Impact of social isolation and enriched environment during adolescence on voluntary ethanol intake and anxiety in C57BL/6J mice

Abstract

This study was designed to determine the impact of an enriched environment in a previously established stress model of isolation during early development that induces high alcohol (ethanol) self-administration. The study was conducted with male and female C57BL/6J mice housed in isolation or in groups that were either provided or withheld enrichment during adolescence. The impact of these housing conditions was assessed during adulthood by measuring weight gain, quantifying voluntary ethanol intake, measuring plasma corticosterone levels, and assessing anxiety-like behavior. Results showed that, regardless of sex, mice that were single-housed during adolescence showed a significant increase in voluntary ethanol intake, which was not observed in isolated mice that were provided with nesting material during adolescence (compared to group-housed non-enriched control group). Basal corticosterone was not affected by housing, enrichment conditions, or sex. Corticosterone levels did not relate to levels of voluntary ethanol intake. However, corticosterone levels were higher after three weeks of ethanol intake. Surprisingly, mice that were group-housed during adolescence showed higher levels of anxiety-like behavior in the light/dark test. Overall, these results indicate that housing conditions during a critical developmental period can significantly modulate voluntary ethanol intake later in life.

Keywords: Adolescence; Alcohol; Enriched environment; Isolation.

Figure 1

Timeline of the different stages of the study

Figure 2

Plasma corticosterone concentrations (µg/dl) registered in male and female mice in all four housing conditions either before (top) or after (bottom) the voluntary ethanol intake test period. Values are mean ± SEM.

Figure 3

Plasma corticosterone concentrations (µg/dl) registered before or after the ethanol intake testing in A) single or group housed mice (collapsed across sex and enrichment conditions) and B) No Enriched or Enriched housing conditions (collapsed across sex and group or single housing conditions). Values are mean ± SEM. * indicates a significant difference from the Before group.

Figure 4

Anxiety response measured as time in the dark side of the apparatus (seconds) from male and female mice in all four housing conditions evaluated either before (top) or after (bottom) the voluntary ethanol intake test period. Values are mean ± SEM. * indicates a significant main effect of group vs. single housing.

Figure 5

Ethanol intake levels (g/kg) for male (top) and female (bottom) in the four different housing conditions registered at the beginning of the ethanol intake test period. Data is averaged over the first 5 days of testing. Values are mean ± SEM. * indicates a significant difference from Group No enriched group.