Peptidergic modulation of motor neuron output via CART signaling at C bouton synapses.

The intensity of muscle contraction, and therefore movement vigor, needs to be adaptable to enable complex motor behaviors. This can be achieved by adjusting the properties of motor neurons, which form the final common pathway for all motor output from the central nervous system. Here, we identify roles for a neuropeptide, cocaine- and amphetamine-regulated transcript (CART), in the control of movement vigor. We reveal distinct but parallel mechanisms by which CART and acetylcholine, both released at C bouton synapses on motor neurons, selectively amplify the output of subtypes of motor neurons that are recruited during intense movement. We find that mice with broad genetic deletion of CART or selective elimination of acetylcholine from C boutons exhibit deficits in behavioral tasks that require higher levels of motor output. Overall, these data uncover spinal modulatory mechanisms that control movement vigor to support movements that require a high degree of muscle force.

Influence of polyethylene terephthalate (PET) microplastic on selected active substances in the intramural neurons of the porcine duodenum.

BACKGROUND: Currently, society and industry generate huge amounts of plastics worldwide. The ubiquity of microplastics is obvious, but its impact on the animal and human organism remains not fully understood. The digestive tract is one of the first barriers between pathogens and xenobiotics and a living organism. Its proper functioning is extremely important in order to maintain homeostasis. The aim of this study was to determine the effect of microplastic on enteric nervous system and histological structure of swine duodenum. The experiment was carried out on 15 sexually immature gilts, approximately 8 weeks old. The animals were randomly divided into 3 study groups (n = 5/group). The control group received empty gelatin capsules once a day for 28 days, the first research group received daily gelatin capsules with polyethylene terephthalate (PET) particles as a mixture of particles of various sizes (maximum particle size 300 µm) at a dose of 0.1 g/animal/day. The second study group received a dose ten times higher-1 g/animal/day. RESULTS: A dose of 1 g/day/animal causes more changes in the enteric nervous system and in the histological structure of duodenum. Statistically significant differences in the expression of cocaine and amphetamine regulated transcript, galanin, neuronal nitric oxide synthase, substance P, vesicular acetylcholine transporter and vasoactive intestinal peptide between control and high dose group was noted. The histopathological changes were more frequently observed in the pigs receiving higher dose of PET. CONCLUSION: Based on this study it may be assumed, that oral intake of microplastic might have potential negative influence on digestive tract, but it is dose-dependent.

The Role of Cocaine- and Amphetamine-Regulated Transcript (CART) in Cancer: A Systematic Review.

The functions of cocaine- and amphetamine-regulated transcript (CART) neuropeptide encoded by the CARTPT gene vary from modifying behavior and pain sensitivity to being an antioxidant. Putative CART peptide receptor GPR160 was implicated recently in the pathogenesis of cancer. However, the exact role of CART protein in the development of neoplasms remains unclear. This systematic review includes articles retrieved from the Scopus, PubMed, Web of Science and Medline Complete databases. Nineteen publications that met the inclusion criteria and describe the association of CART and cancer were analyzed. CART is expressed in various types of cancer, e.g., in breast cancer and neuroendocrine tumors (NETs). The role of CART as a potential biomarker in breast cancer, stomach adenocarcinoma, glioma and some types of NETs was suggested. In various cancer cell lines, CARTPT acts an oncogene, enhancing cellular survival by the activation of the ERK pathway, the stimulation of other pro-survival molecules, the inhibition of apoptosis or the increase in cyclin D1 levels. In breast cancer, CART was reported to protect tumor cells from tamoxifen-mediated death. Taken together, these data support the role of CART activity in the pathogenesis of cancer, thus opening new diagnostic and therapeutic approaches in neoplastic disorders.

Unique, Specific CART Receptor-Independent Regulatory Mechanism of CART(55-102) Peptide in Spinal Nociceptive Transmission and Its Relation to Dipeptidyl-Peptidase 4 (DDP4).

Cocaine- and amphetamine-regulated transcript (CART) peptides are involved in several physiological and pathological processes, but their mechanism of action is unrevealed due to the lack of identified receptor(s). We provided evidence for the antihyperalgesic effect of CART(55-102) by inhibiting dipeptidyl-peptidase 4 (DPP4) in astrocytes and consequently reducing neuroinflammation in the rat spinal dorsal horn in a carrageenan-evoked inflammation model. Both naturally occurring CART(55-102) and CART(62-102) peptides are present in the spinal cord. CART(55-102) is not involved in acute nociception but regulates spinal pain transmission during peripheral inflammation. While the full-length peptide with a globular motif contributes to hyperalgesia, its N-terminal inhibits this process. Although the anti-hyperalgesic effects of CART(55-102), CART(55-76), and CART(62-76) are blocked by opioid receptor antagonists in our inflammatory models, but not in neuropathic Seltzer model, none of them bind to any opioid or G-protein coupled receptors. DPP4 interacts with Toll-like receptor 4 (TLR4) signalling in spinal astrocytes and enhances the TLR4-induced expression of interleukin-6 and tumour necrosis factor alpha contributing to inflammatory pain. Depending on the state of inflammation, CART(55-102) is processed in the spinal cord, resulting in the generation of biologically active isoleucine-proline-isoleucine (IPI) tripeptide, which inhibits DPP4, leading to significantly decreased glia-derived cytokine production and hyperalgesia.

Neuropeptide CART modulates dopamine turnover in the nucleus accumbens: Insights into the anatomy of rewarding circuits.

Neuropeptide cocaine- and amphetamine-regulated transcript (CART) is known to influence the activity of the canonical mesolimbic dopaminergic pathway and modulate reward seeking behaviour. CART neurons of the lateral hypothalamus (LH) send afferents to the ventral tegmental area (VTA) and paraventricular thalamic nucleus (PVT) and these nuclei, in turn, send secondary projections to nucleus accumbens. We try to dissect the precise sites of CART's action in these circuits in promoting reward. Rats were implanted with bipolar electrode targeted at the lateral hypothalamus-medial forebrain bundle (LH-MFB) and trained to press the lever through intracranial self-stimulation (ICSS) protocol. CART (55-102) administered directly into posterior VTA (pVTA) or PVT of the conditioned rats significantly increased the number of lever presses, indicating reward-promoting activity of the peptide. Concomitant increase in dopamine (DA) and 3, 4-dihydroxyphenylacetic acid (DOPAC) efflux was noted in the microdialysate collected from the nucleus accumbens shell (AcbSh). On the other hand, immunoneutralization of endogenous CART with CART antibodies injected directly in the pVTA or PVT reduced the lever press activity as well as DA and DOPAC efflux in the AcbSh. Injection of CART (1-39) in pVTA or PVT was ineffective. We suggest that CART cells in the LH-MFB area send afferents to (a) pVTA and influence dopaminergic neurons projecting to AcbSh and (b) PVT, from where the secondary neurons may feed into the AcbSh. Excitation of the CARTergic pathway to the pVTA as well as the PVT seems to promote DA release in the AcbSh and contribute to the generation of reward.

Signaling in rat brainstem via Gpr160 is required for the anorexigenic and antidipsogenic actions of cocaine- and amphetamine-regulated transcript peptide.

Recent work identified Gpr160 as a candidate receptor for cocaine- and amphetamine-regulated transcript peptide (CARTp) and described its role in pain modulation. The aims of the present study were to determine if Gpr160 is required for the CARTp's ability to reduce food intake and water intake and to initially identify the distribution of Gpr160-like immunoreactivity (Gpr160ir) in the rat brain. A passive immunoneutralization approach targeting Gpr160 was used to block the behavioral effects of a pharmacological dose of CARTp in the fourth cerebroventricle (4V) of rats and to determine the importance of endogenously produced CARTp in the control of ingestive behaviors. Passive immunoneutralization of Gpr160 in the 4V blocked the actions of CARTp to inhibit food intake and water intake. Blockade of Gpr160 in the 4V, independent of pharmacological CART treatment, caused an increase in both overnight food intake and water intake. The decrease in food intake, but not water intake, caused by central injection of CARTp was demonstrated to be interrupted by prior administration of a glucagon-like peptide 1 (GLP-1) receptor antagonist. Gpr160ir was observed in several, distinct sites throughout the rat brain, where CARTp staining has been described. Importantly, Gpr160ir was observed to be present in both neuronal and nonneuronal cell types. These data support the hypothesis that Gpr160 is required for the anorexigenic actions of central CARTp injection and extend these findings to water drinking. Gpr160ir was observed in both neuronal and nonneuronal cell types in regions known to be important in the multiple pharmacological effects of CARTp, identifying those areas as targets for future compromise of function studies.

Cocaine and Amphetamine Regulated Transcript (CART) Expression Changes in the Stomach Wall Affected by Experimentally Induced Gastric Ulcerations.

Cocaine- and amphetamine-regulated transcript (CART) is a peptide suggested to play a role in gastrointestinal tract tissue reaction to pathology. Gastric ulceration is a common disorder affecting huge number of people, and additionally, it contributes to the loss of pig livestock production. Importantly, ulceration as a focal disruption affecting deeper layers of the stomach wall differs from other gastrointestinal pathologies and should be studied individually. The pig's gastrointestinal tract, due to its many similarities to the human counterpart, provides a valuable experimental model for studying digestive system pathologies. To date, the role of CART in gastric ulceration and the expression of the gene encoding CART in porcine gastrointestinal tube are completely unknown. Therefore, we aimed to verify the changes in the CART expression by Q-PCR (gene encoding CART in the tissue) and double immunofluorescence staining combined with confocal microscopy (CART immunofluorescence in enteric nervous system) in the porcine stomach tissues adjacent to gastric ulcerations. Surprisingly, we found that gastric ulcer caused a significant decrease in the expression of CART-encoding gene and huge reduction in the percentage of CART-immunofluorescent myenteric perikarya and neuronal fibers located within the circular muscle layer. Our results indicate a unique CART-dependent gastric response to ulcer disease.

Anorexigenic Effects of Intermittent Hypoxia on the Gut-Brain Axis in Sleep Apnea Syndrome.

Sleep apnea syndrome (SAS) is a breathing disorder characterized by recurrent episodes of upper-airway collapse, resulting in intermittent hypoxia (IH) during sleep. Experimental studies with animals and cellular models have indicated that IH leads to attenuation of glucose-induced insulin secretion from pancreatic ß cells and to enhancement of insulin resistance in peripheral tissues and cells, such as the liver (hepatocytes), adipose tissue (adipocytes), and skeletal muscles (myocytes), both of which could lead to obesity. Although obesity is widely recognized as a major factor in SAS, it is controversial whether the development of SAS could contribute directly to obesity, and the effect of IH on the expression of appetite regulatory genes remains elusive. Appetite is regulated appropriately by both the hypothalamus and the gut as a gut-brain axis driven by differential neural and hormonal signals. In this review, we summarized the recent epidemiological findings on the relationship between SAS and feeding behavior and focused on the anorexigenic effects of IH on the gut-brain axis by the IH-induced up-regulation of proopiomelanocortin and cocaine- and amphetamine-regulated transcript in neuronal cells and the IH-induced up-regulation of peptide YY, glucagon-like peptide-1 and neurotensin in enteroendocrine cells and their molecular mechanisms.

LPS immune challenge reduces arcuate nucleus TSHR and CART mRNA and elevates plasma CART peptides.

BACKGROUND: The aim was to examine the impact of lipopolysaccharide-induced systemic inflammation on expression of mRNA for cocaine- and amphetamine-regulated transcript (CART) and the thyrotropin receptor (TSHR) and its ligands in CNS areas of relevance for feeding controls and metabolism. Lipopolysaccharide effects on plasma levels of TSH and CART peptides were also examined. METHODS: Lipopolysaccharide (150-200 µg/mouse) was injected in C57BL/6J mice and tissue and plasma samples taken after 24 h. To establish if plasma increase in CART peptide levels were prostanoid dependent, indomethacin was given via the drinking water beginning 48 h prior to LPS. We evaluated mRNA expression for CART, TSHR, TSHß, and thyrostimulin in brain and pituitary extracts. Plasma levels of TSH, CARTp, and serum amyloid P component were analyzed by ELISA. RESULTS: Lipopolysaccharide suppressed TSHR mRNA expression in the arcuate nucleus and the pituitary. CART mRNA expression was reduced in the arcuate nucleus but elevated in the pituitary of mice treated with Lipopolysaccharide, whereas plasma TSH remained unchanged. Plasma CART peptide concentration increased after LPS treatment in a prostanoid-independent manner, and CART peptide levels correlated positively to degree of inflammation. CONCLUSIONS: Our findings suggest that central and peripheral CART is affected by acute inflammation. Considering the role of the arcuate nucleus in feeding controls, our data highlight TSHR and CART as putative neuroendocrine signaling components that respond to inflammation, perhaps to maintain weight and metabolic homeostasis during states of disease.

Nucleobindin-2/Nesfatin-1 in the Human Hypothalamus Is Reduced in Obese Subjects and Colocalizes with Oxytocin, Vasopressin, Melanin-Concentrating Hormone, and Cocaine- and Amphetamine-Regulated Transcript.

BACKGROUND/AIMS: Nesfatin-1, processed from nucleobindin-2 (NUCB2), is a potent anorexigenic peptide being expressed in rodent hypothalamic nuclei and involved in the regulation of feeding behavior and body weight in animals. The present study aimed to investigate NUCB2/nesfatin-1 protein expression in the human hypothalamus as well as its correlation with body weight. METHODS: Sections of hypothalamus and adjacent cholinergic basal forebrain nuclei, including the nucleus basalis of Meynert (NBM) and the diagonal band of Broca (DBB), from 25 autopsy cases (17 males, 8 females; 8 lean, 9 overweight, 8 obese) were examined using immunohistochemistry and double immunofluorescence labeling. RESULTS: Prominent NUCB2/nesfatin-1 immunoexpression was detected in supraoptic, paraventricular, and infundibular nuclei, lateral hypothalamic area (LHA)/perifornical region, and NBM/DBB. NUCB2/nesfatin-1 was found to extensively colocalize with (a) oxytocin and vasopressin in paraventricular and supraoptic nuclei, (b) melanin-concentrating hormone in the LHA, and (c) cocaine- and amphetamine-regulated transcript in infundibular and paraventricular nuclei and LHA. Interestingly, in the LHA, NUCB2/nesfatin-1 protein expression was significantly decreased in obese, compared with lean (p < 0.01) and overweight (p < 0.05) subjects. CONCLUSIONS: The findings of the present study are suggestive of a potential role for NUCB2/nesfatin-1 as an integral regulator of food intake and energy homeostasis in the human hypothalamus. In the LHA, an appetite- and reward-related brain area, reduced NUCB2/nesfatin-1 immunoexpression may contribute to dysregulation of homeostatic and/or hedonic feeding behavior and obesity. NUCB2/nesfatin-1 localization in NBM/DBB might imply its participation in the neuronal circuitry controlling cognitive influences on food intake and give impetus towards unraveling additional biological actions of NUCB2/nesfatin-1 in human neuronal networks.

Neuropeptide CART prevents memory loss attributed to withdrawal of nicotine following chronic treatment in mice.

Although chronic nicotine administration does not affect memory, its withdrawal causes massive cognitive deficits. The underlying mechanisms, however, have not been understood. We test the role of cocaine- and amphetamine-regulated transcript peptide (CART), a neuropeptide known for its procognitive properties, in this process. The mice on chronic nicotine treatment/withdrawal were subjected to novel object recognition task. The capability of the animal to discriminate between the novel and familiar objects was tested and represented as discrimination index (DI); reduction in the index suggested amnesia. Nicotine for 49 days had no effect on DI, but 8-hour withdrawal caused a significant reduction, followed by full recovery at 24-hour withdrawal timepoint. Bilateral CART infusion in dorsal hippocampus rescued deficits in DI at 8-hours, whereas CART-antibody infusion into the dorsal hippocampus attenuated the recovery at 24-hours. Commensurate changes were observed in the CART as well as CART mRNA profiles in the hippocampus. CART mRNA expression and the peptide immunoreactivity did not change significantly following chronic nicotine treatment. However, there was a significant reduction at 8-hour withdrawal, followed by a drastic increase in CART immunoreactivity as well as CART mRNA at 24-hour withdrawal, compared with 8-hour withdrawal. Distinct α7-nicotinic receptor immunoreactivity was detected on the hippocampal CART neurons, suggesting cholinergic inputs. An increase in the synaptophysin immunoreactive elements around CART cells in the dentate gyrus, cornu ammonis 3 and subiculum at 24-hour post-withdrawal timepoint suggested neuronal plasticity. CART circuit dynamics in the hippocampus seems to modulate short-term memory associated with nicotine withdrawal.

Three forms of cocaine- and amphetamine-regulated transcript may be involved in food intake regulation in gibel carp (Carassius auratus gibelio).

In fish, as in mammals, several studies have demonstrated that the cocaine- and amphetamine-regulated transcript (CART) plays an important role in feeding. However, thus far, the function of CART in gibel carp (Carassius auratus gibelio) feeding regulation has not been reported. In our study, we first identified three forms of CART peptide precursors from gibel carp brain and named these CART-1, CART-2, and CART-3. The full-length cDNA sequences of CART-1, CART-2, and CART-3 were 616 bp, 705 bp, and 760 bp, respectively, encoding peptides of 118, 120, and 104 amino acid residues. We detected mRNA expression of CART-1, CART-2, and CART-3 in a wide range of peripheral and central tissues, with the highest expression detected in the brain. After a meal, mRNA expression of CART-1, CART-2, and CART-3 was significantly elevated, suggesting that CART-1, CART-2, and CART-3 may act as postprandial satiety signals. Moreover, mRNA expression of all three CART-1, CART-2, and CART-3 was significantly reduced during fasting and significantly elevated with refeeding. Our findings indicate that CART-1, CART-2, and CART-3 might function as a satiety factor in the gibel carp.

High-fat-diet-induced inflammation depresses the appetite of blunt snout bream (Megalobrama amblycephala) through the transcriptional regulation of leptin/mammalian target of rapamycin.

The aim of this article was to investigate the mechanism of appetite suppression induced by high-fat diets (HFD) in blunt snout bream (Megalobrama amblycephala). Fish (average initial weight 40·0 (sem 0·35) g) were fed diets with two fat levels (6 and 11 %) with four replicates. HFD feeding for 30 d could significantly increase the weight gain rate, but feeding for 60 d cannot. Food intake of M. amblycephala began to decline significantly in fish fed the HFD for 48 d. HFD feeding for 60 d significantly reduced the expression of neuropeptide Y and elevated the expression of cocaine- and amphetamine-regulated transcript (CART), actions both in favour of suppression of appetite. The activation of fatty acid sensing was partly responsible for the weakened appetite. In addition, inflammatory factors induced by the HFD may be involved in the regulation of appetite by increasing the secretion of leptin and then activating the mammalian target of rapamycin (mTOR). Lipopolysaccharide (LPS, 2·0 mg/kg of fish weight) was administered to induce inflammation, and sampling was performed after 3, 6, 9, 12, 18, 24 and 48 h of LPS injection. Within 6-24 h of LPS injection, the food intake and appetite of M. amblycephala decreased significantly, whereas the mRNA expression of leptin and mTOR increased significantly. Our results indicate that inflammatory cytokines may be the cause of appetite suppression in M. amblycephala fed a HFD.

RANKL Reduces Body Weight and Food Intake via the Modulation of Hypothalamic NPY/CART Expression.

The receptor activator of nuclear factor-κB ligand (RANKL) modulates energy metabolism. However, how RANKL regulates energy homeostasis is still not clear. This study aims to investigate the central mechanisms by which central administration of RANKL inhibits food intake and causes weight loss in mice. We carried out a systematic and in-depth analysis of the neuronal pathways by which RANKL mediates catabolic effects. After intracerebroventricle (i.c.v.) injection of RANKL, the expression of neuropeptide Y (NPY) mRNA in the Arc was significantly decreased, while the CART mRNA expression dramatically increased in the Arc and DMH. However, the agouti-related protein (AgRP) and pro-opiomelanocortin (POMC) mRNA had no significant changes compared with control groups. Together, the results suggest that central administration of RANKL reduces food intake and causes weight loss via modulating the hypothalamic NPY/CART pathways.

Distribution Patterns of Cocaine- and Amphetamine-Regulated Transcript- and/or Galanin-Containing Neurons and Nerve Fibers Located in the Human Stomach Wall Affected by Tumor.

The aim of the study was to investigate the distribution patterns of cocaine- and amphetamine-regulated transcript- (CART-) and galanin-immunoreactive (GAL-IR) neuronal structures in the human stomach wall, focusing on differences observed in regions directly affected by the cancer process, and those from the surgical margin. Samples from the stomach wall were collected from 10 patients (3 women and 7 men, the mean age 67.0 ± 11.9). Next, triple-immunofluorescence staining was used to visualize the changes in the frequency of neurons inside myenteric plexi and intramural fibers containing CART and/or GAL, as well as protein gene product 9.5 (as panneuronal marker). Tumor into the stomach wall caused a decrease in the number of CART-positive (+) nerve fibers in the longitudinal (LML) and circular muscle layers (CML). Notable changes in the dense network of CART+/GAL+ nerve fibers (an increase) were observed in the LML and lamina muscularis mucosae (LMM) within carcinoma-affected areas of the human stomach. Additionally, an elevated number of these nerve fibers from LMM were accompanied by an increase in the number of fibers containing GAL in the vicinity of the neoplastic proliferation. Obtained results suggest that a carcinoma invasion may affect the innervation pattern of the human stomach wall and their function(s).

Changes in the Distribution of Cocaine- and Amphetamine-Regulated Transcript-Containing Neural Structures in the Human Colon Affected by the Neoplastic Process.

The present study analysed changes in the distribution pattern of cocaine- and amphetamine-regulated transcript (CART) in the enteric nervous system (ENS) of the human colon challenged by adenocarcinoma invasion, using the double-labelling immunofluorescence technique. In control specimens, CART immunoreactivity was found in neurons of all studied plexuses, representing 30.1 ± 4.1%, 12.9 ± 5.2%, and 4.1 ± 1.3% of all neurons forming the myenteric plexus (MP), outer submucous plexus (OSP), and inner submucous plexus (ISP), respectively. Tumour growth into the colon wall caused an increase in the relative frequency of CART-like immunoreactive (CART-LI) neurons in enteric plexuses located in the vicinity of the infiltrating neoplasm (to 36.1 ± 6.7%, 32.7 ± 7.3% and 12.1 ± 3.8% of all neurons in MP, OSP and ISP, respectively). The density of CART-LI nerves within particular layers of the intestinal wall did not differ between control and adenocarcinoma-affected areas of the human colon. This is the first detailed description of the CART distribution pattern within the ENS during the adenocarcinoma invasion of the human colon wall. The obtained results suggest that CART probably acts as a neuroprotective factor and may be involved in neuronal plasticity evoked by the progression of a neoplastic process.

Cocaine- and amphetamine-regulated transcript (CART) peptide in the nerve fibres of the porcine gallbladder wall under physiological conditions and after Salmonella Enteritidis lipopolysaccharides administration.

BACKGROUND: Cocaine- and amphetamine-regulated transcript (CART) peptide is the substance distributed in various parts of the nervous system. The majority of previous studies described this substance in the brain, where it takes part in regulatory processes connected with the food intake. CART is also present in the peripheral nervous system, especially in the enteric neurons and nerves located in the wall of the stomach and intestine, but many aspects of distribution and functions of this peptide in the digestive organs remain unknown. The aim of the present study was to investigate the changes of CART-positive nerves in the porcine gallbladder after administration of low-dose Salmonella Enteritidis lipopolysaccharide (LPS) using the single immunofluorescence technique. MATERIALS AND METHODS: Seven days after the injection of 5 µg/kg b.w. LPS S. Enteritidis the gallbladders were collected. CART-positive nerves were studied with standard single immunofluorescence method and counted per observation field (0.1 m2). RESULTS: In control animals the average number of CART-positive nerves per observation field (0.1 mm2) amounted to 5.38 ± 0.32, 11.11 ± 1.56 and 2.97 ± ± 0.24 in gallbladder neck, body and fundus, respectively. LPS administration caused the increase in the number of CART-positive fibres in all parts of gallbladder, and these values amounted to 12.74 ± 0.51, 19.75 ± 0.19 and 5.1 ± 0.05 in the gallbladder neck, body and fundus, respectively. CONCLUSIONS: The obtained results suggest that CART is involved in the neuronal regulatory processes in the porcine gallbladder under physiological conditions, but also during pathological processes, but exact functions of this peptide in this organ remain unexplained and require the further investigation.

CART is overexpressed in human type 2 diabetic islets and inhibits glucagon secretion and increases insulin secretion.

AIMS/HYPOTHESIS: Insufficient insulin release and hyperglucagonaemia are culprits in type 2 diabetes. Cocaine- and amphetamine-regulated transcript (CART, encoded by Cartpt) affects islet hormone secretion and beta cell survival in vitro in rats, and Cart (-/-) mice have diminished insulin secretion. We aimed to test if CART is differentially regulated in human type 2 diabetic islets and if CART affects insulin and glucagon secretion in vitro in humans and in vivo in mice. METHODS: CART expression was assessed in human type 2 diabetic and non-diabetic control pancreases and rodent models of diabetes. Insulin and glucagon secretion was examined in isolated islets and in vivo in mice. Ca(2+) oscillation patterns and exocytosis were studied in mouse islets. RESULTS: We report an important role of CART in human islet function and glucose homeostasis in mice. CART was found to be expressed in human alpha and beta cells and in a subpopulation of mouse beta cells. Notably, CART expression was several fold higher in islets of type 2 diabetic humans and rodents. CART increased insulin secretion in vivo in mice and in human and mouse islets. Furthermore, CART increased beta cell exocytosis, altered the glucose-induced Ca(2+) signalling pattern in mouse islets from fast to slow oscillations and improved synchronisation of the oscillations between different islet regions. Finally, CART reduced glucagon secretion in human and mouse islets, as well as in vivo in mice via diminished alpha cell exocytosis. CONCLUSIONS/INTERPRETATION: We conclude that CART is a regulator of glucose homeostasis and could play an important role in the pathophysiology of type 2 diabetes. Based on the ability of CART to increase insulin secretion and reduce glucagon secretion, CART-based agents could be a therapeutic modality in type 2 diabetes.

Cocaine- and amphetamine-regulated transcript: a novel regulator of energy homeostasis expressed in a subpopulation of pancreatic islet cells.

Type 2 diabetes is characterised by chronic hyperglycaemia and its incidence is highly increased by exaggerated food consumption. It results from a lack of insulin action/production, but growing evidence suggests that it might also involve hyperglucagonaemia and impaired control of glucose homeostasis by the brain. In recent years, the cocaine and amphetamine-regulated transcript (CART) peptides have generated a lot of interest in the battle against obesity because, via the brain, they exert anorexic effects and they increase energy expenditure. They are also localised, outside the brain, in discrete regions of the body and play a hormonal role in controlling various functions. In this issue of Diabetologia, the Wierup group (doi: 10.1007/s00125-016-4020-6 ) shows that CART peptides are expressed heterogeneously in islet cells of various species, including humans, and that their expression is upregulated in diabetes. The authors also shine a spotlight on some interesting effects of CART peptides on islet function, including stimulation of insulin secretion and inhibition of glucagon release. CART peptides would thus be at the centre of a cooperation between the brain and the endocrine pancreas to control glucose homeostasis. Although the mechanisms of action of CART peptides remain enigmatic because no specific receptor for these peptides has so far been discovered, their potential therapeutic use is evident and represents a new challenge for future research.

Pro-cognitive action of CART is mediated via ERK in the hippocampus.

Although cocaine- and amphetamine-regulated transcript peptide (CART) is detected in several cortical and subcortical areas, its role in higher functions has been largely ignored. We examined the significance of CART in memory formation and tested if the downstream actions of CART involve N-methyl-d-aspartate (NMDA) activated extra-cellular signal-regulated kinase (ERK). Newly formed memory was evaluated using novel object recognition test consisting of familiarization (T1) and choice trials (T2). The choice trials were performed at two time points: 30-min (T230-min ) and 24-h (T224-h ) postacquisition. In choice trial (T230-min ), vehicle control rats explored the novel object for significantly longer duration than the familiar object indicating intact memory formation. However, CART-antibody, U0126 [ERK antagonist, both via intracerebroventricular (icv) or intrahippocampal (ih) route] or MK-801 (NMDA antagonist; intraperitoneal) treated rats spent less time exploring novel objects; CART peptide (icv or ih) was ineffective. During choice trial at T224-h , a significant decrease in novel object exploration time was noticed in vehicle control rats suggesting amnesia. However, treatment with CART, prior to familiarization trial (T1), promoted exploration of the novel object even at T224-h . Pretreatment with U0126 or MK-801 blocked pro-cognitive-like effect of CART suggesting involvement of NMDA-ERK pathway in CART's action. Animals subjected to the object familiarization trial showed a drastic increase in the CART-immunoreactivity in the cells of cornu ammonis 3 and polymorph layer of dentate gyrus, and fibers within ento- (ENT) and peri-rhinal (PRH) cortices. Western blot analysis revealed that CART treatment significantly up-regulated the expression of phospo-ERK1/2 in hippocampus, ENT and PRH. This effect was attenuated following pretreatment with U0126 or MK-801, suggesting the activation of ERK signaling cascade through NMDA receptors. Thus, CART system seems to play an important role in recognition memory and that these effects may be mediated by NMDA receptors-ERK signaling in the ENT/PRH-hippocampal circuit. © 2016 Wiley Periodicals, Inc.