FOS and major depressive disorder: We studied the expression of C-Fos expression after the administration of GAL(1–15) + ESC in several nuclei involved in depression and reward-seeking behaviour—lateral (LHb) and medial (mHb) habenula, nucleus accumbens (NAc), prefrontal cortex (CPF) and the rostromedial tegmental nucleus (RMTg)—and performed double immunohistochemical staining of 5-hydroxytryptamine (5-HT) and C-Fos or tyrosine hydroxylase (TH) and C-Fos to study the specific cell activation in the dorsal raphe (DR) and ventral tegmental area (VTA), respectively.