Trace amine-associated receptor 1 regulation of Kv1.4 channels in trigeminal ganglion neurons contributes to nociceptive behaviors.

Background: Trace amines, such as tyramine, are endogenous amino acid metabolites that have been hypothesized to promote headache. However, the underlying cellular and molecular mechanisms remain unknown.

Methods: Using patch-clamp recording, immunostaining, molecular biological approaches and behaviour tests, we elucidated a critically functional role of tyramine in regulating membrane excitability and pain sensitivity by manipulating Kv1.4 channels in trigeminal ganglion (TG) neurons.

Results: Application of tyramine to TG neurons decreased the A-type K current (I) in a manner dependent on trace amine-associated receptor 1 (TAAR1). Either siRNA knockdown of Gαo or chemical inhibition of βγ subunit (G) signaling abrogated the response to tyramine. Antagonism of protein kinase C (PKC) prevented the tyramine-induced I response, while inhibition of conventional PKC isoforms or protein kinase A elicited no such effect. Tyramine increased the membrane abundance of PKC in TG neurons, and either pharmacological or genetic inhibition of PKC blocked the TAAR1-mediated I decrease. Furthermore, PKC-dependent I suppression was mediated by Kv1.4 channels. Knockdown of Kv1.4 abrogated the TAAR1-induced I decrease, neuronal hyperexcitability, and pain hypersensitivity. In a mouse model of migraine induced by electrical stimulation of the dura mater surrounding the superior sagittal sinus, blockade of TAAR1 signaling attenuated mechanical allodynia; this effect was occluded by lentiviral overexpression of Kv1.4 in TG neurons.

Conclusion: These results suggest that tyramine induces Kv1.4-mediated I suppression through stimulation of TAAR1 coupled to the G-dependent PKC signaling cascade, thereby enhancing TG neuronal excitability and mechanical pain sensitivity. Insight into TAAR1 signaling in sensory neurons provides attractive targets for the treatment of headache disorders such as migraine.