Cholecystokinin CCK(B) receptor mRNA isoforms: expression in schizophrenic brains

Cholecystokinin-Mediated Neuromodulation of Anxiety and Schizophrenia: A "Dimmer-Switch" Hypothesis

Cholecystokinin (CCK), the most abundant brain neuropeptide, is involved in relevant behavioral functions like memory, cognition, and reward through its interactions with the opioid and dopaminergic systems in the limbic system. CCK excites neurons by binding two receptors, CCK1 and CCK2, expressed at low and high levels in the brain, respectively. Historically, CCK2 receptors have been related to the induction of panic attacks in humans. Disturbances in brain CCK expression also underlie the physiopathology of schizophrenia, which is attributed to the modulation by CCK1 receptors of the dopamine flux in the basal striatum. Despite this evidence, neither CCK2 receptor antagonists ameliorate human anxiety nor CCK agonists have consistently shown neuroleptic effects in clinical trials. A neglected aspect of the function of brain CCK is its neuromodulatory role in mental disorders. Interestingly, CCK is expressed in pivotal inhibitory interneurons that sculpt cortical dynamics and the flux of nerve impulses across corticolimbic areas and the excitatory projections to mesolimbic pathways. At the basal striatum, CCK modulates the excitability of glutamate, the release of inhibitory GABA, and the discharge of dopamine. Here we focus on how CCK may reduce rather than trigger anxiety by regulating its cognitive component. Adequate levels of CCK release in the basal striatum may control the interplay between cognition and reward circuitry, which is critical in schizophrenia. Hence, it is proposed that disturbances in the excitatory/ inhibitory interplay modulated by CCK may contribute to the imbalanced interaction between corticolimbic and mesolimbic neural activity found in anxiety and schizophrenia.

Validating reference genes using minimally transformed qpcr data: findings in human cortex and outcomes in schizophrenia

BACKGROUND

It is common practice, when using quantitative real time polymerase chain reaction (qPCR), to normalise levels of mRNA to reference gene mRNA which, by definition, should not vary between tissue, with any disease aetiology or after drug treatments. The complexity of human CNS means it unlikely that any gene could fulfil these criteria.

METHODS

To address this issue we measured levels of mRNA for six potential reference genes (GAPDH, PPIA, SNCA, NOL9, TFB1M and SKP1) in three cortical regions (Brodmann's areas (BA) 8, 9 and 44) from 30 subjects with schizophrenia and 30 age and sex matched controls. We used a structured statistical approach to examine the characteristics of these data to determine their suitability as reference genes. We also analysed our data using reference genes selected by rank as defined using the average of the standard deviation of pair-gene ΔCt and the BestKeeper, NormFinder and geNorm algorithms to determine if they suggested the same reference genes.

RESULTS

Our minimally derived data showed that levels of mRNA for all of the six genes varied between cortical regions and therefore no gene fulfilled the absolute requirements for use as reference genes. As levels of some mRNA for some genes did not vary with diagnoses within a cortical region from subjects with schizophrenia compared to controls, we normalised levels of mRNA for all the other genes to mRNA for one, two or three reference genes in each cortical region. This showed that using the geometric mean of at least two reference genes gave more reproducible results. Finally, using the reference gene ranking protocols the average of the standard deviation of pair-gene ΔCt, BestKeeper, NormFinder and geNorm we showed that these approaches ranked potential reference genes differently. We then showed that outcomes of comparing data from subjects with schizophrenia and controls varied depending on the reference genes chosen.

CONCLUSIONS

Our data shows that the selection of reference genes is a significant component of qPCR study design and therefore the process by which reference genes are selected must be clearly listed as a potential confound in studying gene expression in human CNS. This should include showing that, using minimally derived qPCR data, levels of mRNA for proposed reference genes does not vary with variables such as diagnoses and CNS region.

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.

Towards understanding the schizophrenia code: an expanded convergent functional genomics approach

Identifying genes for schizophrenia through classical genetic approaches has proven arduous. Here, we present a comprehensive convergent analysis that translationally integrates brain gene expression data from a relevant pharmacogenomic mouse model (involving treatments with a psychomimetic agent - phencyclidine (PCP), and an anti-psychotic - clozapine), with human genetic linkage data and human postmortem brain data, as a Bayesian strategy of cross validating findings. Topping the list of candidate genes, we have three genes involved in GABA neurotransmission (GABRA1, GABBR1, and GAD2), one gene involved in glutamate neurotransmission (GRIA2), one gene involved in neuropeptide signaling (TAC1), two genes involved in synaptic function (SYN2 and KCNJ4), six genes involved in myelin/glial function (CNP, MAL, MBP, PLP1, MOBP and GFAP), and one gene involved in lipid metabolism (LPL). These data suggest that schizophrenia is primarily a disorder of brain functional and structural connectivity, with GABA neurotransmission playing a prominent role. These findings may explain the EEG gamma band abnormalities detected in schizophrenia. The analysis also revealed other high probability candidates genes (neurotransmitter signaling, other structural proteins, ion channels, signal transduction, regulatory enzymes, neuronal migration/neurite outgrowth, clock genes, transcription factors, RNA regulatory genes), pathways and mechanisms of likely importance in pathophysiology. Some of the pathways identified suggest possible avenues for augmentation pharmacotherapy of schizophrenia with other existing agents, such as benzodiazepines, anticonvulsants and lipid modulating agents. Other pathways are new potential targets for drug development. Lastly, a comparison with our earlier work on bipolar disorder illuminates the significant molecular overlap between schizophrenia and bipolar disorder.

Gastrointestinal hormones regulating appetite

The role of gastrointestinal hormones in the regulation of appetite is reviewed. The gastrointestinal tract is the largest endocrine organ in the body. Gut hormones function to optimize the process of digestion and absorption of nutrients by the gut. In this capacity, their local effects on gastrointestinal motility and secretion have been well characterized. By altering the rate at which nutrients are delivered to compartments of the alimentary canal, the control of food intake arguably constitutes another point at which intervention may promote efficient digestion and nutrient uptake. In recent decades, gut hormones have come to occupy a central place in the complex neuroendocrine interactions that underlie the regulation of energy balance. Many gut peptides have been shown to influence energy intake. The most well studied in this regard are cholecystokinin (CCK), pancreatic polypeptide, peptide YY, glucagon-like peptide-1 (GLP-1), oxyntomodulin and ghrelin. With the exception of ghrelin, these hormones act to increase satiety and decrease food intake. The mechanisms by which gut hormones modify feeding are the subject of ongoing investigation. Local effects such as the inhibition of gastric emptying might contribute to the decrease in energy intake. Activation of mechanoreceptors as a result of gastric distension may inhibit further food intake via neural reflex arcs. Circulating gut hormones have also been shown to act directly on neurons in hypothalamic and brainstem centres of appetite control. The median eminence and area postrema are characterized by a deficiency of the blood-brain barrier. Some investigators argue that this renders neighbouring structures, such as the arcuate nucleus of the hypothalamus and the nucleus of the tractus solitarius in the brainstem, susceptible to influence by circulating factors. Extensive reciprocal connections exist between these areas and the hypothalamic paraventricular nucleus and other energy-regulating centres of the central nervous system. In this way, hormonal signals from the gut may be translated into the subjective sensation of satiety. Moreover, the importance of the brain-gut axis in the control of food intake is reflected in the dual role exhibited by many gut peptides as both hormones and neurotransmitters. Peptides such as CCK and GLP-1 are expressed in neurons projecting both into and out of areas of the central nervous system critical to energy balance. The global increase in the incidence of obesity and the associated burden of morbidity has imparted greater urgency to understanding the processes of appetite control. Appetite regulation offers an integrated model of a brain-gut axis comprising both endocrine and neurological systems. As physiological mediators of satiety, gut hormones offer an attractive therapeutic target in the treatment of obesity.

Overlapping regional distribution of CCK and TPPII mRNAs in Cynomolgus monkey brain and correlated levels in human cerebral cortex (BA 10)

Tripeptidyl peptidase II (TPPII) is a high molecular weight exopeptidase important in inactivating extracellular cholecystokinin (CCK). Our aims were to study the anatomical localization of TPPII and CCK mRNA in the Cynomolgus monkey brain as a basis for a possible functional anatomical connection between enzyme (TPPII) and substrate (CCK) and examine if indications of changes in substrate availability in the human brain might be reflected in changes of levels of TPPII mRNA.

METHODS

mRNA in situ hybridization on postmortem brain from patients having had a schizophrenia diagnosis as compared to controls and on monkey and rat brain slices.

RESULTS

overlapping distribution patterns of mRNAs for TPPII and CCK in rat and monkey. High amounts of TPPII mRNA are seen in the neocortex, especially in the frontal region and the hippocampus. TPPII mRNA is also present in the basal ganglia and cerebellum where CCK immunoreactivity and/or CCK B receptors have been found in earlier studies, suggesting presence of CCK-ergic afferents from other brain regions. Levels of mRNAs for CCK and TPPII show a positive correlation in postmortem human cerebral cortex Brodmann area (BA) 10. TPPII mRNA might be affected following schizophrenia.

DISCUSSION

overall TPPII and CCK mRNA show a similar distribution in rat and monkey brain, confirming and extending earlier studies in rodents. In addition, correlated levels of TPPII and CCK mRNA in human BA 10 corroborate a functional link between CCK and TPPII in the human brain.

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.

Secretin for refractory schizophrenia

In preliminary uncontrolled studies, intravenous injection of the gastrointestinal peptide secretin produced improvements in the symptoms of autism. Because of the phenotypic overlap between autism and some aspects of schizophrenia, we performed a pilot study of secretin for treatment refractory schizophrenia. Twenty-two patients were randomized to a single intravenous dose of porcine secretin or placebo. Patients were evaluated with the Positive and Negative Symptom Scale for Schizophrenia (PANSS) and the Clinical Global Impression Scale (CGI) at baseline, 2 days after secretin infusion and weekly for 4 weeks. There were no statistically significant differences between drug- and placebo-treated patients with repeated measures analysis of variance (ANOVA). However, several patients treated with secretin experienced clinically meaningful, but transient, reductions in symptoms and a greater percentage of patients treated with secretin were rated as improved with the CGI. Further study of brain hypocretins and molecules affecting this system are warranted in schizophrenia.

Near-infrared spectroscopy analysis of frontal lobe dysfunction in schizophrenia

BACKGROUND

Previous studies have shown that near-infrared spectroscopy (NIRS) has high temporal resolution, requires little restraint, and is suitable for examining the effect of psychological tasks on brain circulation. In the present study, frontal function in schizophrenic patients was analyzed by NIRS during random number generation (RNG), ruler-catching (RC), and sequential finger-to-thumb (SFT) tasks.

METHODS

Two sets of NIRS probes were attached to the foreheads of 13 schizophrenic patients and 10 control subjects approximately at Fp1-F7 and Fp2-F8. Near-infrared spectroscopy was conducted at a sampling rate of 1 Hz, with the pathlength being determined by time-resolved spectroscopy with differential pathlength factor measurements. The absolute changes in oxygenated (oxy-Hb) and deoxygenated (deoxy-Hb) hemoglobin concentrations in response to each task were measured, and total hemoglobin (total-Hb) concentration was calculated as the sum of the two.

RESULTS

During RNG task, total- and oxy-Hb concentrations increased, and deoxy-Hb decreased, but the responses were significantly smaller in schizophrenic patients. During RC task, oxy-Hb in schizophrenic patients tended to decrease, in contrast to the mostly increasing response in control subjects. No group difference was observed during SFT task.

CONCLUSIONS

Task-dependent profile of functional abnormalities was observed in schizophrenic frontal brain metabolism. These results support the usefulness of NIRS data in investigating frontal lobe dysfunction and evaluating psychopathologic condition in schizophrenic patients.

Prevalence and relationship to delusions and hallucinations of anxiety disorders in schizophrenia

We investigated the prevalence of anxiety disorders in a sample of individuals with chronic schizophrenia, controlling for anxiety symptoms that may be related to delusions and hallucinations, and the possible differences in clinical variables between the groups. Individuals with a diagnosis of schizophrenia and able to give informed consent were recruited from the community. The Mini International Neuropsychiatric Interview (MINI) was administered to both confirm the DSM-IV diagnosis of schizophrenia and screen for comorbid anxiety disorders. If a comorbid anxiety disorder was found, its relation to the individual's delusions and hallucinations was examined. Clinical rating scales for schizophrenia were administered as well as rating scales for specific anxiety disorders where appropriate. Overall, anxiety disorders ranged from 0% [ for Post Traumatic Stress Disorder (PTSD)] to 26.7% [ for generalized anxiety disorder (GAD) and agoraphobia without panic] with lower rates when controlled for anxiety symptoms related to delusions and hallucinations. In investigating clinical variables, the cohort was initially divided into schizophrenics with no anxiety disorders and those with an anxiety disorder; with further analyses including schizophrenics with anxiety disorders related to delusions and hallucinations and those with anxiety disorders not related to delusions and hallucinations. The most consistent difference between all the groups was on the PANSS-G subscale. No significant differences were found on the remaining clinical variables. Comorbid anxiety disorders in schizophrenia can be related to the individual's delusions and hallucinations, though anxiety disorders can occur exclusive of these positive symptoms. Clinicians must be aware that this comorbidity exists in order to optimize an individual's treatment.

Neuropeptides involved in the pathophysiology of schizophrenia and major depression

The present review summarizes the findings on the role of neuropeptides in the pathophysiology of schizophrenia and major depression. Several neuropeptides as vasopressin and endorphins in particular, beta-endorphin and gamma-type endorphins, cholecystokinin (CCK), neurotensin, somatostatin and Neuropeptide Y have been implicated in schizophrenia. During the last decade, however, few attempts to explore the significance of most of these and other neuropeptides in the pathophysiology of the disease or their therapeutic potential are found in the literature. An exception is neurotensin, which exerts neuroleptic-like effects in animal studies, while CSF, brain and blood studies are inconclusive. Things are different in major depression. Here much attention is paid to the endocrine abnormalities found in this disorder in particular the increased activity of the hypothalamic-pituitary-adrenal (HPA) axis. Neuropeptides as corticotropin-releasing hormone (CRH), vasopressin and corticosteroids are implicated in the symptomatology of this disorder. As a consequence much work is going on investigating the influence of CRH and corticosteroid antagonists or inhibitors of the synthesis of corticosteroids as potential therapeutic agents. This review emphasizes the role of vasopressin in the increased activity of the HPA axis in major depression and suggests exploration of the influence of the now available non-peptidergic vasopressin orally active V1 antagonists.

Upregulation of bradykinin B2 receptor expression by neurotrophic factors and nerve injury in mouse sensory neurons

Bradykinin B2 receptor mRNA was detected at low levels, both by RT-PCR and by in situ hybridization, in freshly isolated dorsal root ganglia (DRG) and in ganglia cultured in the absence of neurotrophic factors, but was strongly upregulated by culture in the presence of nerve growth factor (NGF). The effect of NGF is mediated via TrkA receptors. The related neurotrophins, brain-derived neurotrophic factor, neurotrophin-3, and neurotrophin-4, were ineffective in upregulating B2 mRNA, but a small upregulation was seen with the unrelated neurotrophin glial cell line-derived neurotrophic factor (GDNF). Surface membrane B2 receptor expression, detected by immunofluorescence using a B2-specific antibody, was low in outgrowing axons cultured in the absence of neurotrophic factors, but was elevated by addition of NGF or GDNF. Conditioned media prepared by incubating injured nerve, skin, or muscle had a similar effect to NGF in upregulating B2 mRNA and protein expression, and the activity was largely removed by neutralization of NGF in the conditioned medium with an anti-NGF antibody. After nerve crush injury in vivo an enhancement in B2 mRNA expression was seen, peaking after 7 days and returning to precrush levels after 14 days. In all conditions tested, the proportion of neurons expressing B2 mRNA remained the same at around 23% of small neurons, suggesting that upregulation only occurs in the B2-positive neurons. These experiments show that NGF, and to a lesser extent GDNF, upregulates the expression of bradykinin B2 mRNA and B2 receptor protein in the surface membrane of DRG neurons and that NGF is an important factor responsible for upregulating bradykinin B2 receptor expression after nerve crush injury in vivo.

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

Cholecystokinin A receptors (CCKAR) modulate CCK-stimulated dopamine release, and mutations in the CCKAR gene may predispose affected individuals to schizophrenia. Our previous study suggested that -286A>G polymorphism (previously named 201A>G) in the CCKAR gene promoter is associated with schizophrenia. In the present study, we carried out a further investigation of the promoter and intron 1 of the CCKAR gene. In addition to polymorphisms reported previously (-333G>T, -286A>G, -241G>A, 773A>T, and 779T>C), two novel polymorphisms (-388(GT)(8)>(GT)(9) and -85C>G) were identified. These polymorphisms were in a linkage disequilibrium. Association analyses between schizophrenic patients and controls revealed that the frequencies of the A allele and AA genotype at the -286 loci, as well as the frequency of the GG genotype at the -333 loci, were significantly higher in patients than in controls. Furthermore, patients with paranoid type schizophrenia, auditory hallucinations, or a positive family history had a significantly higher frequency of the -286A allele than the control group. The results supported our previous data, and suggest the possible involvement of the -333G>T and the -286A>G polymorphisms in the promoter region of the CCKAR gene in the predisposition to schizophrenia.

Effects of antipsychotic drugs on cholecystokinin and preprotachykinin (substance P) mRNA expression in the rat hippocampal formation

To assess the involvement of substance P (SP) and cholecystokinin (CCK) in the effects of antipsychotic drugs, preprotachykinin-A (PPT-A) and CCK mRNA expression was studied in the hippocampal formation using in situ hybridisation following 21 daily i.p. injections with the typical antipsychotic drug haloperidol (1 mg/kg) and the atypical drug clozapine (15 mg/kg). PPT-A mRNA levels were increased in the hippocampal CA3 subregion and in the entorhinal cortex after haloperidol, whereas a decrease was observed in the CA1 after clozapine. CCK mRNA levels increased in the CA1, the entorhinal cortex and in hilus, following both haloperidol and clozapine. It is suggested that earlier findings of increased SP levels in the hippocampal formation of schizophrenics may be a consequence of haloperidol treatment and that reduced hippocampal CCK and CCK mRNA levels found earlier in schizophrenics do not result from antipsychotic drug treatment. These results are consonant to the hypothesis that increased cortical CCK transmission may be beneficial in the treatment of psychosis.