Individuals taking tricyclics antidepressants (amitriptyline in particular) had a lower probability of initiating dopaminergic therapy within the first year of their study. This observation suggested to the researchers that treatment with tricyclic antidepressants may delay the need to initiate dopamine therapy for Parkinson’s.
Amitriptyline treatment resulted in an increase in BDNF in the substantia nigra region both before and during ongoing degeneration, suggesting it may contribute to neuroprotection observed in vivo. Amitriptyline treatment also resulted in an increase in GDNF levels but only before the neurotoxin was given
they concluded that the neuroprotective effect seen in their model was most likely due to the increase in BDNF levels.
Tricyclic antidepressant treatment evokes regional changes in neurotrophic factors over time within the intact and degenerating nigrostriatal system
ncbi.nlm.nih.gov/pmc/articl...
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Amitriptyline for sleep:
In addition to its increasing BDNF and therefore slowing neurodegeneration, might help with sleep.