Cocaine- and amphetamine-regulated transcript peptide modulation of voltage-gated Ca2+ signaling in hippocampal neurons

The role of CART peptide in learning and memory: A potential therapeutic target in memory-related disorders

Cocaine and amphetamine-regulated transcript (CART) mRNA and peptide are vastly expressed in both cortical and subcortical brain areas and are involved in critical cognitive functions. CART peptide (CARTp), described in reward-related brain structures, regulates drug-induced learning and memory, and its role appears specific to psychostimulants. However, many other drugs of abuse, such as alcohol, opiates, nicotine, and caffeine, have been shown to alter the expression levels of CART mRNA and peptides in brain structures directly or indirectly associated with learning and memory processes. However, the number of studies demonstrating the contribution of CARTp in learning and memory is still minimal. Notably, the exact cellular and molecular mechanisms underlying CARTp effects are still unknown. The discoveries that CARTp effects are mediated through a putative G-protein coupled receptor and activation of cellular signaling cascades via NMDA receptor-coupled ERK have enhanced our knowledge about the action of this neuropeptide and allowed us to comprehend better CARTp exact cellular/molecular mechanisms that could mediate drug-induced changes in learning and memory functions. Unfortunately, these efforts have been impeded by the lack of suitable and specific CARTp receptor antagonists. In this review, following a short introduction about CARTp, we report on current knowledge about CART's roles in learning and memory processes and its recently described role in memory-related neurological disorders. We will also discuss the importance of further investigating how CARTp interacts with its receptor(s) and other neurotransmitter systems to influence learning and memory functions. This topic is sure to intrigue and motivate further exploration in the field of neuroscience.

Behavioral characterization of G-protein-coupled receptor 160 knockout mice

ABSTRACT

Neuropathic pain is a devastating condition where current therapeutics offer little to no pain relief. Novel nonnarcotic therapeutic targets are needed to address this growing medical problem. Our work identified the G-protein-coupled receptor 160 (GPR160) as a potential target for therapeutic intervention. However, the lack of small-molecule ligands for GPR160 hampers our understanding of its role in health and disease. To address this void, we generated a global Gpr160 knockout (KO) mouse using CRISPR-Cas9 genome editing technology to validate the contributions of GPR160 in nociceptive behaviors in mice. Gpr160 KO mice are healthy and fertile, with no observable physical abnormalities. Gpr160 KO mice fail to develop behavioral hypersensitivities in a model of neuropathic pain caused by constriction of the sciatic nerve. On the other hand, responses of Gpr160 KO mice in the hot-plate and tail-flick assays are not affected. We recently deorphanized GPR160 and identified cocaine- and amphetamine-regulated transcript peptide (CARTp) as a potential ligand. Using Gpr160 KO mice, we now report that the development of behavioral hypersensitivities after intrathecal or intraplantar injections of CARTp are dependent on GPR160. Cocaine- and amphetamine-regulated transcript peptide plays a role in various affective behaviors, such as anxiety, depression, and cognition. There are no differences in learning, memory, and anxiety between Gpr160 KO mice and their age-matched and sex-matched control floxed mice. Results from these studies support the pronociceptive roles of CARTp/GPR160 and GPR160 as a potential therapeutic target for treatment of neuropathic pain.

Anorexigenic neuropeptides as anti-obesity and neuroprotective agents: exploring the neuroprotective effects of anorexigenic neuropeptides

Since 1975, the incidence of obesity has increased to epidemic proportions, and the number of patients with obesity has quadrupled. Obesity is a major risk factor for developing other serious diseases, such as type 2 diabetes mellitus, hypertension, and cardiovascular diseases. Recent epidemiologic studies have defined obesity as a risk factor for the development of neurodegenerative diseases, such as Alzheimer's disease (AD) and other types of dementia. Despite all these serious comorbidities associated with obesity, there is still a lack of effective antiobesity treatment. Promising candidates for the treatment of obesity are anorexigenic neuropeptides, which are peptides produced by neurons in brain areas implicated in food intake regulation, such as the hypothalamus or the brainstem. These peptides efficiently reduce food intake and body weight. Moreover, because of the proven interconnection between obesity and the risk of developing AD, the potential neuroprotective effects of these two agents in animal models of neurodegeneration have been examined. The objective of this review was to explore anorexigenic neuropeptides produced and acting within the brain, emphasizing their potential not only for the treatment of obesity but also for the treatment of neurodegenerative disorders.

Neurochemistry of the mammillary body

The mammillary body (MB) is a component of the extended hippocampal system and many studies have shown that its functions are vital for mnemonic processes. Together with other subcortical structures, such as the anterior thalamic nuclei and tegmental nuclei of Gudden, the MB plays a crucial role in the processing of spatial and working memory, as well as navigation in rats. The aim of this paper is to review the distribution of various substances in the MB of the rat, with a description of their possible physiological roles. The following groups of substances are reviewed: (1) classical neurotransmitters (glutamate and other excitatory transmitters, gamma-aminobutyric acid, acetylcholine, serotonin, and dopamine), (2) neuropeptides (enkephalins, substance P, cocaine- and amphetamine-regulated transcript, neurotensin, neuropeptide Y, somatostatin, orexins, and galanin), and (3) other substances (calcium-binding proteins and calcium sensor proteins). This detailed description of the chemical parcellation may facilitate a better understanding of the MB functions and its complex relations with other structures of the extended hippocampal system.

GPR160 is not a receptor of anorexigenic cocaine- and amphetamine-regulated transcript peptide

COCAINE: and amphetamine-regulated transcript peptide (CARTp) is an anorexigenic neuropeptide whose receptor is undisclosed. Previously, we reported the specific binding of CART(61-102) to pheochromocytoma PC12 cells, where CART(61-102) affinity and the number of binding sites per cell corresponded to ligand-receptor binding. Recently, Yosten et al. designated orphan GPR160 as the CARTp receptor, because the GPR160 antibody abolished neuropathic pain and anorexigenic effects induced by CART(55-102) and exogenous CART(55-102) coimmunoprecipitated with GPR160 in KATOIII cells. As no direct evidence that CARTp is a ligand for GPR160 has been described, we decided to verify this hypothesis by testing CARTp affinity to the GPR160 receptor. We investigated the GPR160 expression in PC12 cells since it is cell line known to specifically bind CARTp. Moreover, we examined the specific CARTp binding in THP1 cells, with high endogenous GPR160 expression and GPR160-transfected cell lines U2OS and U-251 MG. In PC12 cells, the GPR160 antibody did not compete for specific binding with ¹²⁵I-CART(61-102) or with ¹²⁵I-CART(55-102), and GPR160 mRNA expression and GPR160 immunoreactivity were not detected. Moreover, THP1 cells did not show any ¹²⁵I-CART(61-102) or ¹²⁵I-CART(55-102) specific binding despite GPR160 detection by fluorescent immunocytochemistry (ICC). Finally, no ¹²⁵I-CART(61-102) or ¹²⁵I-CART(55-102) specific binding in the GPR160-transfected cell lines U2OS and U-251 MG, selected due to their negligible endogenous expression of GPR160, was detected, despite the detection of GPR160 by fluorescent ICC. Our binding studies clearly demonstrated that GPR160 cannot be a receptor for CARTp. Further studies are needed to identify true CARTp receptors.

Glycogen Synthase Kinase 3β Is a Key Regulator in the Inhibitory Effects of Accumbal Cocaine- and Amphetamine-Regulated Transcript Peptide 55-102 on Amphetamine-Induced Locomotor Activity

Microinjection of cocaine- and amphetamine-regulated transcript (CART) peptide 55-102 into the nucleus accumbens (NAcc) core significantly attenuates psychostimulant-induced locomotor activity. However, the molecular mechanism remains poorly understood. We examined the phosphorylation levels of Akt, glycogen synthase kinase 3β (GSK3β), and glutamate receptor 1 (GluA1) in NAcc core tissues obtained 60 min after microinjection of CART peptide 55-102 into this site, followed by systemic injection of amphetamine (AMPH). Phosphorylation levels of Akt at Thr308 and GSK3β at Ser9 were decreased, while those of GluA1 at Ser845 were increased, by AMPH treatment. These effects returned to basal levels following treatment with CART peptide 55-102. Furthermore, the negative regulatory effects of the CART peptide on AMPH-induced changes in phosphorylation levels and locomotor activity were all abolished by pretreatment with the S9 peptide, an artificially synthesized indirect GSK3β activator. These results suggest that the CART peptide 55-102 in the NAcc core plays a negative regulatory role in AMPH-induced locomotor activity by normalizing the changes in phosphorylation levels of Akt-GSK3β, and subsequently GluA1 modified by AMPH at this site. The present findings are the first to reveal GSK3β as a key regulator of the inhibitory role of the CART peptide in psychomotor stimulant-induced locomotor activity.

Unravelling biological roles and mechanisms of GABABR on addiction and depression through mood and memory disorders

The metabotropic γ-aminobutyric acid type B receptor (GABA_BR) remains a hotspot in the recent research area. Being an idiosyncratic G-protein coupled receptor family member, the GABA_BR manifests adaptively tailored functionality under multifarious modulations by a constellation of agents, pointing to cross-talk between receptors and effectors that converge on the domains of mood and memory. This review systematically summarizes the latest achievements in signal transduction mechanisms of the GABA_BR-effector-regulator complex and probes how the up-and down-regulation of membrane-delimited GABA_BRs are associated with manifold intrinsic and extrinsic agents in synaptic strength and plasticity. Neuropsychiatric conditions depression and addiction share the similar pathophysiology of synapse inadaptability underlying negative mood-related processes, memory formations, and impairments. In the attempt to emphasize all convergent discoveries, we hope the insights gained on the GABA_BR system mechanisms of action are conducive to designing more therapeutic candidates so as to refine the prognosis rate of diseases and minimize side effects.

The role of CART in islet biology

Cocaine- and amphetamine-regulated transcript (CART) is mostly known for its appetite regulating effects in the central nervous system. However, CART is also highly expressed in the peripheral nervous system as well as in certain endocrine cells. Our group has dedicated more than 20 years to understand the role of CART in the pancreatic islets and in this review we summarize what is known to date about CART expression and function in the islets. CART is expressed in both islet cells and nerve fibers innervating the islets. Large species differences are at hand and CART expression is highly dynamic and increased during development, as well as in Type 2 Diabetes and certain endocrine tumors. In the human islets CART is expressed in alpha cells and beta cells and the expression is increased in T2D patients. CART increases insulin secretion, reduces glucagon secretion, and protects against beta cell death by reducing apoptosis and increasing proliferation. It is still not fully understood how CART mediates its effects or which receptors that are involved. Nevertheless, CART is endowed with several properties that are beneficial in a T2D perspective. Many of the described effects of CART resemble those of GLP-1, and interestingly CART has been found to potentiate some of the effects of GLP-1, paving the way for CART-based treatments in combination with GLP-1-based drugs.

Overcoming Stress, Hunger, and Pain: Cocaine- and Amphetamine-Regulated Transcript Peptide's Promise

Cocaine- and amphetamine-regulated transcript encodes an eponymous peptide, CARTp, which exerts diverse pharmacologic actions in the central and peripheral nervous systems, as well as in several endocrine organs, including pancreas. Here we review those diverse actions, the physiological relevance of which had remained unestablished until recently. With the identification of a CARTp receptor, GPR160, the physiologic importance and therapeutic potential of CARTp or analogs are being revealed. Not only is the CARTp-GPR160 interaction essential for the circadian regulation of appetite and thirst but also for the transmission of nerve injury-induced pain. Molecular approaches now are uncovering additional physiologically relevant actions and the development of acute tissue-specific gene compromise approaches may reveal even more physiologically relevant actions of this pluripotent ligand/receptor pair.

Demystifying functional role of cocaine- and amphetamine-related transcript (CART) peptide in control of energy homeostasis: A twenty-five year expedition

Cocaine- and amphetamine-related transcript (CART) is a neuropeptide first discovered in the striatum of the rat brain. Later, the genetic sequence and function of CART peptide (CARTp) was found to be conserved among multiple mammalian species. Over the 25 years, since its discovery, CART mRNA (Cartpt) expression has been reported widely throughout the central and peripheral nervous systems underscoring its role in diverse physiological functions. Here, we review the localization and function of CARTp as it relates to energy homeostasis. We summarize the expression changes of central and peripheral Cartpt in response to metabolic states and make use of available large data sets to gain additional insights into the anatomy of the Cartpt expressing vagal neurons and their expression patterns in the gut. Furthermore, we provide an overview of the role of CARTp as an anorexigenic signal and its effect on energy expenditure and body weight control with insights from both pharmacological and transgenic animal studies. Subsequently, we discuss the role of CARTp in the pathophysiology of obesity and review important new developments towards identifying a candidate receptor for CARTp signalling. Altogether, the field of CARTp research has made rapid and substantial progress recently, and we review the case for considering CARTp as a potential therapeutic target for stemming the obesity epidemic.

Past, present and future of cocaine- and amphetamine-regulated transcript peptide

The existence of the peptide encoded by the cocaine- and amphetamine-regulated transcript (Cartpt) has been recognized since 1981, but it was not until 1995, that the gene encoding CART peptide (CART) was identified. With the availability of the predicted protein sequence of CART investigators were able to identify sites of peptide localization, which then led to numerous approaches attempting to clarify CART's multiple pharmacologic effects and even provide evidence of potential physiologic relevance. Although not without controversy, a picture emerged of the importance of CART in ingestive behaviors, reward behaviors and even pain sensation. Despite the wealth of data hinting at the significance of CART, in the absence of an identified receptor, the full potential for this peptide or its analogs to be developed into therapeutic agents remained unrealized. There was evidence favoring the action of CART via a G protein-coupled receptor (GPCR), but despite multiple attempts the identity of that receptor eluded investigators until recently. Now with the identification of the previously orphaned GPCR, GPR160, as a receptor for CART, focus on this pluripotent neuropeptide will in all likelihood experience a renaissance and the potential for the development of pharmcotherapies targeting GPR160 seems within reach.

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.

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.

Cocaine- and amphetamine-regulated transcript (CART): A multifaceted neuropeptide

Over the last 35 years, the continuous discovery of novel neuropeptides has been the key to the better understanding of how the central nervous system has integrated with neuronal signals and behavioral responses. Cocaine and amphetamine-regulated transcript (CART) was discovered in 1995 in the rat striatum but later was found to be highly expressed in the hypothalamus. The widespread distribution of CART peptide in the brain complicated the understanding of the role played by this neurotransmitter. The main objective of the current compact review is to piece together the fragments of available information about origin, expression, distribution, projection, and function of CART peptides. Accumulative evidence suggests CART as a neurotransmitter and neuroprotective agent that is mainly involved in regulation of feeding, addiction, stress, anxiety, innate fear, neurological disease, neuropathic pain, depression, osteoporosis, insulin secretion, learning, memory, reproduction, vision, sleep, thirst and body temperature. In spite of the vast number of studies about the CART, the overall pictures about the CART functions are sketchy. First, there is a lack of information about cloned receptor, specific agonist and antagonist. Second, CART peptides are detected in discrete sets of neurons that can modulate countless activities and third; CART peptides exist in several fragments due to post-translational processing. For these reasons the overall picture about the CART peptides are sketchy and confounding.

Intestinal CART is a regulator of GIP and GLP-1 secretion and expression

Impaired incretin effect is a culprit in Type 2 Diabetes. Cocaine- and amphetamine-regulated transcript (CART) is a regulatory peptide controlling pancreatic islet hormone secretion and beta-cell survival. Here we studied the potential expression of CART in enteroendocrine cells and examined the role of CART as a regulator of incretin secretion and expression. CART expression was found in glucose-dependent insulinotropic polypeptide (GIP)-producing K-cells and glucagon-like peptide-1 (GLP-1)-producing L-cells in human duodenum and jejunum and circulating CART levels were increased 60 min after a meal in humans. CART expression was increased by fatty acids and GIP, but unaffected by glucose in GLUTag and STC-1 cells. Exogenous CART had no effect on GIP and GLP-1 expression and secretion in GLUTag or STC-1 cells, but siRNA-mediated silencing of CART reduced GLP-1 expression and secretion. Furthermore, acute intravenous administration of CART increased GIP and GLP-1 secretion during an oral glucose-tolerance test in mice. We conclude that CART is a novel constituent of human K- and L-cells with stimulatory actions on incretin secretion and that interfering with the CART system may be a therapeutic avenue for T2D.

A Rho-kinase inhibitor reverses learning and memory deficits in a Rat model of chronic cerebral ischemia by altering Bcl-2/Bax-NMDAR signaling in the cerebral cortex

The current study investigated whether a Rho-kinase inhibitor alleviated impairments in a rat model of chronic cerebral ischemia and examined the specific pathological mechanisms by which Rho-kinase impacts neuronal damage and cognitive dysfunction. Adult Sprague-Dawley rats underwent permanent bilateral carotid artery occlusion (BCAO) to establish our chronic cerebral ischemia model. Chronic Y27632 administration reversed the abnormal behaviors of BCAO-treated rats in the Morris water maze. We performed Western blot analyses of the apoptosis-related proteins Bcl-2 and Bax to examine the potential mechanism underlying the beneficial effects of Y27632 on cerebral ischemia and showed for the first time that Y27632 reversed the decrease in the Bcl-2/Bax ratio in BCAO model rats. Y27632 restored the depression of NR2A- and NR2B-containing N-methyl-d-aspartate receptors (NMDARs) in the cerebral cortex of BCAO model rats. We also investigated these effects on middle cerebral artery occlusion (MCAO) model rats and observed some differences between the two models. In summary, our data provide evidence supporting the hypothesis that Rho-kinase inhibitors exert neuroprotective effects on cerebral ischemia. The Bcl-2/Bax-NMDAR signaling pathway in the cerebral cortex may be responsible for the protective effects of the Rho-kinase inhibitor, and this pathway may represent a pharmacological target for curative clinical strategies.

Orphan neuropeptides and receptors: Novel therapeutic targets

Neuropeptides are the largest class of intercellular signaling molecules, contributing to a wide variety of physiological processes. Neuropeptide receptors are therapeutic targets for a broad range of drugs, including medications to treat pain, addiction, sleep disorders, and nausea. In addition to >100 peptides with known functions, many peptides have been identified in mammalian brain for which the cognate receptors have not been identified. Similarly, dozens of "orphan" G protein-coupled receptors have been identified in the mammalian genome. While it would seem straightforward to match the orphan peptides and receptors, this is not always easily accomplished. In this review we focus on peptides named PEN and big LEN, which are among the most abundant neuropeptides in mouse brain, and their recently identified receptors: GPR83 and GPR171. These receptors are co-expressed in some brain regions and are able to interact. Because PEN and big LEN are produced from the same precursor protein and co-secreted, the interaction of GPR83 and GPR171 is physiologically relevant. In addition to interactions of these two peptides/receptors, PEN and LEN are co-localized with neuropeptide Y and Agouti-related peptide in neurons that regulate feeding. In this review, using these peptide receptors as an example, we highlight the multiple modes of regulation of receptors and present the emerging view that neuropeptides function combinatorially to generate a network of signaling messages. The complexity of neuropeptides, receptors, and their signaling pathways is important to consider both in the initial deorphanization of peptides and receptors, and in the subsequent development of therapeutic applications.

Cocaine- and Amphetamine-Regulated Transcript Peptide (CART) Alleviates MK-801-Induced Schizophrenic Dementia-Like Symptoms

Exaggerated thoughts, diminished mood and impaired cognition are the hallmarks of the schizophrenia-like condition. These symptoms are attributed to the dysregulation of dopamine and glutamate signaling in the brain. Since cocaine- and amphetamine-regulated transcript peptide (CART) modulates actions of dopamine as well as glutamate, we tested the role of this peptide in MK-801-induced schizophrenic dementia-like condition. MK-801-treated rats were allowed to interact with conspecific juvenile and tested for short-term (30-min) and long-term (24-h) social memory acquisition and recall. While MK-801 impaired the social interaction with a juvenile, the behavior was restored in CART [intracerebroventricular (icv) or intra-ventral tegmental area (VTA)] pre-treated animals. This action of CART was blocked by SCH23390 (dopamine D1 receptor antagonist) administered directly into the prefrontal cortex (PFC). Application of neuronal tracer Di-I in the PFC retrogradely labeled dopamine cells of the VTA, which in turn seem to receive CARTergic innervation. A significant increase in CARTimmunoreactivity was evidenced in the VTA, PFC and accumbens of the animals allowed to interact with a juvenile. However, MK-801 treatment attenuated the peptide expression and induced social memory deficits. The schizophrenic dementia-like symptoms following antagonism of glutamatergic receptors may be attributed to the reduced dopamine activity in the mesocortical system. We suggest that CART may, positively modulate the dopamine system to alleviate cognitive deficits associated with schizophrenia.

CART neurons in the lateral hypothalamus communicate with the nucleus accumbens shell via glutamatergic neurons in paraventricular thalamic nucleus to modulate reward behavior

Paraventricular thalamic nucleus (PVT) serves as a transit node processing food and drug-associated reward information, but its afferents and efferents have not been fully defined. We test the hypothesis that the CART neurons in the lateral hypothalamus (LH) project to the PVT neurons, which in turn communicate via the glutamatergic fibers with the nucleus accumbens shell (AcbSh), the canonical site for reward. Rats conditioned to self-stimulate via an electrode in the right LH-medial forebrain bundle were used. Intra-PVT administration of CART (55-102) dose-dependently (10-50 ng/rat) lowered intracranial self-stimulation (ICSS) threshold and increased lever press activity, suggesting reward-promoting action of the peptide. However, treatment with CART antibody (intra-PVT) or MK-801 (NMDA antagonist, intra-AcbSh) produced opposite effects. A combination of sub-effective dose of MK-801 (0.01 µg/rat, intra-AcbSh) and effective dose of CART (25 ng/rat, intra-PVT) attenuated CART's rewarding action. Further, we screened the LH-PVT-AcbSh circuit for neuroadaptive changes induced by conditioning experience. A more than twofold increase was noticed in the CART mRNA expression in the LH on the side ipsilateral to the implanted electrode for ICSS. In addition, the PVT of conditioned rats showed a distinct increase in the (a) c-Fos expressing cells and CART fiber terminals, and (b) CART and vesicular glutamate transporter 2 immunostained elements. Concomitantly, the AcbSh showed a striking increase in expression of NMDA receptor subunit NR1. We suggest that CART in LH-PVT and glutamate in PVT-AcbSh circuit might support food-seeking behavior under natural conditions and also store reward memory.

CART peptide in the nucleus accumbens regulates psychostimulants: Correlations between psychostimulant and CART peptide effects

In this study, we reexamined the effect of Cocaine-and-Amphetamine-Regulated-Transcript (CART) peptide on psychostimulant (PS)-induced locomotor activity (LMA) in individual rats. The Methods utilized were as previously published. The PS-induced LMA was defined as the distance traveled after PS administration (intraperitoneal), and the CART peptide effect was defined as the change in the PS-induced activity after bilateral intra-NAc administration of CART peptide. The experiments included both male and female Sprague-Dawley rats, and varying the CART peptide dose and the PS dose. While the average effect of CART peptide was to inhibit PS-induced LMA, the effect of CART peptide on individual PS-treated animals was not always inhibitory and sometimes even produced an increase or no change in PS-induced LMA. Upon further analysis, we observed a linear correlation, reported for the first time, between the magnitude of PS-induced LMA and the CART peptide effect. Because CART peptide inhibits PS-induced LMA when it is large, and increases PS-induced LMA when it is small, the peptide can be considered a homeostatic regulator of dopamine-induced LMA, which supports our earlier homeostatic hypothesis.

Wide-field diffuse amacrine cells in the monkey retina contain immunoreactive Cocaine- and Amphetamine-Regulated Transcript (CART)

The goals of this study were to localize the neuropeptide Cocaine- and Amphetamine-Regulated Transcript (CART) in primate retinas and to describe the morphology, neurotransmitter content and synaptic connections of the neurons that contain it. Using in situ hybridization, light and electron microscopic immunolabeling, CART was localized to GABAergic amacrine cells in baboon retinas. The CART-positive cells had thin, varicose dendrites that gradually descended through the inner plexiform layer and ramified extensively in the innermost stratum. They resembled two types of wide-field diffuse amacrine cells that had been described previously in macaque retinas using the Golgi method and also A17, serotonin-accumulating and waterfall cells of other mammals. The CART-positive cells received synapses from rod bipolar cell axons and made synapses onto the axons in a reciprocal configuration. The CART-positive cells also received synapses from other amacrine cells. Some of these were located on their primary dendrites, and the presynaptic cells there included dopaminergic amacrine cells. Although some CART-positive somas were localized in the ganglion cell layer, they did not contain the ganglion cell marker RNA binding protein with multiple splicing (RBPMS). Based on these results and electrophysiological studies in other mammals, the CART-positive amacrine cells would be expected to play a major role in the primary rod pathway of primates, providing feedback inhibition to rod bipolar cells.

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.

The brain in bone and fuel metabolism

Obesity and osteoporosis have become major public health challenges worldwide. The brain is well established as a pivotal regulator of energy homeostasis, appetite and fuel metabolism. However, there is now clear evidence for regulation between the brain and bone. Similarly, evidence also indicates that the involvement of the brain in bone and adipose regulation is both related and interdependent. The hypothalamus, with its semi-permeable blood brain barrier, is one of the most powerful regulatory regions within the body, integrating and relaying signals not only from peripheral tissues but also from within the brain itself. Two main neuronal populations within the arcuate nucleus of the hypothalamus regulate energy homeostasis: The orexigenic, appetite-stimulating neurons that co-express neuropeptide Y and agouti-related peptide and the anorexigenic, appetite-suppressing neurons that co-express proopiomelanocortin and cocaine- and amphetamine related transcript. From within the arcuate, these four neuropeptides encompass some of the most powerful control of energy homeostasis in the entire body. Moreover, they also regulate skeletal homeostasis, identifying a co-ordination network linking the processes of bone and energy homeostasis. Excitingly, the number of central neuropeptides and neural factors known to regulate bone and energy homeostasis continues to grow, with cannabinoid receptors and semaphorins also involved in bone homeostasis. These neuronal pathways represent a growing area of research that is identifying novel regulatory axes between the brain and the bone, and links with other homeostatic networks; thereby revealing a far more complex, and interdependent bone biology than previously envisioned. This review examines the current understanding of the central regulation of bone and energy metabolism.

Cocaine- and amphetamine-regulated transcript and calcium binding proteins immunoreactivity in the subicular complex of the guinea pig

In this study we present the distribution and colocalization pattern of cocaine- and amphetamine-regulated transcript (CART) and three calcium-binding proteins: calbindin (CB), calretinin (CR) and parvalbumin (PV) in the subicular complex (SC) of the guinea pig. The subiculum (S) and presubiculum (PrS) showed higher CART-immunoreactivity (-IR) than the parasubiculum (PaS) as far as the perikarya and neuropil were concerned. CART- IR cells were mainly observed in the pyramidal layer and occasionally in the molecular layer of the S. In the PrS and PaS, single CART-IR perikarya were dispersed, however with a tendency to be found only in superficial layers. CART-IR fibers were observed throughout the entire guinea pig subicular neuropil. Double-labeling immunofluorescence showed that CART-IR perikarya, as well as fibers, did not stain positively for any of the three CaBPs. CART-IR fibers were only located near the CB-, CR-, PV-IR perikarya, whereas CART-IR fibers occasionally intersected fibers containing one of the three CaBPs. The distribution pattern of CART was more similar to that of CB and CR than to that of PV. In the PrS, the CART, CB and CR immunoreactivity showed a laminar distribution pattern. In the case of the PV, this distribution pattern in the PrS was much less prominent than that of CART, CB and CR. We conclude that a heterogeneous distribution of the CART and CaBPs in the guinea pig SC is in keeping with findings from other mammals, however species specific differences have been observed.

Hippocampal Gene Expression Is Highly Responsive to Estradiol Replacement in Middle-Aged Female Rats

In the hippocampus, estrogens are powerful modulators of neurotransmission, synaptic plasticity and neurogenesis. In women, menopause is associated with increased risk of memory disturbances, which can be attenuated by timely estrogen therapy. In animal models of menopause, 17β-estradiol (E2) replacement improves hippocampus-dependent spatial memory. Here, we explored the effect of E2 replacement on hippocampal gene expression in a rat menopause model. Middle-aged ovariectomized female rats were treated continuously for 29 days with E2, and then, the hippocampal transcriptome was investigated with Affymetrix expression arrays. Microarray data were analyzed by Bioconductor packages and web-based softwares, and verified with quantitative PCR. At standard fold change selection criterion, 156 genes responded to E2. All alterations but 4 were transcriptional activation. Robust activation (fold change > 10) occurred in the case of transthyretin, klotho, claudin 2, prolactin receptor, ectodin, coagulation factor V, Igf2, Igfbp2, and sodium/sulfate symporter. Classification of the 156 genes revealed major groups, including signaling (35 genes), metabolism (31 genes), extracellular matrix (17 genes), and transcription (16 genes). We selected 33 genes for further studies, and all changes were confirmed by real-time PCR. The results suggest that E2 promotes retinoid, growth factor, homeoprotein, neurohormone, and neurotransmitter signaling, changes metabolism, extracellular matrix composition, and transcription, and induces protective mechanisms via genomic effects. We propose that these mechanisms contribute to effects of E2 on neurogenesis, neural plasticity, and memory functions. Our findings provide further support for the rationale to develop safe estrogen receptor ligands for the maintenance of cognitive performance in postmenopausal women.

Differences in inhibitory avoidance, cortisol and brain gene expression in TL and AB zebrafish

Recently, we established an inhibitory avoidance paradigm in Tupfel Long-Fin (TL) zebrafish. Here, we compared task performance of TL fish and fish from the AB strain; another widely used strain and shown to differ genetically and behaviourally from TL fish. Whole-body cortisol and telencephalic gene expression related to stress, anxiety and fear were measured before and 2 h post-task. Inhibitory avoidance was assessed in a 3-day paradigm: fish learn to avoid swimming from a white to a black compartment where a 3V-shock is given: day 1 (first shock), day 2 (second shock) and day 3 (no shock, sampling). Tupfel Long-Fin fish rapidly learned to avoid the black compartment and showed an increase in avoidance-related spatial behaviour in the white compartment across days. In contrast, AB fish showed no inhibitory avoidance learning. AB fish had higher basal cortisol levels and expression levels of stress-axis related genes than TL fish. Tupfel Long-Fin fish showed post-task learning-related changes in cortisol and gene expression levels, but these responses were not seen in AB fish. We conclude that AB fish show higher cortisol levels and no inhibitory avoidance than TL fish. The differential learning responses of these Danio strains may unmask genetically defined risks for stress-related disorders.

The effects of environmental enrichment and age-related differences on inhibitory avoidance in zebrafish (Danio rerio Hamilton)

The inhibitory avoidance paradigm allows the study of mechanisms underlying learning and memory formation in zebrafish (Danio rerio Hamilton). For zebrafish, the physiology and behavior associated with this paradigm are as yet poorly understood. We therefore assessed the effects of environmental enrichment and fish age on inhibitory avoidance learning. Fish raised in an environmentally enriched tank showed decreased anxiety-like behavior and increased exploration. Enrichment greatly reduced inhibitory avoidance in 6-month (6M)- and 12-month (12 M)-old fish. Following inhibitory avoidance, telencephalic mRNA levels of proliferating cell nuclear antigen (pcna), neurogenic differentiation (neurod), cocaine- and amphetamine-regulated transcript 4 (cart4), and cannabinoid receptor 1 (cnr1) were lower in enriched-housed fish, while the ratios of mineralocorticoid receptor (nr3c2)/glucocorticoid receptor α [nr3c1(α)] and glucocorticoid receptor β [nr3c1(β)]/glucocorticoid receptor α [nr3c1(α)] were higher. This was observed for 6M-old fish only, not for 24-month (24 M) old fish. Instead, 24 M-old fish showed delayed inhibitory avoidance, no effects of enrichment, and reduced expression of neuroplasticity genes. Overall, our data show strong differences in inhibitory avoidance behavior between zebrafish of different ages and a clear reduction in avoidance behavior following housing under environmental enrichment.

CART in the regulation of appetite and energy homeostasis

The cocaine- and amphetamine-regulated transcript (CART) has been the subject of significant interest for over a decade. Work to decipher the detailed mechanism of CART function has been hampered by the lack of specific pharmacological tools like antagonists and the absence of a specific CART receptor(s). However, extensive research has been devoted to elucidate the role of the CART peptide and it is now evident that CART is a key neurotransmitter and hormone involved in the regulation of diverse biological processes, including food intake, maintenance of body weight, reward and addiction, stress response, psychostimulant effects and endocrine functions (Rogge et al., 2008; Subhedar et al., 2014). In this review, we focus on knowledge gained on CART's role in controlling appetite and energy homeostasis, and also address certain species differences between rodents and humans.

Unpredictable chronic stress decreases inhibitory avoidance learning in Tuebingen long-fin zebrafish: stronger effects in the resting phase than in the active phase

Zebrafish (Danio rerio Hamilton) are increasingly used as a model to study the effects of chronic stress on brain and behaviour. In rodents, unpredictable chronic stress (UCS) has a stronger effect on physiology and behaviour during the active phase than during the resting phase. Here, we applied UCS during the daytime (active phase) for 7 and 14 days or during the night-time (resting phase) for 7 nights in an in-house-reared Tuebingen long-fin (TLF) zebrafish strain. Following UCS, inhibitory avoidance learning was assessed using a 3 day protocol where fish learn to avoid swimming from a white to a black compartment where they will receive a 3 V shock. Latencies of entering the black compartment were recorded before training (day 1; first shock) and after training on day 2 (second shock) and day 3 (no shock, tissue sampling). Fish whole-body cortisol content and expression levels of genes related to stress, fear and anxiety in the telencephalon were quantified. Following 14 days of UCS during the day, inhibitory avoidance learning decreased (lower latencies on days 2 and 3); minor effects were found following 7 days of UCS. Following 7 nights of UCS, inhibitory avoidance learning decreased (lower latency on day 3). Whole-body cortisol levels showed a steady increase compared with controls (100%) from 7 days of UCS (139%), to 14 days of UCS (174%) to 7 nights of UCS (231%), suggestive of an increasing stress load. Only in the 7 nights of UCS group did expression levels of corticoid receptor genes (mr, grα, grβ) and of bdnf increase. These changes are discussed as adaptive mechanisms to maintain neuronal integrity and prevent overload, and as being indicative of a state of high stress load. Overall, our data suggest that stressors during the resting phase have a stronger impact than during the active phase. Our data warrant further studies on the effect of UCS on stress axis-related genes, especially grβ; in mammals this receptor has been implicated in glucocorticoid resistance and depression.

Electrophysiological characteristics of paraventricular thalamic (PVT) neurons in response to cocaine and cocaine- and amphetamine-regulated transcript (CART)

Recent work has established that the paraventricular thalamus (PVT) is a central node in the brain reward-seeking pathway. This role is mediated in part through projections from hypothalamic peptide transmitter systems such as cocaine- and amphetamine-regulated transcript (CART). Consistent with this proposition, we previously found that inactivation of the PVT or infusions of CART into the PVT suppressed drug-seeking behavior in an animal model of contingent cocaine self-administration. Despite this work, few studies have assessed how the basic physiological properties of PVT neurons are influenced by exposure to drugs such as cocaine. Further, our previous work did not assess how infusions of CART, which we found to decrease cocaine-seeking, altered the activity of PVT neurons. In the current study we address these issues by recording from anterior PVT (aPVT) neurons in acutely prepared brain slices from cocaine-treated (15 mg/ml, n = 8) and saline-treated (control) animals (n = 8). The excitability of aPVT neurons was assessed by injecting a series of depolarizing and hyperpolarizing current steps and characterizing the resulting action potential (AP) discharge properties. This analysis indicated that the majority of aPVT neurons exhibit tonic firing (TF), and initial bursting (IB) consistent with previous studies. However, we also identified PVT neurons that exhibited delayed firing (DF), single spiking (SS) and reluctant firing (RF) patterns. Interestingly, cocaine exposure significantly increased the proportion of aPVT neurons that exhibited TF. We then investigated the effects of CART on excitatory synaptic inputs to aPVT neurons. Application of CART significantly suppressed excitatory synaptic drive to PVT neurons in both cocaine-treated and control recordings. This finding is consistent with our previous behavioral data, which showed that CART signaling in the PVT negatively regulates drug-seeking behavior. Together, these studies suggest that cocaine exposure shifts aPVT neurons to a more excitable state (TF). We propose that the capacity of CART to reduce excitatory drive to this population balances the enhanced aPVT excitability to restore the net output of this region in the reward-seeking pathway. This is in line with previous anatomical evidence that the PVT can integrate reward-relevant information and provides a putative mechanism through which drugs of abuse can dysregulate this system in addiction.

Inhibitory avoidance learning in zebrafish (Danio rerio): effects of shock intensity and unraveling differences in task performance

The zebrafish (Danio rerio) is increasingly used as a model in neurobehavioral and neuroendocrine studies. The inhibitory avoidance paradigm has been proposed as tool to study mechanisms underlying learning and memory in zebrafish. In this paradigm subjects receive a shock after entering the black compartment of a black-white box. On the next day, latency to enter the black compartment is assessed; higher latencies are indicative of increased avoidance learning. Here, we aimed to understand the effects of different shock intensities (0, 1, 3, and 9 V) and to unravel variation in inhibitory avoidance learning in an in-house reared Tuebingen Long-Fin zebrafish (D. rerio) strain. While median latencies had increased in the 1, 3, and 9 V groups, no increase in median latency was found in the 0 V group. In addition, higher shock intensities resulted in a higher number of avoiders (latency ≥180 s) over nonavoiders (latency <60 s). Both changes are indicative of increased avoidance learning. We assessed whole-body cortisol content and the expression levels of genes relevant to stress, anxiety, fear, and learning 2 h after testing. Shock intensity was associated with whole-body cortisol content and the expression of glucocorticoid receptor alpha [nr3c1(alpha)], cocaine- and amphetamine-regulated transcript (cart4), and mineralocorticoid receptor (nr3c2), while avoidance behavior was associated with whole-body cortisol content only. The inhibitory avoidance paradigm in combination with measuring whole-body cortisol content and gene expression is suitable to unravel (genetic) mechanisms of fear avoidance learning. Our data further show differences in brain-behavior relationships underlying fear avoidance learning and memory in zebrafish. These findings serve as starting point for further unraveling differences in brain-behavior relationships underlying (fear avoidance) learning and memory in zebrafish.

CART in the brain of vertebrates: circuits, functions and evolution

Cocaine- and amphetamine-regulated transcript peptide (CART) with its wide distribution in the brain of mammals has been the focus of considerable research in recent years. Last two decades have witnessed a steady rise in the information on the genes that encode this neuropeptide and regulation of its transcription and translation. CART is highly enriched in the hypothalamic nuclei and its relevance to energy homeostasis and neuroendocrine control has been understood in great details. However, the occurrence of this peptide in a range of diverse circuitries for sensory, motor, vegetative, limbic and higher cortical areas has been confounding. Evidence that CART peptide may have role in addiction, pain, reward, learning and memory, cognition, sleep, reproduction and development, modulation of behavior and regulation of autonomic nervous system are accumulating, but an integration has been missing. A steady stream of papers has been pointing at the therapeutic potentials of CART. The current review is an attempt at piecing together the fragments of available information, and seeks meaning out of the CART elements in their anatomical niche. We try to put together the CART containing neuronal circuitries that have been conclusively demonstrated as well as those which have been proposed, but need confirmation. With a view to finding out the evolutionary antecedents, we visit the CART systems in sub-mammalian vertebrates and seek the answer why the system is shaped the way it is. We enquire into the conservation of the CART system and appreciate its functional diversity across the phyla.

Co-expression patterns of cocaine- and amphetamine-regulated transcript (CART) with neuropeptides in dorsal root ganglia of the pig

In the present study the neuronal distribution of CART was evaluated immunohistochemically in porcine dorsal root ganglia (DRGs). In co-localization studies the co-expression patterns of CART with SP, CGRP, galanin, CALB and LENK were investigated by means of triple immunohistochemical stainings. In porcine DRGs, the expression of CART was found in approximately 5% of primary sensory neurons. The vast majority (ca. 95%) of CART-immunoreactive (IR) neurons were small and middle sized, and only 5% were categorized as large. CART-IR neurons additionally exhibiting the presence of SP/CGRP (ca. 12%), SP/CALB (ca. 12%), SP/LENK (ca. 5%) were found. The vast majority of CART-IR/CGRP-IR neurons did not display immunoreaction to SP (ca. 60%). Subclasses of CART-IR/LENK-IR/SP-negative (ca. 5%), as well as CART-IR/CALB-IR/SP-negative neurons (ca. 10%), were also visualized. In addition, CART-IR neurons with no immunoreactivities to any of the neuropeptides studied were also shown. In porcine DRGs none of the CART-IR neurons exhibited the presence of galanin. The results obtained in the study suggest that CART may functionally modulate the activity of the porcine primary sensory neurons. It is concluded that co-expression of CART with CGRP, SP, LENK and CALB in subsets of the pig L1-L6 DRGs neurons provide anatomical evidence for a CART role in pain processing.

Inhibitory modulation of CART peptides in accumbal neuron through decreasing interaction of CaMKIIα with dopamine D3 receptors

Previous studies in rats have shown that microinjections of cocaine- and amphetamine-regulated transcript (CART) peptide into the nucleus accumbens (NAc; the area of the brain that mediates drug reward and reinforcement) attenuate the locomotor effects of psychostimulants. CART peptide has also been shown to induce decreased intracellular concentrations of calcium (Ca(2+)) in primary cultures of hippocampus neurons. The purpose of this study was to characterize the interaction of Ca(2+)/calmodulin-dependent kinases (CaMKIIα) with dopamine D3 (D3) receptors (R) in primary cultures of accumbal neurons. This interaction is involved in inhibitory modulation of CART peptides. In vitro, CART (55-102) peptide (0.1, 0.5 or 1μM) was found to dose-dependently inhibit K(+) depolarization-elicited Ca(2+) influx and CaMKIIα phosphorylation in accumbal neurons. Moreover, CART peptides were also found to block cocaine (1μM)-induced Ca(2+) influx, CaMKIIα phosphorylation, CaMKIIα-D3R interaction, and CREB phosphorylation. In vivo, repeated microinjections of CART (55-102) peptide (2μg/1μl/side) into the NAc over a 5-day period had no effect on behavioral activity but blocked cocaine-induced locomotor activity. These results indicate that D3R function in accumbal neurons is a target of CART (55-102) peptide and suggest that CART peptide by dephosphorylating limbic D3Rs may have potential as a treatment for cocaine abuse.

Peptides and food intake

The mechanisms for controlling food intake involve mainly an interplay between gut, brain, and adipose tissue (AT), among the major organs. Parasympathetic, sympathetic, and other systems are required for communication between the brain satiety center, gut, and AT. These neuronal circuits include a variety of peptides and hormones, being ghrelin the only orexigenic molecule known, whereas the plethora of other factors are inhibitors of appetite, suggesting its physiological relevance in the regulation of food intake and energy homeostasis. Nutrients generated by food digestion have been proposed to activate G-protein-coupled receptors on the luminal side of enteroendocrine cells, e.g., the L-cells. This stimulates the release of gut hormones into the circulation such as glucagon-like peptide-1 (GLP-1), oxyntomodulin, pancreatic polypeptides, peptide tyrosine tyrosine, and cholecystokinin, which inhibit appetite. Ghrelin is a peptide secreted from the stomach and, in contrast to other gut hormones, plasma levels decrease after a meal and potently stimulate food intake. Other circulating factors such as insulin and leptin relay information regarding long-term energy stores. Both hormones circulate at proportional levels to body fat content, enter the CNS proportionally to their plasma levels, and reduce food intake. Circulating hormones can influence the activity of the arcuate nucleus (ARC) neurons of the hypothalamus, after passing across the median eminence. Circulating factors such as gut hormones may also influence the nucleus of the tractus solitarius (NTS) through the adjacent circumventricular organ. On the other hand, gastrointestinal vagal afferents converge in the NTS of the brainstem. Neural projections from the NTS, in turn, carry signals to the hypothalamus. The ARC acts as an integrative center, with two major subpopulations of neurons influencing appetite, one of them coexpressing neuropeptide Y and agouti-related protein (AgRP) that increases food intake, whereas the other subpopulation coexpresses pro-opiomelanocortin (POMC) and cocaine and amphetamine-regulated transcript that inhibits food intake. AgRP antagonizes the effects of the POMC product, α-melanocyte-stimulating hormone (α-MSH). Both populations project to areas important in the regulation of food intake, including the hypothalamic paraventricular nucleus, which also receives important inputs from other hypothalamic nuclei.

CART (cocaine- and amphetamine-regulated transcript) peptide specific binding sites in PC12 cells have characteristics of CART peptide receptors

CART (cocaine- and amphetamine-regulated transcript) peptide is a neuropeptide with a powerful central anorexigenic effect. Specific CART peptide binding sites, most likely CART peptide receptors, have been found in PC12 cells. This study further characterizes the CART peptide binding sites in PC12 cells. After differentiation to a neuronal phenotype with nerve growth factor, the number of CART peptide binding sites in PC12 cells tripled. Following dexamethasone treatment, which transforms PC12 cells into chromaffin-like cells, the number of CART peptide binding sites substantially decreased. CART peptide did not affect the differentiation or acetylcholinesterase activity of PC12 cells, indicating that CART peptide does not participate in differentiation or neuronal activity. CART peptide increased the phosphorylation of SAPK/JNK (stress-activated protein kinase/c-Jun-amino-terminal kinase) and subsequent c-Jun protein expression. These effects were reversed by SP600125, a specific JNK-kinase inhibitor. CART peptide did not significantly affect ERK (extracellular signal-regulated kinase), CREB (cAMP responsive element binding protein), or p38 phosphorylation and c-Fos protein expression. Central administration of CART peptide into mice also resulted in increased c-Jun positive cells in dorsomedial hypothalamic nucleus and nucleus of the solitary tract, areas involved in food intake regulation. Activation of c-Jun by CART peptide might indicate a possible role of CART peptide in managing stress conditions rather than a role in cell proliferation or differentiation as well as the more complex and/or specific regulation ways by transcription factors in some nuclei involved in food intake regulation. The characteristics of stress that CART peptide potentially mediates should be further studied.

Colocalization pattern of calbindin and cocaine- and amphetamine-regulated transcript in the mammillary body-anterior thalamic nuclei axis of the guinea pig

The study describes for the first time the colocalization pattern of calbindin (CB) and cocaine- and amphetamine-regulated transcript (CART) in the mammillary body (MB) and anterior thalamic nuclei (ATN) - structures connected in a topographically organized manner by the mammillothalamic tract (mtt). Immunohistochemical study was performed on fetal (E40, E50, E60), newborn (P0) and postnatal (P20, P80) brains of the guinea pig, but the coexistence pattern of the substances was invariable throughout the examined developmental stages. CB and CART colocalized in the perikarya of the lateral part of the medial mammillary nucleus (MMl), whereas in its medial part (MMm) only CB was detected. In the mtt, which originates from the MB, both the substances were present and colocalized in single fibers. Next, fibers from the mtt spread toward the ATN in a particular way: fibers containing CB ran to both the anteromedial thalamic nucleus (AM) and anteroventral thalamic nucleus (AV), while fibers containing CART ran mostly to the latter one. In the ventral part of AV, CB and CART colocalized vastly in the neuropil. The lateral mammillary nucleus and anterodorsal thalamic nucleus were virtually devoid of CB- and CART-positive structures. Based on the known connections between the MB and ATN, we conclude that the studied substances may cooperate in the MMl-AV part of the axis and CB plays a significant role in the MMm-AM part.

Regulation of granulosa cell cocaine and amphetamine regulated transcript (CART) binding and effect of CART signaling inhibitor on granulosa cell estradiol production during dominant follicle selection in cattle

We previously established a potential role for cocaine and amphetamine regulated transcript (CARTPT) in dominant follicle selection in cattle. CARTPT expression is elevated in subordinate versus dominant follicles, and treatment with the mature form of the CARTPT peptide (CART) decreases follicle-stimulating hormone (FSH)-stimulated granulosa cell estradiol production in vitro and follicular fluid estradiol and granulosa cell CYP19A1 mRNA in vivo. However, mechanisms that regulate granulosa cell CART responsiveness are not understood. In this study, we investigated hormonal regulation of granulosa cell CART-binding sites in vitro and temporal regulation of granulosa cell CART-binding sites in bovine follicles collected at specific stages of a follicular wave. We also determined the effect of inhibition of CART receptor signaling in vivo on estradiol production in future subordinate follicles. Granulosa cell CART binding in vitro was increased by FSH, and this induction was blocked by estrogen receptor antagonist treatment. In follicles collected in vivo at specific stages of a follicular wave, granulosa cell CART binding in the F2 (second largest), future subordinate follicle increased during dominant follicle selection. Injection into the F2 follicle (at onset of diameter deviation) of an inhibitor of the o/i subclass of G proteins (previously shown to block CART actions in vitro) resulted in increased follicular fluid estradiol concentrations in vivo. Collectively, results demonstrate hormonal regulation of granulosa cell CART binding in vitro and temporal regulation of CART binding in subordinate follicles during dominant follicle selection. Results also suggest that CART signaling may help suppress estradiol-producing capacity of the F2 (subordinate) follicle during this time period.

Effect of cocaine on ion channels and glutamatergic EPSCs in noradrenergic locus coeruleus neurons

The locus coeruleus (LC) is an important brainstem area involved in cocaine addiction. However, evidence to elucidate how cocaine modulates the activity of LC neurons remains incomplete. Here, we performed whole recordings in brain slices to evaluate the effects of cocaine on the sodium (Na(+)), potassium (K(+)), calcium (Ca(2+)) channels, and glutamatergic synaptic transmission in the locus coeruleus neurons. Local application of cocaine significantly and reversibly reduced the spontaneous firing rate but did not affect action potential amplitude, rising time, decay time, or half width of noradrenergic locus coeruleus neurons. Moreover, cocaine attenuated the sodium current but did not affect potassium and calcium currents. The N-methyl-D-aspartate receptor mediated excitatory postsynaptic currents were reduced by neuropeptide galanin but not cocaine. All those data demonstrate that cocaine has inhibitory effect on the spontaneous activities and sodium current in locus coeruleus neurons. Therefore, neuromodulation of sodium channel in locus coeruleus neurons may play an important role in drug addiction.

Pituitary adenylate cyclase-activating polypeptide 6-38 blocks cocaine- and amphetamine-regulated transcript Peptide-induced hypophagia in rats

Cocaine- and amphetamine-regulated transcript peptides (CARTp) suppress nutritional intake after administration into the fourth intracerebral ventricle. Recent in vitro studies have shown that PACAP 6-38, a pituitary adenylate cyclase-activating polypeptide (PACAP) fragment, could act as a competitive antagonist against CARTp 55-102 on a common CARTp-sensitive receptor structure. Here, we show for the first time in vivo that the reduction in solid food intake induced by exogenous CARTp 55-102 (0.3 nmol: 1.5 µg) administered fourth i.c.v. is blocked by pretreatment with PACAP 6-38 (3 nmol). The PACAP 6-38 fragment had no effect by itself either when given into the fourth ventricle or subcutaneously. Although effective to block the CARTp-effect on feeding and short-term body weight, PACAP 6-38 failed to attenuate CARTp-associated gross motor behavioral changes suggesting at least two CARTp-sensitive receptor subtypes. In conclusion, PACAP 6-38 acts as a functional CARTp antagonist in vivo and blocks its effects on feeding and short term weight gain.

Roles of cocaine- and amphetamine-regulated transcript in the central nervous system

1. Cocaine- and amphetamine-regulated transcript (CART), first isolated from the ovine hypothalamus, is a potential neurotransmitter widely distributed throughout the central and peripheral nervous systems, as well as in endocrine cells in the pituitary and adrenal glands, pancreatic islets and stomach. 2. Numerous studies have established the role of CART in food intake, maintenance of bodyweight, stress control, reward and pain transmission. Recently, it was demonstrated that CART, as a neurotrophic peptide, had a cerebroprotective against focal ischaemic stroke and inhibited the neurotoxicity of β-amyloid protein, which focused attention on the role of CART in the central nervous system (CNS) and neurological diseases. 3. In fact, little is known about the way in which CART peptide interacts with its receptors, initiates downstream cascades and finally exerts its neuroprotective effect under normal or pathological conditions. The literature indicates that there are many factors, such as regulation of the immunological system and protection against energy failure, that may be involved in the cerebroprotection afforded by CART. 4. The present review provides a brief summary of the current literature on CART synthesis and active fragments, its distribution in the CNS and, in particular, the role of CART peptide (and its receptors and signalling) in neurological diseases.

CART peptide stimulation of G protein-mediated signaling in differentiated PC12 cells: identification of PACAP 6-38 as a CART receptor antagonist

CART peptides are peptide neurotransmitters and hormones that are involved in many different physiological responses. While much is known about the peptides regarding their structure, processing and gene regulation, less is known about their postsynaptic actions and receptors. Using (125)I-CART 61-102 as a ligand and unlabeled CART 61-102 or CART 55-102 as displacers, high-affinity specific binding was detected in PC12 cells. Differentiation of the PC12 cells increased specific binding several-fold. The increase in specific binding found after differentiation was inhibited by actinomycin D and cycloheximide, suggesting that the increase in specific binding was dependent on RNA and protein synthesis. CART 1-27, a peptide that has never been shown to elicit responses, did not displace (125)I-CART 61-102 binding, nor did more than 20 other peptides that were examined. Surprisingly, however, PACAP 1-38 and PACAP 6-38 were found to be low-affinity inhibitors of CART binding. CART treatment increased binding of (35)S-GTPgamma-S to PC12 cell membranes. Moreover, CART treatment of intact PC12 cells elicited robust increases in phospho-ERK in a manner that was increased with differentiation, blocked by pertussis toxin and antagonized by PACAP 6-38. These findings extend previous research and suggest that the CART binding site in PC12 cells reflects a G protein-coupled receptor linked with Gi/o, and also demonstrate that PACAP 6-38 may be useful as a CART receptor antagonist.