Early maternal deprivation enhances voluntary alcohol intake induced by exposure to stressful events later in life

Abstract

In the present study, we aimed to assess the impact of early life stress, in the form of early maternal deprivation (MD, 24 h on postnatal day, pnd, 9), on voluntary alcohol intake in adolescent male and female Wistar rats. During adolescence, from pnd 28 to pnd 50, voluntary ethanol intake (20%, v/v) was investigated using the two-bottle free choice paradigm. To better understand the relationship between stress and alcohol consumption, voluntary alcohol intake was also evaluated following additional stressful events later in life, that is, a week of alcohol cessation and a week of alcohol cessation combined with exposure to restraint stress. Female animals consumed more alcohol than males only after a second episode of alcohol cessation combined with restraint stress. MD did not affect baseline voluntary alcohol intake but increased voluntary alcohol intake after stress exposure, indicating that MD may render animals more vulnerable to the effects of stress on alcohol intake. During adolescence, when animals had free access to alcohol, MD animals showed lower body weight gain but a higher growth rate than control animals. Moreover, the higher growth rate was accompanied by a decrease in food intake, suggesting an altered metabolic regulation in MD animals that may interact with alcohol intake.

Figure 1

Schedule of experimental design. A total of ten litters were assigned to either of these two experimental groups: exposure to a single episode of early maternal deprivation (24 h on pnd 9, MD) or not deprived (control group, Co). All animals were given free access to alcohol (20%, v/v) and water in the two-bottle choice paradigm for (1) the whole adolescent period (from pnd 28 to pnd 50), for (2) four days (pnd 57 to pnd 60) after one week of alcohol cessation, and for (3) four days (pnd 67 to pnd 70) after a second period of alcohol cessation combined with 30 min. of restraint stress under white light conditions on the last three days of alcohol cessation. n = 18–20 animals per experimental group.

Figure 2

Voluntary alcohol intake during adolescence. (a) Daily alcohol intake (g/kg/day) along the whole adolescent period. Data are presented as mean ± S.E.M and were analyzed by a repeated measures two-way ANOVA. (b) Adolescent averaged alcohol intake (g/kg/day). Data were analyzed by a two-way ANOVA. Rats were exposed to a single episode of early maternal deprivation (24 h on pnd 9, MD) or not deprived (control group, Co) and exposed during adolescence, from postnatal day (pnd) 28 to pnd 50, to voluntary alcohol intake (20% v/v, in a two-bottle choice paradigm). n = 9-10 cages per experimental group.

Figure 3

Voluntary alcohol intake following one week of alcohol cessation (a) and following a second week of alcohol cessation combined with restraint stress (b). Data are presented as mean ± S.E.M of the averaged alcohol intake (g/kg/2 h) during the first 2 h of alcohol exposure during the four days period of alcohol exposure (from pnd 57 to pnd 60, panel (a), and from pnd 67 to pnd 70, panel (b)). Rats were exposed to a single episode of early maternal deprivation (24 h on pnd 9, MD) or not deprived (control group, Co) and exposed to voluntary alcohol intake (20% v/v, in a two-bottle choice paradigm) during adolescence and following one week of alcohol cessation and after a second period of alcohol cessation combined with exposure to restraint immobilization stress (30 min. per day under white light conditions) on the last three days of alcohol cessation. Data were analyzed by a two-way ANOVA, P < 0.05; (A) general effect of sex, (B) general effect of the neonatal condition. n = 9-10 cages per experimental group.

Figure 4

Metabolic parameters during adolescence in response to voluntary alcohol intake. (a) Body weight (BW) gain (g), (b) growth rate (%), and (c) accumulated food intake (g). Rats were exposed to a single episode of early maternal deprivation (24 h on pnd 9, MD) or not deprived (control group, Co) and exposed during adolescence, from postnatal day (pnd) 28 to pnd 50, to voluntary alcohol intake (20% v/v, in a two-bottle choice paradigm). Data are presented as mean ± S.E.M and were analyzed by a repeated measures two-way ANOVA (BW gain and growth rate) or by a two-way ANOVA (accumulated food intake). P < 0.05; (A) general effect of sex and (B) general effect of the neonatal condition; n = 18–20 animals per experimental group.

Figure 5

Metabolic parameters following stressful events in young adult rats in response to voluntary alcohol intake. ((a), (c)) Growth rate (%) and ((b), (d)) accumulated food intake (g). Rats were exposed to a single episode of early maternal deprivation (24 h on pnd 9, MD) or not deprived (control group, Co) and exposed to voluntary alcohol intake (20% v/v, in a two-bottle choice paradigm) during adolescence and following one week of alcohol cessation (from pnd 57 to pnd 60, upper panels) and after a second period of alcohol cessation combined with exposure to restraint immobilization stress (30 min. per day under white light conditions) on the last three days of alcohol cessation (from pnd 67 to pnd 70, lower panels). Data are presented as mean ± S.E.M and were analyzed by a repeated measures two-way ANOVA (BW gain). Tukey post hoc comparisons: ^*** P < 0.005, MD males versus Co males; ^### P < 0.005, Co females versus Co males; or by a two-way ANOVA (accumulated food intake). P < 0.05; (A) general effect of sex, (B) general effect of the neonatal condition; n = 18–20 animals per experimental group.