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The human liver and pancreas are central to metabolic regulation, with the autonomic nervous system orchestrating processes that maintain glucose homeostasis and respond to dynamic physiological demands—ranging from acute energy mobilization during stress to postprandial glucose uptake and storage. However, visualizing and examining the intricate three-dimensional (3D) neural networks within clinical liver and pancreas specimens remains challenging, as conventional two-dimensional (2D) histological methods cannot fully resolve the spatial complexity of autonomic innervation in the liver and pancreas. This review identifies and discusses key biological and technical factors—including tissue autofluorescence, autolysis, photobleaching, and steatosis—that compromise the reliability of 3D neurohistological analysis of the human liver and pancreas. We also highlight emerging optical and chemical methodologies that enable high- and super-resolution 3D tissue imaging, improving signal fidelity, preserving structural detail, and supporting consistent, reproducible analysis. Ultimately, these advances aim to facilitate precise mapping of human liver and pancreas innervation, offering deeper insight into the neural regulation of nutrient assimilation, glucose utilization, and metabolic homeostasis in both physiological and pathological contexts.

Hepatic steatosis develops when lipid influx and production exceed the liver’s ability to utilize/export triglycerides. Obesity promotes steatosis and is characterized by leptin resistance. A role of leptin in hepatic lipid handling is highlighted by the observation that recombinant leptin reverses steatosis of hypoleptinemic patients with lipodystrophy by an unknown mechanism. Since leptin mainly functions via CNS signaling, we here examine in rats whether leptin regulates hepatic lipid flux via the brain in a series of stereotaxic infusion experiments. We demonstrate that brain leptin protects from steatosis by promoting hepatic triglyceride export and decreasing de novo lipogenesis independently of caloric intake. Leptin’s anti-steatotic effects are generated in the dorsal vagal complex, require hepatic vagal innervation, and are preserved in high-fat-diet-fed rats when the blood brain barrier is bypassed. Thus, CNS leptin protects from ectopic lipid accumulation via a brain-vagus-liver axis and may be a therapeutic strategy to ameliorate obesity-related steatosis. Obesity is associated with leptin resistance and rising blood leptin levels while central leptin exposure may be limited. Here, the authors show that brain leptin infusion reduces hepatic lipid content in rats by increasing hepatic VLDL secretion and lowering liver de novo lipogenesis via a vagal mechanism.

Hepatic lipid metabolism is regulated by the autonomic nervous system of the liver, with the sympathetic innervation being extensively studied, while the parasympathetic efferent innervation is less understood despite its potential importance. In this study, we investigate the consequences of disrupted brain–liver communication on hepatic lipid metabolism in mice exposed to obesogenic conditions. We found that a subset of hepatocytes and cholangiocytes are innervated by parasympathetic nerve terminals originating from the dorsal motor nucleus of the vagus. The elimination of the brain–liver axis by deleting parasympathetic cholinergic neurons innervating the liver prevents hepatic steatosis and promotes browning of inguinal white adipose tissue (ingWAT). The loss of liver-innervating cholinergic neurons increases hepatic Cyp7b1 expression and fasting serum bile acid levels. Furthermore, knockdown of the G protein-coupled bile acid receptor 1 gene in ingWAT reverses the beneficial effects of the loss of liver-innervating cholinergic neurons, leading to the reappearance of hepatic steatosis. Deleting liver-innervating cholinergic neurons has a small but significant effect on body weight, which is accompanied by an increase in energy expenditure. Taken together, these data suggest that targeting the parasympathetic cholinergic innervation of the liver is a potential therapeutic approach for enhancing hepatic lipid metabolism in obesity and diabetes.

Tools for noninvasively modulating neural signaling in peripheral organs will advance the study of nerves and their effect on homeostasis and disease. Herein, we demonstrate a noninvasive method to modulate specific signaling pathways within organs using ultrasound (U/S). U/S is first applied to spleen to modulate the cholinergic anti-inflammatory pathway (CAP), and US stimulation is shown to reduce cytokine response to endotoxin to the same levels as implant-based vagus nerve stimulation (VNS). Next, hepatic U/S stimulation is shown to modulate pathways that regulate blood glucose and is as effective as VNS in suppressing the hyperglycemic effect of endotoxin exposure. This response to hepatic U/S is only found when targeting specific sub-organ locations known to contain glucose sensory neurons, and both molecular (i.e. neurotransmitter concentration and cFOS expression) and neuroimaging results indicate US induced signaling to metabolism-related hypothalamic sub-nuclei. These data demonstrate that U/S stimulation within organs provides a new method for site-selective neuromodulation to regulate specific physiological functions. Stimulation of peripheral nerve activity may be used to treat metabolic and inflammatory disorders, but current approaches need implanted devices. Here, the authors present a non-invasive approach, and show that ultrasound-mediated stimulation can be targeted to specific sub-organ locations in preclinical models and alter the response of metabolic and inflammatory neural pathways.

Engineering replacement organs is the next frontier in therapeutic technologies. Yet, the integration of innervation—critical for organ development, function, and homeostasis—remains underexplored. This review highlights the role of neural inputs in regulating critical organs including pancreas, liver, salivary gland, and spleen. We examine organ-specific neuroanatomy and emerging strategies to incorporate neuronal-axonal networks in engineered organs, drawing from innovations in scaffold design, multi-cell culture techniques, neural engineering, and biofabrication. Finally, we discuss tools for evaluating innervation across in vitro, preclinical, and clinical settings, advocating for innervation as a core design element in next-generation artificial organs. As tissue engineering has developed it has become apparent that multiple inputs are needed to fully replicate tissues, neuronal-axonal networks are an important part of this. In this review, the authors explore the advances in biomanufacturing and multi cell techniques aiming to generate tissues with integrated neuronal networks.

ObjectiveHepatic steatosis accompanying obesity is a major health concern, since it may initiate non-alcoholic fatty liver disease (NAFLD) and associated complications like cirrhosis or cancer. Intestinal gluconeogenesis (IGN) is a recently described function that contributes to the metabolic benefits of specific macronutrients as protein or soluble fibre, via the initiation of a gut-brain nervous signal triggering brain-dependent regulations of peripheral metabolism. Here, we investigate the effects of IGN on liver metabolism, independently of its induction by the aforementioned macronutrients.DesignTo study the specific effects of IGN on hepatic metabolism, we used two transgenic mouse lines: one is knocked down for and the other overexpresses glucose-6-phosphatase, the key enzyme of endogenous glucose production, specifically in the intestine.ResultsWe report that mice with a genetic overexpression of IGN are notably protected from the development of hepatic steatosis and the initiation of NAFLD on a hypercaloric diet. The protection relates to a diminution of de novo lipogenesis and lipid import, associated with benefits at the level of inflammation and fibrosis and linked to autonomous nervous system. Conversely, mice with genetic suppression of IGN spontaneously exhibit increased hepatic triglyceride storage associated with activated lipogenesis pathway, in the context of standard starch-enriched diet. The latter is corrected by portal glucose infusion mimicking IGN.ConclusionWe conclude that IGN per se has the capacity of preventing hepatic steatosis and its eventual evolution toward NAFLD.

Systemic immunosuppression has been associated with stroke for many years, but the underlying mechanisms are poorly understood. In this study, we demonstrated that stroke induced profound behavioral changes in hepatic invariant NKT (iNKT) cells in mice. Unexpectedly, these effects were mediated by a noradrenergic neurotransmitter rather than a CD1d ligand or other well-characterized danger signals. Blockade of this innervation was protective in wild-type mice after stroke but had no effect in mice deficient in iNKT cells. Selective immunomodulation of iNKT cells with a specific activator (α-galactosylceramide) promoted proinflammatory cytokine production and prevented infections after stroke. Our results therefore identify a molecular mechanism that leads to immunosuppression after stroke and suggest an attractive potential therapeutic alternative to antibiotics, namely, immunomodulation of iNKT cells to prevent stroke-associated infections.

The visceral organ-brain axis, mediated by vagal sensory neurons, is essential for maintaining various physiological functions. Here, we investigate the impact of liver-projecting vagal sensory neurons on energy balance, hepatic steatosis, and anxiety-like behavior in mice under obesogenic conditions. A small subset of vagal sensory neurons innervate the liver and project centrally to the nucleus of the tractus solitarius, area postrema, and dorsal motor nucleus of the vagus, and peripherally to the periportal areas in the liver. The loss of these neurons prevents diet-induced obesity, and these outcomes are associated with increased energy expenditure. Although males and females exhibit improved glucose homeostasis following disruption of liver-projecting vagal sensory neurons, only male mice display increased insulin sensitivity. Furthermore, the loss of liver-projecting vagal sensory neurons limits the progression of hepatic steatosis. Intriguingly, mice lacking liver-innervating vagal sensory neurons also exhibit less anxiety-like behavior compared to control mice. Modulation of the liver-brain axis may aid in designing effective treatments for both psychiatric and metabolic disorders associated with obesity and MAFLD. Liver-projecting vagal sensory neurons play a key role in regulating energy balance, hepatic steatosis, and anxiety-like behavior in mice under obesogenic conditions. Modulating the liver-brain axis via the vagus nerve may offer a promising therapeutic approach for improving lipid metabolism, glucose homeostasis, and affective disorders in obesity and diabetes.

The liver communicates with the brain by transmitting interoceptive signals, including nutrients, hormones, and cytokines, potentially via the liver-innervating vagal sensory neurons. This communication is crucial for maintaining metabolic homeostasis and emotional stability.

This study quantified the distribution of nerves and adjacent anatomies surrounding human common hepatic artery (CHA) as guidance for catheter based denervation. CHA collected from cadaveric human donors (n = 20) were histologically evaluated and periarterial dimensions and distributions of nerves, lymph nodes, pancreas and blood vessels quantified by digital morphometry. Nerve abundance decreased significantly with distance from the aortic ostium (P < 0.0001) and was higher in the Superior/Inferior compared to the Anterior/Posterior quadrants (P = 0.014). In each locational group, nerves were absent from the artery wall, and starting 0.5–1.0 mm from the lumen exhibited a first order dependence on radial distance, fully defined by the median distance. Median subject-averaged nerve distance to the lumen was 2.75 mm, ranging from 2.1–3.1 mm in different arterial segments and quadrants and 2.0–3.5 mm in individuals. Inter-individual variance was high, with certain individuals exhibiting 50th and 75th nerve distances of, respectively, 3.5 and 6.5 mm The pancreas rarely approached within 4 mm of the lumen proximally and 2.5 mm more distally. The data indicate that the CHA is a rich and accessible target for sympathetic denervation regardless of sex and diabetes, with efficacy and safety most optimally balanced proximally.