Modulation by trace amine-associated receptor 1 of experimental parkinsonism, L-DOPA responsivity, and glutamatergic neurotransmission

Parkinson’s disease (PD) is a movement disorder characterized by a progressive loss of nigrostriatal dopaminergic neurons. Restoration of dopamine transmission by L-DOPA relieves symptoms of PD but causes dyskinesia. Trace Amine-Associated Receptor 1 (TAAR1) modulates dopaminergic transmission, but its role in experimental Parkinsonism and L-DOPA responses has been neglected. Here, we report that TAAR1 knock-out (KO) mice show a reduced loss of dopaminergic markers in response to intrastriatal 6-OHDA administration compared with wild-type (WT) littermates. In contrast, the TAAR1 agonist RO5166017 aggravated degeneration induced by intrastriatal6-OHD Ain WT mice. Subchronic L-DOPAtreatment ofTAAR1KOmice unilaterally lesioned with6-OHDAin the medial forebrain bundle resulted in more pronounced rotational behavior and dyskinesia than in their WT counterparts. The enhanced behavioral sensitization to L-DOPA in TAAR1 KO mice was paralleled by increased phosphorylation of striatal GluA1 subunits of AMPA receptors. Conversely, RO5166017 counteracted both L-DOPA-induced rotation and dyskinesia as well as AMPA receptor phosphorylation. Underpinning a role for TAAR1 receptors in modulating glutamate neurotransmission, intrastriatal application of RO5166017 prevented the increase of evoked corticostriatal glutamate release provoked by dopamine deficiency after 6-OHDA-lesions or conditional KO of Nurr1. Finally, inhibition of corticostriatal glutamate release by TAAR1 showed mechanistic similarities to that effected by activation of dopamineD₂ receptors. These data unveil a role for TAAR1 in modulating the degeneration of dopaminergic neurons, the behavioral response to L-DOPA, and presynaptic and postsynaptic glutamate neurotransmission in the striatum, supporting their relevance to the pathophysiology and, potentially, management of PD.