C57bl 6jico

Mice were obtained at an age of 8 weeks and individually housed upon arrival at constant 12-h dark-light cycle under controlled temperature (21 ± 1°C) and humidity (55 ± 10%) conditions with ad libitum access to food and water. Experiments started after an acclimation period of 1–2 weeks to the housing facility with shifted 12-h dark-light cycle (lights off at 2 p.m.). The illuminance during the light phase was approximately 40 lx, whereas red light was provided during the dark phase. Mice were 9–11-weeks-old during the experiment. Data from 24 male C57BL/6JIco and 27 male C57BL/6NCrl mice (Charles River, Netherlands) were analyzed in these experiments. All studies involving animals were approved by the animal research committee of the VU University Amsterdam according to Dutch regulations and comply with the European Council Directive (86/609/EEC).

Three-week-old DBA/2J@Ico (DBA), CD 1 (CD1; used for Social stimulus, Figure 1a), C57BL/6J@Ico (C57, used for correlation experiment) male and female mice were purchased from Charles River Laboratories (Calco, Italy). Mice were group-housed on a 12:12 light:dark cycle with lights on at 0700 hours. For the production of pups, DBA mice were mated at 12 weeks of age, and only litters with a number of pups variable between four and eight were included. All procedures were carried out in accordance with European legislation (EEC no. 86/609) and Italian national legislation (DL no. 116/92) governing the use of animals for research. Behavioral, gene/protein expression, correlation and pharmacological experiments were performed in separate groups of animals, resulting in a total number of 133 mice. The experimental sample size was determined with the aid of an online available software (http://www.stat.ubc.ca/~rollin/stats/ssize). Previous experiments that were performed in our laboratory provided the values (for example, means and common s.d.) that are required for the calculation. The investigators were blinded to the group allocation during the experiments and data analysis.

Male C57BL/6JIco (Charles River, Como, Italy) were purchased at 6–7 weeks of age and housed four per cage on a 12-h light–dark cycle (lights on between 07.00 a.m. and 07.00 p.m.) for 3 weeks. Two days before experiments, animals were individually housed. Each experimental group consisted of 7–10 animals. All experiments were carried out in accordance with Italian national law (DL 116/92 and DL 26/2014) on the use of animals and with the European Communities Council Directives (86/609/EEC and 2010/63/UE), and approved by the ethics committee of the Italian Ministry of Health (license/approval ID #: 10/2011-B and 42/2015-PR).