Abstract
The trace amine-associated receptor 1 (TAAR1) is expressed by dopaminergic neurons, but the precise influence of trace amines upon their functional activity remains to be fully characterized. Here, we examined the regulation of tyrosine hydroxylase (TH) by tyramine and beta-phenylethylamine (β-PEA) compared to 3-iodothyronamine (T1AM). Immunoblotting and amperometry were performed in dorsal striatal slices from wild-type (WT) and TAAR1 knockout (KO) mice. T1AM increased TH phosphorylation at both Ser19 and Ser40, actions that should promote functional activity of TH. Indeed, HPLC data revealed higher rates of L-dihydroxyphenylalanine (DOPA) accumulation in WT animals treated with T1AM after the administration of a DOPA decarboxylase inhibitor. These effects were abolished both in TAAR1 KO mice and by the TAAR1 antagonist, EPPTB. Further, they were specific inasmuch as Ser845 phosphorylation of the post-synaptic GluA1 AMPAR subunit was unaffected. The effects of T1AM on TH phosphorylation at both Ser19 (CamKII-targeted), and Ser40 (PKA-phosphorylated) were inhibited by KN-92 and H-89, inhibitors of CamKII and PKA respectively. Conversely, there was no effect of an EPAC analog, 8-CPT-2Me-cAMP, on TH phosphorylation. In line with these data, T1AM increased evoked striatal dopamine release in TAAR1 WT mice, an action blunted in TAAR1 KO mice and by EPPTB. Mass spectrometry imaging revealed no endogenous T1AM in the brain, but detected T1AM in several brain areas upon systemic administration in both WT and TAAR1 KO mice. In contrast to T1AM, tyramine decreased the phosphorylation of Ser40-TH, while increasing Ser845-GluA1 phosphorylation, actions that were not blocked in TAAR1 KO mice. Likewise, β-PEA reduced Ser40-TH and tended to promote Ser845-GluA1 phosphorylation. The D1 receptor antagonist SCH23390 blocked tyramine-induced Ser845-GluA1 phosphorylation, but had no effect on tyramine- or β-PEA-induced Ser40-TH phosphorylation. In conclusion, by intracellular cascades involving CaMKII and PKA, T1AM, but not tyramine and β-PEA, acts via TAAR1 to promote the phosphorylation and functional activity of TH in the dorsal striatum, supporting a modulatory influence on dopamine transmission.
Highlights
IntroductionClassical trace amines (TAs), including tyramine, betaphenylethylamine (β-PEA), tryptamine and octopamine, have been implicated in a number of neuropsychiatric disorders associated with monoaminergic dysfunction, including schizophrenia, major depression, and Parkinson’s disease (Boulton, 1980; Premont et al, 2001; Branchek and Blackburn, 2003; Burchett and Hicks, 2006; Berry, 2007; Sotnikova et al, 2009; Millan, 2014; Khan and Nawaz, 2016; Berry et al, 2017)
We found that bath application of T1AM (10 μM) significantly increased the amplitude of evoked DA release measured with carbon fiber electrodes coupled to amperometry in dorsal striatal brain slices from WT mice, and that this effect was significantly reduced in TAAR1 KO mice
This study demonstrates that TAAR1 mediates the effects of T1AM on dorsal striatal tyrosine hydroxylase (TH) phosphorylation, activity and evoked dopamine release
Summary
Classical trace amines (TAs), including tyramine, betaphenylethylamine (β-PEA), tryptamine and octopamine, have been implicated in a number of neuropsychiatric disorders associated with monoaminergic dysfunction, including schizophrenia, major depression, and Parkinson’s disease (Boulton, 1980; Premont et al, 2001; Branchek and Blackburn, 2003; Burchett and Hicks, 2006; Berry, 2007; Sotnikova et al, 2009; Millan, 2014; Khan and Nawaz, 2016; Berry et al, 2017). TA levels are enhanced by inhibition of monoamine oxidase A and B in animals where the corresponding genes have been deleted (Holschneider et al, 2001)
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