Environment is not the most important variable in determining oral morphine consumption in Wistar rats

The role of differential housing on sucrose-morphine consumption in outbred Wistar rats was investigated in two studies. The results of earlier research, indicating rats housed in a quasinatural colony drank significantly less sucrose-morphine than rats isolated in standard laboratory cages, could not be replicated, as the consumption of sucrose-morphine by the isolated animals in the present two studies was reduced. It is possible that during a colony conversion the supplier inadvertently introduced strain differences making the present rats more resistant to xenobiotic consumption. Discussion documents the role of genetics in morphine consumption.