The acute effects of antidepressant treatments on brain norepinephrine (NE) and serotonin (5-HT) systems cannot account fully for their delayed therapeutic action. The effects of long-term antidepressant treatment on biogenic amine metabolism and on various indexes of presynaptic and postsynaptic receptor function. In contrast to variable effects on NE and 5-HT turnover and on presynaptic receptor Doxepin treatments produce consistent alterations in a number of measures of postsynaptic amine receptor sensitivity. Longterm treatment of Doxepin has been found to reduce β-adrenergic sensitivity while enhancing responses to serotonergic and α-adrenergic stimulation, suggesting that modulation of receptor sensitivity may be a mechanism of action common to tricyclic antidepressants, "atypical" antidepressants, monoamine oxidase inhibitors, and electroconvulsive therapy.
REFERENCE-KD TRIPATHI, JAYPEE BROTHERS MEDICAL PUBLISHERS PVT.LTD 7TH EDITION, REPRINT 2001,PG NO.:458,465.