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

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.

Low cocaine- and amphetamine-regulated transcript (CART) peptide levels in human cerebrospinal fluid of major depressive disorder (MDD) patients

BACKGROUND

Cocaine- and amphetamine-regulated transcript (CART) peptide is a candidate neuropeptide as a biomarker for major depressive disorder (MDD) because of its effects on emotion and distribution covering brain areas involved in the pathophysiology of MDD symptoms. However, it is unknown whether CART peptide levels are altered in the cerebrospinal fluid (CSF) of patients with MDD patients and are correlated with MDD symptoms.

METHODS

Subjects were 24 patients with MDD and 25 healthy controls matched for age, gender and ethnicity (Japanese). We measured CSF CART levels by a commercially available immunoassay kit and analyzed the relationships of the levels with antidepressant dose and symptoms assessed with the 21 item Hamilton Depression Rating Scale (HAMD-21).

RESULTS

CSF CART levels were significantly decreased in the patients than in the controls (p < 0.05). In MDD patient group, the CART levels had a negative correlation with antidepressant dose (imipramine-equivalent dose) (ρ = -0.55, p < 0.01) and significantly decreased in antidepressant-treated group (AD-treated group) compared to controls (p < 0.05). CSF CART levels showed significant negative correlations with psychomotor retardation, somatic anxiety, and general somatic symptoms (all p < 0.05) and a positive correlation with obsessive and compulsive symptoms (p < 0.05).

LIMITATIONS

In our analysis, all classes of antidepressants were combined together and the effects of medication use in a longitudinal manner did not confirm.

CONCLUSIONS

We report for the first time that CSF CART peptide levels are reduced in patients with MDD compared with healthy controls. The CART levels showed negative correlations with antidepressant dose and some symptoms, supporting the possibility that CART peptide is involved in the development of depressive symptoms.

A New Insight into the Role of CART in Cocaine Reward: Involvement of CaMKII and Inhibitory G-Protein Coupled Receptor Signaling

Cocaine- and amphetamine-regulated transcript (CART) peptides are neuropeptides that are expressed in brain regions associated with reward, such as the nucleus accumbens (NAc), and play a role in cocaine reward. Injection of CART into the NAc can inhibit the behavioral effects of cocaine, and injecting CART into the ventral tegmental area (VTA) reduces cocaine-seeking behavior. However, the exact mechanism of these effects is not clear. Recent research has demonstrated that Ca²⁺/calmodulin-dependent protein kinase II (CaMKII) and inhibitory G-protein coupled receptor (GPCR) signaling are involved in the mechanism of the effect of CART on cocaine reward. Hence, we review the role of CaMKII and inhibitory GPCR signaling in the effect of CART on cocaine reward and provide a new insight into the mechanism of that effect. In this article, we will first review the biological function of CART and discuss the role of CART in cocaine reward. Then, we will focus on the role of CaMKII and inhibitory GPCR signaling in cocaine reward. Furthermore, we will discuss how CaMKII and inhibitory GPCR signaling are involved in the mechanistic action of CART in cocaine reward. Finally, we will provide our opinions regarding the future directions of research on the role of CaMKII and inhibitory GPCR signaling in the effect of CART on cocaine reward.

Evaluation of CART peptide level in rat plasma and CSF: Possible role as a biomarker in opioid addiction

It has been shown previously that cocaine- and amphetamine-regulated transcript (CART) peptide has a modulatory role and homeostatic regulatory effect in motivation to and reward of the drugs of abuse specially psychostimulants. Recent data also showed that in addition to psychostimulants, CART is critically involved in the different stages of opioid addiction. Here we have evaluated the fluctuations in the level of CART peptide in plasma and CSF in different phases of opioid addiction to find out whether CART can serve as a suitable marker in opioid addiction studies. Male rats were randomly distributed in groups of control, acute low-dose (10mg/kg) morphine, acute high-dose morphine (80mg/kg), chronic escalating doses of morphine, withdrawal syndrome precipitated by administration of naloxone (1mg/kg), and abstinent after long-term drug-free maintenance of addicted animals. The level of CART peptide in CSF and plasma samples was measured by enzyme immunoassay. CART peptide concentration in the CSF and plasma was significantly elevated in acute high-dose morphine and withdrawal state animals and down-regulated in addicted rats. In abstinent group, CART peptide level was up-regulated in plasma but not in CSF samples. As the observed results are in agreement with data regarding the CART mRNA and protein expression in the brain reward pathway in opioid addiction phases, it may be suggested that evaluation of CART peptide level in CSF or plasma could be a suitable marker which reflects the rises and falls of the peptide concentration in brain in the development of opioid addiction.

CART peptide and opioid addiction: Expression changes in male rat brain

Previous studies have shown the prominence of cocaine- and amphetamine-regulated transcript (CART) peptide in rewarding and reinforcing effects of drugs of abuse specially psychostimulants. The data regarding the effects of different stages of opioid addiction on CART expression and the interconnection between CART and opioids are not much available. Here we have studied the changes in the expression level of CART mRNA and protein in various parts of the brain reward pathway in different stages of opioid addiction. Groups of male rats received acute low-dose (10mg/kg), acute high-dose (80mg/kg) and chronic escalating doses of morphine. In addition, withdrawal and abstinence states were evaluated after injection of naloxone (1mg/kg) and long-term maintenance of addicted animals, respectively. Expression of CART mRNA in the brain was measured by real-time PCR method. Western blotting was used to quantify the protein level. CART mRNA and protein were both up-regulated in high-dose morphine-administered animals and also in the withdrawal group in the nucleus accumbens (NAc), striatum and prefrontal cortex (PFC). In the addicted group, CART mRNA and protein were both down-regulated in NAc and striatum. In the abstinent group, CART mRNA was down-regulated in NAc. In the hippocampus, the only observed change was the up-regulation of CART mRNA in the withdrawal group. We suggest that the modulatory role of CART peptide in rewarding and reinforcing effects of opioids weakens when opioids are used for a long time and is stimulated when acute stress such as naloxone-induced withdrawal syndrome or acute high-dose administration of morphine occurs to the animal.

Microinjection of cocaine- and amphetamine-regulated transcript 55-102 peptide into the nucleus accumbens could modulate anxiety-related behavior in rats

Cocaine- and amphetamine-regulated transcript (CART) peptide is abundantly expressed in the nucleus accumbens (NAcc) and is involved in stress, anxiety and reward responses. To examine the role of CART peptide in anxiety-related behavior, naïve rats were bilaterally injected with CART 55-102 peptide (0.5, 1.0 or 2.5 µg/0.5 µl/side) or vehicle into the NAcc. Following this, their anxiety-related behavior was assessed using the elevated plus maze and the open field tests with a one-week interval between the tests. There was no difference in the time spent in open arms, or number of entries into open arms on the elevated plus maze in the CART-treated animals at any dose, when compared with the vehicle-treated group. However, there was a significant increase in the time spent in the center of the open field with administration of the low dose of CART peptide (0.5 µg/0.5 µl/side), although this effect disappeared at the high dose (2.5 µg/0.5 µl/side). None of the doses of CART peptide altered total locomotion in these tests. To further determine the possible anxiety-modulating effect of CART peptide at low dosages, the light and dark test was performed. Additional groups of rats given doses of 0.01 µg/0.5 µl/side or 0.5 µg/0.5 µl/side of CART peptide showed increased exploration time in the light side. These results suggest that accumbal-CART peptide reduces anxiety-like behavior in a dose-dependent manner.

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.

Cocaine-and-Amphetamine Regulated Transcript (CART) peptide attenuates dopamine- and cocaine-mediated locomotor activity in both male and female rats: lack of sex differences

Cocaine-and-Amphetamine Regulated Transcript peptide (CART peptide) is known for having an inhibitory effect on dopamine (DA)- and cocaine-mediated actions and is postulated to be a homeostatic, regulatory factor in the nucleus accumbens (NAc). Some sex differences in cocaine-mediated locomotor activity (LMA) and in the expression and function of CART peptide have been reported. However, it is not known if the inhibitory effect of CART peptide on cocaine-mediated LMA is sexually dimorphic. In this study, the effects of CART 55-102 on LMA due to intra-NAc DA and i.p. cocaine were determined in male and female Sprague-Dawley rats. The results show that CART 55-102 blunted or reduced both the DA- and cocaine-induced LMA in both males and females. In conclusion, CART peptide is effective in blunting DA- and cocaine-mediated LMA in both males and females.

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.

The manifestation of cocaine-induced midline destructive lesion in bone tissue and its identification in human skeletal remains

Cocaine-induced midline destructive lesion (CIMDL) is a condition that may arise in response to chronic insufflation ("snorting") of cocaine. It is clinically diagnosed when the nasal septum, lateral nasal walls, and/or hard palate show signs of destruction in association with cocaine use. Although its true incidence is unknown, CIMDL is not an uncommon clinical finding amongst intranasal cocaine abusers and is likely to be encountered by forensic anthropologists and medical examiners working worldwide. Given the preponderance of drug abusers amongst the subjects of forensic casework, the ability to diagnose CIMDL in dry bone may provide crucial insight into an investigation and even help confirm an individual identification. This paper aims to make practicing forensic anthropologists aware of CIMDL. Through the analysis of existing clinical literature, patient CT scans, and histology sections, it works toward the establishment of formal diagnostic criteria for identifying CIMDL in human skeletal remains. Lytic destruction regularly involves the vomer and frequently extends to the perpendicular plate of the ethmoid, the palatal process of the maxillae or the palatine bones, and the inferior nasal conchae. The middle nasal conchae, medial walls of the maxillary sinuses, ethmoid sinuses, and cribriform plate are often damaged. Destruction may also implicate the superior nasal conchae, the orbit, and the sphenoid. Bones affected by CIMDL may contain necrotic lesions or may be absent entirely. Lesions show minimal, if any, signs of repair. The author proposes that this lack of new bone formation may be mediated by potentially elevated leptin levels in cocaine abusers and CIMDL patients and may be the key to differentiating CIMDL from other lytic processes of the midface.

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).

Estradiol acts via estrogen receptors alpha and beta on pathways important for synaptic plasticity in the mouse hippocampal formation

Estradiol affects hippocampal-dependent spatial memory and underlying structural and electrical synaptic plasticity in female mice and rats. Using estrogen receptor (ER) alpha and beta knockout mice and wild-type littermates, we investigated the role of ERs in estradiol effects on multiple pathways important for hippocampal plasticity and learning. Six hours of estradiol administration increased immunoreactivity for phosphorylated Akt throughout the hippocampal formation, whereas 48 h of estradiol increased immunoreactivity for phosphorylated TrkB receptor. Estradiol effects on phosphorylated Akt and TrkB immunoreactivities were abolished in ER alpha and ER beta knockout mice. Estradiol also had distinct effects on immunoreactivity for post-synaptic density 95 (PSD-95) and brain derived-neurotrophic factor (BDNF) mRNA in ER alpha and beta knockout mice. Thus, estradiol acts through both ERs alpha and beta in several subregions of the hippocampal formation. The different effects of estradiol at 6 and 48 h indicate that several mechanisms of estrogen receptor signaling contribute to this female hormone's influence on hippocampal synaptic plasticity. By further delineating these mechanisms, we will better understand and predict the effects of endogenous and exogenous ovarian steroids on mood, cognition, and other hippocampal-dependent behaviors.

CART peptide following social novelty in the prairie vole (Microtus ochrogaster)

Prairie voles (Microtus ochrogaster) are monogamous rodents that display high levels of affiliative behaviors, including pair-bonding, biparental care, and cooperative breeding. Species differences in basal cocaine- and amphetamine-regulated transcript (CART) mRNA and peptide expression have been found between prairie voles and polygamous meadow voles. Therefore, we hypothesized that the CART system may play a role in the regulation of social behavior in this species. Male and female adult prairie voles were placed in a cage either alone, or with a novel social partner of the same or opposite sex. After 45 min, subjects were sacrificed and CART peptide expression was examined using immunohistochemistry. We examined fifteen hypothalamic, limbic, and hindbrain regions of interest, focusing on areas that show species-specific patterns of expression. We found that subjects paired with a novel conspecific had lower levels of peptide in the bed nucleus of the stria terminalis (BNST) than isolated animals. This may reflect increased peptide release following increased dopaminergic activity in animals exposed to a novel conspecific. Additionally, CART peptide was higher in the nucleus accumbens (NAc) of subjects paired with an opposite sex partner compared to those paired with a same-sex conspecific, although there was no difference between isolated subjects and either socially housed group. These findings suggest that CART in the NAc is differentially responsive to the sex of adult conspecifics and that the social environment influences CART expression in the prairie vole in a region- and stimulus-specific manner.

CART peptide inhibits locomotor activity induced by simultaneous stimulation of D1 and D2 receptors, but not by stimulation of individual dopamine receptors

CART (Cocaine- and amphetamine-regulated transcript) peptide has been implicated in playing a modulatory role in reward and reinforcement. Previously, our laboratory demonstrated that injections of CART peptide (CART 55-102) into the nucleus accumbens (NAc) attenuated both cocaine- and dopamine-induced increases in locomotor activity (LMA), and attenuated cocaine reward as well. In this study, the effects of CART peptide on LMA induced by dopamine receptor agonists were evaluated after intraaccumbal injections in male, Sprague-Dawley rats. Effects of the D1 receptor agonist SKF-81,297, saline, CART 55-102, or CART 55-102 and SKF-81,297 together were compared. The SKF-81,297-induced increase in LMA was potentiated by coadministration of CART, while injection of CART alone had no significant effect. Injection of the D2 agonist 7-OH-DPAT had no effect on LMA, and the combination of both 7-OH-DPAT and CART peptide also had no effect. Quinelorane, a D3 receptor agonist, did not alter LMA, nor did the combination of CART peptide and quinelorane. The next experiment examined the effects of CART peptide on LMA induced by coinjection of both the D1 agonist SKF-81,297 and the D2 agonist 7-OH-DPAT. The combination of SKF-81,297 and 7-OH-DPAT induced greater LMA than SKF-81,297 alone. Coadministration of CART peptide along with the D1 and D2 agonists reduced LMA. These results strongly suggest that CART peptide reduces the effects of psychostimulants by modulating the simultaneous activation of both D1 and D2 dopamine receptors rather than by affecting the action of any individual dopamine receptor.

Chromatin immunoprecipitation assays revealed CREB and serine 133 phospho-CREB binding to the CART gene proximal promoter

Both over expression of cyclic AMP response element binding protein (CREB) in the nucleus accumbens (NAc), and intra-accumbal injection of cocaine- and amphetamine-regulated transcript (CART) peptides, have been shown to decrease cocaine reward. Also, over expression of CREB in the rat NAc increased CART mRNA and peptide levels, but it is not known if this was due to a direct action of P-CREB on the CART gene promoter. The goal of this study was to test if CREB and P-CREB bound directly to the CRE site in the CART promoter, using chromatin immunoprecipitation (ChIP) assays. ChIP assay with anti-CREB antibodies showed an enrichment of the CART promoter fragment containing the CRE region over IgG precipitated material, a non-specific control. Forskolin, which was known to increase CART mRNA levels in GH3 cells, was utilized to show that the drug increased levels of P-CREB protein and P-CREB binding to the CART promoter CRE-containing region. A region of the c-Fos promoter containing a CRE cis-regulatory element was previously shown to bind P-CREB, and it was used here as a positive control. These data suggest that the effects of CREB over expression on blunting cocaine reward could be, at least in part, attributed to the increased expression of the CART gene by direct interaction of P-CREB with the CART promoter CRE site, rather than by some indirect action.

BDNF variant Val66Met interacts with estrous cycle in the control of hippocampal function

Natural fluctuations in circulating estradiol are associated with behavioral changes, including severe disturbances in mood and cognition in some women. Common genetic variation in some of the molecular mediators of estradiol effects on these behaviors, in brain regions such as the hippocampus, may explain individual variation in estradiol effects on behavior. We tested whether the common human variant BDNF Val66Met interacts with estradiol in the control of hippocampal function in cycling female mice homozygous for the wild-type Val or BDNF Met variant. BDNF Met increased anxiety behavior, impaired memory, and increased expression of BDNF and its receptor TrkB in the hippocampal formation. BDNF Met also dramatically altered the fluctuation of spatial memory, hippocampal Akt phosphorylation, and PSD-95 protein expression across the estrous cycle. The variant BDNF Val66Met should therefore be considered as a strong candidate for mediating genetic differences in ovarian steroid-related behavioral changes and disorders.

Measuring levels of proteins by various technologies: can we learn more by measuring turnover?

In routine experiments, scientists measure the levels of various substances such as proteins after various treatments. Detection of a change in levels suggests an impact of treatment on that particular protein. However, we sometimes forget the importance of turnover in this process. Proteins have half-lives that may change in response to treatments (which is in fact why levels may change), and an examination of half-lives may yield better clues as to how treatment affects the protein. After an exploration of the quantitative aspects of protein turnover, several interesting conclusions may be drawn. (1) Even though levels of some proteins may NOT change after treatments, their half-lives and turnovers do change, and these may be more sensitive indicators of the impact of treatments on the proteins of interest. (2) Treatments can affect protein levels because they alter either the synthesis or degradation of the protein or both. But, the rate of change of the levels depends on the half-life of the protein. If the experimenter waits only a fraction of a half-life of the protein after treatment, no significant change in level may be found since it can take up to 5 half-lives for the protein level to adjust to about 97% of its new level after treatment. (3) Half-lives of the same protein can vary in different species and experimental conditions may have to be altered if using different species. These factors suggest that a consideration of protein turnover and half-lives will be useful for future studies of this type.

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.

Transient up-regulation of cocaine- and amphetamine-regulated transcript peptide (CART) immunoreactivity following ethanol withdrawal in rat hypothalamus

We investigated the profile of CART immunoreactivity in some discrete hypothalamic nuclei following chronic ethanol treatment and withdrawal conditions. Adult, male, Sprague-Dawley rats were fed with liquid diet (pair-fed) or liquid diet containing ethanol (ethanol-fed) for 15 days. Thereafter, all the animals were given access to ethanol free nutritionally balanced liquid diet and killed at 0, 24, 48 and 72 h post-withdrawal, and their brains processed for immunocytochemistry using monoclonal antibodies against CART. CART-immunoreactive fibers, but not the cells, were significantly increased in the paraventricular nucleus (PVN). However, the profile of CART-immunoreactive cells and/or fibers in the periventricular area (PeA), arcuate nucleus (ARC), perifornical area inclusive of lateral hypothalamus (LH) and tuber cinereum (TC), dorsomedial (DMH), and ventromedial (VMH) hypothalamus at the 0 h ethanol withdrawal time point was quite similar to that in the pair-fed control rats. Twenty-four hours following ethanol withdrawal, the immunoreactivity in all these areas was dramatically increased. While significant reduction in CART immunoreactivity was noticed in the PVN, PeA, ARC and VMH at 48 h, immunoreactive profile was restored to normal by 72 h post-ethanol withdrawal. The immunoreactive profile in the LH, TC and DMH resembled that of the pair-fed groups at 48 and 72 h post-withdrawal intervals. However, CART-immunoreactive profile in the supraoptic nucleus did not respond to the chronic ethanol treatment and/or withdrawal. We suggest that transient up-regulation of CART in some discrete hypothalamic nuclei following ethanol withdrawal, at least in part, may contribute to the pathogenesis of ethanol withdrawal-induced symptoms like anxiety and anorexia.

Persistent alterations in mesolimbic gene expression with abstinence from cocaine self-administration

Cocaine-responsive gene expression changes have been described after either no drug abstinence or short periods of abstinence. Little data exist on the persistence of these changes after long-term abstinence. Previously, we reported that after discrete-trial cocaine self-administration and 10 days of forced abstinence, incubation of cocaine reinforcement was observable by a progressive ratio schedule. The present study used rat discrete-trial cocaine self-administration and long-term forced abstinence to examine extinction responding, mRNA abundance of known cocaine-responsive genes, and chromatin remodeling. At 30 and 100 days of abstinence, extinction responding increased compared to 3-day abstinent rats. Decreases in both medial prefrontal cortex (mPFC) and nucleus accumbens c-fos, Nr4a1, Arc, and EGR1 mRNA were observed, and in most cases persisted, for 100 days of abstinence. The signaling peptides CART and neuropeptide Y (NPY) transiently increased in the mPFC, but returned to baseline levels following 10 days of abstinence. To investigate a potential regulatory mechanism for these persistent mRNA changes, levels of histone H3 acetylation at promoters for genes with altered mRNA expression were examined. In the mPFC, histone H3 acetylation decreased after 1 and 10 days of abstinence at the promoter for EGR1. H3 acetylation increased for NPY after 1 day of abstinence and returned to control levels by 10 days of abstinence. Behaviorally, these results demonstrate incubation after discrete-trial cocaine self-administration and prolonged forced abstinence. This incubation is accompanied by changes in gene expression that persist long after cessation of drug administration and may be regulated by chromatin remodeling.

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.

Genetic variants in the cocaine- and amphetamine-regulated transcript gene (CARTPT) and cocaine dependence

Dopaminergic brain systems have been implicated to play a major role in drug reward, thus making genes involved in these circuits plausible candidates for susceptibility to substance use disorders. The cocaine- and amphetamine-regulated transcript peptide (CARTPT) is involved in reward and feeding behavior and has functional characteristics of an endogenous psychostimulant. In this study we tested the hypothesis that variation in the CARTPT gene increases susceptibility to cocaine dependence in individuals of African descent. Genotypes of three HapMap tagging SNPs (rs6894758; rs11575893; rs17358300) across the CARTPT gene region were obtained in cocaine dependent individuals (n=348) and normal controls (n=256). All subjects were of African descent. There were no significant differences in allele, genotype or haplotype frequencies between cases and controls for any of the tested SNPs. Our results do not support an association of the CARTPT gene with cocaine dependence; however, additional studies using larger samples, comprehensive SNP coverage, and different populations are necessary to conclusively rule out CARTPT as a contributing factor in the etiology of cocaine dependence.

Chronic social stress, hedonism and vulnerability to obesity: lessons from rodents

Obesity is a current health pandemia. Determinants of this pathology are rather complex and include genetic, developmental and environmental factors only partially disclosed. Stress related neuroendocrine dysregulation and overconsumption of high palatable high caloric food and are likely to contribute to this modern health threats. Despite the evidence that psychosocial stress is one of the main sources of stress in humans and may play an important role in the development of the stress disorders, including obesity and metabolic syndrome, animal models focusing on the relationship between chronic stress and energy homeostasis are scattered and most of them encompasses physical rather than psychosocial stress. Aim of the present paper is to review rodent studies on the effect of psychosocial stress throughout life on body weight and food intake regulation. In the second part of the review special focus will be given on the mechanisms linking stress and the reward system.

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.

Genetic regulation of hypothalamic cocaine and amphetamine-regulated transcript (CART) in BxD inbred mice

Cocaine and Amphetamine-Regulated Transcript (CART) peptides are implicated in a wide range of behaviors including in the reinforcing properties of psychostimulants, feeding and energy balance and stress and anxiety responses. We conducted a complex trait analysis to examine natural variation in the regulation of CART transcript abundance (CARTta) in the hypothalamus. CART transcript abundance was measured in total hypothalamic RNA from 26 BxD recombinant inbred (RI) mouse strains and in the C57BL/6 (B6) and DBA/2J (D2) progenitor strains. The strain distribution pattern for CARTta was continuous across the RI panel, which is consistent with this being a quantitative trait. Marker regression and interval mapping revealed significant quantitative trait loci (QTL) on mouse chromosome 4 (around 58.2 cM) and chromosome 11 (between 20-36 cM) that influence CARTta and account for 31% of the between strain variance in this phenotype. There are numerous candidate genes and QTL in these chromosomal regions that may indicate shared genetic regulation between CART expression and other neurobiological processes referable to known actions of this neuropeptide.

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.

Regulation of CART mRNA by stress and corticosteroids in the hippocampus and amygdala

CART (Cocaine-Amphetamine-Regulated Transcript) has been shown to be regulated by corticosteroids in the hypothalamus, but its regulation by corticosteroids and stress has not been well examined in the hippocampus or the amygdala. Further, CART has been implicated in the transition to puberty. In this study we examine the effects of acute (30 min) stress on CART mRNA in prepubescent and adult rats. In addition, we examined chronic (21 day x 6 h) restraint stress upon the expression of CART mRNA in the hippocampus and the amygdala and the effects of 7 days of adrenalectomy and corticosteroid replacement upon CART expression in these regions of the adult rat brain. We found an up-regulation of CART mRNA in the central amygdala induced by acute but not chronic stress and an up-regulation in the dentate gyrus induced by chronic but not acute stress. Adrenalectomy reduced CART expression in the dentate gyrus but not the amygdala and this effect was blocked by corticosterone but not RU28,362 or aldosterone replacement, suggesting a synergism of mineralocorticoid and glucocorticoid receptors. Our data establish that CART expression is regulated by stress in a regionally and time specific manner and that CART is regulated by corticosteroid actions in the hippocampus.

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.

Cocaine- and amphetamine related transcript (CART) and anxiety

CART is a neuropeptide that appears to play an important role in a variety of physiological processes. The major research focus into the function of CART peptide has been on feeding behavior, modulation of mesolimbic dopamine, and actions of psychostimulant drugs. The neuroanatomic expression profile of CART does however suggest other functions as well, and its presence within the limbic system points to a possible role in emotionality. There are now several published reports which describe a new role for CART as a mediator of anxiety-like behaviors in rodents. This review will summarize these findings and speculate on the mechanisms by which CART might be involved in the modulation of these behaviors. We will also consider what future studies need to be done to further clarify the role of this peptide in anxiety.

The role of CART in body weight homeostasis

Cocaine-amphetamine regulated transcript (CART) was first identified as a complete mRNA transcript 10 years ago. Since then it has been demonstrated that CART is a peptide neurotransmitter which has a role in a number of physiological processes, including body weight homeostasis and energy balance, in a number of vertebrate species. Research to date has demonstrated a role for CART in the control of food intake at a number of levels within the brain of both animals and man.

Cocaine- and amphetamine-regulated transcript peptide and sympatho-adrenal axis

Cocaine- and amphetamine-regulated transcript peptide (CART) is constitutively expressed in discrete regions of the mammalian central and peripheral nervous system. Immunohistochemical studies reveal a well-defined network of CART-immunoreactive (irCART) neurons organized along the sympatho-adrenal axis. Sympathetic preganglionic neurons, but not parasympathetic preganglionic neurons, in the lateral horn area are CART-positive; which in turn innervate postganglionic neurons in the paravertebral and prevertebral sympathetic ganglia as well as the adrenal medulla. A population of chromaffin cells in the adrenal medulla is CART-positive; whereas, postganglionic neurons are not. Sympathetic preganglionic neurons themselves are contacted by irCART cell processes arising from neurons in the arcuate nucleus, the retrochiasmatic nucleus and the rostral ventrolateral medulla. Results from several recent studies suggest CART directly excites neurons along the sympathetic neural axis or indirectly by potentiating the action of glutamate on NMDA receptors, as evidenced by an elevation of blood pressure and heart rate following intracerebroventricular, intracisternal or intrathecal administration of the peptide to anesthetized rats or conscious rabbits.

Cocaine and amphetamine regulated transcript (CART) and the stress response

CART is expressed abundantly in the hypothalamic paraventricular nucleus and locus coeruleus, major corticotropin releasing factor (CRF) and noradrenaline sources, respectively. There is a bidirectional relation between CART and hypothalamo-pituitary-adrenal axis activity. CART stimulates CRF, adrenocorticotropic hormone and glucocorticoid secretion, whereas CRF and glucocorticoids increase the transcriptional activity of the CART gene; adrenalectomy declines CART expression in the hypothalamus. Stress exposure modulates CART expression in hypothalamus and amygdala in rat brain in a region and sex specific manner. CART may be a mediator peptide in the interaction between stress, drug abuse, and feeding. The review discusses the established role of CART as it relates to the stress response.

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 gene: structure and regulation

CART peptides are important neuropeptides that are involved in a variety of physiologic processes. The regulation of the CART gene is critical since peptides are regulated and secreted in response to specific stimuli. CART mRNA must also be controlled in order to respond to specific stimuli such as psychostimulant drugs and leptin. The regulation of the CART gene is central to maintaining homeostasis of peptide production. The 5' upstream region of the CART gene contains powerful regulatory elements that must be involved in transcriptional regulation via different signaling pathways. This review touches on several aspects related to CART gene regulation such as: (i) CART genomic structure, (ii) stimuli that alter CART mRNA levels, (iii) promoter characterization, (iv) role of the cAMP/PKA/CREB signal transduction pathway, and (v) role of the CART 5' and 3' ends in CART mRNA regulation. The goal of this review is to present current data so as to encourage further work in the field of CART gene regulation.

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.

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.