Calcitonin gene-related peptide differentially modulates intracellular calcium levels in response to depolarizing stimuli in trigeminal ganglion neurons and glial cells.

Elevated levels of calcitonin gene-related peptide (CGRP) are implicated in migraine pathology, but its effects on the excitability state of trigeminal ganglion Aδ and C-fiber neurons and glia have not been fully investigated. The goal of this study was to determine changes mediated by CGRP on intracellular calcium levels in trigeminal neurons and glia in response to depolarizing stimulation. Intracellular calcium levels were determined in Aδ and C-fiber neurons of primary trigeminal ganglion cultures obtained from neonatal Sprague Dawley rats using Fura-2 and fluorescent microscopy. Cells were left untreated or preincubated for 2 h with CGRP, then incubated with the depolarizing stimuli KCl or ATP. Data analysis was performed using Olympus CellSens Dimension software and JASP. CGRP greatly increased the calcium amplitude in response to 60 mM KCl and 100 µM ATP in Aδ neurons, while causing a smaller, similar response in C-fiber neurons. CGRP also increased the percentage of Aδ neurons responsive to 60 mM KCl and enhanced the magnitude of the calcium response. In glial cells, CGRP increased the magnitude of the 60 mM KCl-mediated response. However, CGRP suppressed the stimulatory calcium response to 15 mM KCl in neurons and glial cells and differentially modulated the calcium response to 30 mM KCl in Aδ and C-fiber neurons. These results provide evidence of a novel role of CGRP to regulate the excitability state of Aδ and C-fiber neurons and glial cells implicated in pain signaling in migraine differently in response to the strength of the depolarizing stimulus.