Nucleus Accumbens Shell Orexin-1 Receptors Are Critical Mediators of Binge Intake in Excessive-Drinking Individuals

Abstract

Excessive, binge alcohol drinking is a potent and pernicious obstacle to treating alcohol use disorder (AUD), and heavy-drinking humans are responsible for much of the substantial costs and harms of AUD. Thus, identifying key mechanisms that drive intake in higher-drinking individuals may provide important, translationally useful therapeutic interventions. Orexin-1-receptors (Ox1Rs) promote states of high motivation, and studies with systemic Ox1R inhibition suggest a particular role in individuals with higher intake levels. However, little has been known about circuits where Ox1Rs promote pathological intake, especially excessive alcohol consumption. We previously discovered that binge alcohol drinking requires Ox1Rs in medial nucleus accumbens shell (Shell), using two-bottle-choice Drinking-in-the-Dark (2bc-DID) in adult, male C57BL/6 mice. Here, we show that Shell Ox1Rs promoted intake during intermittent-access alcohol drinking as well as 2bc-DID, and that Shell inhibition with muscimol/baclofen also suppressed 2bc-DID intake. Importantly, with this large data set, we were able to demonstrate that Shell Ox1Rs and overall activity were particularly important for driving alcohol consumption in higher-drinking individuals, with little overall impact in moderate drinkers. Shell inhibition results were compared with control data combined from drug treatments that did not reduce intake, including NMDAR or PKC inhibition in Shell, Ox1R inhibition in accumbens core, and systemic inhibition of dopamine-1 receptors; these were used to understand whether more specific Shell Ox1R contributions in higher drinkers might simply result from intrinsic variability in mouse drinking. Ineffectiveness of Shell inhibition in moderate-drinkers was not due to a floor effect, since systemic baclofen reduced alcohol drinking regardless of basal intake levels, without altering concurrent water intake or saccharin consumption. Finally, alcohol intake in the first exposure predicted consumption levels weeks later, suggesting that intake level may be a stable trait in each individual. Together, our studies indicate that Shell Ox1Rs are critical mediators of binge alcohol intake in higher-drinking individuals, with little net contribution to alcohol drinking in more moderate bingers, and that targeting Ox1Rs may substantially reduce AUD-related harms.

Differential importance of nucleus accumbens Ox1Rs and AMPARs for female and male mouse binge alcohol drinking

“…Here, we demonstrate that shell Ox1Rs did not regulate binge alcohol drinking in female C57BL/6 mice, in strong contrast to our previously demonstrated Ox1R regulation of binge intake in male mice 29 , 43 . However, lower doses of systemic Ox1R inhibition did reduce compulsion-like alcohol drinking in females, similar to males 48 , indicating that females have Ox1Rs that can regulate some aspects of pathological alcohol-directed behavior.…”

“…All procedures followed Guide for Care and Use of Laboratory Animals provided by the NIH, with approval of the UCSF IACUC. Single housed adult C57BL6/J mice (Jackson Labs) drank under a limited daily access (LDA) paradigm, which is a two-bottle choice (2BC) variant of Drinking-in-the-Dark (with 15% alcohol (v/v) versus water), as we 29 , 43 , 48 , 54 (see also 55 ) have used previously. At 7–8 weeks of age, mice had a single 24-h 2BC session.…”

“…Thereafter, we began intracranial injection experiments (details below). These methods and those below were the same as those used in our previous studies of shell Ox1Rs in male mice 29 , 43 , 48 , 54 . Systemic injection studies occurred with equivalent timing except without surgery.…”

“…For saccharin drinking (tested in separate cohorts of mice), the timing and length of the session across days was the same as for alcohol, except mice instead consumed 0.05% saccharin. We have previously used this 29 , 43 , 48 since mice drink approximately the same volume of this concentration of saccharin as with alcohol. Blood alcohol concentrations were determined exactly as previously described 48 .…”

“…Orexin/hypocretins regulate many adaptive behavioral and physiological responses 37 , 38 , and Ox1Rs are of particular interest because they drive responding for high-value natural and drug rewards, including alcohol, with little role for less-motivating substances 37 – 42 . Indeed, shell Ox1R inhibition decreases binge intake in males, especially higher drinkers 29 , 43 (as seen with systemic block of Ox1Rs 44 – 46 ), and systemic Ox1R inhibition reduces many forms of pathological alcohol intake 38 , 44 – 50 . In addition, calcium-permeable AMPARs (CP-AMPARs) are observed in the shell after exposure to alcohol 51 – 53 and other intoxicants and stress-related conditions (see 22 ).…”