One series of sections were collected in 10% formaldehyde solution in 0.1 M PB (pH 7.4) and postfixed at 4°C for 4 weeks prior to Nissl staining with thionin. All other series were collected in tissue collection solution (TCS) and kept at −70°C until further processing (see below for c-fos immunohistochemistry). The procedure for Nissl-stained sections followed our standard laboratory protocol (Lavenex et al. 2009 (link)). Briefly, sections were taken from the 10% formaldehyde solution, thoroughly washed, mounted on gelatin-coated slides, and air-dried overnight at 37°C. Sections were then defatted 2 × 2 hours in a mixture of chloroform/ethanol (1:1, vol.), partially rehydrated and air-dried overnight at 37°C. Sections were then fully rehydrated and stained 20 seconds in a 0.25% thionin solution (Fisher Scientific, Waltham, MA, USA; T-409), dehydrated, and coverslipped with DePeX (VWR chemicals, Radnor, PA, USA; 361254D).