BDNF and depressive disorder: The 5-HT2A receptor has attracted particular attention from neuroscientists since it has been shown to be upregulated in depression and anxiety [41] and to regulate the dopaminergic, glutamatergic, noradrenergic and brain-derived neurotrophic factor (BDNF) systems, all of which are relevant to mood regulation, motivation and cognition [17,42,43].