ABSTRACT

According to the monoaminergic hypothesis, depression is related to an impairment of neurotransmission by serotonin, norepinephrine (noradrenaline) and dopamine. These deficiencies can result from several mechanisms: (1) decreased synthesis or increased degradation of neurotransmitters; (2) altered expression or function of the respective neurotransmitter receptors; or (3) impairment of signal transduction systems activated by post-synaptic receptors. Most antidepressant drugs act primarily via the first mechanism, aiming to improve monoaminergic transmission by increasing the presence of neurotransmitters inside the synapse. It is still unclear how the various antidepressants with their different modes of action (e.g. serotonin or norepinephrine re-uptake or degradation inhibitors) finally induce emotional and behavioural improvements.