Browsing by Subject "BDNF"

Accumulating evidence indicates that the plasticity-inducing effects of conventional antidepressant drugs like fluoxetine are mediated by their direct binding to TrkB. TrkB is the receptor of the brain-derived neurotrophic factor (BDNF), a neurotrophic factor of critical importance for neuron survival and synaptic plasticity. In addition, it has recently been reported that LSD and psilocybin, two psychedelic compounds with therapeutic potential, also bind to TrkB with higher affinity than antidepressants. It has been proposed that the differences in binding affinity between conventional antidepressants and psychedelics may help explain the much faster and longer-lasting antidepressant effects of psychedelics. Psychedelics and classical antidepressants bind to the transmembrane domain of TrkB dimers, where they act as positive allosteric modulators by potentiating the action of endogenous BDNF. The transmembrane binding sites of LSD and fluoxetine, despite being partially overlapping, are distinct and induce different conformational changes when bound to TrkB dimers. However, it is still unknown whether there are differences in the TrkB dimerization dynamics and neurotrophic signalling pathways induced by psychedelics when compared to conventional antidepressants. In this study, we investigated whether psychedelics and classical antidepressants promote TrkB dimerization and neurotrophic signalling in a differential manner. The effects of psychedelics on the TrkB dimerization dynamics and neurotrophic signalling associated with plasticity were studied treating N2a cells and primary cortical neuronal cultures with LSD or fluoxetine. Dimerization of the TrkB receptor in the presence of experimental compounds is assayed by protein-fragment complementation assay (PCA). Results show a significant dimerization in cells treated with LSD, whereas non-significant response in the ones treated with fluoxetine. The phosphorylation state of the neuronal TrkB receptor in three different tyrosines (Y515, Y706, and Y816) was checked as a marker of its activation by Western blot. Primary cortical cultures were treated with classical antidepressant fluoxetine (10uM) or psychedelic LSD (100nM) for 1 hour, when their effects on TrkB phosphorylation were compared. This experiment showed a significant increase of phosphorylation in TrkB Y816 after LSD treatment in cortical neuronal cultures, while fluoxetine treatment showed no significant effect. This indicates that LSD is able to activate the BDNF-TrkB signalling pathway associated with PLCg1 recruitment and induction of plasticity at an early time point and with a much lower concentration than fluoxetine, which would support LSD’s much more potent antidepressant and plasticity-inducing effects when compared to fluoxetine’s. Together, these results suggest that psychedelics that bind to TrkB, like LSD, are more potent than classical antidepressants in inducing TrkB-BDNF signalling. Overall, this study provides further evidence that TrkB is a critical mediator of psychedelics’ actions on neurotrophic signalling preceding their plasticity-enhancing and antidepressant effects and sheds more light on the common and differential mechanisms used by psychedelics and conventional antidepressants to produce their therapeutic effects.