Fos but not Cart (cocaine and amphetamine regulated transcript) is overexpressed by several drugs of abuse: a comparative study using real-time quantitative polymerase chain reaction in rat brain

Direct measurement of neuronal ensemble activity using photoacoustic imaging in the stimulated Fos-LacZ transgenic rat brain: A proof-of-principle study

Measuring neuroactivity underlying complex behaviors facilitates understanding the microcircuitry that supports these behaviors. We have developed a functional and molecular photoacoustic tomography (F/M-PAT) system which allows direct imaging of Fos-expressing neuronal ensembles in Fos-LacZ transgenic rats with a large field-of-view and high spatial resolution. F/M-PAT measures the beta-galactosidase catalyzed enzymatic product of exogenous chromophore X-gal within ensemble neurons. We used an ex vivo imaging method in the Wistar Fos-LacZ transgenic rat, to detect neuronal ensembles in medial prefrontal cortex (mPFC) following cocaine administration or a shock-tone paired stimulus. Robust and selective F/M-PAT signal was detected in mPFC neurons after both conditions (compare to naive controls) demonstrating successful and direct detection of Fos-expressing neuronal ensembles using this approach. The results of this study indicate that F/M-PAT can be used in conjunction with Fos-LacZ rats to monitor neuronal ensembles that underlie a range of behavioral processes, such as fear learning or addiction.

Disease-associated polymorphisms within the conserved ECR1 enhancer differentially regulate the tissue-specific activity of the cannabinoid-1 receptor gene promoter; implications for cannabinoid pharmacogenetics

Cannabinoid receptor‐1 (CB1) represents a potential drug target against conditions that include obesity and substance abuse. However, drug trials targeting CB1 (encoded by the CNR1 gene) have been compromised by differences in patient response. Toward addressing the hypothesis that genetic changes within the regulatory regions controlling CNR1 expression contribute to these differences, we characterized the effects of disease‐associated allelic variation within a conserved regulatory sequence (ECR1) in CNR1 intron 2 that had previously been shown to modulate cannabinoid response, alcohol intake, and anxiety‐like behavior. We used primary cell analysis of reporters carrying different allelic variants of the human ECR1 and found that human‐specific C‐allele variants of ECR1 (ECR1(C)) drove higher levels of CNR1prom activity in primary hippocampal cells than did the ancestral T‐allele and demonstrated a differential response to CB1 agonism. We further demonstrate a role for the AP‐1 transcription factor in driving higher ECR1(C) activity and evidence that the ancestral t‐allele variant of ECR1 interacted with higher affinity with the insulator binding factor CTCF. The cell‐specific approaches used in our study represent an important step in gaining a mechanistic understanding of the roles of noncoding polymorphic variation in disease and in the increasingly important field of cannabinoid pharmacogenetics.

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.

Cocaine inhibits leptin-induced increase of the cocaine- and amphetamine-regulated transcript peptide in the nucleus accumbens in rats

Two well-known appetite-regulatory peptides, leptin and cocaine- and amphetamine-regulated transcript (CART), are known to be involved in the brain rewarding pathway. However, it is not yet known how they interact in the nucleus accumbens, an important region mediating the rewarding effects of drugs of abuse. Using the immunoassay method, we found that a microinjection of leptin into the nucleus accumbens core induces an immediate and transient increase of the CART peptide in this site, whereas these effects were inhibited by cocaine. These results expand the role of accumbal leptin to the regulation of the CART peptide and further suggest that possible interaction of these appetite-regulating peptides may be involved in cocaine-mediated rewarding effects.

Distinct roles for the deacetylase domain of HDAC3 in the hippocampus and medial prefrontal cortex in the formation and extinction of memory

Histone deacetylases (HDACs) are chromatin modifying enzymes that have been implicated as powerful negative regulators of memory processes. HDAC3has been shown to play a pivotal role in long-term memory for object location as well as the extinction of cocaine-associated memory, but it is unclear whether this function depends on the deacetylase domain of HDAC3. Here, we tested whether the deacetylase domain of HDAC3has a role in object location memory formation as well as the formation and extinction of cocaine-associated memories. Using a deacetylase-dead point mutant of HDAC3, we found that selectively blocking HDAC3 deacetylase activity in the dorsal hippocampus enhanced long-term memory for object location, but had no effect on the formation of cocaine-associated memory. When this same point mutant virus of HDAC3 was infused into the prelimbic cortex, it failed to affect cocaine-associated memory formation. With regards to extinction, impairing the HDAC3 deacetylase domain in the infralimbic cortex had no effect on extinction, but a facilitated extinction effect was observed when the point mutant virus was delivered to the dorsal hippocampus. These results suggest that the deacetylase domain of HDAC3 plays a selective role in specific brain regions underlying long-term memory formation of object location as well as cocaine-associated memory formation and extinction.

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.

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.

Predominant D1 Receptors Involvement in the Over-expression of CART Peptides after Repeated Cocaine Administration

The aim of this study was to investigate the involvement of dopaminergic receptors (DR) in behavioral sensitization, as measured by locomotor activity, and the over-expression of cocaine- and amphetamine-regulated transcript (CART) peptides after repeated administration of cocaine in mice. Repeated administrations of cocaine induced behavioral sensitization and CART over-expression in mice. The levels of striatal CART mRNA were significantly increased on the 3^rd day. CART peptides were over-expressed on the 5^th day in the striata of behaviorally sensitized mice. A higher proportion of CART⁺ cells in the cocaine-treated mice were present in the nucleus accumbens (NAc) shell than in the dorsolateral (DL) part of caudate putamen (CP). The concomitant administration of both D₁R and D₂R antagonists, SCH 23390 (D₁R selective) and raclopride (D₂R selective), blocked cocaine induced-behavioral sensitization, CART over-expression, and cyclic adenosine 5'-monophosphate (cAMP)/protein kinase A (PKA)/phospho-cAMP response element-binding protein (pCREB) signal pathways. SCH 23390 more predominantly inhibited the locomotor activity, CART over-expression, pCREB and PKA activity than raclopride. Cocaine induced-behavioral sensitization was also attenuated in the both D₁R and D₂R knockout (KO) mice, respectively. CART over-expression and activated cAMP/PKA/pCREB signal pathways were inhibited in the D₁R-KO mice, but not in the D₂R-KO mice. It is suggested that behavioral sensitization, CART over-expression and activated cAMP/PKA/pCREB signal pathways induced by repeated administration of cocaine could be more predominantly mediated by D₁R.

Delta FosB and AP-1-mediated transcription modulate cannabinoid CB₁ receptor signaling and desensitization in striatal and limbic brain regions

Repeated Δ(9)-tetrahydrocannabinol (THC) administration produces cannabinoid type 1 receptor (CB₁R) desensitization and downregulation, as well as tolerance to its in vivo pharmacological effects. However, the magnitude of CB₁R desensitization varies by brain region, with CB₁Rs in the striatum and its output nuclei undergoing less desensitization than other regions. A growing body of data indicates that regional differences in CB₁R desensitization are produced, in part, by THC-mediated induction of the stable transcription factor, ΔFosB, and subsequent regulation of CB₁Rs. The purpose of the present study was to determine whether THC-mediated induction of ΔFosB in the striatum inhibits CB₁R desensitization in the striatum and output nuclei. This hypothesis was tested using bitransgenic mice with inducible expression of ΔFosB or ΔcJun, a dominant negative inhibitor of AP-1-mediated transcription, in specific forebrain regions. Mice were treated repeatedly with escalating doses of THC or vehicle for 6.5 days, and CB₁R-mediated G-protein activation was assessed using CP55,940-stimulated [(35)S]GTPγS autoradiography. Overexpression of ΔFosB in striatal dopamine type 1 receptor-containing (D1R) medium spiny neurons (MSNs) attenuated CB₁R desensitization in the substantia nigra, ventral tegmental area (VTA) and amygdala. Expression of ΔcJun in striatal D1R- and dopamine type 2 receptor (D2R)-containing MSNs enhanced CB₁R desensitization in the caudate-putamen and attenuated desensitization in the hippocampus and VTA. THC-mediated in vivo pharmacological effects were then assessed in ΔcJun-expressing mice. Tolerance to THC-mediated hypomotility was enhanced in ΔcJun-expressing mice. These data reveal that ΔFosB and possibly other AP-1 binding proteins regulate CB₁R signaling and adaptation in the striatum and limbic system.

Alterations in brain-derived neurotrophic factor in the mouse hippocampus following acute but not repeated benzodiazepine treatment

Benzodiazepines (BZs) are safe drugs for treating anxiety, sleep, and seizure disorders, but their use also results in unwanted effects including memory impairment, abuse, and dependence. The present study aimed to reveal the molecular mechanisms that may contribute to the effects of BZs in the hippocampus (HIP), an area involved in drug-related plasticity, by investigating the regulation of immediate early genes following BZ administration. Previous studies have demonstrated that both brain derived neurotrophic factor (BDNF) and c-Fos contribute to memory- and abuse-related processes that occur within the HIP, and their expression is altered in response to BZ exposure. In the current study, mice received acute or repeated administration of BZs and HIP tissue was analyzed for alterations in BDNF and c-Fos expression. Although no significant changes in BDNF or c-Fos were observed in response to twice-daily intraperitoneal (i.p.) injections of diazepam (10 mg/kg + 5 mg/kg) or zolpidem (ZP; 2.5 mg/kg + 2.5 mg/kg), acute i.p. administration of both triazolam (0.03 mg/kg) and ZP (1.0 mg/kg) decreased BDNF protein levels within the HIP relative to vehicle, without any effect on c-Fos. ZP specifically reduced exon IV-containing BDNF transcripts with a concomitant increase in the association of methyl-CpG binding protein 2 (MeCP2) with BDNF promoter IV, suggesting that MeCP2 activity at this promoter may represent a ZP-specific mechanism for reducing BDNF expression. ZP also increased the association of phosphorylated cAMP response element binding protein (pCREB) with BDNF promoter I. Future work should examine the interaction between ZP and DNA as the cause for altered gene expression in the HIP, given that BZs can enter the nucleus and intercalate into DNA directly.

Role of dorsal hippocampal orexin-1 receptors in associating morphine reward with contextual stimuli

In this study, we evaluated the role of orexin receptors in the dorsal hippocampus (dHPC) in the development of morphine-induced conditioned place preference (CPP) and modification of hippocampal c-Fos and cyclic AMP response element-binding protein (CREB) levels. Orexin-A (0.5, 5, and 50 pmol) and the orexin-1 receptor antagonist, SB334867 (10, 20, and 40 nmol), were bilaterally infused into the dHPC immediately before conditioning with morphine (0.5 or 7.5 mg/kg) using the CPP task. Western blotting was then used to measure the protein levels of c-Fos, total CREB, and phosphorylated CREB (pCREB) in the hippocampus. Orexin did not enhance the rewarding efficacy of morphine (0.5 mg/kg), but caused a reduction in hippocampal c-Fos. Successful conditioning with morphine (7.5 mg/kg) was associated with increased levels of hippocampal c-Fos and CREB, but with decreased CREB phosphorylation. Intrahippocampal administration of SB334867 before conditioning sessions disrupted the rewarding effect of morphine (7.5 mg/kg) and blocked morphine-induced increases in hippocampal CREB protein levels. The results suggest that orexin signaling within the dHPC is necessary for the development of morphine CPP. Morphine reward is related to altered levels of hippocampal c-Fos and CREB. Inhibition of morphine-induced increases in CREB levels might be the underlying mechanism for the disruption of morphine CPP.

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).

Brain regional differences in CB1 receptor adaptation and regulation of transcription

Cannabinoid CB1 receptors (CB1Rs) are expressed throughout the brain and mediate the central effects of cannabinoids, including Δ(9)-tetrahydrocannabinol (THC), the main psychoactive constituent of marijuana. Repeated THC administration produces tolerance to cannabinoid-mediated effects, although the magnitude of tolerance varies by effect. Consistent with this observation, CB1R desensitization and downregulation, as well as induction of immediate early genes (IEGs), vary by brain region. Zif268 and c-Fos are induced in the forebrain after acute THC administration. Phosphorylation of the cAMP response-element binding protein (CREB) is increased in a region-specific manner after THC administration. Results differ between acute versus repeated THC injection, and suggest that tolerance to IEG activation might develop in some regions. Repeated THC treatment produces CB1R desensitization and downregulation in the brain, although less adaption occurs in the striatum as compared to regions such as the hippocampus. Repeated THC treatment also induces expression of ΔFosB, a very stable isoform of FosB, in the striatum. Transgenic expression of ∆FosB in the striatum enhances the rewarding effects of several drugs, but its role in THC-mediated effects is not known. The inverse regional relationship between CB1R desensitization and ∆FosB induction suggests that these adaptations might inhibit each other, although this possibility has not been investigated. The differential regional expression of individual IEGs by acute or repeated THC administration suggests that regulation of target genes and effects on CB1R signaling will contribute to the behavioral effects of THC.

Inhibitory role of inducible cAMP early repressor (ICER) in methamphetamine-induced locomotor sensitization

Background

The inducible cyclic adenosine monophosphate (cAMP) early repressor (ICER) is highly expressed in the central nervous system and functions as a repressor of cAMP response element-binding protein (CREB) transcription. The present study sought to clarify the role of ICER in the effects of methamphetamine (METH).

Methods and Findings

We tested METH-induced locomotor sensitization in wildtype mice, ICER knockout mice, and ICER I-overexpressing mice. Both ICER wildtype mice and knockout mice displayed increased locomotor activity after continuous injections of METH. However, ICER knockout mice displayed a tendency toward higher locomotor activity compared with wildtype mice, although no significant difference was observed between the two genotypes. Moreover, compared with wildtype mice, ICER I-overexpressing mice displayed a significant decrease in METH-induced locomotor sensitization. Furthermore, Western blot analysis and quantitative real-time reverse transcription polymerase chain reaction demonstrated that ICER overexpression abolished the METH-induced increase in CREB expression and repressed cocaine- and amphetamine-regulated transcript (CART) and prodynorphin (Pdyn) expression in mice. The decreased CART and Pdyn mRNA expression levels in vivo may underlie the inhibitory role of ICER in METH-induced locomotor sensitization.

Conclusions

Our data suggest that ICER plays an inhibitory role in METH-induced locomotor sensitization.

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.

Effect of 5-aza-2-deoxycytidine microinjecting into hippocampus and prelimbic cortex on acquisition and retrieval of cocaine-induced place preference in C57BL/6 mice

The long lasting addiction-related abnormal memory is one of the most important foundations for relapse. DNA methylation may be a possible mechanism for persistence of such memory. Here we injected the DNA methyltransferases (DNMTs) inhibitor, 5-aza-2-deoxycytidine (5-aza) into hippocampus CA1 area and prelimbic cortex during the stages of acquisition and expression of cocaine-induced place preference in C57BL/6 mice. Results showed that in CA1 DNA methylation inhibitors could restrain acquisition but had no impact on expression of the cocaine-induced conditioned place preference (CPP). On the contrary, in prelimbic cortex, 5-aza had no effect on acquisition but blocked expression. Our results indicated that DNA methylation in hippocampus is required for learning; while DNA methylation in prelimbic cortex is necessary for memory retrieval. The present finding is consistent with the role of the hippocampus as a structure contributing to cocaine-induced memory acquisition, and prelimbic cortex, a part of prefrontal cortex as an area responsible for cocaine-induced memory retrieval. In conclusion, DNA methylation does play an important role in drug-induced learning and memory although the detailed effect still calls for further research.

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.

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.

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.

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.

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.

Gonadal hormones-mediated effects on the stimulation of dopamine turnover in mesolimbic and nigrostriatal systems by cocaine- and amphetamine-regulated transcript (CART) peptide in male rats

Estradiol and testosterone modulated behavioral and neurochemical activities in the mesolimbic and nigrostriatal dopaminergic systems have been reported. We examined whether estradiol and testosterone affect stimulation of cocaine- and amphetamine-regulated transcript (CART) peptide in the mesolimbic and nigrostriatal dopaminergic systems in this study. Intracerebroventricular administration of CART peptide increased dopamine turnover in the nucleus accumbens and striatum in male rats. Stimulation of dopamine turnover in nucleus accumbens and striatum by CART peptide were found in intact male rats, but not in castrated male rats. This stimulation was restored in castrated male rats by testosterone or estradiol priming, or by treatment with the water-soluble form of estradiol, but not by treatment with the membrane-impermeable form of estradiol. Estradiol and testosterone antagonists blocked testosterone's effects, but only estradiol antagonist blocked estradiol's effects. Moreover, treatment of dihydrotestosterone also restored the stimulation in castrated male rats. This dihydrotestosterone's effect was blocked by a testosterone antagonist, but not by an estradiol antagonist. All of these findings indicate that gonadal hormones play a regulatory role in stimulation of CART peptide in mesolimbic and nigrostriatal dopaminergic systems, and suggest that acts through intracellular rather than extracellular mechanisms.

Microinjection of CART peptide 55-102 into the nucleus accumbens blocks both the expression of behavioral sensitization and ERK phosphorylation by cocaine

The role of the biologically active CART 55-102 peptide in the nucleus accumbens (NAcc) in the expression of cocaine-induced behavioral sensitization was investigated. Rats were divided into four groups: one for saline and the other three for cocaine pre-exposures (15 mg/kg, i.p., once daily for 7 days). After 3 weeks of withdrawal, rats were microinjected into the NAcc either saline or CART 55-102 (1.0, or 2.5 microg/0.5 microl/side) followed by cocaine challenge (10 mg/kg, i.p.). Microinjection into the NAcc of CART 55-102 peptide dose-dependently blocked the expression of locomotor sensitization produced by repeated cocaine pre-exposures. Next, we further examined the effect of CART 55-102 microinjection on extracellular signal-regulated kinase 1/2 (ERK1/2) phosphorylation levels in the NAcc. Additional four groups of rats were all cocaine pre-exposed and, after 3 weeks of withdrawal, they were either saline or cocaine challenged systemically following microinjection into the NAcc of either saline, CART 55-102 (2.5 microg/0.5 microl/side), or the equivalent mole amount of inactive CART 1-27 peptide. The increase of ERK1/2 phosphorylation levels in the NAcc by cocaine was completely blocked by CART 55-102 microinjection in this site, while it remains unaffected by inactive CART 1-27 peptide. These results suggest that CART 55-102 peptide in the NAcc may play a compensatory inhibitory role in the expression of behavioral sensitization by cocaine and these effects may be mediated by its inhibition of ERK1/2 phosphorylation in this site.

CART mRNA expression in rat monkey and human brain: relevance to cocaine abuse

The neuropeptide CART (cocaine and amphetamine regulated transcript) is suggested to be regulated by psychostimulant administration. We review here the localization of CART mRNA expression in the human brain and its possible relevance to human cocaine abuse. Except for strong hypothalamic expression, the CART transcript is predominately expressed in target regions of the mesocorticolimbic dopamine system, such as the nucleus accumbens shell, amygdala complex, extended amygdala and orbitofrontal, enthorhinal and piriform cortices. The discrete limbic localization strongly implies involvement in reward and reinforcement behaviors. We therefore examined CART mRNA expression in both Sprague Dawley rats and Rhesus monkeys that had self-administered cocaine. Cocaine self-administration in the rat (1.5 mg/kg/inj, on a fixed ratio 1 schedule of reinforcement for 1 week) and monkey (0.03 or 0.3 mg/kg/inj on a fixed 3 min interval schedule of reinforcement for 5 or 100 days) did not alter transcript levels in CART expressing nucleus accumbens (monkey not studied), amygdala nuclei or cortical areas. However, in the monkey sublenticular extended amygdala, low dose cocaine self-administration resulted in increased CART transcript levels after both 5 and 100 days of self-administration, whereas no difference was found after high dose self-administration. In conclusion, we found no substantial alterations CART mRNA expression during cocaine self-administration, but this neuropeptide has the anatomical and functional potential to modulate brain areas relevant for cocaine abuse. Further studies are needed to evaluate the involvement of CART in other components of the cocaine abuse cycle.

Role of cocaine- and amphetamine-regulated transcript in estradiol-mediated neuroprotection

Estrogen reduces brain injury after experimental cerebral ischemia in part through a genomic mechanism of action. Using DNA microarrays, we analyzed the genomic response of the brain to estradiol, and we identified a transcript, cocaine- and amphetamine-regulated transcript (CART), that is highly induced in the cerebral cortex by estradiol under ischemic conditions. Using in vitro and in vivo models of neural injury, we confirmed and characterized CART mRNA and protein up-regulation by estradiol in surviving neurons, and we demonstrated that i.v. administration of a rat CART peptide is protective against ischemic brain injury in vivo. We further demonstrated binding of cAMP response element (CRE)-binding protein to a CART promoter CRE site in ischemic brain and rapid activation by CART of ERK in primary cultured cortical neurons. The findings suggest that CART is an important player in estrogen-mediated neuroprotection and a potential therapeutic agent for stroke and other neurodegenerative diseases.

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.

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.

Regulation of genes involved in dopamine transporter modulation by acute cocaine in rat striatum

It is well established that acute administration of psychostimulants alters dopamine transport. However, the exact mechanism of this modulation is still unknown. In this study we examined the mRNA levels of several proteins involved in the various proposed processes following cocaine administration. The expression levels of several immediate early genes were also studied. This was performed in rat striatum using real-time quantitative PCR. As expected, a marked increase of the immediate early genes Fos, Egr1 and Egr3 was observed. Egr2 was also found up-regulated. Among the different genes studied only Synaptotagmin4 in the SNARE family and Synphilin1 in the synaptic vesicles binding family were modulated by acute cocaine treatment. Interestingly, acute amphetamine treatment did not increase either Synaptotagmin4 and Synphilin1 mRNA levels, although increases in early genes expression were noted.

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.

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.

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.

Differential effects of melanin concentrating hormone on the central dopaminergic neurons induced by the cocaine- and amphetamine-regulated transcript peptide

Stimulatory effects of cocaine- and amphetamine-regulated transcript (CART) peptide on central mesolimbic, nigrostriatal and mesocortical dopaminergic (DA) neurons were examined in female Sprague-Dawley rats. We also determined the different blocking effects of melanin concentrating hormone (MCH) on the stimulation by CART peptide in central DA systems. Intracerebroventricular administration of 1 microg CART peptide (55-102) produced increases in 3,4-dihydroxyphenylacetic acid (DOPAC) levels in the nucleus accumbens (NA) at 15 and 45 min, and in the striatum (ST) at 15 min, but not in the medial prefrontal cortex (MPFC). We found that the agonist of alpha-melanocyte stimulating hormone (alpha-MSH), MT II, at 10 microg had a stimulatory effect on the NA and ST DOPAC levels similar to the CART peptide. In contrast, 1 microg MCH and the antagonist of alpha-MSH, HS014, significantly decreased NA and ST DOPAC levels. However, only MCH prevented the stimulatory effect of CART peptide on DOPAC levels in the NA, but not in the ST. These results indicate that the stimulation of CART peptide on central DA neurons is region-specific, and that this effect can be blocked by MCH but not by the antagonist of alpha-MSH.

CART Peptides: Modulators of Mesolimbic Dopamine, Feeding, and Stress

CART peptides have been shown to be peptide neurotransmitters and endocrine factors in a series of cumulative studies over the past eight years or so. This brief review touches on three aspects of CART: CART as a mediator or modulator of mesolimbic dopamine, CART's regulation by glucocorticoids, and CART as a regulator of feeding, satiety, and body weight. There have been several recent reviews and publications on various aspects of CART peptides. These aspects include the sequence and numbering of the peptides, and their structure, processing, and roles in various physiologic processes.