Temporal analysis of individual ethanol consumption in socially housed mice and the effects of oxytocin

Abstract

Rationale: The majority of preclinical studies assessing treatments for alcohol use disorder use singly housed animals. Because social factors affect ethanol intake, studies investigating such treatments in group-housed animals are needed.

Objectives: We investigated the effects of repeated oxytocin treatment on ethanol intake in socially housed male and female C57BL/6J mice.

Methods: We used the novel "Herdsman" system implementing radiotracking technology to measure individual ethanol intake in group-housed animals. Mice were housed in same-sex groups of 4 per cage and exposed to 3 and 6% ethanol solutions. After baseline drinking was established, half of the animals in each cage received repeated intraperitoneal injections of 3 mg/kg oxytocin.

Results: During baseline, females consumed more ethanol than males partly due to greater number of ethanol drinks taken by females. We also observed a gradual development of two peaks of ethanol consumption during the dark phase of the circadian cycle. The effects of oxytocin treatment were short-acting and varied across treatment days. Oxytocin significantly decreased ethanol intake on three out the four treatment days. On the fourth treatment day, oxytocin decreased ethanol intake and water intake.

Conclusion: The greater intake of ethanol in female mice is associated with the number of drinks taken. Oxytocin treatments not only cause an acute decrease in ethanol consumption, but can also change in efficacy over time. While the oxytocin system remains a promising therapeutic target for alcoholism, studies investigating longer periods of repeated oxytocin treatment and those using additional oxytocin receptor agonists are warranted.

Keywords: Alcohol; Drink size; Ethanol preference; HM2; Oxytocin; RFID; Radiofrequency identification; Sex differences; Socially housed; Two-bottle choice.

Fig 1

a Experimental timeline. b HM2 schematic

Fig. 2

Baseline ethanol (EtOH) and water (H2O) consumption, drinks, drink size, and channel entries. Darker shaded regions indicate when the mice had access to 3% EtOH and the lighter shaded regions indicate when the mice had access to 6% EtOH. a EtOH intake (g/kg). b H2O intake (g/kg). c EtOH drinks. d H2O drinks. e EtOH drink size. f H2O drink size. g EtOH channel entries. h H2O channel entries. Data expressed as mean ± SEM. *p < 0.05, compared to opposite sex. n = 24/sex

Fig. 3

Baseline correlational analyses. a Average baseline ethanol (EtOH) intake positively correlated with average number of EtOH drinks for males (r-squared = 0.78, p < 0.0001) and females (r squared = 0.78, p < 0.0001). b Average baseline water (H2O) intake positively correlated with average number of H2O drinks for males (r-squared = 0.73, p< 0.0001) and females (r-squared = 0.95, p < 0.0001). c Average baseline EtOH intake was not correlated with EtOH drink size for males (r-squared = 0.0004, p = 0.93) or females (r-squared = 0.02, p = 0.54). d Average baseline H2O intake was not correlated with H2O drink size for males (r-squared < 0.0001, p = 0.97) or females (r-squared = 0.0002, p = 0.95). e Average baseline EtOH intake was not correlated with average number of EtOH channel entries for males (r-squared = 0.07, p = 0.21) or females (r-squared = 0.12, p = 0.09). f Average baseline H2O intake was not correlated with average number of H2O channel entries for males (r-squared = 0.05, p = 0.30) or females (r-squared = 0.10, p = 0.13). n = 24/sex

Fig. 4

Time-dependent effects of oxytocin on ethanol (EtOH) consumption (g/kg). Shaded regions of the graph are representative of the dark cycle. a EtOH intake on the first day of treatment. b EtOH intake on the second day of treatment. c EtOH intake on the third and fourth day of treatment. Treatment days three and four were combined for display purposes. Data expressed as mean ± SEM. *p < 0.05, *p < 0.01, ***p < 0.001, ****p < 0.0001, compared to vehicle. n = 12/group

Fig. 5

Time-dependent effects of oxytocin on water consumption (g/kg). Shaded regions of the graph are representative of the dark cycle. a Water intake on the first day of treatment. b Water intake on the second day of treatment. c Water intake on the third and fourth days of treatment. Treatment days 3 and 4 were combined for display purposes. There were no significant differences. n = 12/group

Fig. 6

Time-dependent effects of oxytocin on ethanol drinks. Shaded regions of the graph are representative of the dark cycle. a Ethanol drinks on the first day of treatment. b Ethanol drinks on the second day of treatment. c Ethanol drinks on the third and fourth day of treatment. Treatment days 3 and 4 where combined for display purposes. Data expressed as mean ± SEM. *p < 0.05, *p < 0.01, compared to vehicle. n = 12/group