Top-down control of conditioned overconsumption is mediated by insular cortex Nos1 neurons

Conditioned overconsumption is dependent on reinforcer type in lean, but not obese, mice

Associative learning can drive many different types of behaviors, including food consumption. Previous studies have shown that cues paired with food delivery while mice are hungry will lead to increased consumption in the presence of those cues at later times. We previously showed that overconsumption can be driven in male mice by contextual cues, using chow pellets. Here we extended our findings by examining other parameters that may influence the outcome of context-conditioned overconsumption training. We found that the task worked equally well in males and females, and that palatable substances such as high-fat diet and Ensure chocolate milkshake supported learning and induced overconsumption. Surprisingly, mice did not overconsume when sucrose was used as the reinforcer during training, suggesting that nutritional content is a critical factor. Interestingly, we also observed that diet-induced obese mice did not learn the task. Overall, we find that context-conditioned overconsumption can be studied in lean male and female mice, and with multiple reinforcer types.

A critical size volumetric muscle loss model in mouse masseter with impaired mastication on nutrition

Orofacial muscle defect due to congenital anomalies, tumour ablation or traumatic accident that exceeds endogenous regeneration capacity may lead to sustained deficits in masticatory function and nutrition intake. Functional recovery has always been the goal of muscle tissue repair, but currently, there is no suitable model for quantitative analyses of either functional consequences or treatment efficacy of orofacial muscle defect. This study proposed a critical size volumetric muscle loss (VML) model in mouse masseter with impaired mastication on nutrition. Full-thickness VML defects in diameter of 1.0, 1.5, 2.0 and 3.0 mm were generated in the centre of the mouse masseter using a biopsy punch to determine the critical size for functional impairment. In the VML region, myogenesis was dampened but fibrogenesis was activated, as long with a reduction in the density of the neuromuscular junction and an increase in vascular density. Accordingly, persistent fibrosis was observed in the centre region of VML in all diameters. The 2.0 mm diameter was the critical threshold to masticatory function impairment after VML in the masseter. VML of 3.0 mm diameter led to a significant impact on nutrition intake and body weight gain. Autologous muscle graft effectively relieved the fibrosis and functional deficit after VML injury in the masseter. This model serves as a reliable tool in studying functional recovery strategies for orofacial muscle defects.

Multiple cholinergic receptor subtypes coordinate dual modulation of acetylcholine on anterior and posterior paraventricular thalamic neurons

Paraventricular thalamus (PVT) plays important roles in the regulation of emotion and motivation through connecting many brain structures including the midbrain and the limbic system. Although acetylcholine (ACh) neurons of the midbrain were reported to send projections to PVT, little is known about how cholinergic signaling regulates PVT neurons. Here, we used both RNAscope and slice patch-clamp recordings to characterize cholinergic receptor expression and ACh modulation of PVT neurons in mice. We found ACh excited a majority of anterior PVT (aPVT) neurons but predominantly inhibited posterior PVT (pPVT) neurons. Compared to pPVT with more inhibitory M2 receptors, aPVT expressed higher levels of all excitatory receptor subtypes including nicotinic α4, α7, and muscarinic M1 and M3. The ACh-induced excitation was mimicked by nicotine and antagonized by selective blockers for α4β2 and α7 nicotinic ACh receptor (nAChR) subtypes as well as selective antagonists for M1 and M3 muscarinic ACh receptors (mAChR). The ACh-induced inhibition was attenuated by selective M2 and M4 mAChR receptor antagonists. Furthermore, we found ACh increased the frequency of excitatory postsynaptic currents (EPSCs) on a majority of aPVT neurons but decreased EPSC frequency on a larger number of pPVT neurons. In addition, ACh caused an acute increase followed by a lasting reduction in inhibitory postsynaptic currents (IPSCs) on PVT neurons of both subregions. Together, these data suggest that multiple AChR subtypes coordinate a differential modulation of ACh on aPVT and pPVT neurons.

Cannabinoids regulate an insula circuit controlling water intake

The insular cortex, or insula, is a large brain region involved in the detection of thirst and the regulation of water intake. However, our understanding of the topographical, circuit, and molecular mechanisms for controlling water intake within the insula remains parcellated. We found that type-1 cannabinoid (CB1) receptors in the insular cortex cells participate in the regulation of water intake and deconstructed the circuit mechanisms of this control. Topographically, we revealed that the activity of excitatory neurons in both the anterior insula (aIC) and posterior insula (pIC) increases in response to water intake, yet only the specific removal of CB1 receptors in the pIC decreases water intake. Interestingly, we found that CB1 receptors are highly expressed in insula projections to the basolateral amygdala (BLA), while undetectable in the neighboring central part of the amygdala. Thus, we recorded the neurons of the aIC or pIC targeting the BLA (aIC-BLA and pIC-BLA) and found that they decreased their activity upon water drinking. Additionally, chemogenetic activation of pIC-BLA projection neurons decreased water intake. Finally, we uncovered CB1-dependent short-term synaptic plasticity (depolarization-induced suppression of excitation [DSE]) selectively in pIC-BLA, compared with aIC-BLA synapses. Altogether, our results support a model where CB1 receptor signaling promotes water intake by inhibiting the pIC-BLA pathway, thereby contributing to the fine top-down control of thirst responses.

Stereotyped goal-directed manifold dynamics in the insular cortex

The insular cortex is involved in diverse processes, including bodily homeostasis, emotions, and cognition. However, we lack a comprehensive understanding of how it processes information at the level of neuronal populations. We leveraged recent advances in unsupervised machine learning to study insular cortex population activity patterns (i.e., neuronal manifold) in mice performing goal-directed behaviors. We find that the insular cortex activity manifold is remarkably consistent across different animals and under different motivational states. Activity dynamics within the neuronal manifold are highly stereotyped during rewarded trials, enabling robust prediction of single-trial outcomes across different mice and across various natural and artificial motivational states. Comparing goal-directed behavior with self-paced free consumption, we find that the stereotyped activity patterns reflect task-dependent goal-directed reward anticipation, and not licking, taste, or positive valence. These findings reveal a core computation in insular cortex that could explain its involvement in pathologies involving aberrant motivations.

INGEsT: An Open-Source Behavioral Setup for Studying Self-motivated Ingestive Behavior and Learned Operant Behavior

Ingestive behavior is driven by negative internal hunger and thirst states, as well as by positive expected rewards. Although the neural substrates underlying feeding and drinking behaviors have been widely investigated, they have primarily been studied in isolation, even though eating can also trigger thirst, and vice versa. Thus, it is still unclear how the brain encodes body states, recalls the memory of food and water reward outcomes, generates feeding/drinking motivation, and triggers ingestive behavior. Here, we developed an INstrument for Gauging Eating and Thirst (INGEsT), a custom-made behavioral chamber which allows for precise measurement of both feeding and drinking by combining a FED3 food dispenser, lickometers for dispensing liquid, a camera for behavioral tracking, LED light for optogenetics, and calcium imaging miniscope. In addition, in vivo calcium imaging, optogenetics, and video recordings are well synchronized with animal behaviors, e.g., nose pokes, pellet retrieval, and water licking, by using a Bpod microprocessor and timestamping behavioral and imaging data. The INGEsT behavioral chamber enables many types of experiments, including free feeding/drinking, operant behavior to obtain food or water, and food/water choice behavior. Here, we tracked activity of insular cortex and mPFC Htr3a neurons using miniscopes and demonstrate that these neurons encode many aspects of ingestive behavior during operant learning and food/water choice and that their activity can be tuned by internal state. Overall, we have built a platform, consisting of both hardware and software, to precisely monitor innate ingestive, and learned operant, behaviors and to investigate the neural correlates of self-motivated and learned feeding/drinking behaviors.

Conditioned overconsumption is dependent on reinforcer type in lean, but not obese, mice

Associative learning can drive many different types of behaviors, including food consumption. Previous studies have shown that cues paired with food delivery while mice are hungry will lead increased consumption in the presence of those cues at later times. We previously showed that overconsumption can be driven in male mice by contextual cues, using chow pellets. Here we extended our findings by examining other parameters that may influence the outcome of context-conditioned overconsumption training. We found that the task worked equally well in males and females, and that palatable substances such as high-fat diet and Ensure chocolate milkshake supported learning and induced overconsumption. Surprisingly, mice did not overconsume when sucrose was used as the reinforcer during training, suggesting that nutritional content is a critical factor. Interestingly, we also observed that diet-induced obese mice did not learn the task. Overall, we find that context-conditioned overconsumption can be studied in lean males and female mice, and with multiple reinforcer types.

Acute inhibition of hunger-sensing AgRP neurons promotes context-specific learning in mice

OBJECTIVE

An environmental context, which reliably predicts food availability, can increase the appetitive food drive within the same environment context. However, hunger is required for the development of such a context-induced feeding (CIF) response, suggesting the neural circuits sensitive to hunger link an internal energy state with a particular environment context. Since Agouti related peptide (AgRP) neurons are activated by energy deficit, we hypothesised that AgRP neurons are both necessary and sufficient to drive CIF.

METHODS

To examine the role of AgRP neurons in the CIF process, we used fibre photometry with GCaMP7f, chemogenetic activation of AgRP neurons, as well as optogenetic control of AgRP neurons to facilitate acute temporal control not permitted with chemogenetics.

RESULTS

A CIF response at test was only observed when mice were fasted during context training and AgRP population activity at test showed an attenuated inhibitory response to food, suggesting increased food-seeking and/or decreased satiety signalling drives the increased feeding response at test. Intriguingly, chemogenetic activation of AgRP neurons during context training did not increase CIF, suggesting precise temporal firing properties may be required. Indeed, termination of AgRP neuronal photostimulation during context training (ON-OFF in context), in the presence or absence of food, increased CIF. Moreover, photoinhibition of AgRP neurons during context training in fasted mice was sufficient to drive a subsequent CIF in the absence of food.

CONCLUSIONS

Our results suggest that AgRP neurons regulate the acquisition of CIF when the acute inhibition of AgRP activity is temporally matched to context exposure. These results establish acute AgRP inhibition as a salient neural event underscoring the effect of hunger on associative learning.

Insula Dynorphin and Kappa Opioid Receptor Systems Regulate Alcohol Drinking in a Sex-Specific Manner in Mice

Alcohol use disorder is complex and multifaceted, involving the coordination of multiple signaling systems across numerous brain regions. Previous work has indicated that both the insular cortex and dynorphin (DYN)/kappa opioid receptor (KOR) systems contribute to excessive alcohol use. More recently, we identified a microcircuit in the medial aspect of the insular cortex that signals through DYN/KOR. Here, we explored the role of insula DYN/KOR circuit components on alcohol intake in a long-term intermittent access (IA) procedure. Using a combination of conditional knock-out strategies and site-directed pharmacology, we discovered distinct and sex-specific roles for insula DYN and KOR in alcohol drinking and related behavior. Our findings show that insula DYN deletion blocked escalated consumption and decreased the overall intake of and preference for alcohol in male and female mice. This effect was specific to alcohol in male mice, as DYN deletion did not impact sucrose intake. Further, insula KOR antagonism reduced alcohol intake and preference during the early phase of IA in male mice only. Alcohol consumption was not affected by insula KOR knockout in either sex. In addition, we found that long-term IA decreased the intrinsic excitability of DYN and deep layer pyramidal neurons (DLPNs) in the insula of male mice. Excitatory synaptic transmission was also impacted by IA, as it drove an increase in excitatory synaptic drive in both DYN neurons and DLPNs. Combined, our findings suggest there is a dynamic interplay between excessive alcohol consumption and insula DYN/KOR microcircuitry.SIGNIFICANCE STATEMENT The insular cortex is a complex region that serves as an integratory hub for sensory inputs. In our previous work, we identified a microcircuit in the insula that signals through the kappa opioid receptor (KOR) and its endogenous ligand dynorphin (DYN). Both the insula and DYN/KOR systems have been implicated in excessive alcohol use and alcohol use disorder (AUD). Here, we use converging approaches to determine how insula DYN/KOR microcircuit components contribute to escalated alcohol consumption. Our findings show that insula DYN/KOR systems regulate distinct phases of alcohol consumption in a sex-specific manner, which may contribute to the progression to AUD.

Dissection of insular cortex layer 5 reveals two sublayers with opposing modulatory roles in appetitive drinking behavior

The insular cortex (insula) is known to play a modulatory role in feeding and drinking. Previous studies have revealed anterior-posterior differences of subcortical projections and roles for the insula, yet the anatomical and functional heterogeneity among the cortical layers remains poorly understood. Here, we show that layer 5 of the mouse dysgranular insula has two distinct neuronal subpopulations along the entire anterior-posterior axis: The L5a population, expressing NECAB1, projects bilaterally to the lateral and capsular divisions of the central amygdala, and the L5b population, expressing CTIP2, projects ipsilaterally to the parasubthalamic nucleus and the medial division of the central amygdala. Optogenetically activating L5a and L5b neuronal populations in thirsty male mice led to suppressed and facilitated water spout licking, respectively, without avoidance against or preference for the spout paired with the opto-stimulation. Our results suggest sublayer-specific bidirectional modulatory roles of insula layer 5 in the motivational aspect of appetitive behavior.

Physiological Needs: Sensations and Predictions in the Insular Cortex

Physiological needs create powerful motivations (e.g., thirst and hunger). Studies in humans and animal models have implicated the insular cortex in the neural regulation of physiological needs and need-driven behavior. We review prominent mechanistic models of how the insular cortex might achieve this regulation and present a conceptual and analytical framework for testing these models in healthy and pathological conditions.

The impact of familiarity on cortical taste coding

The role of the gustatory region of the insular cortex in mediating associative taste learning, such as conditioned taste aversion, has been well studied. However, while associative learning plays a role in some taste behaviors, such as avoiding toxins, animals often encounter taste stimuli in their natural environment without explicit consequences. This type of inconsequential experience with sensory stimuli has been studied in other sensory systems, generally with the finding that neuronal responses habituate with repeated sensory exposure. This study sought to determine the effect of taste familiarity on population taste coding in the mouse gustatory cortex (GC). Using microendoscope calcium imaging, we studied the taste responses of visually identifiable neurons over 5 days of taste experience, during which animals could freely choose to consume taste stimuli. We found that the number of active cells in the insular cortex, as well as the number of cells characterized as taste-responsive, significantly decreased as animals became familiar with taste stimuli. Moreover, the magnitude of taste-evoked excited responses increased while inhibited responses decreased with experience. By tracking individual neurons over time, we identified a subpopulation of stable neurons present on all days of the taste familiarity paradigm and further characterized their taste coding properties. The population-level response across these stable cells was distinct for each taste quality when taste stimuli were novel, but population responses for readily consumed stimuli became more correlated as the stimuli became familiar. Overall, these results highlight the effects of familiarity on both taste-specific and non-taste responses in the gustatory cortex.

Molecular and Cellular Adaptations in Hippocampal Parvalbumin Neurons Mediate Behavioral Responses to Chronic Social Stress

Parvalbumin-expressing interneurons (PV neurons) maintain inhibitory control of local circuits implicated in behavioral responses to environmental stressors. However, the roles of molecular and cellular adaptations in PV neurons in stress susceptibility or resilience have not been clearly established. Here, we show behavioral outcomes of chronic social defeat stress (CSDS) are mediated by differential neuronal activity and gene expression in hippocampal PV neurons in mice. Using in vivo electrophysiology and chemogenetics, we find increased PV neuronal activity in the ventral dentate gyrus is required and sufficient for behavioral susceptibility to CSDS. PV neuron-selective translational profiling indicates mitochondrial oxidative phosphorylation is the most significantly altered pathway in stress-susceptible versus resilient mice. Among differentially expressed genes associated with stress-susceptibility and resilience, we find Ahnak, an endogenous regulator of L-type calcium channels which are implicated in the regulation of mitochondrial function and gene expression. Notably, Ahnak deletion in PV neurons impedes behavioral susceptibility to CSDS. Altogether, these findings indicate behavioral effects of chronic stress can be controlled by selective modulation of PV neuronal activity or a regulator of L-type calcium signaling in PV neurons.

Higher-Order Inputs Involved in Appetite Control

The understanding of the neural control of appetite sheds light on the pathogenesis of eating disorders such as anorexia nervosa and obesity. Both diseases are a result of maladaptive eating behaviors (overeating or undereating) and are associated with life-threatening health problems. The fine regulation of appetite involves genetic, physiological, and environmental factors, which are detected and integrated in the brain by specific neuronal populations. For centuries, the hypothalamus has been the center of attention in the scientific community as a key regulator of appetite. The hypothalamus receives and sends axonal projections to several other brain regions that are important for the integration of sensory and emotional information. These connections ensure that appropriate behavioral decisions are made depending on the individual's emotional state and environment. Thus, the mechanisms by which higher-order brain regions integrate exteroceptive information to coordinate feeding is of great importance. In this review, we will focus on the functional and anatomical projections connecting the hypothalamus to the limbic system and higher-order brain centers in the cortex. We will also address the mechanisms by which specific neuronal populations located in higher-order centers regulate appetite and how maladaptive eating behaviors might arise from altered connections among cortical and subcortical areas with the hypothalamus.

Brain circuits for promoting homeostatic and non-homeostatic appetites

As the principal means of acquiring nutrients, feeding behavior is indispensable to the survival and well-being of animals. In response to energy or nutrient deficits, animals seek and consume food to maintain energy homeostasis. On the other hand, even when animals are calorically replete, non-homeostatic factors, such as the sight, smell, and taste of palatable food, or environmental cues that predict food, can stimulate feeding behavior. These homeostatic and non-homeostatic factors have traditionally been investigated separately, but a growing body of literature highlights that these factors work synergistically to promote feeding behavior. Furthermore, recent breakthroughs in cell type-specific and circuit-specific labeling, recording, and manipulation techniques have markedly accelerated the discovery of well-defined neural populations underlying homeostatic and non-homeostatic appetite control, as well as overlapping circuits that contribute to both types of appetite. This review aims to provide an update on our understanding of the neural circuit mechanisms for promoting homeostatic and non-homeostatic appetites, focusing on the function of recently identified, genetically defined cell types.

Research on the neural circuit mechanisms underlying feeding behaviors is critical to identifying therapeutic targets for food-related disorders like obesity and anorexia. Sung-Yon Kim and colleagues at Seoul National University, South Korea, reviewed the current understanding of neural circuits promoting feeding behavior, which is regulated by homeostatic and non-homeostatic appetites. In response to deficits in energy (caloric) or nutrients, specific populations of neurons sensitive to hormones leptin and ghrelin generate homeostatic appetite and promote feeding. In addition, diverse neural populations stimulate non-homeostatic appetite in the absence of immediate internal needs and are thought to drive overconsumption in the modern obesogenic environment. These appetites extensively interact through overlapping neural circuits to jointly promote feeding behaviors.

Volume and Connectivity Differences in Brain Networks Associated with Cognitive Constructs of Binge Eating

Bulimia nervosa (BN) and binge eating disorder (BED) are characterized by episodes of eating large amounts of food while experiencing a loss of control. Recent studies suggest that the underlying causes of BN/BED consist of a complex system of environmental cues, atypical processing of food stimuli, altered behavioral responding, and structural/functional brain differences compared with healthy controls (HC). In this narrative review, we provide an integrative account of the brain networks associated with the three cognitive constructs most integral to BN and BED, namely increased reward sensitivity, decreased cognitive control, and altered negative affect and stress responding. We show altered activity in BED/BN within several brain networks, specifically in the striatum, insula, prefrontal cortex (PFC) and orbitofrontal cortex (OFC), and cingulate gyrus. Numerous key nodes in these networks also differ in volume and connectivity compared with HC. We provide suggestions for how this integration may guide future research into these brain networks and cognitive constructs.

A circuit from lateral septum neurotensin neurons to tuberal nucleus controls hedonic feeding

Feeding behavior is regulated by both the homeostatic needs of the body and hedonic values of the food. Easy access to palatable energy-dense foods and the consequent obesity epidemic stress the urgent need for a better understanding of neural circuits that regulate hedonic feeding. Here, we report that neurotensin-positive neurons in the lateral septum (LS^Nts) play a crucial role in regulating hedonic feeding. Silencing LS^Nts specifically promotes feeding of palatable food, whereas activation of LS^Nts suppresses overall feeding. LS^Nts neurons project to the tuberal nucleus (TU) via GABA signaling to regulate hedonic feeding, while the neurotensin signal from LS^Nts→the supramammillary nucleus (SUM) is sufficient to suppress overall feeding. In vivo calcium imaging and optogenetic manipulation reveal two populations of LS^Nts neurons that are activated and inhibited during feeding, which contribute to food seeking and consumption, respectively. Chronic activation of LS^Nts or LS^Nts→TU is sufficient to reduce high-fat diet-induced obesity. Our findings suggest that LS^Nts→TU is a key pathway in regulating hedonic feeding.

UBE2E3 regulates cellular senescence and osteogenic differentiation of BMSCs during aging

Background

Osteoporosis has gradually become a public health problem in the world. However, the exact molecular mechanism of osteoporosis still remains unclear. Senescence and osteogenic differentiation inhibition of bone marrow mesenchymal stem cells (BMSCs ) are supposed to play an important part in osteoporosis.

Methods

We used two gene expression profiles (GSE35956 and GSE35958) associated with osteoporosis and selected the promising gene Ubiquitin-conjugating enzyme E2 E3 (UBE2E3). We then verified its function and mechanism by in vitro experiments.

Results

UBE2E3 was highly expressed in the bone marrow and positively associated with osteogenesis related genes. Besides, UBE2E3 expression reduced in old BMSCs compared with that in young BMSCs. In in vitro experiments, knockdown of UBE2E3 accelerated cellular senescence and inhibited osteogenic differentiation of young BMSCs. On the other hand, overexpression of UBE2E3 attenuated cellular senescence as well as enhanced osteogenic differentiation of old BMSCs. Mechanistically, UBE2E3 might regulate the nuclear factor erythroid 2-related factor (Nrf2) and control its function, thus affecting the senescence and osteogenic differentiation of BMSCs.

Conclusion

UBE2E3 may be potentially involved in the pathogenesis of osteoporosis by regulating cellular senescence and osteogenic differentiation of BMSCs.

Cellular activity in insular cortex across seconds to hours: Sensations and predictions of bodily states

Our wellness relies on continuous interactions between our brain and body: different organs relay their current state to the brain and are regulated, in turn, by descending visceromotor commands from our brain and by actions such as eating, drinking, thermotaxis, and predator escape. Human neuroimaging and theoretical studies suggest a key role for predictive processing by insular cortex in guiding these efforts to maintain bodily homeostasis. Here, we review recent studies recording and manipulating cellular activity in rodent insular cortex at timescales from seconds to hours. We argue that consideration of these findings in the context of predictive processing of future bodily states may reconcile several apparent discrepancies and offer a unifying, heuristic model for guiding future work.