M40: lab peptide that blocks a brain calming signal (studied for pain and seizures)
A lab-made research peptide that blocks galanin, a natural brain chemical that quiets nerve cells. In animal studies it reduced nerve pain and seizure activity. Used only as a research tool, not a medicine.
A researcher, an agent, or an algorithm wrote down the sequence and picked a target to hit.
An AI model like OpenFold3 or AlphaFold built a 3D structure and scored how well it fits the binding site.
A second contributor repeated the computation on their own hardware and the scores matched.
A chemistry service or a researcher ordered the sequence, it was manufactured, and mass spectrometry confirmed the right molecule was produced.
A binding or activity measurement confirmed that it actually does what the computer predicted — or didn't.
What this is
M40 is a synthetic peptide designed to block the action of galanin, a small neuropeptide that the brain uses to dampen the firing of certain nerve cells. Structurally, M40 is a chimera: it splices the first 13 residues of galanin onto a short artificial tail (Pro-Pro-Ala-Leu-Ala-Leu-Ala, with a C-terminal amide cap that the raw 20-letter sequence does not show). The galanin "head" lets it dock onto galanin receptors; the artificial tail prevents it from triggering the receptor the way native galanin would. M40 is a research tool rather than a clinical drug — it is used in laboratory studies to ask "what happens when galanin signaling is switched off?"
History
M40 belongs to a family of galanin chimeric peptide antagonists developed in the early 1990s, alongside related sequences such as M35, M617, and M871, which share the galanin (1-13) N-terminal segment joined to different synthetic C-terminal tails (Webling 2012). These chimeras were among the first pharmacological tools that allowed researchers to probe galanin's role in feeding, memory, and pain pathways before subtype-selective small molecules existed. Leibowitz and colleagues (1992) used a galanin antagonist of this class to test how blocking galanin affects food intake patterns in rats — one of the early behavioral applications of the approach.
What it does
In the body, native galanin slows the firing of neurons by acting on three closely related receptors — GALR1, GALR2, and GALR3 (Kolakowski 1998). All three are G-protein-coupled receptors. By binding to these receptors but failing to activate them in the normal way, M40 keeps galanin from delivering its inhibitory signal, which lets affected neurons fire more freely in experimental settings. On the Peptidopedia card, M40's target is listed as GALR1, the receptor subtype where galanin's central effects on neurotransmission are best characterized (Webling 2012).
Galanin itself influences several physiological processes — hormone release, feeding behavior, smooth-muscle contractility, and the relay of sensory information from the periphery into the spinal cord (Kolakowski 1998). M40 is the tool that scientists reach for when they want to see what falls apart, behaviorally or electrically, when that galanin influence is removed.
Mechanism
M40 is built from the N-terminal galanin (1-13) recognition sequence — the segment of native galanin most important for receptor docking — fused to a Pro-Pro-(Ala-Leu)₂-Ala tail and capped as a C-terminal amide. The galanin head retains affinity for galanin receptors, but the non-natural tail occupies (or disorders) the region of the receptor that would normally be engaged by the C-terminus of native galanin, so the receptor binds the ligand without transducing the full inhibitory signal. Freimann and colleagues (2015) and Webling and colleagues (2012) catalog M40's reported affinities at GALR1, GALR2, and GALR3 alongside the rest of the chimeric antagonist series (M35, M617, M871, Gal-B2), and these reviews remain the standard reference points for the pharmacology of this family.
Note on receptor subtype selectivity: the chimeric galanin antagonists were originally characterized before all three receptor subtypes had been cloned, and later work showed that several of them — and even short fragments such as galanin (2-11) — bind multiple subtypes (Lu 2005). M40 is therefore best described as a pan-galanin-receptor antagonist with the GALR1-focused use case captured in the platform metadata.
Evidence
- Human: No human trials of M40.
- Animal: Used as a pharmacological probe in rodent studies of galanin signalling; the historical Leibowitz (1992) feeding work is one well-documented in-vivo application.
- In vitro: Receptor binding and signalling assays at cloned galanin receptors (GALR1/2/3) are reported in the chimeric-antagonist literature reviewed by Webling (2012) and Freimann (2015), and in the original GALR2/GALR3 cloning papers (Bloomquist 1998; Kolakowski 1998; Smith 1998).
Known effects
- Block of galanin-mediated neuronal inhibition — Mechanistic, in cell and tissue preparations (Webling 2012; Freimann 2015).
- Modulation of galanin-driven feeding behavior in rodents — Preclinical (Leibowitz 1992).
- Use as a reference antagonist in galanin receptor pharmacology — Established in review literature (Webling 2012; Freimann 2015).
Regulatory status
M40 is a research-use peptide. It is not approved by the FDA, the EMA, or any other regulator for clinical use, and no clinical development programme is on file. It is not listed by name on the WADA Prohibited List, though substances that act on peptide-hormone signalling pathways fall under WADA's general categories.
Related peptides
- Galanin — the endogenous 29- or 30-residue neuropeptide that M40 antagonizes (Kolakowski 1998).
- M35, M617, M871 — sibling chimeric antagonists in the same galanin (1-13)-based design series, differing only in the synthetic C-terminal tail (Webling 2012).
- Galanin (2-11) — a short N-terminal fragment historically used as a GALR2-preferring probe; its subtype selectivity is more limited than originally claimed (Lu 2005).
Research directions for this peptide, selected from the current sources — hypotheses you can explore and model. None of it is proven yet; tap any one to see the full thinking.
Could blocking the galanin calming signal M40 targets help reduce opioid craving?
If M40 can lift a brain signal that opioids suppress, it might ease craving or withdrawal without being addictive itself, offering a non-opioid option that works on a different circuit.
Could a small chemical change to M40 let it be delivered by injection or nasal spray instead of direct brain injection?
Today M40 is used in lab animals via direct brain injection. A tail redesign for better brain penetration could make it a candidate for pain, memory loss, or obesity research.
Does M40 block only GALR1, or also GALR2 and GALR3 with similar strength?
If M40 hits all three receptor variants, studies that used it to pin effects on GALR1 alone may need rechecking. That could redirect drug development for pain and memory toward the correct target.
Does M40 push neurons into a more excitable state than simply removing galanin would?
If M40 acts as an inverse agonist, it could lower basal calming signals below what a plain blocker would, which might explain strong excitability effects and guide safer anti-seizure or memory drugs.
Could a low dose of M40 help prevent seizures instead of making them worse?
If a small amount of M40 can fine-tune, rather than eliminate, the brain's calming signal, it could point toward a new treatment strategy for people with drug-resistant epilepsy who currently have few options.
▸full evidence table1 metrics
| metric | value | tool |
|---|---|---|
| Ki | 0.1 nM | GPCRDB/ChEMBL |
▸3-letter notation
▸recipeboltz-2 2.2.1
| parameter | value |
|---|---|
| model | boltz-2 2.2.1 |
| weights | — |
| hardware | vast_v100_32gb |
| mlx version | — |
| python | — |
| random seed | 1 |
| msa strategy | colabfold_local |
| runtime | — |
| predicted by | — |
| predicted at | 2026-05-22 |
▸citationbibtex
@peptide{pep10340,
sequence = {GWTLNSAGYLLGPPPALALA},
target = {galr1},
author = {peptidemodel},
year = {2026},
status = {bioassayed}
}