Alterations in hippocampal non-phosphorylated MAP2 protein expression in schizophrenia

More than a marker: potential pathogenic functions of MAP2

Microtubule-associated protein 2 (MAP2) is the predominant cytoskeletal regulator within neuronal dendrites, abundant and specific enough to serve as a robust somatodendritic marker. It influences microtubule dynamics and microtubule/actin interactions to control neurite outgrowth and synaptic functions, similarly to the closely related MAP Tau. Though pathology of Tau has been well appreciated in the context of neurodegenerative disorders, the consequences of pathologically dysregulated MAP2 have been little explored, despite alterations in its immunoreactivity, expression, splicing and/or stability being observed in a variety of neurodegenerative and neuropsychiatric disorders including Huntington’s disease, prion disease, schizophrenia, autism, major depression and bipolar disorder. Here we review the understood structure and functions of MAP2, including in neurite outgrowth, synaptic plasticity, and regulation of protein folding/transport. We also describe known and potential mechanisms by which MAP2 can be regulated via post-translational modification. Then, we assess existing evidence of its dysregulation in various brain disorders, including from immunohistochemical and (phospho) proteomic data. We propose pathways by which MAP2 pathology could contribute to endophenotypes which characterize these disorders, giving rise to the concept of a “MAP2opathy”—a series of disorders characterized by alterations in MAP2 function.

Specific phosphorylation of microtubule-associated protein 2c by extracellular signal-regulated kinase reduces interactions at its Pro-rich regions

Microtubule-associated protein 2 (MAP2) is an important neuronal target of extracellular signal-regulated kinase 2 (ERK2) involved in Raf signaling pathways, but mechanistic details of MAP2 phosphorylation are unclear. Here, we used NMR spectroscopy to quantitatively describe the kinetics of phosphorylation of individual serines and threonines in the embryonic MAP2 variant MAP2c. We carried out real-time monitoring of phosphorylation to discover major phosphorylation sites that were not identified in previous studies relying on specific antibodies. Our comparison with phosphorylation of MAP2c by a model cyclin-dependent kinase CDK2 and with phosphorylation of the MAP2c homolog Tau revealed differences in phosphorylation profiles that explain specificity of regulation of biological functions of MAP2c and Tau. To probe the molecular basis of the regulatory effect of ERK2, we investigated the interactions of phosphorylated and unphosphorylated MAP2c by NMR with single-residue resolution. As ERK2 phosphorylates mostly outside the regions binding microtubules, we studied the binding of proteins other than tubulin, namely regulatory subunit RIIα of cAMP-dependent protein kinase (PKA), adaptor protein Grb2, Src homology domain 3 of tyrosine kinases Fyn and Abl, and ERK2 itself. We found ERK2 phosphorylation interfered mostly with binding to proline-rich regions of MAP2c. Furthermore, our NMR experiments in SH-SY5Y neuroblastoma cell lysates showed that the kinetics of dephosphorylation are compatible with in-cell NMR studies and that residues targeted by ERK2 and PKA are efficiently phosphorylated in the cell lysates. Taken together, our results provide a deeper characterization of MAP2c phosphorylation and its effects on interactions with other proteins.

mTOR-Related Brain Dysfunctions in Neuropsychiatric Disorders

The mammalian target of rapamycin (mTOR) is an ubiquitously expressed serine-threonine kinase, which senses and integrates several intracellular and environmental cues to orchestrate major processes such as cell growth and metabolism. Altered mTOR signalling is associated with brain malformation and neurological disorders. Emerging evidence indicates that even subtle defects in the mTOR pathway may produce severe effects, which are evident as neurological and psychiatric disorders. On the other hand, administration of mTOR inhibitors may be beneficial for a variety of neuropsychiatric alterations encompassing neurodegeneration, brain tumors, brain ischemia, epilepsy, autism, mood disorders, drugs of abuse, and schizophrenia. mTOR has been widely implicated in synaptic plasticity and autophagy activation. This review addresses the role of mTOR-dependent autophagy dysfunction in a variety of neuropsychiatric disorders, to focus mainly on psychiatric syndromes including schizophrenia and drug addiction. For instance, amphetamines-induced addiction fairly overlaps with some neuropsychiatric disorders including neurodegeneration and schizophrenia. For this reason, in the present review, a special emphasis is placed on the role of mTOR on methamphetamine-induced brain alterations.

The microtubular cytoskeleton of olfactory neurons derived from patients with schizophrenia or with bipolar disorder: Implications for biomarker characterization, neuronal physiology and pharmacological screening

Schizophrenia (SZ) and Bipolar Disorder (BD) are highly inheritable chronic mental disorders with a worldwide prevalence of around 1%. Despite that many efforts had been made to characterize biomarkers in order to allow for biological testing for their diagnoses, these disorders are currently detected and classified only by clinical appraisal based on the Diagnostic and Statistical Manual of Mental Disorders. Olfactory neuroepithelium-derived neuronal precursors have been recently proposed as a model for biomarker characterization. Because of their peripheral localization, they are amenable to collection and suitable for being cultured and propagated in vitro. Olfactory neuroepithelial cells can be obtained by a non-invasive brush-exfoliation technique from neuropsychiatric patients and healthy subjects. Neuronal precursors isolated from these samples undergo in vitro the cytoskeletal reorganization inherent to the neurodevelopment process which has been described as one important feature in the etiology of both diseases. In this paper, we will review the current knowledge on microtubular organization in olfactory neurons of patients with SZ and with BD that may constitute specific cytoskeletal endophenotypes and their relation with alterations in L-type voltage-activated Ca(2+) currents. Finally, the potential usefulness of neuronal precursors for pharmacological screening will be discussed.

Dendritic spine alterations in schizophrenia

Schizophrenia is a chronic illness affecting approximately 0.5-1% of the world's population. The etiology of schizophrenia is complex, including multiple genes, and contributing environmental effects that adversely impact neurodevelopment. Nevertheless, a final common result, present in many subjects with schizophrenia, is impairment of pyramidal neuron dendritic morphology in multiple regions of the cerebral cortex. In this review, we summarize the evidence of reduced dendritic spine density and other dendritic abnormalities in schizophrenia, evaluate current data that informs the neurodevelopment timing of these impairments, and discuss what is known about possible upstream sources of dendritic spine loss in this illness.

Microtubule-associated proteins in mesial temporal lobe epilepsy with and without psychiatric comorbidities and their relation with granular cell layer dispersion

Background. Despite strong association between epilepsy and psychiatric comorbidities, biological substrates are unknown. We have previously reported decreased mossy fiber sprouting in mesial temporal lobe epilepsy (MTLE) patients with psychosis and increased in those with major depression. Microtubule associated proteins (MAPs) are essentially involved in dendritic and synaptic sprouting. Methods. MTLE hippocampi of subjects without psychiatric history, MTLE + major depression, and MTLE + interictal psychosis derived from epilepsy surgery and control necropsies were investigated for neuronal density, granular layer dispersion, and MAP2 and tau immunohistochemistry. Results. Altered MAP2 and tau expression in MTLE and decreased tau expression in MTLE with psychosis were found. Granular layer dispersion correlated inversely with verbal memory scores, and with MAP2 and tau expression in the entorhinal cortex. Patients taking fluoxetine showed increased neuronal density in the granular layer and those taking haloperidol decreased neuronal density in CA3 and subiculum. Conclusions. Our results indicate relations between MAPs, granular layer dispersion, and memory that have not been previously investigated. Differential MAPs expression in human MTLE hippocampi with and without psychiatric comorbidities suggests that psychopathological states in MTLE rely on differential morphological and possibly neurochemical backgrounds. This clinical study was approved by our institution's Research Ethics Board (HC-FMRP no. 1270/2008) and is registered under the Brazilian National System of Information on Ethics in Human Research (SISNEP) no. 0423.0.004.000-07.

Potential application as screening and drug designing tools of cytoarchitectural deficiencies present in three animal models of schizophrenia

BACKGROUND

The development of new treatment alternatives for schizophrenia has been prevented by the unknown etiology of the illness and the divergence of results in the field. However, consistent neuropathological findings are emerging from anatomical areas known to be at the core of schizophrenia. If these deficiencies are replicated in animal models then such anomalies could become the target for a new generation of drugs.

OBJECTIVE

To determine if the methylazoxymethanol acetate (MAM) model, the heterozygote reeler mouse (HRM) and NMDA-antagonists treated rats replicate neuropathological deficits encountered in patients with schizophrenia and to establish if such changes could lead the search for developing novel treatment alternatives.

METHODS

Databases including MEDLINE, Cochrane and Ovid were searched; search terms included neuropathology, schizophrenia and animal models.

RESULTS/CONCLUSIONS

NMDA-antagonist treated animals partially replicate schizophrenia anomalies in parvalbumin positive interneurons. In contrast, neuroanatomical deficiencies replicated by the MAM model and the HRM in the hippocampus and the prefrontal cortex seem promising targets for future pharmacological research in schizophrenia. Such neuroanatomical findings along with evidence from molecules and genes associated with schizophrenia suggest new drugs should aim to correct deficits in the formation of dendrites and axons that seems to be implicated in this illness pathophysiology.

A plausible model of schizophrenia must incorporate psychological and social, as well as neuro developmental, risk factors

Subtle alterations in brain development caused by genes or early environmental hazards, such as obstetric complications, play a role in projecting some individuals on a trajectory toward schizophrenia. High-risk and cohort studies demonstrate that children destined to develop schizophrenia tend to have delayed milestones and subtle neuromotor and cognitive impairments (particularly in coordination and language). These neurocognitive problems lead to difficulties in interpersonal relations, and their progressive alienation makes these at-risk children more likely to harbor odd or paranoid ideas. This cascade of increasingly deviant development may then be compounded by brain maturational changes during adolescence with a resultant lability of the dopaminergic response to stress. As a result, the individual is more susceptible to the effects of the abuse of dopamine-releasing drugs, and to other risk factors such as migration or stressful life events; social isolation may be a common pathway underlying several of the social risk factors.

Molecules, signaling, and schizophrenia

Schizophrenia is one of the most common psychiatric disorders, but despite some progress in identifying the genetic factors implicated in its development, the molecular mechanisms underlying its etiology and pathogenesis remain poorly understood. However, accumulating evidence suggests that regardless of the underlying genetic complexity, the mechanisms of the disease may impact a small number of common signaling pathways. In this review, we discuss the evidence for a role of schizophrenia susceptibility genes in intracellular signaling cascades by focusing on three prominent candidate genes: AKT, PPP3CC (calcineurin), and DISC1. We describe the regulation of a number of signaling cascades by AKT and calcineurin through protein phosphorylation and dephosphorylation, and the recently uncovered functions of DISC1 in cAMP and GSK3beta signaling. In addition, we present independent evidence for the involvement of their downstream signaling pathways in schizophrenia. Finally, we discuss evidence supporting an impact of these susceptibility genes on common intracellular signaling pathways and the convergence of their effects on neuronal processes implicated in schizophrenia.

The biochemical womb of schizophrenia: A review

The conclusive identification of specific etiological factors or pathogenic processes in the illness of schizophrenia has remained elusive despite great technological progress. The convergence of state-of-art scientific studies in molecular genetics, molecular neuropathophysiology, in vivo brain imaging and psychopharmacology, however, indicates that we may be coming much closer to understanding the genesis of schizophrenia. In near future, the diagnosis and assessment of schizophrenia using biochemical markers may become a "dream come true" for the medical community as well as for the general population. An understanding of the biochemistry/ visa vis pathophysiology of schizophrenia is essential to the discovery of preventive measures and therapeutic intervention.

Do mood symptoms subdivide the schizophrenia phenotype? Association of the GMP6A gene with a depression subgroup

Genetic studies of clinically defined subgroups of schizophrenia patients may reduce the phenotypic heterogeneity of schizophrenia and thus facilitate the identification of genes that confer risk to this disorder. Several latent class analyses have provided subgroups of psychotic disorders that show considerable consistency over these studies. The presence or absence of mood symptoms was found to contribute most to the delineations of these subgroups. In this study we used six previously published subtypes of psychosis derived from latent class analysis of a large sample of psychosis patients. In 280 schizophrenia patients and 525 healthy controls we investigated the associations of these subgroups with myelin related genes. After bonferroni correction we found an association of the glycoprotein M6A gene (GPM6A) with the subgroup of schizophrenia patients with high levels of depression (P-corrected = 0.006). Borderline association of the microtubulin associated protein tau (MAPT) with a primarily non-affective group of schizophrenia patients (P-corrected = 0.052) was also observed. GPM6A modulates the influence of stress on the hippocampus in animals. Thus our findings could suggest that GMP6A plays a role in the stress-induced hippocampal alterations that are found in psychiatric disorders in general and schizophrenia in particular. Overall, these finding suggests that investigating subgroups of schizophrenia based symptoms profile and particularly mood symptoms can facilitate genetic studies of schizophrenia.

Investigating the neurodevelopmental hypothesis of schizophrenia

1. An optimal intra-uterine environment is critical for normal development of the brain. It is now thought that abnormal development in a compromised prenatal and/or early postnatal environment may be a risk factor for several neurological disorders that manifest postnatally, such as cerebral palsy, schizophrenia and epilepsy. 2. The present review examines some of the effects of abnormal prenatal brain development and focuses on one disorder that has been hypothesized to have, at least in part, an early neurodevelopmental aetiology: schizophrenia. 3. The key neuropathological alterations and changes in some of the neurotransmitter systems observed in patients with schizophrenia are reviewed. Evidence in support of a neurodevelopmental hypothesis for schizophrenia is examined. 4. A summary of the animal models that have been used by researchers in an attempt to elucidate the origins of this disorder is presented. Although no animal model of a complex human disorder is ever likely to emulate deficits in all aspects of structure and function observed in patients with a neuropsychiatric illness, our findings and those of others give support to the early neurodevelopmental hypothesis. 5. Thus, it is possible that an adverse event in utero disrupts normal brain development and creates a vulnerability of the brain that predisposes an already at-risk individual (e.g. genetic inheritance) to develop the disorder later in life.

Effect of hypothermia on postmortem alterations in MAP2 immunostaining in the human hippocampus

Ischemic neuronal injury induce degradation of microtubule-associated protein 2 (MAP2). In addition to ischemia, postmortem brains show alterations in MAP2 immunoreactivity in the hippocampus, suggesting that the factors inducing cytoskeletal disruption in postmortem brain are similar to those in ischemic brains. Hypothermia reduces the severity of ischemic injury including disruption of MAP2 in the hippocampus. However, whether hypothermia reduces postmortem changes of MAP2 was not clear. In this study, we evaluated the effect of hypothermia on postmortem degradation of MAP2 in the human hippocampus at various postmortem intervals using immunohistochemistry. In postmortem brains without hypothermia (the normothermic group), the locus of MAP2 immunoreactivity moved from the dendrites to the cell bodies prior to becoming undetectable with increasing postmortem interval, particularly in the CA1-subiculum region. On the other hand, the change in MAP2 immunoreactivity was remarkably attenuated in brains of death from cold (the hypothermic group). The present study demonstrated that MAP2 disruption is remarkable in the CA1-subiculum region of autopsied brains and that hypothermia reduces the postmortem change of MAP2, as observed in ischemic brain. Therefore, immunostaining of MAP2 in the hippocampus could be used to diagnose hypothermia.

The tumor suppressor adenomatous polyposis coli gene is associated with susceptibility to schizophrenia

The etiology of schizophrenia is unclear, although family, twin, and linkage studies implicate genetic factors. Here, we identified adenomatous polyposis coli (APC), a tumor suppressor gene, as a risk factor for schizophrenia. We compared leukocytic gene expression patterns of six pairs of patients with schizophrenia and healthy controls by microarray. APC expression levels were significantly increased in all patients compared to healthy controls. To confirm the findings of microarray analysis, we measured expression levels of APC in the leukocytes from 30 relapse patients taking antipsychotic medication, 29 first-episode drug-naïve patients, and 30 healthy controls using real-time quantitative reverse transcription (RT)-polymerase chain reaction (PCR). APC expression levels were significantly increased in leukocytes of schizophrenics both taking and not taking antipsychotic medication and hence the increase of APC expression was not due to antipsychotic medication. APC is located at 5q21-22, which has been previously reported to be linked with schizophrenia. Further, we performed the transmission disequilibrium test (TDT) and TDT based on haplotypes to search for the association between schizophrenia and APC by examining 163 parent-offspring trios of Chinese descent. We analyzed three single-nucleotide polymorphisms (SNPs) (rs2229992, rs42427, rs465899) at the exon region of APC. TDT showed that the three SNPs are significantly associated with schizophrenia (TDT chi(2)=4.23, P<0.05; 4.15, P<0.05; 8.49 P<0.01, respectively; HHRRchi(2)=5.54, P<0.05; 4.40, P<0.05; 9.79, P<0.01, respectively). We found a significant association between the APC haplotypes from rs2229992-rs42427-rs465899 and schizophrenia (Global chi(2)=44.376,df=7, P<0.001). The C-A-T haplotype has a frequency of more than 57% and has a strong association with schizophrenia (chi(2)=15.04, P<0.001). These results indicate that the APC may be a candidate gene conferring susceptibility to schizophrenia and also may be associated with reduced vulnerability to cancer in schizophrenia.

Low GSK-3beta in schizophrenia as a consequence of neurodevelopmental insult

Glycogen synthase kinase-3 (GSK-3) is a protein kinase highly abundant in brain and involved in signal transduction cascades, particularly neurodevelopment. Its activity and protein levels have been reported to be over 40% lower in postmortem frontal cortex of schizophrenic patients. GSK-3beta in occipital cortex of schizophrenic patients was not reduced, suggesting regional specificity. There was no reduction in GSK-3beta protein levels in fresh and immortalized lymphocytes and both GSK-3 activity and GSK-3beta mRNA levels in fresh lymphocytes from schizophrenic patients. In the schizophrenia-related neonatal ventral hippocampal lesion rat model, we measured GSK-3beta protein levels and GSK-3 activity in the frontal cortex. GSK-3beta protein levels in lesioned rats were significantly lower than in sham rats, favoring perinatal insult as a cause of low GSK-3beta in schizophrenia. Taken together, these studies suggest that low GSK-3 in postmortem brain of schizophrenic patients is a late consequence of perinatal neurodevelopmental insult in schizophrenia. In rats, acute or chronic cold restraint stress did not change GSK-3beta protein levels. Chronic treatment of rats with lithium, valproate, haloperidol or clozapine did not change rat cortical GSK-3beta protein levels ex vivo, supporting the concept that low GSK-3beta in schizophrenia is not secondary to stress or drug treatment. Our initial findings of low GSK-3beta protein levels in postmortem brain have been replicated by another group. Our own group has found additionally that GSK-3beta mRNA levels were 40% lower in postmortem dorsolateral prefrontal cortex (DLPFC) of schizophrenic patients, supporting our previous findings. Further studies will be aimed at determining whether nonspecific neonatal damage or only specific factors cause low GSK-3 as a late effect. We plan to study whether low GSK-3beta activity is associated with biochemical effects such as elevated beta-catenin levels.

Effect of hypothermia on postmortem alterations in MAP2 immunostaining in the human hippocampus

Ischemic neuronal injury induce degradation of microtubule-associated protein 2 (MAP2). In addition to ischemia, postmortem brains show alterations in MAP2 immunoreactivity in the hippocampus, suggesting that the factors inducing cytoskeletal disruption in postmortem brain are similar to those in ischemic brains. Hypothermia reduces the severity of ischemic injury including disruption of MAP2 in the hippocampus. However, whether hypothermia reduces postmortem changes of MAP2 was not clear. In this study, we evaluated the effect of hypothermia on postmortem degradation of MAP2 in the human hippocampus at various postmortem intervals using immunohistochemistry. In postmortem brains without hypothermia (the normothermic group), the locus of MAP2 immunoreactivity moved from the dendrites to the cell bodies prior to becoming undetectable with increasing postmortem interval, particularly in the CA1-subiculum region. On the other hand, the change in MAP2 immunoreactivity was remarkably attenuated in brains of death from cold (the hypothermic group). The present study demonstrated that MAP2 disruption is remarkable in the CA1-subiculum region of autopsied brains and that hypothermia reduces the postmortem change of MAP2, as observed in ischemic brain. Therefore, immunostaining of MAP2 in the hippocampus could be used to diagnose hypothermia.

Microtubule-associated protein MAP2 expression in olfactory bulb in schizophrenia

Previous studies have described alterations in presynaptic and postsynaptic elements in various parts of the CNS in schizophrenia, which may, at least in part, be due to abnormalities in neurodevelopmental processes. The olfactory bulb (OB) is a unique CNS area for examining synaptic development and plasticity in schizophrenia because it undergoes continuous reinnervation throughout life. Moreover, olfactory deficits and reduced OB volume have been observed in schizophrenia. We investigated the expression in the OB of the microtubule-associated protein MAP2, which has been shown to be abnormally expressed in the hippocampal region in schizophrenia. In both developing and mature neurons, MAP2 is an important structural component of dendrites and participates in the modification of synaptic organization. We used immunocytochemistry with phosphoepitope-specific and phosphorylation-state-independent antibodies to examine MAP2 expression in the glomerular layer of the OB in elderly subjects with chronic schizophrenia and controls. Phosphorylation-independent MAP2 expression was significantly reduced in schizophrenia, while phosphorylated MAP2 expression did not differ between groups. These results are consistent with faulty OB innervation in schizophrenia.

The hippocampus in schizophrenia: a review of the neuropathological evidence and its pathophysiological implications

This paper puts the case for the hippocampus as being central to the neuropathology and pathophysiology of schizophrenia. The evidence comes from a range of approaches, both in vivo (neuropsychology, structural and functional imaging) and post mortem (histology, morphometry, gene expression, and neurochemistry). Neuropathologically, the main positive findings concern neuronal morphology, organisation, and presynaptic and dendritic parameters. The results are together suggestive of an altered synaptic circuitry or "wiring" within the hippocampus and its extrinsic connections, especially with the prefrontal cortex. These changes plausibly represent the anatomical component of the aberrant functional connectivity that underlies schizophrenia. Glutamatergic pathways are prominently but not exclusively affected. Changes appear somewhat greater in the left hippocampus than the right, and CA1 is relatively uninvolved compared to other subfields. Hippocampal pathology in schizophrenia may be due to genetic factors, aberrant neurodevelopment, and/or abnormal neural plasticity; it is not due to any recognised neurodegenerative process. Hippocampal involvement is likely to be associated with the neuropsychological impairments of schizophrenia rather than with its psychotic symptoms.

Decrease of serotonin receptor 2C in schizophrenia brains identified by high-resolution mRNA expression analysis

BACKGROUND

RNA expression profiling can provide hints for the selection of candidate susceptibility genes, for formulation of hypotheses about the development of a disease, and/or for selection of candidate gene targets for novel drug development. We measured messenger RNA expression levels of 16 candidate genes in brain samples from 55 schizophrenia patients and 55 controls. This is the largest sample so far used to identify genes differentially expressed in schizophrenia brains.

METHODS

We used a sensitive real-time polymerase chain reaction methodology and a novel statistical approach, including the development of a linear model of analysis of covariance type.

RESULTS

We found two genes differentially expressed: monoamine oxidase B was significantly increased in schizophrenia brain (p =.001), whereas one of the serotonin receptor genes, serotonin receptor 2C, was significantly decreased (p =.001). Other genes, previously proposed to be differentially expressed in schizophrenia brain, were invariant in our analysis.

CONCLUSIONS

The differential expression of serotonin receptor 2C is particularly relevant for the development of new atypical antipsychotic drugs. The strategy presented here is useful to evaluate hypothesizes for the development of the disease proposed by other investigators.

Does schizophrenia result from developmental or degenerative processes?

The debate as to whether schizophrenia is a neurodevelopmental or a neurodegenerative disorder has its roots in the latter part of the 19th century when authorities such as Clouston (1891) posited that at least some insanities were "developmental" in origin. These views were soon eclipsed by Kraepelin's (1896) concept of dementia praecox as a degenerative disease, and the latter view carried not only the day but also much of the 20th century. Then, in the 1980s several research groups again began to speculate that schizophrenia might have a significant developmental component (Feinberg, 1982-1983; Schulsinger et al., 1984; Murray et al., 1985; Murray and Lewis, 1987; Weinberger et al., 1987). What became known as the "neurodevelopmental hypothesis" received support from neuropathological studies implicating anomalies in early brain development such as aberrant migration of neurons. Unfortunately, these studies proved difficult, if not impossible, to replicate (Harrison, 1999). The pendulum, therefore, began to swing again, and in the latter part of the 1990s came renewed claims that the clinical progression of the illness was accompanied by continued cerebral ventricular enlargement and reduction in the volumes of certain brain structures. Nevertheless, since few doubt that there is a developmental component to schizophrenia, the question which we will address in this paper is whether schizophrenia is a) simply the final consequence of a cascade of increasing developmental deviance (Bramon et al., 2001), or b) whether there is an additional brain degeneration following onset of psychosis which is superimposed on the developmental impairment (Lieberman, 1999).

Schizophrenia: from phenomenology to neurobiology

Schizophrenia is a common and debilitating illness, characterized by chronic psychotic symptoms and psychosocial impairment that exact considerable human and economic costs. The literature in electronic databases as well as citations and major articles are reviewed with respect to the phenomenology, pathology, treatment, genetics and neurobiology of schizophrenia. Although studied extensively from a clinical, psychological, biological and genetic perspective, our expanding knowledge of schizophrenia provides only an incomplete understanding of this complex disorder. Recent advances in neuroscience have allowed the confirmation or refutation of earlier findings in schizophrenia, and permit useful comparisons between the different levels of organization from which the illness has been studied. Schizophrenia is defined as a clinical syndrome that may include a collection of diseases that share a common presentation. Genetic factors are the most important in the etiology of the disease, with unknown environmental factors potentially modulating the expression of symptoms. Schizophrenia is a complex genetic disorder in which many genes may be implicated, with the possibility of gene-gene interactions and a diversity of genetic causes in different families or populations. A neurodevelopmental rather than degenerative process has received more empirical support as a general explanation of the pathophysiology, although simple dichotomies are not particularly helpful in such a complicated disease. Structural brain changes are present in vivo and post-mortem, with both histopathological and imaging studies in overall agreement that the temporal and frontal lobes of the cerebral cortex are the most affected. Functional imaging, neuropsychological testing and clinical observation are also generally consistent in demonstrating deficits in cognitive ability that correlate with abnormalities in the areas of the brain with structural abnormalities. The dopamine and other neurotransmitter systems are certainly involved in the treatment or modulation of psychotic symptoms. These broad findings represent the distillation of a large body of disparate data, but firm and specific findings are sparse, and much about schizophrenia remains unknown.

Hippocampus as comparator: role of the two input and two output systems of the hippocampus in selection and registration of information

Processing of multimodal sensory information by the morphological subdivisions of the hippocampus and its input and output structures was investigated in unanesthetized rabbits by extracellular recording of neuronal activity. Analysis shows principal differences between CA3 neurons with uniform multimodal, mainly inhibitory, rapidly habituating sensory responses, and CA1-subicular neurons, substantial parts of which have phasic reactions and patterned on-responses, depending on the characteristics of the stimuli. These differences result from the organization of the afferent inputs to CA1 and CA3. Analysis of neuronal responses in sources of hippocampal inputs, their electrical stimulation, and chronic disconnection show the greater functional significance of the brain-stem reticular input for tonic responses characteristic of CA3. This input signal before entering the hippocampus is additionally preprocessed at the MS-DB relay, where it becomes more uniform and frequency-modulated in the range of theta-rhythm. It is shown that the new sensory stimuli produce inhibitory reset, after which synchronized theta-modulation is triggered. Other stimuli, appearing at the background of the ongoing theta, do not evoke any responses of the hippocampal neurons. Thus, theta-modulation can be regarded as a mechanism of attention, which prolongs response to a selected stimulus and simultaneously protects its processing against interference. The cortical input of the hippocampus introduces highly differentiated information analyzed at the highest levels of the neocortex through the intermediary of the entorhinal cortex and presubiculum. However, only CA1-subiculum receives this information directly; before its entrance into CA3, it is additionally preprocessed at the FD relay, where the secondary simplification of signals occurs. As a result, CA3 receives by its two inputs (MS-DB and FD) messages just about the presence and level of input signals in each of them, and performs relatively simple functions of determination of match/mismatch of their weights. For this comparator system, the presence of signal only in the reticulo-septal input is equivalent to quality of novelty. The cortical signal appears with some delay, after its analysis in the neocortex and shaping in the prehippocampal structures; besides, it is gradually increased due to LTP-like incremental changes in PP and mossy fiber synapses. The CA3 neurons with potentiated synapses of cortical input do not respond to sensory stimuli; that is, the increased efficacy of the cortical signals can be regarded as "familiarity" of a signal, terminating the reactive state of the CA3 neurons. The integrity of both inputs is necessary for gradual habituation of sensory responses in the hippocampus. The output signals of CA3 following in the precommissural fornix to the output relay-LS nucleus and to the brain-stem structures have strong regulatory influence on the level of brain activity (arousal), which is an important condition for processing and registration of information. The primary targets of this output signal are raphe nuclei, which suppress activity of the ascending excitatory RF. In the background state, activity of the CA3 neurons through the intermediary of raphe keeps RF under tonic inhibitory control. Inhibition of the majority of CA3 pyramidal neurons during a novel stimulus action decreases the volume of its output signal to raphe and releases RF from tonic inhibition (increase in level of activity of the forebrain, arousal). When the responses of CA3 neurons habituate, the initial high background activity is reinstated, as well as tonic suppression of RF. Analysis of the second output of CA3 (by Schaffer's collaterals to CA1) shows that activity in this pathway can block access of cortical signals from PP to CA1 neurons by action upon the local system of inhibitory neurons, or by shunting the propagation of signals in apical dendrites. Thus, CA3 can act as a filter controlling the information transmission by CA1; such transmission at any given moment is allowed only in those CA1 neurons which receive SC from CA3 neurons, responding to the sensory stimulus by suppression of their activity. Disconnection of the CA3 output fibers results in disappearance of habituation in all its target structures (raphe, RF, CA1). The output signal of CA1-subiculum follows by postcommissural fornix to the chain of structures of the main limbic circuit: mammillary bodies (medial nucleus), anterior thalamic nuclei (mainly antero-ventral nucleus), and cingulate limbic cortex (mainly posterior area). In each of these links, the signal is additionally processed. Habituation is nearly absent in these structures; instead, st

Neuropathological studies of synaptic connectivity in the hippocampal formation in schizophrenia

Cytoarchitectural changes in the hippocampal formation have been prominent among the various neuropathological abnormalities reported in schizophrenia. Replicated positive findings include decreased neuronal size and alterations in presynaptic and dendritic markers. These findings, in the absence of neurodegenerative changes, suggest that there are alterations in the neural circuitry in schizophrenia. These may represent the anatomical correlate of the aberrant functional connectivity described in neuroimaging studies, which in turn contributes to the psychotic and cognitive symptomatology of the disorder. The identity of the affected hippocampal circuits remains unclear; there is evidence for both glutamatergic and GABAergic involvement, and perhaps for a gradient of pathology in which changes are most apparent in CA4 and the subiculum, and least in CA1. The data, their interpretation, and their limitations are discussed, with particular emphasis upon molecular and immunological studies of synaptic protein gene expression.

GSK-3 and the neurodevelopmental hypothesis of schizophrenia

The Neurodevelopmental Hypothesis of schizophrenia suggests that interaction between genetic and environmental events occurring during critical early periods in neuronal growth may negatively influence the way by which nerve cells are laid down, differentiated and selectively culled by apoptosis. Recent advances offer insights into the regulation of brain development. The Wnt family of genes plays a central role in normal brain development. Activation of the Wnt cascade leads to inactivation of glycogen synthase kinase-3beta (GSK-3beta), accumulation and activation of beta-catenin and expression of genes involved in neuronal development. Alteration in the Wnt transduction cascade, which may represent an aberrant neurodevelopment in schizophrenia, is discussed. Programmed cell death is also an essential component of normal brain development. Abnormal neuronal distribution found in schizophrenic patients' brains may imply aberrant programmed cell death. GSK-3 participates in the signal transduction cascade of apoptosis. The possible role of aberrant GSK-3 in the etiology of schizophrenia is discussed.

Low GSK-3 activity in frontal cortex of schizophrenic patients

Glycogen synthase kinase-3 (GSK-3) (EC 2.7.1.37) is a protein kinase highly abundant in brain and involved in signal transduction cascades of multiple cellular processes, particularly neurodevelopment. Two forms of the enzyme, GSK-3alpha and -3beta have been previously identified. We have previously reported reduced GSK-3beta protein levels in postmortem frontal cortex of schizophrenic patients. In an attempt to explore whether reduction of GSK-3beta levels is brain region specific we examined it in occipital cortex. In order to find out if the reduction in frontal cortex is reflected in altered activity we measured GSK-3 enzymatic activity in this brain region. Western-blot analysis of GSK-3beta was carried out in postmortem occipital cortex of 15 schizophrenic, 15 bipolar, and 15 unipolar patients, and 15 normal controls. GSK-3 activity was measured by quantitating the phosphorylation of the specific substrate phospho-CREB in the frontal cortex specimens. GSK-3beta levels in occipital cortex did not differ between the four diagnostic groups. GSK-3 activity in the frontal cortex of schizophrenic patients was 45% lower than that of normal controls (0.196+/-0.082 and 0.357+/-0.084 pmol/mg proteinxmin, respectively; Kruskal-Wallis analysis: chi-square=8.27, df=3, p=0.04). The other two diagnostic groups showed no difference from the control group. Our results are consistent with the notion that schizophrenia involves neurodevelopmental pathology.

Antipsychotic treatment induces alterations in dendrite- and spine-associated proteins in dopamine-rich areas of the primate cerebral cortex

BACKGROUND

Mounting evidence indicates that long-term treatment with antipsychotic medications can alter the morphology and connectivity of cellular processes in the cerebral cortex. The cytoskeleton plays an essential role in the maintenance of cellular morphology and is subject to regulation by intracellular pathways associated with neurotransmitter receptors targeted by antipsychotic drugs.

METHODS

We have examined whether chronic treatment with the antipsychotic drug haloperidol interferes with phosphorylation state and tissue levels of a major dendritic cytoskeleton-stabilizing agent, microtubule-associated protein 2 (MAP2), as well as levels of the dendritic spine-associated protein spinophilin and the synaptic vesicle-associated protein synaptophysin in various regions of the cerebral cortex of rhesus monkeys.

RESULTS

Among the cortical areas examined, the prefrontal, orbital, cingulate, motor, and entorhinal cortices displayed significant decreases in levels of spinophilin, and with the exception of the motor cortex, each of these regions also exhibited increases in the phosphorylation of MAP2. No changes were observed in either spinophilin levels or MAP2 phosphorylation in the primary visual cortex. Also, no statistically significant changes were found in tissue levels of MAP2 or synaptophysin in any of the cortical regions examined.

CONCLUSIONS

Our findings demonstrate that long-term haloperidol exposure alters neuronal cytoskeleton- and spine-associated proteins, particularly in dopamine-rich regions of the primate cerebral cortex, many of which have been implicated in the psychopathology of schizophrenia. The ability of haloperidol to regulate cytoskeletal proteins should be considered in evaluating the mechanisms of both its palliative actions and its side effects.

Cytokine and growth factor involvement in schizophrenia--support for the developmental model

Medical treatment with various cytokines can provoke psychiatric symptoms. Conversely, psychiatric patients can display abnormalities in cytokine and neurotrophic factor expression. Such observations have pointed to the potential contribution of cytokines and growth factors to schizophrenic pathology and/or etiology. The cellular targets of the relevant factors and the nature of their actions remain to be explored in mental illness, however. Recent physiological studies demonstrate that cytokines and neurotrophic factors can markedly influence synaptic transmission and plasticity upon acute or chronic application. Moreover, many of the molecular alterations observed in the schizophrenic brain are consistent with abnormalities in cytokine and neurotrophic factor regulation of these molecules. In this review, we summarize these molecular pathology findings for schizophrenia and highlight the neurodevelopmental activities of cytokines and neurotrophic factors that may contribute to the etiology or pathology of this illness.

Cellular and molecular neuropathology of the parahippocampal region in schizophrenia

The entorhinal cortex, subiculum, and hippocampus have been regions of great interest in both clinical and neuropathological investigations of schizophrenia. Postmortem studies have identified numerous abnormalities, although many remain controversial or unconfirmed. Among the cellular and molecular neuropathological findings are (1) abnormal cytoarchitecture of the entorhinal cortex characterized by poorly formed layer II neuron clusters and laminar disorganization; (2) normal neuron density but smaller neuron size in the superficial lamina of the entorhinal cortex and subiculum; (3) abnormal expression of the microtubule-associated protein MAP2 in the entorhinal cortex and subiculum; (4) aberrant glutamatergic and catecholaminergic innervation of the entorhinal cortex; (5) abnormal mRNA expression of various transcription factors, ion channels, and neurosecretory pathway-related proteins in entorhinal stellate neurons; and (6) an absence of any neurodegeneration. Altogether, these findings suggest that aberrant neurodevelopmental processes play a key role in the pathobiology of schizophrenia and provide a neuroanatomic basis for understanding many of the clinical and neuropsychological abnormalities in the disorder.

Increased dendritic MAP2 expression in the hippocampus in schizophrenia

Microtubule associated proteins (MAPs) are central to the development of normal neuronal cytoarchitecture and have been reported to be altered in schizophrenia. In 12 schizophrenic (DSM-III-R criteria) and 12 control hippocampi, we estimated the MAP2 immunoreactive dendritic length using antibodies that recognize total MAP2 (MAP2-T), and a non-phosphorylated form of MAP2 (MAP2-NP). Within the corona ammonis (CA) subregions, and the subiculum, we estimated, for each antibody, the length of the immunoreactive dendritic arborisation using a stereological length estimation technique based on Bouffon's Needle principle and image analysis computer software. Controlling for the confounding effects of age and post-mortem delay, we have found an elevation in overall MAP2-NP immunoreactive dendritic length among schizophrenic subjects in the CA3 (F=5.9, p=0.03), CA2 (F=6.5, p=0.02), CA1 (F=8.3, p=0.01) and subicular (F=9.5, p=0.008) hippocampal subregions. Similar analyses of MAP2-T immunoreactive dendritic length demonstrated significant elevations in the CA1 (F=8.3, p=0.02), CA4 (F=4.9, p=0.04) and subicular (F=7.4, p=0.01) regions. The findings of this quantitative study of increased MAP2 immunoreactive dendritic arborisation in schizophrenia are most likely to reflect either an altered dendritic arborisation or a generalised increase in levels of MAP2 with the hippocampal pyramidal neurons. These findings add to the growing literature indicating the presence of synaptodendritic abnormalities in schizophrenia.

Mitogen-activated protein kinases in schizophrenia

BACKGROUND

Mitogen-activated protein kinases (MAPKs) are important mediators of signal transduction from the cell surface to the nucleus and have been implicated in the integration of a variety of physiologic processes in most cells, including neurons. To investigate the possible involvement of MAPKs in schizophrenia, we compared the levels of the MAPK intermediates in postmortem brain tissue obtained from schizophrenic and control subjects. Our focus was on the cerebellar vermis because of evidence suggesting that schizophrenia is associated with abnormalities of structure, function, and signal transduction in this brain region.

METHODS

Cytosolic proteins were fractionated by gel electrophoresis and subjected to Western blot analysis using polyclonal MAPK antibody, which detects total extracellular signal-regulated kinases (ERKs) 1 and 2 levels, and monoclonal MAP kinase phosphatase (MKP) 2 antibody.

RESULTS

Schizophrenic subjects had increased levels of ERK2 [2763 +/- (SD) 203 vs. 2286 +/- 607 arbitrary units, U = 17, p < .05] in cerebellar vermis. The levels of a dual specificity tyrosine phosphatase, MKP2, were significantly decreased in cerebellar vermis (1716 +/- 465 versus 2372 +/- 429 arbitrary units, U = 12, p < .02) from schizophrenic patients. ERK1/MKP2 and ERK2/MKP2 ratios in cerebellar vermis, but not in other brain regions, were significantly different in schizophrenic subjects as compared to control subjects (U = 15, p < or = .027; U = 3, p < .001, respectively).

CONCLUSIONS

MAPK levels are elevated in the cerebellar vermis of schizophrenic subjects. This could result from a protein dephosphorylation defect in vivo and might be involved in the pathology of the disease.

Mechanisms underlying epileptogenesis in cortical malformations

The presence of developmental cortical malformations is associated with epileptogenesis and other neurological disorders. In recent years, animal models specific to certain malformations have been developed to study the underlying epileptogenic mechanisms. Teratogens (chemical, thermal or radiation) applied during cortical neuroblast division and migration result in lissencephaly and focal cortical dysplasia. Animals with these malformations have a lowered seizure threshold as well as histopathologies typical of those found in human dysgenic brains. Alterations that may promote epileptogenesis have been identified in lissencephalic brains, such as increased numbers of bursting types of neurons, and abnormal connections between hippocampus, subcortical heterotopia, and neocortex. A distinct set of pathological properties is present in animal models of 4-layered microgyria, induced with cortical lesions made during late stages of cortical neuroblast migration. Hyperexcitability has been demonstrated in cortex adjacent to the microgyrus (paramicrogyral zone) in in vitro slice preparations. A number of observations suggest that cellular differentiation is delayed in microgyric brains. Other studies show increases in postsynaptic glutamate receptors and decreases in GABA(A) receptors in microgyric cortex. These alterations could promote epileptogenesis, depending on which cell types have the altered receptors. The microgyrus lacks thalamic afferents from sensory relay nuclei, that instead appear to project to the paramicrogyral region, thereby increasing excitatory connectivity within this epileptogenic zone. These studies have provided a necessary first step in understanding molecular and cellular mechanisms of epileptogenesis associated with cortical malformations.

Increased expression of Wnt-1 in schizophrenic brains

The regulated expression of Wnt-1, one member of the wingless/Wnt pathway, in the brain is critical for many neurodevelopmental processes. Recently, it has been reported that the wingless/Wnt pathway participates in a complex behavioral phenomenon and suggested that this pathway's molecules are candidate genes for neuropsychiatric disorders. Thus, we investigated the expression of Wnt-1 in the hippocampal region, which is believed to be closely involved in the pathophysiology of schizophrenia, of postmortem brains from 10 schizophrenic and 10 control individuals. Immunohistochemical analysis with polyclonal antibodies recognizing Wnt-1 revealed immunoreactivity primarily in the pyramidal cell layer, particularly in CA3 and CA4 regions. We observed a significant elevation in the number of Wnt-1-immunoreactive neurons in the great majority of schizophrenic brains relative to that in controls. The expression of Wnt-1 may be related to cell adhesion, synaptic rearrangement, and plasticity. Therefore, the increase in Wnt-1 immunoreactivity in schizophrenic hippocampi suggests an altered plasticity of this structure in a large proportion of schizophrenic brains. These findings suggest an abnormality of the wingless/Wnt pathway present in the schizophrenic brain and may support the 'neurodevelopmental hypothesis' of schizophrenia.

The neuropathology of schizophrenia. A critical review of the data and their interpretation

Despite a hundred years' research, the neuropathology of schizophrenia remains obscure. However, neither can the null hypothesis be sustained--that it is a 'functional' psychosis, a disorder with no structural basis. A number of abnormalities have been identified and confirmed by meta-analysis, including ventricular enlargement and decreased cerebral (cortical and hippocampal) volume. These are characteristic of schizophrenia as a whole, rather than being restricted to a subtype, and are present in first-episode, unmedicated patients. There is considerable evidence for preferential involvement of the temporal lobe and moderate evidence for an alteration in normal cerebral asymmetries. There are several candidates for the histological and molecular correlates of the macroscopic features. The probable proximal explanation for decreased cortical volume is reduced neuropil and neuronal size, rather than a loss of neurons. These morphometric changes are in turn suggestive of alterations in synaptic, dendritic and axonal organization, a view supported by immunocytochemical and ultrastructural findings. Pathology in subcortical structures is not well established, apart from dorsal thalamic nuclei, which are smaller and contain fewer neurons. Other cytoarchitectural features of schizophrenia which are often discussed, notably entorhinal cortex heterotopias and hippocampal neuronal disarray, remain to be confirmed. The phenotype of the affected neuronal and synaptic populations is uncertain. A case can be made for impairment of hippocampal and corticocortical excitatory pathways, but in general the relationship between neurochemical findings (which centre upon dopamine, 5-hydroxytryptamine, glutamate and GABA systems) and the neuropathology of schizophrenia is unclear. Gliosis is not an intrinsic feature; its absence supports, but does not prove, the prevailing hypothesis that schizophrenia is a disorder of prenatal neurodevelopment. The cognitive impairment which frequently accompanies schizophrenia is not due to Alzheimer's disease or any other recognized neurodegenerative disorder. Its basis is unknown. Functional imaging data indicate that the pathophysiology of schizophrenia reflects aberrant activity in, and integration of, the components of distributed circuits involving the prefrontal cortex, hippocampus and certain subcortical structures. It is hypothesized that the neuropathological features represent the anatomical substrate of these functional abnormalities in neural connectivity. Investigation of this proposal is a goal of current neuropathological studies, which must also seek (i) to establish which of the recent histological findings are robust and cardinal, and (ii) to define the relationship of the pathological phenotype with the clinical syndrome, its neurochemistry and its pathogenesis.

Preferential involvement of excitatory neurons in medial temporal lobe in schizophrenia

BACKGROUND

The anatomical basis of schizophrenia involves the cytoarchitecture of the cerebral cortex, but the phenotype of the affected neurons and synapses remains unclear. In mice, the presynaptic protein complexin I is a marker of axosomatic (inhibitory) synapses, whereas complexin II is a marker of axodendritic (mainly excitatory) synapses. These findings suggest that the complexins might be useful in the investigation of the synaptic pathology of schizophrenia.

METHODS

We characterised the expression of the complexins in tissue taken at necropsy from human medial temporal lobe (hippocampus, parahippocampal gyrus) and cerebellum using in-situ hybridisation and immunoautoradiography. We then measured the concentrations of the complexins and their messenger RNAs (mRNAs) in the medial temporal lobe of 11 patients with schizophrenia and 11 non-schizophrenic controls.

FINDINGS

The distribution of complexin I and II was consistent with the data on mice, with predominant expression of complexin I by inhibitory neurons, and complexin II by excitatory neurons. The amounts of both complexin mRNAs were lower in schizophrenic than in control patients (p<0.001), but the difference of complexin II mRNA was greater. The amount of complexin I protein was unchanged in schizophrenia, but complexin II protein was decreased (p<0.001). For both mRNA and protein, the complexin II/complexin I ratio was lower in schizophrenia, confirming the relatively greater loss of the excitatory marker. The findings did not seem attributable to medication.

INTERPRETATION

The synaptic pathology of schizophrenia, at least in medial temporal lobe, primarily affects excitatory (glutamatergic) neurons. The inferred imbalance between excitatory and inhibitory circuitry may contribute to the involvement of this region in the pathophysiology of the disorder.