Antidepressants and synaptic plasticity: a hypothesis

The assumption is introduced that there are two types of adaptive responses in central neurons in response to significantly changed circuit activity. Morphological synaptic modifications and synapse turnover are thought to be involved in both of these responses, in such a way that in the first case they are to restore the circuit activity level as it was in the past, and in the second case they are to switch it to a new pattern. The events eliciting synaptogenesis are proposed to be different in these instances. The role of compensatory extrasynaptic receptors insertion and preferential insertion of synaptic receptors induced by enhanced presynaptic activity are discussed. The hypothesis as to how these two adaptive responses come into action during depression and antidepressant treatment is then proposed.