How neural mediation of anticipatory and compensatory insulin release helps us tolerate food

Mice Condition Cephalic-Phase Insulin Release to Flavors Associated with Postoral Actions of Concentrated Glucose

Rats can condition cephalic-phase insulin responses (CPIRs) to specific sounds or times of the day that predict food availability. The present study asked whether mice can condition a CPIR to the flavor of sapid solutions that produce postoral glucose stimulation. To this end, we subjected C57BL/6 mice to one of six experimental protocols. We varied both the duration of the five training sessions (i.e., 23 h or 1 h) and the nature of the training solution. In Experiment 1, consumption of a 0.61% saccharin solution was paired with IG co-infusion of a 16% glucose solution. In Experiments 2-6, the mice consumed a training solution containing a mixture of 0.61% saccharin + 16% glucose, 32% sucrose, 32% maltodextrin, flavored 32% maltodextrin, or 16% maltodextrin. We subsequently asked whether consumption of any of these fluids conditioned a CPIR to a test solution that produced a similar flavor, but which did not elicit a CPIR in naïve mice. The mice did condition a CPIR, but only to the solutions containing 32% maltodextrin. We attribute this conditioning to postoral actions of the concentrated maltodextrin solutions.

The Regulation of Metabolic Homeostasis by Incretins and the Metabolic Hormones Produced by Pancreatic Islets

In healthy humans, the complex biochemical interplay between organs maintains metabolic homeostasis and pathological alterations in this process result in impaired metabolic homeostasis, causing metabolic diseases such as diabetes and obesity, which are major global healthcare burdens. The great advancements made during the last century in understanding both metabolic disease phenotypes and the regulation of metabolic homeostasis in healthy individuals have yielded new therapeutic options for diseases like type 2 diabetes (T2D). However, it is unlikely that highly desirable more efficacious treatments will be developed for metabolic disorders until the complex systemic regulation of metabolic homeostasis becomes more intricately understood. Hormones produced by pancreatic islet beta-cells (insulin) and alpha-cells (glucagon) are pivotal for maintaining metabolic homeostasis; the activity of insulin and glucagon are reciprocally correlated to achieve strict control of glucose levels (normoglycaemia). Metabolic hormones produced by other pancreatic islet cells and incretins produced by the gut are also crucial for maintaining metabolic homeostasis. Recent studies highlighted the incomplete understanding of metabolic hormonal synergism and, therefore, further elucidation of this will likely lead to more efficacious treatments for diseases such as T2D. The objective of this review is to summarise the systemic actions of the incretins and the metabolic hormones produced by the pancreatic islets and their interactions with their respective receptors.

Individual differences in cephalic-phase insulin response are stable over time and predict glucose tolerance in mice

Oral stimulation by glucose triggers a rapid insulin response, which enhances glucose tolerance. This so-called cephalic-phase insulin response (CPIR) has been documented in many mammal species, but its functional properties are poorly characterized. Here, we studied CPIR in lean C57BL/6 mice. Experiment 1 asked whether the large individual differences in CPIR magnitude were real or reflected experimental noise. We measured CPIR magnitude four times across a period of 30 days in the same mice. The individual differences in CPIR magnitude were remarkably stable across the repeated trials, indicating that they were real. Experiment 2 examined the functional consequences of individual differences in CPIR magnitude. We found that higher CPIR magnitudes contributed to larger postprandial insulin responses and greater glucose tolerance. Experiment 3 examined the observation that the CPIRs in Experiments 1 and 2 were associated with a rapid rise in blood glucose. To determine whether the rapid rise in blood glucose caused the CPIRs, we asked whether mice would generate a CPIR if we prevented cephalic-phase stimulation of beta cells by either delivering the glucose intragastrically or blocking parasympathetic input to the pancreatic beta cells with atropine. The mice subjected to these treatments experienced a rapid rise in blood glucose, but they did not exhibit a CPIR. This indicates that it was the oral glucose stimulation, and not the rise in blood glucose, that triggered the CPIRs in Experiments 1 and 2. We conclude that (i) individual differences in CPIR magnitude are stable over time; (ii) CPIR magnitudes predicted postprandial insulin responses and glucose tolerance; and (iii) a rapid rise in blood glucose is not sufficient to trigger a CPIR in mice.

Vagal pathways for systemic regulation of glucose metabolism

Maintaining blood glucose at an appropriate physiological level requires precise coordination of multiple organs and tissues. The vagus nerve bidirectionally connects the central nervous system with peripheral organs crucial to glucose mobilization, nutrient storage, and food absorption, thereby presenting a key pathway for the central control of blood glucose levels. However, the precise mechanisms by which vagal populations that target discrete tissues participate in glucoregulation are much less clear. Here we review recent advances unraveling the cellular identity, neuroanatomical organization, and functional contributions of both vagal efferents and vagal afferents in the control of systemic glucose metabolism. We focus on their involvement in relaying glucoregulatory cues from the brain to peripheral tissues, particularly the pancreatic islet, and by sensing and transmitting incoming signals from ingested food to the brain. These recent findings - largely driven by advances in viral approaches, RNA sequencing, and cell-type selective manipulations and tracings - have begun to clarify the precise vagal neuron populations involved in the central coordination of glucose levels, and raise interesting new possibilities for the treatment of glucose metabolism disorders such as diabetes.

Molecular cell types as functional units of the efferent vagus nerve

The vagus nerve vitally connects the brain and body to coordinate digestive, cardiorespiratory, and immune functions. Its efferent neurons, which project their axons from the brainstem to the viscera, are thought to comprise "functional units" - neuron populations dedicated to the control of specific vagal reflexes or organ functions. Previous research indicates that these functional units differ from one another anatomically, neurochemically, and physiologically but have yet to define their identity in an experimentally tractable way. However, recent work with genetic technology and single-cell genomics suggests that genetically distinct subtypes of neurons may be the functional units of the efferent vagus. Here we review how these approaches are revealing the organizational principles of the efferent vagus in unprecedented detail.

Sweet, bloody consumption - what we eat and how it affects vascular ageing, the BBB and kidney health in CKD

In today's industrialized society food consumption has changed immensely toward heightened red meat intake and use of artificial sweeteners instead of grains and vegetables or sugar, respectively. These dietary changes affect public health in general through an increased incidence of metabolic diseases like diabetes and obesity, with a further elevated risk for cardiorenal complications. Research shows that high red meat intake and artificial sweeteners ingestion can alter the microbial composition and further intestinal wall barrier permeability allowing increased transmission of uremic toxins like p-cresyl sulfate, indoxyl sulfate, trimethylamine n-oxide and phenylacetylglutamine into the blood stream causing an array of pathophysiological effects especially as a strain on the kidneys, since they are responsible for clearing out the toxins. In this review, we address how the burden of the Western diet affects the gut microbiome in altering the microbial composition and increasing the gut permeability for uremic toxins and the detrimental effects thereof on early vascular aging, the kidney per se and the blood-brain barrier, in addition to the potential implications for dietary changes/interventions to preserve the health issues related to chronic diseases in future.

The elusive cephalic phase insulin response: triggers, mechanisms, and functions

The cephalic phase insulin response (CPIR) is classically defined as a head receptor-induced early release of insulin during eating that precedes a postabsorptive rise in blood glucose. Here we discuss, first, the various stimuli that elicit the CPIR and the sensory signaling pathways (sensory limb) involved; second, the efferent pathways that control the various endocrine events associated with eating (motor limb); and third, what is known about the central integrative processes linking the sensory and motor limbs. Fourth, in doing so, we identify open questions and problems with respect to the CPIR in general. Specifically, we consider test conditions that allow, or may not allow, the stimulus to reach the potentially relevant taste receptors and to trigger a CPIR. The possible significance of sweetness and palatability as crucial stimulus features and whether conditioning plays a role in the CPIR are also discussed. Moreover, we ponder the utility of the strict classical CPIR definition based on what is known about the effects of vagal motor neuron activation and thereby acetylcholine on the β-cells, together with the difficulties of the accurate assessment of insulin release. Finally, we weigh the evidence of the physiological and clinical relevance of the cephalic contribution to the release of insulin that occurs during and after a meal. These points are critical for the interpretation of the existing data, and they support a sharper focus on the role of head receptors in the overall insulin response to eating rather than relying solely on the classical CPIR definition.

Oral stimulation with maltodextrin: Effect on cephalic phase insulin release

Cephalic phase insulin release (CPIR) occurs following sensory stimulation with food-related stimuli, and has been shown to limit postabsorptive hyperglycemia. While the specific stimuli that elicit CPIR in humans have not been clearly defined, previous research points to sugars as having potential importance. Maltodextrins are a starch-derived food ingredient commonly found in a variety of processed food products. When consumed, salivary α-amylase rapidly cleaves its component saccharides into smaller units, leading to the production of sugars in the mouth. Here, we investigated whether humans elicit CPIR after tasting but not swallowing maltodextrin, and whether the degree of CPIR exhibited is affected by individuals' salivary α-amylase activity. We found that a gelatin-based stimulus containing 22% w/v maltodextrin elicited CPIR in healthy individuals (N = 22) following a modified sham-feeding protocol using both insulin and c-peptide as indices of the response. However, the degree of CPIR measured did not differ across three groupings (low, medium, or high) of effective α-amylase activity by either index. In a follow-up experiment, a subset of participants (N = 14) underwent the same protocol using a gelatin stimulus without maltodextrin, and no observable CPIR ensued. These findings suggest that oral stimulation with maltodextrin elicits CPIR in humans, but that individual differences in effective salivary α-amylase activity may not necessarily be predictive of the degree of CPIR.

Comparison of aspartame- and sugar-sweetened soft drinks on postprandial metabolism

Aim: We compared the impact of artificially- and sugar-sweetened beverages co-ingested with a mixed meal on postprandial fat and carbohydrate oxidation, blood glucose, and plasma insulin and triglyceride concentrations. Methods: Eight college-aged, healthy males completed three randomly assigned trials, which consisted of a mixed macronutrient meal test with 20oz of Diet-Coke (AS), Coca-Cola (NS), or water (CON). One week separated each trial and each participant served as his own control. Resting energy expenditure (REE) via indirect calorimetry, blood pressure, and blood samples were obtained immediately before, 5, 10, 30, 60, 120, and 180 min after meal and beverage ingestion. A two-way (treatment × time) repeated-measures ANOVA was conducted to assess REE, fat and carbohydrate oxidation rates, blood glucose, and plasma insulin and triglyceride concentrations. Results: There was a significant main effect of treatment on total fat oxidation (P = 0.006), fat oxidation was significantly higher after AS (P = 0.006) and CON (P = 0.001) compared to following NS. There was a significant main effect of treatment on total carbohydrate oxidation (P = 0.005), carbohydrate oxidation was significantly lower after AS (P = 0.014) and CON (P = 0.001) compared to following NS. Plasma insulin concentration AUC was significantly lower after AS (P = 0.019) and trended lower in CON (P = 0.054) compared to following NS. Conclusion: Ingestion of a mixed meal with an artificially-sweetened beverage does not impact postprandial metabolism, whereas a sugar-sweetened beverage suppresses fat oxidation and increases carbohydrate oxidation compared to artificially-sweetened beverage and water.

Consequences of spinal cord injury on the sympathetic nervous system

Spinal cord injury (SCI) damages multiple structures at the lesion site, including ascending, descending, and propriospinal axons; interrupting the conduction of information up and down the spinal cord. Additionally, axons associated with the autonomic nervous system that control involuntary physiological functions course through the spinal cord. Moreover, sympathetic, and parasympathetic preganglionic neurons reside in the spinal cord. Thus, depending on the level of an SCI, autonomic function can be greatly impacted by the trauma resulting in dysfunction of various organs. For example, SCI can lead to dysregulation of a variety of organs, such as the pineal gland, the heart and vasculature, lungs, spleen, kidneys, and bladder. Indeed, it is becoming more apparent that many disorders that negatively affect quality-of-life for SCI individuals have a basis in dysregulation of the sympathetic nervous system. Here, we will review how SCI impacts the sympathetic nervous system and how that negatively impacts target organs that receive sympathetic innervation. A deeper understanding of this may offer potential therapeutic insight into how to improve health and quality-of-life for those living with SCI.

Fatty Acid Transport and Signaling: Mechanisms and Physiological Implications

Long-chain fatty acids (FAs) are components of plasma membranes and an efficient fuel source and also serve as metabolic regulators through FA signaling mediated by membrane FA receptors. Impaired tissue FA uptake has been linked to major complications of obesity, including insulin resistance, cardiovascular disease, and type 2 diabetes. Fatty acid interactions with a membrane receptor and the initiation of signaling can modify pathways related to nutrient uptake and processing, cell proliferation or differentiation, and secretion of bioactive factors. Here, we review the major membrane receptors involved in FA uptake and FA signaling. We focus on two types of membrane receptors for long-chain FAs: CD36 and the G protein-coupled FA receptors FFAR1 and FFAR4. We describe key signaling pathways and metabolic outcomes for CD36, FFAR1, and FFAR4 and highlight the parallels that provide insight into FA regulation of cell function.

Mapping and targeted viral activation of pancreatic nerves in mice reveal their roles in the regulation of glucose metabolism

A lack of comprehensive mapping of ganglionic inputs into the pancreas and of technology for the modulation of the activity of specific pancreatic nerves has hindered the study of how they regulate metabolic processes. Here we show that the pancreas-innervating neurons in sympathetic, parasympathetic and sensory ganglia can be mapped in detail by using tissue clearing and retrograde tracing (the tracing of neural connections from the synapse to the cell body), and that genetic payloads can be delivered via intrapancreatic injection to target sites in efferent pancreatic nerves in live mice through optimized adeno-associated viruses and neural-tissue-specific promoters. We also show that, in male mice, the targeted activation of parasympathetic cholinergic intrapancreatic ganglia and neurons doubled plasma-insulin levels and improved glucose tolerance, and that tolerance was impaired by stimulating pancreas-projecting sympathetic neurons. The ability to map the peripheral ganglia innervating the pancreas and to deliver transgenes to specific pancreas-projecting neurons will facilitate the examination of ganglionic inputs and the study of the roles of pancreatic efferent innervation in glucose metabolism.

Use of c-peptide as a measure of cephalic phase insulin release in humans

Cephalic phase insulin release (CPIR) is a rapid pulse of insulin secreted within minutes of food-related sensory stimulation. Understanding the mechanisms underlying CPIR in humans has been hindered by its small observed effect size and high variability within and between studies. One contributing factor to these limitations may be the use of peripherally measured insulin as an indicator of secreted insulin, since a substantial portion of insulin is metabolized by the liver before delivery to peripheral circulation. Here, we investigated the use of c-peptide, which is co-secreted in equimolar amounts to insulin from pancreatic beta cells, as a proxy for insulin secretion during the cephalic phase period. Changes in insulin and c-peptide were monitored in 18 adults over two repeated sessions following oral stimulation with a sucrose-containing gelatin stimulus. We found that, on average, insulin and c-peptide release followed a similar time course over the cephalic phase period, but that c-peptide showed a greater effect size. Importantly, when insulin and c-peptide concentrations were compared across sessions, we found that changes in c-peptide were significantly correlated at the 2 min (r = 0.50, p = 0.03) and 4 min (r = 0.65, p = 0.003) time points, as well as when participants' highest c-peptide concentrations were considered (r = 0.64, p = 0.004). In contrast, no significant correlations were observed for changes in insulin measured from the sessions (r = -0.06-0.35, p > 0.05). Herein, we detail the individual variability of insulin and c-peptide concentrations measured during the cephalic phase period, and identify c-peptide as a valuable metric for insulin secretion alongside insulin concentrations when investigating CPIR.

Prolonged Consumption of glucose syrup enhances glucose tolerance in mice

There is debate about the metabolic impact of sugar-sweetened beverages. Here, we tested the hypothesis that ad lib consumption of glucose (Gluc) or high-fructose (HiFruc) syrups improves glucose tolerance in mice. We provided C57BL/6 mice with a control (chow and water) or experimental (chow, water and sugar solution) diet across two consecutive 28-day exposure periods, and monitored changes in body composition, glucose tolerance, cephalic-phase insulin release (CPIR) and insulin sensitivity. The sugar solutions contained 11% concentrations of Gluc or HiFruc syrup; these syrups were derived from either corn starch or cellulose. In Experiment 1, consumption of the Gluc diets reliably enhanced glucose tolerance, while consumption of the HiFruc diets did not. Mice on the Gluc diets exhibited higher CPIR (relative to baseline) by the end of exposure period 1, whereas mice on the control and HiFruc diets did not do so until the end of exposure period 2. Mice on the Gluc diets also exhibited higher insulin sensitivity than control mice at the end of exposure period 2, while mice on the HiFruc diets did not. In Experiment 2, we repeated the previous experiment, but limited testing to the corn-based Gluc and HiFruc syrups. We found, once again, that consumption of the Gluc (but not the HiFruc) diet enhanced glucose tolerance, in part by increasing CPIR and insulin sensitivity. These results show that mice can adapt metabolically to high glucose diets, and that this adaptation process involves upregulating at least two components of the insulin response system.

Interorgan crosstalk in pancreatic islet function and pathology

Pancreatic β cells secrete insulin in response to glucose, a process that is regulated at multiple levels, including a network of input signals from other organ systems. Impaired islet function contributes to the pathogenesis of type 2 diabetes mellitus (T2DM), and targeting inter-organ communications, such as GLP-1 signalling, to enhance β-cell function has been proven to be a successful therapeutic strategy in the last decade. In this review, we will discuss recent advances in inter-organ communication from the metabolic, immune and neural system to pancreatic islets, their biological implication in normal pancreas endocrine function and their role in the (mal)adaptive responses of islet to nutrition-induced stress.

Cephalic phase insulin release: A review of its mechanistic basis and variability in humans

Cephalic phase insulin release (CPIR) is a transient pulse of insulin that occurs within minutes of stimulation from foods or food-related stimuli. Despite decades of research on CPIR in humans, the body of literature surrounding this phenomenon is controversial due in part to contradictory findings . This has slowed progress towards understanding the sensory and neural basis of CPIR, as well as its overall relevance to health. This review examines up-to-date knowledge in CPIR research and identifies sources of CPIR variability in humans in an effort to guide future research. The review starts by defining CPIR and discussing its presumed functional roles in glucose homeostasis and feeding behavior. Next, the types of stimuli that have been reported to elicit CPIR, as well as the sensory and neural mechanisms underlying the response in rodents and humans are discussed, and areas where knowledge is limited are identified. Finally, factors that may contribute to the observed variability of CPIR in humans are examined, including experimental design, test procedure, and individual characteristics. Overall, oral stimulation appears to be important for eliciting CPIR, especially when combined with other sensory modalities (vision, olfaction, somatosensation). While differences in experimental design and testing procedure likely explain some of the observed inter- and intra-study variability, individual differences also appear to play an important role. Understanding sources of these individual differences in CPIR will be key for establishing its health relevance.

Central nervous system regulation of organismal energy and glucose homeostasis

Growing evidence implicates the brain in the regulation of both immediate fuel availability (for example, circulating glucose) and long-term energy stores (that is, adipose tissue mass). Rather than viewing the adipose tissue and glucose control systems separately, we suggest that the brain systems that control them are components of a larger, highly integrated, 'fuel homeostasis' control system. This conceptual framework, along with new insights into the organization and function of distinct neuronal systems, provides a context within which to understand how metabolic homeostasis is achieved in both basal and postprandial states. We also review evidence that dysfunction of the central fuel homeostasis system contributes to the close association between obesity and type 2 diabetes, with the goal of identifying more effective treatment options for these common metabolic disorders.

Food anticipatory hormonal responses: A systematic review of animal and human studies

Food anticipatory hormonal responses (cephalic responses) are proactive physiological processes, that allow animals to prepare for food ingestion by modulating their hormonal levels in response to food cues. This process is important for digesting food, metabolizing nutrients and maintaining glucose levels within homeostasis. In this systematic review, we summarize the evidence from animal and human research on cephalic responses. Thirty-six animal and fifty-three human studies were included. The majority (88 %) of studies demonstrated that hormonal levels are changed in response to cues previously associated with food intake, such as feeding time, smell, and sight of food. Most evidence comes from studies on insulin, ghrelin, pancreatic polypeptide, glucagon, and c-peptide. Moreover, impaired cephalic responses were found in disorders related to metabolism and food intake such as diabetes, pancreatic insufficiency, obesity, and eating disorders, which opens discussions about the etiological mechanisms of these disorders as well as on potential therapeutic opportunities.

Brain control of blood glucose levels: implications for the pathogenesis of type 2 diabetes

Despite a rapidly growing literature, the role played by the brain in both normal glucose homeostasis and in type 2 diabetes pathogenesis remains poorly understood. In this review, we introduce a framework for understanding the brain's essential role in these processes based on evidence that the brain, like the pancreas, is equipped to sense and respond to changes in the circulating glucose level. Further, we review evidence that glucose sensing by the brain plays a fundamental role in establishing the defended level of blood glucose, and that defects in this control system contribute to type 2 diabetes pathogenesis. We also consider the possibility that the close association between obesity and type 2 diabetes arises from a shared defect in the highly integrated neurocircuitry governing energy homeostasis and glucose homeostasis. Thus, whereas obesity is characterised by an increase in the defended level of the body's fuel stores (e.g. adipose mass), type 2 diabetes is characterised by an increase in the defended level of the body's available fuel (e.g. circulating glucose), with the underlying pathogenesis in each case involving impaired sensing of (or responsiveness to) relevant humoral negative feedback signals. This perspective is strengthened by growing preclinical evidence that in type 2 diabetes the defended level of blood glucose can be restored to normal by therapies that restore the brain's ability to properly sense the circulating glucose level. Graphical abstract.

Evidence for cephalic phase insulin release in humans: A systematic review and meta-analysis

The initial release of insulin in response to food stimuli acting on receptors in the head and oropharynx is called the cephalic phase of insulin secretion. Insulin has been shown to act centrally to regulate food intake and glucose metabolism and the cephalic phase of insulin secretion may contribute to these functions. Though well documented in laboratory animals, the existence of cephalic phase insulin release in humans has recently come into question. We therefore performed a systematic review and meta-analysis of studies of cephalic phase insulin release in humans. Efficacy outcomes included any change in circulating insulin levels in healthy human volunteers post any food stimulus as compared to baseline or control in a time period of no longer than 10 min. Primary outcome: The overall pooled effect size estimate for cephalic phase insulin release was 0.47 [0.36, 0.58] p-value <0.0001. Secondary outcomes: A random effects meta-analysis with an added moderator for type of stimulus presentation (one, two, four or five sensory qualities) and type of stimulus offered (liquid, solid formulation) also significantly influenced results p = 0.0116 and p = 0.0024 respectively, while sex had no significant effect. Sensitivity Analysis: More restrictive analyses only including studies that used non-ingestive stimuli (p = 0.0001), or studies that reported insulin values within 5 min post stimulus presentation (p < 0.0001) still showed significant positive overall effect size estimates. In summary, our analysis shows that there is evidence for the presence of cephalic phase insulin secretion in humans. Secondary analyses suggest that the type and presentation of stimulus may significantly influence cephalic phase insulin secretion, while sex had no significant effect on cephalic phase insulin secretion.

Visual food cues decrease blood glucose and glucoregulatory hormones following an oral glucose tolerance test in normal-weight and obese men

Previous experiments of our group have demonstrated that preprandial processing of food cues attenuates postprandial blood glucose excursions. Here we systematically re-evaluated the glucose-lowering effect of visual food cues by submitting 40 healthy fasted men (20 normal-weight men, mean age 24.8 ± 3.7 years, BMI 21.9 ± 0.3 kg/m²; 20 obese men, 26.8 ± 4.2 years, 34.3 ± 1.3 kg/m²) to an oral glucose tolerance test (OGTT) following exposure to pictures of high-calorie food items versus neutral items. OGTT-related changes in blood concentrations of glucose and relevant glucoregulatory hormones including GLP-1 were assessed and analyzed according to the oral minimal model. Independent of body weight, food-cue compared to neutral stimulus presentation reduced postprandial concentrations of glucose (p = 0.041), insulin (p = 0.026) and C-peptide (p = 0.007); accordingly, oral minimal model analyses yielded a food-cue induced decrease of dynamic-phase insulin secretion (p = 0.036). We also observed a trend towards lower GLP-1 levels directly after food cue stimulation in both body weight groups (p = 0.057), as well as a trend towards decreased heart rate (p = 0.093) and significantly decreased diastolic blood pressure (p = 0.019). While we did not detect indicators of an early rise in insulin levels in terms of a 'cephalic phase insulin response', our findings support the assumption that preprandial processing of food cues exerts marked effect on postprandial glucose regulation, with possible contributions of changes in GLP-1. The mechanisms linking food cue exposure and glucoregulatory improvements should be investigated in greater detail, to potentially open new treatment options for metabolic dysfunctions.

Obesity blunts cephalic-phase microvascular responses to food

Neurally mediated anticipatory responses, also named cephalic-phase responses, and microcirculatory regulation are two important mechanisms to maintain metabolic homeostasis. Altered cephalic-phase responses in obesity and its metabolic consequences have been proposed. There is, however, a lack of studies focusing on in vivo assessment of the microcirculation during this phase in patients with obesity. In this randomized controlled trial, we selected patients with obesity and healthy subjects after clinical and laboratory assessments. Those with obesity were randomized into two groups: experimental (cephalic-phase microvascular response stimulation - CP group, n = 13) and controls (n = 14). Healthy subjects (n = 17) were also included to form a CP control group. Skin microvascular assessment was used as a model of systemic microcirculation. Resting functional capillary density (FCD) and peak FCD during post-occlusive reactive hyperemia (PORH) were measured by dorsal finger videocapillaroscopy and expressed mainly capillary recruitment capacity. Resting red blood cell velocity (RBCV), peak RBCV during PORH (RBCV_max), and time taken to reach RBCV_max (TRBCV_max) were assessed by dynamic nailfold videocapillaroscopy and expressed the microhemodynamics. Patients with obesity (with or without stimulus) failed to show an increase on FCD during PORH post-stimulus (p = 0.221 and p = 0.307, respectively) depicting lack of capillary recruitment. In contrast, healthy subjects presented an increase in this microvascular outcome (p = 0.004). Changes in all variables of microhemodynamics occurred in both CP groups (healthy and those with obesity). During CP, we originally demonstrated an absence of capillary recruitment in subjects with obesity. These findings might contribute to the literature of microvascular impairment and metabolic conditions.

CNS control of the endocrine pancreas

Increasing evidence suggests that, although pancreatic islets can function autonomously to detect and respond to changes in the circulating glucose level, the brain cooperates with the islet to maintain glycaemic control. Here, we review the role of the central and autonomic nervous systems in the control of the endocrine pancreas, including mechanisms whereby the brain senses circulating blood glucose levels. We also examine whether dysfunction in these systems might contribute to complications of type 1 diabetes and the pathogenesis of type 2 diabetes. Graphical abstract.

Endocrine Cephalic Phase Responses to Food Cues: A Systematic Review

Cephalic phase responses (CPRs) are conditioned anticipatory physiological responses to food cues. They occur before nutrient absorption and are hypothesized to be important for satiation and glucose homeostasis. Cephalic phase insulin responses (CPIRs) and pancreatic polypeptide responses (CPPPRs) are found consistently in animals, but human literature is inconclusive. We performed a systematic review of human studies to determine the magnitude and onset time of these CPRs. The Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) guidelines were used to develop a search strategy. The terms included in the search strategy were cephalic or hormone response or endocrine response combined with insulin and pancreatic polypeptide (PP). The following databases were searched: Scopus (Elsevier), Science Direct, PubMed, Google Scholar, and The Cochrane Library. Initially, 582 original research articles were found, 50 were included for analysis. An insulin increase (≥1μIU/mL) was observed in 41% of the treatments (total n = 119). In 22% of all treatments the increase was significant from baseline. The median (IQR) insulin increase was 2.5 (1.6-4.5) μIU/mL, 30% above baseline at 5± 3 min  after food cue onset (based on study treatments that induced ≥1 μIU/mL insulin increase). A PP increase (>10 pg/mL) was found in 48% of the treatments (total n = 42). In 21% of the treatments, the increase was significant from baseline. The median (IQR) PP increase was 99 (26-156) pg/mL, 68% above baseline at 9± 4 min  after food cue onset (based on study treatments that induced ≥1 μIU/mL insulin increase). In conclusion, CPIRs are small compared with spontaneous fluctuations. Although CPPPRs are of a larger magnitude, both show substantial variation in magnitude and onset time. We found little evidence for CPIR or CPPPR affecting functional outcomes, that is, satiation and glucose homeostasis. Therefore, CPRs do not seem to be biologically meaningful in daily life.

Neuroendocrine and Metabolic Effects of Low-Calorie and Non-Calorie Sweeteners

Since excessive sugar consumption has been related to the development of chronic metabolic diseases prevalent in the western world, the use of sweeteners has gradually increased worldwide over the last few years. Although low- and non-calorie sweeteners may represent a valuable tool to reduce calorie intake and prevent weight gain, studies investigating the safety and efficacy of these compounds in the short- and long-term period are scarce and controversial. Therefore, future studies will need to elucidate the potential beneficial and/or detrimental effects of different types of sweeteners on metabolic health (energy balance, appetite, body weight, cardiometabolic risk factors) in healthy subjects and patients with diabetes, obesity and metabolic syndrome. In this regard, the impact of different sweeteners on central nervous system, gut hormones and gut microbiota is important, given the strong implications that changes in such systems may have for human health. The aim of this narrative review is to summarize the current evidence for the neuroendocrine and metabolic effects of sweeteners, as well as their impact on gut microbiota. Finally, we briefly discuss the advantages of the use of sweeteners in the context of very-low calorie ketogenic diets.

How oro-sensory exposure and eating rate affect satiation and associated endocrine responses-a randomized trial

BACKGROUND

Longer oral processing decreases food intake. This can be attributed to greater oro-sensory exposure (OSE) and a lower eating rate (ER). How these factors contribute to food intake, and the underlying physiological mechanisms, remain unclear.

OBJECTIVES

We aimed to determine the independent and simultaneous effects of OSE and ER on satiation and associated endocrine responses.

METHODS

Forty participants in study 1 [mean ± SD age: 24 ± 4 y; BMI (in kg/m2): 22 ± 2] and 20 in study 2 (mean ± SD age: 23 ± 3 y; BMI: 23 ± 2) participated in a 2 × 2 randomized trial. In both studies, participants ate chocolate custard with added caramel sauce (low OSE) or caramel fudge (high OSE) and with short (fast ER) or long breaks (slow ER) in between bites, until fullness. In study 2, endocrine responses were measured during the meal.

RESULTS

In study 1, participants ate (mean ± SEM) 42 ± 15 g less in the slow- than in the fast-ER condition, only within the high-OSE condition (P = 0.04). In study 2, participants ate 66 ± 21 g less in the high- than in the low-OSE condition and there were no intake differences between slow and fast ER (P = 0.35). Eight minutes after starting to eat, insulin concentrations increased by 42%-65% in all treatments compared with the control. At the end of the meal, insulin concentrations were 81% higher in the high-OSE, slow-ER than in the low-OSE, fast-ER condition (P = 0.049). Pancreatic polypeptide (PP) increased by 62%, 5 min after meal onset in the low-OSE, fast-ER condition (P = 0.005). Ghrelin concentrations did not change.

CONCLUSIONS

Greater OSE increases insulin responsiveness. In contrast, PP responses are stronger when OSE is reduced and ER is fast. Insulin and PP responses may mediate the independent effects of OSE and ER on food intake. These may be beneficial eating strategies, particularly for type 2 diabetic patients, to control food intake and maintain glucose homeostasis.This trial was registered at trialregister.nl as NL6544.

Appetite, the enteroendocrine system, gastrointestinal disease and obesity

The enteroendocrine system is located in the gastrointestinal (GI) tract, and makes up the largest endocrine system in the human body. Despite that, its roles and functions remain incompletely understood. Gut regulatory peptides are the main products of enteroendocrine cells, and play an integral role in the digestion and absorption of nutrients through their effect on intestinal secretions and gut motility. Several peptides, such as cholecystokinin, polypeptide YY and glucagon-like peptide-1, have traditionally been reported to suppress appetite following food intake, so-called satiety hormones. In this review, we propose that, in the healthy individual, this system to regulate appetite does not play a dominant role in normal food intake regulation, and that there is insufficient evidence to wholly link postprandial endogenous gut peptides with appetite-related behaviours. Instead, or additionally, top-down, hedonic drive and neurocognitive factors may have more of an impact on food intake. In GI disease however, supraphysiological levels of these hormones may have more of an impact on appetite regulation as well as contributing to other unpleasant abdominal symptoms, potentially as part of an innate response to injury. Further work is required to better understand the mechanisms involved in appetite control and unlock the therapeutic potential offered by the enteroendocrine system in GI disease and obesity.

The Local Paracrine Actions of the Pancreatic α-Cell

Secretion of glucagon from the pancreatic α-cells is conventionally seen as the first and most important defense against hypoglycemia. Recent findings, however, show that α-cell signals stimulate insulin secretion from the neighboring β-cell. This article focuses on these seemingly counterintuitive local actions of α-cells and describes how they impact islet biology and glucose metabolism. It is mostly based on studies published in the last decade on the physiology of α-cells in human islets and incorporates results from rodents where appropriate. As this and the accompanying articles show, the emerging picture of α-cell function is one of increased complexity that needs to be considered when developing new therapies aimed at promoting islet function in the context of diabetes.

Pavlovian Conditioning of Immunological and Neuroendocrine Functions

The phenomenon of behaviorally conditioned immunological and neuroendocrine functions has been investigated for the past 100 yr. The observation that associative learning processes can modify peripheral immune functions was first reported and investigated by Ivan Petrovic Pavlov and his co-workers. Their work later fell into oblivion, also because so little was known about the immune system’s function and even less about the underlying mechanisms of how learning, a central nervous system activity, could affect peripheral immune responses. With the employment of a taste-avoidance paradigm in rats, this phenomenon was rediscovered 45 yr ago as one of the most fascinating examples of the reciprocal functional interaction between behavior, the brain, and peripheral immune functions, and it established psychoneuroimmunology as a new research field. Relying on growing knowledge about efferent and afferent communication pathways between the brain, neuroendocrine system, primary and secondary immune organs, and immunocompetent cells, experimental animal studies demonstrate that cellular and humoral immune and neuroendocrine functions can be modulated via associative learning protocols. These (from the classical perspective) learned immune responses are clinically relevant, since they affect the development and progression of immune-related diseases and, more importantly, are also inducible in humans. The increased knowledge about the neuropsychological machinery steering learning and memory processes together with recent insight into the mechanisms mediating placebo responses provide fascinating perspectives to exploit these learned immune and neuroendocrine responses as supportive therapies, the aim being to reduce the amount of medication required, diminishing unwanted drug side effects while maximizing the therapeutic effect for the patient’s benefit.

Low-calorie sweeteners cause only limited metabolic effects in mice

There are widespread concerns that low-calorie sweeteners (LCSs) cause metabolic derangement. These concerns stem in part from prior studies linking LCS consumption to impaired glucose tolerance in humans and rodents. Here, we examined this linkage in mice. In experiment 1, we provided mice with chow, water, and an LCS-sweetened solution (saccharin, sucralose, or acesulfame K) for 28 days and measured glucose tolerance and body weight across the exposure period. Exposure to the LCS solutions did not impair glucose tolerance or alter weight gain. In experiment 2, we provided mice with chow, water, and a solution containing saccharin, glucose, or a mixture of both for 28 days, and tested for metabolic changes. Exposure to the saccharin solution increased the insulinemic response of mice to the glucose challenge, and exposure to the saccharin + glucose solution increased the rate of glucose uptake during the glucose challenge. However, neither of these test solutions altered glucose tolerance, insulin sensitivity, plasma triglycerides, or percent body fat. In contrast, exposure to the glucose solution increased glucose tolerance, early insulin response, insulin sensitivity, and percent body fat. We conclude that whereas the LCS-containing solutions induced a few metabolic changes, they were modest compared with those induced by the glucose solution.

Human pancreatic afferent and efferent nerves: mapping and 3-D illustration of exocrine, endocrine, and adipose innervation

The pancreas consists of both the exocrine (acini and ducts) and endocrine (islets) compartments to participate in and regulate the body's digestive and metabolic activities. These activities are subjected to neural modulation, but characterization of the human pancreatic afferent and efferent nerves remains difficult because of the lack of three-dimensional (3-D) image data. Here we prepare transparent human donor pancreases for 3-D histology to reveal the pancreatic microstructure, vasculature, and innervation in a global and integrated fashion. The pancreatic neural network consists of the substance P (SP)-positive sensory (afferent) nerves, the vesicular acetylcholine transporter (VAChT)-positive parasympathetic (efferent) nerves, and the tyrosine hydroxylase (TH)-positive sympathetic (efferent) nerves. The SP⁺ afferent nerves were found residing along the basal domain of the interlobular ducts. The VAChT⁺ and TH⁺ efferent nerves were identified at the peri-acinar and perivascular spaces, which follow the blood vessels to the islets. In the intrapancreatic ganglia, the SP⁺ (scattered minority, ~7%) and VAChT⁺ neurons co-localize, suggesting a local afferent-efferent interaction. Compared with the mouse pancreas, the human pancreas differs in 1) the lack of SP⁺ afferent nerves in the islet, 2) the lower ganglionic density, and 3) the obvious presence of VAChT⁺ and TH⁺ nerves around the intralobular adipocytes. The latter implicates the neural influence on the pancreatic steatosis. Overall, our 3-D image data reveal the human pancreatic afferent and efferent innervation patterns and provide the anatomical foundation for future high-definition analyses of neural remodeling in human pancreatic diseases.NEW & NOTEWORTHY Modern three-dimensional (3-D) histology with multiplex optical signals identifies the afferent and efferent innervation patterns of human pancreas, which otherwise cannot be defined with standard histology. Our 3-D image data reveal the unexpected association of sensory and parasympathetic nerves/neurons in the intrapancreatic ganglia and identify the sympathetic and parasympathetic nerve contacts with the infiltrated adipocytes. The multiplex approach offers a new way to characterize the human pancreas in remodeling (e.g., fatty infiltration and duct lesion progression).

The effect of smell and taste of milk during tube feeding of preterm infants (the Taste trial): a protocol for a randomised controlled trial

INTRODUCTION

Smell and taste of milk are not generally considered when tube feeding preterm infants. Preterm infants have rapid growth, particularly of the brain, and high caloric needs. Enteral feeding is often poorly tolerated which may lead to growth failure and long-term neurodevelopmental impairment. Smell and taste are strong stimulators of digestion and metabolism. We hypothesise that regular smell and taste during tube feeding will improve weight z-scores of very preterm infants at discharge from hospital.

METHODS AND ANALYSIS

Taste is a randomised, unblinded two-centre trial. Infants born at <29 weeks' gestation and/or <1250 g at birth and admitted to a participating neonatal intensive care unit are eligible. Randomisation occurs before infants receive two hourly feeds for 24 hours. Infants are randomised to either smell and taste of milk with each tube feed or tube feeding without the provision of smell and taste. The primary outcome is weight z-score at discharge. Secondary outcomes include: days to full enteral feeds, duration of parenteral nutrition, rate of late-onset sepsis, post menstrual age at removal of nasogastric tube and at discharge from hospital, anthropometric data and neurodevelopmental outcomes at 2 years of corrected age.

ETHICS AND DISSEMINATION

Human Research Ethics Committees of Mater Misericordiae (trial reference number: HREC/16/MHS/112) and the Royal Women's Hospital (trial reference number: 17/21) last approved the trial protocol (version 4.2; Date: 18 December 2018) and recruitment commenced in May 2017 and November 2017, respectively. The trial results will be published in a peer-reviewed journal and will be presented at national and international conferences.

TRIAL REGISTRATION NUMBER

ACTRN12617000583347.

Modeling the effect of the cephalic phase of insulin secretion on glucose metabolism

The nervous system has a significant impact in glucose homeostasis and endocrine pancreatic secretion in humans, especially during the cephalic phase of insulin release (CPIR); that is, before a meal is absorbed. However, the underlying mechanisms of this neural-pancreatic interaction are not well understood and therefore often neglected, despite their significance to achieving an optimal glucose control. As a result, the dynamics of insulin release from the pancreas are currently described by mathematical models that reproduce the behavior of the β cells using exclusively glucose levels and other hormones as inputs. To bridge this gap, we have combined, for the first time, metabolic and neural mathematical models in a unified system to reproduce to a great extent the ideal glucoregulation observed in healthy subjects. Our results satisfactorily replicate the CPIR and its impact during the post-absorptive phase. Furthermore, the proposed model gives insight into the physiological interaction between the brain and the pancreas in healthy people and suggests the potential of considering the neural information for restoring glucose control in people with diabetes. Graphical Abstract (a) Physiological scenario. Diagram of the biological interaction among the most important organs involved in glucose control during meal intake. (b) Scheme of the unified bio-inspired neural-metabolic model. Each of the boxes represents one subsystem of the model. The pink shades boxes depicts the novel subsystems introduced to the current metabolic models (grey shaded boxes). Insulin-related action and mass fluxes (solid black lines) and glucose-related action and mass flux (dotted black lines) are depicted to show the relationship among the blocks. I(t), Ic(t), G(t) and SI related to plasma insulin, plasma cephalic insulin, plasma glucose and insulin sensitivity, respectively.

Nutritional management of moderate-late preterm infants: Survey of current practice

AIM

Moderate-late preterm (MLPT) babies account for over 80% of preterm babies born world-wide. Many MLPT babies require early nutritional support while full sucking feeds are established, but there is little evidence to guide practice. We aimed to determine current practice in Australia and New Zealand.

METHODS

An electronic survey was sent to neonatal clinical directors within the Australia and New Zealand Neonatal Network requesting dissemination to colleagues involved in the care of MLPT babies (32-35⁺⁶ weeks' gestation). The questionnaire asked about respondents' nutritional management of MLPT babies and included scenarios for both moderate- (MPT) and late preterm (LPT) babies.

RESULTS

There were 83 respondents. While waiting for mothers' milk to meet prescribed fluid volumes, 61% (MPT) to 53% (LPT) of respondents would provide dextrose 10% as the first nutritional support, with 15% (MPT) to 38% (LPT) providing infant formula. Of clinicians providing 10% dextrose, 31% (MPT) to 49% (LPT) were happy to do so for ≥3 days, with 5% comfortable doing so for 5 days in moderately preterm babies, before providing additional support. This additional support was infant formula in 73% (MPT) to 90% (LPT) of respondents.

CONCLUSIONS

There is variation in the nutritional management of MLPT infants amongst neonatal clinicians, likely due to the lack of evidence from randomised controlled trials on which to base clinical practice. The majority of clinicians are happy providing only dextrose 10% for up to 2-3 days despite this form of nutritional support containing only carbohydrate.

Impact of Nutrient Type and Sequence on Glucose Tolerance: Physiological Insights and Therapeutic Implications

Pharmacological and dietary interventions targeting postprandial glycemia have proved effective in reducing the risk for type 2 diabetes and its cardiovascular complications. Besides meal composition and size, the timing of macronutrient consumption during a meal has been recently recognized as a key regulator of postprandial glycemia. Emerging evidence suggests that premeal consumption of non-carbohydrate macronutrients (i.e., protein and fat "preloads") can markedly reduce postprandial glycemia by delaying gastric emptying, enhancing glucose-stimulated insulin release, and decreasing insulin clearance. The same improvement in glucose tolerance is achievable by optimal timing of carbohydrate ingestion during a meal (i.e., carbohydrate-last meal patterns), which minimizes the risk of body weight gain when compared with nutrient preloads. The magnitude of the glucose-lowering effect of preload-based nutritional strategies is greater in type 2 diabetes than healthy subjects, being comparable and additive to current glucose-lowering drugs, and appears sustained over time. This dietary approach has also shown promising results in pathological conditions characterized by postprandial hyperglycemia in which available pharmacological options are limited or not cost-effective, such as type 1 diabetes, gestational diabetes, and impaired glucose tolerance. Therefore, preload-based nutritional strategies, either alone or in combination with pharmacological treatments, may offer a simple, effective, safe, and inexpensive tool for the prevention and management of postprandial hyperglycemia. Here, we survey these novel physiological insights and their therapeutic implications for patients with diabetes mellitus and altered glucose tolerance.

Oral Post-Oral Actions of Low-Calorie Sweeteners: A Tale of Contradictions and Controversies

OBJECTIVE

Many scientists and laypeople alike have concerns about low-calorie sweeteners (LCSs). These concerns stem from both a dissatisfaction with the taste of LCSs and reports that they cause metabolic disruptions (e.g., weight gain, glucose intolerance).

METHODS

This article provides a critical review of the literature on LCSs from the standpoint of their taste, gastrointestinal, and metabolic effects; biological fate in the body; and impact on ingestion and glucose homeostasis.

RESULTS AND CONCLUSIONS

Mammals can readily discriminate between LCSs and sugars because both types of sweetener activate distinct oral and post-oral sensory pathways. LCSs differ in their ability to access post-oral tissues, but few studies have incorporated this observation into their design. It is difficult to extrapolate results between mice, rats, and humans because of interspecies differences in the taste and post-oral actions of LCSs and the fact that investigators often use different response measures in rodents and humans. There is confounding in the experimental design of some of the most widely cited studies of LCS-induced metabolic disruptions. The uncritical acceptance of these studies has generated considerable controversy. More work is needed to obtain a clearer understanding of the metabolic effects of LCSs.

The Role of Accessory Cells in Islet Homeostasis

PURPOSES OF REVIEW

Scattered throughout the pancreas, the endocrine islets rely on neurovascular support for signal relay to regulate hormone secretion and for maintaining tissue homeostasis. The islet accessory cells (or components) of neurovascular tissues include the endothelial cells, pericytes, smooth muscle cells, neurons (nerve fibers), and glia. Research results derived from experimental diabetes and islet transplantation indicate that the accessory cells are reactive in islet injury and can affect islet function and homeostasis in situ or in an ectopic environment.

RECENT FINDINGS

Recent advances in cell labeling and tissue imaging have enabled investigation of islet accessory cells to gain insights into their network structures, functions, and remodeling in disease. It has become clear that in diabetes, the islet neurovascular tissues are not just bystanders damaged in neuropathy and vascular complications; rather, they participate in islet remodeling in response to changes in the microenvironment. Because of the fundamental differences between humans and animal models in neuroinsular cytoarchitecture and cell proliferation, examination of islet accessory cells in clinical specimens and donor pancreases warrants further attention.

Contribution of parasympathetic muscarinic augmentation of insulin secretion to olanzapine-induced hyperinsulinemia

Atypical antipsychotic drugs have been associated with the development of obesity and diabetes. In particular, olanzapine can induce peripheral insulin resistance and compensatory hyperinsulinemia independent of weight gain or psychiatric disease. To determine if this compensatory increase in insulin is mediated by parasympathetic muscarinic stimulation, we randomized 15 healthy subjects 2:1 to receive double-blind olanzapine or placebo for 9 days under diet- and activity-controlled inpatient conditions. Before and after 7 days of study drug administration, subjects underwent frequently sampled intravenous glucose tolerance tests with either saline or atropine infused on subsequent days to assess insulin secretion and hepatic insulin extraction in the absence or presence of muscarinic blockade. We found that olanzapine led to an increase in the acute insulin response to glucose, which was not seen with placebo, and was attenuated in the olanzapine group by atropine. Deconvolution of C-peptide data confirmed an increase in insulin secretion with olanzapine, which was blocked by atropine, with a modest reduction in hepatic insulin extraction with olanzapine. These results support the contribution of muscarinic augmentation of insulin secretion to olanzapine-induced hyperinsulinemia, and provide a mechanism for the compensatory hyperinsulinemia that normally serves to prevent deterioration of glucose tolerance under conditions of metabolic challenge.

The DIAMOND trial - DIfferent Approaches to MOderate & late preterm Nutrition: Determinants of feed tolerance, body composition and development: protocol of a randomised trial

BACKGROUND

Babies born at moderate-late preterm gestations account for > 80% of all preterm births. Although survival is excellent, these babies are at increased risk of adverse neurodevelopmental outcomes. They also are at increased risk of adverse long-term health outcomes, such as cardiovascular disease, obesity and diabetes. There is little evidence guiding optimal nutritional practices in these babies; practice, therefore, varies widely. This factorial design clinical trial will address the role of parenteral nutrition, milk supplementation and exposure of the preterm infant to taste and smell with each feed on time to tolerance of full feeds, adiposity, and neurodevelopment at 2 years.

METHODS/DESIGN

The DIAMOND trial is a multi-centre, factorial, randomised, controlled clinical trial. A total of 528 babies born between 32+ 0 and 35+ 6 weeks' gestation receiving intravenous fluids and whose mothers intend to breastfeed will be randomised to one of eight treatment conditions that include a combination of each of the three interventions: (i) intravenous amino acid solution vs. intravenous dextrose solution until full milk feeds established; (ii) milk supplement vs. exclusive breastmilk, and (iii) taste/smell given or not given before gastric tube feeds. Babies will be excluded if a particular mode of nutrition is clinically indicated or there is a congenital abnormality. Primary study outcome: For parenteral nutrition and milk supplement interventions, body composition at 4 months' corrected age. For taste/smell intervention, time to full enteral feeds defined as 150 ml.kg- 1.day- 1 or exclusive breastfeeding.

SECONDARY OUTCOMES

Days to full sucking feeds; days in hospital; body composition at discharge; growth to 2 years' corrected age; development at 2 years' corrected age; breastfeeding rates.

DISCUSSION

This trial will provide the first direct evidence to inform feeding practices in moderate- to late-preterm infants that will optimise their growth, metabolic and developmental outcomes.

TRIAL REGISTRATION

Australian New Zealand Clinical Trials Registry - ACTRN12616001199404 . This trial is endorsed by the IMPACT clinical trials network ( https://impact.psanz.com.au ).

Exacting Responses: Lack of Endocrine Cephalic Phase Responses Upon Oro-Sensory Exposure

Oro-sensory exposure (OSE) to food plays an important role in the regulation of food intake. One proposed underlying mechanism is the occurrence of cephalic phase responses (CPRs). CPRs include the pre-digestive endocrine responses induced by food-related sensory input. Yet, whether OSE duration or sweetness intensity affects CPRs is unknown. The objective of this study was to determine the independent and interactive effects of oro-sensory duration (chewing) and stimulation intensity (sweetness) on endocrine CPRs and satiation. Eighteen males (22 ± 2 years, BMI 22 ± 2 kg/m2) participated in a 2 × 2 randomized study with a control condition. Each session participants performed modified sham feeding (MSF) with one of the four gel-based model foods. During the control session no MSF was performed. Model foods differed in chewing duration (hard or soft texture) and sweetness (low or high intensity). During each session, eight blood samples were collected up till 25 min after MSF onset. Subsequently, food intake from an ad libitum lunch was measured. No typical CPR was found for insulin, pancreatic polypeptide (PP), and ghrelin. However, the overall PP response was 1.1 times greater for the hard sweet MSF condition compared to control (p = 0.02). Overall ghrelin responses were 1.1 times greater for the hard model food compared to the soft model food conditions (p = 0.003). These differences in endocrine response were not associated with differences in food intake at the subsequent meal. Exploratory sub-analysis of the responsive insulin curves showed that after 2.5 min of MSF the hard texture model foods insulin concentrations were 1.2 greater compared to the soft texture. These findings indicate that texture hardness and sweetness increase the overall PP response and that MSF on hard texture increases the overall ghrelin response compared to soft texture model foods. However, MSF on model foods does not lead to a typical CPR. This study, among others, shows that there are major dissimilarities in the endocrine responses to food stimulation between individuals. This emphasizes the importance of considering cephalic responders and non-responders. More research is needed to understand CPRs in relation to food texture and taste properties.

CD36 Modulates Fasting and Preabsorptive Hormone and Bile Acid Levels

CONTEXT

Abnormal fatty acid (FA) metabolism contributes to diabetes and cardiovascular disease. The FA receptor CD36 has been linked to risk of metabolic syndrome. In rodents CD36 regulates various aspects of fat metabolism, but whether it has similar actions in humans is unknown. We examined the impact of a coding single-nucleotide polymorphism in CD36 on postprandial hormone and bile acid (BA) responses.

OBJECTIVE

To examine whether the minor allele (G) of coding CD36 variant rs3211938 (G/T), which reduces CD36 level by ∼50%, influences hormonal responses to a high-fat meal (HFM).

DESIGN

Obese African American (AA) women carriers of the G allele of rs3211938 (G/T) and weight-matched noncarriers (T/T) were studied before and after a HFM.

SETTING

Two-center study.

PARTICIPANTS

Obese AA women.

INTERVENTION

HFM.

MAIN OUTCOME MEASURES

Early preabsorptive responses (10 minutes) and extended excursions in plasma hormones [C-peptide, insulin, incretins, ghrelin fibroblast growth factor (FGF)19, FGF21], BAs, and serum lipoproteins (chylomicrons, very-low-density lipoprotein) were determined.

RESULTS

At fasting, G-allele carriers had significantly reduced cholesterol and glycodeoxycholic acid and consistent but nonsignificant reductions of serum lipoproteins. Levels of GLP-1 and pancreatic polypeptide (PP) were reduced 60% to 70% and those of total BAs were 1.8-fold higher. After the meal, G-allele carriers displayed attenuated early (-10 to 10 minute) responses in insulin, C-peptide, GLP-1, gastric inhibitory peptide, and PP. BAs exhibited divergent trends in G allele carriers vs noncarriers concomitant with differential FGF19 responses.

CONCLUSIONS

CD36 plays an important role in the preabsorptive hormone and BA responses that coordinate brain and gut regulation of energy metabolism.

Intestinal CD36 and Other Key Proteins of Lipid Utilization: Role in Absorption and Gut Homeostasis

Several proteins have been implicated in fatty acid (FA) transport by enterocytes including the scavenger receptor CD36 (SR-B2), the scavenger receptor B1 (SR-B1) a member of the CD36 family and the FA transport protein 4 (FATP4). Here, we review the regulation of enterocyte FA uptake and its function in lipid absorption including prechylomicron formation, assembly and transport. Emphasis is given to CD36, which is abundantly expressed along the digestive tract of rodents and humans and has been the most studied. We also address the pleiotropic functions of CD36 that go beyond lipid absorption and metabolism to include recent evidence of its impact on intestinal homeostasis and barrier maintenance. Areas of progress involving contribution of membrane phospholipid remodeling and of cytosolic FA-binding proteins, FABP1 and FABP2 to fat absorption will be covered. © 2018 American Physiological Society. Compr Physiol 8:493-507, 2018.

Human pancreatic neuro-insular network in health and fatty infiltration

AIMS/HYPOTHESIS

Identification of a pancreatic neuro-insular network in mice suggests that a similar integration of islets and nerves may be present in the human pancreas. To characterise the neuro-insular network and the intra-pancreatic ganglia in a clinically related setting, we examined human pancreases in health and with fatty infiltration via 3-dimensional (3D) histology and compared the human pancreatic microenvironment with its counterpart in mice.

METHODS

Human pancreatic specimens from individuals with normal BMI, high BMI (≥ 25) and type 2 diabetes were used to investigate the neuro-insular network. Transparent specimens were prepared by tissue clearing for transmitted light and deep-tissue fluorescence imaging to simultaneously visualise infiltrated adipocytes, islets and neurovascular networks.

RESULTS

High-definition images of human islets reveal that both the sympathetic and parasympathetic nerves enter the islet core and reside in the immediate microenvironment of islet cells. Around the islets, the neuro-insular network is visualised with 3D histology to identify the intra-pancreatic ganglia (peri-lobular and intra-parenchymal ganglia) and the islet-ganglionic association. In humans, but not in mice, pancreatic fatty infiltration (BMI dependent) features adipocytes infiltrating into the parenchyma and accumulating in the peri-lobular space, in which the peri-lobular ganglia also reside. We identified the formation of adipose-ganglionic complexes in the peri-lobular space and enlargement of ganglia around adipocytes. In the specimen from the individual with type 2 diabetes, an increase in the number of nerve projections from the intra-parenchymal ganglia is associated with severe fatty infiltration.

CONCLUSIONS/INTERPRETATION

We present new perspectives of human pancreas and islet innervation via 3D histology. Our results strongly suggest that fatty infiltration in the human pancreas creates a neurotrophic microenvironment and promotes remodelling of pancreatic innervation.

Insulin-mediated synaptic plasticity in the CNS: Anatomical, functional and temporal contexts

For decades the brain was erroneously considered an insulin insensitive organ. Although gaps in our knowledge base remain, conceptual frameworks are starting to emerge to provide insight into the mechanisms through which insulin facilitates critical brain functions like metabolism, cognition, and motivated behaviors. These diverse physiological and behavioral activities highlight the region-specific activities of insulin in the CNS; that is, there is an anatomical context to the activities of insulin in the CNS. Similarly, there is also a temporal context to the activities of insulin in the CNS. Indeed, brain insulin receptor activity can be conceptualized as a continuum in which insulin promotes neuroplasticity from development into adulthood where it is an integral part of healthy brain function. Unfortunately, brain insulin resistance likely contributes to neuroplasticity deficits in obesity and type 2 diabetes mellitus (T2DM). This neuroplasticity continuum can be conceptualized by the mechanisms through which insulin promotes cognitive function through its actions in brain regions like the hippocampus, as well as the ability of insulin to modulate motivated behaviors through actions in brain regions like the nucleus accumbens and the ventral tegmental area. Thus, the goals of this review are to highlight these anatomical, temporal, and functional contexts of insulin activity in these brain regions, and to identify potentially critical time points along this continuum where the transition from enhancement of neuroplasticity to impairment may take place.

The Association Between Artificial Sweeteners and Obesity

PURPOSE OF REVIEW

The purpose of this paper is to review the epidemiology of obesity and the evolution of artificial sweeteners; to examine the latest research on the effects of artificial sweeteners on the host microbiome, the gut-brain axis, glucose homeostasis, and energy consumption; and to discuss how all of these changes ultimately contribute to obesity.

RECENT FINDINGS

Although artificial sweeteners were developed as a sugar substitute to help reduce insulin resistance and obesity, data in both animal models and humans suggest that the effects of artificial sweeteners may contribute to metabolic syndrome and the obesity epidemic. Artificial sweeteners appear to change the host microbiome, lead to decreased satiety, and alter glucose homeostasis, and are associated with increased caloric consumption and weight gain. Artificial sweeteners are marketed as a healthy alternative to sugar and as a tool for weight loss. Data however suggests that the intended effects do not correlate with what is seen in clinical practice. Future research should focus on the newer plant-based sweeteners, incorporate extended study durations to determine the long-term effects of artificial sweetener consumption, and focus on changes in the microbiome, as that seems to be one of the main driving forces behind nutrient absorption and glucose metabolism.

Great Expectations: Anticipatory Control of Magnocellular Vasopressin Neurons

Real-time activity measurements of genetically identified neuroendocrine vasopressin neurons show they can anticipate osmotic challenges. In this issue of Neuron, Mandelblat-Cerf et al. (2017) show that correlating these results with ongoing behavior and plasma osmolality points to the existence of brain networks that integrate exterosensory cues with interosensory signals to drive neuroendocrine output.