Genetics and epigenetics: paternal adolescent ethanol consumption in serotonin transporter knock-out rats and offspring sensitivity to ethanol

Abstract

Rationale: Alcohol use disorder (AUD) is shown to have an overall heritability of around 50%. One of the genes associated with AUD is SLC6A4 (solute carrier family 6 member A4) which codes for the serotonin transporter (SERT). The study looked at serotonin dysfunction on ethanol consumption in adolescents and the subsequent intergenerational effects of drinking by using a rat model: SERT^+/+ (regular functioning), SERT^+/- (50% transporter reduction) and SERT^-/- (complete reduction).

Objectives: We investigated sex and genotype differences in ethanol consumption in SERT knock-out Wistar rats (F0) followed by studying behaviour in the offspring (F1) of the male drinkers to assess effects of paternal alcohol consumption.

Methods: An intermittent access two-bottle choice paradigm (IA2BC) was used to yield ethanol drinking behaviour in F0 adolescent Wistar rats. The highest drinking males were mated to alcohol-naive females and their offspring were compared with controls. Drinking behaviour (IA2BC) and ethanol-induced motor coordination effects (via rotarod) were measured in the F1s.

Results: F0 drinking saw no SERT genotype differences in males. However, females consumed higher volumes of ethanol compared to males, with SERT^-/- females showing the highest intake. A clearer genotype effect was seen in the F1 animals, with reduction in SERT activity leading to enhanced ethanol intake in both sexes. Importantly, paternal exposure to ethanol significantly reduced the ethanol induced motor side effects in offspring, independent of sex and genotype.

Conclusions: These indicate a difference in the way genetic factors may act across sexes and suggest the involvement of epigenetic mechanisms in the intergenerational effects of alcohol.

Keywords: Alcohol drinking; Alcohol use disorder; Ethanol; Paternal drinking; Serotonin transporter.

Fig. 1

Illustration of the sample sizes, sequence and experiments performed in each generation. PND, postnatal day, IA2BC, intermittent access 2-bottle choice. Created with BioRender.com

Fig. 2

Average ethanol consumption and ethanol preference F0 generation across the 7-h and 24-h drinking sessions. SERT^−/− females showed the highest voluntary consumption followed by SERT^+/− and SERT^+/+ (a) while no such pattern was observed in males (b). There were no differences in preference of ethanol c and d between the genotypes or across sexes

Fig. 3

Ethanol consumption reduced with increase in dose. There was no statistically significant difference in compulsive ethanol intake between genotypes. Females (a) still consumed more per bodyweight than males (b). Bars denote standard error

Fig. 4

Average ethanol consumption F1 drinking offspring and controls. There was a significant main effect of genotype. SERT^−/− rats consumed the highest levels of alcohol of all groups. Females (a and c) always consumed significantly more alcohol than males (b and d)

Fig. 5

Average ethanol preference for F1 generation and matched F1 controls across the 7-h and 24-h drinking sessions. A significant effect of sex was seen with females (a and c) having greater ethanol preference than males (b and d), but this difference was not seen in the 24-h session

Fig. 6

Motor coordination measured by latency to stay on a rotarod after a dose of saline, 1 g/kg ethanol, or 2 g/kg ethanol intraperitoneal injection. Animals with drinking fathers performed better on the task under the influence of ethanol. Female animals performed better than males. Bars denote standard error

Fig. 7

Ethanol consumption of F0. The g/kg intake increased from 7-hour sessions (days 1–12) to 24-hour sessions (days 13–24) in both females (a) and males (b). Error bars denote SEM

Fig. 8

Ethanol consumption of F1 offspring. The g/kg intake g/kg increased from 7-hour sessions (days 1–12) to 24-hour sessions (days 13–24) in both females (a) and males (b). Error bars denote SEM

Fig. 9

Ethanol consumption of controls for the F1 generation. The g/kg increased from 7-hour sessions (days 1–12) to 24-hour sessions (days 13–24) in both females (a) and males (b). Error bars denote SEM