Similar rewarding effects of testosterone in mice rated as short and long attack latency individuals

An attempt was made to confirm and extend the findings of an earlier study on the rewarding properties of testosterone in male mice using conditioned place preference (CPP). Previous results had only partially demonstrated such an effect because the reinforcement depended on environmental cues such as the colour of the compartment. High individual variability was evident, suggesting that basal levels of aggressiveness may modulate such effects. Animals were pre-screened for aggressive behaviour and allocated to short and long attack latency (SAL and LAL) categories. Five days later the CPP procedure started. This involved pre-conditioning tests, conditioning and post-conditioning tests. SAL and LAL animals were treated with vehicle, 1 or 2 mg/kg of testosterone. During conditioning (on alternate days), a distinctive floor was paired four times with testosterone. On the intervening days animals were paired with a different floor with vehicle. CPP was clearly observed after testosterone treatment when the colour of the compartment was controlled in both SAL and LAL animals. These results provide additional support for the idea that testosterone and its derivatives have rewarding properties, which could explain processes of dependence.