Cholecystokinin-dopamine interactions

The neuropeptide drosulfakinin enhances choosiness and protects males from the aging effects of social perception

The motivation to reproduce is a potent natural drive, and the social behaviors that induce it can severely impact animal health and lifespan. Indeed, in Drosophila males, accelerated aging associated with reproduction arises not from the physical act of courtship or copulation but instead from the motivational drive to court and mate. To better understand the mechanisms underlying social effects on aging, we studied male choosiness for mates. We found that increased activity of insulin-producing cells (IPCs) of the fly brain potentiated choosiness without consistently affecting courtship activity. Surprisingly, this effect was not caused by insulins themselves, but instead by drosulfakinin (DSK), another neuropeptide produced in a subset of the IPCs, acting through one of the two DSK receptors, CCKLR-17D1. Activation of Dsk+ IPC neurons also decreased food consumption, while activation of Dsk+ neurons outside of IPCs affected neither choosiness nor feeding, suggesting an overlap between Dsk+neurons modulating choosiness and those influencing satiety. Broader activation of Dsk+ neurons (both within and outside of the IPCs) was required to rescue the detrimental effect of female pheromone exposure on male lifespan, as was the function of both DSK receptors. The same broad set of Dsk+ neurons was found to reinforce normally aversive feeding interactions, but only after exposure to female pheromones, suggesting that perception of the opposite sex gates rewarding properties of these neurons. We speculate that broad Dsk+ neuron activation is associated with states of satiety and social experience, which under stressful conditions is rewarding and beneficial for lifespan.

Gut microbes and food reward: From the gut to the brain

Inappropriate food intake behavior is one of the main drivers for fat mass development leading to obesity. Importantly the gut microbiota-mediated signals have emerged as key actors regulating food intake acting mainly on the hypothalamus, and thereby controlling hunger or satiety/satiation feelings. However, food intake is also controlled by the hedonic and reward systems leading to food intake based on pleasure (i.e., non-homeostatic control of food intake). This review focus on both the homeostatic and the non-homeostatic controls of food intake and the implication of the gut microbiota on the control of these systems. The gut-brain axis is involved in the communications between the gut microbes and the brain to modulate host food intake behaviors through systemic and nervous pathways. Therefore, here we describe several mediators of the gut-brain axis including gastrointestinal hormones, neurotransmitters, bioactive lipids as well as bacterial metabolites and compounds. The modulation of gut-brain axis by gut microbes is deeply addressed in the context of host food intake with a specific focus on hedonic feeding. Finally, we also discuss possible gut microbiota-based therapeutic approaches that could lead to potential clinical applications to restore food reward alterations. Therapeutic applications to tackle these dysregulations is of utmost importance since most of the available solutions to treat obesity present low success rate.

Psychosis in Parkinson's Disease: A Lesson from Genetics

Psychosis in Parkinson's disease (PDP) represents a common and debilitating condition that complicates Parkinson's disease (PD), mainly in the later stages. The spectrum of psychotic symptoms are heterogeneous, ranging from minor phenomena of mild illusions, passage hallucinations and sense of presence to severe psychosis consisting of visual hallucinations (and rarely, auditory and tactile or gustatory) and paranoid delusions. PDP is associated with increased caregiver stress, poorer quality of life for patients and carers, reduced survival and risk of institutionalization with a significant burden on the healthcare system. Although several risk factors for PDP development have been identified, such as aging, sleep disturbances, long history of PD, cognitive impairment, depression and visual disorders, the pathophysiology of psychosis in PD is complex and still insufficiently clarified. Additionally, several drugs used to treat PD can aggravate or even precipitate PDP. Herein, we reviewed and critically analyzed recent studies exploring the genetic architecture of psychosis in PD in order to further understand the pathophysiology of PDP, the risk factors as well as the most suitable therapeutic strategies.

Cell–Cell Communication Alterations via Intercellular Signaling Pathways in Substantia Nigra of Parkinson’s Disease

Parkinson’s disease (PD) is a neurodegenerative movement disorder characterized with dopaminergic neuron (DaN) loss within the substantia nigra (SN). Despite bulk studies focusing on intracellular mechanisms of PD inside DaNs, few studies have explored the pathogeneses outside DaNs, or between DaNs and other cells. Here, we set out to probe the implication of intercellular communication involving DaNs in the pathogeneses of PD at a systemic level with bioinformatics methods. We harvested three online published single-cell/single-nucleus transcriptomic sequencing (sc/snRNA-seq) datasets of human SN (GSE126838, GSE140231, and GSE157783) from the Gene Expression Omnibus (GEO) database, and integrated them with one of the latest integration algorithms called Harmony. We then applied CellChat, the latest cell–cell communication analytic algorithm, to our integrated dataset. We first found that the overall communication quantity was decreased while the overall communication strength was enhanced in PD sample compared with control sample. We then focused on the intercellular communication where DaNs are involved, and found that the communications between DaNs and other cell types via certain signaling pathways were selectively altered in PD, including some growth factors, neurotrophic factors, chemokines, etc. pathways. Our bioinformatics analysis showed that the alteration in intercellular communications involving DaNs might be a previously underestimated aspect of PD pathogeneses with novel translational potential.

Daidzein modulates cocaine-reinforcing effects and cue-induced cocaine reinstatement in CD-1 male mice

RATIONALE

Cocaine addiction is a chronic relapsing disorder that lacks of an effective treatment. Isoflavones are a family of compounds present in different plants and vegetables like soybeans that share a common chemical structure. Previous studies have described that synthetic derivatives from the natural isoflavone daidzin can modulate cocaine addiction, by a mechanism suggested to involve aldehyde-dehydrogenase (ALDH) activities.

OBJECTIVES

Based on these previous studies, we investigated the effects of three natural isoflavones, daidzin, daidzein, and genistein, on the modulation of the cocaine reinforcing effects and on cue-induced reinstatement in an operant mouse model of cocaine self-administration.

RESULTS

Chronic treatment with daidzein or genistein decreased operant responding to obtain cocaine intravenous infusions. On the other hand, daidzein and daidzin, but not genistein, were effective in decreasing cue-induced cocaine reinstatement. Complementary studies revealed that daidzein effects on cocaine reinforcement were mediated through a mechanism that involved dopamine type-2/3 receptors (DA-D2/3) activities.

CONCLUSIONS

Our results suggest that these natural compounds alone or in combination can be a potential therapeutic approach for cocaine addiction. Further clinical studies are required in order to ascertain their potential therapeutic use.

Regulation of dynamic pigment cell states at single-cell resolution

Cells bearing pigment have diverse roles and are often under strict evolutionary selection. Here, we explore the regulation of pigmented cells in the purple sea urchin Strongylocentrotus purpuratus, an emerging model for diverse pigment function. We took advantage of single cell RNA-seq (scRNAseq) technology and discovered that pigment cells in the embryo segregated into two distinct populations, a mitotic cluster and a post-mitotic cluster. Gcm is essential for expression of several genes important for pigment function, but is only transiently expressed in these cells. We discovered unique genes expressed by pigment cells and test their expression with double fluorescence in situ hybridization. These genes include new members of the fmo family that are expressed selectively in pigment cells of the embryonic and in the coelomic cells of the adult - both cell-types having immune functions. Overall, this study identifies nodes of molecular intersection ripe for change by selective evolutionary pressures.

The potential role of cholecystokinin in schizophrenia: review and update

The role of the neuropeptide cholecystokinin in schizophrenia has been widely explored because of its modulating action on midbrain dopamine neurons. The recent discovery of more specific receptor subtype cholecystokinin antagonists should be considered as potential treatment for schizophrenia with fewer side effects. This paper reviews cholecystokinin/dopamine interactions in animal and human studies. Clinical trials with cholecystokinin agonists and antagonists in schizophrenia are updated.

Neurochemical Markers in the Mammalian Brain: Structure, Roles in Synaptic Communication, and Pharmacological Relevance

BACKGROUND

Knowledge of molecular marker (typically protein or mRNA) expression in neural systems can provide insight to the chemical blueprint of signal processing and transmission, assist in tracking developmental or pathological progressions, and yield key information regarding potential medicinal targets. These markers are particularly relevant in the mammalian brain in the light of its unsurpassed cellular diversity. Accordingly, molecular expression profiling is rapidly becoming a major approach to classify neuron types. Despite a profusion of research, however, the biological functions of molecular markers commonly used to distinguish neuron types remain incompletely understood. Furthermore, most molecular markers of mammalian neuron types are also present in other organs, therefore complicating considerations of their potential pharmacological interactions.

OBJECTIVE

Here, we survey 15 prominent neurochemical markers from five categories, namely membrane transporters, calcium-binding proteins, neuropeptides, receptors, and extracellular matrix proteins, explaining their relation and relevance to synaptic communication.

METHOD

For each marker, we summarize fundamental structural features, cellular functionality, distributions within and outside the brain, as well as known drug effectors and mechanisms of action.

CONCLUSION

This essential primer thus links together the cellular complexity of the brain, the chemical properties of key molecular players in neurotransmission, and possible biomedical opportunities.

Pain modulation from the brain during diabetic neuropathy: Uncovering the role of the rostroventromedial medulla

Diabetic neuropathy has a profound impact in the quality of life of patients who frequently complain of pain. The mechanisms underlying diabetic neuropathic pain (DNP) are no longer ascribed only to damage of peripheral nerves. The effects of diabetes at the central nervous system are currently considered causes of DPN. Management of DNP may be achieved by antidepressants that act on serotonin (5-HT) uptake, namely specific serotonin reuptake inhibitors. The rostroventromedial medulla (RVM) is a key pain control center involved in descending pain modulation at the spinal cord through local release of 5-HT and plays a peculiar role in the balance of bidirectional control (i.e. inhibitory and facilitatory) from the brain to the spinal cord. This review discusses recently uncovered neurobiological mechanisms that mediate nociceptive modulation from the RVM during diabetes installation. In early phases of the disease, facilitation of pain modulation from the RVM prevails through a triplet of mechanisms which include increase in serotonin expression at the RVM and consequent rise of serotonin levels at the spinal cord and upregulation of local facilitatory 5HT3 receptors, enhancement of spontaneous activity of facilitatory RVM neurons and up-regulation of the expression of transient receptor potential vanilloid type 1 (TRPV1) receptor. With the progression of diabetes the alterations in the RVM increase dramatically, with oxidative stress and neuronal death associated to microglia-mediated inflammation. In a manner similar to other central areas, like the thalamus, the RVM is likely to be a "pain generator/amplifier" during diabetes, accounting to increase DNP. Early interventions in DNP prevention using strategies that simultaneously tackle the exacerbation of 5-HT3 spinal receptors and of microglial RVM activity, namely those that increase the levels of anti-inflammatory cytokines, should be considered in the future of DNP treatment.

Multiplexed neurochemical signaling by neurons of the ventral tegmental area

The ventral tegmental area (VTA) is an evolutionarily conserved structure that has roles in reward-seeking, safety-seeking, learning, motivation, and neuropsychiatric disorders such as addiction and depression. The involvement of the VTA in these various behaviors and disorders is paralleled by its diverse signaling mechanisms. Here we review recent advances in our understanding of neuronal diversity in the VTA with a focus on cell phenotypes that participate in 'multiplexed' neurotransmission involving distinct signaling mechanisms. First, we describe the cellular diversity within the VTA, including neurons capable of transmitting dopamine, glutamate or GABA as well as neurons capable of multiplexing combinations of these neurotransmitters. Next, we describe the complex synaptic architecture used by VTA neurons in order to accommodate the transmission of multiple transmitters. We specifically cover recent findings showing that VTA multiplexed neurotransmission may be mediated by either the segregation of dopamine and glutamate into distinct microdomains within a single axon or by the integration of glutamate and GABA into a single axon terminal. In addition, we discuss our current understanding of the functional role that these multiplexed signaling pathways have in the lateral habenula and the nucleus accumbens. Finally, we consider the putative roles of VTA multiplexed neurotransmission in synaptic plasticity and discuss how changes in VTA multiplexed neurons may relate to various psychopathologies including drug addiction and depression.

Genetic substrates of psychosis in patients with Parkinson's disease: A critical review

Patients with Parkinson's disease (PD) may develop several non-motor symptoms such as psychosis, depression, cognitive impairment, autonomic disturbances and sleep disturbances. Psychosis is one of the common non-motor symptoms, which commonly manifests as visual hallucinations and minor hallucinations such as sense of passage and presence. Though long-term dopaminergic therapy, longer duration of PD and cognitive impairment have been described as risk factors for emergence of psychosis in PD, predicting psychosis in PD remains challenging. Multiple studies have explored the genetic basis of psychosis in PD by studying polymorphisms of several genes. Most of the studies have focused on apolipoprotein E polymorphism followed by polymorphisms in cholecystokinin (CCK) system, dopamine receptors and transporters, HOMER gene, serotonin, catechol-o-methyltransferase, angiotensin converting enzyme and tau. Other than the studies on polymorphisms of CCK, most of the studies have reported conflicting results regarding association with psychosis in PD. Three out of four studies on CCK polymorphism have reported significant association of -45C>T polymorphism with the presence of hallucinations. The discrepancies in the results across the studies reviewed are possibly due to racial differences as well as differences in the patient characteristics. This review critically analyzes the published studies on genetic polymorphisms in patients with PD and psychosis.

The role of antisecretory factor in pancreatic exocrine secretion: studies in vivo and in vitro

NEW FINDINGS

What is the central question of this study? Antisecretory factor, an endogenous protein detected in many tissues of the body, is known as an inhibitor of intestinal secretion, but its role in pancreatic exocrine secretory function has not yet been investigated. What is the main finding and its importance? In a rodent model, we show that antisecretory factor reduces pancreatic exocrine secretion, probably via its direct action on the pancreatic acini and via modulation of the enteropancreatic reflexes involving cholecystokinin and sensory nerves. Antisecretory factor (AF) regulates ion and water transport through the intestinal cell membrane. Antisecretory factor inhibits intestinal secretion, but its effect on the exocrine pancreas has not yet been shown. We investigated the effect of AF on pancreatic amylase secretion in vivo and in vitro using pancreatic acini isolated by collagenase digestion. For the in vivo study, Wistar rats were surgically equipped with silicone catheters, inserted into the pancreaticobiliary duct and into the duodenum. Capsaicin was used to deactivate the sensory nerves in turn to assess their involvement in the effects of AF on the exocrine pancreas. Antisecretory factor (1, 3 or 10 μg kg(-1) i.p.) was given in basal conditions or following stimulation of pancreatic secretion with diversion of pancreaticobiliary juice. For the in vitro study, rat pancreatic acini were incubated in the presence of increasing doses of AF (from 10(-8) to 10(-5)  m) alone or in combination with caerulein (10(-12)  m). Cytoplasmic cholecystokinin 1 (CCK1 ) receptor protein was detected by Western blot and immunoprecipitation studies. Antisecretory factor markedly reduced the output of pancreatic amylase both in basal conditions and when stimulated by diversion of pancreaticobiliary juice. Deactivation of the sensory nerves with capsaicin completely reversed the inhibitory effects of AF on the exocrine pancreas. Caerulein-induced enzyme secretion from the pancreatic acini was inhibited by AF, whereas basal secretion was unaffected. Administration of AF to the rats significantly diminished the synthesis of CCK1 receptor protein. We conclude that AF inhibits pancreatic exocrine secretion indirectly via sensory nerves and directly decreases amylase release from isolated pancreatic acini. The direct inhibitory action of AF on the exocrine pancreas could be related, at least in part, to a reduction of CCK1 receptors on pancreatic acinar cells.

An update on the connections of the ventral mesencephalic dopaminergic complex

This review covers the intrinsic organization and afferent and efferent connections of the midbrain dopaminergic complex, comprising the substantia nigra, ventral tegmental area and retrorubral field, which house, respectively, the A9, A10 and A8 groups of nigrostriatal, mesolimbic and mesocortical dopaminergic neurons. In addition, A10dc (dorsal, caudal) and A10rv (rostroventral) extensions into, respectively, the ventrolateral periaqueductal gray and supramammillary nucleus are discussed. Associated intrinsic and extrinsic connections of the midbrain dopaminergic complex that utilize gamma-aminobutyric acid (GABA), glutamate and neuropeptides and various co-expressed combinations of these compounds are considered in conjunction with the dopamine-containing systems. A framework is provided for understanding the organization of massive afferent systems descending and ascending to the midbrain dopaminergic complex from the telencephalon and brainstem, respectively. Within the context of this framework, the basal ganglia direct and indirect output pathways are treated in some detail. Findings from rodent brain are briefly compared with those from primates, including humans. Recent literature is emphasized, including traditional experimental neuroanatomical and modern gene transfer and optogenetic studies. An attempt was made to provide sufficient background and cite a representative sampling of earlier primary papers and reviews so that people new to the field may find this to be a relatively comprehensive treatment of the subject.

The role of cholecystokinin in the induction of aggressive behavior: a focus on the available experimental data (review)

Cholecystokinin (CCK) is a neuropeptide that is (among others) reportedly involved in the pathophysiology of psychiatric disorders. The excitatory role of CCK in negative affective emotions as well as in aversive reactions, antisocial behaviors and memories, has been indicated by numerous electrophysiological, neurochemical and behavioral methodologies on both animal models for anxiety and human studies. The current review article summarizes the existing experimental evidence with regards to the role of CCK in the induction of aggressive behavior, and: (a) synopsizes the anatomical circuits through which it could potentially mediate all types of aggressive behavior, as well as (b) highlights the potential use of these experimental evidence in the current research quest for the clinical treatment of mood and anxiety disorders.

Cholecystokinin A receptor (CCKAR) gene variation is associated with language lateralization

Schizophrenia is a psychiatric disorder associated with atypical handedness and language lateralization. However, the molecular mechanisms underlying these functional changes are still poorly understood. Therefore, the present study was aimed at investigating whether variation in schizophrenia-related genes modulates individual lateralization patterns. To this end, we genotyped 16 single nucleotide polymorphisms that have previously been linked to schizophrenia on a meta-analysis level in a sample of 444 genetically unrelated healthy participants and examined the association of these polymorphisms with handedness, footedness and language lateralization. We found a significant association of the cholecystokinin-A receptor (CCKAR) gene variation rs1800857 and language lateralization assessed using the dichotic listening task. Individuals carrying the schizophrenia risk allele C of this polymorphism showed a marked reduction of the typical left-hemispheric dominance for language processing. Since the cholecystokinin A receptor is involved in dopamine release in the central nervous system, these findings suggest that genetic variation in this receptor may modulate language lateralization due to its impact on dopaminergic pathways.

Isolation and expression of the Drosophila drosulfakinin neural peptide gene product, DSK-I

The Drosophila drosulfakinin (dsk) gene encodes the cholecystokinin homologues drosulfakinin-I (DSK-I) and drosulfakinin-II (DSK-II). The naturally occurring DSKI peptide was isolated from an extract of adult flies and its sequence determined by automated Edman degradation and sequence-specific radioimmunoassay. The dsk cDNA is expressed during the larval, pupal, and adult stages of development and is an abundant adult head transcript. Sequence-specific DSK antibodies localized DSK expression in the Drosophila larval central nervous system to medial neurosecretory cells and projections that extend from the neurons anteriorly into the brain and posteriorly down the ventral ganglion. The availability of the dsk transcript, sequence-specific DSK antibodies and the application of molecular genetics provide the opportunity to elucidate the role(s) of Drosophila CCK homologues in brain structure and function.

New thoughts on thought disorders in Parkinson's disease: review of current research strategies and challenges

Psychosis is a frequent nonmotor complication in Parkinson's disease (PD), characterized by a broad phenomenology and likely due to a variety of intrinsic (i.e., PD-related) and extrinsic factors. Safe and effective therapies are greatly needed as PD psychosis contributes significantly to morbidity, mortality, nursing home placement, and quality of life. Novel research strategies focused on understanding the pharmacology and pathophysiology of PD psychosis, utilizing translational research including animal models, genetics, and neuroimaging, and even looking beyond the dopamine system may further therapeutic advances. This review discusses new research strategies regarding the neurobiology and treatment of PD psychosis and several associated challenges.

Repeated administration of methamphetamine blocked cholecystokinin-octapeptide injection-induced c-fos mRNA expression without change in capsaicin-induced junD mRNA expression in rat cerebellum

In the cerebellum, there are numerous cholecystokinin (CCK-8)-containing fibers. Since systemic CCK-8 injection-induced anxiety (psychological stress) activates the locus coeruleus cells that send mossy fiber inputs to the cerebellum, we examined whether systemic CCK-8 injections activate the rat and mouse cerebellum. First, injections of CCK-8 were found to induce c-fos mRNA expression in a vague patchy pattern that is different from single methamphetamine-induced Zebrin band-like c-fos mRNA expression, suggesting that the CCK-8 activating mossy fibers induce gene expression differently from the dopamine-containing mossy fibers in the ventral tegmental area. Second, since CCK-8 facilitates neural activity of dopamine in the midbrain, we examined whether repeated methamphetamine administration that induced behavioral sensitization had similar effects on the cerebellar CCK system. Repeated administration of methamphetamine suppressed the CCK-8-induced c-fos mRNA expression in the rat cerebellum. Third, capsaicin injections (physical stress) into a hind limb of the rat increased junD mRNA expression with no effect on c-fos mRNA expression, and repeated methamphetamine injections had no effect on the capsaicin-induced expression of junD mRNA. Fourth, either single injection of methamphetamine or CCK-8 to mice increased c-fos mRNA expression in the locus coeruleus, and so noradrenalin, but not dopamine, might interact with CCK-8-activating system. However, we considered the possibility unlikely. Thus, we conclude that repeated methamphetamine administration though dopamine selectively inhibits the c-fos mRNA expression after CCK-8 injection in the cerebellum.

Altered orosensory sensitivity to oils in CCK-1 receptor deficient rats

CCK-1 receptor deficient Otsuka Long Evans Tokushima Fatty (OLETF) rats are hyperphagic, which leads to subsequent obesity and diabetes. Additionally, they have increased sham intake and enhanced preference for sucrose solutions relative to control, Long Evans Tokushima Otsuka (LETO) rats. To determine the effects of oil on ingestion, we first measured real feeding of various concentrations of oil emulsions (12.5, 25, 50, 75, and 100%) in rats that were fed ad libitum. Secondly, to isolate the orosensory compontent of oils from post-ingestive consequences, as well as determine the contribution of energy status, we measured sham feeding in OLETF and LETO rats using one-bottle acceptance tests while non-deprived and overnight food deprived. Finally, to assess the orosensory effects of nutritive and non-nutritive oils, we used two-bottle preference tests in sham fed OLETF and LETO rats. We found that real feeding resulted in increased intake of high oil concentrations for OLETF rats relative to LETO rats. Similarly, OLETF rats consumed significantly more of higher concentration corn oils than LETO while non-deprived sham feeding. Conversely, OLETF rats overconsumed low concentration corn oil compared to LETO during overnight deprived sham-feeding tests. In two-bottle sham-feeding preference tests, both non-deprived OLETF and LETO rats preferred corn to mineral oil. Collectively, these results show that increased oil intake in OLETF rats is driven by both peripheral deficits to satiation and altered orosensory sensitivity.

The production and role of gastrin-17 and gastrin-17-gly in gastrointestinal cancers

The gastrointestinal peptide hormone gastrin is responsible for initiating the release of gastric acid in the stomach in response to the presence of food and/or humoral factors such as gastrin releasing peptide. However, it has a role in the growth and maintenance of the gastric epithelium, and has been implicated in the formation and growth of gastric cancers. Hypergastrinemia resulting from atrophic gastritis and pernicious anemia leads to hyperplasia and carcinoid formation in rats, and contributes to tumor formation in humans. Additionally, gastrin has been suspected to play a role in the formation and growth of cancers of the colon, but recent studies have instead implicated gastrin processing intermediates, such as gastrin-17-Gly, acting upon a putative, non-cholecystokinin receptor. This review summarizes the production and chemical structures of gastrin and of the processing intermediate gastrin-17-Gly, as well as their activities in the gastrointestinal tract, particularly the promotion of colon cancers.

Gastrin, cholecystokinin and gastrointestinal tract functions in mammals

The aim of the present review is to synthesise and summarise our recent knowledge on the involvement of cholecystokinin (CCK) and gastrin peptides and their receptors in the control of digestive functions and more generally their role in the field of nutrition in mammals. First, we examined the release of these peptides from the gut, focusing on their molecular forms, the factors regulating their release and the signalling pathways mediating their effects. Second, general physiological effects of CCK and gastrin peptides are described with regard to their specific receptors and the role of CCK on vagal mucosal afferent nerve activities. Local effects of CCK and gastrin in the gut are also reported, including gut development, gastrointestinal motility and control of pancreatic functions through vagal afferent pathways, including NO. Third, some examples of the intervention of the CCK and gastrin peptides are exposed in diseases, taking into account intervention of the classical receptor subtypes (CCK1 and CCK2 receptors) and their heterodimerisation as well as CCK-C receptor subtype. Finally, applications and future challenges are suggested in the nutritional field (performances) and in therapy with regards to the molecular forms or in relation with the type of receptor as well as new techniques to be utilised in detection or in therapy of disease. In conclusion, the present review underlines recent developments in this field: CCK and gastrin peptides and their receptors are the key factor of nutritional aspects; a better understanding of the mechanisms involved may increase the efficiency of the nutritional functions and the treatment of abnormalities under pathological conditions.

Phenotype, compartmental organization and differential vulnerability of nigral dopaminergic neurons

The degeneration of nigral dopaminergic (DA-) neurons is the histopathologic hallmark of Parkinson's disease (PD), but not all nigral DA-cells show the same susceptibility to degeneration. This starts in DA-cells in the ventrolateral and caudal regions of the susbtantia nigra (SN) and progresses to DA-cells in the dorsomedial and rostral regions of the SN and the ventral tegmental area, where many neurons remain intact until the final stages of the disease. This fact indicates a relationship between the topographic distribution of midbrain DA-cells and their differential vulnerability, and the possibility that this differential vulnerability is associated with phenotypic differences between different subpopulations of nigral DA-cells. Studies carried out during the last two decades have contributed to establishing the existence of different compartments of nigral DA-cells according to their neurochemical profile, and a possible relationship between the expression of some factors and the relative vulnerability or resistance of DA-cell subpopulations to degeneration. These aspects are reviewed and discussed here.

Association study between the cholecystokinin A receptor gene and schizophrenia in the Japanese population

Cholecystokinin A receptor (CCK-AR) has been implicated in the pathophysiology of schizophrenia through its mediation of dopamine-release in the central nervous system. Several studies have observed the association between the CCK-AR gene and schizophrenia. Especially, the association has been repeatedly observed between the 779T/C polymorphism and auditory hallucinations or positive symptoms of schizophrenia. In this study, we investigated the association between the 779T/C polymorphism of the CCK-AR gene and schizophrenia in 290 Japanese patients with schizophrenia and 290 controls. As a result, no significant difference was observed in genotypic distributions or allelic frequencies between the patients and controls, although there was a trend for the association between the C allele of the polymorphism and hallucination (P=0.024) or hallucinatory-paranoid state (P=0.049). In conclusion, the present results may not provide evidence for the association between the CCK-AR gene and schizophrenia in the Japanese population.

Altered emotional behaviors in the diabetes mellitus OLETF type 1 congenic rat

GPR10 is a G-protein-coupled receptor expressed in thalamic and hypothalamic brain regions, including the reticular thalamic nucleus (RTN) and periventricular nucleus (Pev), and the endogenous ligand for this receptor, prolactin-releasing peptide (PrRP), has demonstrated regulatory effects on the stress response. We produced a congenic rat by introducing the Dmo1 allele from the OLETF rat which encodes the amino acid sequences of GPR10 with a truncated NH2-terminus, into the Brown-Norway background. Using receptor autoradiography, we determined a lack of specific [125I]PrRP binding in the RTN and Pev of these mutant rats compared to the control rats. Furthermore, intracerebroventricular injection of PrRP did not induce a significant increase of c-fos-like immunoreactivity in the paraventricular nucleus of the mutant rats compared to the control rats. The mutant rats also displayed a less anxious-like phenotype in three behavioral-based models of anxiety-like behavior (open field, elevated plus maze and defensive withdrawal test). These data show the mutant congenic rat, of which GPR10 neither binds nor responds to PrRP, expresses less anxious-like phenotypes. On the basis of these observations, the GPR10 might be a novel target for the developing new drugs against anxiety and/or other stress-related diseases.

Dopamine D2 receptors contribute to increased avidity for sucrose in obese rats lacking CCK-1 receptors

Accumulating evidence has indicated a link between dopamine signaling and obesity in both animals and humans. We have recently demonstrated heightened avidity to sapid sweet solutions in the obese cholecystokinin (CCK)-1 receptor deficient Otsuka Long Evans Tokushima fatty (OLETF) rat. To investigate the dopamine dependence and the respective contribution of D1 and D2 receptor subtypes in this phenomenon, real and sham intake of 0.3 M sucrose solution was compared between prediabetic, obese OLETF and age-matched lean Long-Evans Tokushima Otsuka (LETO) cohorts following peripheral (i.p.) administration of equimolar doses (50-800 nmol/kg) of the D1 (R-(+) 7-chloro-8-hydroxy-3-methyl-1-phenyl-2,3,4,5-tetrahydro-1H-3-benzazepine, SCH23390) and D2 (raclopride) selective receptor antagonists. Both antagonists were potent in reducing sucrose intake in both strains with both drugs suppressing sham intake starting at lower doses than real intake (200 nmol/kg vs. 400 nmol/kg for SCH23390, and 400 nmol/kg vs. 600 nmol/kg for raclopride, respectively). Furthermore, when percent suppression of intake, a measure that controlled for the higher baseline sucrose intake by obese rats was analyzed, OLETF rats expressed an increased sensitivity to raclopride in reducing ingestion of sucrose with a 1.7- and 2.9-fold lower inhibitory dose threshold (ID50) for real and sham intake conditions, respectively, compared with LETO controls. In contrast, SCH23390 caused no differential strain effect with respect to dosage whether sucrose was real or sham fed. These findings demonstrate that D2 receptors are involved in heightened increased consumption of sucrose observed in the OLETF obese rat.

Diurnal and nocturnal nursing behavior in the OLETF rat

The Otsuka Long Evans Tokushima Fatty (OLETF) rat model of obesity has been recently found to develop hyperphagia and obesity early in life. Our goal was to investigate the dams' nursing behavior during the day and the night in order to elucidate their contribution to the pre-obesity of the pups. We examined nursing bout number, length, posture, initiative, nursing total time and frequency of other maternal behaviors over the three postpartum (PP) weeks. In the first week, OLETF dams nursed more during the day and presented more self-directed activities during the night. In the third PP week, OLETF dams displayed increased nursing time, bout number, nursing frequency, and supine postures at the beginning of the nursing episodes and less active self-directed behaviors, both day and night, while OLETF pups displayed more initiative in starting nursing bouts. The results suggest a circadian difference in nursing behavior and self-directed activities between the strains on PP week 1 and a strong influence of the OLETF pups on the nursing behavior of the dam on PP week 3, which contributes to their obese features.

Altered basal and stimulated accumbens dopamine release in obese OLETF rats as a function of age and diabetic status

The Otsuka Long-Evans Tokushima Fatty (OLETF) rat lacking the CCK-1 receptor is hyperphagic, prefers palatable and high-calorie meals, and gradually develops obesity and type 2 diabetes. To determine dopamine levels in this strain, we used in vivo quantitative (no net flux) microdialysis at three different ages representing nondiabetic (8 wk), prediabetic (18 wk), and diabetic (56 wk) stages in OLETF and age-matched lean Long-Evans Tokushima Otsuka (LETO) controls. Results showed significantly elevated basal dopamine levels in the caudomedial nucleus accumbens of OLETF rats compared with LETO at younger ages (8 wk: 20.10 +/- 5.61 nM vs. 15.85 +/- 5.63 nM; 18 wk: 7.37 +/- 3.71 nM vs. 4.75 +/- 1.25 nM, means +/- SD). In contrast, at 56 wk of age, a profound decline in extracellular dopamine concentrations was seen in both strains with a tendency for a greater effect in OLETF rats (1.78 +/- 0.40 nM vs. 2.39 +/- 0.42 nM). Further, extracellular fraction, an index for reuptake, was higher in 56-wk-old OLETF compared with LETO (0.648 +/- 0.049 vs. 0.526 +/- 0.057). Potassium-stimulated dopamine efflux revealed an increased capacity of vesicular pool in OLETF rats compared with LETO across all age groups with an accentuated strain difference at 56 wk. These findings demonstrate altered striatal dopamine functions (i.e., increased stimulated release and uptake) in obese OLETF rat. This could be due to the lack of functional CCK-1 receptors, or metabolic and hormonal factors associated with the development of obesity and insulin resistance, or both.

Conditioned preference for sweet stimuli in OLETF rat: effects of food deprivation

The Otsuka Long-Evans Tokushima Fatty (OLETF) rat, an outbred strain of Long- Evans Tokushima Otsuka rat (LETO) that lacks CCK-1 receptor expression, is hyperphagic and develops obesity and type-2 diabetes. The present study sought to assess how OLETF rats alter intake, preference, and conditioned preference of palatable solutions after acute food deprivation. Our results show that after 24 h chow restriction, LETO rats increase both sucrose intake and two-bottle sucrose preference relative to their free-fed baseline, whereas OLETF rats do not increase sucrose intake (0.3 M or 1.0 M sucrose) or preference (1.0 M vs. 0.3 M sucrose) when they are food deprived. In contrast, OLETF rats exhibit a higher conditioned flavor preference when sucrose is used as unconditioned stimulus (US) relative to LETO rats, whether overnight food restricted (81% vs. 71% for OLETF and LETO rats, respectively) or free fed (82% vs. 54% for OLETF and LETO rats, respectively) during the test. When a noncaloric saccharin solution is used as US, OLETF rats show a higher preference for the saccharin-associated flavor relative to LETO rats when nondeprived (76% vs. 58% for OLETF and LETO rats, respectively); however, neither strain shows differential conditioned flavor preference for saccharin in the deprivation state during the test. These findings suggest that OLETF rats fail to integrate postabsorptive and orosensory effects of sucrose in a conditioning setting to influence intake. Thus, it appears that OLETF rats form preferences for sucrose based largely on orosensory and hedonic properties of the solution, rather than caloric value.

Cholecystokinin hyperresponsiveness in functional dyspepsia

Functional dyspepsia (FD) is a common disorder of yet uncertain etiology. Dyspeptic symptoms are usually meal related and suggest an association to gastrointestinal (GI) sensorimotor dysfunction. Cholecystokinin (CCK) is an established brain-gut peptide that plays an important regulatory role in gastrointestinal function. It inhibits gastric motility and emptying via a capsaicin sensitive vagal pathway. The effects on emptying are via its action on the proximal stomach and pylorus. CCK is also involved in the regulation of food intake. It is released in the gut in response to a meal and acts via vagal afferents to induce satiety. Furthermore CCK has also been shown to be involved in the pathogenesis of panic disorder, anxiety and pain. Other neurotransmitters such as serotonin and noradrenaline may be implicated with CCK in the coordination of GI activity. In addition, intravenous administration of CCK has been observed to reproduce the symptoms in FD and this effect can be blocked both by atropine and loxiglumide (CCK-A antagonist). It is possible that an altered response to CCK may be responsible for the commonly observed gastric sensorimotor dysfunction, which may then be associated with the genesis of dyspeptic symptoms.

Disturbance of Response to Acute Thermal Pain in Naturally Occurring Cholecystokinin-A Receptor Gene Knockout Otsuka Long-Evans Tokushima Fatty (OLETF) Rats

Otsuka Long-Evans Tokushima Fatty (OLETF) rats lack cholecystokinin-A receptor (CCK-AR) because of a genetic abnormality. We observed that body temperature homeostasis in response to changes in ambient temperature was deteriorated in OLETF rats, while the functions of the signal outputs from the hypothalamus to effectors were not impaired. Deteriorated homeostasis was also seen in CCK-AR deficient (-/-) mice. In the present study, we examined whether the sensory pathway involved in transmitting signals about temperature from the skin to the brain was impaired in OLETF rats. To elucidate the involvement of CCK-AR function, we conducted the same experiment in CCK-AR(-/-) mice. Responses to thermal pain were assessed using the Hargreaves' plantar test apparatus. Shortening of withdrawal latency was observed in OLETF rats compared to control rats, indicating thermal hyperalgesia. Behavioral responses following paw withdrawal were disturbed in OLETF rats. The 5-hydroxytryptamine (5-HT) and 5-hydroxyindole acetic acid contents in the hippocampus and frontal cortex of OLETF rats were significantly higher than in those of the controls. CCK-AR(-/-) mice did not show any differences from wild-type mice. In conclusion, OLETF rats showed thermal hyperalgesia and disturbed responses to thermal pain, and an alteration of 5-HT function might have a role in this disturbance.

Overeating after restraint stress in cholecystokinin-a receptor-deficient mice

In mammals, including humans, a brain-gut hormone, cholecystokinin (CCK) mediates the satiety effect via CCK-A receptor (R). We generated CCK-AR gene-deficient (-/-) mice and found that the daily food intake, energy expenditure, and gastric emptying of a liquid meal did not change compared with those of wild-type mice. Because CCK-AR(-/-) mice show anxiolytic status, we examined the effects of restraint stress. Seven hours of restraint stress was found to significantly decrease both body weight and food intake during the subsequent 3 days in all tested animals. On the fourth day after restraint stress, the CCK-AR(-/-) mice showed a significantly higher level of daily food intake than prior to stress, and food intake recovered to prestress levels in the wild-type mice. Since peripheral CCK-AR has been known to mediate gastric emptying, both gastric emptying and gastric acid secretion were determined to examine the mechanism of overeating in CCK-AR(-/-) mice. Neither gastric emptying nor gastric acid secretion differed between CCK-AR(-/-) and wild-type mice on the fourth day after stress. In contrast, however, the contents of dopamine and its metabolites in the cerebral cortex of CCK-AR(-/-) mice were increased by stress, but were rather decreased in wild-type mice. Changes in 5-hydroxytryptamine (5-HT) and its metabolite 5HIAA did not differ between the genotypes. In conclusion, CCK-AR(-/-) mice showed overeating after restraint stress, and dopaminergic hyperfunction in the brain of these mice was observed. The present evidence suggests that the CCK-AR function, possibly via altering the dopaminergic function, might be involved in overeating after stress.

Brief intermittent access to sucrose differentially modulates prepulse inhibition and acoustic startle response in obese CCK-1 receptor deficient rats

Otsuka Long-Evans Tokushima Fatty (OLETF) rats lack the CCK-1 receptor and are hyperphagic and obese. CCK-1 receptors play a role in prepulse inhibition (PPI) by modulating mesolimbic dopamine transmission, a modulator of sensorimotor gating. Therefore, the present study assessed the effects of brief, daily sucrose access on PPI and acoustic startle response (ASR) in OLETF rat and age-matched non-mutant Long-Evans Tokushima Otsuka (LETO) rats. The results revealed that OLETF rats with sucrose access showed an increased ASR [F(1,16) = 6.84; P < 0.01)], relative to sucrose receiving LETO rats. No significant sucrose effect (P = 0.283) on PPI was noted in OLETF rats, whereas sucrose receiving LETO rats had a significantly lower (P < 0.05) PPI percentage than non-sucrose controls. In contrast, sucrose-receiving OLETF rats expressed significantly higher PPI percentage than LETO rats with identical sucrose presentation (P < 0.01). Taken together, these results suggest that sucrose access alters PPI and ASR in general, and the CCK-1 receptors play a modulatory role in facilitating or inhibiting these responses, respectively. A similar effect may be contributory to the hyperphagic behavioral phenotype of obese animal models with altered central dopamine regulation.

Independent ingestion and microstructure of feeding patterns in infant rats lacking CCK-1 receptors

Otsuka Long-Evans Tokushima fatty (OLETF) rats are a strain of Long-Evans Tokushima Otsuka (LETO) rats that do not express CCK-1 receptors, developing in adulthood, hyperphagia, obesity, and non-insulin-dependent diabetes mellitus (NIDDM). We examined weight gain and meal patterns during a 30-min independent ingestion test on postnatal days 2-4 and again on days 9-11 in OLETF and LETO rat pups. OLETF pups were significantly heavier compared with their LETO controls at both ages, and they consumed significantly more of the sweet milk diet. The difference in intake can be attributed to a significant increase in meal size and duration. Number of clusters and bursts of licking within a meal were greater in OLETF rat pups, with no difference between strains in burst and cluster size. Interlick interval (ILI) was not significantly different between OLETF and LETO pups. This measure decreased on days 9-11 compared with days 2-4 in both strains. Latency to start feeding was significantly shorter on days 2-4 in OLETF vs. LETO pups, but this difference disappeared at the second test at the older age. Two- to four-day-old OLETF pups consumed a larger volume of milk during the first minute of feeding, and their initial lick rate and decay of lick rate were significantly larger compared with their LETO controls. Lack of CCK-1 receptors, or other OLETF-related abnormalities, therefore, resulted in a satiation deficit, leading to increased meal size, hyperphagia, and increased weight gain as early as 2-4 postnatal days.

Laparophobia: a cognitive perspective on appetite control in anorexia nervosa

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

Cholecystokinin-A receptor antagonists: therapies for gastrointestinal disorders

Cholecystokinin (CCK) is a peptide that exerts several regulatory functions in the periphery, as well as in the brain. The biological functions attributed to CCK are mediated by two receptor subtypes, termed CCKA and CCKB, located predominantly in the gastrointestinal (GI) tract and in the brain, respectively. Several selective and potent non-petide CCKA receptor antagonists have been synthesised and fully characterised in preclinical studies. A few of them have been, and continue to be tested in humans. This paper focuses on the data available on the effect of CCKA receptor antagonist administration in humans, and shows how, in addition to allowing a more exact definition of the role of CCK in the regulation of some GI functions, these drugs may also possess therapeutic potential in GI disorders.

Different pathways mediated by CCK1 and CCK2 receptors: effect of intraperitonal mrna antisense oligodeoxynucleotides to cholecystokinin on anxiety-like and learning behaviors in rats

Cholecystokinin (CCK) and its analogs generate anxiety in humans and measurable anxiety-like behaviors in rats. CCK receptor blockers have been reported to have variable effects in the treatment of anxiety disorders. In a prior study, intracerebroventricular administration of CCK-antisense oligodeoxynucleotides (ASODN) for 3 days significantly diminished anxiety-like behavior in rats. Counter to our expectations, intraperitoneal (i.p.) administration of CCK-ASODN significantly increased anxiety-like behavior and impaired retention performance in the Morris water maze. The aim of the present study was to manipulate CCK-mediated anxiety-like behavior and spatial memory in rats by peripheral (i.p.) administration of ASODN to preproCCK in the presence of antagonists to CCK1 and CCK2 receptor subtypes to further elucidate the roles of these two receptors and better understand the effects of i.p. CCK-ASODN. CCK-ASODN was injected i.p. to rats five times at 24-hr intervals with and without administration of CCK1R antagonist PD135158 or CCK2 antagonist benzotrip. Control groups received injections of either a scrambled oligodeoxynucleotide (ScrODN) or vehicle. On Day 6, the rats were assessed in the elevated plus maze paradigm and in the Morris water maze. The rats were sacrificed and their blood was assessed for corticosterone, ACTH, and prolactin levels. The results show that i.p. CCK-ASODN significantly increased anxiety-like behavior and impaired retention performance in the Morris water maze, compared to both control groups, accompanied by increased plasma corticosterone and plasma ACTH concentrations. In contrast, administration of CCK-ASODN together with CCK2R antagonist, but not with CCK1R antagonist, significantly decreased anxiety-like behavior in rats, but still impaired retention performance in the Morris water maze paradigm. Lower levels of plasma corticosterone and ACTH in CCK-ASODN+CCK2R antagonist-treated rats accompanied the reduced anxiety-like behavior. The present study showed an anxiolytic effect of i.p. CCK-ASODN in the presence of CCK2R, but not CCK1R.

Differences in ethanol ingestion between cholecystokinin-A receptor deficient and -B receptor deficient mice

AIMS

Cholecystokinin (CCK) modulates dopamine release in the nucleus accumbens through the CCK-A receptor (CCK-AR). The dopaminergic neurotransmission between the ventral tegmental area and the limbic forebrain is a critical neurobiological component of alcohol and drug self-administration. Based on the evidence of interaction between CCK and dopamine, we had found previously that the CCK-AR gene -81A/G polymorphism was associated with alcohol dependence. Since the precise mechanism underlying this association has not been elucidated, the role of CCK-AR in ethanol ingestion was examined using CCK-AR gene deficient (-/-) mice and compared with those of CCK-BR(-/-) and wild-type mice.

METHODS

The two-bottle choice protocol was conducted and the righting reflex was examined in these three genotypes. Furthermore, the protein level of dopamine 2 receptor (D2R) in the nucleus accumbens was determined by western blotting.

RESULTS

CCK-AR(-/-) mice consumed more ethanol than CCK-BR(-/-) and wild-type mice, and showed no aversion to high concentrations of ethanol solution. However, the difference was actually in the total fluid consumption and alcohol preference remained unchanged, indicating that the differences were not specific to alcohol. Behavioral sensitivity to ethanol, examined using the righting reflex, did not differ significantly between the groups. D2R expression in the nucleus accumbens was significantly lower in the CCK-BR(-/-) mice and was significantly higher in CCK-AR(-/-) mice than in wild-type mice.

CONCLUSIONS

Voluntary ingestion of ethanol differed between CCK-AR(-/-) and CCK-BR(-/-) mice. The difference might be attributable in part to the different levels of D2R expression in the nucleus accumbens.

Serotonergic and dopaminergic systems in anorexia nervosa: a role for atypical antipsychotics?

OBJECTIVE

To review serotonergic and dopaminergic system function in anorexia nervosa in terms of potential modulation by atypical antipsychotic medications.

METHOD

A systematic review of clinical, neurobiological and functional neuroimaging findings of serotonergic and dopaminergic system activity in anorexia nervosa was conducted via MEDLINE, PsycINFO and EMBASE psychiatry databases, with a critical review of dysregulation of these systems as therapeutic targets for atypical antipsychotics, in context of evidence regarding the utility and efficacy of these medications in this syndrome.

RESULTS

There is evidence of persistently altered serotonergic and dopaminergic function in anorexia nervosa independent to weight-recovery. Case reports, open-label and single-blinded studies, albeit sparse, suggest that atypical antipsychotics may be beneficial in the management of anorexia nervosa psychopathology beyond weight gain.

CONCLUSIONS

Double-blind placebo controlled studies of atypical antipsychotics in anorexia nervosa with well defined outcome measures are required.

Serotonergic and dopaminergic systems in anorexia nervosa: a role for atypical antipsychotics?

OBJECTIVE

To review serotonergic and dopaminergic system function in anorexia nervosa in terms of potential modulation by atypical antipsychotic medications.

METHOD

A systematic review of clinical, neurobiological and functional neuroimaging findings of serotonergic and dopaminergic system activity in anorexia nervosa was conducted via MEDLINE, PsycINFO and EMBASE psychiatry databases, with a critical review of dysregulation of these systems as therapeutic targets for atypical antipsychotics, in context of evidence regarding the utility and efficacy of these medications in this syndrome.

RESULTS

There is evidence of persistently altered serotonergic and dopaminergic function in anorexia nervosa independent to weight-recovery. Case reports, open-label and single-blinded studies, albeit sparse, suggest that atypical antipsychotics may be beneficial in the management of anorexia nervosa psychopathology beyond weight gain.

CONCLUSIONS

Double-blind placebo controlled studies of atypical antipsychotics in anorexia nervosa with well defined outcome measures are required.

Cholecystokinin (CCK) and the CCKA receptor gene polymorphism, and smoking behavior

We analyzed genetic variants of the promoter region of the cholecystokinin (CCK; which modulates the release of dopamine) gene, and intron 1 and exon 5 of the CCKA receptor gene, and performed association analyses of nicotine dependence using an allele-specific amplification (ASA) method and PCR-RFLP methods. There was a significant difference between the current smoking and nonsmoking groups in the allele frequency of the CCK-45C/T polymorphism. However, there was no significant difference in the CCKA PstI polymorphism, and the HincII polymorphism was not detected in our study. Our data suggest that polymorphisms of the CCK gene may be one of the risk factors for smoking behavior.

Increased oral and decreased intestinal sensitivity to sucrose in obese, prediabetic CCK-A receptor-deficient OLETF rats

CCK-A receptor-deficient Otsuka Long-Evans Tokushima fatty (OLETF) rats are hyperphagic and develop obesity and Type 2 diabetes. In this strain, taste preference functions have not been investigated. Therefore, a series of short-access, two-bottle tests were performed in age-matched prediabetic OLETF and nonmutant Long-Evans Tokushima Otsuka (LETO) rats to investigate preference for sucrose (0.03, 0.1, 0.3, or 1.0 M) presented with a choice of water. To discern orosensory from postgastric factors that may contribute to this preference, in a separate experiment, rats were allowed to sham feed sucrose in the absence or presence of duodenal sucrose infusion (0.3, 0.6, or 1.0 M). In the two-bottle real-feeding tests, OLETF rats exhibited a greater preference for 0.3 M sucrose (91.2 +/- 1.7 and 78.5 +/- 3.4% for OLETF and LETO, respectively; P < 0.01) and 1.0 M sucrose (65.3 +/- 1.2 and 57.5 +/- 2.7% for OLETF and LETO, respectively; P < 0.05) than LETO rats. OLETF rats also sham fed less of the lowest (0.03 M; 33.8 +/- 4.8 and 58.3 +/- 7.3 ml for OLETF and LETO, respectively; P < 0.05) and more of the highest (1.0 M; 109.9 +/- 6.5 and 81.0 +/- 3.9 ml for OLETF and LETO, respectively; P < 0.01) concentration of sucrose relative to LETO rats. Finally, intraduodenal sucrose infusions (0.6 and 1.0 M) produced a smaller reduction of 0.3 M sham sucrose intake [14.1 +/- 8.1 vs. 52.5 +/- 3.3 ml and 49.4 +/- 8.0 vs. 82.4 +/- 3.2 ml for 0.6 M (P < 0.01) and 1.0 M (P < 0.05) infusions in OLETF and LETO, respectively]. These findings demonstrate that OLETF rats display an increased preference for sucrose, an effect that is at least partially influenced by the orosensory stimulating effect of sucrose. This enhanced responsiveness to oral stimulation, coupled with the deficit in responding to the postingestive feedback of intestinal sucrose, may contribute additively to the development of hyperphagia and weight gain in OLETF rats.

5-(Tryptophylamino)-1,3-dioxoperhydropyrido[1,2-c]pyrimidine-Based Cholecystokinin Receptor Antagonists: Reversal of CCK1 Receptor Subtype Selectivity toward CCK2 Receptors

With the aim of reversing selectivity or antagonist/agonist functionality in the 5-(tryptophylamino)-1,3-dioxoperhydropyrido[1,2-c]pyrimidine-derived potent and highly selective CCK(1) antagonists, a series of 4-benzyl and 4-methyl derivatives have been synthesized. Whereas the introduction of the benzyl group led, in all cases, to complete loss of the binding affinity, the incorporation of the methyl group gave a different result depending on the stereochemistry of the 1,3-dioxoperhydropyrido[1,2-c]pyrimidine scaffold. Thus, the introduction of the methyl group into the (4aS,5R)-diastereoisomers, giving a (4S)-configuration, produced a 3-fold increase in the CCK(1) binding potency and selectivity. However, the same structural manipulation in the opposite (4aR,5S)-stereochemistry, leading to a (4R,4aR,5S)-configuration, produced reversal of the selectivity for CCK(1) to the CCK(2) receptors. The replacement of the Boc group at the tryptophan moiety by a 2-adamantyloxycarbonyl group also contributed to that reversal. The resulting compounds displayed moderate CCK(2) antagonist activity in rat and human receptors, and a very small partial agonist effect on the production of inositol phosphate in COS-7 cells transfected with the wild-type human CCK(2) receptor.

Effect of CCK1 and CCK2 receptor blockade on amphetamine-stimulated exploratory behavior and sensitization to amphetamine

Interactions between dopaminergic neurotransmission and cholecystokinin (CCK) in the CNS may be important in the pathogenesis of psychotic disorders and substance abuse. In this study, the effect of coadministration of the selective CCK receptor antagonists devazepide and L-365,260 (for selectively blocking CCK1 and CCK2 receptors, respectively), on the effect of amphetamine on the rat exploratory behavior, and on sensitization of locomotor response to amphetamine, were studied. Amphetamine (0.5 mg/kg) increased exploratory activity in the exploration box for 5 consecutive testing days, while devazepide (10 microg/kg) blocked and L-365,260 (10 microg/kg) enhanced amphetamine-induced stimulation of activity. Devazepide coadministration prevented the development of sensitization to amphetamine, while coadministration of L-365,260 with amphetamine potentiated the locomotor effect of a challenge dose of amphetamine. These results suggest that endogenous CCK, released during exploratory activity, shapes behavioral responses to amphetamine by acting on both receptor subtypes, and modulates the development of sensitization to amphetamine.

Atypical behavioural responses to CCK-B receptor ligands in Fawn-Hooded rats

At present there is an increasing literature demonstrating heterogeneity of the CCK-B receptor. Recent reports by our laboratory have demonstrated that the Fawn-Hooded rat demonstrates atypical neurochemical responses to CCK4, in vitro. Since the ability of CCK-B receptor ligands to modulate affective state is dependent on the putative receptor subtype activated, the aim of the present study was to examine the behavioural effects of the CCK-B receptor agonist, t-boc-CCK4, and the CCK-B receptor antagonist, Ci-988 in Fawn-Hooded and Wistar Kyoto rats. Interestingly, both t-boc-CCK4 and Ci-988 produced an anxiolytic profile in FH rats as determined by an increased time spent on the open arms of an elevated plus maze, while both drugs were devoid of any behavioural effect in WKY rats, lending further support to the theory that the FH rat strain has an atypical relative proportion of these putative subtypes apparently resulting in a predominantly CCK-B2 receptor effect.

Cholecystokinin activates CCKB receptors to excite cells and depress EPSCs in the rat rostral nucleus accumbens in vitro

The peptide cholecystokinin (CCK) is abundant in the rat nucleus accumbens (NAc). Although it is colocalized with dopamine (DA) in afferent terminals in this region, neurochemical and behavioural reports are equally divided as to whether CCK enhances or diminishes DA's actions in this nucleus. To better understand the role of this peptide in the physiology of the NAc, we examined the effects of CCK on excitatory synaptic transmission and tested whether these are dependent on DA and/or other neuromodulators. Using whole-cell recording in rat forebrain slices containing the NAc, we show that sulphated CCK octapeptide (CCK-8S), the endogenously active neuropeptide, consistently depolarized cells and depressed evoked excitatory postsynaptic currents (EPSCs) in the rostral NAc. It caused a reversible, dose-dependent decrease in evoked EPSC amplitude that was accompanied by an increase in the decay constant of the EPSC but with no apparent change in paired pulse ratio. It was mimicked by unsulphated CCK-8 (CCK-8US), a CCK(B) receptor-selective agonist, and blocked by LY225910, a CCK(B) receptor-selective antagonist. Both CCK-8S and CCK-8US induced an inward current with a reversal potential around -90 mV that was accompanied by an increase in input resistance and action potential firing. The CCK-8S-induced EPSC depression was slightly reduced in the presence of SCH23390 but not in the presence of sulpiride or 8-cyclopentyltheophylline. By contrast, it was completely blocked by CGP55845, a potent GABA(B) receptor-selective antagonist. These results indicate that CCK excites NAc cells directly while depressing evoked EPSCs indirectly, mainly through the release of GABA.

Transient agonist-induced regulation of the cholecystokinin-A and cholecystokinin-B receptor mRNA levels in rat pancreatic acinar AR42J cells

BACKGROUND

CCK-8 and gastrin exert multiple effects in the gastrointestinal tract and the nervous system. Their actions are mediated via the G-protein coupled CCK-A and CCK-B receptors.

METHODS

Rat pancreatic acinar tumor AR42J cells express both CCK receptor subtypes. This cell line was used to characterize the agonist-dependent regulation of CCK-A and CCK-B receptor gene expression.

RESULTS

CCK-8 (10 nM) or gastrin (10 nM) reduced CCK-A receptor mRNA expression to 56% and 53%, respectively 2 h after hormonal exposure. In contrast, the level of CCK-B receptor gene expression was upregulated to 157% and 153%, respectively. These effects are most probably linked to the CCK-B receptor in AR42J cells. The phorbolester PMA (100 nM), a protein kinase C activator, downregulated CCK-A receptor expression but did not affect CCK-B receptor gene transcription. Activation of protein kinase A by forskolin (10 microM) or Bt(2)cAMP (100 microM) is not involved in the transient regulation of CCK receptor mRNA expression. Both elevated CCK-B and decreased CCK-A receptor mRNA expression returned to basal levels 6 h after continuous stimulation.

CONCLUSION

These results demonstrate that CCK-A and CCK-B receptor mRNA levels are differentially regulated by their agonists via distinct signal transduction mechanisms in AR42J cells.

Altered extracellular dopamine concentration in the brains of cholecystokinin-A receptor deficient rats

The gut-brain peptide cholecystokinin (CCK) has been implicated in the regulation of dopamine (DA) transmission in the brain. CCK agonists have been shown to modify baseline and stimulant-induced DA release in the brain via CCK-A mediated mechanisms. However, the role of endogenous CCK in regulating brain DA via CCK-A receptors has not been fully elucidated. Recently, a strain of rats (Otsuka Long Evans Tokushima Fatty (OLETF)), lacking the CCK-A receptor due to a genetic mutation, was discovered, providing a potentially useful tool to study the DA regulatory role of CCK-A receptors. In order to further clarify the role of CCK-A receptors in the regulation of central DA transmission, extracellular DA levels in the nucleus accumbens (NAC) and the caudate-putamen (CP) of OLETF rats, and their non-mutant counterparts, Long Evans Tokushimo Otsuka rats, was assessed by microdialysis at baseline and in response to cocaine (15 mg/kg) and amphetamine (0.5 mg/kg) administration. Baseline levels of extracellular DA were significantly elevated in the CP but not in the NAC of OLETF rats. In contrast, the NAC exhibited a greater DA response to cocaine (15 mg/kg) and amphetamine (0.5 mg/kg) in OLETF rats. This is the first direct evidence, of which we are aware, supporting altered DA regulation in OLETF rats. These findings suggest that CCK-A receptors play an important role in the regulation of central DA transmission, and support the notion that the OLETF rat is a useful model to study this regulation.