title: Amitriptyline protects against TNF-α-induced atrophy and reduction in synaptic markers via a Trk-dependent mechanism.
abstract: Neuritic degeneration and synaptic loss are features of both neuroinflammation and neurodegenerative disease. The tricyclic antidepressant amitriptyline has neurotrophic and anti-inflammatory properties and acts as a novel agonist of the neurotrophin Trk receptors. Primary cortical neurons were treated with amitriptyline, nortriptyline and NGF and tested for neuronal complexity by Sholl analysis, protein expression by Western immunoblotting, and synapse number by colocalization of pre and postsynaptic makers. Amitriptyline (500 nmol/L) and its active metabolite nortriptyline (50 nmol/L) are found to induce neurite outgrowth in rat primary cortical neurons. Amitriptyline-induced neurite outgrowth is blocked by inhibition of Trk signaling using Trk antagonist K252a (200 nmol/L) but not by the neurotrophin inhibitor Y1036 (40 μmol/L), indicating that amitriptyline binds directly to the Trk receptor to initiate neurite outgrowth. MEK inhibitor PD98059 (10 μmol/L) also blocks amitriptyline-induced neurite outgrowth, implicating activation of the MAPK signaling pathway downstream of Trk receptor activation. Furthermore, pretreatment of primary cortical neurons with amitriptyline and nortriptyline prevents the effects of the proinflammatory cytokine TNF-α (10 ng/mL) on neurite outgrowth and colocalization of synaptic proteins. These findings suggest that amitriptyline and nortriptyline can exert neurotrophic effects in primary cortical neurons via activation of a Trk/MAPK signaling pathway. These compounds therefore have significant potential to be used in the treatment of neurodegenerative conditions where atrophy and loss of synaptic connections contribute to progression of disease.
authors.affiliation: Neuropsychopharmacology Research Group School of Pharmacy & Pharmaceutical Sciences and Trinity College Institute of Neuroscience Dublin Ireland; Neuroimmunology Research Group Department of Physiology School of Medicine and Trinity College Institute of Neuroscience Dublin Ireland.
authors.forename: Eimear
authors.initials: E
authors.lastname: O'Neill
authors.affiliation: Neuroimmunology Research Group Department of Physiology School of Medicine and Trinity College Institute of Neuroscience Dublin Ireland.
authors.forename: Billy
authors.initials: B
authors.lastname: Kwok
authors.affiliation: Neuroimmunology Research Group Department of Physiology School of Medicine and Trinity College Institute of Neuroscience Dublin Ireland.
authors.forename: Jennifer S
authors.initials: JS
authors.lastname: Day
authors.affiliation: Neuroimmunology Research Group Department of Physiology School of Medicine and Trinity College Institute of Neuroscience Dublin Ireland.
authors.forename: Thomas J
authors.initials: TJ
authors.lastname: Connor
authors.affiliation: Neuropsychopharmacology Research Group School of Pharmacy & Pharmaceutical Sciences and Trinity College Institute of Neuroscience Dublin Ireland.
authors.forename: Andrew
authors.initials: A
authors.lastname: Harkin
keywords: Amitriptyline; PSD‐95; Trk receptor; neurite outgrowth; neurotrophin; nortriptyline; synaptogenesis; synaptophysin