Diabetes Drug Targets Found Hidden in the Brain’s Thirst and Water-Conservation Neurons

One of the most widely prescribed drug classes in modern medicine may owe part of its remarkable success to an unexpected destination: the brain. Sodium-glucose cotransporter 2 inhibitors, or SGLT2 inhibitors, were originally developed to lower blood sugar by blocking glucose reabsorption in the kidney, yet large clinical trials have shown that they protect the heart and kidneys in patients with or without diabetes. A new study in rats now offers the first cellular-resolution map of where the molecular target of these drugs sits inside the fluid-regulating circuitry of the brain, and the answer may explain a long-standing puzzle about why these medicines consistently make animals and patients drink more water and release more vasopressin, the hormone that helps the body hold on to water.

The research, published in Physiological Reports by a team led by Takahiro Masuda and Masahide Yoshida of Jichi Medical University together with colleagues in Japan and the United States, examined whether the gene encoding SGLT2, known formally as Slc5a2, is switched on in the neurons that govern thirst and vasopressin synthesis. For years, physiologists have observed that SGLT2 inhibitors stimulate water intake and vasopressin secretion even when blood volume and plasma osmolality remain normal, which suggests that something beyond simple dehydration is driving these responses. Because the drugs can cross the blood-brain barrier and SGLT2 immunoreactivity had previously been reported in brain tissue, the team suspected that the transporter might be present in the very neurons that control drinking behavior and hormone release.

To find out, the researchers studied male Sprague-Dawley rats and combined two complementary techniques: droplet digital PCR, an ultra-sensitive method for quantifying gene transcripts, and in situ hybridization, which reveals exactly which cells express a given gene. Using droplet digital PCR on micro-punched tissue samples, they detected Sglt2 messenger RNA in four key regions: the organum vasculosum of the lamina terminalis (OVLT) and the subfornical organ (SFO), two sensory circumventricular organs that form the brain’s thirst center, and the supraoptic nucleus (SON) and paraventricular nucleus (PVN) of the hypothalamus, where vasopressin is synthesized. The relative abundance of Sglt2 transcripts in these regions, normalized to the housekeeping gene Polr2a, fell in the range of 0.02 to 0.04, a level comparable to that of Agtr1a, the angiotensin II receptor type 1a gene that is well established as a central regulator of drinking and vasopressin release.

Brain expression was, unsurprisingly, far lower than in the kidney, the body’s dominant site of SGLT2 expression. Depending on which of three internal control genes was used for normalization, Sglt2 expression in the paraventricular nucleus, the region with the strongest signal, was roughly 76 to 205 times lower than in kidney tissue. Yet the authors argue that low abundance does not mean functional irrelevance. The fact that Sglt2 transcripts appear at levels similar to those of Agtr1a, a gene whose central role in thirst regulation is beyond dispute, suggests that even modest neuronal expression could be physiologically meaningful, particularly if the neurons involved are the direct targets of circulating drug.

The anatomical story became far more compelling when the team turned to double fluorescent in situ hybridization, a technique that can visualize two genes simultaneously within single cells. In the OVLT and the SFO, Sglt2 messenger RNA was clearly present in neurons that also express Nos1, the gene encoding neuronal nitric oxide synthase. These NOS1-expressing neurons are known from landmark studies to be the excitatory, thirst-promoting cells of the circumventricular organs; when activated, they drive drinking behavior, and they send direct projections to the vasopressin-producing nuclei of the hypothalamus. Quantification showed that approximately 48.1 percent of NOS1-positive neurons in the OVLT and 60.3 percent in the SFO expressed Sglt2. In other words, the molecular target of SGLT2 inhibitors sits within roughly half of the very neurons that command an animal to drink.

The co-localization in the hypothalamus was even more striking. In the supraoptic nucleus, 80.8 percent of vasopressin-expressing neurons carried Sglt2 transcripts, and in the paraventricular nucleus the figure reached 84.0 percent. The researchers also examined oxytocin neurons, the other major neuroendocrine population in these nuclei, and found Sglt2 expression in 58.9 percent of oxytocin neurons in the SON and 65.7 percent in the PVN. Chromogenic in situ hybridization confirmed the pattern at the tissue level, with Sglt2 signals appearing not only in the four fluid-regulating regions but also in the choroid plexus, consistent with earlier reports in human and mouse brains that identified the transporter in choroid plexus epithelial cells and ependymal cells. Prior work had also located SGLT2 in brain pericytes and in neurons of the rostral ventrolateral medulla, a master controller of sympathetic nerve activity, but this study is the first to pin the transporter down at single-cell resolution within the thirst and vasopressin circuits themselves.

These findings provide an anatomical basis for a hypothesis that has been gathering force in the literature: that SGLT2 inhibitors act directly on the brain, not merely through the kidney. Two features of the circumventricular organs make this plausible. First, the OVLT and SFO sit outside a functional blood-brain barrier, meaning drugs circulating in the bloodstream can reach them directly. Second, SGLT2 inhibitors as a class have been shown to penetrate the blood-brain barrier, and central administration of the drug tofogliflozin has already been demonstrated to stimulate water intake in non-diabetic rats, just as peripheral administration of ipragliflozin does in both diabetic and non-diabetic animals. If SGLT2 inhibitors enhance the excitability of NOS1 thirst neurons in the OVLT and SFO, that could trigger drinking independently of any actual fluid deficit, which would explain the paradoxical observation that these drugs increase vasopressin secretion and copeptin levels, a stable clinical surrogate for vasopressin, even under normal osmotic conditions.

The authors go further, weaving in evidence from glucose-sensing physiology. In the SFO, a subset of so-called glucose-inhibited neurons, cells that become excited when intracellular glucose falls, shares properties with NOS1 neurons, and many glucose-inhibited neurons also respond to angiotensin II, a potent dipsogenic hormone. Roughly 27 percent of SFO neurons show this glucose-inhibited character, and the majority of them respond to angiotensin II. The team speculates that by reducing intracellular glucose uptake through SGLT2, the inhibitors might directly stimulate a NOS1-positive, glucose-sensing population, initiating drinking before osmotic diuresis has had time to deplete body fluids. Intriguingly, a parallel logic operates in the kidney: in macula densa cells, which behave in many ways like neurons, SGLT1-mediated glucose uptake supports NOS1 activity that modulates tubuloglomerular feedback. The authors suggest that SGLT-dependent glucose sensing linked to nitric oxide synthase may thus push systemic fluid balance in a negative direction in both organs, a conceptual echo of coupled hunger-and-thirst sensing described in the fly brain.

Important caveats remain, and the authors are careful about them. This study mapped gene expression; it did not directly test function. Whether blocking SGLT2 in these neurons actually changes their electrical activity, drinking behavior, or vasopressin release has not yet been demonstrated, and global SGLT2 knockout mice, which drink more and secrete more vasopressin than wild-type animals, cannot disentangle central from renal mechanisms because fluid balance disturbances confound the interpretation. Brain-region-specific knockout models and intracerebroventricular drug administration will be needed to establish causality, along with electrophysiological recordings and activity markers such as Fos in SGLT2-expressing neurons. It is also uncertain how much of the vasopressin response during SGLT2 inhibition reflects direct central action versus classical osmotic pathways, since clinical studies show copeptin remains strongly tied to plasma osmolality during treatment. Still, the finding that Sglt2 is expressed in the majority of vasopressin neurons and roughly half of thirst-promoting NOS1 neurons reframes how scientists think about these drugs. Beyond fluid balance, vasopressin and oxytocin neurons influence social behavior, stress responses, and learning and memory, raising the speculative but testable possibility that SGLT2 inhibitors touch neuroendocrine circuits far beyond hydration. If the central mechanisms are confirmed, they could deepen understanding of the brain-kidney axis and help explain why a drug class designed to squeeze glucose out of urine has turned out to be one of the most versatile cardiorenal therapies ever developed.

Subject of Research: SGLT2 gene expression in thirst-promoting NOS1 neurons and vasopressin-synthesizing neurons in the rat brain

Article Title: SGLT2 gene expression in thirst‐promoting NOS1 neurons and vasopressin‐synthesizing neurons in male rats

Article References: Masuda, T., Yoshida, M., Kim, Y. C., Vallon, V., Morishita, Y., Nagata, D., & Onaka, T. (2026). SGLT2 gene expression in thirst‐promoting NOS1 neurons and vasopressin‐synthesizing neurons in male rats. Physiological Reports, 14(17), Article e71100. https://doi.org/10.14814/phy2.71100

Image Credits: AI Generated

DOI: 10.14814/phy2.71100

Keywords: SGLT2, Slc5a2, thirst, vasopressin, NOS1 neurons, subfornical organ, organum vasculosum laminae terminalis, supraoptic nucleus, paraventricular nucleus, fluid homeostasis, in situ hybridization, cardiorenal