Goldfish CB1 mRNA expression is affected by fasting and anandamide administration

Endocannabinoid receptors are involved in enhancing food intake in rainbow trout

The mechanisms involved in hedonic regulation of food intake, including endocannabinoid system (ECs) are scarcely known in fish. We recently demonstrate in rainbow trout the presence of a rewarding response mediated by ECs in hypothalamus and telencephalon when fish fed a lipid-enriched diet, and that central administration of main agonists of ECs namely AEA or 2-AG exert a bimodal effect on feed intake in fish with low doses inducing an increase that disappears with the high dose of both endocannabinoids (EC). To assess the precise involvement of the different receptors of the ECs (CNR1, TRPV1, and GPR55) in this response we injected intracerebroventricularly AEA or 2-AG in the absence/presence of specific receptor antagonists (AM251, capsazepine, and ML193; respectively). The presence of antagonists clearly counteracts the effect of EC supporting the specificity of EC action inducing changes not only in ECs but also in GABA and glutamate metabolism ultimately leading to the increase observed in food intake response.

The Endocannabinoid System and Eating Behaviours: a Review of the Current State of the Evidence

PURPOSE OF THE REVIEW

The endocannabinoid system (ENS) has emerged as an important factor in food intake and may have implications for nutrition research. The objective of the current report is to summarise the available evidence on the ENS and eating behaviour from both animal and human studies.

RECENT FINDINGS

The literature reviewed demonstrates a clear link between the ENS and eating behaviours. Overall, studies indicate that 2-arachidonoylglycerol (2-AG) and N-arachidonoylethanolamine (AEA) via cannabinoid receptor-1 (CNR1) binding may stimulate hunger and food intake while oleylethanolamide (OEA) may inhibit hunger. Mechanisms of these associations are not yet well understood, although the evidence suggests that there may be interactions with other physiological systems to consider. Most studies have been conducted in animal models, with few human studies available. Additional research is warranted among human populations into the ENS and eating behaviour. Evaluation of relationships between variation in ENS genes and dietary outcomes is an important area for investigation.

Central administration of endocannabinoids exerts bimodal effects in food intake of rainbow trout

The endocannabinoid system (ECs) is known to participate in several processes in mammals related to synaptic signaling including regulation of food intake, appetite and energy balance. In fish, the relationship of ECs with food intake regulation is poorly understood. In the present study, we assessed in rainbow trout Oncorhynchus mykiss the effect of intracerebroventricular administration (ICV) of low and high doses of the endocannabinoids anandamide (AEA) and 2-arachidonoylglycerol (2-AG) on food intake. We assessed endocannabinoid levels in hypothalamus, telencephalon and plasma as well as the effect of AEA and 2-AG administration at central level on gene expression of receptors involved in ECs (cnr1, gpr55 and trpv1) and markers of neural activity (fos, ntrk2 and GABA-related genes). The results obtained indicate that whereas high doses of endocannabinoids did not elicit changes in food intake levels, low doses of the endocannabinoids produce an orexigenic effect that could be due to a possible inhibition of gabaergic neurotransmission and the modulation of neural plasticity in brain areas related to appetite control, such as hypothalamus and telencephalon.

The endocannabinoid system is affected by a high-fat-diet in rainbow trout

The endocannabinoid system (ECs) is a well known contributor to the hedonic regulation of food intake (FI) in mammals whereas in fish, the knowledge regarding hedonic mechanisms that control FI is limited. Previous studies reported the involvement of ECs in FI regulation in fish since anandamide (AEA) treatment induced enhanced FI and changes of mRNA abundance of appetite-related neuropeptides through cannabinoid receptor 1 (cnr1). However, no previous studies in fish evaluated the impact of palatable food like high-fat diets (HFD) on mechanisms involved in hedonic regulation of FI including the possible involvement of ECs. Therefore, we aimed to evaluate the effect of feeding a HFD on the response of ECs in rainbow trout (Oncorhynchus mykiss). First, we demonstrated a higher intake over 4 days of HFD compared with a control diet (CD). Then, we evaluated the postprandial response (1, 3 and 6 h) of components of the ECs in plasma, hypothalamus, and telencephalon after feeding fish with CD and HFD. The results obtained indicate that the increased FI of HFD occurred along with increased levels of 2-arachidonoylglycerol (2-AG) and AEA in plasma and in brain areas like hypothalamus and telencephalon putatively involved in hedonic regulation of FI in fish. Decreased mRNA abundance of EC receptors like cnr1, gpr55 and trpv1 suggest a feed-back counter-regulatory mechanism in response to the increased levels of EC. Furthermore, the results also suggest that neural activity players associated to FI regulation in mammals as cFOS, γ-Amino butyric acid (GABA) and brain derived neurotrophic factor (BDNF)/neurotrophic receptor tyrosine kinase (NTRK) systems could be involved in the hedonic eating response to a palatable diet in fish.

Biphasic effects of methanandamide on murine gastric vagal afferent mechanosensitivity

KEY POINTS

The fine control of food intake is important for the maintenance of a healthy metabolic state. Gastric vagal afferents (GVAs) are involved in the peripheral regulation of food intake via signalling the degree of distension of the stomach which ultimately leads to feelings of fullness and satiety. This study provides evidence that endocannabinoids such as anandamide are capable of regulating GVA sensitivity in a concentration-dependent biphasic manner. This biphasic effect is dependent upon interactions between the CB1, TRPV1 and GHSR receptors. These data have important implications for the peripheral control of food intake.

ABSTRACT

Gastric vagal afferents (GVAs) signal to the hindbrain resulting in satiety. Endocannabinoids are endogenous ligands of cannabinoid 1 receptor (CB1) and transient receptor potential vanilloid-1 (TRPV1) channels. The endocannabinoid anandamide (AEA) is expressed in the stomach, and its receptor CB1 is expressed in ghrelin-positive gastric mucosal cells. Further, TRPV1, CB1 and growth hormone secretagogue receptor (ghrelin receptor, GHSR) are expressed in subpopulations of GVA neurons. This study aimed to determine the interaction between TRPV1, CB1, GHSR and endocannabinoids in the modulation of GVA signalling. An in vitro electrophysiology preparation was used to assess GVA mechanosensitivity in male C57BL/6 mice. Effects of methanandamide (mAEA; 1-100 nm), on GVA responses to stretch were determined in the absence and presence of antagonists of CB1, TRPV1, GHSR, protein kinase-A (PKA), protein kinase-C (PKC) and G-protein subunits Gα_i/o , or Gα_q . Low doses (1-10 nm) of mAEA reduced GVA responses to 3 g stretch, whereas high doses (30-100 nm) increased the response. The inhibitory and excitatory effects of mAEA (1-100 nm) were reduced/lost in the presence of a CB1 and TRPV1 antagonist. PKA, Gα_i/o or GHSR antagonists prevented the inhibitory effect of mAEA on GVA mechanosensitivity. Conversely, in the presence of a PKC or Gα_q antagonist the excitatory effect of mAEA was reduced or lost, respectively. Activation of CB1, by mAEA, can activate or inhibit TRPV1 to increase or decrease GVA responses to stretch, depending on the pathway activated. These interactions could play an important role in the fine control of food intake.

Fish as models for understanding the vertebrate endocrine regulation of feeding and weight

The frequencies of eating disorders and obesity have increased worldwide in recent years. Their pathophysiologies are still unclear, but recent evidence suggests that they might be related to changes in endocrine and neural factors that regulate feeding and energy homeostasis. In order to develop efficient therapeutic drugs, a more thorough knowledge of the neuronal circuits and mechanisms involved is needed. Although to date, rodents have mostly been used models in the area of neuroscience and neuroendocrinology, an increasing number of studies use non-mammalian vertebrates, in particular fish, as model systems. Fish present several advantages over mammalian models and they share genetic and physiological homology to mammals with close similarities in the mechanisms involved in the neural and endocrine regulation of appetite. This review briefly describes the regulation of feeding in two model species, goldfish and zebrafish, how this regulation compares to that in mammals, and how these fish could be used for studies on endocrine regulation of eating and weight and its dysregulations.

Countering the Modern Metabolic Disease Rampage With Ancestral Endocannabinoid System Alignment

When primitive vertebrates evolved from ancestral members of the animal kingdom and acquired complex locomotive and neurological toolsets, a constant supply of energy became necessary for their continued survival. To help fulfill this need, the endocannabinoid (eCB) system transformed drastically with the addition of the cannabinoid-1 receptor (CB1R) to its gene repertoire. This established an eCB/CB1R signaling mechanism responsible for governing the whole organism's energy balance, with its activation triggering a shift toward energy intake and storage in the brain and the peripheral organs (i.e., liver and adipose). Although this function was of primal importance for humans during their pre-historic existence as hunter-gatherers, it became expendable following the successive lifestyle shifts of the Agricultural and Industrial Revolutions. Modernization of the world has further increased food availability and decreased energy expenditure, thus shifting the eCB/CB1R system into a state of hyperactive deregulated signaling that contributes to the 21st century metabolic disease pandemic. Studies from the literature supporting this perspective come from a variety of disciplines, including biochemistry, human medicine, evolutionary/comparative biology, anthropology, and developmental biology. Consideration of both biological and cultural evolution justifies the design of improved pharmacological treatments for obesity and Type 2 diabetes (T2D) that focus on peripheral CB1R antagonism. Blockade of peripheral CB1Rs, which universally promote energy conservation across the vertebrate lineage, represents an evolutionary medicine strategy for clinical management of present-day metabolic disorders.

Care and feeding of the endocannabinoid system: a systematic review of potential clinical interventions that upregulate the endocannabinoid system

Background

The “classic” endocannabinoid (eCB) system includes the cannabinoid receptors CB₁ and CB₂, the eCB ligands anandamide (AEA) and 2-arachidonoylglycerol (2-AG), and their metabolic enzymes. An emerging literature documents the “eCB deficiency syndrome” as an etiology in migraine, fibromyalgia, irritable bowel syndrome, psychological disorders, and other conditions. We performed a systematic review of clinical interventions that enhance the eCB system—ways to upregulate cannabinoid receptors, increase ligand synthesis, or inhibit ligand degradation.

Methodology/Principal Findings

We searched PubMed for clinical trials, observational studies, and preclinical research. Data synthesis was qualitative. Exclusion criteria limited the results to 184 in vitro studies, 102 in vivo animal studies, and 36 human studies. Evidence indicates that several classes of pharmaceuticals upregulate the eCB system, including analgesics (acetaminophen, non-steroidal anti-inflammatory drugs, opioids, glucocorticoids), antidepressants, antipsychotics, anxiolytics, and anticonvulsants. Clinical interventions characterized as “complementary and alternative medicine” also upregulate the eCB system: massage and manipulation, acupuncture, dietary supplements, and herbal medicines. Lifestyle modification (diet, weight control, exercise, and the use of psychoactive substances—alcohol, tobacco, coffee, cannabis) also modulate the eCB system.

Conclusions/Significance

Few clinical trials have assessed interventions that upregulate the eCB system. Many preclinical studies point to other potential approaches; human trials are needed to explore these promising interventions.

Appetite regulation: the central role of melatonin in Danio rerio

Melatonin is the hormonal mediator of photoperiodic information to the central nervous system in vertebrates and allows the regulation of energy homeostasis through the establishment of a proper balance between energy intake and energy expenditure. The aim of this study was to evaluate the role of melatonin in appetite central control analyzing the involvement of this hormone in the regulation of feeding behavior in the zebrafish Danio rerio. For this purpose, the effect of two different melatonin doses (100nM and 1μM) administered for 10 days, via water, to zebrafish adults was evaluated at both physiological and molecular level and the effect of melatonin was considered in relation to the most prominent systems involved in appetite regulation. For the first time, in fact, melatonin control of food intake by the modulation of leptin, MC4R, ghrelin, NPY and CB1 gene expression was evaluated. The results obtained indicate that melatonin significantly reduces food intake and the reduction is in agreement with the changes observed at molecular level. A significant increase in genes codifying for molecules involved in feeding inhibition, such as leptin and MC4R, and a significant reduction in the major orexigenic signals including ghrelin, NPY and CB1 are showed here. Taken together these results support the idea that melatonin falls fully into the complex network of signals that regulate food intake thus playing a key role in central appetite regulation.

CB1 cannabinoid receptor expression is regulated by glucose and feeding in rat pancreatic islets

Endocannabinoid system is involved in food intake and energy balance. Beside the hypothalamus, pancreatic islet also expresses CB1 cannabinoid receptor, however little is known about its physiological role and regulation. Since gene expression of many specific proteins of the islet depends on the concentration of glucose, we studied CB1 receptor expression in response to fasting and feeding. Whole pancreas or islets were isolated from food-deprived adult Wistar rats, with or without a previous 1.5 g/kg glucose oral-intake. CB1, insulin and glucagon expressions were analyzed by confocal immunofluorescence and PCR. In vitro, rat islets were cultured at different glucose concentrations, in the presence of anandamide, or with Rimonabant analog BAR-1. CB1, insulin, glucagon, glucokinase, and PDX-1 expression were determined by real-time RT-PCR, and insulin secretion and islet content by ELISA. CB1 expression in pancreatic islets is upregulated during food restriction, and decreases in response to glucose intake or feeding. In cultured islets, 16 mmol/l glucose, BAR-1, and anandamide at low glucose reduced CB1 mRNA. Insulin, glucagon, glucokinase and PDX-1 expression increased in islets treated with anandamide at low glucose, while BAR-1 modified PDX-1 and glucagon mRNA at high glucose. Basal insulin secretion and insulin content in islets increased with anandamide, but not the glucose-stimulated response. Our results suggest that the endocannabinoid system has an important role in gene expression on islets and its close relationship with glucose response.

Anandamide and AM251, via water, modulate food intake at central and peripheral level in fish

The endocannabinoid system is a major regulator of food intake in many animal species. Studies conducted so far have mostly focused on mammals, and, therefore, in this study, the role of the endocannabinoid system in food intake in the sea bream Sparus aurata was investigated. The effect of different doses of the endocannabinoid anandamide (AEA), administered via water, was evaluated after different exposure times (30, 60 and 120 min) at both physiological and molecular levels. The results obtained indicate that fish exposed to AEA via water present approximately 1000-fold higher levels of AEA in both the brain and liver, which correlated with a significant increase in food intake and with the elevation of cannabinoid receptor 1 (CB(1)) and neuropeptide Y (NPY) mRNA levels in the brain. A peripheral effect of AEA was also observed, since a time-dependent increase in hepatic CB(1) mRNA and protein levels was detected. These effects were attenuated by the administration, again via water, of a selective cannabinoid CB(1) receptor antagonist (AM251). These findings indicate that the endocannabinoid AEA, at doses that stimulate food intake in fish, concomitantly stimulates the expression of the orexigenic peptide NPY as well that of its own receptor, thereby potentially enhancing its effect on food consumption. In agreement with a role of AEA in food intake in S. aurata, we found increased brain levels of both this and the other endocannabinoid, 2-arachidonoylglycerol (2-AG), following food deprivation.