Effects of social housing conditions on ethanol-induced behavioral sensitization in mice

The processes underlying drug addiction are, for most drugs, explained by the phenomenon of sensitization. This phenomenon refers to the progressive increase in the mental, somatic or behavioral effects of the same dose of drug following its absorption. It can be studied in animal models by investigating the repeated administrations of ethanol in mice.
Optimization of the environmental condition such as such as social refinement constitute one of many strategies widely used to study the protective effect of environment on behavioral response to drug addiction. The aim of this study was to investigate the optimization of the social environment on psychomotor sensitization to ethanol in mice. Young mice were first single housed or group housed during 6 weeks of pre-testing and then i.p. injected for eight consecutive days with ethanol 2.5 g/kg (moderate dose), and locomotion was recorded for 5 min. The day after the last sensitization session, expression of ethanol sensitization was tested in all mice following a 30-min test session. The main results showed that all groups of mice developed a psychomotor sensitization to a moderate dose of ethanol (2.5 g/kg). While the process of sensitization per se was not affected by the housing social conditions, both the initial and chronic sensitivities to the stimulant effects of ethanol were significantly affected by the size of the housing groups. Isolated mice and mice housed in pairs were the most sensitive to the stimulant effects of ethanol, while mice housed in groups of 8 showed a delay in the development and the lower sensitivity to these effects (staircase effect). These effects may be related to the stress induced by social isolation and indicate that optimal social conditions might prevent the risks of ethanol addiction.