Concurrent chronic methamphetamine exposure may influence behavioral outcomes following repetitive mild traumatic brain injury.

RATIONALE: Traumatic brain injury (TBI) and substance use disorder (SUD) share several characteristics, including neurological outcomes and pathological traits. Misuse of stimulants, both non-prescription use of medications and illicit use of methamphetamine, is rising. Despite potential for misuse, stimulants are prescribed as treatment for some TBI-induced symptoms. Given that 40% of TBI patients have a history of SUD prior to injury, studies of the role that chronic substance misuse plays on the deleterious outcomes of TBI are warranted.

OBJECTIVES

Our study explores the role that chronic methamphetamine exposure plays in the acute and long-term behavioral outcomes of repetitive mild TBI (rmTBI). We hypothesized that chronic methamphetamine exposure would exacerbate the behavioral deficits induced by rmTBI.

METHODS

We developed a model combining non-contingent dosing of methamphetamine with the Closed Head Model of Engineered Rotational Acceleration (CHIMERA). Behavioral assays were employed one month after the final TBI to assess short-term effects and were repeated six months following the final TBI for long-term effects.

RESULTS

The Loss of Righting Reflex showed that chronic methamphetamine exposure impacted neither TBI severity nor immediate recovery. The T-maze and NORT revealed that rmTBI concurrent to chronic methamphetamine exposure induced short- and long-term cognitive deficits. Methamphetamine negatively impacted balance and coordination on the accelerated rotarod at the later timepoint only.

CONCLUSIONS

Together, these findings suggest that chronic methamphetamine exposure could potentially increase long-term, but not acute, TBI-induced deficits.