Sex differences in traumatic stress reactivity in rats with and without a history of alcohol drinking

Abstract

Background: Alcohol misuse and post-traumatic stress disorder (PTSD) are highly comorbid, and treatment outcomes are worse in individuals with both conditions. Although more men report experiencing traumatic events than women, the lifetime prevalence of PTSD is twice as high in females. Despite these data trends in humans, preclinical studies of traumatic stress reactivity have been performed almost exclusively in male animals.

Methods: This study was designed to examine sex differences in traumatic stress reactivity in alcohol-naive rats (experiment 1) and rats given intermittent access to 20% ethanol in a 2-bottle choice paradigm for 5 weeks (experiment 2). Animals were exposed to predator odor (bobcat urine) and tested for contextual avoidance 24 h later; unstressed controls were never exposed to predator odor. We evaluated changes in physiological arousal using the acoustic startle response (ASR) test at day 2 post-stress and anxiety-like behavior measured in the elevated plus-maze (EPM) at day 17 post-stress. In experiment 3, time course of corticosterone response was examined in male and female rats following exposure to predator odor stress.

Results: Alcohol-naive males and females exposed to predator odor displayed blunted weight gain 24 h post-stress, but only a subset of stressed animals exhibited avoidance behavior. In alcohol-drinking animals, the proportion of avoiders was higher in males than females, and predator odor exposure increased ASR in males only. Stressed females exhibited blunted ASR relative to unstressed females and stressed males, regardless of alcohol drinking history. Alcohol-experienced females presented lower anxiety-like behavior and higher general activity in the EPM in comparison with alcohol-experienced males. Plasma corticosterone levels were higher in females immediately after predator odor exposure until 60 min post-stress relative to males.

Conclusions: We report robust sex differences in behavioral and endocrine responses to bobcat urine exposure in adult Wistar rats. Also, males with a history of chronic moderate alcohol drinking exhibited increased traumatic stress reactivity relative to alcohol-drinking females. Our findings emphasize the importance of considering sex as a biological variable in the investigation of traumatic stress effects on physiology and behavior.

Keywords: Alcohol; Arousal; Bobcat urine; Corticosterone; Predator odor; Sex differences; Startle; Stress; Trauma.

Fig. 1

Traumatic stress response in alcohol-naive male and female rats. a Experimental design. Rats underwent the conditioned place aversion paradigm using bobcat urine. Controls were never exposed to predator odor (PO) stress. Avoidance behavior was measured 24 h post-stress (day 1). Acoustic startle reactivity was evaluated at day 2 post-stress and is expressed as Vmax normalized by body weight in kilograms (Vmax/kg b.w.). Anxiety-like behavior was tested at day 17 after PO exposure. b Change in time spent in PO-paired chamber in rats indexed as avoiders or non-avoiders. c Avoidance distribution of stressed rats (avoiders × non-avoiders). d Weight gain measured 24 h after exposure to PO. e Acoustic startle response at 95 dB. f Acoustic startle response at 105 dB. g Acoustic startle response at 115 dB. Data presented as mean ± SEM. Asterisk denotes P < .05

Fig. 2

Traumatic stress response in alcohol-drinking male and female rats. a Experimental design. Rats were given intermittent access to 20% ethanol in a 2-bottle choice paradigm for 5 weeks followed by conditioned place aversion using bobcat urine. Controls were never exposed to predator odor (PO) stress. Avoidance behavior was measured 24 h post-stress (day 1). Acoustic startle reactivity was evaluated at day 2 post-stress and is expressed as Vmax normalized by body weight in kilograms (Vmax/kg b.w.). Anxiety-like behavior was tested at day 17 after PO exposure. b Change in time spent in PO-paired chamber in rats indexed as avoiders or non-avoiders. c Avoidance distribution of stressed rats (avoiders × non-avoiders). d Alcohol consumption presented as grams of ethanol per body weight in kilograms per rat (estimated from the pair of rats) in 24 h. Insert: blood alcohol concentrations at 2 h after the start of alcohol access during the last drinking session. e Acoustic startle response at 95 dB. f Acoustic startle response at 105 dB. g Acoustic startle response at 115 dB. Data presented as mean ± SEM. Asterisk denotes P < .05

Fig. 3

Plasma corticosterone response in male and female rats following exposure to predator odor (PO) stress. a Experimental design. Rats were exposed to bobcat urine in a clean cage. Tail blood samples were collected before exposure to PO, immediately after, 30 min, 60 min, and 90 min post-stress. b Plasma corticosterone concentrations at the indicated time points. Data presented as mean ± SEM. Asterisk denotes P < .05 between sexes; number sign denotes P < .05 in comparison with the baseline (− 15 min time point)