March 1, 2021

Adenosine modulates extracellular glutamate levels via adenosine A2A receptors in the delayed-ethanol induced headache.

Identifying the mechanism behind delayed ethanol-induced headache (DEIH), otherwise known as the hangover headache, may provide insight into the mechanisms behind common headache triggers. Acetate was previously shown to be the key ethanol metabolite behind DEIH in the recurrent inflammatory stimulation (IS) rat model of headache. The reversal of trigeminal sensitivity following ethanol exposure with caffeine previously suggested a role of adenosine in DEIH. To characterize this, behavioral analysis and measurement of brainstem adenosine and glutamate with microdialysis and HPLC was performed while pharmacologically manipulating adenosine signaling in the IS and Spontaneous Trigeminal Allodynia (STA) rat models of headache. Blocking adenosine A2A receptor activation with istradefylline or acetate transport into astrocytes with the monocarboxylate transporter competitive inhibitor, alpha-cyano-4-hydroxycinnamate (4-CIN), prevented acetate-induced trigeminal sensitivity. Blocking adenosine A1, A2B, and A3 receptor signaling did not prevent trigeminal sensitivity. Compared to control rats, IS rats had greater increases in extracellular adenosine and glutamate within the trigeminal nucleus caudalis (TNC) of the brainstem during local acetate perfusion. Blocking transport of acetate into astrocytes with 4-CIN prevented the increase in adenosine and glutamate. Blocking A2A receptor activation prevented the increase in extracellular glutamate, but not adenosine in the TNC. These data are the first to demonstrate the physiological consequence of acetate on adenosinergic systems within trigeminal pain by suggesting that acetate-induced trigeminal sensitivity in DEIH is mediated by adenosine A2A receptor activation which modulates extracellular glutamate levels in the TNC.

 bioRxiv Subject Collection: Neuroscience

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