Skip to main content
. 2023 Sep 28;28(11):4666–4678. doi: 10.1038/s41380-023-02256-z

Fig. 2. Individual differences in the tendency to develop compulsive adjunctive behaviors in rat.

Fig. 2

A, B Rats having completed experiments 1 and 2 with cannula tips (orange and violet for experiment 1 and 2, respectively) located in the anterior dorsolateral striatum (aDLS) according to the rat brain atlas (black arrows) [149] as assessed following staining with Cresyl Violet were included in the final analyses. C, D At the population level, and similarly across each independent group for experiment 1, food restricted rats exposed to intermittent food delivery progressively developed adjunctive polydipsic water drinking over five (Experiment 1, n = 22) and twenty (Experiment 2, n = 38) sessions. Experiment was designed to reveal marked individual differences in the tendency to engage in polydipsic water drinking that emerged early on in training. While at the population level individuals developed a polydipsic water drinking response, some individuals, developed an excessive, compulsive polydipsic behavior while others did not engage in a displacement strategy whatsoever. Thus, high drinker (HD) and low drinker rats (LD), selected respectively in the upper and lower quartiles of the population stratified on the average water consumption over the last 3 sessions of SIP with water (Late SIPw, green rectangle), greatly differed in their trajectory of polydipsic water drinking. HD rats developed a compulsive water drinking behavior that reached more than 16.65 ± 1.08 ml/h by the last session, or two times more than the whole population, whereas LD rats maintained throughout a water drinking behavior similar to that associated with their homeostatic need displayed at baseline (B). The introduction of alcohol resulted in significant changes in coping behavior. Thus, HD and LD rats still differed in their level of adjunctive drinking at the beginning of the SIP training with alcohol (Early SIPa, blue rectangle), mostly due to the fact that HD rats, who had developed an hyperdipsia with water persisted following the introduction of alcohol, albeit to a lower level. However, while HD rats maintained overall a steady level of polydipsic alcohol drinking over time, LD rats acquired a coping response with alcohol and eventually developed compulsive polydipsic alcohol drinking so that they no longer differed from HD rats by the end of training (Late SIPa, orange rectangle). This increase in alcohol drinking shown by LD rats was not attributable to an increase in fluid intake over time since once adjunctive drinking was established in an independent cohort of rats over 20 sessions (Experiment 3, n = 10), polydipsic water drinking remained stable so that by session 40 (S40 dashed-line rectangle, average of sessions 38–40) rats displayed a similar level of fluid intake as they did by the end of the first 20 session period (S20 dashed-line rectangle, average of sessions 18–20). The reliance of early (Tests 1 and 3) and well-established (Tests 2 and 4) polydipsic water or alcohol drinking on aDLS DA was assessed as the sensitivity of drinking behavior to bilateral infusion of α-flupentixol (α-flu) at each time point identified by an arrow. ♯ p < 0.001 group × time interaction; *** p < 0.001, ** p < 0.01, HD different from LD rats; ns: no significant.