The article discusses the heterogeneous mechanisms of the pharmacodynamics of antidepressants that underlie the therapeutic response. Sharing the similar clinical activity, antidepressants determine the development of drug-induced homeostasis by means of different molecular mechanisms (selective or nonselective blockade of monoamine reuptake, inhibition of monoamine oxidase, blockade of certain monoamine receptors). However, an increase of serotonin and other monoamines concentrations in the synapses of the central nervous system is only the initiating factor in the development of specific clinical effects. The latter are probably determined by other neurochemical effects, including changes in the density of postsynaptic receptors and an increase in the synthesis of neurotrophic factors. However, the primary mechanisms that increase monoamine concentrations in the synapses might not always “work properly”, leading to the lack of efficacy of the initial antidepressant, while the probability of the therapeutic response to the subsequent antidepressant remains rather high. Thus, the efficacy of an antidepressant may depend on the baseline differences in the neurochemical state contributing to the pathological “depressive” homeostasis. The heterogeneous neurochemical effects of antidepressants can determine the dissociation of existing neuronal interactions, leading to the development of the new — druginduced — homeostasis. At the same time, it is possible that stimulation of general neurotrophic processes by antidepressants may contribute to the progression and chronicity of pathology due to the ambiguous influence on certain stages of the pathological process. This determines the significance of neurophysiological studies of central disturbances in depression and search of fundamentally new neurochemical targets for the treatment of depressive states associated with various mental disorders.
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