The alpha-isoform of calcium/calmodulin-dependent protein kinase II (α-CaMKII) is expressed abundantly in the forebrain and is considered to have an essential role in synaptic plasticity and cognitive function. Previously, we reported that mice heterozygous for a null mutation of α-CaMKII (α-CaMKII+/−) have profoundly dysregulated behaviors including a severe working memory deficit, which is an endophenotype of schizophrenia and other psychiatric disorders. In addition, we found that almost all the neurons in the dentate gyrus (DG) of the mutant mice failed to mature at molecular, morphological and electrophysiological levels. In the present study, to identify the brain substrates of the working memory deficit in the mutant mice, we examined the expression of the immediate early genes (IEGs), c-Fos and Arc, in the brain after a working memory version of the eight-arm radial maze test. c-Fos expression was abolished almost completely in the DG and was reduced significantly in neurons in the CA1 and CA3 areas of the hippocampus, central amygdala, and medial prefrontal cortex (mPFC). However, c-Fos expression was intact in the entorhinal and visual cortices. Immunohistochemical studies using arc promoter driven dVenus transgenic mice demonstrated that arc gene activation after the working memory task occurred in mature, but not immature neurons in the DG of wild-type mice. These results suggest crucial insights for the neural circuits underlying spatial mnemonic processing during a working memory task and suggest the involvement of α-CaMKII in the proper maturation and integration of DG neurons into these circuits.
α-CaMKII; working memory; dentate gyrus; schizophrenia; immediate-early genes; c-fos
Elucidating the neural and genetic factors underlying psychiatric illness is hampered by current methods of clinical diagnosis. The identification and investigation of clinical endophenotypes may be one solution, but represents a considerable challenge in human subjects. Here we report that mice heterozygous for a null mutation of the alpha-isoform of calcium/calmodulin-dependent protein kinase II (alpha-CaMKII+/-) have profoundly dysregulated behaviours and impaired neuronal development in the dentate gyrus (DG). The behavioral abnormalities include a severe working memory deficit and an exaggerated infradian rhythm, which are similar to symptoms seen in schizophrenia, bipolar mood disorder and other psychiatric disorders. Transcriptome analysis of the hippocampus of these mutants revealed that the expression levels of more than 2000 genes were significantly changed. Strikingly, among the 20 most downregulated genes, 5 had highly selective expression in the DG. Whereas BrdU incorporated cells in the mutant mouse DG was increased by more than 50 percent, the number of mature neurons in the DG was dramatically decreased. Morphological and physiological features of the DG neurons in the mutants were strikingly similar to those of immature DG neurons in normal rodents. Moreover, c-Fos expression in the DG after electric footshock was almost completely and selectively abolished in the mutants. Statistical clustering of human post-mortem brains using 10 genes differentially-expressed in the mutant mice were used to classify individuals into two clusters, one of which contained 16 of 18 schizophrenic patients. Nearly half of the differentially-expressed probes in the schizophrenia-enriched cluster encoded genes that are involved in neurogenesis or in neuronal migration/maturation, including calbindin, a marker for mature DG neurons. Based on these results, we propose that an "immature DG" in adulthood might induce alterations in behavior and serve as a promising candidate endophenotype of schizophrenia and other human psychiatric disorders.
Schizophrenia is a complex genetic disorder caused by multiple genetic and environmental factors. The dystrobrevin-binding protein 1 (DTNBP1: dysbindin-1) gene is a major susceptibility gene for schizophrenia. Genetic variations in DTNBP1 are associated with cognitive functions, general cognitive ability and memory function, and clinical features of patients with schizophrenia including negative symptoms and cognitive decline. Since reduced expression of dysbindin-1 has been observed in postmortem brains of patients with schizophrenia, the sandy (sdy) mouse, which has a deletion in the Dtnbp1 gene and expresses no dysbindin-1 protein, could be an animal model of schizophrenia. To address this issue, we have carried out a comprehensive behavioral analysis of the sdy mouse in this study.
In a rotarod test, sdy mice did not exhibit motor learning whilst the wild type mice did. In a Barnes circular maze test both sdy mice and wild type mice learned to selectively locate the escape hole during the course of the training period and in the probe trial conducted 24 hours after last training. However, sdy mice did not locate the correct hole in the retention probe tests 7 days after the last training trial, whereas wild type mice did, indicating impaired long-term memory retention. A T-maze forced alternation task, a task of working memory, revealed no effect of training in sdy mice despite the obvious effect of training in wild type mice, suggesting a working memory deficit.
Sdy mouse showed impaired long-term memory retention and working memory. Since genetic variation in DTNBP1 is associated with both schizophrenia and memory function, and memory function is compromised in patients with schizophrenia, the sdy mouse may represent a useful animal model to investigate the mechanisms of memory dysfunction in the disorder.
Schnurri-2 (Shn-2), an nuclear factor-κB site-binding protein, tightly binds to the enhancers of major histocompatibility complex class I genes and inflammatory cytokines, which have been shown to harbor common variant single-nucleotide polymorphisms associated with schizophrenia. Although genes related to immunity are implicated in schizophrenia, there has been no study showing that their mutation or knockout (KO) results in schizophrenia. Here, we show that Shn-2 KO mice have behavioral abnormalities that resemble those of schizophrenics. The mutant brain demonstrated multiple schizophrenia-related phenotypes, including transcriptome/proteome changes similar to those of postmortem schizophrenia patients, decreased parvalbumin and GAD67 levels, increased theta power on electroencephalograms, and a thinner cortex. Dentate gyrus granule cells failed to mature in mutants, a previously proposed endophenotype of schizophrenia. Shn-2 KO mice also exhibited mild chronic inflammation of the brain, as evidenced by increased inflammation markers (including GFAP and NADH/NADPH oxidase p22 phox), and genome-wide gene expression patterns similar to various inflammatory conditions. Chronic administration of anti-inflammatory drugs reduced hippocampal GFAP expression, and reversed deficits in working memory and nest-building behaviors in Shn-2 KO mice. These results suggest that genetically induced changes in immune system can be a predisposing factor in schizophrenia.
Animal models; Dentate Gyrus; Endophenotype; Inflammation; Mood/Anxiety/Stress Disorders; Psychiatry & Behavioral Sciences; Schizophrenia/Antipsychotics; animal models; dentate gyrus; endophenotype; inflammation; mood/anxiety/stress disorders; psychiatry & behavioral sciences; schizophrenia/antipsychotics
Densin is an abundant scaffold protein in the postsynaptic density (PSD) that forms a high affinity complex with αCaMKII and α-actinin. To assess the function of densin, we created a mouse line with a null mutation in the gene encoding it (LRRC7). Homozygous knockout mice display a wide variety of abnormal behaviors that are often considered endophenotypes of schizophrenia and autism spectrum disorders. At the cellular level, loss of densin results in reduced levels of α-actinin in the brain and selective reduction in the localization of mGluR5 and DISC1 in the PSD fraction; whereas, the amounts of ionotropic glutamate receptors and other prominent PSD proteins are unchanged. In addition, deletion of densin results in impairment of mGluR- and NMDA receptor-dependent forms of long-term depression (LTD), alters the early dynamics of regulation of CaMKII by NMDA-type glutamate receptors (NMDARs), and produces a change in spine morphology. These results indicate that densin influences the function of mGluRs and CaMKII at synapses, and contributes to localization of mGluR5 and DISC1 in the PSD fraction. They are consistent with the hypothesis that mutations that disrupt the organization and/or dynamics of postsynaptic signaling complexes in excitatory synapses can cause behavioral endophenotypes of mental illness.
AKT1, encoding the protein kinase B, has been associated with the genetic etiology of schizophrenia and bipolar disorder. However, minuscule data exist on the role of different alleles of in measurable quantitative endophenotypes, such as cognitive abilities and neuroanatomical features, showing deviations in schizophrenia and bipolar disorder. We evaluated the contribution of AKT1 to quantitative cognitive traits and 3D high-resolution neuroanatomical images in a Finnish twin sample consisting of 298 twins: 61 pairs with schizophrenia (8 concordant), 31 pairs with bipolar disorder (5 concordant) and 65 control pairs matched for age, sex and demographics. An AKT1 allele defined by the SNP rs1130214 located in the UTR of the gene revealed association with cognitive traits related to verbal learning and memory (P=0.0005 for a composite index). This association was further fortified by a higher degree of resemblance of verbal memory capacity in pairs sharing the rs1130214 genotype compared to pairs not sharing the genotype. Furthermore, the same allele was also associated with decreased gray matter density in medial and dorsolateral prefrontal cortex (P < 0.05). Our findings support the role of AKT1 in the genetic background of cognitive and anatomical features, known to be affected by psychotic disorders. The established association of the same allelic variant of AKT1 with both cognitive and neuroanatomical aberrations could suggest that AKT1 exerts its effect on verbal learning and memory via neural networks involving prefrontal cortex.
AKT1; quantitative trait loci; magnetic resonance imaging; association
Deficits in auditory processing are among the best documented endophenotypes in schizophrenia, possibly due to loss of excitatory synaptic connections. Dendritic spines, the principal post-synaptic target of excitatory projections, are reduced in schizophrenia. p21-activated kinase 1 (PAK1) regulates both the actin cytoskeleton and dendritic spine density, and is a downstream effector of both kalirin and CDC42, both of which have altered expression in schizophrenia. This study sought to determine if there is decreased auditory cortex PAK1 protein expression in schizophrenia through the use of quantitative western blots of 25 schizophrenia subjects and matched controls. There was no significant change in PAK1 level detected in the schizophrenia subjects in our cohort. PAK1 protein levels within subject pairs correlated positively with prior measures of total kalirin protein in the same pairs. PAK1 level also correlated with levels of a marker of dendritic spines, spinophilin. These latter two findings suggest that the lack of change in PAK1 level in schizophrenia is not due to limited sensitivity of our assay to detect meaningful differences in PAK1 protein expression. Future studies are needed to evaluate whether alterations in PAK1 phosphorylation states, or alterations in protein expression of other members of the PAK family, are present in schizophrenia.
Behavioral genetic studies of humans have associated variation in the DTNBP1 gene with schizophrenia and its cognitive deficit phenotypes. The protein coded for by DTNBP1, dysbindin, is expressed within forebrain glutamatergic neurons, where it interacts with proteins involved in vesicular trafficking and exocytosis. In order to further delineate the cellular, physiological and behavioral phenotypes associated with reduced dysbindin expression, we conducted studies in mice carrying a null mutation within the dtnbp1 gene. Dysbindin mutants exhibited impairments of spatial working memory as compared with wild-type controls; heterozygous mice exhibited intermediate levels of cognitive dysfunction. Deep layer pyramidal neurons recorded in the prefrontal cortex of mutant mice exhibited reductions in paired-pulse facilitation, and evoked and miniature excitatory post-synaptic currents, indicating a difference in the function of pre-synaptic glutamatergic terminals, as well as elevated spike thresholds. Taken together, these data indicate that dysbindin potently regulates excitatory transmission in prefrontal cortex, potentially through a pre-synaptic mechanism, and consequently modulates cognitive functions depending upon this brain region, providing new insights into the molecular mechanisms underlying cortical dysfunction in schizophrenia.
working memory; schizophrenia; glutamate; cognition; excitatory; pre-synaptic
The role of the cerebellum in coordinating mental activity is supported by its connections with cerebral regions involved in cognitive/affective functioning, with decreased activities on functional neuroimaging observed in the cerebellum of schizophrenia patients performing mental tasks. Brain-derived neurotrophic factor (BDNF)-induced activation of tyrosine kinase B (TrkB) is essential to synaptic plasticity. We hypothesized that alterations in BDNF and TrkB expression in the cerebellum were associated with schizophrenia and affective disorders.
We employed immunohistochemistry and immunoblotting to quantify protein expression of BDNF and TrkB in the cerebellum of patients with schizophrenia, bipolar disorder, and major depression compared to controls (n=15 each).
While TrkB immunoreactivity in each of the molecular and granule-cell layers was reduced in all 3 disease groups (12–34%) compared to the control (P=0.018 and 0.038, respectively, ANOVA), only the reduction in bipolar disorder remained statistically significant upon Tukey-Kramer post hoc analyses (P=0.019 and 0.021, respectively). Apparent decreases in BDNF immunoreactivity in all 3 disease groups (12–30%) compared to the control were not statistically significant. TrkB immunoreactivity was not significantly associated with any of the demographic, clinical, and postmortem variables. Immunoblotting displayed an 85-kDa TrkB-immunoreactive band, consistent with a truncated isoform, in all 60 cases.
On immunoblotting, apparent decreases in 85-kDa-TrkB levels in all 3 disease groups compared to the control were not statistically significant.
Our finding of reduced TrkB expression in bipolar disorder suggests that dysregulation of TrkB-mediated neurotrophin signaling in the cerebellum may play a role in the pathophysiology of this disease.
Bipolar disorder; Brain-derived neurotrophic factor; Cerebellum; Major depression; Schizophrenia; TrkB
SREB2/GPR85, a member of the super-conserved receptor expressed in brain (SREB) family, is the most conserved G-protein-coupled receptor in vertebrate evolution. Previous human and mouse genetic studies have indicated a possible link between SREB2 and schizophrenia. SREB2 is robustly expressed in the hippocampal formation, especially in the dentate gyrus, a structure with an established involvement in psychiatric disorders and cognition. However, the function of SREB2 in the hippocampus remains elusive. Here we show that SREB2 regulates hippocampal adult neurogenesis, which impacts on cognitive function. Bromodeoxyuridine incorporation and immunohistochemistry were conducted in SREB2 transgenic (Tg, over-expression) and knockout (KO, null-mutant) mice to quantitatively assay adult neurogenesis and newborn neuron dendritic morphology. Cognitive responses associated with adult neurogenesis alteration were evaluated in SREB2 mutant mice. In SREB2 Tg mice, both new cell proliferation and new neuron survival were decreased in the dentate gyrus, whereas an enhancement of new neuron survival occurred in SREB2 KO mouse dentate gyrus. Doublecortin staining revealed dendritic morphology deficits of newly generated neurons in SREB2 Tg mice. In a spatial pattern separation task, SREB2 Tg mice displayed a decreased ability to discriminate spatial relationships, whereas SREB2 KO mice had enhanced abilities in this task. Additionally, SREB2 Tg and KO mice had reciprocal phenotypes in a Y-maze working memory task. Our results indicate that SREB2 is a negative regulator of adult neurogenesis and consequential cognitive functions. Inhibition of SREB2 function may be a novel approach to enhance hippocampal adult neurogenesis and cognitive abilities to ameliorate core symptoms of psychiatric patients.
bromodeoxyuridine; cognition; dentate gyrus; mutant mouse; psychiatric disease
Schizophrenia is a widespread psychiatric disorder, affecting 1% of people. Despite this high prevalence, schizophrenia is not well treated because of its enigmatic developmental origin. We explore here the developmental etiology of endophenotypes associated with schizophrenia using a regulated transgenic approach in mice. Recently, a polymorphism that increases mRNA levels of the G-protein subunit Gαs was genetically linked to schizophrenia. Here we show that regulated overexpression of Gαs mRNA in forebrain neurons of mice is sufficient to cause a number of schizophrenia-related phenotypes, as measured in adult mice, including sensorimotor gating deficits (prepulse inhibition of acoustic startle, PPI) that are reversed by haloperidol or the phosphodiesterase inhibitor rolipram, psychomotor agitation (hyperlocomotion), hippocampus-dependent learning and memory retrieval impairments (hidden water maze, contextual fear conditioning), and enlarged ventricles. Interestingly, overexpression of Gαs during development plays a significant role in some (PPI, spatial learning and memory and neuroanatomical deficits) but not all of these adulthood phenotypes. Pharmacological and biochemical studies suggest the Gαs-induced behavioral deficits correlate with compensatory decreases in hippocampal and cortical cyclic AMP (cAMP) levels. These decreases in cAMP may lead to reduced activation of the guanine exchange factor Epac (also known as RapGEF 3/4) as stimulation of Epac with the select agonist 8-pCPT-2′-O-Me-cAMP increases PPI and improves memory in C57BL/6J mice. Thus, we suggest that the developmental impact of a given biochemical insult, such as increased Gαs expression, is phenotype specific and that Epac may prove to be a novel therapeutic target for the treatment of both developmentally regulated and non-developmentally regulated symptoms associated with schizophrenia.
GNAS; cAMP; Rap-GEF 4; learning and memory; cognition; schizophrenia
Single nucleotide polymorphisms (SNPs) within the gene encoding the serine/threonine kinase KIS (Kinase Interacting with Stathmin, also known as UHMK1) have recently been associated with schizophrenia. As none of the disease associated SNPs are coding, they may confer susceptibility by altering some facet of KIS expression. Here we have characterised the cellular distribution of KIS in human brain using in situ hybridisation and immunohistochemistry, and quantified KIS protein and mRNA in two large brain series to determine if KIS expression is altered in schizophrenia or bipolar disorder or in relation to a schizophrenia-associated SNP (rs7513662). Post-mortem tissue from the superior temporal gyrus of schizophrenia and control subjects, and also dorsolateral prefrontal cortex, anterior cingulate cortex, and cerebellum from schizophrenia, bipolar disorder, and control subjects were used. KIS expression was measured by quantitative PCR (mRNA) and immunoautoradiography (protein), and was also quantified by immunoblot in lymphoblast cell lines derived from schizophrenia and control subjects. Our results demonstrate that KIS is expressed in neurons, and its encoded protein is localised to the nucleus and cytoplasm. No difference in KIS expression was found between diagnostic groups, or in the lymphoblast cell lines, and no effect of rs7513662 genotype on KIS expression was found. Hence, these data do not provide support for the hypothesis that altered expression is the mechanism by which genetic variation of KIS may increase susceptibility to schizophrenia, nor evidence that KIS expression is altered in the disease itself, at least in terms of the parameters studied here.
bipolar disorder; gene expression; psychosis; schizophrenia; UHMK1
Converging evidence has implicated endogenous neurotensin (NT) in the pathophysiology of brain processes relevant to schizophrenia. Prepulse inhibition of the startle reflex (PPI) is a measure of sensorimotor gating and considered to be of strong relevance to neuropsychiatric disorders associated with psychosis and cognitive dysfunction. Mice genetically engineered to not express NT display deficits in PPI that model the PPI deficits seen in schizophrenia patients. NT1 receptors have been most strongly implicated in mediating the psychosis relevant effects of NT such as attenuating PPI deficits. To investigate the role of NT1 receptors in the regulation of PPI, we measured baseline PPI in wildtype (WT) and NT1 knockout (KO) mice. We also tested the effects of amphetamine and dizocilpine, a dopamine agonist and NMDA antagonist, respectively, that reduce PPI as well as the NT1 selective receptor agonist, PD149163, known to increase PPI in rats.
Baseline PPI and acoustic startle response were measured in WT and NT1 knockout KO mice. After baseline testing, mice were tested again after receiving intraperatoneal (IP) saline or one of three doses of amphetamine (1.0, 3.0 and 10.0 mg/kg), dizocilpine (0.3, 1.0 and 3.0 mg/kg) and PD149163 (0.5, 2.0 and 6.0 mg/kg) on separate test days.
Baseline PPI and acoustic startle response in NT1 KO mice were not significantly different from NT1 WT mice. WT and KO mice exhibited similar responses to the PPI-disrupting effects of dizocilpine and amphetamine. PD149163 significantly facilitated PPI (P < 0.004) and decreased the acoustic startle response (P < 0.001) in WT but not NT1 KO mice.
The data does not support the regulation of baseline PPI or the PPI disruptive effects of amphetamine or dizocilpine by endogenous NT acting at the NT1 receptor, although they support the antipsychotic potential of pharmacological activation of NT1 receptors by NT1 agonists.
schizophrenia; neurotensin; animal model; PD149163; amphetamine; dizocilpine
Recent genetics research focusing on schizophrenia has led to candidate cognitive and neuroimaging variables as intermediate phenotypes or “endophenotype” markers for the illness. Among other stringent criteria, to be an endophenotype, a marker must demonstrate heritability. In an effort to explore the validity of a selection of cognitive and neuroimaging endophenotypes, the present study was designed to determine estimates of their heritability. One hundred fourteen subjects, including 27 with schizophrenia and 39 unaffected relatives from 23 multiplex schizophrenia families, participated in a comprehensive neuropsychological test battery and structural brain imaging with diffusion tensor imaging (DTI). Variables were selected if they previously have been demonstrated to show differences between people with schizophrenia and normal controls. Significant evidence of heritability was confirmed for overall cognitive function (“g”), as well as expressive and receptive language, verbal and visual memory, processing speed and cognitive inhibition. In addition, significant heritability estimates were determined for specific regions in the frontal, central, parietal, and occipital areas. These results suggest that the variables chosen may be useful endophenotypes for genetic and early detection studies, although further work with larger cohorts should be conducted to show that deficits in these functions and structures also segregate with schizophrenia within families and thus fully satisfy the definition of an endophenotype. In addition, other cognitive and neuroimaging variables that were not studied here may be candidates for schizophrenia endophenotypes.
genetic; cognition; neuroimaging; DTI
Twin and family studies have shown the importance of biological variation in psychiatric disorders. Heritability estimates vary from 50% to 80% for cognitive disorders, such as schizophrenia, attention deficit hyperactivity disorder and autism, and from 40% to 65% for affective disorders, such as major depression, anxiety disorders and substance abuse. Pinpointing the actual genetic variants responsible for this heritability has proven difficult, even in the recent wave of genome-wide association studies. Brain endophenotypes derived from electroencephalography (EEG) have been proposed as a way to support gene-finding efforts. A variety of EEG and event-related-potential endophenotypes are linked to psychiatric disorders, and twin studies have shown a striking genetic contribution to these endophenotypes. However, the clear need for very large sample sizes strongly limits the usefulness of EEG endophenotypes in gene-finding studies. They require extended laboratory recordings with sophisticated and expensive equipment that are not amenable to epidemiology-scaled samples. Instead, EEG endophenotypes are far more promising as tools to make sense of candidate genetic variants that derive from association studies; existing clinical data from patients or questionnaire-based assessment of psychiatric symptoms in the population at large are better suited for the association studies themselves. EEG endophenotypes can help us understand where in the brain, in which stage and during what type of information processing these genetic variants have a role. Such testing can be done in the more modest samples that are feasible for EEG research. With increased understanding of how genes affect the brain, combinations of genetic risk scores and brain endophenotypes may become part of the future classification of psychiatric disorders.
Structural MRI data indicate schizophrenics have reduced left-sided temporal lobe gray matter volumes, especially in the superior temporal gyrus (STG) and medial temporal lobe. Our data further suggest a specificity to schizophrenia spectrum disorders of STG volume reduction. Interpretation of research studies involving schizophrenics may be complicated by the effects of exposure to neuroleptics and chronic illness. Sharing the same genetic diathesis of schizophrenics, subjects with schizotypal personality disorder (SPD) offer a unique opportunity to evaluate commonalities between schizophrenia and SPD, particularly as SPD subjects are characterized by cognitive and perceptual distortions, an inability to tolerate close friendships, and odd behavior, but they are not psychotic and so have generally not been prescribed neuroleptics nor hospitalized. Evaluation of brain structure in SPD may thus offer insight into the “endophenotype” common to both disorders. In addition, differences between groups may suggest which are the brain structures of schizophrenics that contribute to the development of psychosis.
To test the hypothesis of whether SPD subjects might show similar STG abnormalities, STG and medial temporal lobe regions of interest (ROI) were manually drawn on high resolution coronal MRI 1.5 mm thick slices. Images were derived from 16 right-handed male SPD subjects, without regard to family history, and 14 healthy, right-handed, comparison males who did not differ from the SPD group on parental socio-economic status, age, or verbal IQ.
As predicted, SPD subjects showed a reduction in left STG gray matter volume compared with age and gender matched comparison subjects. SPD subjects also showed reduced parahippocampal left/right asymmetry and a high degree of disordered thinking. Comparisons with chronic schizophrenics previously studied by us showed the SPD group had a similarity of left STG gray matter volume reduction, but fewer medial temporal lobe abnormalities.
These abnormalities strengthen the hypothesis of a temporal lobe abnormality in SPD, and the similarity of STG findings in schizophrenia and SPD suggest that STG abnormalities may be part of the spectrum “endophenotype.” It is also possible that presence of medial temporal lobe abnormalities may help to differentiate who will develop schizophrenia and who will develop the less severe schizophrenia spectrum disorder, SPD.
Schizotypal personality disorder; schizophrenia; magnetic resonance imaging; temporal lobe; superior temporal gyrus
Endophenotypes are quantitative, laboratory-based measures representing intermediate links in the pathways between genetic variation and the clinical expression of a disorder. Ideal endophenotypes exhibit deficits in patients, are stable over time and across shifts in psychopathology, and are suitable for repeat testing. Unfortunately, many leading candidate endophenotypes in schizophrenia have not been fully characterized simultaneously in large cohorts of patients and controls across these properties. The objectives of this study were to characterize the extent to which widely-used neurophysiological and neurocognitive endophenotypes are: 1) associated with schizophrenia, 2) stable over time, independent of state-related changes, and 3) free of potential practice/maturation or differential attrition effects in schizophrenia patients (SZ) and nonpsychiatric comparison subjects (NCS). Stability of clinical and functional measures was also assessed.
Participants (SZ n = 341; NCS n = 205) completed a battery of neurophysiological (MMN, P3a, P50 and N100 indices, PPI, startle habituation, antisaccade), neurocognitive (WRAT-3 Reading, LNS-forward, LNS-reorder, WCST-64, CVLT-II). In addition, patients were rated on clinical symptom severity as well as functional capacity and status measures (GAF, UPSA, SOF). 223 subjects (SZ n = 163; NCS n = 58) returned for retesting after 1 year.
Most neurophysiological and neurocognitive measures exhibited medium-to-large deficits in schizophrenia, moderate-to-substantial stability across the retest interval, and were independent of fluctuations in clinical status. Clinical symptoms and functional measures also exhibited substantial stability. A Longitudinal Endophenotype Ranking System (LERS) was created to rank neurophysiological and neurocognitive biomarkers according to their effect sizes across endophenotype criteria.
The majority of neurophysiological and neurocognitive measures exhibited deficits in patients, stability over a 1-year interval and did not demonstrate practice or time effects supporting their use as endophenotypes in neural substrate and genomic studies. These measures hold promise for informing the “gene-to-phene gap” in schizophrenia research.
To understand the pathophysiology of neuropsychiatric disorders such as schizophrenia requires consideration of multiple genetic and non-genetic factors. However, very little is known about the consequences of combining models of synaptic dysfunction with controlled environmental manipulations. Therefore, to generate new insights into gene–environment interactions and complex behaviour, we examined the influence of variable prenatal stress (PNS) on two mouse lines with mutations in synaptosomal-associated protein of 25 kDa (Snap-25): the blind-drunk (Bdr) point mutant and heterozygous Snap-25 knockout mice. Neonatal development was analysed in addition to an assessment of adult behavioural phenotypes relevant to the psychotic, cognitive and negative aspects of schizophrenia. These data show that PNS influenced specific anxiety-related behaviour in all animals. In addition, sensorimotor gating deficits previously noted in Bdr mutants were markedly enhanced by PNS; significantly, these effects could be reversed with the application of anti-psychotic drugs. Moreover, social interaction abnormalities were observed only in Bdr animals from stressed dams but not in wild-type littermates or mutants from non-stressed mothers. These results show for the first time that combining a synaptic mouse point mutant with a controlled prenatal stressor paradigm produces both modified and previously unseen phenotypes, generating new insights into the interactions between genetics and the environment relevant to the study of psychiatric disease.
Sleep and circadian rhythm disruption has been widely observed in neuropsychiatric disorders including schizophrenia  and often precedes related symptoms . However, mechanistic basis for this association remains unknown. Therefore, we investigated the circadian phenotype of blind-drunk (Bdr), a mouse model of synaptosomal-associated protein (Snap)-25 exocytotic disruption that displays schizophrenic endophenotypes modulated by prenatal factors and reversible by antipsychotic treatment [3, 4]. Notably, SNAP-25 has been implicated in schizophrenia from genetic [5–8], pathological [9–13], and functional studies [14–16]. We show here that the rest and activity rhythms of Bdr mice are phase advanced and fragmented under a light/dark cycle, reminiscent of the disturbed sleep patterns observed in schizophrenia. Retinal inputs appear normal in mutants, and clock gene rhythms within the suprachiasmatic nucleus (SCN) are normally phased both in vitro and in vivo. However, the 24 hr rhythms of arginine vasopressin within the SCN and plasma corticosterone are both markedly phase advanced in Bdr mice. We suggest that the Bdr circadian phenotype arises from a disruption of synaptic connectivity within the SCN that alters critical output signals. Collectively, our data provide a link between disruption of circadian activity cycles and synaptic dysfunction in a model of neuropsychiatric disease.
► A mouse Snap-25 mutant shows abnormal circadian behavior reminiscent of schizophrenia ► The phase advance of activity is mirrored by SCN output and corticosterone release ► Importantly, the core molecular clock of the Snap-25 mutant is not affected ► We discuss a link between neurotransmission, circadian defects, and schizophrenia
d-serine is an endogenous coagonist of the N-methyl-d-aspartate subtype glutamate receptor. Genetic association studies have implicated genes coding for enzymes associated with d-serine metabolism in schizophrenia and bipolar disorder.
Protein expression of serine racemase (SR) and its binding partner, protein interacting with C-kinase (PICK1), were examined by Western blotting in brains from wildtype and PICK1 knockout mice. Levels of d-serine in wildtype and PICK1 mice were also examined by an established high-pressure liquid chromatography protocol.
Expression of SR and PICK1 proteins was developmentally regulated. Although no change was observed in the level of SR protein, levels of d-serine were selectively decreased in the forebrain of neonatal PICK1 knockout mice, compared with those in wildtype mice.
PICK1 may be involved in the regulation of brain d-serine levels and SR in a spatially and temporally specific manner.
Bipolar disorder; d-serine; knockout mice; PICK1; schizophrenia; serine racemase
Schizophrenia is a complex disorder characterized by wide-ranging cognitive impairments, including deficits in learning as well as sensory gating. The causes of schizophrenia are unknown, but alterations in intracellular G-protein signaling pathways are among the molecular changes documented in patients with schizophrenia. Using the CaMKIIα promoter to drive expression in neurons within the forebrain, we have developed transgenic mice that express a constitutively active form of Gsα (Gsα*), the G protein that couples receptors such as the D1 and D5 dopamine receptors to adenylyl cyclase. We have also generated mice in which the CaMKIIα promoter drives expression of a dominant-negative form of protein kinase A, R(AB). Here, we examine startle responses and prepulse inhibition of the startle reflex (PPI) in these Gsα* and R(AB) transgenic mice. Gsα* transgenic mice exhibited selective deficits in PPI, without exhibiting alterations in the startle response, whereas no deficit in startle or PPI was found in the R(AB) transgenic mice. Thus, overstimulation of the cAMP/PKA pathway disrupts PPI, but the cAMP/PKA pathway may not be essential for sensorimotor gating. Gsα* transgenic mice may provide an animal model of certain endophenotypes of schizophrenia, because of the similarities between them and patients with schizophrenia in G-protein function, hippocampus-dependent learning, and sensorimotor gating.
G proteins; protein kinase A; startle response; prepulse inhibition; schizophrenia; animal model
Brain-derived neurotrophic factor (bdnf) is one of numerous gene products necessary for long-term memory formation and dysregulation of bdnf has been implicated in the pathogenesis of cognitive and mental disorders. Recent work indicates that epigenetic-regulatory mechanisms including the markings of histone proteins and associated DNA remain labile throughout the lifespan and represent an attractive molecular process contributing to gene regulation in the brain. In this review, important information will be discussed on epigenetics as a set of newly identified dynamic transcriptional mechanisms serving to regulate gene expression changes in the adult brain with particular emphasis on bdnf transcriptional readout in learning and memory formation. This review will also highlight evidence for the role of epigenetics in aberrant bdnf gene regulation in the pathogenesis of cognitive dysfunction associated with seizure disorders, Rett syndrome, Schizophrenia, and Alzheimer’s disease. Such research offers novel concepts for understanding epigenetic transcriptional mechanisms subserving adult cognition and mental health, and furthermore promises novel avenues for therapeutic approach in the clinic.
There is substantial evidence, both pharmacological and genetic, that hypofunction of the N-methyl-D-aspartate receptor (NMDAR) is a core pathophysiological feature of schizophrenia. There are morphological brain changes associated with schizophrenia, including perturbations in the dendritic morphology of cortical pyramidal neurons and reduction in cortical volume. Our experiments investigated whether these changes in dendritic morphology could be recapitulated in a genetic model of NMDAR hypofunction, the serine racemase knockout (SR−/−) mouse. Pyramidal neurons in primary somatosensory cortex (S1) of SR−/− mice had reductions in the complexity, total length, and spine density of apical and basal dendrites. In accordance with reduced cortical neuropil, SR−/− mice also had reduced cortical volume as compared to wild type mice. Analysis of S1 mRNA by DNA microarray and gene expression analysis revealed gene changes in SR−/− that are associated with psychiatric and neurologic disorders, as well as neurodevelopment. The microarray analysis also identified reduced expression of brain derived neurotrophic factor (BDNF) in SR−/− mice. Follow-up analysis by ELISA confirmed a reduction of BDNF protein levels in the S1 of SR−/− mice. Finally, S1 pyramidal neurons in glycine transporter heterozygote (GlyT1+/−) mutants, which display enhanced NMDAR function, had increased dendritic spine density. These results suggest that proper NMDAR function is important for the arborization and spine density of pyramidal neurons in cortex. Moreover, they suggest that NMDAR hypofunction might, in part, be contributing to the dendritic and synaptic changes observed in schizophrenia and highlight this signaling pathway as a potential target for therapeutic intervention.
serine racemase; glycine; NMDA receptor; somatosensory cortex; BDNF; dendritic spines; schizophrenia
The challenges in gene identification for psychiatric disorders have awakened interest toward quantitative traits and endophenotypes that are potentially more closely related to the underlying biology and provide more power in the linkage and association analyses. Previously, we successfully replicated schizophrenia linkage on chromosome 7q21-32 in Finnish families and demonstrated that an intragenic short tandem repeat (STR) allele of the regional Reelin (RELN) gene is associated with multiple cognitive traits representing central cognitive functions regarded as valid endophenotypes for schizophrenia.
Here, we used an extended sample of 290 Finnish families with schizophrenia and 375 control subjects in an association analysis between 96 SNPs and three STRs in RELN and diagnostic categories, clinical disorder features, as well as central cognitive functions impaired in schizophrenia.
We replicated the original association between RELN intragenic STR allele and working memory in individuals (n = 342) not overlapping with the previous study. This risk allele remained central in the whole study sample by being associated with impaired cognitive functioning and more severe positive and negative symptoms of schizophrenia (p = .0005–.00002). Additionally, multiple SNPs indicated association with the severity of positive symptoms of schizophrenia and together showed potential additive effect on the severity of the symptoms (p = .0000001). However, no significant associations with clinical diagnostic categories emerged.
The strongest effects on cognitive functions were detected among the affected individuals. We thus propose a particular role for RELN as a modifier gene of the pathogenesis of schizophrenia.
Endophenotype; memory; neuropsychology; psychiatry; RELN; schizophrenia
Cyclin-dependent kinase 5 (Cdk5) is a proline-directed serine/threonine kinase that is ubiquitous in the nervous system and interacts with a myriad of substrates. Its modulation of synaptic plasticity and associated mechanisms of learning and memory as well as neurodegeneration and cognitive disease highlights its importance in the human brain. Cdk5 is active throughout the neuron via its kinase activity, protein-protein interactions, and nuclear associations. It regulates functions thought vital to memory and plasticity, including synaptic vesicle recycling, dendritic spine formation, neurotransmitter receptor density, and neuronal excitability. Although conditional knockout of Cdk5 improves learning and plasticity, the associated deleterious effects of increased excitability cast doubts on the therapeutic efficacy of systemic inhibitors. However, through further work on the regulation of Cdk5 and its effectors, this important molecule promises to aid in elucidating key pathways involved in learning and memory and uncover innovative therapeutic targets to treat neurodegenerative and neuropsychiatric diseases.
Cdk5; Learning and memory; Plasticity; Neurodegeneration; Cognition