Materials and Reagents

1. Tissue paper 
2. Experimental mice (e.g., C57BL/6J and CD1 male mice, 12-16 weeks old, Charles River Laboratory)
3. Stranger mice (STR mice) (e.g., juvenile 3-4 weeks old (postnatal day 21 to 28) male C57BL/6J mice, Charles River Laboratory)
4. 30% ethanol (v/v)

Equipment

1. Vsoc-maze
   We used a modified version of the V-shaped maze (Busquets-Garcia et al., 2011) (Vsoc-maze, Figure 1). It consists of two structures: the maze wall (150 mm high), made of black Plexiglas (6 mm width) and the maze lid, made of transparent Plexiglas. Corridors in the Vsoc-maze are 300 mm long and 45 mm wide (internal measures). Two small chambers (82 mm long) were created at the end of the corridors when the lid was inserted into the Vsoc-maze. These chambers were used to allocate the juvenile stranger mice. The design was deliberately simple to enhance the exploratory activity of the experimental mouse under analysis, and to facilitate the handling of the animals and the cleaning between sessions. 
2. Three-chamber apparatus
   It consisted in a rectangular box made of Plexiglas (405 mm wide x 600 mm long x 150 mm high) divided in three-identical-chambers (405 mm wide x 200 mm long x 150 mm high) by two Plexiglas walls containing small openings, which measure 100 mm wide x 50 mm high, to allow mouse access between chambers as previously described (Kaidanovich-Beilin et al., 2011). The juvenile stranger mice were enclosed in a round wire cage in the side chambers. The wire cage was 110 mm high x 105 mm diameter and had vertical bars spaced 10 mm, which allow sniffing and exploration. There was a weighted cup on top of the wire cage to prevent the experimental animal from climbing. 
3. Video Camera (e.g., Sony Handycam camcorder, HDR-CX240)
4. Stopwatches (x2) (e.g., Sper Scientific, 810029)
   
   
   Figure 1. Design of the Vsoc-maze. Top view (A and C) and side view (B and D) of the Vsoc-maze and the Plexiglas transparent lid showing its dimensions (in mm) used in Martínez-Navarro et al. (2019). Photographs show the Vsoc-maze with the transparent lid (C), and a detail of the lid which includes the Plexiglas bars for mice to interact (D).
   
   
   
   Video 1. Vsoc-maze set-up and mouse handling for the test. (All animal procedures were conducted following ARRIVE (Animals in Research: Reporting In Vivo Experiments) (Kilkenny et al., 2010) guidelines and standard ethical guidelines (European Communities Directive 2010/63/EU) and approved by the local ethical committee (Comitè Ètic d'Experimentació Animal-Parc de Recerca Biomèdica de Barcelona, CEEA-PRBB).)

Software

1. STATISTICA (StatSoft) software, is used to performed the statistical analysis
2. GraphPad Prism software (GraphPad Software, USA) is used for artwork
   

Procedure