Effect of sepsis severity on the leukocyte adhesion in pial blood vessels, locomotor activity and depressive-like behavior in mice

Abstract

Sepsis is defined as a dysregulated immunological response triggered by an infectious disease that can lead to death. In the cases where symptoms get worse, sepsis can evolve to septic shock, which is characterized by circulatory and metabolic impairments and is associated with a higher risk of death. Together, both diseases are considered the major cause of death in intensive care units worldwide. In Brazil, mortality rates can get up to 65%. Epidemiological studies have shown that, during the course of the disease and after hospital discharge, patients affected by sepsis can present depression and other neurological symptoms such as hallucinations, panic attacks, worsening in cognitive abilities and difficulty in concentration. In this regard, animal models are of great importance to evaluate the involvement of molecular pathways and in the search of efficient treatments. The cecal ligation and puncture (CLP) model is one the most used in studies of sepsis, however there is still a lack of consensus related to neurological and/or locomotor symptoms observed. Additionally, there is a possibility that different degrees of inflammation can lead to different neurological-associated phenotypes. In fact, it has been observed that cytokines, chemokines and oxidative stress can lead to neuronal death in brain regions responsible for emotions, locomotor activity, and cognition. Thus, this project aims to analyze the relation between different degrees of sepsis CLP-induced brain inflammation and affective disorders, particularly that similar to depression, and locomotor dysfunction. To do that, mice will be divided according to severity of sepsis, as follows: (I) sham, no sepsis; (II) mild sepsis; (III) moderate sepsis; and (IV) severe sepsis. Severity of sepsis is determined by distance of the ligature in relation to the ileocecal valve, number of perforations in the cecum, and extrusion or not of feces. To measure inflammation in brain, adhesion leucocytes in pial venules will be counted by intravital microscopy six hours after sepsis induction. Survival curve and clinical parameters (body temperature, presence of piloerection, alterations in the eyelids, abdominal contraction) will be measured for ten days, starting just after sepsis induction. Neurological-related symptoms will be measured thirty days after sepsis induction, i.e., when mice are clinically recovered, particularly: (I) Depressive-like behavior: through the following assays, sucrose consumption and tail suspension; II) Locomotor activity: "rotarod" and open field test. Molecular mechanisms related to synaptic disbalance will be evaluated by measuring expression of neurotransmitters by "western blotting".