Methamphetamine neurotoxicity, microglia, and neuroinflammation

Methamphetamine (METH) is an illicit psychostimulant that is subject to abuse worldwide. While the modulatory effects of METH on dopamine neurotransmission and its neurotoxicity in the central nervous system are well studied, METH's effects on modulating microglial neuroimmune functions and on eliciting neuroinflammation to affect dopaminergic neurotoxicity has attracted considerable attention in recent years. The current review illuminates METH-induced neurotoxicity from a neuropathological perspective by summarizing studies reporting microglial activation after METH administration in rodents. Assessing microglial reactivity in terms of the cells' morphology and immunophenotype offers an opportunity for comprehensive and objective assessment of the severity and nature of METH-induced neuronal perturbations in the CNS and can thus contribute to a better understanding of the nature of METH toxicity. We reach the conclusion here that the intensity of microglial activation reported in the majority of animal models after METH administration is quite modest, indicating that the extent of dopaminergic neuron damage directly caused by this neurotoxicant is relatively minor. Our conclusion stands in contrast to claims of excessive and detrimental neuroinflammation believed to contribute and exacerbate METH neurotoxicity. Thus, our analysis of published studies does not support the idea that suppression of microglial activity with anti-inflammatory agents could yield beneficial effects in terms of treating addiction disorders.