Sex Differences in the Physiological Response to Ethanol of Rat Basolateral Amygdala Neurons Following Single-Prolonged Stress

Abstract

Females are more likely to develop post-traumatic stress disorder (PTSD) than males. Also, symptoms of PTSD frequently precede alcohol abuse in females. Stressful, threat-related stimuli are evaluated by the amygdala, which is critical for establishing the emotional salience of environmental stimuli. Ethanol and stress have been shown to modify amygdala excitability, but effects of acute ethanol on neurons of the basolateral amygdala (BLA) in both males and females exposed to stress is unknown. The purpose of this study is to determine stress-induced changes in membrane properties of BLA neurons and to determine how ethanol modulates these changes in male and female rats. Whole-cell recordings were obtained from BLA neurons of both male and female rats exposed to single-prolonged stress (SPS). Neuronal excitability, quantified as the number of action potentials, was determined in current clamp mode by applying a series of depolarizing current steps. Hyperpolarization-activated current (Ih) was elicited in voltage clamp. Excitability and Ih amplitude were determined before and during the superfusion of ethanol (EtOH; 30 mM) in BLA neurons from SPS-treated male and female rats. SPS alone did not alter the firing properties of BLA neurons from either males or females. However, following SPS, BLA neurons from males and females respond differently to ethanol. Superfusion of EtOH (30 mM) inhibited spike firing in BLA neurons from rats exposed to SPS, and EtOH-induced inhibition was greater in females than in males exposed to stress. Also, EtOH (30 mM) selectively decreased Ih amplitude in BLA neurons from SPS-treated male rats from 171 ± 46 pA in (pre-EtOH) control to 53 ± 51 pA in the presence of EtOH (30 mM). EtOH did not reduce Ih in BLA neurons from SPS-treated females. Together, these suggest important sex differences in the physiological responses to EtOH in stress disorders such as PTSD, that have high comorbidity with alcohol use disorders.

Increased alcohol self-administration following exposure to the predator odor TMT in active coping female rats

“…First, the mechanisms by which stress impacts alcohol drinking may be different between male and female rats. For example, female, but not male rats show greater ethanol-induced inhibition on action potential firing in basolateral amygdala (BLA) neurons following exposure to the single prolonged stress (SPS) model, suggesting that ethanol plays a larger role in modulating stress-induced excitability in females [51]. In addition, ethanol selectively decreased the amplitude of hyperpolarization-activated current in BLA neurons in SPS-treated males, but not SPS-treated females, further suggesting sex differences in physiological mechanisms that regulate neuronal excitability in response to stress and ethanol [51].…”

“…For example, female, but not male rats show greater ethanol-induced inhibition on action potential firing in basolateral amygdala (BLA) neurons following exposure to the single prolonged stress (SPS) model, suggesting that ethanol plays a larger role in modulating stress-induced excitability in females [51]. In addition, ethanol selectively decreased the amplitude of hyperpolarization-activated current in BLA neurons in SPS-treated males, but not SPS-treated females, further suggesting sex differences in physiological mechanisms that regulate neuronal excitability in response to stress and ethanol [51]. In another study, chronic mild stress increased alcohol consumption and preference in female Wistar rats compared to males, as well as an increase in synaptophysin expression in the frontal cortex, suggestive of elevated presynaptic plasticity in females [52].…”

Systematic Review and Methodological Considerations for the Use of Single Prolonged Stress and Fear Extinction Retention in Rodents

“…For example, in an identical number of studies utilizing predator cues to model features of PTSD, of those that reported the biological sex of the animals, 97% used only male rats (3% not specified). Preliminary studies have documented sex-specificity in behavioral and neurological outcomes following SPS, e.g., females do not consistently exhibit the effects of SPS on extinction retention (Keller et al, 2015b;Ornelas and Keele, 2018;Pooley et al, 2018a,b;Nahvi et al, 2019;Nwokafor et al, 2020). However, females are equally sensitive to SPS effects on depressive-like behavior, increased anxiety, and elevated hippocampal glucocorticoid receptor expression (Keller et al, 2015a;Nahvi et al, 2019).…”

The synthetically produced predator odor 2,5-dihydro-2,4,5-trimethylthiazoline increases alcohol self-administration and alters basolateral amygdala response to alcohol in rats

“…One study that examined sex differences in alcohol consumption following predator odor exposure found that only low-drinking female rats increased alcohol consumption (Finn et al, 2018), suggesting that the mechanism by which stress impacts alcohol drinking may be different between sexes. This is supported by data from the single prolonged stress (SPS) model showing potentiation of alcohol-induced inhibition of basolateral amygdala neurons in female rats but not males following stress exposure (Ornelas and Keele, 2018). Other studies have shown sex differences in gene expression following predator odor stress, with females but not males showing upregulations in PFC and hippocampal p450scc, an enzyme responsible for synthesis of neuroactive steroids that can regulate alcohol drinking (Devaud et al, 2018), and males but not females showing changes in hippocampal CREB and ERK (Homiack et al, 2017).…”