α1 Adrenergic Receptors Mediate Panic-like Defensive Behavior in Alcohol-Drinking but Not Alcohol-Naïve Rats

Abstract

Background: Most animals display different defensive behavioral strategies during imminent or potential threats. These responses are relevant for understanding human behavioral disorders. In addition, α1 adrenergic receptors (α1ARs) are blocked by prazosin and regulate a diverse set of behaviors, including alcohol drinking related to anxiety in humans, alcohol intake in rats, responses to strong acute stresses (like restraint), and several forms of cognitive flexibility. However, the role of α1ARs in regulating panic-like escape behavior remains unexplored. Methods: Male and female Wistar rats were chronic alcohol drinkers and age-matched alcohol naïves. Animals received an injection of 0.75 mg/kg of prazosin or vehicle and then were exposed to the elevated T maze (ETM) to evaluate avoidance and escape behavior. One week later, animals underwent the light-dark test (LDT) and open field test. Results: α1AR inhibition with prazosin increased latency for escape in male and female alcohol drinkers, with no significant effects in alcohol-naïve controls. There were also interesting impacts from alcohol drinking, including a decrease in ETM avoidance in female but not male drinkers. In addition, prazosin increased latency to enter the dark in LDT in female drinkers and male naïves. Although prazosin also decreased the number of transitions in males, no differences were found in open-field locomotion. Conclusions: These results suggest that α1ARs mediate escape-like behavior in male and female alcohol drinkers, shedding light on a novel therapy for alcohol problems related to panic and anxiety.

Keywords: alcohol drinking; anxiety; panic; α1 adrenergic receptors.

Figure 1

Experimental timeline. Drinking rats first had 3 months of Intermittent Access to two-bottle choice drinking of alcohol (IA2BC), then ~2 months of Limited Access Drinking (20 min/d 5 d/wk alcohol). Alcohol-naïve were age-matched (see Section 4). Behavior tests were at the same time when drinkers would normally have access to alcohol, but no alcohol was given before the Elevated T-Maze (ETM) or other tests. On ETM test day, rats were injected with 0.75 mg/kg prazosin or vehicle 30 min before ETM testing. After ETM testing, rats drank alcohol for 20 min that day and returned to Limited Access Drinking. One week after ETM, rats were injected with prazosin or vehicle (the same treatment, within-rat, as occurred during ETM) and then tested in the Light Dark box Task (LDT) and then 10 min later in open field. ETM, LDT, and open field details are in Section 4.

Figure 2

α1ARs regulate escape in ETM in alcohol drinkers but not alcohol-naive. (A) Latency to enter the open arms from the closed arm. Longer latency from baseline to avoidance tests 1 and 2 indicates learning to avoid entering the open arm, a critical first step to assure proper ETM behavioral responding. Learned avoidance, or lack thereof, is then typically compared during the Avoidance 2 trial. No significant differences looking at interactions between trial and drinking [F(2,116) = 2.953, p = 0.056], trial and treatment [F(2,116) = 0.872, p = 0.421], trial and sex and drinking [F(2,116) = 2.914, p = 0.058], trial and sex and treatment [F(2,116) = 0.032, p = 0.968], trial and drink and treatment [F(2,116) = 1.577, p = 0.211], and between trial and sex and drinking and treatment [F(2,116) = 0.721, p = 0.488]. (B) Latency to escape from the open arm to the closed arm. No interactions between sex and drinking [F(1,58) = 0.022, p = 0.883], sex and treatment [F(1,58) = 0.365, p = 0.548], drinking and treatment [F(1,58) = 0.134, p = 0.716], sex and drinking and treatment [F(1,58) = 1.003, p = 0.321]. Significant main effects and interactions are shown above each figure, with post-hocs indicating differences between a specific pair of conditions. *: p < 0.05.

Figure 3

LDT behaviors. Rats are first placed on the lit side, facing away from the opening to the dark chamber. (A) Latency to first enter the dark chamber. For latency to first enter the dark chamber, there were no interactions between factors. [Sex and Drinking: F(1,61) = 1.190, p = 0.280; Sex and Treatment: F(1,61) = 0.008, p = 0.928; Drinking and Treatment: F(1,61) = 0.053, p = 0.819; Sex and Drinking and Treatment: F(1,61) = 0.202, p = 0.655]. (B) Total time in the lit chamber. No interactions for [Sex and Drinking: F(1,61) = 1.117, p = 0.295; Sex and Treatment: F(1,61) = 0.015, p = 0.903; Drinking and Treatment: F(1,61) = 0.181, p = 0.672; Sex and Drinking and Treatment: F(1,61) = 0.037, p = 0.849]. (C) Time to first re-enter the lit chamber after (A). No interactions for [Sex and Drinking: F(1,61) = 3.657, p = 0.061; Sex and Treatment: F(1,61) = 1.388, p = 0.244; Drinking and Treatment: F(1,61) = 0.042, p = 0.838; Sex and Drinking and Treatment: F(1,61) = 0.137, p = 0.713]. (D) Number of transitions between chambers. A three-way ANOVA showed no interactions for number of transitions [Sex and Drinking: F(1,61) = 3.888, p = 0.054; Sex and Treatment: F(1,61) = 0.695, p = 0.408; Drinking and Treatment: F(1,61) = 0.231, p = 0.633; Sex and Drinking and Treatment: F(1,61) = 0.165, p = 0.686]. (E) Number of rears. Significant main effects and interactions are shown above each figure, with post-hocs indicating differences between a specific pair of conditions. * p < 0.05.