Mice Without Both Substance P and CGRP Still Feel Pain Normally — Challenging Decades of Assumptions

Researchers generated Tac1/Calca double knockout (DKO) mice lacking both Substance P and CGRPα. Complete peptide absence was confirmed throughout the nervous system. Pain behavior was assessed using a comprehensive battery: mechanical stimuli, thermal stimuli, chemical irritants, visceral pain models, itch assays, chronic inflammatory pain, neurogenic inflammation, nerve injury-induced neuropathic pain, and chemotherapy-induced neuropathic pain.

Substance P and CGRP have been the two most prominent neuropeptide targets for pain treatment for decades. Billions of dollars were spent developing drugs targeting each individually, and both failed as pain treatments in clinical trials. The prevailing hypothesis was that their co-expression meant both needed to be blocked simultaneously. This study demolishes that hypothesis — even eliminating both completely doesn't stop pain. This fundamentally reshapes our understanding of pain neurobiology and redirects the search for pain targets away from these neuropeptides.

This is potentially one of the most important findings in pain neuroscience in years. It explains the clinical failure of Substance P receptor (NK1) antagonists for pain and suggests that CGRP-targeting migraine drugs (erenumab, fremanezumab) work through non-pain mechanisms — perhaps by reducing neurogenic inflammation or vascular changes rather than blocking pain signals directly. It also redirects the search for pain targets toward other molecules and pathways.

This is a preprint (bioRxiv), not yet peer-reviewed. Genetic knockouts from birth may allow compensatory mechanisms to develop that mask the peptides' roles in normally functioning adults. CGRPβ (from the Calcb gene) was not eliminated and could provide partial compensation. The study cannot address whether acute pharmacological blockade of both peptides in adult animals would have different results than lifelong genetic absence. Mouse pain models may not fully recapitulate human pain experiences.