Clozapine and dopamine D3 receptor antisense reduce cocaine- and amphetamine-regulated transcript expression in the rat nucleus accumbens shell

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.

A role of neuropeptide CART in hyperphagia and weight gain induced by olanzapine treatment in rats

Although olanzapine is highly efficacious and most widely used second generation antipsychotic drug, the success of treatment has been hampered by its propensity to induce weight gain. While the underlying neuronal mechanisms are unclear, their elucidation may help to target alternative pathways regulating energy balance. The present study was undertaken to define the role of cocaine- and amphetamine-regulated transcript (CART), a well-known anorexic peptide, in olanzapine-induced hyperphagia and body weight gain in female rats. Olanzapine was administered daily by intraperitoneal route, alone or in combination with CART (intracerebroventricular) for a period of two weeks. Immediately after drug administrations, preweighed food was offered to the animals at the commencement of the dark phase. The food intake and body weight were measured daily just prior to next injection. Furthermore, the brains of olanzapine-treated rats were processed for the immunohistochemical analysis of CART-containing elements in the hypothalamus. Treatment with olanzapine (0.5 mg/kg) for the duration of 14 days produced a significant increase in food intake and body weight as compared to control. However, concomitant administration of CART (0.5 µg) attenuated the olanzapine-induced hyperphagia and weight gain. Olanzapine administration resulted in a significant reduction in CART immunoreactivity in the hypothalamic arcuate, paraventricular, dorsomedial and ventromedial nuclei. We suggest that decreased CART contents in the hypothalamus may be causally linked with the hyperphagia and weight gain induced by olanzapine.

Cocaine- and amphetamine-regulated transcript peptide in the nucleus accumbens shell inhibits cocaine-induced locomotor sensitization to transient over-expression of α-Ca2+ /calmodulin-dependent protein kinase II

Cocaine- and amphetamine-regulated transcript (CART) peptide is a widely distributed neurotransmitter that attenuates cocaine-induced locomotor activity when injected into the nucleus accumbens (NAc). Our previous work first confirmed that the inhibitory mechanism of the CART peptide on cocaine-induced locomotor activity is related to a reduction in cocaine-enhanced phosphorylated Ca²⁺ /calmodulin-dependent protein kinaseIIα (pCaMKIIα) and the enhancement of cocaine-induced D3R function. This study investigated whether CART peptide inhibited cocaine-induced locomotor activity via inhibition of interactions between pCaMKIIα and the D3 dopamine receptor (D3R). We demonstrated that lentivirus-mediated gene transfer transiently increased pCaMKIIα expression, which peaked at 10 days after microinjection into the rat NAc shell, and induced a significant increase in Ca²⁺ influx along with greater behavioral sensitivity in the open field test after intraperitoneal injections of cocaine (15 mg/kg). However, western blot analysis and coimmunoprecipitation demonstrated that CART peptide treatment in lentivirus-transfected CaMKIIα-over-expressing NAc rat tissues or cells prior to cocaine administration inhibited the cocaine-induced Ca²⁺ influx and attenuated the cocaine-increased pCaMKIIα expression in lentivirus-transfected CaMKIIα-over-expressing cells. CART peptide decreased the cocaine-enhanced phosphorylated cAMP response element binding protein (pCREB) expression via inhibition of the pCaMKIIα-D3R interaction, which may account for the prolonged locomotor sensitization induced by repeated cocaine treatment in lentivirus-transfected CaMKIIα-over-expressing cells. These results provide strong evidence for the inhibitory modulation of CART peptide in cocaine-induced locomotor sensitization. Cover Image for this issue: doi: 10.1111/jnc.14187.

Neurochemical evidence that cocaine- and amphetamine-regulated transcript (CART) 55-102 peptide modulates the dopaminergic reward system by decreasing the dopamine release in the mouse nucleus accumbens

CART (Cocaine- and Amphetamine-Regulated Transcript) peptide is a neurotransmitter naturally occurring in the CNS and found mostly in nucleus accumbens, ventrotegmental area, ventral pallidum, amygdalae and striatum, brain regions associated with drug addiction. In the nucleus accumbens, known for its significant role in motivation, pleasure, reward and reinforcement learning, CART peptide inhibits cocaine and amphetamine-induced dopamine-mediated increases in locomotor activity and behavior, suggesting a CART peptide interaction with the dopaminergic system. Thus in the present study, we examined the effect of CART (55-102) peptide on the basal, electrical field stimulation-evoked (EFS-evoked) (30V, 2Hz, 120 shocks) and returning basal dopamine (DA) release and on the release of the DA metabolites 3,4-dihydroxyphenyl acetaldehyde (DOPAL), 3,4-dihydroxyphenylacetic acid (DOPAC), homovanillic acid (HVA), 3,4-dihydroxyphenylethanol (DOPET), 3-methoxytyramine (3-MT) as well as on norepinephrine (NE) and dopamine-o-quinone (Daq) in isolated mouse nucleus accumbens, in a preparation, in which any CART peptide effects on the dendrites or soma of ventral tegmental projection neurons have been excluded. We further extended our study to assess the effect of CART (55-102) peptide on basal cocaine-induced release of dopamine and its metabolites DOPAL, DOPAC, HVA, DOPET and 3-MT as well as on NE and Daq. To analyze the amount of [³H]dopamine, dopamine metabolites, Daq and NE in the nucleus accumbens superfusate, a high-pressure liquid chromatography (HPLC), coupled with electrochemical, UV and radiochemical detections was used. CART (55-102) peptide, 0.1μM, added alone, exerted: (i) a significant decrease in the basal and EFS-evoked levels of extracellular dopamine (ii) a significant increase in the EFS-evoked and returning basal levels of the dopamine metabolites DOPAC and HVA, major products of dopamine degradation and (iii) a significant decrease in the returning basal levels of DOPET. At the same concentration, 0.1μM, CART (55-102) peptide did not have any effect on the release of noradrenaline. In the presence of CART (55-102) peptide, 0.1μM, the effect of cocaine, 30μM, on the basal dopamine release was inhibited and the effect on the basal DOPAC release substantially increased. To our knowledge, our findings are the first to show direct neurochemical evidence that CART (55-102) peptide plays a neuromodulatory role on the dopaminergic reward system by decreasing dopamine in the mouse nucleus accumbens and by attenuating cocaine-induced effects on dopamine release.

Decreased Caffeine-Induced Locomotor Activity via Microinjection of CART Peptide into the Nucleus Accumbens Is Linked to Inhibition of the pCaMKIIa-D3R Interaction

The purpose of this study was to characterize the inhibitory modulation of cocaine- and amphetamine-regulated transcript (CART) peptides, particularly with respect to the function of the D3 dopamine receptor (D3R), which is activated by its interaction with phosphorylated CaMKIIα (pCaMKIIα) in the nucleus accumbens (NAc). After repeated oral administration of caffeine (30 mg/kg) for five days, microinjection of CART peptide (0.08 μM/0.5 μl/hemisphere) into the NAc affected locomotor behavior. The pCaMKIIα-D3R interaction, D3R phosphorylation and cAMP/PKA/phosphorylated CREB (pCREB) signaling pathway activity were measured in NAc tissues, and Ca2+ influx and pCaMKIIα levels were measured in cultured NAc neurons. We found that CART attenuated the caffeine-mediated enhancement of depolarization-induced Ca2+ influx and CaMKIIα phosphorylation in cultured NAc neurons. Repeated microinjection of CART peptides into the NAc decreased the caffeine-induced enhancement of Ca2+ channels activity, pCaMKIIα levels, the pCaMKIIα-D3R interaction, D3R phosphorylation, cAMP levels, PKA activity and pCREB levels in the NAc. Furthermore, behavioral sensitization was observed in rats that received five-day administration of caffeine following microinjection of saline but not in rats that were treated with caffeine following microinjection of CART peptide. These results suggest that caffeine-induced CREB phosphorylation in the NAc was ameliorated by CART peptide due to its inhibition of D3R phosphorylation. These effects of CART peptides may play a compensatory role by inhibiting locomotor behavior in rats.

Nicotine regulates cocaine-amphetamine-Regulated Transcript (Cart) in the mesocorticolimbic system

Cocaine-and-Amphetamine Regulated Transcript (CART) mRNA and peptides are intensely expressed in the brain regions comprising mesocorticolimbic system. Studies suggest that CART peptides may have a role in the regulation of reward circuitry. The present study aimed to examine the effect of nicotine on CART expression in the mesocorticolimbic system. Three different doses of nicotine (0.2, 0.4, 0.6 mg/kg free base) were injected subcutaneously for 5 days, and on day 6, rats were decapitated following a challenge dose. CART mRNA and peptide levels in medial prefrontal cortex (mPFC), nucleus accumbens (NAc), dorsal striatum (DST), amygdala (AMG), lateral hypothalamic area (LHA), and ventral tegmental area (VTA) were measured by quantitative real-time PCR (qPCR) and Western Blot analysis, respectively. In the mPFC, 0.4 and 0.6 mg/kg nicotine, decreased CART peptide levels whereas there was no effect on CART mRNA levels. In the VTA, a down-regulation of CART peptide expression was observed with 0.2 and 0.6 mg/kg nicotine. Conversely, 0.4 and 0.6 mg/kg nicotine increased CART mRNA levels in the AMG without affecting the CART peptide expression. Nicotine did not regulate CART mRNA or CART peptide expression in the NAc, DST, and LHA. We conclude that nicotine regulates CART expression in the mesocorticolimbic system and this regulation may play an important role in nicotine reward. Synapse 70:283-292, 2016. © 2016 Wiley Periodicals, Inc.

Differential expression of CART in feeding and reward circuits in binge eating rat model

Binge eating (BE) disrupts feeding and subverts reward mechanism. Since cocaine- and amphetamine-regulated transcript peptide (CART) mediates satiety as well as reward, its role in BE justifies investigation. To induce BE, rats were provided restricted access to high fat sweet palatable diet (HFSPD) for a period of 4 weeks. Immunoreactivity profile of the CART elements, and accompanying neuroplastic changes were studied in satiety- and reward-regulating brain nuclei. Further, we investigated the effects of CART, CART-antibody or rimonabant on the intake of normal chow or HFSPD. Rats fed on HFSPD showed development of BE-like phenotype as reflected by significant consumption of HFSPD in short time frame, suggestive of dysregulated satiety mechanisms. At the mid-point during BE, CART-immunoreactivity was significantly increased in hypothalamic arcuate (ARC), lateral (LH), nucleus accumbens shell (AcbSh) and paraventricular nucleus of thalamus (PVT). However, for next 22-h post-binge time-period, the animals showed no interest in food, and low CART expression. Pre-binge treatment with rimonabant, a drug recommended for the treatment of BE, produced anorexia, increased CART expression in ARC and LH, but not in AcbSh and PVT. Higher dose of CART was required to produce anorexia in binged rats. While neuronal tracing studies confirmed CART fiber connectivity from ARC and LH to AcbSh, increase in CART and synaptophysin immunostaining in this pathway in BE rats suggested strengthening of the CART connectivity. We conclude that CART bearing ARC-LH-PVT-AcbSh reward circuit may override the satiety signaling in ARC-PVN pathway in BE rats.

Blood serum levels of CART peptide in patients with schizophrenia on clozapine monotherapy

CART (cocaine- and amphetamine-regulated transcript) is an endogenous inhibitor of food intake. We compared fasting serum CART levels in subjects with schizophrenia on clozapine monotherapy (n=24) with sex- and age-matched healthy controls (n=24). CART levels were higher in the clozapine group (262.76±359.91 vs. 90.40±169.90 pg/mL). CART levels were higher in subjects with metabolic syndrome compared to subjects without metabolic syndrome in the clozapine group (415.63±416.93 vs. 122.62±237.17 pg/mL, n=12 and 12, respectively) and in the whole study group (377.73±401.09 vs. 88.58±172.35 pg/mL, n=16 and 32, respectively). In the control group CART levels were higher in subjects with total body fat lower than the target maximum compared to subjects with total body fat below the target maximum (121.71±154.91 vs. 66.32±182.96 pg/mL, n=14 and 10, respectively). CART levels did not correlate with age, weight, BMI, abdominal, waist and hip circumferences, WHR, blood pressure, laboratory tests, clozapine dose, antipsychotic or clozapine treatment duration, body composition, and markers of insulin resistance in the study group. Further studies are required to confirm whether increased levels of circulating CART are compensatory in response to treatment-induced weight gain and abdominal obesity or a primary feature of schizophrenia.

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.

Investigation of melanocortin system gene variants in antipsychotic-induced weight gain

OBJECTIVES

The use of second-generation antipsychotic medications may result in substantial weight gain in a subset of schizophrenia patients. Distinct populations of neurons expressed in the hypothalamus, including the cocaine- and amphetamine-regulated transcript (CART), the polypeptide pro-opiomelanocortin (POMC) and the agouti-related protein (AGRP), have regulatory roles in weight control and energy homeostasis. Thus, we investigated the potential role of CART, POMC and AGRP genetic variants in antipsychotic-induced weight gain (AIWG).

METHODS

Five CART single nucleotide polymorphisms (SNPs) (rs10515115, rs3763153, rs3857384, rs11575893, rs16871471), three POMC SNPs (rs6713532, rs1047521, rs3754860) and one AGRP SNP (rs1338993), were genotyped in 218 patients treated with antipsychotics for chronic schizophrenia and evaluated for AIWG. We compared weight change (%) across genotypic groups using analysis of covariance.

RESULTS

None of the SNPs in POMC, CART, AGRP were significantly associated with AIWG in the refined samples stratified by ethnicity and medication treatment.

CONCLUSIONS

In this exploratory study, we observed that POMC, CART and AGRP gene variants are not a major contributor to AIWG. However larger samples are required to completely rule out their effect on AIWG.

The inhibition of cocaine-induced locomotor activity by CART 55-102 is lost after repeated cocaine administration

CART peptide is known for having an inhibitory effect on cocaine- and dopamine-mediated actions after acute administration of cocaine and dopamine. In this regard, it is postulated to be a homeostatic, regulatory factor on dopaminergic activity in the nucleus accumbens (NAc). However, there is no data on the effect of CART peptide after chronic administration of cocaine, and this study addresses this. It was found that CART peptide blunted cocaine-induced locomotion (LMA) after acute administration of cocaine, as expected, but it did not affect cocaine-mediated LMA after chronic administration of cocaine. The loss of CART peptide's inhibitory effect did not return for up to 9 weeks after stopping the repeated cocaine administration. It may not be surprising that homeostatic regulatory mechanisms in the NAc are lost after repeated cocaine administration, and that this may be a mechanism in the development of addiction.

Intra-accumbal administration of shRNAs against CART peptides cause increases in body weight and cocaine-induced locomotor activity in rats

In order to examine the effect of cocaine and amphetamine regulated transcript (CART) peptide depletion in adult rats, CART shRNAs or scrambled control shRNAs were administered bilaterally into the nucleus accumbens (NAc). There was an increase in body weight of the shRNA injected rats compared with the rats injected with the scrambled RNA. This is compatible with the data showing a role for the peptide in body weight and food intake. Also at this time, there was about a two-and-a-half fold increase in cocaine-mediated locomotion in the shRNA injected rats compared to the control rats. This finding is critical support for the hypothesis that endogenous CART peptides in the NAc inhibit the actions of cocaine and other psychostimulants. In immunohistochemical experiments on these same animals, there was a decrease in the staining density of CART peptide in the NAc of the shRNA injected rats. These data show that shRNA can reduce CART peptides in the NAc and that endogenous CART peptides influence body weight and cocaine-induced locomotor activity (LMA).

Atypical antipsychotic-induced weight gain: insights into mechanisms of action

Prescriptions for second-generation antipsychotics (SGAs) have surpassed those for first-generation agents in the treatment of schizophrenia and bipolar disorder. While SGAs have the benefit of a much reduced risk of causing movement disorders, they have been associated with weight gain and metabolic effects. These adverse reactions are not uncommon, and threaten to have a significant impact on the patient's health over the long-term treatment that the patient requires. Currently, the aetiology of these effects is not known. This article reviews the data exploring the weight gain phenomenon. The literature was reviewed from searches of PubMed and the references of major articles in the field. The SGAs present a heterogeneous risk for weight gain. In addition, different individuals receiving the same drug can exhibit substantially different weight changes. This pattern suggests that a group of factors are associated with the weight gain phenomenon rather than a single mechanism. Coupled with the genetic profile that the patient brings to the treatment, the risk for SGA-induced weight gain will be different for different drugs and different individuals. Targets for exploration of the weight gain phenomenon include receptor interactions involving serotonin, histamine, dopamine, adrenergic, cannabinoid and muscarinic receptors. The association of SGA-induced weight gain and the role of orexigenic and anorexigenic peptides are reviewed. Also, a brief discussion of genetic factors associated with SGA-induced weight gain is presented, including that of the serotonin 5-HT(2C) receptor gene (HTR2C) and the cannabinoid 1 receptor gene (CNR1). The most promising data associated with SGA-induced weight gain include investigations of the histamine H(1), 5-HT(2A), 5-HT(2C), muscarinic M(3) and adrenergic receptors. In addition, work in the genetic area promises to result in a better understanding of the variation in risk associated with different individuals.

Regulation of cocaine- and amphetamine-regulated transcript mRNA expression by calcium-mediated signaling in GH3 cells

Cocaine- and amphetamine-regulated-transcript (CART) peptides are associated with multiple physiological processes, including, feeding, body weight, and the response to drugs of abuse. CART mRNA and peptide levels and the expression of the CART gene appears to be under the control of a number of extra- and intra-cellular factors including the transcription factor, cAMP response element binding protein (CREB). Similar to the effects of CART, Ca(2+) signaling leads to the phosphorylation of CREB and has been associated with both feeding and the actions of psychostimulants; therefore, we hypothesized that Ca(2+) may play a role in CART gene regulation. We used real-time PCR (rtPCR) and GH3 cells to examine the effect of ionomycin, which increases intracellular Ca(2+), on CART mRNA levels. Ionomycin increased CART mRNA in a dose- and time-dependent manner. The effect of ionomycin appeared transient as CART mRNA had returned to control levels 3 h following treatment. Calmidazolium and KN93, inhibitors of calmodulin and Ca(2+)-modulated protein (CaM) kinases respectively, attenuated the effect of ionomycin (10 microM) on CART mRNA levels suggesting a calmodulin-dependent mechanism. Western immunoblotting indicated that ionomycin increased phosphorylated cAMP response element binding protein (pCREB) levels and electrophoretic mobility shift assay/supershift assay using antibodies against pCREB demonstrated increased levels of a CART oligo/pCREB protein complex. Finally, we showed that injection of ionomycin into the rat nucleus accumbens increases CART mRNA levels. To our knowledge, this is the first study providing evidence that the CART gene is, in part, regulated by Ca(2+)/CaM/CREB-dependent cell signaling.

CART peptides: regulators of body weight, reward and other functions

Over the past decade or so, CART (cocaine- and amphetamine-regulated transcript) peptides have emerged as major neurotransmitters and hormones. CART peptides are widely distributed in the CNS and are involved in regulating many processes, including food intake and the maintenance of body weight, reward and endocrine functions. Recent studies have produced a wealth of information about the location, regulation, processing and functions of CART peptides, but additional studies aimed at elucidating the physiological effects of the peptides and at characterizing the CART receptor(s) are needed to take advantage of possible therapeutic applications.

The once-daily human GLP-1 analog, liraglutide, reduces olanzapine-induced weight gain and glucose intolerance

Therapeutic use of atypical antipsychotic agents is often associated with weight gain and impaired glucose tolerance. The once-daily human GLP-1 analog liraglutide improves glycemic control and reduces body weight. We have investigated the ability of liraglutide to improve olanzapine-induced metabolic effects in female rats. Female Sprague-Dawley rats were implanted with subcutaneous osmotic mini pumps for delivery of olanzapine (1.75 mg/24 h) or vehicle for 28 days (n=20). After 14 days, ten animals from each group were given liraglutide (0.2 mg/kg) or vehicle twice daily for the remainder of the study. Compared to vehicle treated animals, olanzapine infusion for 4 weeks significantly increased end point cumulated food intake (667.3+/-7.0 versus 593.2+/-13.2g, p<0.01), body weight (306.6+/-4.2 versus 276.4+/-3.6 g, p<0.001), subcutaneous inguinal fat (3.4+/-0.3 versus 1.9+/-0.1 g, p<0.001), mesenteric fat (3.1+/-0.2 versus 1.7+/-0.2g, p<0.001), retroperitoneal fat (6.2+/-0.6 versus 2.8+/-0.3 g, p<0.001), and impaired glucose tolerance, measured as total area under the glucose curve during an oral glucose tolerance test (1906+/-66 versus 1770+/-28 mMxmin, p<0.05). These olanzapine-induced elevations were significantly reduced by liraglutide (cumulated food intake: 601.8+/-20.4 g, p<0.01; body weight: 280.2+/-5.6 g, p<0.001; subcutaneous inguinal fat: 2.4+/-0.2 g, p<0.001; mesenteric fat: 1.8+/-0.1 g, p<0.001; retroperitoneal fat: 3.5+/-0.4 g, p<0.001; AUC: 1764+/-32 mMxmin, p<0.05). In conclusion, subcutaneous olanzapine infusion in female rats leads to weight gain and metabolic changes of which several are reversed following liraglutide treatment. It may therefore be relevant to study these effects of liraglutide in patients treated with atypically antipsychotics.

Cocaine administration increases the fraction of CART cells in the rat nucleus accumbens that co-immunostain for c-Fos

In order to further test whether or not psychostimulant drugs activate CART peptide-containing cells in the nucleus accumbens, we examined the fraction of CART positive cells that co-immunostained for c-Fos after administration of saline or cocaine (10 and 25 mg/kg i.p.). There was about a 45% increase in the fraction of cells that stained for both CART and c-Fos after administration of cocaine, but there was no change in the fraction after administration of saline. Moreover, the increase was not found 24h after injection and is therefore reversible. These results support the notion that psychostimulant drugs activate CART cells in the nucleus accumbens, even under conditions where it is difficult to show a change in CART levels.

Injection of CART (cocaine- and amphetamine-regulated transcript) peptide into the nucleus accumbens reduces cocaine self-administration in rats

Cocaine- and amphetamine-regulated transcript (CART) peptides appear to modulate various effects of psychostimulant drugs. Injections of CART peptide into the nucleus accumbens (NAcc) inhibit locomotion produced by systemic injections of the psychostimulants cocaine and amphetamine. Intra-NAcc injections of CART peptide also inhibit locomotion produced by microinfusions of dopamine into the NAcc, suggesting that the effects of CART peptides may be due to an interaction with the dopaminergic system in the NAcc. We sought to determine if this inhibitory effect of CART peptide generalizes to other measures of dopaminergic function such as reward/reinforcement by testing the effect of bilateral intra-NAcc CART infusions (0, 0.25, 1.0 and 2.5 microg per side) on cocaine and food self-administration. One group of rats self-administered cocaine (0.75 mg/kg per 140 microl IV infusion) on a progressive ratio schedule. A separate group received 45 mg food pellets on the same progressive ratio schedule. Bilateral intra-NAcc injections of CART peptide dose-dependently decreased the number of cocaine infusions, the breakpoint of cocaine self-administration, and the total number of bar presses on the cocaine-associated lever. There were no effects of CART injections on the breakpoint for food reward. Thus, we conclude that injections of CART into the NAcc appear to functionally antagonize a major site of action for cocaine self-administration in rats.

CART peptides as modulators of dopamine and psychostimulants and interactions with the mesolimbic dopaminergic system

Cocaine- and amphetamine-regulated transcript (CART) peptides (CART 55-102 and CART 62-102) are peptidergic neurotransmitters that are widely but specifically distributed throughout the brain, gut and other parts of the body. They are found in many brain regions associated with drug addiction including the nucleus accumbens, ventral tegmental area and ventral pallidum. Injections of CART 55-102 into the nucleus accumbens have no effect on basal locomotor activity. However, an injection of CART just before an i.p. injection of cocaine reduces the locomotor activating effects of cocaine. These and other data suggest that CART in the accumbens blunts the effects of cocaine. A hypothesis is that CART is homeostatic in the accumbens and tends to oppose large increases in dopamine signaling. These actions would therefore be able to regulate the effects of some abused drugs such as the psychostimulants.

Colocalization of CART peptide with prodynorphin and dopamine D1 receptors in the rat nucleus accumbens

CART peptide is a peptidergic neurotransmitter that is expressed in brain regions involved in critical biological processes such as feeding and stress, and in areas associated with drug reward and abuse including the dopamine-rich nucleus accumbens (NAcc), which can be considered part of the basal ganglia. Because CART has been shown to colocalize with substance P, a marker of the basal ganglia direct pathway, we now test for colocalization with other markers of the direct pathway to determine if CART colocalizes with dynorphin and dopamine D1 receptors. In the NAcc, CART peptide immunoreactivity (IR) was colocalized with prodynorphin-IR in neurons. Approximately 80.1% of CART-IR cells colocalized with prodynorphin-IR, while only 27.6% of prodynorphin-IR neurons contained CART-IR, suggesting that CART cells are a subset of dynorphin cells. In contrast, only about 25% of CART-IR cell bodies demonstrated dopamine D1 receptor-IR. Because dynorphin and D1 receptors are markers for the basal ganglia direct pathway, from the NAcc to the basal ganglia output nuclei, and because CART significantly colocalizes with these markers, some CART neurons are part of the direct pathway or some comparable pathway in the accumbens. The presence of CART in NAcc neurons and the fact that NAcc projection neurons have extensive local collaterals suggest that CART may have effects in both terminal and cell body regions of the accumbens and may therefore affect information processing in the NAcc by modulating accumbal neurons.

CART peptide and the mesolimbic dopamine system

Over the past decade, CART peptide has been commonly associated with the rewarding and reinforcing properties of drugs of abuse and natural rewards such as food. The mesolimbic dopamine system is the predominant pathway involved in mediating reward and reinforcement. Many behavioral and neuroanatomical studies have been conducted in order to further elucidate the importance of CART-containing neurons within the mesolimbic dopamine system. This chapter will review the current knowledge of the localization, synaptic connectivity and neurochemical content of CART peptidecontaining neurons in nuclei of the mesolimbic reward pathway. These nuclei include the nucleus accumbens (NA), ventral midbrain, and the lateral hypothalamus (LH). In conclusion, an interconnected CART-containing loop between the NA, ventral midbrain and LH has evolved from these neuroanatomical studies that may have functional implications for CART peptide's involvement in reward and reinforcement.

The role of CART in the reward/reinforcing properties of psychostimulants

Cocaine- and amphetamine-regulated transcript (CART) peptides are putative neurotransmitters which appear to play a role in the rewarding and reinforcing effects of both natural (food) and unnatural (psychostimulants) stimuli. There is extensive anatomical, pharmacological, and behavioral evidence supporting the importance of CART peptides in psychostimulant, namely cocaine and amphetamine, abuse. For instance, CART mRNA and peptides are found in brain regions considered important in the reward and reinforcement of psychostimulants including the ventral tegmental area and the nucleus accumbens, which are part of the mesolimbic dopamine system. Consequently, in a pharmacological sense, CART peptides have been closely linked to the actions of mesolimbic dopamine. In addition, under certain conditions, psychostimulants alter CART mRNA and peptide levels. However, the exact conditions and mechanisms are unclear and may involve CART modulation by corticosterone and/or cyclic AMP response element binding protein (CREB). Finally, behavioral studies on CART and psychostimulants suggest a modulatory role for CART in the actions of psychostimulants as central administration of CART attenuates the behavioral effects of cocaine. This review discusses the anatomical, pharmacological, and behavioral evidence implicating a role for CART peptide in the rewarding and reinforcing properties of psychostimulants.

The CART (Cocaine- and Amphetamine-Regulated Transcript) System in Appetite and Drug Addiction

CART (cocaine- and amphetamine-regulated transcript) peptides are neuromodulators that are involved in feeding, drug reward, stress, cardiovascular function, and bone remodeling. CART peptides are abundant but discretely distributed in the brain, pituitary and adrenal glands, pancreas, and gut. High expression of CART in discrete hypothalamic nuclei associated with feeding has led to behavioral and pharmacological studies that strongly support an anorectic action of CART in feeding. Subsequent studies on humans and transgenic animals provide additional evidence that CART is important in the regulation of appetite as mutations in the CART gene are linked to eating disorders, including obesity and anorexia. The expression of CART in the mesolimbic dopamine circuit has lead to functional studies demonstrating CART's psychostimulant-like effects on locomotor activity and conditioned place preference in rats. These and other findings demonstrated that CART modulates mesolimbic dopamine systems and affects psychostimulant-induced reward and reinforcing behaviors. The link between CART and psychostimulants was substantiated by demonstrating alterations of the CART system in human cocaine addicts. CART seems to regulate the mesolimbic dopamine system, which serves as a common mechanism of action for both feeding and addiction. Indeed, recent studies that demonstrated CART projections from specific hypothalamic areas associated with feeding to specific mesolimbic areas linked to reward/motivation behaviors provide evidence that CART may be an important connection between food- and drug-related rewards. Given the enormous public health burden of both obesity and drug addiction, future studies exploring the pharmacotherapies targeting CART peptide represent an exciting and challenging research area.

Regulation of CART mRNA in the rat nucleus accumbens via D3 dopamine receptors

A variety of studies indicate that CART in the nucleus accumbens (NAcc) is involved in the action of psychostimulants. In order to understand in more detail if and how dopamine is involved in the regulation of CART mRNA in the NAcc, the present studies of individual receptors were performed. The D1 agonist, dihydrexidine, and the D1 antagonist, SCH23,390, were administered separately and in combination to adult male rats; however, no changes were found in CART mRNA as measured by in situ hybridization. The D2/3 agonist, quinpirole, was administered either separately or in combination with the D2 selective antagonist, L741,626, or the D3 selective antagonist, GR103,691. Quinpirole produced a decrease in CART mRNA of up to 43%. This effect was blocked by pretreatment with the D3 antagonist GR103, 691, but not by the D2 antagonist, L741,626. CART peptide levels showed a similar decrement after acute quinpirole. CART mRNA levels in the NAcc of D3 mutant mice were found to be higher than that in wild-type animals, but treating the mutants with quinpirole failed to produce a decrease in CART expression like that observed in wild-type rodents. These findings demonstrate that CART is regulated by dopamine in the NAcc, at least partly by D3 dopamine receptors.

Cocaine self-administration and locomotor sensitization are not altered in CART knockout mice

Cocaine- and amphetamine-regulated transcript (CART) is a neuropeptide found throughout the brain, particularly in the nucleus accumbens (NAcc) and hypothalamus. CART was initially discovered and named based on the upregulation of its mRNA in the striatum after acute cocaine or amphetamine injection in rats. CART is also known to participate in a wider range of physiological functions including feeding, anxiety, bone resorption, and insulin regulation. In this report, we demonstrate that knockout mice lacking a functional CART gene show similar cocaine-induced locomotor sensitization and cocaine self-administration to their wild type siblings. Intravenous cocaine self-administration did not differ between CART wild type and knockout mice during acquisition, during schedules of reinforcement that require higher response ratios, or across a range of doses. In conclusion, these data indicate that CART is not integral to the effects of psychostimulants in mice lacking CART throughout development, although it may play a regulatory role in the intact animal.

Ethanol enhancement of cocaine- and amphetamine-regulated transcript mRNA and peptide expression in the nucleus accumbens

Cocaine- and amphetamine-regulated transcript (CART) is a peptide neurotransmitter that has been implicated in drug reward and reinforcement. CART mRNA and peptide expression are highly concentrated in several compartments of the mesolimbic reward pathway. Several lines of evidence suggest that CART peptides may contribute to rewarding behaviors and the addiction liability of psychostimulants; however, there are no reports of basic work concerning CART in relation to alcohol and mechanisms of alcohol dependence development. Therefore, in this study we investigated the response of CART transcript and peptide to acute ethanol administration in vivo. Rats were administered ethanol (1 g/kg or 3.5 g/kg, 1 h, ip) and CART expression was measured by RT-PCR in the nucleus accumbens (NAcc). Ethanol (3.5 g/kg) increased CART transcription markedly. The interactions of dopamine on ethanol-induced CART expression were further evaluated pharmacologically using D1 and D2/D3 receptor antagonists. Both SCH 23390 (0.25 mg/kg) or raclopride (0.2 mg/kg) pre-treatment significantly suppressed ethanol-enhancement of CART mRNA transcription. Confocal immunofluorescence microscopy revealed that CART peptide immunoreactivity was also enhanced in both the core and the shell of the NAcc by ethanol administration. These findings demonstrate that CART mRNA and peptide expression are responsive to acute ethanol administrated in vivo and suggests that CART peptides may be important in regulating the rewarding and reinforcing properties of ethanol.

Cocaine-amphetamine-regulated transcript expression in the rat nucleus accumbens is regulated by adenylyl cyclase and the cyclic adenosine 5'-monophosphate/protein kinase a second messenger system

Cocaine-amphetamine-regulated transcript (CART), a neuropeptide involved in the brain's reward/reinforcement circuit, modulates the effects of psychostimulants, including cocaine. The CART gene has been characterized, and binding sites for multiple transcription factors have been identified within the promoter region, including the cAMP-response element, which serves as a binding site for cAMP-response element-binding protein (CREB). CART expression appears to be regulated via cAMP/protein kinase A (PKA)/CREB-mediated signaling in cell culture. Therefore, the goal of these studies was to examine the involvement of cAMP/PKA/CREB-mediated signaling in CART mRNA and peptide expression in vivo in the rat nucleus accumbens. Intra-accumbal injections of forskolin, an adenylyl cyclase activator, stimulated the phosphorylation of CREB and increased both CART mRNA and peptide levels, an effect attenuated by inhibition of PKA with H89 [N-(2-[p-bromocinnamylamino]ethyl)-5-isoquinoline-sulfonamide hydrochloride] and adenosine-3',5'-cyclic monophosphorothioate, Rp-isomer (Rp-cAMPS). In addition, Rp-cAMPS alone decreased CART mRNA compared with saline-injected controls, suggesting that CART expression may be tonically regulated by PKA. Under certain conditions, cocaine increases CART mRNA levels; thus, we examined the effects of cocaine on forskolin-induced CART mRNA expression in the rat nucleus accumbens. Cocaine plus forskolin significantly increased CART mRNA over either of the drugs administered independently, suggesting that under conditions of heightened cAMP signaling, cocaine may impact CART gene expression. These results suggest that CART expression in vivo in the rat nucleus accumbens is regulated by adenylyl cyclase and cAMP/PKA-mediating signaling and, likely, through the activation of CREB.

Colocalization of CART with substance P but not enkephalin in the rat nucleus accumbens

CART peptide is a novel neurotransmitter that, due to its distribution in the brain and its modulation of dopamine systems, may be involved in aspects of reward and drug abuse. In the nucleus accumbens (NAcc), CART peptide immunoreactivity (IR) is colocalized with substance P-IR in neurons. Approximately 86% of CART-IR cells colocalize with substance P, while only 19% of substance P-IR neurons contain CART. CART peptide does not colocalize with enkephalin-IR in this region. The substance P-CART colocalization exists in a rostro-caudal gradient with more colocalization in rostral regions. The presence of CART in substance P NAcc neurons suggests that CART neurons may be a subset of the basal ganglia direct pathway or that CART neurons are involved in limbic projections of the NAcc, such as to the ventral pallidum.

Cocaine- and amphetamine-regulated transcript peptides play a role in drug abuse and are potential therapeutic targets

Cocaine- and amphetamine-regulated transcript (CART) peptides (55 to 102 and 62 to 102) are neurotransmitters with important roles in a number of physiologic processes. They have a role in drug abuse by virtue of the fact that they are modulators of mesolimbic function. Key findings supporting a role in drug abuse are as follows. First, high densities of CART-containing nerve terminals are localized in mesolimbic areas. Second, CART 55 to 102 blunts some of the behavioral effects of cocaine and dopamine (DA). This functional antagonism suggests that CART peptides be considered as targets for medications development. Third, CREB in the nucleus accumbens has been shown to have an opposing effect on cocaine self-administration. CREB may activate CART expression in that region, and, if so, CART may mediate at least some of the effects of CREB. Fourth, in addition to the effects of CART on DA, DA can influence CART in the accumbens. Thus a complex interacting circuitry likely exists. Fifth, in humans, CART is altered in the ventral tegmental area of cocaine overdose victims, and a mutation in the CART gene associates with alcoholism. Overall, it is clear that there are functional interactions among CART, DA, and cocaine and that plausible cellular mechanisms exist to explain some of these actions. Future studies will clarify and extend these findings.

Antipsychotic-induced weight gain

Novel 'atypical' antipsychotic drugs represent a substantial improvement on older 'typical' drugs. However, clinical experience has shown that some, but not all, of these drugs can induce substantial weight gain. This interferes with compliance with drug taking and has expected effects on morbidity and mortality. In this review, we summarize current thinking on: (i) the extent to which different 'atypical' drugs induce weight gain; (ii) the possible roles of various neurotransmitters and neuropeptides in this adverse drug reaction; and (iii) the state of development of animal models in this area. We also outline major areas for future research.

Laparophobia: a cognitive perspective on appetite control in anorexia nervosa

Decades of research have demonstrated that anorexia nervosa (AN) may be associated with aberrant cognition, yet, its role in maintaining stringent dieting has received relatively little attention from mainstream researchers of eating disorders. The purpose of the present article is to highlight cognitive ('top-down') factors that are considered responsible for anticipatory anxiety of stoutness and frank fat-phobia (laparophobia). A cognitive model proposed departs from the formulation suggesting that phobia of over-eating is superimposed on avoidant tendencies ('environmental autonomy syndrome'), whereas excessive exercising becomes a natural coping strategy with laparophobia, an instrument of reward. AN ideation involves complex neuronal circuitries and multiple neurochemical components that may conceivably represent a mirror image of those underlying obesity. The emphasis on phobia and aberrant membrane excitability akin to channelopathies behoves the clinicians to be aware of potential uses of drugs acting at the gamma-aminobutyric acid and the N-methyl-D-aspartate/AMPA [2-amino-3-(3-hydroxy-5-methylisoxazol-4-yl) propionic acid] receptors sites as the adjuncts to conventional agents in managing AN.

The effects of cocaine on CART expression in the rat nucleus accumbens: A possible role for corticosterone

CART (Cocaine- and Amphetamine-Regulated Transcript) was initially described as an mRNA which had increased expression in the rat striatum following administration of acute cocaine or amphetamine but not saline. However, not all subsequent studies confirmed this. The present study aimed to repeat experiments with conflicting results and to reexamine and extend the original finding of acute regulation of nucleus accumbens CART mRNA by cocaine. Acute administration of cocaine failed to produce any change in levels of CART mRNA or peptide. Chronic administration of cocaine, as well as unilateral 6-hydroxydopamine lesions, also failed to alter CART mRNA levels in the accumbens. However, binge administration of cocaine, which also caused some seizures, did cause a significant increase in CART message. Given the involvement of corticosteroids with both stress and the effects of psychostimulants, we examined the possible effects of corticosteroids. We acutely administered ascending doses of corticosterone and found an increase in CART message. Similar effects were seen on CART peptides after acute corticosterone administration, and acute metyrapone administration was found to reduce CART peptide levels in the accumbens. This suggests that CART mRNA may be regulated by cocaine under certain conditions, such as binge administration, and this may at least partly involve corticosterone.

Analysis of sequence variability in the CART gene in relation to obesity in a Caucasian population

Background

Cocaine and amphetamine regulated transcript (CART) is an anorectic neuropeptide located principally in hypothalamus. CART has been shown to be involved in control of feeding behavior, but a direct relationship with obesity has not been established. The aim of this study was to evaluate the effect of polymorphisms within the CART gene with regards to a possible association with obesity in a Caucasian population.

Results

Screening of the entire gene as well as a 3.7 kb region of 5' upstream sequence revealed 31 SNPs and 3 rare variants ; 14 of which were subsequently genotyped in 292 French morbidly obese subjects and 368 controls. Haplotype analysis suggested an association with obesity which was found to be mainly due to SNP-3608T>C (rs7379701) (p = 0.009). Genotyping additional cases and controls also of European Caucasian origin supported further this possible association between the CART SNP -3608T>C T allele and obesity (global p-value = 0.0005). Functional studies also suggested that the SNP -3608T>C could modulate nuclear protein binding.

Conclusion

CART SNP -3608T>C may possibly contribute to the genetic risk for obesity in the Caucasian population. However confirmation of the importance of the role of the CART gene in energy homeostasis and obesity will require investigation and replication in further populations.