barrier (BBB) integrity, and cytokine status in the brain and serum. Adult female C57BL/6 mice were infected by gavage with 5 cysts of the ME-49 type II T. gondii strain, and analyzed as independent groups at 30, 60 and 90 days postinfection (dpi). Anxiety, depressive-like behavior, and hyperactivity were detected in the early (30 dpi) and long-term (60 and 90 dpi) chronic T. gondii infection, in a direct association with the presence of parasite cysts and neuroinflammation, independently of the brain tissue areas, and linked to BBB disruption. These behavioral alterations paralleled the upregulation of expression of tumor necrosis factor (TNF) and CC-chemokines (CCL2/MCP-1, CCL3/MIP-1α, CCL4/MIP-1β and CCL5/RANTES) in the brain tissue. In addition, increased levels of interferon-gamma (IFNγ), TNF and CCL2/MCP-1 were detected in the peripheral blood, at 30 and 60 dpi. Our data suggest that the persistence of parasite cysts induces sustained neuroinflammation, and BBB disruption, thus allowing leakage of cytokines of circulating plasma into the brain tissue. Therefore, all these factors may contribute to behavioral changes (anxiety, depressive-like behavior, and hyperactivity) in chronic T. gondii infection.

Behavioral and Neuropathological Changes After Toxoplasma gondii Ocular Conjunctival Infection in BALB/c Mice

“…Acute T. gondii infection is associated with the rapid replication of tachyzoites followed by their conversion to bradyzoites, which can form infectious cysts within the brain, muscle, and other tissues, which establishes a life-long, latent infection ( Sullivan and Jeffers, 2012 ; Rougier et al., 2017 ) that can give rise to neuroinflammation, vascular injury, and damage to the blood–brain barrier ( Castaño Barrios et al., 2021 ; Egorov et al., 2021 ).…”

Sulfadiazine Plus Pyrimethamine Therapy Reversed Multiple Behavioral and Neurocognitive Changes in Long-Term Chronic Toxoplasmosis by Reducing Brain Cyst Load and Inflammation-Related Alterations

“…On the other hand, psychiatric and behavioral changes such as schizophrenia ( 13 , 14 ), obsessive-compulsive disorders, personality and bipolar disorders ( 14 ), depression ( 15 ) and alteration of neurocognitive functioning ( 16 ) have been associated with chronic T. gondii infection in human beings. Several studies investigated the influence of T. gondii infection in behavioral and neurocognitive disorders using animal models, replicating aspects present in humans as locomotor alteration ( 17 ), anxiety-like disorder ( 18 – 22 ), hyperactivity ( 20 , 22 – 25 ), and also alterations in aversive memory consolidation ( 26 , 27 ), spatial memory loss ( 28 ), and long-term memory impairment ( 21 ).…”

“…In ME-49 T. gondii -infected male B6CBAF1/J mice, behavioral alterations were associated with inflammation-related processes and a continuous increase in cyst load in the CNS ( 34 ). Conversely, a recent study showed that in female C57BL/6 mice ME-49 infection evolves from the early to the long-term chronic phase with reduction of the number, suggestive of gradual infection control, as immune response is established ( 22 ). However, multiple behavioral changes (anxiety-like disorder, depressive-like behavior and hyperactivity) were detected in the early and long-term chronic infection ( 22 ).…”

“…Conversely, a recent study showed that in female C57BL/6 mice ME-49 infection evolves from the early to the long-term chronic phase with reduction of the number, suggestive of gradual infection control, as immune response is established ( 22 ). However, multiple behavioral changes (anxiety-like disorder, depressive-like behavior and hyperactivity) were detected in the early and long-term chronic infection ( 22 ). Further, these behavioral alterations occur in a scenario of upregulation of inflammatory cytokines and chemokines in the CNS, neuroinflammation, blood-brain barrier (BBB) disruption, and increase in systemic Th1 cytokine levels ( 22 ).…”

“…However, multiple behavioral changes (anxiety-like disorder, depressive-like behavior and hyperactivity) were detected in the early and long-term chronic infection ( 22 ). Further, these behavioral alterations occur in a scenario of upregulation of inflammatory cytokines and chemokines in the CNS, neuroinflammation, blood-brain barrier (BBB) disruption, and increase in systemic Th1 cytokine levels ( 22 ). Altogether, these findings support the participation of inflammation-related processes in behavioral changes, probably reflecting brain cyst load, still undisclosed.…”