Search

Suture-line injections of onabotulinumtoxinA alter a neuronal function along a central nervous system pathway involved in the pathophysiology of migraine that is secondary to appearance of SNAP25 in dural nerve fibers., OnabotulinumtoxinA (BoNT-A) is an Food and Drug Administration-approved, peripherally acting preventive migraine drug capable of inhibiting meningeal nociceptors. Expanding our view of how else this neurotoxin attenuates the activation of the meningeal nociceptors, we reasoned that if the stimulus that triggers the activation of the nociceptor is lessened, the magnitude and/or duration of the nociceptors' activation could diminish as well. In the current study, we further examine this possibility using electrocorticogram recording techniques, immunohistochemistry, and 2-photon microscopy. We report (1) that scalp (head) but not lumbar (back) injections of BoNT-A shorten the period of profound depression of spontaneous cortical activity that follows a pinprick-induced cortical spreading depression (CSD); (2) that neither scalp nor lumbar injections prevent the induction, occurrence, propagation, or spreading velocity of a single wave of CSD; (3) that cleaved SNAP25—one of the most convincing tools to determine the anatomical targeting of BoNT-A treatment—could easily be detected in pericranial muscles at the injection sites and in nerve fibers of the intracranial dura, but not within any cortical area affected by the CSD; (4) that the absence of cleaved SNAP25 within the cortex and pia is unrelated to whether the blood–brain barrier is intact or compromised; and (5) that BoNT-A does not alter vascular responses to CSD. To the best of our knowledge, this is the first report of peripherally applied BoNT-A's ability to alter a neuronal function along a central nervous system pathway involved in the pathophysiology of migraine.

The mechanism of action of botulinum neurotoxin type A (BoNT/A) is well characterized, but some published evidence suggests the potential for neuronal retrograde transport and cell-to-cell transfer (transcytosis) under certain experimental conditions. The present study evaluated the potential for these processes using a highly selective antibody for the BoNT/A-cleaved substrate (SNAP25197) combined with 3-dimensional imaging. SNAP25197 was characterized in a rat motor neuron (MN) pathway following toxin intramuscular injections at various doses to determine whether SNAP25197 is confined to MNs or also found in neighboring cells or nerve fibers within spinal cord (SC). Results demonstrated that SNAP25197 immuno-reactive staining was colocalized with biomarkers for MNs, but not with markers for neighboring neurons, nerve fibers or glial cells. Additionally, a high dose of BoNT/A, but not a lower dose, resulted in sporadic SNAP25197 signal in distal muscles and associated SC regions without evidence for transcytosis, suggesting that the staining was due to systemic spread of the toxin. Despite this spread, functional effects were not detected in the distal muscles. Therefore, under the present experimental conditions, our results suggest that BoNT/A is confined to MNs and any evidence of distal activity is due to limited systemic spread of the toxin at higher doses and not through transcytosis within SC. Lastly, at higher doses of BoNT/A, SNAP25197 was expressed throughout MNs and colocalized with synaptic markers on the plasma membrane at 6 days post-treatment. These data support previous studies suggesting that SNAP25197 may be incorporated into SNARE-protein complexes within the affected MNs.