Linked polymorphisms (-333G>T and -286A>G) in the promoter region of the CCK-A receptor gene may be associated with schizophrenia

The Etiology of Auditory Hallucinations in Schizophrenia: From Multidimensional Levels

Enormous efforts have been made to unveil the etiology of auditory hallucinations (AHs), and multiple genetic and neural factors have already been shown to have their own roles. Previous studies have shown that AHs in schizophrenia vary from those in other disorders, suggesting that they have unique features and possibly distinguishable mechanisms worthy of further investigation. In this review, we intend to offer a comprehensive summary of current findings related to AHs in schizophrenia from aspects of genetics and transcriptome, neurophysiology (neurometabolic and electroencephalogram studies), and neuroimaging (structural and functional magnetic resonance imaging studies and transcriptome–neuroimaging association study). Main findings include gene polymorphisms, glutamate level change, electroencephalographic alterations, and abnormalities of white matter fasciculi, cortical structure, and cerebral activities, especially in multiple regions, including auditory and language networks. More solid and comparable research is needed to replicate and integrate ongoing findings from multidimensional levels.

The unappreciated roles of the cholecystokinin receptor CCK(1) in brain functioning

The CCK(1) receptor is a G-protein-coupled receptor activated by the sulfated forms of cholecystokinin (CCK), a gastrin-like peptide released in the gastrointestinal tract and mammal brain. A substantial body of research supports the hypothesis that CCK(1)r stimulates gallbladder contraction and pancreatic secretion in the gut, as well as satiety in brain. However, this receptor may also fulfill relevant roles in behavior, thanks to its widespread distribution in the brain. The strategic location of CCK(1)r in mesolimbic structures and specific hypothalamic and brainstem nuclei lead to complex interactions with neurotransmitters like dopamine, serotonin, and glutamate, as well as hypothalamic hormones and neuropeptides. The activity of CCK(1)r maintains adequate levels of dopamine and regulates the activity of serotonin neurons of raphe nuclei, which makes CCK(1)r an interesting therapeutic target for the development of adjuvant treatments for schizophrenia, drug addiction, and mood disorders. Unexplored functions of CCK(1)r, like the transmission of interoceptive sensitivity in addition to the regulation of hypothalamic hormones and neurotransmitters affecting emotional states, well-being, and attachment behaviors, may open exciting roads of research. The absence of specific ligands for the CCK(1) receptor has complicated the study of its distribution in brain so that research about its impact on behavior has been published sporadically over the last 30 years. The present review reunites all this body of evidence in a comprehensive way to summarize our knowledge about the actual role of CCK in the neurobiology of mental illness.

Semaphorin and plexin gene expression is altered in the prefrontal cortex of schizophrenia patients with and without auditory hallucinations

Auditory hallucinations (AH) are clinical hallmarks of schizophrenia, however little is known about molecular genetics of these symptoms. In this study, gene expression profiling of postmortem brain samples from prefrontal cortex of schizophrenic patients without AH (SNA), patients with AH (SA) and control subjects were compared. Genome-wide expression analysis was conducted using samples of three individuals of each group and the Affymetrix GeneChip Human-Gene 1.0 ST-Array. This analysis identified the Axon Guidance pathway as one of the most differentially expressed network among SNA, SA and CNT. To confirm the transcriptome results, mRNA level quantification of seventeen genes involved in this pathway was performed in a larger sample. PLXNB1, SEMA3A, SEMA4D and SEM6C were upregulated in SNA or SA patients compared to controls. PLXNA1 and SEMA3D showed down-regulation in their expression in the patient's samples, but differences remained statistically significant between the SNA patients and controls. Differences between SNA and SA were found in PLXNB1 expression which is decreased in SA patients. This study strengthens the contribution of brain plasticity in pathophysiology of schizophrenia and shows that non-hallucinatory patients present more alterations in frontal regions than patients with hallucinations concerning neural plasticity.

Association of single-nucleotide polymorphism of cholecystokinin receptor A gene with schizophrenia in an Eastern Indian population

CONTEXT

Cholecystokinin A receptor (CCK-AR) gene polymorphism is being increasingly reported in schizophrenia. It varies among different population groups but is associated with several complications of schizophrenia.

AIMS

The present study was undertaken to assess whether the CCK-AR polymorphism is stabilized and is more consistently associated with schizophrenia in an Eastern Indian sub-population.

SETTINGS AND DESIGN

It was carried out as a cross-sectional, observational, hospital-based study on 95 schizophrenia patients and 138 control subjects selected by the method of convenience.

MATERIALS AND METHODS

Single-nucleotide polymorphisms located in the regulatory region of the CCK-AR gene were assessed by restriction fragment length polymorphism (RFLP) in the polymerase chain reaction (PCR) amplified product of CCK-AR gene in study subjects. RFLP was done by the digestion of the PCR product by the restriction enzyme Pst-1 followed by gel electrophoresis.

STATISTICAL ANALYSIS

Assessment of the stability of C/T polymorphism in the study population was done by applying Hardy-Weinberg equilibrium rule. The significance of difference in the allelic distribution between case and controls was analyzed by Chi-square (χ(2)) test and odds ratio (OR) analysis.

RESULT

CCK-R polymorphism was in Hardy-Weinberg equilibrium in both groups. Distribution of the C allele of this gene was significantly higher in schizophrenia patients (χ(2) = 4.35, OR = 1.51; confidence interval at 95% =1.04-2.20).

CONCLUSION

C/T polymorphism of the CCK-R gene is a stable polymorphism in our study population. Moreover, the C allele is significantly more abundant in schizophrenia patients imparting them a greater risk of development of complications like auditory hallucination.

Meta-analyses of 10 polymorphisms associated with the risk of schizophrenia

Schizophrenia (SCZ) is a severe complex psychiatric disorder that generates problems for the associated family and society and causes disability with regards to work for patients. The aim of the present study was to assess the contribution of 10 genetic polymorphisms to SCZ susceptibility. Meta-analyses were conducted using the data without a limitation for time or language. A total of 27 studies with 7 genes and 10 polymorphisms were selected for the meta-analyses. Two polymorphisms were found to be significantly associated with SCZ. SNAP25 rs3746544 was shown to increase the SCZ risk by 18% [P=0.01; odds ratio (OR), 1.18; 95% confidence interval (CI), 1.05-1.34] and GRIK3 rs6691840 was found to increase the risk by 30% (P=0.008; OR, 1.30; 95% CI, 1.07-1.58). Significant results were found under the dominant (P=0.001; OR, 1.36; 95% CI, 1.13-1.65) and additive (P=0.02; OR, 1.45; 95% CI, 1.06-1.98) model for the SNAP25 rs3746544 polymorphism and under the additive model for the GRIK3 rs6691840 polymorphism (P=0.03; OR, 1.73; 95% CI, 1.04-2.85). There were no significant results observed for the other eight polymorphisms, which were CCKAR rs1800857, CHRNA7 rs904952, CHRNA7 rs6494223, CHRNA7 rs2337506, DBH Ins>Del, FEZ1 rs559668, FEZ1 rs597570 and GCLM rs2301022. In conclusion, the present meta-analyses indicated that the SNAP25 rs3746544 and GRIK3 rs6691840 polymorphisms were risk factors of SCZ, which may provide valuable information for the clinical diagnosis of SCZ.

Evaluating the links between schizophrenia and sleep and circadian rhythm disruption

Sleep and circadian rhythm disruption (SCRD) and schizophrenia are often co-morbid. Here, we propose that the co-morbidity of these disorders stems from the involvement of common brain mechanisms. We summarise recent clinical evidence that supports this hypothesis, including the observation that the treatment of SCRD leads to improvements in both the sleep quality and psychiatric symptoms of schizophrenia patients. Moreover, many SCRD-associated pathologies, such as impaired cognitive performance, are routinely observed in schizophrenia. We suggest that these associations can be explored at a mechanistic level by using animal models. Specifically, we predict that SCRD should be observed in schizophrenia-relevant mouse models. There is a rapidly accumulating body of evidence which supports this prediction, as summarised in this review. In light of these emerging data, we highlight other models which warrant investigation, and address the potential challenges associated with modelling schizophrenia and SCRD in rodents. Our view is that an understanding of the mechanistic overlap between SCRD and schizophrenia will ultimately lead to novel treatment approaches, which will not only ameliorate SCRD in schizophrenia patients, but also will improve their broader health problems and overall quality of life.

Investigation of allelic heterogeneity of the CCK-A receptor gene in paranoid schizophrenia

The cholecystokinin type A receptor (CCKAR) gene has been found to be associated with positive symptoms in patients with schizophrenia but the results reported to date are inconsistent. Considering the involvement of allelic heterogeneity in poor replication of the CCKAR finding, we genotyped five single nucleotide polymorphisms (SNPs) located in the 5' putative regulatory region of the CCKAR gene in a Chinese case-control sample and then applied the 5-SNP haplotype analysis to extract allelic heterogeneity information. The results showed that three individual haplotypes were strongly associated with increased risk of schizophrenia (corrected P = 2.9 × 10(-4), P = 2.5 × 10(-5), and P = 1.4 × 10(-5), respectively) and their combination gave an odds ratio (OR) of 6.12 with 95% CI 3.67-10.21 (P = 6.7 × 10(-15)). The haplotypes were also associated with some clinical symptoms including hallucination, suspiciousness, and hostility. Our work provided further evidence in support of the CCKAR hypothesis of schizophrenia and also suggested that haplotype-based association analysis may be a powerful approach for identification of allelic heterogeneity of a disease-underlying gene, which is very likely to be attributable to poor replication of an initial finding due to the reduction of sample power and the complexity of genetic architectures.

Peptide therapeutics for CNS indications

Neuropeptides play a crucial role in the normal function of the central nervous system and peptide receptors hold great promise as therapeutic targets for the treatment of several CNS disorders. In general, the development of peptide therapeutics has been limited by the lack of drug-like properties of peptides and this has made it very difficult to transform them into marketable therapeutic molecules. Some of these challenges include poor in vivo stability, poor solubility, incompatibility with oral administration, shelf stability, cost of manufacture. Recent technical advances have overcome many of these limitations and have led to rapid growth in the development of peptides for a wide range of therapeutic indications such as diabetes, cancer and pain. This review examines the therapeutic potential of peptide agonists for the treatment of major CNS disorders such as schizophrenia, anxiety, depression and autism. Both clinical and preclinical data has been accumulated supporting the potential utility of agonists at central neurotensin, cholecystokinin, neuropeptide Y and oxytocin receptors. Some of the successful approaches that have been developed to increase the stability and longevity of peptides in vivo and improve their delivery are also described and potential strategies for overcoming the major challenge that is unique to CNS therapeutics, penetration of the blood-brain barrier, are discussed.

Avoiding mouse traps in schizophrenia genetics: lessons and promises from current and emerging mouse models

Schizophrenia is one of the most common psychiatric disorders, but despite progress in identifying the genetic factors implicated in its development, the mechanisms underlying its etiology and pathogenesis remain poorly understood. Development of mouse models is critical for expanding our understanding of the causes of schizophrenia. However, translation of disease pathology into mouse models has proven to be challenging, primarily due to the complex genetic architecture of schizophrenia and the difficulties in the re-creation of susceptibility alleles in the mouse genome. In this review we highlight current research on models of major susceptibility loci and the information accrued from their analysis. We describe and compare the different approaches that are necessitated by diverse susceptibility alleles, and discuss their advantages and drawbacks. Finally, we discuss emerging mouse models, such as second-generation pathophysiology models based on innovative approaches that are facilitated by the information gathered from the current genetic mouse models.

A review of smoking behavior and smokers evidence (chemical modification, inducing nicotine metabolism, and individual variations by genotype: dopaminergic function and personality traits)

The nicotine metabolism of CYP2A6 (CYP2A6*1A,*1B, and *1C), and the cholecystokinin (CCK; which modulates the release of dopamine) and CCK-A receptor gene and personality traits for NEO-FFI, was investigated for the mechanism for elucidation of the smoking behavior in Japanese populations. The frequency of the CYP2A6*4C allele, which is a whole deleted allele of the human CYP2A6 gene, was higher, whereas that of CYP2A6*1A/*1B heterozygotes with higher nicotine metabolism activity was lower in nonsmokers than in smokers. There was also a significant difference between the current smoking and nonsmoking groups in the allele frequency of the CCK -45C/T polymorphism. It was also shown that the Openness (O) factor for smokers was significantly higher than that of nonsmokers; however, there were no significant differences in the Neuroticism (N), Extraversion (E), Agreeable (A), and Conscientiousness (C) scores among smokers than nonsmokers. It was suggested that the CYP2A6*4C allele may prevent the carrier from smoking, and being a CYP2A6*1A/*1B heterozygote and the CCK T allele may be risk factors for developing smoking behavior. Also, it is possible that persons with a low score in Openness may be refraining from smoking because they have a general negative impression toward smoking.

Association between CCK-AR gene and schizophrenia with auditory hallucinations

OBJECTIVE

Previous studies on a possible association between CCK-AR polymorphisms and schizophrenia have been controversial. The aim of the present study was to assess a potential association between schizophrenic patients with auditory hallucinations and polymorphisms of the CCK-AR gene.

METHODS

A set of single nucleotide polymorphisms mainly located in the regulatory region of the CCK-AR gene was analysed in a sample of 163 Diagnostic and statistical manual of mental disorders-IV-diagnosed schizophrenic patients and 162 healthy controls.

RESULTS

Significant differences in the genotype (P=0.011) and allele (P=0.0009) frequencies of the +121C/G SNP (located in the 5' regulatory region) were found between patients and controls. The excess of the C allele in the patient group remained significant after Bonferroni correction (P=0.03). However, functional in vitro assays, did not reveal significant differences on gene expression between +121G and +121C alleles of this SNP. Further investigations revealed two risk haplotypes: +121C/+978A/+984T (P=0.01) and +121C/+978T/+984C (P=0.0091) as well as a protective haplotype: +121G/+978T/+984T (P=0.0001).

CONCLUSION

Our data support a possible role of the CCK-AR gene in the vulnerability to schizophrenia in patients with auditory hallucinations, and suggest remarkable allele heterogeneity.

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.

Involvement of neuropeptide systems in schizophrenia: human studies

Neuropeptides are heterogeneously distributed throughout the digestive, circulatory, and nervous systems and serve as neurotransmitters, neuromodulators, and hormones. Neuropeptides are phylogenetically conserved and have been demonstrated to regulate numerous behaviors. They have been hypothesized to be pathologically involved in several psychiatric disorders, including schizophrenia. On the basis of preclinical data, numerous studies have sought to examine the role of neuropeptide systems in schizophrenia. This chapter reviews the clinical data, linking alterations in neuropeptide systems to the etiology, pathophysiology, and treatment of schizophrenia. Data for the following neuropeptide systems are included: arginine-vasopressin, cholecystokinin (CCK), corticotropin-releasing factor (CRF), interleukins, neuregulin 1 (NRG1), neurotensin (NT), neuropeptide Y (NPY), opioids, secretin, somatostatin, tachykinins, thyrotropin-releasing hormone (TRH), and vasoactive intestinal peptide (VIP). Data from cerebrospinal fluid (CSF), postmortem and genetic studies, as well as clinical trials are described. Despite the inherent difficulties associated with human studies (including small sample size, variable duration of illness, medication status, the presence of comorbid psychiatric disorders, and diagnostic heterogeneity), several findings are noteworthy. Postmortem studies support disease-related alterations in several neuropeptide systems in the frontal and temporal cortices. The strongest genetic evidence supporting a role for neuropeptides in schizophrenia are those studies linking polymorphisms in NRG1 and the CCKA receptor with schizophrenia. Finally, the only compounds that act directly on neuropeptide systems that have demonstrated therapeutic efficacy in schizophrenia are neurokinin receptor antagonists. Clearly, additional investigation into the role of neuropeptide systems in the etiology, pathophysiology, and treatment of schizophrenia is warranted.

Gene regulation by hypoxia and the neurodevelopmental origin of schizophrenia

Neurodevelopmental changes may underlie the brain dysfunction seen in schizophrenia. While advances have been made in our understanding of the genetics of schizophrenia, little is known about how non-genetic factors interact with genes for schizophrenia. The present analysis of genes potentially associated with schizophrenia is based on the observation that hypoxia prevails in the embryonic and fetal brain, and that interactions between neuronal genes, molecular regulators of hypoxia, such as hypoxia-inducible factor 1 (HIF-1), and intrinsic hypoxia occur in the developing brain and may create the conditions for complex changes in neurodevelopment. Consequently, we searched the literature for currently hypothesized candidate genes for susceptibility to schizophrenia that may be subject to ischemia-hypoxia regulation and/or associated with vascular expression. Genes were considered when at least two independent reports of a significant association with schizophrenia had appeared in the literature. The analysis showed that more than 50% of these genes, particularly AKT1, BDNF, CAPON, CCKAR, CHRNA7, CNR1, COMT, DNTBP1, GAD1, GRM3, IL10, MLC1, NOTCH4, NRG1, NR4A2/NURR1, PRODH, RELN, RGS4, RTN4/NOGO and TNF, are subject to regulation by hypoxia and/or are expressed in the vasculature. Future studies of genes proposed as candidates for susceptibility to schizophrenia should include their possible regulation by physiological or pathological hypoxia during development as well as their potential role in cerebral vascular function.

A possible association between the CCK-AR gene and persistent auditory hallucinations in schizophrenia

Recent studies have suggested that DNA variations in the CCK-AR gene might predispose individuals to schizophrenia and particularly to auditory hallucinations (AH). The aim of this study is to assess the association between AH, using a specific scale for AH in schizophrenia (PSYRATS), and the CCK-AR polymorphism at 779 in a Spanish sample. A total of 105 DSM-IV schizophrenic patients with AH and 93 unrelated controls were studied. Twenty-two patients were considered as persistent auditory hallucinators, which showed similar clinical and demographic characteristic than patients with episodic AH, but with the exception of the PSYRATS values. The persistent AH group showed an excess of the A1 allele when was compared with episodic or control groups. Our data support the possible role of the CCK-AR gene in the development of persistent AH in schizophrenic patients.

Involvement of endogenous CCK and CCK1 receptors in colonic motor function

Cholecystokinin (CCK) is a brain-gut peptide; it functions both as a neuropeptide and as a gut hormone. Although the pancreas and the gallbladder were long thought to be the principal peripheral targets of CCK, CCK receptors are found throughout the gut. It is likely that CCK has a physiological role not only in the stimulation of pancreatic and biliary secretions but also in the regulation of gastrointestinal motility. The motor effects of CCK include postprandial inhibition of gastric emptying and inhibition of colonic transit. It is now evident that at least two different receptors, CCK(1) and CCK(2) (formerly CCK-A and CCK-B, respectively), mediate the actions of CCK. Both localization and functional studies suggest that the motor effects of CCK are mediated by CCK(1) receptors in humans. Since CCK is involved in sensory and motor responses to distension in the intestinal tract, it may contribute to the symptoms of constipation, bloating and abdominal pain that are often characteristic of functional gastrointestinal disorders in general and irritable bowel syndrome (IBS), in particular. CCK(1) receptor antagonists are therefore currently under development for the treatment of constipation-predominant IBS. Clinical studies suggest that CCK(1) receptor antagonists are effective facilitators of gastric emptying and inhibitors of gallbladder contraction and can accelerate colonic transit time in healthy volunteers and patients with IBS. These drugs are therefore potentially of great value in the treatment of motility disorders such as constipation and constipation-predominant IBS.

Involvement of endogenous CCK and CCK1 receptors in colonic motor function

Cholecystokinin (CCK) is a brain-gut peptide; it functions both as a neuropeptide and as a gut hormone. Although the pancreas and the gallbladder were long thought to be the principal peripheral targets of CCK, CCK receptors are found throughout the gut. It is likely that CCK has a physiological role not only in the stimulation of pancreatic and biliary secretions but also in the regulation of gastrointestinal motility. The motor effects of CCK include postprandial inhibition of gastric emptying and inhibition of colonic transit. It is now evident that at least two different receptors, CCK(1) and CCK(2) (formerly CCK-A and CCK-B, respectively), mediate the actions of CCK. Both localization and functional studies suggest that the motor effects of CCK are mediated by CCK(1) receptors in humans. Since CCK is involved in sensory and motor responses to distension in the intestinal tract, it may contribute to the symptoms of constipation, bloating and abdominal pain that are often characteristic of functional gastrointestinal disorders in general and irritable bowel syndrome (IBS), in particular. CCK(1) receptor antagonists are therefore currently under development for the treatment of constipation-predominant IBS. Clinical studies suggest that CCK(1) receptor antagonists are effective facilitators of gastric emptying and inhibitors of gallbladder contraction and can accelerate colonic transit time in healthy volunteers and patients with IBS. These drugs are therefore potentially of great value in the treatment of motility disorders such as constipation and constipation-predominant IBS.

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.

Association between the CCK-A receptor gene and panic disorder

Cholecystokinin (CCK) is one of the most abundant neurotransmitter peptides in the brain. CCK appears to play an important role in the neurobiology of anxiety and panic disorders (PD) in both humans and animals. Recently, we reported that lack of CCKAR had a significant anxiogenic-like effect in rats. In this study, to investigate the role of CCKAR in PD, we compared the CCKAR gene in PD patients and normal controls. Subjects who fulfilled the DSM-IV criteria for PD were 17 males and 26 females. The sequence containing the Pst I polymorphic site in the boundary between intron 1 and exon 2 of the CCKAR gene was studied. Pst I digestion of the PCR products gave two individual alleles: A1 and A2. The A1 allele was the undigested fragment and the A2 allele was the digested one with two variant bands at 264 and 180 bp. Genotypic frequencies were 20.9% (A1-A1), 55.8% (A1-A2), and 41.7% (A2-A2) in patients, and 20.5% (A1-A1), 46.2% (A1-A2), and 33.3% (A2-A2) in controls. Allelic frequencies were 48.8% (A1) and 51.2% (A2) in patients, and 43.6% (A1) and 56.4% (A2) in controls. The chi-square test did not show a significant difference in either genotypic or allelic frequencies between patients and control subjects. The Pst polymorphism of CCKAR may not be associated with PD.