Changes in daily and seasonalmood variations [43, 44, 45], brainactivity [46, 47], core body temperature (e.g.,elevation of mean nocturnal body temperature [48]), sleep/wake cycle (e.g., 50 to 90% ofdepressed patients complain about impairment of sleep quality/duration [47]), and hormone secretion(e.g., cortisol, norepinephrine, prolactin, thyroidstimulating hormone [49, 50, 51]) are among the most consistent circadian alterations associated withmajor depression. This evidence concerns the gene PRL and major depressive disorder.