Glycerol trinitrate (an NO donor) increased CGRP production in trigeminal ganglia and suppressed rat behavior regardless of fremanezumab treatment, suggesting NO acts downstream of CGRP in the migraine pain pathway.
NO acts downstream of CGRPbased on evidence that GTN increased trigeminal CGRP independently of fremanezumab, and fremanezumab only partly compensated for GTN's effects
What the researchers found
GTN treatment (5 mg/kg) tended to increase CGRP concentration in trigeminal ganglia after single administration, but repetitive GTN treatment decreased CGRP levels, suggesting store depletion. No significant difference in CGRP concentration was observed between fremanezumab-treated and control antibody-treated animals, indicating GTN increases CGRP production independently of antibody treatment.
Behaviorally, GTN-treated rats spent less time at a sugar solution source and consumed less, indicating suppressed activity and increased facial sensitivity. Under mechanical barrier conditions, fremanezumab partly compensated for GTN's depressive effects, with treated animals being more active. The findings suggest that if CGRP and NO share the same pathway in sensitizing trigeminal afferents, NO acts downstream of CGRP.
Why it matters
Understanding the relationship between CGRP and NO in migraine is critical for improving treatment. If NO acts downstream of CGRP, this explains why anti-CGRP therapies (like fremanezumab) help many but not all migraine patients — some migraine signaling may bypass CGRP entirely through NO. This insight could guide development of combination therapies targeting both pathways.
How the study worked
Wistar rats of both sexes received subcutaneous fremanezumab (30 mg/kg) or isotype control antibody, followed 1-several days later by intraperitoneal GTN (5 mg/kg, single or 3 consecutive days). Trigeminal ganglia were harvested for CGRP quantification by ELISA. Behavioral testing used a semi-automated system where rats accessed a sugar solution through mechanical or thermal barriers, measuring approach frequency, residence time, and consumption.
What this study cannot tell us
The behavioral findings showed trends rather than statistically significant differences in many comparisons, likely due to small group sizes. The GTN model, while established for migraine research, may not fully replicate human migraine mechanisms. Sex differences in CGRP levels add complexity. The pathway inference (NO downstream of CGRP) is based on indirect evidence from antibody and GTN interactions, not direct pathway mapping.
How to read the evidence
This is a preclinical mechanistic study in rats using pharmacological tools (fremanezumab, GTN) and behavioral/biochemical endpoints. It provides pathway-level evidence but with some results reaching trend rather than significance levels.
When this study was published
Published in 2024, this study contributes to the ongoing effort to map the CGRP-NO interaction in migraine, a question with direct therapeutic implications.
The bigger picture
CGRP and NO are the two best-characterized mediators in migraine, but their interaction has been debated. This study provides evidence that they share a signaling pathway with NO acting downstream. This has implications for understanding treatment resistance in migraine: patients who don't respond to anti-CGRP therapies may have predominantly NO-driven sensitization that bypasses the CGRP checkpoint.
Questions still open
- Would combining anti-CGRP therapy with NO pathway inhibitors produce better migraine outcomes than either alone?
- Why do males have higher baseline CGRP levels despite lower migraine prevalence?
- Does repetitive GTN-induced CGRP depletion model the progression from episodic to chronic migraine?
Common questions
Why don't anti-CGRP drugs work for all migraine patients?
What is the connection between CGRP and nitric oxide in migraine?
Read the original research
Glycerol Trinitrate Acts Downstream of Calcitonin Gene-Related Peptide in Trigeminal Nociception-Evidence from Rodent Experiments with Anti-CGRP Antibody Fremanezumab.
Cells, 13(7)
Citation
Benedicter, Nicola; Vogler, Birgit; Kuhn, Annette; Schramm, Jana; Mackenzie, Kimberly D; Stratton, Jennifer; Dux, Mária; Messlinger, Karl. (2024). Glycerol Trinitrate Acts Downstream of Calcitonin Gene-Related Peptide in Trigeminal Nociception-Evidence from Rodent Experiments with Anti-CGRP Antibody Fremanezumab.. Cells, 13(7). https://doi.org/10.3390/cells13070572