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Intact mast cell content during mild head injury is required for the development of latent pain sensitization - implications for mechanisms underlying post-traumatic headache

Posttraumatic headache (PTH) is one of the most common, debilitating and difficult symptoms to manage after a traumatic head injury. While the mechanisms underlying PTH remain elusive, recent studies in rodent models suggest the potential involvement of calcitonin gene-related peptide (CGRP), a mediator of neurogenic inflammation, and the ensuing activation of meningeal mast cells (MCs), pro-algesic resident immune cells that can lead to the activation of the headache pain pathway. Here, we investigated the relative contribution of MCs to the development of PTH-like pain behaviors in a model of mild closed head injury (mCHI) in male rats. We initially tested the relative contribution of peripheral CGRP signaling to the activation of meningeal MCs following mCHI using an anti-CGRP monoclonal antibody. We then employed a prophylactic MC granule depletion approach to address the hypotheses that intact meningeal MC granule content is necessary for the development of PTH-related pain-like behaviors. The data suggest that following mCHI, ongoing activation of meningeal MCs is not mediated by peripheral CGRP signaling, and does not contribute to development of the mCHI-evoked cephalic mechanical pain hypersensitivity. Our data, however, also reveals that the development of latent sensitization, manifested as persistent hypersensitivity upon the recovery from mCHI-evoked acute cranial hyperalgesia to the headache trigger glyceryl trinitrate requires intact MC content during and immediately after mCHI. Collectively, our data implicate the acute activation of meningeal MCs as mediator of chronic pain hypersensitivity following a concussion or mCHI. Targeting MCs may be explored for early prophylactic treatment of PTH.