In vivo microdialysis and dopamine release measurements

For the measurements of accumbal dopamine release, the mice were implanted with a microdialysis custom‐made probe (Blomqvist et al. 1993) positioned in NAc shell (coordinates relative to bregma of 1.5 mm AP, ±0.6 ML and 4.7 mm DV were used (Paxinos & Watson 1998)), after surgical procedures that have been previously described in detail (Jerlhag et al. 2009). For protocol description, see Supporting Information.

After 1 hour of habituation to the microdialysis set‐up, perfusion samples were collected in 20‐minute intervals during the entire experimental protocol (from −40 to 260 minutes). The baseline dopamine level was defined as the average of three consecutive samples (−40 to 0 minutes) before the first alcohol (1.75 g/kg, IP) or vehicle (saline solution, IP) challenge (time 0). The dopamine release was determined as the percent increase from baseline.

In the first experiment, an initial alcohol challenge was given to establish that the mice respond with an accumbal dopamine release to alcohol compared with vehicle treatment. Seven consecutive 20‐minute samples were collected after this initial challenge. At 150 minutes, sCT (5 μg/kg, IP) or an equal volume of vehicle (saline solution, IP) was administered. Thirty minutes later, vehicle (saline solution, IP) or alcohol (1.75 g/kg, IP) was administered (180 minutes). Thereafter, four additional samples were collected (experiment terminated at 260 minutes). Collectively, the following three treatment groups were created: alcohol–vehicle–alcohol (Alc‐Veh‐Alc), alcohol–sCT–alcohol (Alc‐sCT‐Alc) and vehicle–sCT–vehicle (Veh‐sCT‐Veh).

In the second microdialysis experiment, the effects of sCT on the initial alcohol‐induced accumbal dopamine release were investigated in animals that received only a single alcohol injection, in order to identify the ability of sCT to affect the initial alcohol‐induced accumbal dopamine release. Firstly, sCT (5 μg/kg, IP) or an equal volume of vehicle (saline solution, IP) was administered after the collection of the three baseline samples at 10 minutes, and 30 minutes later, an alcohol injection (1.75 g/kg, IP) was administered (40 minutes). Thereafter, nine additional samples were collected (experiment terminated at 220 minutes). Collectively, the following two treatment groups were created: vehicle–alcohol (Veh‐Alc) and sCT–alcohol (sCT‐Alc).