Brain mGlu5 is linked to cognition and cigarette smoking but does not differ from control in early abstinence from chronic methamphetamine use.

BACKGROUND: The group-I metabotropic glutamate receptor subtype five (mGlu5) has been implicated in methamphetamine exposure in animals, and in human cognition. Because people with Methamphetamine Use Disorder (MUD) exhibit cognitive deficits, we evaluated mGlu5 in people with MUD and controls and tested its association with cognitive performance.

METHODS: Positron emission tomography was performed to measure the total volume of distribution (VT) of [18F]FPEB, a radiotracer for mGlu5, in brains of participants with MUD (abstinent from methamphetamine for at least two weeks, n = 14) and a control group (n = 14). Drug use history questionnaires and tests of verbal learning, spatial working memory, and executive function were administered. Associations of VT with methamphetamine use, tobacco use, and cognitive performance were tested.

RESULTS: MUD participants did not differ from controls in global or regional VT, and measures of methamphetamine use were not correlated with VT. VT was significantly higher globally in nonsmoking vs. smoking participants (main effect, p = 0.0041). MUD participants showed nonsignificant weakness on the Rey Auditory Verbal Learning Task (RAVLT) and the Stroop Test vs. controls (p = 0.08 and p = 0.13, respectively) with moderate to large effect sizes, and significantly underperformed controls on the SCAP (p = 0.015). Across groups, RAVLT performance correlated with VT in the dorsolateral prefrontal cortex (DLPFC) and superior frontal gyrus.

CONCLUSION: Abstinent MUD patients show no evidence of mGlu5 downregulation in brain, but association of VT in dlPFC with verbal learning suggests that medications that target mGlu5 may improve cognitive performance.