Biology subjects

Knight, Z. A.

Publications and source records attributed to Knight, Z. A..

14 recordsLinked to original sources

bioRxiv2026

A learned oral signal drives long-lasting thirst satiation

Drinking quenches thirst long before the ingested water has been absorbed. Here we investigate the mechanism by combining sham drinking, which uncouples water ingestion from rehydration, with recordings of thirst-promoting neurons in the brain. We show that sham drinking suppresses thirst and rapidly inhibits thirst-promoting neurons despite no water absorption. Remarkably, this suppression of thirst neurons in the absence of rehydration is proportional to the amount of water consumed and persists for tens of minutes after drinking has stopped. This sustained inhibition is triggered by passage of water through the oral cavity, but not licking or swallowing alone, and undergoes extinction with repeated sham drinking, indicating it is learned. Complementary experiments using hypertonic saline demonstrate this learning is bidirectional. These findings reveal that the experience of rapid thirst quenching is not a hard-wired response to the consumption of water, but rather a learned prediction of future bodily state.

neuroscience↗

bioRxiv2026

Reciprocal control of the stomach and intestine by viscerosensory neurons in caudal brainstem

Digestion requires precisely timed transit of food through the gastrointestinal tract. Here we show that emptying of food from the stomach occurs in discrete pulses, separated by pauses that allow the proximal duodenum to clear before the next bolus arrives. By combining X-ray fluoroscopy of the gut with calcium imaging of the brainstem, we identify a population of neurons defined by expression of neuropeptide FF (NPFF) that tracks these duodenal dynamics. Stimulation of NPFF neurons induces a coordinated response that inhibits gastric emptying and accelerates intestinal transit, thereby clearing the proximal intestine for the next bolus of food. These neurons also bidirectionally control food intake through cholinergic signaling in the gut. These findings reveal a mechanism by which brainstem transforms the sensory detection of nutrients in the duodenum into the opposing control of the stomach and intestine. They also establish an experimental approach for dissecting gut-brain signaling in behaving animals.

neuroscience↗

bioRxiv2026

Opposing GIPR brainstem circuits differentially control feeding behaviour

Central glucose-dependent insulinotropic polypeptide receptor (GIPR) signalling is required for the efficacy of GIP-based obesity therapeutics, yet how distinct subpopulations of GIPR neurons shape appetite remains undefined. Here we show that GIPR neurons in adjacent brainstem nuclei, the area postrema (AP) and nucleus tractus solitarius (NTS), exert opposing control over ingestion. We find GIPRAP neurons dampen post-ingestive satiation, permitting hyperphagia, whereas GIPRNTS neurons are anorectic. In line with this model, we show Gipr expression in AP, but not NTS, neurons is necessary for appetite suppression following GIPR antagonism. Additionally, we reveal that GIPR neurons in the AP and NTS occupy distinct gut-brain circuits, and are differentially sensitive to obesity-driven circuit remodelling. These data offer a framework for understanding how current GIPR agonist and antagonist strategies elicit weight loss.

neuroscience↗

bioRxiv2026

Functional segregation of body-brain signals in the area postrema

Nausea arises from activation of specialized neurons in the area postrema (AP)1-8. The AP also mediates much of the satiety produced by GLP1R agonists9-12, suggesting a broader role in non-aversive physiology, yet the functions of AP cell types are not well understood. Here, we have used optical recordings in behaving mice to systematically define the natural regulation of an array of AP neurons, including the cell types that are principal targets of widely-used weight loss drugs. We discover that neurons expressing GFRAL, the receptor for the sickness-related hormone GDF15, are unexpectedly activated when mice consume food rich in fat. This fat-specific GFRAL neuron activation is required for fat satiation but does not involve GDF15 or canonical gut-brain pathways. Instead, "anti-nausea" neurons expressing GIPR, which directly inhibit GFRAL neurons, are selectively activated by sugar, enabling macronutrient-specific gating of GFRAL responses. In addition, we show that CALCR neurons link intestinal hyperosmolality to the suppression of feeding, whereas PRLHR neurons respond to changes in blood volume and pressure. These findings reveal a broad role for AP cell types in sensing and responding to physiologic signals unrelated to nausea. They also reveal that GFRAL and GIPR neurons, which are key targets of the weight-loss drug tirzepatide, have a natural function in sensing ingestion of fat and sugar, respectively.

neuroscience↗

bioRxiv2026

Age-related morphological changes in the C57BL/6J mouse calvaria: implications for stereotaxic neurosurgery

The mouse skull serves as the coordinate framework for stereotaxic neurosurgery, yet whether aging alters surgically critical calvarial geometry has not been examined. We measured three parameters in large cohorts of young (2-3 months) and aged (23-30 months) male and female C57BL/6J mice: bregma-lambda distance and the dorsoventral depth at rostral-lateral (X = {+/-} 2.5 mm, Y = 0) and caudal-lateral (X = {+/-} 2.5 mm, Y = -0.65 mm) calvarial sites. Bregma-lambda distance was significantly reduced with aging in both sexes. Similarly, the rostral-lateral calvaria showed age-related flattening in both male and female mice. The more caudal-lateral site showed smaller but significant age-related flattening, with males exhibiting significantly greater reductions than females. Aging increased caudal-lateral shape variability while reducing bregma-lambda distance variability in males. On the contrary, aging reduced rostral-lateral shape variability in females. These findings demonstrate that the mouse skull undergoes significant, spatially non-uniform, and sexually dimorphic remodeling into old age, where skull shrinks along the midline and flattens more significantly at the rostral than caudal plane. Stereotaxic protocols designed for young adult mice may systematically misestimate skull geometry in aged animals. Age-stratified reference data should be incorporated into stereotaxic practice for aged rodent models.

neuroscience↗

bioRxiv2025

Need-selective gating of dopamine neuron cue responses by real and virtual hunger

The midbrain dopamine system is important for linking reward-predictive cues to learning and 20 motivation. Here we investigated how dopamine neuron responses to food and water cues are modulated by changes in internal state. We developed a flexible cued-approach task that allowed us to examine behavioral and neural responses to both food- and water-predictive cues within the same recording session. We found that overlapping subsets of dopamine neurons respond to food and water cues, but that the magnitude of these responses is gated in a need-25 specific way. Stimulation of hunger-promoting AgRP neurons amplified dopamine neuronresponses to food cues, but not water cues, and the magnitude of these responses exceeded those observed in natural hunger. These findings indicate that changes in internal state modulate, in a need-appropriate way, the responses of a common set of dopamine neurons to environmental signals of food and water availability.

neuroscience↗

bioRxiv2025

An orthogonal TRAP enables intersectional genetic access to activated neurons in the mouse brain

The study of neural circuits has been greatly enabled by methods for obtaining genetic access to activated neurons. However, these approaches typically tag neurons based on their response to only a single stimulus, which limits the ability to define precise subpopulations of cells. Here we describe an approach (X-TRAP) in which the activity-dependent expression of Flp recombinase is gated by branaplam, a small molecule that triggers splicing of the X-ON switch. We show that X-TRAP knock-in mice exhibit undetectable Flp recombination in the absence of drug and that branaplam treatment results in robust induction of recombination selectively in neurons that express FOS. Moreover, we show that X-TRAP is orthogonal to the widely-used TRAP system, such that these two approaches can be used in the same animal to label cells with Cre and Flp recombination in response to two different stimuli. We apply this strategy to map neural circuits that control food intake. This approach for intersectional, activity-dependent genetic labeling should enhance our ability to identify the neural correlates of behavior.

neuroscience↗

bioRxiv2025

Cellular coding of ingestion in the caudal brainstem

The termination of a meal is triggered by sensory feedback from the stomach and intestines that reports on ingested food1-10 and is relayed to the caudal nucleus of the solitary tract (cNTS) in the brainstem11-14. This sensory feedback is thought to gradually intensify as a meal progresses, resulting in the progressive activation of cNTS circuits that promote satiety15,16, but this idea has never been tested by recording the single-cell activity of cNTS neurons while animals eat. Here, we have used a preparation for calcium imaging in the caudal brainstem of behaving animals17 to characterize how food ingestion is encoded in the cNTS. We find that when food is delivered directly to the stomach, most cNTS neurons exhibit ramping activation over many minutes that tracks cumulative food consumed and depends on canonical gut-brain pathways. However, when the same food is consumed by mouth, this widespread ramping activation is gone, and most cNTS neurons instead exhibit phasic, seconds-timescale responses to oral contact with food. We show that these rapid responses are driven by a combination of mechanical, gustatory and nutritive signals from the mouth and throat and do not require traditional gut-brain pathways, including gut-innervating vagal afferents, although GI feedback modulates their duration. We show that one source of this rapid input is descending projections from the paraventricular hypothalamus, which track ingestion dynamics and are required for proper meal termination. These findings reveal that sensory feedback from the stomach and intestines, which is directly transmitted to the cNTS and thought to be critical for satiety, is not the major driver of cNTS activity during ingestion. Instead, these circuits make extensive use of rapid, pregastric signals that report on the dynamics of behavior.

neuroscience↗

bioRxiv2025

A genetic screen in enteroendocrine cells reveals mechanisms that control protein sensing and GLP-1 release

Enteroendocrine cells (EECs) are the principal nutrient sensors in the gastrointestinal (GI) tract and release hormones such as glucagon-like-peptide 1 (GLP-1) that modulate GI function and appetite. While some of the molecules involved in nutrient sensing within EECs have been described, there have been no systematic studies to map the relevant genes and pathways. Here, we developed a strategy to perform a high-throughput screen for genes that are required for nutrient-induced activation of EECs, and we applied this to probe mechanisms for sensing dietary protein. We found that all of the genes previously proposed to function as protein sensors in EECs are, collectively, dispensable for protein sensing in an EEC cell line. Instead, a screen of >20,000 sgRNAs identified numerous genes associated with mitochondrial respiration as being necessary for this process. We showed through secondary assays that impairing oxidative phosphorylation (OXPHOS) reduced EEC activation and GLP-1 release in response to nutrients but not in response to a non-nutritive stimulus. On the other hand, boosting OXPHOS increased EEC activation and GLP-1 release. These data reveal that intracellular metabolism within EECs controls the detection of dietary protein, possibly by monitoring the entry of ingested amino acids into the TCA cycle. More broadly, these findings suggest a general strategy to screen for genes and pathways that might be used to boost the nutrient-regulated release of gut peptides such as GLP-1.

physiology↗

bioRxiv2025

Ingestion-activated CGRP neurons control learning but not satiety

Calcitonin Gene-Related Peptide (CGRP) neurons in the parabrachial nucleus are critical for sickness and malaise but have also been proposed to control non-aversive (rewarding) satiation. How one cell type can coordinate these opposing processes has not been explained. Here we reinvestigate the function of these cells using single-cell imaging as well as optical and chemogenetic manipulations. Contrary to current models, we show that CGRP neurons do not track cumulative food consumption, and their activity is not necessary for meal termination. Instead, we identify two distinct populations of CGRP cells, one of which responds rapidly to appetitive signals during ingestion and the other of which responds slowly to aversive visceral cues. Surprisingly, the ingestion-activated CGRP neurons are important for learning about post-ingestive effects but have little effect on food consumption. This reveals two populations of CGRP neurons that are sequentially engaged during, and responsible for, the distinct stages of post-ingestive learning.

neuroscience↗

bioRxiv2025

A lateralized pathway for associating nutrients with flavors

Animals learn about the external world, in part, via interoceptive signals1,2. For example, the nutrient content of food is first estimated in the mouth, in the form of flavor, and then measured again via slower signals from the gut. How these signals from the mouth and gut are integrated to drive learning is unknown. Here we identify a lateralized dopamine pathway that is specialized for learning about the nutrient content of food. We show that dopamine neurons in the ventral tegmental area (VTADA) are necessary for associating nutrients with flavors, and that post-ingestive nutrients trigger DA release selectively in a small region of the anterior basolateral amygdala (BLA) but not canonical DA targets in striatum. Remarkably, this nutrient-triggered DA release occurs preferentially on the left side of the brain in both mice and humans, revealing that the DA system is functionally lateralized. We identify the gut sensors that are responsible for nutrient-triggered DA release; show that they activate BLA-projecting DA neurons defined by expression of cholecystokinin (CCK); and demonstrate that stimulation of DA axon terminals in the anterior BLA drives flavor-nutrient learning but not other aspects of feeding behavior. Two-photon imaging of neurons in the left anterior BLA reveals that they integrate gustatory and post-ingestive cues, and silencing these neurons prevents flavor-nutrient learning. These findings establish a neural basis for how animals learn about the nutrient content of their food. They also reveal unexpectedly that post-ingestive nutrients are differentially represented on the right and left sides of the brain.

neuroscience↗

bioRxiv2024

Dysregulation of the fluid homeostasis system by aging

Chronic dehydration is a leading cause of morbidity for the elderly, but how aging alters the fluid homeostasis system is not well understood. Here, we used a combination of physiologic, behavioral and circuit analyses to characterize how fluid balance is affected by aging in mice. We found that old mice have a primary defect in sensing and producing the anti-diuretic hormone vasopressin, which results in chronic dehydration. Recordings and manipulations of the thirst circuitry revealed that old mice retain the ability to sense systemic cues of dehydration but are impaired in detecting presystemic, likely oropharyngeal, cues generated during eating and drinking, resulting in disorganized drinking behavior on short timescales. Surprisingly, old mice had increased drinking and motivation after 24-hour water deprivation, indicating that aging does not result in a general impairment in the thirst circuit. These findings reveal how a homeostatic system undergoes coordinated changes during aging.

neuroscience↗

bioRxiv2023

Negative feedback control of hunger circuits by the taste of food

The rewarding taste of food is critical for motivating animals to eat, but whether taste has a parallel function in promoting meal termination is not well understood. Here we show that hunger-promoting AgRP neurons are rapidly inhibited during each bout of ingestion by a signal linked to the taste of food. Blocking these transient dips in activity via closed-loop optogenetic stimulation increases food intake by selectively delaying the onset of satiety. We show that upstream leptin receptor-expressing neurons in the dorsomedial hypothalamus (DMHLepR) are tuned to respond to sweet or fatty tastes and exhibit time-locked activation during feeding that is the mirror image of downstream AgRP cells. These findings reveal an unexpected role for taste in the negative feedback control of ingestion. They also reveal a mechanism by which AgRP neurons, which are the primary cells that drive hunger, are able to influence the moment-by-moment dynamics of food consumption.

neuroscience↗

bioRxiv2021

Enteroendocrine cell types that drive food reward and aversion

Animals must learn through experience which foods are nutritious and should be consumed, and which are toxic and should be avoided. Enteroendocrine cells (EECs) are the principal chemosensors in the GI tract, but investigation of their role in behavior has been limited by the difficulty of selectively targeting these cells in vivo. Here we describe an intersectional genetic approach for manipulating EEC subtypes in behaving mice. We show that multiple EEC subtypes inhibit food intake but have different effects on learning. Conditioned flavor preference is driven by release of cholecystokinin whereas conditioned taste aversion is mediated by serotonin and substance P. These positive and negative valence signals are transmitted by vagal and spinal afferents, respectively. These findings establish a cellular basis for how chemosensing in the gut drives learning about food.

physiology↗