Mapping Dural and Periosteal SV2C, a Botulinum Toxin A Receptor, in the Mouse.

OBJECTIVES: There has been a long-standing debate over the presence or absence of receptors for botulinum toxin A (BoNT/A) in cephalic areas relevant to migraine pathophysiology and onabotulinumtoxinA (onabotA) sites of action in migraine prevention. To address this issue, we sought to investigate for the first time whether synaptic vesicle protein 2C (SV2C), one member of the SV2 receptor family, is present in axons innervating the dura and periosteum. METHODS: Single- and double- labeling immunohistochemical techniques were used to map and characterize the distribution of axons containing SV2C, the third isoform of the SV2 glycoprotein, in the mouse dura and periosteum. RESULTS: Dense networks of axons containing SV2C receptors were distributed throughout all regions of the dura and periosteum. In the dura, SV2C-LIR axons were found in 43% of all peripherin-LIR fibers, 49% of all CGRP-LIR fibers, and 75% of all NaV1.8-LIR fibers. In the periosteum, SV2C-LIR was found in 38% of all peripherin-LIR fibers, 53% of all CGRP-LIR fibers, and 68% of all NaV1.8-LIR fibers. CONCLUSIONS: We interpret these findings as suggesting that many of the labeled axons are peripheral nerve axons (peripherin-positive) of unmyelinated sensory and possibly parasympathetic origin (CGRP-positive), and that some of these sensory axons are nociceptors (NaV1.8-positive). Clinically, these findings demonstrate an abundance of axons containing onabotA receptors in the vicinity of scalp structures commonly injected with onabotA for the treatment of chronic migraine. Dense labeling in the periosteum provides another rationale for the possibility that onabotA injections in this layer of the scalp may be advantageous.