CART peptide-immunoreactive projection from the nucleus accumbens targets substantia nigra pars reticulata neurons in the rat

Cocaine- and amphetamine-regulated transcript peptide- and dopamine-containing systems interact in the ventral tegmental area of the zebra finch, Taeniopygia guttata, during dynamic changes in energy status

The mesolimbic dopamine (DA)-pathway regulates food-reward, feeding-related behaviour and energy balance. Evidence underscores the importance of feeding-related neuropeptides in modulating activity of these DA neurons. The neuropeptide, CART, a crucial regulator of energy balance, modulates DA-release, and influences the activity of ventral tegmental area (VTA) DAergic neurons in the mammalian brain. Whether CART- and DA-containing systems interact at the level of VTA to regulate energy balance, however, is poorly understood. We explored the interaction between CART- and DA-containing systems in midbrain of the zebra finch, Taeniopygia guttata, an interesting model to study dynamic changes in energy balance due to higher BMR/daytime body temperature, and rapid responsiveness of the feeding-related neuropeptides to changes in energy state. Further, its midbrain DA-neurons share similarities with those in mammals. In the midbrain, tyrosine hydroxylase-immunoreactive (TH-i) neurons were seen in the substantia nigra (SN) and VTA [anterior (VTAa), mid (VTAm) and caudal (VTAc)]; those in VTA were smaller. In the VTA, CART-immunoreactive (CART-i)-fibers densely innervated TH-i neurons, and both CART-immunoreactivity (CART-ir) and TH-immunoreactivity (TH-ir) responded to energy status-dependent changes. Compared to fed and fasted birds, refeeding dramatically enhanced TH-ir and the percentage of TH-i neurons co-expressing FOS in the VTA. Increased prepro-CART-mRNA, CART-ir and a transient appearance of CART-i neurons was observed in VTAa of fasted, but not fed birds. To test the functional interaction between CART- and DA-containing systems, ex-vivo superfused midbrain-slices were treated with CART-peptide and changes in TH-ir analysed. Compared to control tissues, CART-treatment increased TH-ir in VTA but not SN. We propose that CART is a potential regulator of VTA DA-neurons and energy balance in T. guttata.

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

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

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.

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

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

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.

Caffeine induces behavioural sensitization and overexpression of cocaine-regulated and amphetamine-regulated transcript peptides in mice

This study examined whether repeated administration of caffeine would induce behavioural sensitization and overexpression of cocaine-regulated and amphetamine-regulated transcript (CART) peptides in mice. The involvement of dopaminergic receptors and adenosine receptors in caffeine-induced behavioural sensitization and CART overexpression was studied. The relevance of D₁R and D₂R, and A₁R and A(2A)R in the overexpression of CART peptides in mouse striatum was also evaluated. Repeated administration of caffeine induced behavioural sensitization in mice. Significant increases in CART mRNA levels were observed on day 3 and peaked at day 5 of caffeine administration, and then decreased gradually. Higher proportions of CART⁺ cells were observed in the dorsolateral and ventrolateral part of the caudate putamen than in the nucleus accumbens shell and core. The behavioural sensitization induced by caffeine was inhibited by dopaminergic receptor antagonists and adenosine receptor agonists. D₁R and D₂R, and cyclic AMP (cAMP)/protein kinase A (PKA)/phospho-cAMP response element-binding protein (pCREB) signalling were activated by caffeine, but A₁R and A(2A)R were inhibited. Overexpression of caffeine-induced CART peptides and pCREB activity were blocked by N-cyclopentyladenosine (CPA, an A₁R agonist) and 4-[2-[[6-amino-9-(N-ethyl-β-D-ribofuranuronamidosyl)-9H-purin-2-yl]amino]ethyl]benzenepropanoic acid hydrochloride (CGS 21680, an A(2A)R agonist), but not by R(+)-7-chloro-8-hydroxy-3-methyl-1-phenyl-2,3,4,5-tetrahydro-1H-3-benzazepine hydrochloride (SCH 23390, a D₁R antagonist) or raclopride (a D₂R antagonist). Caffeine-induced overexpression of CART peptides was associated with the inhibition of A₁R and A(2A)R, and the activation of cAMP/PKA/pCREB signalling. Moreover, the A(2A)R-D₂R heterodimer might be involved in the overexpression of CART peptides induced by caffeine.

Microinjection of CART (cocaine- and amphetamine-regulated transcript) peptide into the nucleus accumbens inhibits the cocaine-induced upregulation of dopamine receptors and locomotor sensitization

Repeated exposure to addictive drugs enhances dopamine receptor (DR) signaling and the ultimate phosphorylation of the cyclic adenosine 5'-monophosphate (cAMP)-response element-binding protein (CREB)-regulated cocaine- and amphetamine-regulated transcript (CART) expression in the nucleus accumbens (NAcc). These effects are known to contribute to the expression of behavioral sensitization. CART peptides are neuropeptides that modulate drug reward and reinforcement. The present experiments investigated the effects of CART 55-102 microinjection into the NAcc on (1) the phosphorylation of CREB, (2) cAMP/protein kinase A (PKA) signaling and (3) extracellular signal-regulated kinase (ERK) phosphorylated kinase signaling. Here, we show that repeated microinjections into the NAcc of CART 55-102 peptides (1.0 or 2.5μg, 0.5μl/side) attenuates cocaine-induced enhancements of D1R, D2R and D3R phosphorylation in this sites. Furthermore, the microinjection of CART 55-102 followed by repeated injections of cocaine (15mg/kg) dose-dependently blocked the enhancement of cAMP levels, PKA activity and pERK and pCREB levels on the fifth day of cocaine administration. The cocaine-induced locomotor activity and behavioral sensitization in rats were also inhibited by the 5-day-microinjection of CART peptides. These results suggest that the phosphorylation of CREB by cocaine in the NAcc was blocked by the CART 55-102 peptide via the inhibition of D1R and D2R stimulation, D3R phosphorylation, cAMP/PKA signaling and ERK phosphorylated kinase signaling. These effects may have played a compensatory inhibitory role in the behavioral sensitization of rats that received microinjections of CART 55-102.

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.

Neurotransmitter CART as a New Therapeutic Candidate for Parkinson's Disease

Parkinson's disease (PD) is one of the most common neurodegenerative diseases. To date, there is no effective treatment that halts its progression. Increasing evidence indicates that mitochondria play an important role in the development of PD. Hence mitochondria-targeted approaches or agents may have therapeutic promise for treatment of the disease. Neuropeptide CART (cocaine-amphetamine-regulated transcript), a hypothalamus and midbrain enriched neurotransmitter with an antioxidant property, can be found in mitochondria, which is the main source of reactive oxygen species. Systemic administration of CART has been found to ameliorate dopaminergic neuronal loss and improve motor functions in a mouse model of PD. In this article, we summarize recent progress in studies investigating the relationship between CART, dopamine, and the pathophysiology of PD, with a focus on mitochondria-related topics.

CART peptide is a potential endogenous antioxidant and preferentially localized in mitochondria

The multifunctional neuropeptide Cocaine and Amphetamine Regulated Transcript (CART) is secreted from hypothalamus, pituitary, adrenal gland and pancreas. It also can be found in circulatory system. This feature suggests a general role for CART in different cells. In the present study, we demonstrate that CART protects mitochondrial DNA (mtDNA), cellular proteins and lipids against the oxidative action of hydrogen peroxide, a widely used oxidant. Using cis-parinaric acid as a sensitive reporting probe for peroxidation in membranes, and a lipid-soluble azo initiator of peroxyl radicals, 2,2'-azobis(2,4-dimethylvaleronitrile) we found that CART is an antioxidant. Furthermore, we found that CART localized to mitochondria in cultured cells and mouse brain neuronal cells. More importantly, pretreatment with CART by systemic injection protects against a mouse oxidative stress model, which mimics the main features of Parkinson's disease. Given the unique molecular structure and biological features of CART, we conclude that CART is an antioxidant peptide (or antioxidant hormone). We further propose that it may have strong therapeutic properties for human diseases in which oxidative stress is strongly involved such as Parkinson's disease.

Expression of cocaine- and amphetamine-regulated transcript in the rat forebrain during postnatal development

Cocaine- and amphetamine-regulated transcript (CART) is widespread in the rodent brain. CART has been implicated in many different functions including reward, feeding, stress responses, sensory processing, learning and memory formation. Recent studies have suggested that CART may also play a role in neural development. Therefore, in the present study we compared the distribution pattern and levels of CART mRNA expression in the forebrain of male and female rats at different stages of postnatal development: P06, P26 and P66. At 6 days of age (P06), male and female rats showed increased CART expression in the somatosensory and piriform cortices, indusium griseum, dentate gyrus, nucleus accumbens, and ventral premammillary nucleus. Interestingly, we found a striking expression of CART mRNA in the ventral posteromedial and ventral posterolateral thalamic nuclei. This thalamic expression was absent at P26 and P66. Contrastingly, at P06 CART mRNA expression was decreased in the arcuate nucleus. Comparing sexes, we found increased CART mRNA expression in the anteroventral periventricular nucleus of adult females. In other regions including the CA1, the lateral hypothalamic area and the dorsomedial nucleus of the hypothalamus, CART expression was not different comparing postnatal ages and sexes. Our findings indicate that CART gene expression is induced in a distinct temporal and spatial manner in forebrain sites of male and female rats. They also suggest that CART peptide participate in the development of neural pathways related to selective functions including sensory processing, reward and memory formation.

Cortico-Basal Ganglia reward network: microcircuitry

Many of the brain's reward systems converge on the nucleus accumbens, a region richly innervated by excitatory, inhibitory, and modulatory afferents representing the circuitry necessary for selecting adaptive motivated behaviors. The ventral subiculum of the hippocampus provides contextual and spatial information, the basolateral amygdala conveys affective influence, and the prefrontal cortex provides an integrative impact on goal-directed behavior. The balance of these afferents is under the modulatory influence of dopamine neurons in the ventral tegmental area. This midbrain region receives its own complex mix of excitatory and inhibitory inputs, some of which have only recently been identified. Such afferent regulation positions the dopamine system to bias goal-directed behavior based on internal drives and environmental contingencies. Conditions that result in reward promote phasic dopamine release, which serves to maintain ongoing behavior by selectively potentiating ventral subicular drive to the accumbens. Behaviors that fail to produce an expected reward decrease dopamine transmission, which favors prefrontal cortical-driven switching to new behavioral strategies. As such, the limbic reward system is designed to optimize action plans for maximizing reward outcomes. This system can be commandeered by drugs of abuse or psychiatric disorders, resulting in inappropriate behaviors that sustain failed reward strategies. A fuller appreciation of the circuitry interconnecting the nucleus accumbens and ventral tegmental area should serve to advance discovery of new treatment options for these conditions.

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.

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.

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.

Mesolimbic dopamine and cortico-accumbens glutamate afferents as major targets for the regulation of the ventral striato-pallidal GABA pathways by neurotensin peptides

The tridecapeptide neurotensin (NT) acts in the mammalian brain as a primary neurotransmitter or neuromodulator of classical neurotransmitters. Morphological and functional in vitro and in vivo studies have demonstrated the existence of close interactions between NT and dopamine both in limbic and in striatal brain regions. Additionally, biochemical and neurochemical evidence indicates that in these brain regions NT plays also a crucial role in the regulation of the aminoacidergic signalling. It is suggested that in the nucleus accumbens the regulation of prejunctional dopaminergic transmission induced by NT may be primarily due to indirect mechanism(s) involving mediation via the aminoacidergic neuronal systems with increased glutamate release followed by increased GABA release in the nucleus accumbens rather than a direct action of the peptide on accumbens dopaminergic terminals. The neurochemical profile of action of NT in the control of the pattern of dopamine, glutamate and GABA release in the nucleus accumbens differs to a substantial degree from that shown by the peptide in the dorsal striatum. The neuromodulatory NT mechanisms in the regulation of the ventral striato-pallidal GABA pathways are discussed and their relevance for schizophrenia is underlined.

Immunohistochemical localization of cocaine- and amphetamine-regulated transcript peptide in the brain of the catfish,Clarias batrachus (Linn.)

The organization of cocaine- and amphetamine-regulated transcript peptide (CARTp, 54-102) immunoreactivity was investigated in the brain of the catfish, Clarias batrachus. CARTp-immunoreactivity was observed in several granule cells of the olfactory bulbs, in dot-like terminals around mitral cells, and in the fibers of the medial olfactory tracts. While several groups of discrete cells in the telencephalon showed CARTp-immunoreactivity, the immunostained fibers were widely distributed in the area dorsalis and ventralis telencephali. Immunoreactivity was seen in several periventricular and a few magnocellular neurons, and in a dense fiber network throughout the preoptic area. Varying degrees of immunoreactive fibers were seen in the periventricular region in the thalamus, hypothalamus, and pituitary. Some neurons in the nucleus preglomerulosus medialis and lateralis, central nucleus of the inferior lobes, nucleus lobobulbaris of the posterior tuberculum, and nucleus recessus posterioris showed distinct CARTp-immunoreactivity. Considerable immunoreactivity was seen in the optic tectum, rostral torus semicircularis, central pretectal area, and granule cells of the cerebellum. While only isolated immunoreactive cells were seen at three distinct sites in the metencephalon, a fiber network was seen in the facial and vagal lobes and periventricular and ventral regions of the medulla oblongata. The pattern of the CARTp distribution in the brain of C. batrachus suggests that it may play an important role in the processing of sensory information, the regulation of hormone secretion by hypophysial cell types, and motor and vegetative function. Finally, as in other animal species, CARTp seems to play a role in the processing of gustatory information.

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.

Innervation of the paraventricular nucleus of the thalamus from cocaine- and amphetamine-regulated transcript (CART) containing neurons of the hypothalamus

The paraventricular nucleus of the thalamus (PVT) is a midline thalamic nucleus with heavy projections to the nucleus accumbens and other limbic regions. Previous studies have shown that the PVT contains fibers immunoreactive for cocaine- and amphetamine-related transcript (CART). The purpose of the present study was to determine the location of CART neurons innervating the PVT of the rat by using retrograde tracing with cholera toxin B (CTb) combined with immunofluorescence for CTb and CART (amino acid sequence 55-102). Immunohistochemical analysis of CART in the dorsal thalamus showed that the PVT is densely innervated by CART fibers whereas adjacent midline and intralaminar thalamic nuclei are unlabeled. Injections of CTb in the dorsal midline thalamus retrogradely labeled neurons in several areas of the hypothalamus and brainstem which also contained CART neurons. The largest number of double-labeled neurons (CTb/CART) was found in the arcuate nucleus of the hypothalamus. CTb/CART neurons were also found in the lateral hypothalamus, zona incerta, and periventricular hypothalamus. These results indicate that the arcuate nucleus is a major source of CART fibers in the PVT. CART neurons in the arcuate nucleus monitor circulating hormonal signals and may regulate food intake and hypothalamic-pituitary-adrenal (HPA) activity. Consequently, CART neurons in the arcuate nucleus may transmit signals to the PVT which in turn may influence limbic regions involved in regulating food intake and the HPA.

CART peptide and the mesolimbic dopamine system

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

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.

On the retention of neurotensin in the ventral tegmental area (VTA) despite destruction of the main neurotensinergic afferents of the VTA--implications for the organization of forebrain projections to the VTA

Neurotensin (NT) modulates ventral tegmental area (VTA) signaling in a manner relevant to psychostimulant drug actions, thus inviting evaluation of psychostimulant effects in conditions of reduced or absent VTA NT. However, in a preliminary study, NT immunoreactivity (-ir) in the VTA was unaffected following destruction of the main concentration of forebrain neurotensinergic VTA afferents in the lateral preoptic-rostral lateral hypothalamic continuum (LPH) and adjacent lateral part of the medial preoptic area (MPOA). This study attempted to determine what measures are necessary to obtain a significant reduction of VTA NT-ir. Large unilateral ibotenic acid lesions were made in several structures containing NTergic, VTA-projecting neurons, including the LPH-MPOA, nucleus accumbens, VTA itself and dorsal raphe. None of these was associated with substantial ipsilateral loss of NT-ir in the VTA, lateral hypothalamus or lateral habenula. Combinations of lesions, such as LPH-MPOA plus VTA and LPH-MPOA plus dorsal raphe, also failed to substantially reduce NT-ir in these structures. Transections of the medial forebrain bundle (mfb) likewise failed to produce a substantial loss of VTA NT-ir measured with immunohistochemistry and radioimmunoassay. Transections of the mfb were carried out in combination with infusions of retrograde and anterograde axonal tract-tracers, revealing that the routes taken by some forebrain NT-ir VTA afferents circumvent mfb transections. All of these results together are consistent with the hypothesis that the connectional organization of forebrain and brainstem, potentially in combination with limited adaptive synaptogenesis, renders the VTA relatively insensitive to moderate losses of neurotensinergic and, perhaps, other peptidergic afferents.

Cocaine- and amphetamine-regulated transcript is localized in pituitary lactotropes and is regulated during lactation

Cocaine- and amphetamine-regulated transcript (CART) is a highly expressed peptide implicated in the regulation of feeding, reward and reinforcement, and stress-related behaviors. CART has been localized to discrete cell populations in the brain, gut, adrenal gland, and pancreas. In contrast, CART-producing cell types in the pituitary gland remain ill defined. In the present study, double-label immunohistochemistry, employing a high-affinity antiserum we generated against CART-(62-102), was used to identify CART-producing cells in the pituitary gland. In the anterior pituitary, the majority of CART immunoreactivity (-ir) was localized in lactotropes; minor populations of CART-ir cells were identified as somatotropes and corticotropes. In the posterior pituitary, CART-ir extensively colocalized with oxytocin-containing fibers; in contrast, only a few vasopressin fibers contained CART-ir. As expected, CART colocalized with oxytocin in magnocellular neurons of the supraoptic nucleus. The effects of bromocriptine, a potent dopamine receptor agonist, were examined to determine whether CART mRNA expression and protein release are regulated in a similar fashion as prolactin. Similar to prolactin, CART mRNA expression and protein release were significantly decreased after bromocriptine treatment of dispersed rat anterior pituitary cells in culture. To explore the putative physiological role of pituitary CART, we compared levels of CART mRNA expression in lactating and nonlactating female rats. CART mRNA levels were significantly increased in the anterior pituitary and supraoptic nucleus of lactating rats. Furthermore, levels of CART in the systemic circulation were significantly elevated at the onset of lactation, peaked on d 10 of lactation and returned to baseline values 10 d after pups were weaned. The current study describes the cellular localization and regulation of CART expression and protein release from the rat pituitary gland. These findings suggest a putative role for CART in lactation.

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

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

A cocaine-and-amphetamine-regulated-transcript peptide projection from the lateral hypothalamus to the ventral tegmental area

Cocaine-and-amphetamine-regulated-transcript peptides play a role in the modulation of feeding and psychomotor stimulant-like behaviors. The ventral tegmental area and the lateral hypothalamus are likely structures where cocaine-and-amphetamine-regulated-transcript peptides mediate both of these functions. Although lateral hypothalamus inputs to the ventral tegmental area have long been known, the chemical nature of this pathway remains poorly understood. To address this issue, we tested the possibility that cocaine-and-amphetamine-regulated-transcript peptide-containing neurons in the lateral hypothalamus project to the ventral tegmental area using the retrograde transport of cholera toxin subunit B combined with cocaine-and-amphetamine-regulated-transcript peptide immunostaining. The largest density of retrogradely-labeled neurons in the hypothalamus after cholera toxin subunit B injection in the ventral tegmental area was found, ipsi- and contralaterally, in the lateral hypothalamus/perifornical area, although substantial numbers of retrogradely-labeled cells were also found in the medial preoptic area, lateral preoptic area, paraventricular nucleus, dorsomedial hypothalamus and ventromedial hypothalamus. More than 80% of the retrogradely-labeled cocaine-and-amphetamine-regulated-transcript peptide-immunoreactive neurons in the hypothalamus were found in the lateral hypothalamus/perifornical area both ipsilateral and contralateral to the injection sites. Although retrogradely-labeled neurons were seen in the amygdala, locus coeruleus, and raphe nucleus, none of them displayed cocaine-and-amphetamine-regulated-transcript peptide immunoreactivity. Therefore, the hypothalamic projection to the ventral tegmental area provides a substrate whereby cocaine-and-amphetamine-regulated-transcript peptides could mediate the rewarding aspects of feeding and psychomotor stimulant-like behaviors. These findings, combined with the fact that the lateral hypothalamus receives strong inputs from the shell of the nucleus accumbens and ventral pallidum, suggest that these structures are part of integrative functional loops that control reward and appetitive behaviors.

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 peptide: central mediator of leptin-induced adipose tissue apoptosis?

Because of connections between CART peptide containing neurons and the sympathetic nervous system (SNS) and the possible role of the SNS in leptin-induced adipose apoptosis, CART may act as a downstream effector of leptin-induced adipose apoptosis. Male Sprague-Dawley rats received continuous intracerebroventricular (i.c.v.) infusion for 4 days of either artificial cerebrospinal fluid (aCSF, 12 microl/day), leptin (15 microg/day), or CART55-102 at 2.4 microg/day (CART2.4) or 9.6 microg/day (CART9.6). Food intake (FI) was decreased 10.8% for CART2.4, 41.9% for CART9.6 and 33.4% for leptin (p<0.05). CART9.6 and leptin reduced meal size and meal number. Body weight (BW) was reduced by CART9.6 (14.6%) and leptin (11.6%) (p<0.05), but not by CART2.4. CART9.6 and CART2.4, but not leptin, caused hypothermia, and CART9.6 inhibited physical activity (p<0.05). Epididymal, inguinal and retroperitoneal fat pad weights were reduced (p<0.05) by both CART treatments and leptin; CART9.6 also reduced gastrocnemius muscle weight (18.1%, p<0.05). Leptin, but not CART, increased serum free fatty acid concentrations by 31.1% (p<0.05) and increased adipose apoptosis by 48% (p<0.05). These data show that although leptin and CART55-102 have some similar actions, CART55-102 is probably not a mediator for leptin-induced adipose apoptosis in the brain.

Cocaine- and amphetamine-regulated transcript in the nucleus accumbens participates in the regulation of feeding behavior in rats

The present studies aimed to determine whether cocaine- and amphetamine-regulated transcript (CART) peptide in the nucleus of accumbens shell (AcbSh) is implicated in the regulation of food intake. Bilateral intranuclear injections of CART peptide (55-102, 1 microg/microl/side) into the AcbSh decreased food intake with no change in locomotion activity and attenuated the orexigenic effect of the GABA(A) agonist muscimol (100 ng/microl/side) in male Sprague-Dawley rats. Decreased food intake after bilateral intranuclear injections of CART was more sustained in freely fed rats than in food-deprived rats, suggesting fuel availability is an important factor in modulating the function of CART in the regulation of feeding. Our anatomical findings indicate that in addition to the perifornical region and the arcuate nucleus, some neurons within the AcbSh also project within the AcbSh. Moreover, many of these efferent cells contain CART immunoreactivity, including those which reside within the AcbSh, suggesting that accumbal CART circuitry is involved in the central function of the nucleus accumbens. Furthermore, fasting suppressed CART mRNA levels in the AcbSh, paraventricular nucleus of the hypothalamus, arcuate nucleus, and the perifornical region, indicating that the Acb is sensitive to fuel availability to an extent similar to those regions in the hypothalamus. Our findings are the first to demonstrate that CART mRNA in the AcbSh is sensitive to metabolic challenges and that injection of CART peptide into the AcbSh has an inhibitory effect on food intake.

Effects of the cocaine- and amphetamine-regulated transcript peptide on the turnover of dopamine in tuberoinfundibular neurons and serum prolactin levels: studies using estrogen, melanin concentrating hormone, and melanocortin

Effects of the cocaine- and amphetamine-regulated transcript (CART) peptide on tuberoinfundibular dopaminergic (TIDA) neurons were examined in female and male Sprague-Dawley rats in the morning and afternoon. We also examined the blocking effects of melanin concentrating hormone (MCH) and the antagonists of alpha-melanocyte stimulating hormone (alpha-MSH), SHU9119 and HS014, on stimulation induced by the CART peptide in TIDA systems. Intracerebroventricular administration of 1 mug CART peptide (55-102) at 45 min, either in the morning or afternoon, produced an increase in the median eminence (ME) DOPAC (3,4-dihydroxyphenylacetic acid) level and a corresponding decrease in serum prolactin (PRL) levels. This resulted from stimulation of TIDA neurons regardless of castration, and whether or not male and female rats were estrogen-primed. The stimulatory effects of the CART peptide on ME DOPAC levels were similar in the morning and afternoon in both male and female rats. Central treatment with 1 microg SHU9119, HS014, or MCH significantly decreased the ME DOPAC levels and elevated serum PRL levels in female rats. However, only MCH prevented the stimulatory effect of the CART peptide on TIDA neurons. These results indicate that stimulation by the CART peptide on TIDA neurons is gender-independent; and this stimulatory effect can be blocked by MCH, but not the antagonists of alpha-MSH.

Immunohistochemical localization of cocaine- and amphetamine-regulated transcript peptide in the central nervous system of the frogRana esculenta

The distribution of cocaine- and amphetamine-regulated transcript peptide (CARTp)- like immunoreactivity was studied only in the rat central nervous system (CNS). In mammals, CART peptides occur among others in brain areas that control feeding behavior. We mapped CARTp-immunoreactive structures in the CNS of the frog Rana esculenta and assumed that differences may exist in the CARTp-containing neuronal populations between the frog, which does not feed in winter, and the rat. In the forebrain, immunoreactive cells and fibers were found in the olfactory bulb, nucleus accumbens, amygdala, medial pallium, septum, striatum, the preoptic nuclei, ventromedial nucleus, central thalamic nucleus, and the hypothalamus. The optic pathway was free of immunoreactivity. The neurohypophysis showed intense immunostaining. In the mesencephalon, many cells were stained in the Edinger-Westphal nucleus, and a few in the optic tectum, where fibers were stained in all plexiform layers. In the retina, some cells in the inner nuclear layer contained CARTp. In the rhombencephalon, cells were stained in the raphe nuclei, central gray, nucleus of the solitary tract, and the vicinity of motor nuclei. Neurons of the motor cranial nerves were densely innervated by CARTp-positive fibers originating from the spinal cord. In the spinal cord, preganglionic cells were stained, and motoneurons were surrounded by immunoreactive varicose axon terminals. Major differences were found between the frog and the rat brains in the distribution of CARTp in the visual system, olfactory bulb, preoptic area, and the motor nuclei. Some of these differences may be related to feeding behavior of these animals.

Quantification of morphological differences in boutons from different afferent populations to the nucleus accumbens

The nucleus accumbens (Acb) receives convergent glutamatergic inputs from the prefrontal cortex (PFC), central thalamus, basolateral amygdala and the ventral subiculum of the hippocampus. The principal neurons of the nucleus accumbens are modulated by specific sets of convergent afferent inputs, the local circuit neurons also receive a substantial number of glutamatergic inputs, but the full complement of these has yet to be established. The aim of these studies was to define characteristics of the different glutamatergic afferent inputs to the nucleus accumbens that would aid their identification. To enable the characterisation of the glutamatergic inputs to nucleus accumbens neurons we first labelled the four main glutamatergic sources of afferent input to the accumbens with the anterograde tracer biotinylated dextran amine (BDA). Using an unbiased systematic sampling method, the morphological characteristics of their synaptic boutons were measured and assessed at the electron microscopic level. From the criteria assessed, a comparison of the four afferent sources was made, characteristics such as bouton size and vesicle density had significantly different population means, however, the only characteristic that allowed discrimination between the four major glutamatergic afferent to the nucleus accumbens was that of vesicle size. The vesicles in boutons from amygdala were larger than the subiculum which, in turn, were larger than the prefrontal cortex, the thalamus were the smallest in size. The methods used also allow a comparison of the relative frequency of different sized postsynaptic structures targeted, the prefrontal cortex almost exclusively targeted spines whereas the thalamus and the subiculum, in addition to spines, targeted proximal and distal dendrites.

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

Cocaine- and amphetamine-regulated transcript (CART) is a neuropeptide highly expressed in the hypothalamus and nucleus accumbens. Hypothalamic CART has been associated with food intake and body weight control, but in the nucleus accumbens the role of CART remains elusive. New generations of antipsychotic drugs show a good efficacy over psychotic symptoms but they induce an important weight gain. The mechanism underlying this unexpected side effect is still unknown. The present results show, for the first time, that acute and chronic treatment with the atypical neuroleptic clozapine, but not the conventional neuroleptic haloperidol, reduced the expression of CART mRNA in the shell of the nucleus accumbens. CART mRNA is colocalized with both dopamine D(2) and D(3) receptor transcripts in the nucleus accumbens shell. However, a dopamine D(3) receptor, but not D(2), antisense oligonucleotide administration reduced CART expression in this brain area. These results suggest that the dopamine D(3) receptor, but not the D(2), is involved in the control of CART expression in the nucleus accumbens and that it may participate in the modulation of CART mRNA levels by clozapine. The modulation of CART, an anorexigenic neuropeptide, in the dopamine mesolimbic pathway may potentially play a role in dysregulated food intake induced by some antipsychotic drugs.

Differential projections of the infralimbic and prelimbic cortex in the rat

The medial prefrontal cortex has been associated with diverse functions including attentional processes, visceromotor activity, decision-making, goal-directed behavior, and working memory. The present report compares and contrasts projections from the infralimbic (IL) and prelimbic (PL) cortices in the rat by using the anterograde anatomical tracer, Phaseolus vulgaris-leucoagglutinin. With the exception of common projections to parts of the orbitomedial prefrontal cortex, olfactory forebrain, and midline thalamus, PL and IL distribute very differently throughout the brain. Main projection sites of IL are: 1) the lateral septum, bed nucleus of stria terminalis, medial and lateral preoptic nuclei, substantia innominata, and endopiriform nuclei of the basal forebrain; 2) the medial, basomedial, central, and cortical nuclei of amygdala; 3) the dorsomedial, lateral, perifornical, posterior, and supramammillary nuclei of hypothalamus; and 4) the parabrachial and solitary nuclei of the brainstem. By contrast, PL projects at best sparingly to each of these structures. Main projection sites of PL are: the agranular insular cortex, claustrum, nucleus accumbens, olfactory tubercle, the paraventricular, mediodorsal, and reuniens nuclei of thalamus, the capsular part of the central nucleus and the basolateral nucleus of amygdala, and the dorsal and median raphe nuclei of the brainstem. As discussed herein, the pattern of IL projections is consistent with a role for IL in the control of visceral/autonomic activity homologous to the orbitomedial prefrontal cortex of primates, whereas those of PL are consistent with a role for PL in limbic-cognitive functions homologous to the dorsolateral prefrontal cortex of primates.

Intra-Accumbal Injection of CART (Cocaine-Amphetamine Regulated Transcript) Peptide Reduces Cocaine-Induced Locomotor Activity

Evidence suggests that CART (cocaine-amphetamine regulated transcript) peptides are mediators or modulators of the actions of psychostimulant drugs. In this study, the effects of intra-accumbal injections of rat long form (rl) CART 55-102 were examined. Injection of the peptide alone had no effect, but pretreatment with the peptide blunted or reduced the locomotor-inducing effects of cocaine after an i.p. injection. This effect was dose related and time limited, as expected. rlCART 1-27, a CART peptide fragment not active in other studies, was without effect on cocaine-induced locomotor activity. Because the actions of cocaine involve dopamine, the effect of rlCART 55-102 on dopamine-induced locomotor activity was examined. Intraaccumbal injection of dopamine produced a dose-related and time-limited increase in locomotor activity, as expected. Coinjection of rlCART 55-102 with dopamine blunted the effect. In summary, these data suggest that CART peptides in the nucleus accumbens would tend to oppose the actions of cocaine.

Neuroanatomical relationship between type 1 cannabinoid receptors and dopaminergic systems in the rat basal ganglia

Dopamine and endocannabinoids are neurotransmitters known to play a role in the activity of the basal ganglia motor circuit. While a number of studies have demonstrated functional interactions between type 1 cannabinoid (CB1) receptors and dopaminergic systems, we still lack detailed neuroanatomical evidence to explain their relationship. Single- and double-labeling methods (in situ hybridization and immunohistochemistry) were employed to determine both the expression and localization of CB1 receptors and tyrosine hydroxylase (TH) in the basal ganglia. In the striatum, we found an intense signal for CB1 receptor transcripts but low signal for CB1 receptor protein, whereas in the globus pallidus and substantia nigra we found the opposite; no hybridization signal but intense immunoreactivity. Consequently, CB1 receptors are synthesized in the striatum and mostly transported to its target areas. No co-expression or co-localization of CB1 receptors and TH was found. In the caudate-putamen, globus pallidus and substantia nigra, TH-immunoreactive fibers were interwoven with the CB1 receptor-immunoreactive neuropil and fibers. Our data suggest that the majority of the striatal CB1 receptors are located presynaptically on inhibitory GABAergic terminals, in a position to modulate neurotransmitter release and influence the activity of substantia nigra dopaminergic neurons. In turn, afferent dopaminergic fibers from the substantia nigra innervate CB1 receptor-expressing striatal neurons that are known to also express dopamine receptors. In conclusion, these data provide a neuroanatomical basis to explain functional interactions between endocannabinoid and dopaminergic systems in the basal ganglia.

CART peptides are modulators of mesolimbic dopamine and psychostimulants

CART peptide produces behavioral effects when injected into the VTA or nucleus accumbens. In the VTA, the peptide behaves like an endogenous psychostimulant and produces increased locomotor activity and conditioned place preference. Since this is blocked by dopamine receptor blockers, it presumably involves release of dopamine. But in the nucleus accumbens, CART peptide reduces the locomotor-increasing effects of cocaine. This suggests that the peptide is an interesting target for medications development.

Effects of the cocaine- and amphetamine-regulated transcript peptide on the turnover of central dopaminergic neurons

The effects of the cocaine- and amphetamine-regulated transcript (CART) peptide on central dopaminergic (DA) neurons were examined in ovariectomized, estrogen-primed Sprague-Dawley rats in both the morning and afternoon. Intracerebroventricular administration of 1 microg, but not lower doses of the CART peptide (55-102), either in the morning or afternoon produced a prolonged increase in the 3,4-dihydroxyphenylacetic acid (DOPAC) level in the median eminence (ME) and a corresponding decrease of serum prolactin (PRL) levels, which resulted from stimulation of tuberoinfundibular dopaminergic neurons. The CART peptide stimulated DOPAC levels in the striatum (ST), nucleus accumbens (NA), hypothalamic paraventricular nucleus (PVN), and periventricular (A14), but had no effect in the medial prefrontal cortex (MPFC) or suprachiasmatic nucleus (SCN). These effects of the CART peptide on stimulation of central DA systems and inhibition of PRL levels are specific because the inactive form of the CART peptide (0.1 and 1 microg) could not induce a similar response. Stimulatory effects of the CART peptide on different central DA systems displayed differential time-response profiles in the NA and ST, ME, and PVN and A14. These findings indicate that the CART peptide may selectively regulate certain central DA neuronal activities.

Early and transient ontogenetic expression of the cocaine- and amphetamine-regulated transcript peptide in the rat mesencephalon: correlation with tyrosine hydroxylase expression

The ontogeny of cocaine- and amphetamine-regulated transcript (CART) expression has been analyzed by immunohistochemistry in the mesencephalon of the rat central nervous system, and compared to the pattern of tyrosine hydroxylase- (TH-) expression. CART-producing neurons were first detected on the embryonic day 11 (E11) in the ventral mesencephalic vesicle. These neurons are among the first cells of the mantle layer to differentiate. From E13, a complementary pattern of distribution was observed, dividing the mantle layer into an external TH zone and an internal CART zone. Many TH-positive neurons were found to migrate from the neuroepithelium through the area containing the CART-immunoreactive neurons to settle more laterally. These TH cells exhibited prominent leading and trailing dendrites in the immediate vicinity of CART perikarya. On E16, the number of CART neurons appeared to diminish, and they were confined near the ventricle and around the fasciculus retroflexus. On E18 and E20, only the Edinger-Westphal nucleus exhibited a strong CART staining as described in the adult brain. Thus, the very early detection of CART during prenatal ontogeny led us to speculate that this peptide might have a role in the development of specific regions of the rat brain. In particular, our observations suggest that CART-expressing neurons might help the migration of the dopaminergic neurons of the substantia nigra.

Cocaine- and amphetamine-regulated transcript peptide projections in the ventral midbrain: colocalization with gamma-aminobutyric acid, melanin-concentrating hormone, dynorphin, and synaptic interactions with dopamine neurons

To date, cocaine- and amphetamine-regulated transcript (CART) peptides have been found to influence feeding, locomotor activity, and conditioned place preference. A common brain structure that could mediate these effects is the ventral tegmental area (VTA). For a better understanding of the anatomical substrates that might underlie CART peptides' role in these behaviors, we performed a series of experiments to elucidate the source, synaptic connectivity, and neurochemical content of CART peptide-immunoreactive (CARTir) terminals in the rat VTA. Double-labeling immunofluorescence revealed that approximately 15% of CARTir terminals in the VTA contain the hypothalamic neuropeptide, melanin-concentrating hormone (MCH). Furthermore, CART peptides were also found to colocalize with GABA and, to a small extent, with dynorphin in nerve terminals in both the VTA and the substantia nigra (SN). In the VTA, CARTir terminals form both symmetric and asymmetric synapses onto dopaminergic and nondopaminergic distal dendrites, suggesting that various sources contribute to this innervation. About 30% of CARTir terminals in the VTA and only 15% in the SN appose or form synaptic contact with DA neurons, which support our previous data showing that GABAergic basal ganglia output neurons in the substantia nigra pars reticulata (SNr) receive strong CARTir input from the accumbens core. Results of these studies suggest that the most significant behavioral states influenced by CART peptides, feeding and locomotion, may be mediated by direct and/or indirect modulation of VTA dopaminergic neuronal activity.

Hippocampal and prefrontal cortical inputs monosynaptically converge with individual projection neurons of the nucleus accumbens

Afferents to the nucleus accumbens from different sources innervate specific areas of the central "core" and peripheral "shell" and are related to each other, at the light microscopical level, in an intricate overlapping and nonoverlapping way. This lack of homogeneity suggests that this region consists of circuits involving emsembles of neurons modulated by specific sets of convergent afferent inputs and abnormal regulation of such ensembles has been implicated in mental disorders. Early extracellular studies suggested that individual Acb neurons might respond to activation of afferents from more than one excitatory input: More recent studies of hippocampal and amygdalar or prefrontal cortical afferents suggest that hippocampal afferents gate the input from the prefrontal cortex or amygdala. Electrophysiological evidence for convergence of excitatory afferents in the Acb is strong and suggests that these pathways are monosynaptic. Nevertheless, this convergence has proved difficult to demonstrate anatomically as a result of the spatial distribution of the afferent inputs on the dendritic tree of the target neurons. To establish whether individual accumbens neurons receive monosynaptic input from pairs of afferents, one projection was labelled anterogradely with Phaseolus vulgaris leucoagglutinin and the second with biotinylated dextran amine (BDA) with Vector slate grey and 3,3'-diaminobenzidine tetrahydrochloride as the chromagens. Accumbens neurons possibly postsynaptic to these afferents, labelled by an in vivo focal injection of BDA, were examined using correlated light and electron microscopy to establish the proximal-distal distribution of labelled afferent synaptic inputs on their dendritic arbours. Individual cells were shown to receive monosynaptic afferent input from both ventral subiculum and prefrontal cortex, providing an anatomical framework for the hippocampal gating of other limbic inputs to the accumbens.