Interleukin-6 in the central amygdala is bioactive and co-localised with glucagon-like peptide-1 receptor

Anatomical and Functional Characterization of Central Amygdala Glucagon-Like Peptide 1 Receptor Expressing Neurons

Glucagon-like peptide 1 receptors (GLP-1Rs) are highly expressed in the brain and are responsible for mediating the acute anorexigenic actions of widely prescribed GLP-1R agonists. Neurobiological efforts to localize the hypophagic effects of GLP-1R agonists in the brain have mainly focused on the hypothalamus and hindbrain. In this study, we performed a deep anatomical and neurophysiological characterization of GLP-1Rs in the central nucleus of the amygdala (CeA). At an mRNA level, we found that Glp1r is diffusely coexpressed in known CeA subpopulations like protein kinase c δ (Prkcd), somatostatin (Sst), or tachykinin2 (Tac2). At a cellular level, we used Glp1r-Cre mice and viral Cre-dependent tracing to map the anatomical positions of GLP-1R cells across the rostral-caudal axis of the CeA and in CeA subdivisions. We found that Glp1r^CeA cells are highly enriched in the medial subdivision of the CeA (CeM). Using whole cell patch clamp electrophysiology, we found that Glp1r^CeA neurons are characterized by the presence of I_h-like currents and resemble a low threshold bursting neuronal subtype in response to hyperpolarizing and depolarizing current injections. We observed sex differences in the magnitude of I_h-like currents and membrane capacitance. At rest, we observed that nearly half of Glp1r^CeA neurons are spontaneously active. We observed that active and inactive neurons display significant differences in excitability even when normalized to an identical holding potential. Our data are the first to deeply characterize the pattern of Glp1r in the CeA and study the neurophysiological characteristics of CeA neurons expressing Glp1r. Future studies leveraging these data will be important to understanding the impact of GLP-1R agonists on feeding and motivation.

Gut hormones, adipokines, and pro- and anti-inflammatory cytokines/markers in loss of control eating: A scoping review

Loss of control (LOC) eating is the defining feature of binge-eating disorder, and it has particular relevance for bariatric patients. The biomarkers of LOC eating are unclear; however, gut hormones (i.e., ghrelin, cholecystokinin [CCK], peptide YY [PYY], glucagon-like peptide 1 [GLP-1], and pancreatic polypeptide [PP]), adipokines (i.e., leptin, adiponectin), and pro- and anti-inflammatory cytokines/markers (e.g., high-sensitivity C-reactive protein [hsCRP]) are candidates due to their involvement in the psychophysiological mechanisms of LOC eating. This review aimed to synthesize research that has investigated these biomarkers with LOC eating. Because LOC eating is commonly examined within the context of binge-eating disorder, is sometimes used interchangeably with subclinical binge-eating, and is the latent construct underlying disinhibition, uncontrolled eating, and food addiction, these eating behaviors were included in the search. Only studies among individuals with overweight or obesity were included. Among the identified 31 studies, 2 studies directly examined LOC eating and 4 studies were conducted among bariatric patients. Most studies were case-control in design (n = 16) and comprised female-dominant (n = 13) or female-only (n = 13) samples. Studies generally excluded fasting total ghrelin, fasting CCK, fasting PYY, and fasting PP as correlates of the examined eating behaviors. However, there was evidence that the examined eating behaviors were associated with lower levels of fasting acyl ghrelin (the active form of ghrelin) and adiponectin, higher levels of leptin and hsCRP, and altered responses of postprandial ghrelin, CCK, and PYY. The use of GLP-1 analog was able to decrease binge-eating. In conclusion, this review identified potential biomarkers of LOC eating. Future studies would benefit from a direct focus on LOC eating (especially in the bariatric population), using longitudinal designs, exploring potential mediators and moderators, and increased inclusion of the male population.

Key role for hypothalamic interleukin-6 in food-motivated behavior and body weight regulation

The pro-inflammatory role of interleukin-6 (IL-6) is well-characterized. Blockade of IL-6, by Tocilizumab, is used in patients with rheumatoid arthritis and those diagnosed with cytokine storm. However, brain-produced IL-6 has recently emerged as a critical mediator of gut/adipose communication with the brain. Central nervous system (CNS) IL-6 is engaged by peripheral and central signals regulating energy homeostasis. IL-6 is critical for mediating hypophagia and weight loss effects of a GLP-1 analog, exendin-4, a clinically utilized drug. However, neuroanatomical substrates and behavioral mechanisms of brain IL-6 energy balance control remain poorly understood. We propose that the lateral hypothalamus (LH) is an IL-6-harboring brain region, key to food intake and food reward control. Microinjections of IL-6 into the LH reduced chow and palatable food intake in male rats. In contrast, female rats responded with reduced motivated behavior for sucrose, measured by the progressive ratio operant conditioning test, a behavioral mechanism previously not linked to IL-6. To test whether IL-6, produced in the LH, is necessary for ingestive and motivated behaviors, and body weight homeostasis, virogenetic knockdown by infusion of AAV-siRNA-IL6 into the LH was utilized. Attenuation of LH IL-6 resulted in a potent increase in sucrose-motivated behavior, without any effect on ingestive behavior or body weight in female rats. In contrast, the treatment did not affect any parameters measured (chow intake, sucrose-motivated behavior, locomotion, and body weight) in chow-fed males. However, when challenged with a high-fat/high-sugar diet, the male LH IL-6 knockdown rats displayed rapid weight gain and hyperphagia. Together, our data suggest that LH-produced IL-6 is necessary and sufficient for ingestive behavior and weight homeostasis in male rats. In females, IL-6 in the LH plays a critical role in food-motivated, but not ingestive behavior control or weight regulation. Thus, collectively these data support the idea that brain-produced IL-6 engages the hypothalamus to control feeding behavior.

Overview of the central amygdala role in feeding behaviour

The neural regulation of feeding behaviour, as an essential factor for survival, is an important research area today. Feeding behaviour and other lifestyle habits play a major role in optimising health and obesity control. Feeding behaviour is physiologically controlled through processes associated with energy and nutrient needs. Different brain nuclei are involved in the neural regulation of feeding behaviours. Therefore, understanding the function of these brain nuclei helps develop feeding control methods. Among important brain nuclei, there is scant literature on the central amygdala (CeA) nucleus and feeding behaviour. The CeA is one of the critical brain regions that play a significant role in various physiological and behavioural responses, such as emotional states, reward processing, energy balance and feeding behaviour. It contains γ-aminobutyric acid neurons. Also, it is the major output region of the amygdaloidal complex. Moreover, the CeA is also involved in multiple molecular and biochemical factors and has extensive connections with other brain nuclei and their neurotransmitters, highlighting its role in feeding behaviour. This review aims to highlight the significance of the CeA nucleus on food consumption by its interaction with the performance of reward, digestive and emotional systems.

Nutrition as Metabolic Treatment for Anxiety

Despite the overwhelming prevalence of anxiety disorders in modern society, medications and psychotherapy often fail to achieve complete symptom resolution. A complementary approach to medicating symptoms is to address the underlying metabolic pathologies associated with mental illnesses and anxiety. This may be achieved through nutritional interventions. In this perspectives piece, we highlight the roles of the microbiome and inflammation as influencers of anxiety. We further discuss the evidence base for six specific nutritional interventions: avoiding artificial sweeteners and gluten, including omega-3 fatty acids and turmeric in the diet, supplementation with vitamin D, and ketogenic diets. We attempt to integrate insights from the nutrition science-literature in order to highlight some practices that practitioners may consider when treating individual patients. Notably, this piece is not meant to serve as a comprehensive review of the literature, but rather argue our perspective that nutritional interventions should be more widely considered among clinical psychiatrists. Nutritional psychiatry is in its infancy and more research is needed in this burgeoning low-risk and potentially high-yield field.

GLP-1 receptors are involved in the GLP-1 (7-36) amide-induced modulation of glucose homoeostasis, emesis and feeding in Suncus murinus (house musk shrew)

GLP-1 receptor agonists are used for the treatment of type 2 diabetes but they may reduce appetite and cause nausea and emesis. We investigated if GLP-1 (7-36) amide can modulate glucose homoeostasis, emesis and feeding via an exendin (9-39)-sensitive mechanism in Suncus murinus. The effect of GLP-1 (7-36) amide on glucose homeostasis was examined using an intraperitoneal glucose tolerance test. In conscious fasted animals, food and water consumption and behavior were measured for 1 h following drug administration. c-Fos expression in the brain was measured using immunohistochemistry. GLP-1 (7-36) amide reduced blood glucose levels dose-dependently. Exendin (9-39) did not modify blood glucose levels but suppressed the glucose-lowering effect of GLP-1 (7-36) amide. GLP-1 (7-36) amide inhibited food and water intake, induced emesis and elevated c-Fos expression in the brainstem and hypothalamic nuclei in the brain. Exendin (9-39) antagonised the inhibition of food and water intake and emesis induced by GLP-1 (7-36) amide and the effects on c-Fos expression in the hypothalamus and brainstem, excepting for the bed nucleus of the stria terminalis. These data suggest that the action of GLP-1 (7-36) amide to modulate blood glucose, suppress food and water intake and induce emesis involve GLP-1 receptors in the hypothalamus and brainstem.

Interleukin-6 in the central amygdala is bioactive and co-localised with glucagon-like peptide-1 receptor

Neuronal circuits involving the central amygdala (CeA) are gaining prominence as important centres for regulation of metabolic functions. As a part of the subcortical food motivation circuitry, CeA is associated with food motivation and hunger. We have previously shown that interleukin (IL)-6 can act as a downstream mediator of the metabolic effects of glucagon-like peptide-1 (GLP-1) receptor (R) stimulation in the brain, although the sites of these effects are largely unknown. In the present study, we used the newly generated and validated RedIL6 reporter mouse strain to investigate the presence of IL-6 in the CeA, as well as possible interactions between IL-6 and GLP-1 in this nucleus. IL-6 was present in the CeA, mostly in cells in the medial and lateral parts of this structure, and a majority of IL-6-containing cells also co-expressed GLP-1R. Triple staining showed GLP-1 containing fibres co-staining with synaptophysin close to or overlapping with IL-6 containing cells. GLP-1R stimulation enhanced IL-6 mRNA levels. IL-6 receptor-alpha (IL-6Rα) was found to a large part in neuronal CeA cells. Using electrophysiology, we determined that cells with neuronal properties in the CeA could be rapidly stimulated by IL-6 administration in vitro. Moreover, microinjections of IL-6 into the CeA could slightly reduce food intake in vivo in overnight fasted rats. In conclusion, IL-6 containing cells in the CeA express GLP-1R, are close to GLP-1-containing synapses, and demonstrate increased IL-6 mRNA in response to GLP-1R agonist treatment. IL-6, in turn, exerts biological effects in the CeA, possibly via IL-6Rα present in this nucleus.