Drug runners: mice speed up before meth hit
Methamphetamine-addicted mice run hard for two hours in anticipation of a drug dose. Andrew Masterson reports.
Mice addicted to methamphetamine up their physical activity two hours before scheduled dose of the drug, new research shows.
To conduct the research Silver and colleagues set up two cohorts of mice. Members of each were housed in cages, kitted out with food, water and a running wheel. The wheel was connected by a tunnel to a second chamber, which contained either nebulised methamphetamine or water.
The door to the tunnel was opened for two one-hour periods each day, the first one early, the second one late.
The experiment was set up to test the effects of the drug with as few complications as possible. Using a nebuliser avoided any requirement to inject or surgically implant the meth into the animals.
The researchers found that the rodents exposed to the drug started pounding away, running on the wheel two hours before the scheduled opening of the chamber. The activity played a role in sparking up three brain regions closely associated with reward processing, food anticipation and cravings: the orbitofrontal cortex, the dorsomedial hypothalamus and lateral septum.
The rodents’ compulsion to run hard in anticipation of a meth hit was stronger before the early dose than the later one.
The results do not accord with those of a previous experiment run by a team from the Scripps Research Institute in La Jolla, US, in 2016. In this research, published in the journal Brain Structure and Function, the scientists found that wheel-running reduced cravings in methadone-dependent rats experiencing withdrawal.