Neuropharmacology of pineal secretions

A connection between pineal function and several psychiatric diseases has been shown recently. The diurnal and seasonal rhythmicity of melatonin production is associated with affective disorders and several types of endogenous depression. The cortisolmelatonin ratio was significantly higher in depressed individuals than in healthy controls. Alterations in melatonin secretion may also occur in non-affective psychiatric disorders, such as chronic schizophrenia. Antidepressants and other psychotropic drugs modify melatonin synthesis. In rodents, monoamine oxidase (MAO) inhibitors (e.g. pheniprazine, harmine or nialamide) increase pineal concentrations of the melatonin precursors, serotonin (5HT) and N-acetyl serotonin (NAS), by enhancing N-acetyl transferase activity. These drugs also increase melatonin, 5HT and NAS in the cerebrospinal fluid. Chronically administered tricyclic antidepressants reduce pineal and serum melatonin content in rodents. In humans, both the MAO-A selective inhibitor clorgyline and the non-selective inhibitor tranylcypromine increase serum melatonin levels. In contrast, serum melatonin remains unaltered by the MAO-B selective inhibitor L-deprenyl. The actions of other drugs on melatonin production, including lithium, propranolol, amphetamine and several monoamine precursors, are in accordance with their psychotropic effects and with their effect on monoamine functions.