HTR1A and major depressive disorder: Targeting elevated activity of the hypothalamo-pituitary axis or glucocorticoid signaling in anxiety and depression may have several beneficial effects via alteration in the serotonin system via up-regulation of 5-HT1A heteroreceptors, including a preferential effect to enhance hippocampal 5-HT1A receptors which are the most sensitive to glucocorticoids (Meijer and de Kloet, 1998).