Brain-signaling research fragment (Neurotensin 8-13)
A tiny piece of the natural brain peptide neurotensin that switches on its receptor; used in labs to study pain, dopamine circuits, and pancreatic cancer detection, a research tool, not an approved drug.
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
Neurotensin (8-13) is the six-amino-acid C-terminal fragment of neurotensin, a naturally occurring 13-residue neuropeptide first isolated from bovine hypothalamus in 1973 by Carraway and Leeman. The fragment — sequence Arg-Arg-Pro-Tyr-Ile-Leu — is the shortest portion of the parent peptide that retains full binding and activation of the neurotensin type 1 receptor (NTSR1), making it the defining minimal pharmacophore of the neurotensin family (Besserer-Offroy and colleagues 2017; White and colleagues 2012). Because it captures everything needed to turn on the receptor in just six residues, it has become a widely used research tool for studying NTSR1 biology and as a scaffold for designing more stable drug candidates.
History
Neurotensin itself was discovered in 1973 when Carraway and Leeman were purifying substance P from bovine hypothalamus extracts. The isolation of neurotensin was guided by an unexpected observation: intravenous injection of the crude extract caused a characteristic vasodilatation around the face and ears of experimental animals. The peptide was named "neurotensin" to reflect both its presence in neural tissue and its ability to affect vascular tone. Its full 13-amino-acid sequence — pyroGlu-Leu-Tyr-Glu-Asn-Lys-Pro-Arg-Arg-Pro-Tyr-Ile-Leu — was established by Edman degradation and carboxypeptidase treatment of enzymatic fragments.
The C-terminal (8-13) fragment was subsequently identified as the minimal active sequence required for high-affinity receptor binding and functional activation (Besserer-Offroy and colleagues 2017). It does not occur as a distinct endogenous peptide in vivo, but serves as the essential template for a large body of medicinal chemistry aimed at creating metabolically stable analogs.
What it does
In the brain, neurotensin (8-13) activates NTSR1 to modulate two well-characterized circuits: the dopamine system and pain pathways. On the dopamine side, activation of NTSR1 at dopaminergic axon terminals enhances dopamine release, primarily by inhibiting the function of presynaptic D2 autoreceptors (Threlfell and colleagues 2009). More than 80% of dopaminergic neurons in the mesocortical, mesolimbic, and nigrostriatal pathways express NTSR1, positioning the neurotensin system as a broad modulator of dopaminergic tone. This interaction has attracted interest in the context of schizophrenia, where cerebrospinal fluid neurotensin levels are reduced in drug-free patients and tend to normalize during effective antipsychotic treatment (Austin and colleagues 2000).
On the pain side, neurotensin (8-13) produces antinociceptive effects through both NTS1 and NTS2 receptors by a mechanism that is not blocked by opioid antagonists — distinguishing it from classical analgesic peptides.
Beyond neuroscience, NTSR1 is overexpressed in the majority of pancreatic ductal adenocarcinomas and in several other tumor types, which has made the neurotensin (8-13) scaffold a starting point for radiolabeled tumor-imaging agents. Maes and colleagues (2006) developed ⁹⁹ᵐTc-labeled neurotensin analogs based on this scaffold for imaging NTSR1-positive tumors.
Evidence
- Human: No clinical trials have been conducted with neurotensin (8-13) itself. The peptide's extremely short plasma half-life (under 2 minutes) precludes direct clinical use; it functions as a research and medicinal chemistry tool. No registered trials on ClinicalTrials.gov for "neurotensin 8-13."
- Animal: Neurotensin (8-13) analogs reduce amphetamine-induced hyperactivity and improve prepulse inhibition in rodent models of psychosis, consistent with antipsychotic-like activity (reviewed in Boules and colleagues 2014). Antinociceptive effects have been documented in both acute and inflammatory pain models following intrathecal administration or direct injection into pain-modulating brain regions.
- In vitro: White and colleagues (2012) resolved the crystal structure of NTSR1 bound to neurotensin (8-13), establishing the molecular basis of binding. Deluigi and colleagues (2021) used the peptide as a reference full agonist (EC50 2.06 nM in Gq IP1 accumulation assay) to benchmark NTSR1 agonism across a series of small-molecule ligands. Huang and colleagues (2020) solved the cryo-EM structure of the NTSR1–β-arrestin 1 complex using neurotensin (8-13) as the activating ligand. Maharana and colleagues (2021) determined the NTSR1–Gi complex structure in a lipid environment.
Known effects
- NTSR1 full agonism — Established in vitro; EC50 2.06 nM (Gq pathway, Deluigi and colleagues 2021)
- Dopamine release enhancement — Preclinical; via presynaptic D2 autoreceptor inhibition (Threlfell and colleagues 2009)
- Antipsychotic-like activity — Preclinical animal models only; NT analogs suppress amphetamine-induced hyperactivity and improve prepulse inhibition
- Opioid-independent antinociception — Preclinical; mediated via NTS1 and NTS2 receptors
- Tumor-targeted imaging scaffold — Preclinical; ⁹⁹ᵐTc-labeled analogs show uptake in NTSR1-overexpressing tumors in animal models (Maes and colleagues 2006)
Safety signals
No clinical safety data exist for neurotensin (8-13), as it has not entered human studies. Its native half-life of under 2 minutes in plasma — due to rapid cleavage at Arg8-Arg9 by nephrilysin, at Pro10-Tyr11 by thimetoligopeptidase, and at Tyr11-Ile12 by neurolysin — means that systemic administration delivers negligible intact peptide. Hypothermia and hypotension are known effects of central neurotensin system activation in animals, consistent with known cardiovascular and thermoregulatory actions of NTSR1. These effects inform the safety profile considerations for NT-based analog programs rather than for the native fragment itself.
Mechanism
Neurotensin (8-13) binds to NTSR1, a class A G-protein-coupled receptor, in an extended conformation nearly perpendicular to the membrane plane with its C-terminus oriented toward the receptor core. The binding pocket spans the N-terminus, three extracellular loops, and transmembrane helices TM2-TM7, with positively charged arginines (Arg8, Arg9) engaging an electronegative rim at the extracellular face and the Tyr-Ile-Leu triad making contacts deeper in the pocket (White and colleagues 2012). Upon binding, the peptide induces contraction of the extracellular binding pocket, stabilizing an active receptor conformation that couples preferentially to Gq/11 protein and triggers IP1 accumulation and protein kinase C activation (Besserer-Offroy and colleagues 2017; Deluigi and colleagues 2021). Receptor phosphorylation by GRK5 at intracellular loop 3 and C-terminal sites then enables β-arrestin 1 recruitment — a process structurally characterized at 4.2 Å by Huang and colleagues (2020), who found that a phosphatidylinositol-4,5-bisphosphate molecule bridges the receptor and arrestin. Maharana and colleagues (2021) resolved the complex in a native-like lipid bilayer environment, providing additional detail on the Gi coupling mode.
The fragment's rapid proteolytic degradation (half-life <2 min) at three distinct cleavage sites has driven a field of NT(8-13)-based medicinal chemistry, with backbone modifications — including pseudopeptide bonds and unnatural amino acids at key cleavage positions — extending plasma stability from minutes to over 24 hours in some analogs while preserving NTSR1 agonist activity.
Open questions
- No metabolically stable NT(8-13) analog has yet completed human clinical trials for any indication
- The relative contributions of NTS1 vs NTS2 to opioid-independent antinociception remain under investigation; NTS2-selective analogs are an active area of development
- Selectivity for NTSR1 over NTSR2 (neurotensin type 2 receptor) in the parent NT(8-13) fragment means dual-receptor pharmacology requires structural modification
- The precise mechanism by which NTSR1 activation normalizes CSF neurotensin levels in schizophrenia has not been fully resolved
Related peptides
- Full-length neurotensin (1-13) — the parent 13-residue neuropeptide from which this fragment is derived; carries the N-terminal pyroGlu cap and full sequence not required for NTSR1 activation
- Neuromedin N — a related hexapeptide (Lys-Ile-Pro-Tyr-Ile-Leu) that activates both NTSR1 and NTSR2 and shares structural similarity with NT(8-13); characterized alongside NT(8-13) in Besserer-Offroy and colleagues (2017)
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.
Do the neurotensin and GLP-1 satiety signals travel to the brain through different nerve fibers, making them independently stackable for stronger appetite control?
If the two pathways are separate, combining a neurotensin-based drug with existing obesity medications like semaglutide could produce stronger weight loss with lower doses of each, potentially reducing the nausea and vomiting that cause many patients to stop treatment.
Would swapping one amino acid building block for a fluorine-bearing version force this peptide into its active shape before it even reaches the receptor?
If this single change increases potency, it could help create a more effective non-opioid pain treatment or a neuroprotective drug for stroke, using a modification already proven safe in other drug candidates.
Do the two arginine residues at the front of this peptide grip the outside of its brain receptor and slow the peptide from detaching?
If this slower detachment is confirmed, drug designers could exploit it to create longer-acting treatments for pain or body-temperature disorders, reducing how often patients need dosing.
Do the last two building blocks of this peptide act as a molecular key that fits one neurotensin receptor but not its close relative?
If this selectivity mechanism is confirmed, drug designers could tune the tail of neurotensin-derived compounds to hit only the receptor associated with pain relief, avoiding the one that might worsen chronic pain.
Could activating the neurotensin receptor with this small peptide reduce the brain's excessive response to addictive drugs while leaving everyday enjoyment intact?
If true, this could form the basis of a new class of addiction treatments that reduce relapse-driving cravings without the flat, joyless state that makes existing dopamine-blocking drugs hard to tolerate.
▸full evidence table2 metrics
| metric | value | tool |
|---|---|---|
| ipTM | 0.9769219756126404 | boltz-2 |
| ranking score | 0.794795572757721 | boltz-2 |
▸structural qualityopenfold3
| metric | value | note |
|---|---|---|
| gpde | 0.922 | global PDE — lower = better |
| disorder | NaN | fraction disordered |
▸3-letter notation
▸recipeboltz-2 1.0
| parameter | value |
|---|---|
| model | boltz-2 1.0 |
| weights | — |
| hardware | nvidia_nim_api |
| mlx version | — |
| python | — |
| random seed | — |
| msa strategy | none |
| diffusion samples | 1 |
| runtime | — |
| predicted by | mlx@peptide |
| predicted at | 2026-04-24 |
▸citationbibtex
@peptide{pep10639,
sequence = {RRPYIL},
target = {ntsr1},
author = {peptidemodel},
year = {2026},
status = {synthesized}
}