Chronic Alcohol Drinking Drives Sex-Specific Differences in Affective Behavior and Medial Prefrontal Cortex Activity in CRF1:Cre:Tdtomato Transgenic Rats

In 2021, 131 million adult Americans reported drinking alcohol in the last month, despite the well-known consequences of alcohol consumption. While alcohol use disorders are associated with both mood and chronic pain disorders, the relationship between alcohol drinking and affective and nociceptive behaviors remains unclear. Corticotropin releasing factor receptor-1 (CRF1) has been implicated in alcohol drinking, affective states, and pain sensitivity; often in a sex-dependent manner. In order to probe the effects of alcohol drinking on activity of CRF1+ cells and to also test the hypothesis that alcohol drinking is associated with both basal and subsequent affective and nociceptive readouts, we put male and female CRF1:cre:tdTomato rats through a battery of behavioral tests before and after intermittent access to alcohol. Following baseline testing, rats began alcohol (or water) drinking. Females consumed more alcohol in the first week, but there was no effect of sex on overall alcohol intake. Following 3-4 weeks of drinking, behavioral tests were repeated. Alcohol drinking decreased mechanical sensitivity, but no other effects of alcohol drinking were observed between experimental groups. Individual alcohol intake correlated with affective behavior in both sexes but only correlated with thermal sensitivity in males. There were no main effects of alcohol drinking or sex on CRF1+ neuronal activity in the medial prefrontal cortex but final session alcohol intake correlated with activity in CRF1+ neurons in the infralimbic subregion. Together, our results suggest complex interplay between affective state, alcohol drinking, and the role of prefrontal CRF1+ neurons in mediating these behaviors.SIGNIFICANCE STATEMENTDespite alcohol use being extremely comorbid with mood and pain disorders, there is still a limited understanding of the interaction and directionality between the them. To investigate this problem, rats were tested for affective behavior before and after being allowed to drink alcohol for 6 weeks. While baseline behavior did not predict subsequent intake, alcohol intake predicted subsequent affective behavior on an individual subject basis. These findings were accompanied by increased activity of the corticotropin releasing factor 1 containing neurons in the infralimbic region of the prefrontal cortex. Together, these findings reveal a new mechanism for understanding alcohol use.

Sex-specific effects of psychedelic drug exposure on central amygdala reactivity and behavioral responding

Psilocybin and its active metabolite psilocin have been shown to elicit rapid and long-lasting symptom improvements in a variety of affective psychiatric illnesses. However, the region-specific alterations underlying these therapeutic effects remain relatively unknown. The central amygdala (CeA) is a primary output region within the extended amygdala that is dysregulated in affective psychiatric disorders. Here, we measured CeA activity using the activity marker c-Fos and CeA reactivity using fiber photometry paired with an aversive air-puff stimulus. We found that psilocin administration acutely increased CeA activity in both males and females and increased stimulus specific CeA reactivity in females, but not males. In contrast, psilocin produced time-dependent decreases in reactivity in males, but not in females, as early as 2 days and lasting to 28 days post administration. We also measured behavioral responses to the air-puff stimulus and found sex-dependent changes in threat responding but not exploratory behavior or general locomotion. Repeated presentations of the auditory component of the air-puff were also performed and sex-specific effects of psilocin on CeA reactivity to the auditory-alone stimulus were also observed. This study provides new evidence that a single dose of psilocin produces sex-specific, time-dependent, and enduring changes in CeA reactivity and behavioral responding to specific components of an aversive stimulus.

The effects of electronic nicotine vapor on voluntary alcohol consumption in female and male C57BL/6 J mice

SIGNIFICANCE

Alcohol drinking and nicotine vaping often co-occur and dependence on both substances is common. However, the impact of nicotine vaping on alcohol consumption is not fully understood.

METHODS

We examined the effects of nicotine vaping on ethanol drinking in female and male C57BL/6 J mice using an electronic nicotine delivery system and intermittent access two-bottle choice (IA-2BC) drinking. Mice were exposed to electronic nicotine vapor (3%) or propylene glycol/vegetable glycerol (PG/VG) control for 3 h sessions daily for 4 weeks and voluntary alcohol consumption was monitored. Nicotine vapor exposure was stopped and voluntary alcohol drinking was measured for a 2 week abstinence period. We also examined the effects of alcohol and nicotine on locomotion, temperature, and nicotine metabolism.

RESULTS

Following acute nicotine vapor exposure, alcohol drinking was increased in males but not in females. Thermoregulation was disrupted following nicotine vapor exposure and voluntary drinking. Male and female mice displayed increased locomotor activity immediately following chronic nicotine vapor exposure, and an anxiolytic effect was seen in males. In nicotine vapor abstinence, female mice displayed increased alcohol consumption. Locomotor activity and anxiolytic effects remained elevated in male but not female mice. Female mice displayed higher levels of serum nicotine and hydroxycotinine, suggesting impaired metabolism following chronic drinking and nicotine vapor exposure.

CONCLUSION

Collectively, these results suggest that while both male and female ethanol-drinking mice experience the stimulatory effects of nicotine vapor, only in males is there a parallel increase in ethanol drinking and only females display impairments in nicotine metabolism after drinking.

Sex differences in affective states and association with voluntary ethanol intake in Sprague-Dawley rats

Alcohol use disorders (AUDs) are a major problem across the USA. While AUD remains a complex human condition, it is difficult to isolate the directionality of anxiety and ethanol (EtOH) drinking from outside influences. The present study sought to investigate the relationship between affective states and EtOH intake using male and female Sprague-Dawley rats. Using complementary tests of anxiety- and depressive-like behavior, we found sex- and test-specific differences in basal affective behavior such that females displayed enhanced anxiety-like behavior in the splash test and males displayed enhanced anxiety-like behavior in the novelty-suppressed feeding test. Although, there were no sex differences in EtOH intake and no correlation between baseline anxiety-like behavior and subsequent EtOH intake, we did find that depressive-like behavior predicted future EtOH intake in female rats only. In addition, we observed an increase in depressive-like behavior is male rats in both the water and EtOH drinking groups (compared to baseline levels). Furthermore, post-drinking anxiety-like behavior, but not depressive-like behavior predicted subsequent EtOH intake in female rats. Lastly, we found a history of EtOH intake decreased pain thresholds in male and female rats, but increased anxiety-like and depressive-like behavior was associated with decreased thermal sensitivity only in EtOH-drinking males. Together, these experiments provide important information on the complex interaction between negative affect and EtOH intake and how these two contexts reciprocally do, or do not, influence each other in a sex-specific manner.

Sex-specific plasticity in CRF regulation of inhibitory control in central amygdala CRF1 neurons after chronic voluntary alcohol drinking

Despite strong preclinical evidence for the ability of corticotropin releasing factor 1 (CRF1) antagonists to regulate alcohol consumption, clinical trials have not yet demonstrated therapeutic effects of these compounds in alcohol use disorder (AUD) patients. Several confounding factors may limit the translation of preclinical CRF1 research to patients, including reliance on experimenter-administered alcohol instead of voluntary consumption, a preponderance of evidence collected in male subjects only and an inability to assess the effects of alcohol on specific brain circuits. A population of particular interest is the CRF1-containing neurons of the central amygdala (CeA). CRF1 CeA neurons are sensitive to ethanol, but the effects of alcohol drinking on CRF signalling within this population are unknown. In the present study, we assessed the effects of voluntary alcohol drinking on inhibitory control of CRF1+ CeA neurons from male and female CRF1:GFP mice using ex vivo electrophysiology and determined the contributions of CRF1 signalling to inhibitory control and voluntary alcohol drinking. Chronic alcohol drinking produced neuroadaptations in CRF1+ neurons that increased the sensitivity of GABA_A receptor-mediated sIPSCs to the acute effects of alcohol, CRF and the CRF1 antagonist R121919, but these adaptations were more pronounced in male versus female mice. The CRF1 antagonist CP-154,526 reduced voluntary alcohol drinking in both sexes and abolished sex differences in alcohol drinking. The lack of alcohol-induced adaptation in the female CRF1 system may be related to the elevated alcohol intake exhibited by female mice and could contribute to the ineffectiveness of CRF1 antagonists in female AUD patients.

Enhanced locomotor adaptation aftereffect in the "broken escalator" phenomenon using anodal tDCS

The everyday experience of stepping onto a stationary escalator causes a stumble, despite our full awareness that the escalator is broken. In the laboratory, this "broken escalator" phenomenon is reproduced when subjects step onto an obviously stationary platform (AFTER trials) that was previously experienced as moving (MOVING trials) and attests to a process of motor adaptation. Given the critical role of M1 in upper limb motor adaptation and the potential for transcranial direct current stimulation (tDCS) to increase cortical excitability, we hypothesized that anodal tDCS over leg M1 and premotor cortices would increase the size and duration of the locomotor aftereffect. Thirty healthy volunteers received either sham or real tDCS (anodal bihemispheric tDCS; 2 mA for 15 min at rest) to induce excitatory effects over the primary motor and premotor cortex before walking onto the moving platform. The real tDCS group, compared with sham, displayed larger trunk sway and increased gait velocity in the first AFTER trial and a persistence of the trunk sway aftereffect into the second AFTER trial. We also used transcranial magnetic stimulation to probe changes in cortical leg excitability using different electrode montages and eyeblink conditioning, before and after tDCS, as well as simulating the current flow of tDCS on the human brain using a computational model of these different tDCS montages. Our data show that anodal tDCS induces excitability changes in lower limb motor cortex with resultant enhancement of locomotor adaptation aftereffects. These findings might encourage the use of tDCS over leg motor and premotor regions to improve locomotor control in patients with neurological gait disorders.