Fig. 1: Timeline of the experiments.

Timeline of the four experiments carried out on independent cohorts of male Sprague Dawley rats. Experiment 1: Following a week of habituation to the animal facility, thirty-six rats received bilateral cannulation of their anterior dorsolateral striatum (aDLS). A week later, rats were food restricted to 85% of their theoretical free-feeding weight and trained in a schedule-induced polydipsia (SIP) procedure with water (SIPw). The reliance of the acquisition of adjunctive water drinking on aDLS dopaminergic mechanisms was assessed after 5 SIPw sessions as the sensitivity of drinking behavior to bilateral infusion of the dopamine (DA) receptor antagonist α-flupentixol (α-flu, 0, 6, 12 μg/side, between-subject design) into the aDLS (Test 1, α-flu Early SIPw). Experiment 2: Following a week of habituation to the animal facility, forty-eight rats were food restricted for a week before being trained in the SIPw procedure for 20 sessions, e.g., until the establishment of hyperdipsia in vulnerable individuals. Then, rats were implanted with bilateral cannulae targeting the aDLS and, after at least a week, they were re-baselined under SIPw for 10 sessions. Then, the reliance of well-established, compulsive, adjunctive water drinking behavior on aDLS DA was assessed as the sensitivity of water drinking behavior to bilateral infusion of α-flupentixol (0, 6, 12 μg/side, within-subject design) into the aDLS (Test 2, α-flu Late SIPw). Subsequently, water was replaced by 10% alcohol (SIPa) and the reliance of early and well-established adjunctive alcohol drinking on aDLS DA was measured after 3 (Test 3, α-flu Early SIPa) or 20 (Test 4, α-flu Late SIPa) SIPa sessions, respectively. Experiment 3: In order to test the stability of water intake levels once adjunctive water drinking has been established, ten rats were food restricted after a week of habituation to the colony, and then trained in the SIP procedure for 40 sessions, a period of training similar to that used in experiment 2, but with water as the only available solution throughout. Experiment 4: In order to establish the anxiolytic properties of polydipsic drinking under SIP at the population level but also, specifically in individuals that relied on alcohol to engage in a coping strategy, forty-seven rats were habituated to the animal facility and food restricted for a week before their anxiety levels were assessed as the percentage of time spent in the open arms of an elevated plus maze (EPM) prior to (naïve, EPM 1), and immediately following a session after at least 20 days of training under SIPw (EPM 2) or SIPa (EPM 3).W: week; s: session.