Impact of adolescent intermittent ethanol exposure in male and female rats on social drinking and neuropeptide gene expression

Abstract

Background: Alcohol use during adolescence can alter maturational changes that occur in brain regions associated with social and emotional responding. Our previous studies have shown that adult male, but not female rats demonstrate social anxiety-like alterations and enhanced sensitivity to ethanol-induced social facilitation following adolescent intermittent ethanol exposure (AIE). These consequences of AIE may influence adult social drinking in a sex-specific manner.

Methods: To test the effects of AIE on social drinking, male and female Sprague-Dawley rats exposed to water or ethanol (0 or 4 g/kg, intragastrically, every other day, between postnatal day [P] 25 and 45) were tested as adults (P72-83) in a social drinking paradigm (30-minute access to a 10% ethanol solution in supersac or supersac alone in groups of three same-sex littermates across two 4-day cycles separated by 4 days off). Social behavior was assessed during the last drinking session, along with assessment of oxytocin (OXT), oxytocin receptor (OXTR), vasopressin (AVP), and vasopressin receptors 1a and 1b (AVPR1a, AVPR1b) in the hypothalamus and lateral septum.

Results: Males exposed to AIE consumed more ethanol than water-exposed controls during the second drinking cycle, whereas AIE did not affect supersac intake in males. AIE-exposed females consumed less ethanol and more supersac than water-exposed controls. Water-exposed females drinking ethanol showed more social investigation and significantly higher hypothalamic OXTR, AVP, and AVPR1b gene expression than their counterparts ingesting supersac and AIE females drinking ethanol. In males, hypothalamic AVPR1b gene expression was affected by drinking solution, with significantly higher expression evident in males drinking ethanol than those consuming supersac.

Conclusions: Collectively, these findings provide new evidence regarding sex-specific effects of AIE on social drinking and suggest that the hypothalamic OXT and AVP systems are implicated in the effects of ingested ethanol on social behavior in a sex- and adolescent-exposure-dependent manner.

Keywords: adolescent intermittent ethanol exposure; oxytocin; sex differences; social drinking; vasopressin.

Figure 1.

(A) Timeline of adolescent intermittent ethanol exposure followed by social drinking in adulthood. (B) Illustration of social drinking context and ability to observe individual drinking through video recording.

Figure 2.

Intake of 10% ethanol in supersac under social drinking circumstances in male and female rats with a prior history of water or AIE exposure. (A) Ethanol intake averaged across drinking test days. Ethanol intake in male (B) and (C) female adult rats during each drinking session. Inserts in B and C represent cumulative intakes during the first and the second drinking cycles of 4 test days, with a 4-day interval between them (marked with a vertical grey bar). A significant difference between males and females in ethanol intake averaged across drinking test days (A) within the same adolescent exposure condition is depicted with $, whereas asterisks (B, C) indicate significant differences in ethanol intake between water- and AIE-exposed animals evident at a certain test day (p < 0.05).

Figure 3.

Correlations between ethanol intake and blood ethanol concentrations (BECs) assessed on the last drinking day in water- (A) and AIE-exposed (B) males as well as females exposed to either water (C) or AIE (D). (E) BECs assessed on the last drinking day in males and females. A significant difference between males and females in BECs within the same adolescent exposure condition is depicted with % (p < 0.05).

Figure 4.

Intake of 10% supersac under social drinking circumstances in male and female rats with a prior history of water and AIE exposure. (A) Supersac intake averaged across drinking test days. Supersac intake in male (B) and female (C) adult rats during each drinking session. A significant difference between males and females in supersac intake averaged across drinking test days within the same adolescent exposure condition is depicted with $, whereas asterisks indicate significant differences in supersac intake between water- and AIE-exposed animals evident at a certain test day (p < 0.05).

Figure 5.

Social investigation (A, B) and play flighting (C, D) demonstrated by male and female rats with the history of water or AIE exposure during social drinking of either supersac only or 10% ethanol solution in supersac. (*) indicates a significant difference between water- and AIE-exposed animals drinking the same solution, whereas (#) denotes differences between animals within the same adolescent exposure condition (water or AIE) drinking different solutions under social circumstances (p <0.05).

Figure 6.

Oxytocin (OXT), oxytocin receptor (OXTR), vasopressin (AVP), vasopressin receptors 1a (AVPR1a) and 1b (AVPR1b) gene expression in the hypothalamus of male (A, B, C, D, E) and female (F, G, H, I, J) rats with the history of water or AIE exposure following the last social drinking test with either supersac only or 10% ethanol in supersac. Data were calculated as a relative change in gene expression using the 2^−ΔΔC(t) method, with Cyclophilin A used as a reference gene and the water-exposed animals drinking supersac serving as the ultimate control group within each sex. (*) indicates a significant difference between water and AIE exposure conditions, whereas (#) denotes a significant difference (p < 0.05) in gene expression associated with ethanol versus supersac drinking either within the same adolescent exposure condition (G, H, J) or collapsed across adolescent exposure (E).