Nortriptyline, a tricyclic antidepressant, may have both short and long term therapeutic benefits for PD.

The advantages of nortriptyline have been written about in this forum by the late paula_w. In Post 12, 12/10/2010, of the thread "dyskinesias: with or without agonist?" started by lurkingforacure, Paula wrote [1]:

"I must share this because now I'm convinced that sinemet alone with amantadine and nortriptyline (both help dyskinesia and they balance the neuro transmitters)is a good combination.

i'll be saying this till you are sick of it, but we are also lacking norapinephrine and gaba. ... But nortriptyline is also a nerve painkiller and an antipressant with anticholinergic properties so it helps to balance acertycholine, norapinephrine and maybe more of the transmitters."

New research [2], unfortunately the paper is behind a pay-wall, suggests that nortriptyline:

"may slow progression of α-syn pathology by directly binding to soluble, native, α-syn, thereby inhibiting pathological aggregation and preserving its normal functions."

References:

[1] dyskinesias: with or without agonist?

[2] Neurobiol Dis. 2017 Oct;106:191-204. doi: 10.1016/j.nbd.2017.07.007. Epub 2017 Jul 12.
"Nortriptyline inhibits aggregation and neurotoxicity of alpha-synuclein by enhancing reconfiguration of the monomeric form."
Collier TJ1, Srivastava KR2, et al.
Nortriptyline inhibits aggregation and neurotoxicity of alpha-synuclein by enhancing reconfiguration of the monomeric form. - PubMed - NCBI

John