Intracellular cAMP Signaling Pathway via G Protein-Coupled Receptor Activation in Rat Primary Cultured Trigeminal Ganglion Cells.

G protein-coupled receptors in trigeminal ganglion (TG) neurons are often associated with sensory mechanisms, including nociception. We have previously reported the expression of P2Y receptors, which are G protein-coupled receptors, in TG cells. Activating P2Y receptors decreased the intracellular free Ca concentration ([Ca]). This indicated that intracellular adenosine 3',5'-cyclic monophosphate (cAMP) levels can mediate Ca signaling in TG cells. Here, we report more extensive-expression patterns of G protein-coupled receptors in primary cultured TG neurons isolated from 7-day-old newborn Wistar rats and further examine the roles of these receptors in cAMP signaling using the BacMam sensor in these neurons. To identify TG neurons, we also measured [Ca] using fura-2 in TG cells and measured intracellular cAMP levels. TG neurons were positive for Gα protein-coupled receptors, beta-2 adrenergic (β), calcitonin gene-related peptide (CGRP), adenosine A (A), dopamine 1 (D1), prostaglandin I (IP), and 5-hydroxytriptamine 4 (5-HT) receptor. Application of forskolin (FSK), an activator of adenylyl cyclase, transiently increased intracellular cAMP levels in TG neurons. The application of a phosphodiesterase inhibitor augmented the FSK-elicited intracellular cAMP level increase. These increases were significantly suppressed by the application of SQ22536, an adenylyl cyclase inhibitor, in TG neurons. Application of agonists for β, CGRP, A, D1-like, IP, and 5-HT receptors increased intracellular cAMP levels. These increases were SQ22536-sensitive. These results suggested that TG neurons express β, CGRP, A, D1, IP, and 5-HT receptors, and the activations of these Gα protein-coupled receptors increase intracellular cAMP levels by activating adenylyl cyclase.