Mechanisms mediating the enhanced gene transcription of P2X3 receptor by calcitonin gene-related peptide in trigeminal sensory neurons

The molecular mechanisms underlying migraine pain remain unclear and probably require sustained facilitation in pain-sensing P2X(3) receptors gated by extracellular ATP in nociceptive sensory neurons. The major migraine mediator calcitonin gene-related peptide ( CGRP) is known to sensitize P2X3 receptors to increase impulse flow to brainstem trigeminal nuclei. This process is mediated via changes in the expression and function of P2X3 receptors initially through enhanced trafficking and, later, perhaps through augmented synthesis of P2X3 receptors. To clarify the mechanisms responsible for CGRP-evoked long lasting alterations in P2X3 receptors, we used as a model mouse trigeminal ganglion neurons in culture. CGRP activated Ca2+-calmodulin- dependent kinase II, which became localized to the perimembrane region and neuronal processes, a phenomenon already apparent after 30 min and accompanied by a parallel increase in cAMP-response element-binding protein ( CREB) phosphorylation and nuclear translocation. These effects triggered increased P2X3 receptor transcription and were prevented by expressing a dominant negative form of CREB. Increased P2X3 receptor synthesis was partly mediated by endogenous brain-derived neurotrophic factor ( BDNF) because of its block by anti-BDNF antibodies and mimicry by exogenous BDNF. Immunocytochemistry experiments indicated distinct subpopulations of BDNF- or CGRP-sensitive trigeminal neurons with only partial overlap. The present data indicate a novel mechanism for enhancing P2X3 receptor expression and function in trigeminal sensory neurons by CGRP via CREB phosphorylation. BDNF was an intermediate to extend the sensitizing effect of CGRP also to CGRP-insensitive neurons. This combinatorial action could serve as a powerful process to amplify and prolong pain mediated by P2X3 receptors.