This bar graph shows that compounds that block the action of microglia counter a toxic effect of methamphetamine. Striatal regions of mice exposed to methamphetamine contain decreased dopamine content, compared with those of unexposed controls. Treatment with MK-801 or dextromethorphan (DXM) prior to methamphetamine injection reduced the extent of depletion, suggesting that microglia play a role in methamphetamine's toxic effect on the brain's dopamine system. The data for each category is as follows:

Striatal dopamine (as a percentage of control group level):

• Control: 100 percent
• Meth: approximately 15 percent
• MK-801: approximately 75 percent
• DXM: approximately 54 percent