Participation of the Monoaminergic System in the Antidepressant-Like Actions of Estrogens: A Review in Preclinical Studies

Estrogens are steroid hormones produced by gonads that bind to different receptor types and mediate numerous actions, like growth, development, cognition, neuroprotection and participate in mood regulation (Margeat et al., 2003; Vasudevan & Pfaff, 2007). The classic estrogen receptors (ER) are: ER┙ and ER┚. These receptors are ligand-activated transcription factors (Kuiper & Gustafsson, 1997) with nuclear and non-nuclear distribution (Monje & Boland, 2001; Weiser et al., 2008). In ovariectomized rats, ER┚ and ER┙ are colocalized in various brain regions, including the bed nucleus of the stria terminalis, the medial and cortical amygdaloid nuclei, the preoptic area, the lateral habenula, the periacueductal gray, the locus coeruleus, the hippocampus and the brain cortex (Shughrue et al., 1997). In these last two structures, ER┚ is more abundant than ER┙. Other structures that contain only ER┚ are the olfactory bulb, the ventral tegmental area, the zona incerta, the cerebellum, the pineal gland and some hypothalamic nuclei (such as the supraoptic, the paraventricular, the supraquiasmatic and the tuberal nuclei). By contrast, brain areas with solely ER┙ are the ventromedial hypothalamic nuclei and the subfornical organ (Shughrue et al., 1997).