Using lickometry to infer differential contributions of salience network regions during compulsion-like alcohol drinking

Sex- and estrous-related response patterns for alcohol depend critically on the level of compulsion-like challenge

Alcohol use disorder is a substantial social and economic burden. During the last years, the number of women with drinking problems has been increasing, and one main concern is that they are particularly more vulnerable to negative consequences of alcohol. However, little is known about female-specific response patterns for alcohol, and potential underlying differences in brain mechanisms, including for compulsion-like alcohol drinking (when intake persists despite adverse consequences). We used lickometry to assess behavioral microstructure in adult Wistar male and female rats (n = 28-30) during alcohol-only drinking or moderate- or higher-challenge alcohol compulsion (10 or 60 mg/l quinine in alcohol, respectively). Estrous stages were determined and related to drinking levels and patterns of responding to alcohol, as was ovariectomy. Our findings showed that females (where we didn't determine estrus stage) had similar total licks in a session as males, but significantly longer licking bouts under alcohol-only and moderate-challenge, suggesting greater persistence. Further, greater intake under alcohol-only and moderate-challenge was related to faster licking in males, while female consumption was not related to licking speed. Thus, females could have increased persistence without greater vigor, unlike males. However, under higher-challenge, faster licking did predict higher intake in females, similar to males. To better understand female higher-challenge responding, we examined drinking in relation to phases of the estrous cycle. Higher-challenge had longer bouts only in late diestrus. In addition, ovariectomy led to longer bouts only under higher-challenge, suggesting that conditions with reduced hormone levels could increase female persistence for alcohol under higher-challenge. However, ovariectomy also reduced alcohol-only and moderate-challenge drinking but did not reduce bout length. Thus, intake level and response strategy could be regulated somewhat differently by ovarian hormones. Finally, moderate-challenge licking speed was less variable during early diestrus, and we previously showed more stereotyped responding specifically under moderate-challenge in males. By combining behavioral microstructure and sex- and estrus-related changes in drinking patterns, our results suggest that females have greater persistence for alcohol under lower-challenge drinking, while late diestrus and ovariectomy unmasked greater persistence under higher-challenge. Together, our novel insights could help develop more effective and personalized treatments for problematic alcohol use.

Sex differences in heart rate variability measures that predict alcohol drinking in rats

Problem alcohol drinking continues to be a substantial cost and burden. In addition, alcohol consumption in women has increased in recent decades, and women can have greater alcohol problems and comorbidities. Thus, there is a significant need for novel therapeutics to enhance sex-specific, individualized treatment. Heart rate (HR) and HR variability (HRV) are of broad interest because they may be both biomarkers for and drivers of pathological states. HRV reflects the dynamic balance between sympathetic (SNS, 'fight or flight') and parasympathetic (PNS, 'rest and digest') systems. Evidence from human studies suggest PNS predominance in women and SNS in men during autonomic regulation, indicating the possibility of sex differences in risk factors and physiological drivers of problem drinking. To better understand the association between HRV sex differences and alcohol drinking, we examined whether alcohol consumption levels correlated with time domain HRV measures (SDNN and rMSSD) at baseline, at alcohol drinking onset, and across 10 min of drinking, in adult female and male Wistar rats. In particular, we compared both HRV and HR measures under alcohol-only and compulsion-like conditions (alcohol + 10 mg/L quinine), because compulsion can often be a significant barrier to treatment of alcohol misuse. Importantly, previous work supports the possibility that different HRV measures could be interpreted to reflect PNS versus SNS influences. Here, we show that females with higher putative PNS indicators at baseline and at drinking onset had greater alcohol consumption. In contrast, male intake levels related to increased potential SNS measures at drinking onset. Once alcohol was consumed, HR predicted intake level in females, perhaps a pharmacological effect of alcohol. However, HRV changes were greater during compulsion-like intake versus alcohol-only, suggesting HRV changes (reduced SNS in females, reduced PNS and increased HR in males) specifically related to aversion-resistant intake. We find novel and likely clinically relevant autonomic differences associated with biological sex and alcohol drinking, suggesting that different autonomic mechanisms may promote differing aspects of female and male alcohol consumption.

Heart rate variability measures indicating sex differences in autonomic regulation during anxiety-like behavior in rats

Introduction

Mental health conditions remain a substantial and costly challenge to society, especially in women since they have nearly twice the prevalence of anxiety disorders. However, critical mechanisms underlying sex differences remain incompletely understood. Measures of cardiac function, including heart rate (HR) and HR variability (HRV), reflect balance between sympathetic (SNS) and parasympathetic (PNS) systems and are potential biomarkers for pathological states.

Methods

To better understand sex differences in anxiety-related autonomic mechanisms, we examined HR/HRV telemetry in food-restricted adult rats during novelty suppression of feeding (NSF), with conflict between food under bright light in the arena center. To assess HRV, we calculated the SDNN (reflective of both SNS and PNS contribution) and rMSSD (reflective of PNS contribution) and compared these metrics to behaviors within the anxiety task.

Results

Females had greater HR and lower SNS indicators at baseline, as in humans. Further, females (but not males) with higher basal HR carried this state into NSF, delaying first approach to center. In contrast, males with lower SNS measures approached and spent more time in the brightly-lit center. Further, females with lower SNS indicators consumed significantly more food. In males, a high-SNS subpopulation consumed no food. Among consumers, males with greater SNS ate more food.

Discussion

Together, these are congruent with human findings suggesting women engage PNS more, and men SNS more. Our previous behavior-only work also observed female differences from males during initial movement and food intake. Thus, high basal SNS in females reduced behavior early in NSF, while subsequent reduced SNS allowed greater food intake. In males, lower SNS increased engagement with arena center, but greater SNS predicted higher consumption. Our findings show novel and likely clinically relevant sex differences in HRV-behavior relationships.