Trigeminal nociceptors express prostaglandin receptors

Orofacial inflammation is associated with prostaglandin release and the sensitization of nociceptive receptors such as the transient receptor potential subtype V₁ (TRPV₁). We hypothesized that certain PGE ₂ receptor subtypes (EP1-EP4) are co-expressed with TRPV₁ in trigeminal nociceptors and sensitize responses to a TRPV₁ agonist, capsaicin. Accordingly, combined in situ hybridization was performed with immunohisto-chemistry on rat trigeminal ganglia. We next evaluated the effects of specific EP2 and EP3 agonists (butaprost and sulprostone) in cultured trigeminal ganglia neurons. The results showed that EP2 and EP3 are expressed in trigeminal neurons (58% and 53% of total neurons, respectively) and are co-expressed in TRPV₁-positive neurons (64% and 67 % of TRPV ₁-positive neurons, respectively). Moreover, most of the cells expressing EP2 or EP3 mRNA were of small to medium diameter (< 30 μm). The application of butaprost and sulprostone triggered neuropeptide exocytosis, and butaprost sensitized capsaicin responses. Analysis of these data, collectively, supports the hypothesis that prostaglandins regulate trigeminal TRPV ₁ nociceptors via activation of the EP2 and EP3 receptors.