Probably the first biologic urges of primitive man were what are now called instincts. Closely associated with instincts are the emotions. The emotions represent psychic responses to internal and especially to external stimuli. These responses are mediated through the central and autonomic nervous systems and the hormones of the endocrine glands.
It is known that dysfunction of these ductless glands, by over or under supply of their hormones, can so disturb persons emotionally that they manifest psychoses. Thus psychoses occur in cases of hyperthyroidism, hypothyroidism and pituitary-gonad imbalance. The hormonal conflicts of pregnancy and the necessary postpartum readjustments may cause profound disturbances of the personality. Tremendous emotional upsets result also from fright, fear and anger. Under these conditions a large amount of epinephrine is released by the adrenal glands. This epinephrine acts on the neuromuscular end plates of the sympathetic division of the autonomic nervous system and prepares the person
WERNER AA, HOCTOR EF, AULT CC. INVOLUTIONAL MELANCHOLIAA REVIEW WITH ADDITIONAL CASES. Arch NeurPsych. 1941;45(6):944-952. doi:10.1001/archneurpsyc.1941.02280180056002