Treatment of allodynia by occipital nerve stimulation in chronic migraine rodent

BACKGROUND: Occipital nerve stimulation (ONS) is a therapy that benefits one-third of medically refractory chronic migraine (CM) patients. How ONS affects sensory thresholds and whether modulation of thresholds could predict which patients respond to the therapy remains unclear. OBJECTIVE: To examine the effects of ONS on mechanical and thermal thresholds in a rodent CM model to better elucidate its mechanism of action. METHODS: Male Sprague-Dawley rats were implanted bilaterally with electrodes to produce ONS. The CM cohort was infused with inflammatory media epidurally based on a validated model, whereas shams were not. Thresholds were evaluated with von Frey filaments and hot plate and thermode tests. RESULTS: No baseline differences in sensory thresholds were found between the sham (n 16) and CM (n 16) groups. After headache induction, CM animals demonstrated mechanical allodynia in the occiput, periorbital region, forepaws, and hind paws (P <.05). In CM animals, ONS increased mechanical thresholds in all regions (P <.001), whereas in shams, it did not. ONS did not affect thermal thresholds in either group. CONCLUSION: We show that ONS improves mechanical thresholds in a rodent CM model, but not in shams. Our finding that mechanical but not thermal thresholds are altered with ONS suggests a more significant modulation of A-α/β fibers than of C fibers. Assessing the ability of ONS to reduce mechanical thresholds during a trial period could potentially be used to predict which patients respond. ABBREVIATIONS: CGRP, calcitonin gene-related peptide CM, chronic migraine HPT, hot plate test ONS, occipital nerve stimulation SCS, spinal cord stimulation TT, thermode test VFF, von Frey filament.