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Free floating sections were first rinsed 4 times for 5 min with 0.05 M Tris-buffered saline (TBS; pH 7.6) to remove cryoprotectant, and subsequently rinsed three times for 5 min with TBS between all incubations with reagents. Sections were exposed to 0.1% hydrogen peroxide for 10 min at room temperature to destroy endogenous peroxidases. The sections were then blocked in TBS containing 20% normal goat serum (NGS) and 0.3% Triton X-100 for 60 min. Sections were then incubated overnight at 4°C in 2% NGS and 0.3% Triton X-100 and the pan-FosB rabbit polyclonal antibody (1:10,000 dilution for a final concentration of 0.02 µg/ml; sc-48 Santa Cruz Biotechnology). After primary antibody incubation, the sections were washed in TBS, and then incubated for 1 h in goat anti-rabbit horseradish peroxidase-conjugated secondary antibody (1:500 dilution) containing 2% NGS and 0.3% Triton X-100 in TBS. Then, the sections were incubated in Vectastain ABC Elite kit (Vector) for 1 h at room temperature before visualizing the immunoreactivity with diaminobenzidine (DAB; 0.5 mg/ml plus NiCl with 0.025% H₂O₂). The sections were rinsed in TBS four times before mounting them onto glass slides. The mounted sections were then put through a series of ethanols and xylene before coverslipping.