Experimental design
Fos-TRAP2 mice (n=46) were infused bilaterally in NAc with 300 nL of 1 mg/mL CTB-647 (Invitrogen). At 8-10 days post-surgery, mice were single-caged and, after a further 3-4 days, assigned at random to the following stimulus groups: social reward-social aversion (SR-SA, n=9), SA-SR (n=8) (experimental social mice), SR-SR (n=8), SA-SA (n=8) (control social mice), and no stimulus-no stimulus (No S-No S, n=11). To adjust mice to the procedures of restraint and intraperitoneal (i.p.) injection required for 4-hydroxytamoxifen (4-OHT) administration, on post-surgery days 15-17 they received 2 daily i.p. injections of sterile 0.9% NaCl and 1 i.p. injection of castor oil:sunflower seed oil (1:4, 5 mL/kg). On day 18, mice underwent the first stimulus test, SR or SA (or No S), during t0-90. Directly afterwards they received an i.p. injection of 4-OHT. A period of 7 days was allowed for reporter recombination and expression; this was assumed to be sufficient based on in-house pilot tests and relevant literature . Mice then underwent the second stimulus exposure, SA or SR (or No S), during t0-90. Directly afterwards, mice were deeply anaesthetized by injection of pentobarbital and transcardially perfused-fixed. The brains were further processed for c-Fos immunohistochemistry and quantification of CTB+, tdTomato+, c-Fos+ neurons, and combinations thereof, in the BA.