MacDonald, D. I. | bioRxiv Science

bioRxiv2025

Nociceptors use multiple neurotransmitters to drive pain

Nociceptors are excitatory neurons that express a range of neuropeptides and have the essential role of detecting noxious mechanical, thermal and chemical stimuli. Ablating these neurons profoundly reduces responses to pain. Here we investigated how nociceptive information is transmitted by developing genetic approaches to suppress glutamate transmission and neuropeptide signaling, individually and in combination. Remarkably, many pain responses persisted in mice where either nociceptor glutamate or neuropeptide signaling was blocked. By contrast, mice lacking both glutamate and neuropeptide transmission in nociceptors displayed profound pain insensitivity closely matching the effects of cell ablation. Together our results establish a role for neuropeptides as bone fide pain transmitters and demonstrate redundancy in nociceptor signaling, resolving long-standing questions about how pain is communicated to the brain.

neuroscience↗

bioRxiv2023

Pain persists in mice lacking both Substance P and CGRPα signaling

The neuropeptides Substance P and CGRP have long been thought important for pain sensation. Both peptides and their receptors are expressed at high levels in pain-responsive neurons from the periphery to the brain making them attractive therapeutic targets. However, drugs targeting these pathways individually did not relieve pain in clinical trials. Since Substance P and CGRP are extensively co-expressed we hypothesized that their simultaneous inhibition would be required for effective analgesia. We therefore generated Tac1 and Calca double knockout (DKO) mice and assessed their behavior using a wide range of pain-relevant assays. As expected, Substance P and CGRP peptides were undetectable throughout the nervous system of DKO mice. To our surprise, these animals displayed largely intact responses to mechanical, thermal, chemical, and visceral pain stimuli, as well as itch. Moreover, chronic inflammatory pain and neurogenic inflammation were unaffected by loss of the two peptides. Finally, neuropathic pain evoked by nerve injury or chemotherapy treatment was also preserved in peptide-deficient mice. Thus, our results demonstrate that even in combination, Substance P and CGRP are not required for the transmission of acute and chronic pain.

neuroscience↗