Sickness Behavior: Influence of Immune System Activation Leading to Impairment in Psychological Aspects

One of the interesting topics in the area of psychoneuroimmunology is the study of sickness behaviorSickness behavior due to the collection of specific and non-specific symptoms caused by the disease in different species. In this sense, sickness behaviorSickness behavior arises from the activation of the immune system; while the organism tries to reorganize its defenses to combat the immune challenge, several neurobehavioral changes emerge. Sickness behaviorSickness behavior induces the synthesis of proinflammatory cytokines in the periphery, which can communicate with the central nervous system (CNS) through the choroid plexus and circumventricular organs, increasing the levels of proinflammatory cytokines in the brain. Furthermore, the increase in proinflammatory cytokines activates the kynurenineKynurenine pathway, the main pathway involved in neuroinflammation in the CNS, which has two main branches: one with a neuroprotective effect through the action of kynurenic acid, the other with a neurotoxic effect through the action of 3-hydroxykynurenine acid and quinolinic acidQuinolinic acid. Still, the kynurenineKynurenine pathway, in addition to causing potential neuroinflammation and altering behavioral patterns in rodents and humans, is involved with the symptoms of anhedoniaAnhedonia, which leads to a depressive state.