Kisspeptin and Hot Flashes: The KNDy Neuron Link
Menopause and Peptide Hormones
70% of women
Roughly 70% of women experience vasomotor symptoms during menopause, driven by overactivation of kisspeptin-producing neurons in the hypothalamus.
Rackova, Ceska Gynekologie, 2025
Rackova, Ceska Gynekologie, 2025
View as imageHot flashes are the hallmark symptom of menopause, affecting roughly 70% of women during the menopausal transition. For decades, the mechanism was poorly understood. The breakthrough came from a cluster of hypothalamic neurons that produce three neuropeptides: kisspeptin, neurokinin B, and dynorphin. These KNDy neurons, named for their three peptide products, act as the brain's reproductive thermostat. When estrogen drops during menopause, these neurons become hyperactive, disrupting the body's temperature regulation and triggering the sudden heat, flushing, and sweating that define vasomotor symptoms.[1] This discovery has already produced the first FDA-approved non-hormonal treatment for hot flashes. This article is part of a broader look at how peptide hormones change during menopause.
Key Takeaways
- KNDy neurons produce kisspeptin, neurokinin B, and dynorphin, forming the central pacemaker that controls GnRH pulses and connects to temperature regulation (Lehman et al., 2010)
- When estrogen declines during menopause, KNDy neurons lose their inhibitory brake and become hyperactive, driving both excessive GnRH pulsing and vasomotor symptoms (Rackova, 2025)
- Neurokinin B acts through NK3 receptors to stimulate kisspeptin release and activate nearby thermoregulatory neurons, creating the physiological link between reproductive signaling and hot flashes (Mills and Dhillo, 2022)
- Fezolinetant, an NK3 receptor antagonist targeting this pathway, reduced hot flash frequency by 61% at 45 mg in phase 3 trials and received FDA approval in 2023
- Kisspeptin itself is being studied as a therapeutic target, with clinical trials showing it modulates brain processing in women with hypoactive sexual desire disorder (Mills et al., 2022, n=32)
- Only 15% of clinical kisspeptin studies have addressed metabolic effects despite clear evidence of metabolic regulation through kisspeptin receptors in brain, brown fat, and pancreas (Sliwowska et al., 2024)
What Are KNDy Neurons?
KNDy neurons are a specialized population of cells in the arcuate nucleus of the hypothalamus that colocalize three neuropeptides: kisspeptin (KISS1), neurokinin B (NKB), and dynorphin (Dyn). Lehman, Coolen, and Goodman first defined this population in their 2010 minireview, showing that KNDy cells are "strongly conserved across a range of species from rodents to humans" and form a reciprocally interconnected network with direct projections to GnRH neurons.[2]
Each of the three peptides plays a distinct role. Kisspeptin is the primary stimulator of GnRH release, making it the master switch for the reproductive hormone cascade.[3] Neurokinin B acts locally within the KNDy network to synchronize firing and amplify kisspeptin release.[4] Dynorphin, an endogenous opioid, provides the inhibitory brake that keeps the system in check, creating the pulsatile pattern of GnRH secretion essential for normal reproductive function.[2]
These neurons express receptors for estradiol, progesterone, and testosterone, positioning them as the primary relay point where sex steroid feedback controls the brain's reproductive output.[1]
How KNDy Neuron Hyperactivation Causes Hot Flashes
The connection between reproductive peptides and body temperature was not obvious. KNDy neurons sit adjacent to the hypothalamic thermoregulatory center, and their axonal projections reach directly into the median preoptic nucleus, the brain region that controls core body temperature. This anatomical proximity creates a direct link between reproductive signaling and thermoregulation.
During the reproductive years, estrogen keeps KNDy neurons in a state of regulated activity through negative feedback. When ovarian estrogen production declines during menopause, that feedback disappears. The result is dramatic: KNDy neurons become hypertrophied and hyperactive, overproducing both kisspeptin and neurokinin B while downregulating dynorphin production.[1]
Rackova described this cascade: "Lack of negative feedback of steroid hormones synthesized in the ovary causes overactivation of hypertrophied KNDy neurons, and oversecretion of both kisspeptin and neurokinin B, as well as downregulation of dynorphin."[1]
The overproduced neurokinin B spills into the adjacent thermoregulatory zone, activating NK3 receptors on temperature-sensing neurons. This narrows the thermoneutral zone, the range of core body temperatures the brain considers normal. When the thermoneutral zone narrows, even small fluctuations in core temperature trigger the body's cooling response: peripheral vasodilation (the "flush"), sweating, and the subjective sensation of intense heat.
This is why hot flashes are not random. They are driven by a specific, identifiable peptide cascade: estrogen withdrawal leads to KNDy hyperactivation leads to excessive NKB release leads to thermoregulatory disruption.
Neurokinin B: The Peptide That Bridges Reproduction and Temperature
Of the three KNDy peptides, neurokinin B has emerged as the most direct driver of vasomotor symptoms. Mills and Dhillo reviewed the therapeutic translation of kisspeptin and NKB biology and identified NKB as the primary pharmacological target for menopausal flushing.[5]
NKB acts through the neurokinin 3 receptor (NK3R). Within the KNDy network, NKB signaling through NK3R synchronizes kisspeptin neuron firing, coordinating the pulsatile GnRH release that drives LH surges. But NK3R is also expressed on thermoregulatory neurons adjacent to the KNDy population, which is why excessive NKB release directly disrupts temperature control.
Lasaga and Debeljuk documented how tachykinins, the peptide family that includes NKB, interact with the hypothalamic-pituitary-gonadal axis at multiple levels, highlighting the complexity of this signaling system.[4]
This understanding led directly to drug development. Blocking NK3R with a selective antagonist should reduce hot flashes by preventing the excessive NKB signal from reaching thermoregulatory neurons, without shutting down the entire reproductive axis. That hypothesis proved correct.
From Peptide Biology to Approved Drug: NK3R Antagonists
Fezolinetant (Veozah), a selective NK3 receptor antagonist, received FDA approval in May 2023 for the treatment of moderate-to-severe vasomotor symptoms due to menopause. It was the first drug approved specifically by targeting the KNDy pathway.
In the SKYLIGHT 1 phase 3 trial, fezolinetant 45 mg reduced moderate-to-severe hot flash frequency by 61% at week 12, compared to 35% with placebo. Improvements began within the first week and were sustained through 52 weeks of treatment. Serious adverse events were infrequent: 0-2% across treatment groups.
Elinzanetant (Lynkuet), a dual NK1/NK3 receptor antagonist, received FDA approval in October 2025, providing a second option in this drug class. By targeting both NK1 and NK3 receptors, elinzanetant may offer additional benefits for sleep disturbance alongside hot flash reduction, as NK1 receptor signaling is involved in arousal and mood regulation.
Both drugs validate the KNDy neuron hypothesis: vasomotor symptoms in menopause are driven by specific neuropeptide pathways, and blocking those pathways provides relief without requiring hormone replacement. For a broader view of non-hormonal approaches, see peptide alternatives to hormone replacement therapy.
Kisspeptin as a Therapeutic Target Beyond Hot Flashes
While NKB antagonists have reached clinical use for hot flashes, kisspeptin itself is being investigated for a range of reproductive and metabolic applications.
Roa, Navarro, and Tena-Sempere described kisspeptin's consensus role as the gatekeeper of reproductive function, controlling puberty onset, fertility, and metabolic integration.[6] Tena-Sempere's earlier review characterized kisspeptin signaling as a system that integrates metabolic status with reproductive capacity, explaining why energy imbalance disrupts fertility.[3]
Mills et al. demonstrated kisspeptin's clinical potential in a randomized, double-blind, placebo-controlled crossover trial in 32 premenopausal women with hypoactive sexual desire disorder. Kisspeptin administration modulated sexual brain processing, deactivating the left inferior frontal gyrus and activating the right postcentral and supramarginal gyrus. Participants reported increased feelings of sexual desire and reduced sexual aversion compared to placebo.[7] This trial, published in JAMA Network Open, represents the first evidence that kisspeptin can address sexual dysfunction in women. The neuropeptide mechanisms at play overlap with those explored in GLP-1 drugs and their effects on brain reward systems.
Sliwowska et al. expanded the therapeutic landscape further, reviewing evidence that kisspeptin regulates metabolism through receptors in the brain, brown adipose tissue, and pancreas, in addition to its reproductive functions. Their analysis found that 85% of clinical kisspeptin studies have focused exclusively on fertility, while only 15% have addressed metabolic effects, despite clear preclinical evidence of metabolic regulation.[8]
For menopausal women, this dual role matters. Menopause brings both vasomotor symptoms and metabolic changes (increased abdominal fat, insulin resistance, cardiovascular risk). A peptide system that regulates both reproduction and metabolism could offer therapeutic approaches that address the full constellation of menopausal changes rather than isolated symptoms.
What Kisspeptin Research Reveals About Menopause Biology
The kisspeptin/KNDy neuron framework has transformed the understanding of menopause from "estrogen deficiency" to a more nuanced picture of neuropeptide dysregulation.
Amodei et al. demonstrated that KNDy neuron signaling is active and functional from fetal development onward, with kisspeptin and NKB already regulating LH and testosterone secretion in fetal sheep. Their work showed that more than 85% of arcuate kisspeptin cells costain for NKB, confirming the tight co-expression that defines the KNDy population.[9] This means the system that becomes dysregulated in menopause has been operational for an entire lifetime.
The sex difference is also relevant. Amodei et al. found that female fetal sheep had more abundant kisspeptin and NKB immunoreactive cells in the arcuate nucleus than males, and females showed greater NKB sensitivity. This innate sex difference in KNDy neuron density may partially explain why vasomotor symptoms predominantly affect women.[9]
How KNDy-Targeting Drugs Compare to Hormone Therapy
Hormone replacement therapy (HRT) remains the most effective treatment for vasomotor symptoms, reducing hot flash frequency by 75-90% in most studies. NK3R antagonists fall short of that efficacy ceiling (61% reduction with fezolinetant 45 mg), but they offer a critical advantage: they do not carry the breast cancer, cardiovascular, or thromboembolic risks associated with estrogen-progestogen therapy.
The mechanism is also fundamentally different. HRT replaces the missing estrogen, restoring the negative feedback on KNDy neurons from outside the system. NK3R antagonists work inside the KNDy circuit, blocking the specific peptide signal (NKB) that links reproductive neurons to the thermoregulatory center. This means NK3R antagonists are precisely targeted at the vasomotor mechanism, while HRT is a broad hormonal intervention that affects virtually every organ system.
For women who cannot take estrogen, whether due to breast cancer history, thromboembolic risk, or personal preference, NK3R antagonists represent the first mechanism-based alternative grounded in peptide neuroscience rather than empirical observation.
The dual NK1/NK3 approach of elinzanetant adds sleep benefits that single NK3R blockade may not fully address, as NK1 receptor signaling contributes to arousal and wake-sleep cycling. Whether combining both receptor targets proves superior to NK3R-only blockade in head-to-head trials remains an active area of investigation.
Evidence Gaps and Open Questions
The KNDy hypothesis for hot flashes has strong support, but several questions remain unanswered.
Why do some women get hot flashes and others don't? If estrogen withdrawal drives KNDy hyperactivation, every postmenopausal woman should have hot flashes. Yet roughly 30% do not. Individual differences in KNDy neuron density, NKB receptor expression, or compensatory mechanisms (perhaps involving dynorphin or other opioid pathways) likely explain this variation, but no study has definitively identified the protective factors.
What is the role of kisspeptin versus NKB? Current drugs target NKB (via NK3R antagonism), not kisspeptin directly. Whether kisspeptin antagonism would also reduce hot flashes, and whether it would carry different reproductive side effects, has not been tested in humans.
Long-term safety of NK3R antagonists. Fezolinetant trials extended to 52 weeks with a favorable safety profile. However, NKB signaling has roles beyond thermoregulation, including liver function and mood regulation. The hepatic effects in particular require ongoing monitoring, as liver enzyme elevations were observed in some trial participants.
The metabolic dimension. As Sliwowska et al. noted, kisspeptin's metabolic role is understudied clinically.[8] Whether NK3R antagonists affect the metabolic changes associated with menopause (weight gain, insulin resistance) is an open question that current trials have not been powered to answer.
For the complete picture of hormonal cascades during menopause, see how peptide hormones change during menopause. For a related non-hormonal approach, see fezolinetant: the neurokinin B antagonist that treats hot flashes.
The Bottom Line
Hot flashes are driven by hyperactivation of KNDy neurons in the hypothalamus after menopausal estrogen withdrawal. These neurons produce kisspeptin, neurokinin B, and dynorphin, and their excessive NKB output disrupts the brain's temperature regulation. This mechanism has already led to FDA-approved NK3 receptor antagonists (fezolinetant, elinzanetant) that reduce hot flash frequency by up to 61% without hormones. Kisspeptin itself is being studied for applications ranging from sexual dysfunction to metabolic regulation, suggesting the KNDy pathway holds therapeutic potential well beyond vasomotor symptoms.