What Is Neurokinin B? Definition and What Research Reports

Definition

Neurokinin B (NKB) is a small peptide belonging to the tachykinin family, encoded in humans by the TAC3 gene (Tac2 in rodents) and acting primarily at the neurokinin-3 receptor (NK3R), the product of the TACR3 gene. In the mammalian brain, NKB is produced in large amounts by a population of hypothalamic neurons that also express kisspeptin and dynorphin — commonly abbreviated KNDy neurons — located mainly in the arcuate nucleus (the infundibular nucleus in humans). Within peptide neuroendocrinology, the term "neurokinin B" is used both for the peptide itself and, loosely, as shorthand for the NKB–NK3R signalling arm of the reproductive axis that sits upstream of gonadotropin-releasing hormone (GnRH) release.

This page is for educational purposes only and is not medical advice; consult a licensed physician for any question about health, medication or laboratory testing.

What Class of Molecule Is It?

Tachykinins are a conserved family of short signalling peptides that share a common C-terminal motif and act on G protein-coupled receptors. NKB is one of three classical mammalian tachykinins alongside substance P and neurokinin A, and it shows the strongest relative preference for NK3R. Because it is a genetically encoded neuropeptide rather than a synthetic construct, NKB in the published literature is usually studied as an endogenous signal — measured by immunohistochemistry, gene expression, or serum assay — or as a pharmacological tool alongside NK3R agonists and antagonists.

Receptor-level work has mapped how the peptide engages its target. A mutational analysis of the neurokinin-3 receptor examined the characteristics of NK3R and its binding sites, and the researchers reported structural determinants that contribute to ligand recognition at the receptor (PMID 34681067). Separately, a biochemistry report described NKB and serum albumin as factors that limited copper binding to mammalian GnRH, indicating that the peptide has been studied for chemical as well as neural properties (PMID 29427668).

Quick reference

How the Term Is Used in Peptide Research

In the research literature, "neurokinin B" most often appears in three contexts. First, as one member of the KNDy triad, where it is discussed as part of the machinery thought to shape pulsatile GnRH and downstream luteinising hormone (LH) secretion. Second, as a receptor-pharmacology target, where NK3R agonists and antagonists are used to probe that circuit. Third, as a measurable biomarker in clinical and veterinary studies, where circulating or tissue NKB levels are compared across developmental stages or conditions.

A dedicated review of the interactions between kisspeptins and neurokinin B set out how the two peptides have been treated as interacting components of the same hypothalamic network rather than as independent signals (PMID 23550013). A more recent physiological review of kisspeptin and neurokinin B in reproductive health similarly framed both peptides as central regulators of the reproductive axis across species (PMID 39813600).

What the Published Literature Reports

Puberty and GnRH release

A study in female rhesus monkeys reported that a kisspeptin and neurokinin B signalling network underlies the pubertal increase in GnRH release, linking the two peptides to the developmental rise in hypothalamic output (PMID 28977601). In sheep, researchers examined kisspeptin, neurokinin B and dynorphin expression across pubertal development in females and described how expression of these KNDy markers changed with developmental stage (PMID 34681086).

Nutritional status

The link between metabolic state and this circuit has also been probed. In castrated male sheep, the study reported that undernutrition reduced kisspeptin and neurokinin B expression, consistent with the broader idea that energy availability is relayed to the reproductive axis at the level of KNDy neurons (PMID 35128420).

Thermoregulation and hot flushes

One of the most cited applications of NKB biology concerns menopausal vasomotor symptoms. A review in Frontiers in Neuroendocrinology proposed that hypothalamic KNDy (kisspeptin, neurokinin B and dynorphin) neurons modulate both body temperature and LH secretion, and the authors advanced this as a novel hypothesis on the mechanism of hot flushes (PMID 23872331). That hypothesis is why NK3R pharmacology has been discussed in connection with vasomotor symptoms in subsequent reviews.

Sex differences and anatomy

Anatomical work has looked beyond the arcuate nucleus. A study in sheep reported morphological and functional evidence for sexual dimorphism in neurokinin B signalling in the retrochiasmatic area, indicating that NKB circuitry is not identical between males and females (PMID 32572994).

Non-mammalian models

NKB is conserved well beyond mammals. In the freshwater catfish Clarias batrachus, researchers examined the role of neurokinin B in gametogenesis and steroidogenesis and reported involvement of NKB signalling in reproductive processes in this species (PMID 37278825). Comparative findings of this kind are often used to argue that the peptide's reproductive role is evolutionarily old.

Measurement in clinical populations

NKB has also been measured as a circulating analyte. A pediatric endocrinology study measured serum kisspeptin, leptin, neuropeptide Y and neurokinin B levels in adolescents with polycystic ovary syndrome and compared them with controls (PMID 35170267). Findings of that type are descriptive associations and do not by themselves establish cause.

Therapeutic Discussion and Adverse Events: What Studies Report

An Endocrine Reviews article on the emerging therapeutic potential of kisspeptin and neurokinin B reviewed how these peptides and their receptors have been considered as targets in reproductive and neuroendocrine medicine (PMID 37467734). The broader physiological review of kisspeptin and neurokinin B in reproductive health likewise summarised the state of the evidence across species (PMID 39813600). The verified sources summarised on this page are reviews, animal studies and observational measurements; they were not designed as safety trials of an administered product, and no dosing, administration schedule or tolerability profile is described here because the cited literature above does not supply one in the scope of this entry. Any claim about safety in humans would need to come from trial reports that specifically measured adverse events.

Terms Commonly Confused With Neurokinin B

• Neurokinin A and substance P — the other classical mammalian tachykinins; they prefer NK2R and NK1R respectively rather than NK3R.
• NK3R / TACR3 — the receptor, not the peptide. Loss-of-function variants in TAC3 and TACR3 are discussed in the reproductive literature summarised in reviews of kisspeptin and neurokinin B (PMID 39813600).
• Kisspeptin — a separate peptide co-expressed in the same KNDy neurons; the two are studied together but are distinct molecules with distinct receptors (PMID 23550013).
• Dynorphin — an opioid peptide, the third member of the KNDy triad, examined alongside NKB in pubertal sheep (PMID 34681086).

How to Read Claims About NKB

1. Check whether a statement refers to the peptide, the receptor, or a drug acting at the receptor — these are frequently blurred.
2. Check the species. Much of the mechanistic detail comes from sheep, monkeys and fish rather than humans.
3. Check whether a measurement is an association (for example serum levels in a defined group) or an intervention.
4. Check whether a proposed mechanism, such as the KNDy hypothesis of hot flushes, was framed as a hypothesis by its authors (PMID 23872331).

References

• Kisspeptin and neurokinin B: roles in reproductive health (Physiological Reviews, 2025)
• The Emerging Therapeutic Potential of Kisspeptin and Neurokinin B (Endocrine Reviews, 2024)
• Modulation of body temperature and LH secretion by hypothalamic KNDy (kisspeptin, neurokinin B and dynorphin) neurons: a novel hypothesis on the mechanism of hot flushes (Frontiers in Neuroendocrinology, 2013)
• Kisspeptin, Neurokinin B, and Dynorphin Expression during Pubertal Development in Female Sheep (Biology, 2021)
• Role of Neurokinin B in gametogenesis and steroidogenesis of freshwater catfish, Clarias batrachus (Cell and Tissue Research, 2023)
• Undernutrition reduces kisspeptin and neurokinin B expression in castrated male sheep (Reproduction & Fertility, 2020)
• Morphological and functional evidence for sexual dimorphism in neurokinin B signalling in the retrochiasmatic area of sheep (Journal of Neuroendocrinology, 2020)
• Characteristics of Neurokinin-3 Receptor and Its Binding Sites by Mutational Analysis (Biology, 2021)
• Interactions between kisspeptins and neurokinin B (Advances in Experimental Medicine and Biology, 2013)
• Kisspeptin and Neurokinin B Signaling Network Underlies the Pubertal Increase in GnRH Release in Female Rhesus Monkeys (Endocrinology, 2017)
• Serum kisspeptin, leptin, neuropeptide Y, and neurokinin B levels in adolescents with polycystic ovary syndrome (Journal of Pediatric Endocrinology & Metabolism, 2022)
• Neurokinin B and serum albumin limit copper binding to mammalian gonadotropin releasing hormone (Biochemical and Biophysical Research Communications, 2018)