Data indicate that innate immune cytokines may contribute to the high rate of behavioral co-morbidities found in medically ill patients. Nevertheless, the mechanisms involved have yet to be established. One possibility includes cytokine effects on dopamine (DA) metabolism in the basal ganglia. Basal ganglia DA plays a pivotal role in regulating multiple behaviors including mood, motivation/reward, motor activity, sleep and cognition. To explore effects of cytokines on DA and the basal ganglia, we have studied patients receiving treatment with the innate immune cytokine, interferon (IFN)-alpha. IFN-alpha is associated with marked behavioral changes consistent with decreased DA function including depression, anhedonia, fatigue, motor slowing, impaired sleep and cognitive dysfunction. Relevant to the role of DA and the basal ganglia in these effects, neuroimaging studies using positron emission tomography (PET) in patients undergoing IFN-alpha therapy have revealed increased basal ganglia glucose metabolism and increased uptake of the DA precursor, [18F]fluorodopa (FDOPA), in caudate and putamen. To further characterize these IFN-alpha effects on DA pathways, we have recently developed an animal model of IFN-alpha-induced behavioral change. Preliminary data in this animal model indicate that IFN-alpha may influence behavior in part through depletion of DA. However, the direct impact of IFN-alpha on the extracellular availability of DA and the mechanisms involved has yet to be determined. The proposed research will test the hypothesis that IFN-alpha mediates its effects on behavior by depleting the availability of DA in relevant basal ganglia nuclei. Hypotheses that DA depletion is secondary to decreased synthesis and release and/or increased expression of the DA transporter (DAT) will also be explored. To test these hypotheses, in vivo microdialysis of extracellular DA as well as PET neuroimaging of DAT binding and FDOPA uptake will be conducted in animals treated with IFN- alpha or saline. Induction of cytokines and their signaling pathways including mitogen activated protein kinases (MAPK) in blood and CSF will be correlated with changes in DA metabolism and behavior. Of note, activation of MAPK has been shown to upregulate monoamine transporters, and cytokine-induced activation of kynurenic acid has been shown to decrease DA release. Finally, DA metabolism and behavior will be examined in animals treated with the DAT blocker, RTI-336. These translational studies will establish the impact of IFN-alpha on DA metabolism and its relationship with behavior and activation of innate immune responses. Moreover, the utility of DAT blockers in treating cytokine-induced behavioral change will be determined.
Depression, fatigue, cognitive dysfunction and other behavioral alterations plague patients with a variety of medical disorders and are associated with reduced treatment adherence and poor health outcome including increased morbidity and mortality. Increasing data indicate that activation of the inflammatory response and the release of innate immune cytokines as may occur during medical illnesses and/or chronic stress can lead to behavioral changes and may account for the high rate of behavioral co-morbidities in medically ill patients. This project seeks to determine the nervous system pathways by which innate immune cytokines influence the brain and behavior, with a special emphasis on the effects of cytokines on dopamine metabolism in the basal ganglia, which regulates multiple behaviors including mood, motivation/reward, motor activity, sleep/wake cycles and cognition.
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