Methamphetamine sensitization attenuates the febrile and neuroinflammatory response to a subsequent peripheral immune stimulus.

Methamphetamine (MA) use is associated with activation of microglia and, at high doses, can induce neurotoxicity. Given the changes in the neuroinflammatory environment associated with MA, we investigated whether MA sensitization, a model of stimulant psychosis and an indicator of drug addiction, would interfere with the thermoregulatory and neuroinflammatory response to a subsequent peripheral immune stimulus. C57BL6/J mice were given either 1 mg/kg MA or saline i.p. once a day for 5 days to produce behavioral sensitization. Seventy-two hours following the last MA injection, 100 microg/kg LPS or saline was co-administered with 1 mg/kg MA or saline and blood and brains were collected. Here we report that while co-administration of LPS and MA did not affect the LPS-induced increase in central cytokine mRNA, mice sensitized to MA showed an attenuated central response to LPS. Interestingly, the peripheral response to LPS was not affected by MA sensitization. Plasma cytokines increased similarly in all groups after LPS. Further, c-Fos expression in the nucleus of the solitary tract did not differ between groups, suggesting that the periphery-to-brain immune signal is intact in MA-sensitized mice and that the deficit lies in the central cytokine compartment. We also show that MA sensitization decreased LPS- or acute MA-induced microglial Iba1 expression compared to non-sensitized mice. Taken together, these data show that MA sensitization interferes with the normal central immune response, preventing the CNS from efficiently responding to signals from the peripheral immune system. 2009 Elsevier Inc. All rights reserved.