Evidence for the involvement of the hippocampus in the pathophysiology of schizophrenia

Magnocellular and parvocellular contributions to brain network dysfunction during learning and memory: Implications for schizophrenia

Memory deficits are core features of schizophrenia, and a central aim in biological psychiatry is to identify the etiology of these deficits. Scrutiny is naturally focused on the dorsolateral prefrontal cortex and the hippocampal cortices, given these structures' roles in memory and learning. The fronto-hippocampal framework is valuable but restrictive. Network-based underpinnings of learning and memory are substantially diverse and include interactions between hetero-modal and early sensory networks. Thus, a loss of fidelity in sensory information may impact memorial and cognitive processing in higher-order brain sub-networks, becoming a sensory source for learning and memory deficits. In this overview, we suggest that impairments in magno- and parvo-cellular visual pathways result in degraded inputs to core learning and memory networks. The ascending cascade of aberrant neural events significantly contributes to learning and memory deficits in schizophrenia. We outline the network bases of these effects, and suggest that any network perspectives of dysfunction in schizophrenia must assess the impact of impaired perceptual contributions. Finally, we speculate on how this framework enriches the space of biomarkers and expands intervention strategies to ameliorate this prototypical disconnection syndrome.

Joint-Tissue Integrative Analysis Identified Hundreds of Schizophrenia Risk Genes

Genome-wide association studies (GWAS) have identified a large number of schizophrenia risk variants, and most of them are mapped to noncoding regions. By leveraging multiple joint-tissue gene expression data and GWAS data, we herein performed a transcriptome-wide association study (TWAS) and Mendelian randomization (MR) analysis and identified 144 genes whose mRNA levels were related to genetic risk of schizophrenia. Most of these genes exhibited diametrically opposite trends of expression in prenatal and postnatal brain tissues, despite that their expression levels in dorsolateral prefrontal cortex (DLPFC) tissues did not significantly differ between schizophrenics and healthy controls. We then found significant enrichment of these genes in dopamine-related pathways that were repeatedly implicated in schizophrenia pathogenesis and in the action of antipsychotic drugs. Gene expression analysis using single cell RNA-sequencing (scRNA-seq) data of mid-gestation fetal brains further revealed enrichment of these genes in glutamatergic excitatory neurons and cycling progenitors. These lines of evidence, in consistency with previous findings, confirmed the polygenic nature of schizophrenia and highlighted involvement of early neurodevelopment aberrations in this disorder. Further investigations using advanced algorithms in both bulk brain tissues and in single cells and at different developmental stages are necessary to characterize transcriptomic features of schizophrenia pathogenesis along brain development.

SREBP-1c Deficiency Affects Hippocampal Micromorphometry and Hippocampus-Dependent Memory Ability in Mice

Changes in structural and functional neuroplasticity have been implicated in various neurological disorders. Sterol regulatory element-binding protein (SREBP)-1c is a critical regulatory molecule of lipid homeostasis in the brain. Recently, our findings have shown the potential involvement of SREBP-1c deficiency in the alteration of novel modulatory molecules in the hippocampus and occurrence of schizophrenia-like behaviors in mice. However, the possible underlying mechanisms, related to neuronal plasticity in the hippocampus, are yet to be elucidated. In this study, we investigated the hippocampus-dependent memory function and neuronal architecture of hippocampal neurons in SREBP-1c knockout (KO) mice. During the passive avoidance test, SREBP-1c KO mice showed memory impairment. Based on Golgi staining, the dendritic complexity, length, and branch points were significantly decreased in the apical cornu ammonis (CA) 1, CA3, and dentate gyrus (DG) subregions of the hippocampi of SREBP-1c KO mice, compared with those of wild-type (WT) mice. Additionally, significant decreases in the dendritic diameters were detected in the CA3 and DG subregions, and spine density was also significantly decreased in the apical CA3 subregion of the hippocampi of KO mice, compared with that of WT mice. Alterations in the proportions of stubby and thin-shaped dendritic spines were observed in the apical subcompartments of CA1 and CA3 in the hippocampi of KO mice. Furthermore, the corresponding differential decreases in the levels of SREBP-1 expression in the hippocampal subregions (particularly, a significant decrease in the level in the CA3) were detected by immunofluorescence. This study suggests that the contributions of SREBP-1c to the structural plasticity of the mouse hippocampus may have underlain the behavioral alterations. These findings offer insights into the critical role of SREBP-1c in hippocampal functioning in mice.

Association of cannabis with glutamatergic levels in patients with early psychosis: Evidence for altered volume striatal glutamate relationships in patients with a history of cannabis use in early psychosis

The associative striatum, an established substrate in psychosis, receives widespread glutamatergic projections. We sought to see if glutamatergic indices are altered between early psychosis patients with and without a history of cannabis use and characterise the relationship to grey matter. 92 participants were scanned: Early Psychosis with a history of cannabis use (EPC = 29); Early Psychosis with minimal cannabis use (EPMC = 25); Controls with a history of cannabis use (HCC = 16) and Controls with minimal use (HCMC = 22). Whole brain T1 weighted MR images and localised proton MR spectra were acquired from head of caudate, anterior cingulate and hippocampus. We examined relationships in regions with known high cannabinoid 1 receptor (CB1R) expression (grey matter, cortex, hippocampus, amygdala) and low expression (white matter, ventricles, brainstem) to caudate Glutamine+Glutamate (Glx). Patients were well matched in symptoms, function and medication. There was no significant group difference in Glx in any region. In EPC grey matter volume explained 31.9% of the variance of caudate Glx (p = 0.003) and amygdala volume explained 36.9% (p = 0.001) of caudate Glx. There was no significant relationship in EPMC. The EPC vs EPMC interaction was significant (p = 0.042). There was no such relationship in control regions. These results are the first to demonstrate association of grey matter volume and striatal glutamate in the EPC group. This may suggest a history of cannabis use leads to a conformational change in distal CB1 rich grey matter regions to influence striatal glutamatergic levels or that such connectivity predisposes to heavy cannabis use.

Does Hippocampal Volume Predict Transition to Psychosis in a High-Risk Group? A Meta-Analysis

Schizophrenia has a prodromal phase of several years in most patients, making it possible to identify patients at clinical high risk (CHR) for developing the disorder. So far, these individuals are identified based on clinical criteria alone, and there is no reliable biomarker for predicting the transition to psychosis. It is well-established that reductions in brain volume, especially in the hippocampus, are associated with schizophrenia. Therefore, hippocampal volume may serve as a biomarker for psychosis. Several studies have already investigated hippocampal volume in CHR groups. Based on these studies, the present meta-analysis compares the baseline left and right hippocampal volume of CHR patients who developed a psychosis with that of CHR patients without such a transition. Our results show no statistically significant effect of the hippocampal volume on the transition risk for psychosis.

The Reeler Mouse: A Translational Model of Human Neurological Conditions, or Simply a Good Tool for Better Understanding Neurodevelopment?

The first description of the Reeler mutation in mouse dates to more than fifty years ago, and later, its causative gene (reln) was discovered in mouse, and its human orthologue (RELN) was demonstrated to be causative of lissencephaly 2 (LIS2) and about 20% of the cases of autosomal-dominant lateral temporal epilepsy (ADLTE). In both human and mice, the gene encodes for a glycoprotein referred to as reelin (Reln) that plays a primary function in neuronal migration during development and synaptic stabilization in adulthood. Besides LIS2 and ADLTE, RELN and/or other genes coding for the proteins of the Reln intracellular cascade have been associated substantially to other conditions such as spinocerebellar ataxia type 7 and 37, VLDLR-associated cerebellar hypoplasia, PAFAH1B1-associated lissencephaly, autism, and schizophrenia. According to their modalities of inheritances and with significant differences among each other, these neuropsychiatric disorders can be modeled in the homozygous (reln^−/−) or heterozygous (reln^+/−) Reeler mouse. The worth of these mice as translational models is discussed, with focus on their construct and face validity. Description of face validity, i.e., the resemblance of phenotypes between the two species, centers onto the histological, neurochemical, and functional observations in the cerebral cortex, hippocampus, and cerebellum of Reeler mice and their human counterparts.

Rosuvastatin improves olanzapine's effects on behavioral impairment and hippocampal, hepatic and metabolic damages in isolated reared male rats

BACKGROUND & AIM

Schizophrenia is a chronic, disabling neurological illness. This study investigated the effect of rosuvastatin (RSU) addition to the antipsychotic drug: olanzapine (OLZ) in treatment of post-weaning isolation rearing (IR) damaging effect and assessed behavioral impairment, metabolic and hepatic abnormalities, oxidative stress, and inflammatory markers.

METHODS

Treatment with OLZ (6 mg/kg, P.O.) and/or RSU (10 mg/kg, I.P.) have been started 6 weeks after isolation. We assessed behavioral tests, serum cortisol level, and hippocampal content of neurotransmitters. In addition, we assessed histopathology, inflammatory and oxidative stress markers of hippocampus, liver and adipose tissue RESULTS: Treatment of IR animals with OLZ, and/or RSU significantly counteracted the changes in hippocampus, liver and adipose tissue induced by post-weaning IR. Co-treatment of IR rats with both OLZ and RSU showed additive effects in some areas like improving both tumor necrosis factor alpha (TNFα) in both hippocampus and liver, histopathology of liver, oxidative stress markers of adipose tissue, β₃ adrenergic receptors (ADRβ₃), serum cortisol and total cholesterol. In addition, RSU alone alleviated the damage of IR rats by the same efficacy as OLZ with more benefit in cognition and exploration.

CONCLUSION

post-weaning IR as a model has behavioral, hippocampal, hepatic and marked metabolic changes more relevant to schizophrenia than drug-induced models. These effects were ameliorated by RSU and/or OLZ that are explained by their antioxidant, anti-inflammatory, anti-stress and anti-hyperlipidemic properties. Interestingly, co-treatment with both drugs showed a better effect.

Phytocannabinoids modulate emotional memory processing through interactions with the ventral hippocampus and mesolimbic dopamine system: implications for neuropsychiatric pathology

Growing clinical and preclinical evidence suggests a potential role for the phytocannabinoid cannabidiol (CBD) as a pharmacotherapy for various neuropsychiatric disorders. In contrast, delta-9-tetrahydrocannabinol (THC), the primary psychoactive component in cannabis, is associated with acute and neurodevelopmental propsychotic side effects through its interaction with central cannabinoid type 1 receptors (CB1Rs). CB1R stimulation in the ventral hippocampus (VHipp) potentiates affective memory formation through inputs to the mesolimbic dopamine (DA) system, thereby altering emotional salience attribution. These changes in DA activity and salience attribution, evoked by dysfunctional VHipp regulatory actions and THC exposure, could predispose susceptible individuals to psychotic symptoms. Although THC can accelerate the onset of schizophrenia, CBD displays antipsychotic properties, can prevent the acquisition of emotionally irrelevant memories, and reverses amphetamine-induced neuronal sensitization through selective phosphorylation of the mechanistic target of rapamycin (mTOR) molecular signaling pathway. This review summarizes clinical and preclinical evidence demonstrating that distinct phytocannabinoids act within the VHipp and associated corticolimbic structures to modulate emotional memory processing through changes in mesolimbic DA activity states, salience attribution, and signal transduction pathways associated with schizophrenia-related pathology.

Cannabinoid Transmission in the Hippocampus Activates Nucleus Accumbens Neurons and Modulates Reward and Aversion-Related Emotional Salience

BACKGROUND

Cannabinoid receptor transmission strongly influences emotional processing, and disturbances in cannabinoid signaling are associated with various neuropsychiatric disorders. The mammalian ventral hippocampus (vHipp) is a critical neural region controlling mesolimbic activity via glutamatergic projections to the nucleus accumbens. Furthermore, vHipp abnormalities are linked to schizophrenia-related psychopathology. Nevertheless, the mechanisms by which intra-vHipp cannabinoid signaling may modulate mesolimbic activity states and emotional processing are not currently understood.

METHODS

Using an integrative combination of in vivo electrophysiological recordings and behavioral pharmacologic assays in rats, we tested whether activation of cannabinoid type 1 receptors (CB1R) in the vHipp may modulate neuronal activity in the shell subregion of the nucleus accumbens (NASh). We next examined how vHipp CB1R signaling may control the salience of rewarding or aversive emotional memory formation and social interaction/recognition behaviors via intra-NASh glutamatergic transmission.

RESULTS

We demonstrate for the first time that vHipp CB1R transmission can potently modulate NASh neuronal activity and can differentially control the formation of context-dependent and context-independent forms of rewarding or aversion-related emotional associative memories. In addition, we found that activation of vHipp CB1R transmission strongly disrupts normal social behavior and cognition. Finally, we report that these behavioral effects are dependent upon intra-NASh alpha-amino-3-hydroxy-5-methyl-4-isoxazole propionic acid/N-methyl-D-aspartate receptor transmission.

CONCLUSIONS

Together, these findings demonstrate a critical role for hippocampal cannabinoid signaling in the modulation of mesolimbic neuronal activity states and suggest that dysregulation of CB1R transmission in the vHipp→NASh circuit may underlie hippocampal-mediated affective and social behavioral disturbances present in neuropsychiatric disorders.

Specificity proteins 1 and 4, hippocampal volume and first-episode psychosis

We assessed specificity protein 1 (SP1) and 4 (SP4) transcription factor levels in peripheral blood mononuclear cells and conducted a voxel-based morphometry analysis on brain structural magnetic resonance images from 11 patients with first-episode psychosis and 14 healthy controls. We found lower SP1 and SP4 levels in patients, which correlated positively with right hippocampal volume. These results extend previous evidence showing that such transcription factors may constitute a molecular pathway to the development of psychosis.

CB2 Cannabinoid Receptor Knockout in Mice Impairs Contextual Long-Term Memory and Enhances Spatial Working Memory

Neurocognitive effects of cannabinoids have been extensively studied with a focus on CB1 cannabinoid receptors because CB1 receptors have been considered the major cannabinoid receptor in the nervous system. However, recent discoveries of CB2 cannabinoid receptors in the brain demand accurate determination of whether and how CB2 receptors are involved in the cognitive effects of cannabinoids. CB2 cannabinoid receptors are primarily involved in immune functions, but also implicated in psychiatric disorders such as schizophrenia and depression. Here, we examined the effects of CB2 receptor knockout in mice on memory to determine the roles of CB2 receptors in modulating cognitive function. Behavioral assays revealed that hippocampus-dependent, long-term contextual fear memory was impaired whereas hippocampus-independent, cued fear memory was normal in CB2 receptor knockout mice. These mice also displayed enhanced spatial working memory when tested in a Y-maze. Motor activity and anxiety of CB2 receptor knockout mice were intact when assessed in an open field arena and an elevated zero maze. In contrast to the knockout of CB2 receptors, acute blockade of CB2 receptors by AM603 in C57BL/6J mice had no effect on memory, motor activity, or anxiety. Our results suggest that CB2 cannabinoid receptors play diverse roles in regulating memory depending on memory types and/or brain areas.

Nicotinic ligands as multifunctional agents for the treatment of neuropsychiatric disorders

The challenges associated with developing more effective treatments for neurologic and psychiatric illness such as Alzheimer's disease and schizophrenia are considerable. Both the symptoms and the pathophysiology of these conditions are complex and poorly understood and the clinical presentations across different patients can be very heterogeneous. Moreover, it has become apparent that the reductionist approach to drug discovery for these illnesses that has dominated the field for decades (i.e., the development of highly selective compounds or other treatment modalities focused on a very specific pathophysiologic target) has not been widely successful. Accordingly, a variety of new strategies have emerged including the development of "multitarget-directed ligands" (MTDLs), the development and/or identification of compounds that exhibit "multifunctional" activity (e.g., pro-cognitive plus neuroprotective, pro-cognitive plus antipsychotic activity), "repurposing" strategies for existing compounds that have other clinical indications, and novel "adjunctive" treatment strategies that might enhance the efficacy of the currently available treatments. Interestingly, a variety of ligands at nicotinic acetylcholine receptors (nAChRs) appear to have the potential to fulfill one or more of these desirable properties (i.e., multifunctional, repurposing, or adjunctive treatment potential). The purpose of this review (while not all-inclusive) is to provide an overview of a variety of nAChR ligands that demonstrate potential in these categories, particularly, "multifunctional" properties. Due to their densities in the mammalian brain and the amount of literature available, the review will focus on ligands of the high affinity α4β2 nAChR and the low affinity α7 nAChR.

Hippocampal cannabinoid transmission modulates dopamine neuron activity: impact on rewarding memory formation and social interaction

Disturbances in cannabinoid type 1 receptor (CB1R) signaling have been linked to emotional and cognitive deficits characterizing neuropsychiatric disorders, including schizophrenia. Thus, there is growing interest in characterizing the relationship between cannabinoid transmission, emotional processing, and dopamine (DA)-dependent behavioral deficits. The CB1R is highly expressed in the mammalian nervous system, particularly in the hippocampus. Activation of the ventral hippocampal subregion (vHipp) is known to increase both the activity of DAergic neurons located in the ventral tegmental area (VTA) and DA levels in reward-related brain regions, particularly the nucleus accumbens (NAc). However, the possible functional relationship between hippocampal CB1R transmission and VTA DA neuronal activity is not currently understood. In this study, using in vivo neuronal recordings in rats, we demonstrate that activation of CB1R in the vHipp strongly increases VTA DA neuronal firing and bursting activity, while simultaneously decreasing the activity of VTA non-DA neurons. Furthermore, using a conditioned place preference procedure and a social interaction test, we report that intra-vHipp CB1R activation potentiates the reward salience of normally sub-threshold conditioning doses of opiates and induces deficits in natural sociability and social recognition behaviors. Finally, these behavioral effects were prevented by directly blocking NAc DAergic transmission. Collectively, these findings identify hippocampal CB1R transmission as a critical modulator of the mesolimbic DA pathway and in the processing of reward and social-related behavioral phenomena.

Similar verbal memory impairments in schizophrenia and healthy aging. Implications for understanding of neural mechanisms

Memory is impaired in schizophrenia patients but it is not clear whether this is specific to the illness and whether different types of memory (verbal and nonverbal) or memories in different cognitive domains (executive, object recognition) are similarly affected. To study relationships between memory impairments and schizophrenia we compared memory functions in 77 schizophrenia patients, 58 elderly healthy individuals and 41 young healthy individuals. Tests included verbal associative and logical memory and memory in executive and object recognition domains. We compared relationships of memory functions to each other and to other cognitive functions including psychomotor speed and verbal and spatial working memory. Compared to the young healthy group, schizophrenia patients and elderly healthy individuals showed similar severe impairment in logical memory and in the ability to learn new associations (NAL), and similar but less severe impairment in spatial working memory and executive and object memory. Verbal working memory was significantly more impaired in schizophrenia patients than in the healthy elderly. Verbal episodic memory impairment in schizophrenia may share common mechanisms with similar impairment in healthy aging. Impairment in verbal working memory in contrast may reflect mechanisms specific to schizophrenia. Study of verbal explicit memory impairment tapped by the NAL index may advance understanding of abnormal hippocampus dependent mechanisms common to schizophrenia and aging.

Hippocampal and amygdalar local structural differences in elderly patients with schizophrenia

OBJECTIVES

Morphological abnormalities have been reported for the hippocampi and amygdalae in young schizophrenia patients, but very little is known about the pattern of abnormalities in elderly schizophrenia patients. Here we investigated local structural differences in the hippocampi and amygdalae of elderly schizophrenia patients compared with healthy elderly subjects. We also related these differences to clinical symptom severity.

DESIGN

20 schizophrenia patients (mean age: 67.4 ± 6.2 years; Mini-Mental State Exam: 22.8 ± 4.4) and 20 healthy elderly subjects (70.3 ± 7.5 years; 29.0 ± 1.1) underwent high resolution magnetic resonance imaging of the brain. The Radial Atrophy Mapping technique was used to reconstruct the 3D shape of the amygdala and the hippocampus. Local differences in tissue reductions were computed between groups and permutation tests were run to correct for multiple comparisons, in statistical maps thresholded at p = 0.05.

RESULTS

Significant tissue reduction was observed bilaterally in the amygdala and hippocampus of schizophrenia patients. The basolateral-ventral-medial amygdalar nucleus showed the greatest involvement, with over 30% local tissue reduction. The centro-medial, cortical, and lateral nuclei were also atrophic in patients. The hippocampus showed significant tissue loss in the medio-caudal and antero-lateral aspects of CA1, and in medial section of its left head (pre- and para-subiculum). In the left amygdala and hippocampus, local tissue volumes were significantly correlated with negative symptoms.

CONCLUSIONS

Tissue loss and altered morphology were found in elderly schizophrenia patients. Tissue loss mapped to amygdalo-hippocampal subregions known to have bidirectional and specific connections with frontal cortical and limbic structures and was related to clinical severity.

Increased SP4 and SP1 transcription factor expression in the postmortem hippocampus of chronic schizophrenia

Altered levels of transcription factor specificity protein 4 (SP4) and 1 (SP1) in the cerebellum, prefrontal cortex and/or lymphocytes have been reported in severe psychiatric disorders, including early psychosis, bipolar disorder, and chronic schizophrenia subjects who have undergone long-term antipsychotic treatments. SP4 transgenic mice show altered hippocampal-dependent psychotic-like behaviours and altered development of hippocampal dentate gyrus. Moreover, NMDAR activity regulates SP4 function. The aim of this study was to investigate SP4 and SP1 expression levels in the hippocampus in schizophrenia, and the possible effect of antipsychotics and NMDAR blockade on SP protein levels in rodent hippocampus. We analysed SP4 and SP1 expression levels in the postmortem hippocampus of chronic schizophrenia (n = 14) and control (n = 11) subjects by immunoblot and quantitative RT-PCR. We tested the effect of NMDAR blockade on SP factors in the hippocampus of mouse treated with an acute dose of MK801. We also investigated the effect of subacute treatments with haloperidol and clozapine on SP protein levels in the rat hippocampus. We report that SP4 protein and both SP4 and SP1 mRNA expression levels are significantly increased in the hippocampus in chronic schizophrenia. Likewise, acute treatment with MK801 increased both SP4 and SP1 protein levels in mouse hippocampus. In contrast, subacute treatment with haloperidol and clozapine did not significantly alter SP protein levels in rat hippocampus. These results suggest that SP4 and SP1 upregulation may be part of the mechanisms deregulated downstream of glutamate signalling pathways in schizophrenia and might be contributing to the hippocampal-dependent cognitive deficits of the disorder.

Grey-matter texture abnormalities and reduced hippocampal volume are distinguishing features of schizophrenia

Neurodevelopmental processes are widely believed to underlie schizophrenia. Analysis of brain texture from conventional magnetic resonance imaging (MRI) can detect disturbance in brain cytoarchitecture. We tested the hypothesis that patients with schizophrenia manifest quantitative differences in brain texture that, alongside discrete volumetric changes, may serve as an endophenotypic biomarker. Texture analysis (TA) of grey matter distribution and voxel-based morphometry (VBM) of regional brain volumes were applied to MRI scans of 27 patients with schizophrenia and 24 controls. Texture parameters (uniformity and entropy) were also used as covariates in VBM analyses to test for correspondence with regional brain volume. Linear discriminant analysis tested if texture and volumetric data predicted diagnostic group membership (schizophrenia or control). We found that uniformity and entropy of grey matter differed significantly between individuals with schizophrenia and controls at the fine spatial scale (filter width below 2mm). Within the schizophrenia group, these texture parameters correlated with volumes of the left hippocampus, right amygdala and cerebellum. The best predictor of diagnostic group membership was the combination of fine texture heterogeneity and left hippocampal size. This study highlights the presence of distributed grey-matter abnormalities in schizophrenia, and their relation to focal structural abnormality of the hippocampus. The conjunction of these features has potential as a neuroimaging endophenotype of schizophrenia.

Hippocampus age-related microstructural changes in schizophrenia: a case-control mean diffusivity study

Macrostructural-volumetric abnormalities of the hippocampus have been described in schizophrenia. Here, we characterized age-related changes of hippocampal mean diffusivity as an index of microstructural damage by carrying out a neuroimaging study in 85 patients with a DSM-IV-TR diagnosis of schizophrenia and 85 age- and gender-matched healthy controls. We performed analyses of covariance, with diagnosis as fixed factor, mean diffusivity as dependent variable and age as covariate. Patients showed an early increase in mean diffusivity in the right and left hippocampus that increased with age. Thus, microstructural hippocampal changes associated with schizophrenia cannot be confined to a specific time window.

Hippocampal multimodal structural changes and subclinical depression in healthy individuals

BACKGROUND

Several neuroimaging studies report reduced hippocampal volume in depressed patients. However, it is still unclear if hippocampal changes in healthy individuals can be considered a risk factor for progression to clinical depression. Here, we investigated subclinical depression and its hippocampal correlates in a non-clinical sample of healthy individuals, with particular regard to gender differences.

METHODS

One-hundred-two participants underwent a comprehensive clinical assessment, a high-resolution T1-weighted magnetic resonance imaging and diffusion tensor imaging protocol using a 3T MRI scanner. Data of macro-(volume) and micro-(mean diffusivity, MD) structural changes of the hippocampus were analyzed with reference to the Beck Depression Inventory score.

RESULTS

Results of multivariate regression analyses revealed reduced bilateral volume, along with increased bilateral MD in hippocampal formation predicting subclinical depressive phenomenology only in healthy males. Conversely, subclinical depressive phenomenology in healthy female was accounted for by only lower educational level, in the absence of any hippocampal structure variations.

LIMITATIONS

To date, this is the only evidence reporting a relationship between subclinical depressive phenomenology and changes in hippocampal formation in healthy individuals.

CONCLUSIONS

Our findings demonstrated that reduced volume, along with increased MD in hippocampal formation, is significantly associated with subclinical depressive phenomenology in healthy males. This encourages to study the hypothesis that early macro- and microstructural changes in hippocampi associated with subclinical depression may constitute a risk factor of developing depressive disorders in males.

A conceptual and practical guide to the behavioural evaluation of animal models of the symptomatology and therapy of schizophrenia

Schizophrenia is a chronic debilitating brain disorder characterized by a complex set of perceptual and behavioural symptoms that severely disrupt and undermine the patient's psychological well-being and quality of life. Since the exact disease mechanisms remain essentially unknown, holistic animal models are indispensable tools for any serious investigation into the neurobiology of schizophrenia, including the search for remedies, prevention of the disease and possible biological markers. This review provides some practical advice to those confronted with the task of evaluating their animal models for relevance to schizophrenia, a task that inevitably involves behavioural tests with animals. To a novice, this challenge not only is a technical one but also entails attention to interpretative issues concerning validity and translational power. Here, we attempt to offer some guidance to help overcome these obstacles by drawing on our experience of diverse animal models of schizophrenia based on genetics, strain difference, brain lesions, pharmacological induction and early life developmental manipulations. The review pays equal emphasis to the general (theoretical) considerations of experimental design and the illustration of the problems related to critical test parameters and the data analysis of selected exemplar behavioural tests. Finally, the individual differences of behavioural expression in relevant tests observed in wild-type animals might offer an alternative approach in order to explore the mechanism of schizophrenia-related behavioural dysfunction at the molecular, cellular and structural levels, all of which are of more immediate relevance to cell and tissue research.

Sex and steroid hormones in early brain injury

Brain injury during development can have severe, long-term consequences. Using an array of animal models, we have an understanding of the etiology of perinatal brain injury. However, we have only recently begun to address the consequences of endogenous factors such as genetic sex and developmental steroid hormone milieu. Our limited understanding has sometimes led researchers to make over-generalizing and potentially dangerous statements regarding treatment for brain injury. Therefore this review acts as a cautionary tale, speaking to our need to understand the effects of sex and steroid hormone environment on the response to brain trauma in the neonate.

Tract-specific analysis of white matter integrity disruption in schizophrenia

Several studies have suggested that white matter integrity is disrupted in some brain regions in patients with schizophrenia. The purpose of this study was to assess the white matter integrity of the cingulum, uncinate fasciculus, fornix, and corpus callosum using diffusion tensor imaging (DTI). Participants comprised 39 patients with schizophrenia (19 males and 20 females) and 40 age-matched normal controls (20 males and 20 females). We quantitatively assessed the fractional anisotropy (FA) and apparent diffusion coefficient (ADC) of the anterior cingulum, body of the cingulum, uncinate fasciculus, fornix, and corpus callosum on a tract-specific basis using diffusion tensor tractography (DTT). Group differences in FA and ADC between the patients and normal controls were sought. Additional exploratory analyses of the relationship between the FA or ADC and four clinical parameters (i.e., illness duration, positive symptom scores, negative symptom scores, and medication dosage) were performed. Results were analyzed in gender-combined and gender-separated group comparisons. FA was significantly lower on both sides of the anterior cingulum, uncinate fasciculus, and fornix in the schizophrenia patients irrespective of gender group separation. In the gender-combined analyses, significantly higher ADC values were demonstrated in the schizophrenia patients in both sides of the anterior cingulum, body of the cingulum and uncinate fasciculus, the left fornix, and the corpus callosum, compared with those of the normal controls. In the gender-separated analyses, the male patients showed higher ADC in the left anterior cingulum, the bilateral cingulum bodies, and the bilateral uncinate fasciculi. The female patients showed higher ADC in the right anterior cingulum, the left fornix, and the bilateral uncinate fasciculus. In correlation analyses, a significant negative correlation was found between illness duration and ADC in the right anterior cingulum in the gender-combined analyses. The gender-separated analyses found that the male patients had a significant negative correlation between negative symptom scores and FA in the right fornix, a positive correlation between illness duration and FA in the right anterior cingulum, and a negative correlation between illness duration and FA in the left uncinate fasciculus. Our DTI study showed that the integrity of white matter is disrupted in patients with schizophrenia. The results of our sub-analyses suggest that changes in FA and ADC may be related to negative symptom scores or illness duration.

A structure-function mechanism for schizophrenia

THE MULTIPLE ETIOLOGIES OF SCHIZOPHRENIA PROMPT US TO RAISE THE QUESTION: what final common pathway can induce a convincing sense of the reality of the hallucinations in this disease? The observation that artificial stimulation of an intermediate order of neurons of a normal nervous system induces hallucinations indicates that the lateral entry of activity (not resulting from canonical synaptic transmission) at intermediate neuronal orders may provide a mechanism for hallucinations. Meaningful hallucinations can be de-constructed into an organized temporal sequence of internal sensations of associatively learned items that occur in the absence of any external stimuli. We hypothesize that these hallucinations are autonomously generated by the re-activation of pathological non-specific functional LINKs formed between the postsynaptic membranes at certain neuronal orders and are examined as a final common mechanism capable of explaining most of the features of the disease. Reversible and stabilizable hemi-fusion between simultaneously activated adjacent postsynaptic membranes is viewed as one of the normal mechanisms for functional LINK formation and is dependent on lipid membrane composition. Methods of removing the proteins that may traverse the non-specifically hemi-fused membrane segments and attempts to replace the phospholipid side chains to convert the membrane composition to a near-normal state may offer therapeutic opportunities.

The methylazoxymethanol acetate (MAM-E17) rat model: molecular and functional effects in the hippocampus

Administration of the DNA-alkylating agent methylazoxymethanol acetate (MAM) on embryonic day 17 (E17) produces behavioral and anatomical brain abnormalities, which model some aspects of schizophrenia. This has lead to the premise that MAM rats are a neurodevelopmental model for schizophrenia. However, the underlying molecular pathways affected in this model have not been elucidated. In this study, we investigated the molecular phenotype of adult MAM rats by focusing on the frontal cortex and hippocampal areas, as these are known to be affected in schizophrenia. Proteomic and metabonomic analyses showed that the MAM treatment on E17 resulted primarily in deficits in hippocampal glutamatergic neurotransmission, as seen in some schizophrenia patients. Most importantly, these results were consistent with our finding of functional deficits in glutamatergic neurotransmission, as identified using electrophysiological recordings. Thus, this study provides the first molecular evidence, combined with functional validation, that the MAM-E17 rat model reproduces hippocampal deficits relevant to the pathology of schizophrenia.

Association between hippocampal volume and P300 event related potential in psychosis: support for the Kraepelinian divide

INTRODUCTION

Abnormalities of the P300 event related potential (ERP) and of hippocampal structure are observed in individuals with psychotic disorders and their unaffected relatives. The understanding and clinical management of psychotic disorders are largely based on the descriptive Kraepelinian distinction between 'dementia praecox' and 'manic depressive psychosis', and not dependant on any well demarcated biological underpinnings. The hippocampus is postulated to be one of the main P300 generators, yet it remains unknown whether hippocampal volume decrements are associated with P300 deficits in psychosis, and whether any association is shared across non-affective and affective psychotic disorders.

METHODS

228 subjects from the Maudsley Family Psychosis Study comprising 55 patients with non-affective psychosis, 23 patients with psychotic bipolar disorder, 98 unaffected relatives, and 52 unrelated controls contributed structural MRI and ERP data. To study the relationship between hippocampal volume and P300 ERP, a seemingly unrelated regression methodology was used, accounting for whole brain volumes, clinical groups, age and gender in the analysis.

RESULTS

An association between left hippocampal volume and P300 latency in the combined sample comprising non-affective and affective psychotic patients, their relatives and controls was observed. There was an inverse relationship between brain structure and function in that prolongation of P300 latencies was associated with smaller left hippocampal volumes. On subdividing the sample based on Kraepelinian dichotomy, this association remained significant only for the non-affective psychosis group, comprising patients and their unaffected relatives.

CONCLUSIONS

Based on our findings, P300 latency, a measure of the speed of neural transmission, appears to be related to the size of the left hippocampus in schizophrenia, but not in psychotic bipolar disorder. It seems that underlying neuro-biological characteristics could help in unravelling the traditional Kraepelinian differentiation between the two major psychoses. The specificity of this brain structure-function association for schizophrenia opens the scope for further research using integration of multimodal biological data for objective categorisation of psychosis.

Hippocampal and amygdalar volume changes in elderly patients with Alzheimer's disease and schizophrenia

Patients with Alzheimer's disease (AD) and schizophrenia display cognitive, behavioural disturbances and morphological abnormalities. Although these latter reflect progressive neurodegeneration in AD, their significance in schizophrenia is still unclear. We explored the patterns of hippocampal and amygdalar atrophy in those patients and their associations with clinical parameters. Structural magnetic resonance imaging was performed in 20 elderly schizophrenia patients, 20 AD and 19 healthy older controls. Hippocampal and amygdalar volumes were obtained by manual segmentation with a standardized protocol and compared among groups. In both schizophrenia and AD patients, left hippocampal and amygdalar volumes were significantly smaller. The hippocampus/amygdala ratio was significantly lower in schizophrenia compared to both AD cases [2.4 bilaterally, 95% C.I. 2.2 to 2.7] and healthy controls bilaterally [2.5, 95% C.I. 2.3 to 2.9 in left and 2.7, 95% C.I. 2.4 to 3.1 in right hemisphere]. In schizophrenia patients, a significant positive correlation was found between age at disease onset and the right hippocampus/amygdala volume ratio (Spearman rho=0.56). Negative symptoms correlated with higher right/left amygdala volume ratio (Spearman's rho=0.43). Our data show that unlike AD, the hippocampus/amygdala ratio is abnormally low and correlates with the age at onset in schizophrenia, being a neurodevelopmental signature of the disease.

Hippocampi, thalami, and accumbens microstructural damage in schizophrenia: a volumetry, diffusivity, and neuropsychological study

Volumetric abnormalities in the subcortical structures have been described in schizophrenia. However, it still has to be clarified if subtle microstructural damage is also present. Thus, we aimed to detect subcortical volume and mean diffusivity (MD) alterations in 45 patients with diagnosis of schizophrenia compared with 45 age-, gender-, and educational attainment-matched healthy comparison (HC) participants, by using a combined volumetry and diffusion tensor imaging (DTI) method. A secondary aim was to identify the neuropsychological correlates of subcortical abnormalities in the schizophrenic group. We found thalami and hippocampi bilaterally and left accumbens to show MD increase in the schizophrenic group. No volumetric decrease was found. Moreover, significant correlations between the MD values in subcortical structures (right thalamus and hippocampus and left accumbens) and working memory performance were found. Thus, subcortical microstructural alterations are present in schizophrenia even in absence of volumetric abnormalities. Furthermore, microstructural damage in subcortical areas is linked to working memory, suggesting the presence of a subtle microstructural subcortical dysfunction in the pathoetiological mechanism underlying high cognitive load performances in schizophrenia. Finally, our findings indicate that MD is a more sensitive marker of brain tissue deficits than signal intensity variations measured in T1-weighted imaging data, consistently with previous reports. Thus, DTI appears to be an invaluable tool to investigate subcortical pathology in schizophrenia, greatly enhancing the ability to detect subtle brain changes in this complex disorder.

Neural markers of remission in first-episode schizophrenia: a volumetric neuroimaging study of the hippocampus and amygdala

OBJECTIVE

The temporolimbic region has been implicated in the pathophysiology in schizophrenia. More specifically, significantly smaller hippocampal volumes but not amygdala volumes have been identified at onset in first-episode schizophrenia (FES) patients. However, volumetric differences (namely, in the hippocampus) exhibit an ambiguous relationship with long-term outcome. So, we examined the relationship between hippocampus and amygdala volumes and early remission status.

METHODS

We compared hippocampus and amygdala volumes between 40 non-remitted and 17 remitted FES patients and 57 healthy controls. Amygdala and hippocampus were manually traced with the hippocampus additionally segmented into three parts: body, head, and tail. Remission was defined as mild or less on both positive and negative symptoms over a period of 6 consecutive months as per the 2005 Remission in Schizophrenia Working Group criteria.

RESULTS

A significant [group x structure x side] interaction revealed outcome groups differed in hippocampus tail volumes; significantly on the left (non-remitted=694+/-175 mm(3); remitted=855+/-133 mm(3); p=0.001) with a trend difference on the right (non-remitted=723+/-162 mm(3); remitted=833+/-126 mm(3); p=0.023). Groups did not differ in body, head, or amygdala volumes bi-laterally.

CONCLUSIONS

A smaller hippocampal tail volume may represent a neural marker in FES patients who do not achieve early remission after the first 6 months of treatment. The early identification of patients with poor outcome with respect to the hippocampus tail may encourage the search for new, more target-specific, medications in hope of improving outcome and moving us towards a better understanding of the pathophysiology of schizophrenia.

The hippocampus and nucleus accumbens as potential therapeutic targets for neurosurgical intervention in schizophrenia

Schizophrenia is a chronic and disabling psychiatric illness that is often refractory to treatment. Psychotic symptoms (e.g. hallucinations and delusions) in schizophrenia are reliably correlated with excess dopamine levels in the striatum, and have more recently been related to excess metabolic activity in the hippocampus. Multiple lines of evidence suggest that aberrantly high hippocampal activity may, via hippocampal connections with the limbic basal ganglia, drive excessive dopamine release into the striatum. In the present paper, we hypothesize that inhibition or stabilization of neural activity with high-frequency electrical stimulation of the hippocampus or nucleus accumbens, through different mechanisms, would treat the positive symptoms of schizophrenia. Thus, we suggest a direction for further experimentation aimed at developing neurosurgical therapeutic approaches for this devastating disease.

Challenges in phenotype definition in the whole-genome era: multivariate models of memory and intelligence

Refining phenotypes for the study of neuropsychiatric disorders is of paramount importance in neuroscience. Poor phenotype definition provides the greatest obstacle for making progress in disorders like schizophrenia, bipolar disorder, Attention Deficit/Hyperactivity Disorder (ADHD), and autism. Using freely available informatics tools developed by the Consortium for Neuropsychiatric Phenomics (CNP), we provide a framework for defining and refining latent constructs used in neuroscience research and then apply this strategy to review known genetic contributions to memory and intelligence in healthy individuals. This approach can help us begin to build multi-level phenotype models that express the interactions between constructs necessary to understand complex neuropsychiatric diseases. These results are available online through the http://www.phenowiki.org database. Further work needs to be done in order to provide consensus-building applications for the broadly defined constructs used in neuroscience research.

Hippocampus volume and episodic memory in schizophrenia

Previous studies of schizophrenia have suggested a linkage between neuropsychological (NP) deficits and hippocampus abnormality. The relationship between hippocampus volume and NP functioning was investigated in 24 patients with chronic schizophrenia and 24 matched healthy controls. Overall intracranial, white and gray matter, and anterior (AH) and posterior (PH) hippocampus volumes were assessed from magnetic resonance images (MRI). NP domains of IQ, attention, and executive function were also evaluated with respect to volumetric measures. It was hypothesized that AH and PH volumes and episodic memory scores would be positively associated in controls and that the schizophrenia group would depart from this normative pattern. NP functioning was impaired overall and AH volume was smaller in the schizophrenia group. In the controls, the hippocampus-memory relationships involved AH and PH, and correlations were significant for verbal memory measures. In the schizophrenia group, positive correlations were constrained to PH. Negative correlations emerged between AH and verbal and visual memory measures. For both groups, cortical volume negatively correlated with age, but a negative correlation between age and hippocampus volume was found only in the schizophrenia group. In this sample of adults with schizophrenia, atypical relationships between regional hippocampus volumes and episodic memory ability were found, as was an atypical negative association between hippocampus volume and age.

The stop null mice model for schizophrenia displays [corrected] cognitive and social deficits partly alleviated by neuroleptics

Recently evidence has accumulated that schizophrenia can arise from primary synaptic defects involving structural proteins particularly, microtubule associated proteins. Previous experiments have demonstrated that a STOP (stable tubule only peptide) gene deletion in mice leads to a phenotype mimicking some aspects of positive symptoms classically observed in schizophrenic patients. In the current study, we determined if STOP null mice demonstrate behavioral abnormalities related to the social and cognitive impairments of schizophrenia. Compared with wild-type mice, STOP null mice exhibited deficits in the non-aggressive component of social recognition, short term working memory and social and spatial learning. As described in humans, learning deficits in STOP null mice were poorly sensitive to long term treatment with typical neuroleptics. Since social and cognitive dysfunction have consistently been considered as central features of schizophrenia, we propose that STOP null mice may provide a useful model to understand the neurobiological correlates of social and cognitive defects in schizophrenia and to develop treatments that better target these symptoms.

Disrupted integrity of the fornix is associated with impaired memory organization in schizophrenia

BACKGROUND

The fornix is a major projection of the hippocampus to and from other brain regions. A previous diffusion tensor imaging (DTI) study has reported disrupted integrity of the fornix in patients with schizophrenia. However, functional significance of the DTI abnormalities of the fornix in schizophrenia has not been fully studied yet. We investigated an association between DTI abnormalities of the fornix and impairment of memory organization in schizophrenia.

METHODS

Thirty-one patients with schizophrenia and 65 age- and gender-matched healthy controls underwent DTI, and fractional anisotropy (FA) and mean diffusivity (MD) were measured in cross-sections of fornix tractography. In addition, all of the patients and 32 controls performed a verbal learning task specialized for evaluating memory organization, the verbal memory subscale of the Wechsler Memory Scale-Revised, the category- and letter fluency tests, and the Japanese version of National Adult Reading Test.

RESULTS

Statistically significant reduction of FA and increase of MD were found in the fornix of patients with schizophrenia compared with controls with no significant lateralization. A significant patients-specific correlation was found between increased MD in the left fornix and lower scores on utilization of semantic organization in the verbal learning task. In addition, increased MD in the right fornix showed a patients-specific association with poorer performance on the category fluency test, which indexes organization of long-term semantic memory. These patients-specific correlations, however, were not statistically lateralized to either hemisphere.

CONCLUSIONS

These results indicate that disrupted integrity of the fornix contributes to impaired memory organization in schizophrenia.

Altered resting-state functional connectivity and anatomical connectivity of hippocampus in schizophrenia

Hippocampus has been implicated in participating in the pathophysiology of schizophrenia. However, the functional and anatomical connectivities between hippocampus and other regions are rarely concurrently investigated in schizophrenia. In the present study, both functional magnetic resonance imaging (fMRI) during rest and diffusion tensor imaging (DTI) were performed on 17 patients with paranoid schizophrenia and 14 healthy subjects. Resting-state functional connectivities of the bilateral hippocampi were separately analyzed by selecting the anterior hippocampus as region of interest. The fornix body was reconstructed by diffusion tensor tractography, and the integrity of this tract was evaluated using fractional anisotropy (FA). In patients with schizophrenia, the bilateral hippocampi showed reduced functional connectivities to some regions which have been reported to be involved in episodic memory, such as posterior cingulate cortex, extrastriate cortex, medial prefrontal cortex, and parahippocampus gyrus. We speculated that these reduced connectivity may reflect the disconnectivity within a neural network related to the anterior hippocampus in schizophrenia. Meanwhile the mean FA of the fornix body was significantly reduced in patients, indicating the damage in the hippocampal anatomical connectivity in schizophrenia. The concurrence of the functional disconnectivity and damaged anatomical connectivity between the hippocampus and other regions in schizophrenia suggest that the functional-anatomical relationship need to be further investigated.

Lissencephaly 1 linking to multiple diseases: mental retardation, neurodegeneration, schizophrenia, male sterility, and more

Lissencephaly 1 (LIS1) was the first gene implicated in the pathogenesis of type-1 lissencephaly. More than a decade of research by multiple laboratories has revealed that LIS1 is a key node protein, which participates in several pathways, including association with the molecular motor cytoplasmic dynein, the reelin signaling pathway, and the platelet-activating factor pathway. Mutations in LIS1-interacting proteins, either in human, or in mouse models has suggested that LIS1 might play a role in the pathogenesis of numerous diseases such as male sterility, schizophrenia, neuronal degeneration, and viral infections.

Alpha7 nicotinic acetylcholine receptor mRNA expression and binding in postmortem human brain are associated with genetic variation in neuregulin 1

Studies in cell culture and in animals suggest that neuregulin 1 (NRG1), a probable schizophrenia susceptibility gene, regulates the expression of the alpha7 nicotinic acetylcholine receptors (nAChRs). We hypothesized that schizophrenia-associated allelic variations within the NRG1 gene, via their effects on NRG1 isoform expression, would be associated with alterations in nAChR alpha7 receptor levels. We examined the effects of four disease-associated single-nucleotide polymorphisms (SNPs) in the 5' region of the NRG1 gene on nAChR alpha7 mRNA transcript expression in both the dorsolateral prefrontal cortex (DLPFC) and hippocampus of normal controls and patients with schizophrenia using quantitative real-time PCR. NRG1 risk alleles at SNPs SNP8NRG221132 and rs6994992 predicted significantly lower nAChR alpha7 mRNA expression in the DLPFC. Haplotypes containing the risk alleles at the above SNPs were also associated with lower expression of nAChR alpha7 in the DLPFC. The genotype effect for rs6994992 and the haplotype effect were more pronounced within the schizophrenic patient group. To determine whether receptor levels follow that of mRNA expression, we performed receptor binding and autoradiography using [(125)I] alpha-bungarotoxin in the DLPFC. Consistent with the mRNA findings, we found a decrease in binding in risk allele carriers of SNP8NRG221132 as compared with heterozygous individuals. Together, these results suggest that the molecular mechanism of the association between NRG1 risk alleles and schizophrenia may include down-regulation of nAChR alpha7 expression.

Impaired attention is central to the cognitive deficits observed in alpha 7 deficient mice

alpha7-Nicotinic acetylcholine receptors (alpha7-nAChR) have been implicated in a range of cognitive deficits in schizophrenia. Therefore we examined alpha7-nAChR knockout (KO), heterozygote (HT) and wildtype (WT) littermate mice in the 5-CSR (a rodent model of sustained attention) and odour span (a novel mouse working memory paradigm) tasks, and related performance to nAChR density. Whilst there was no difference between groups in baseline 5-CSR task performance, alpha7-nAChR KO's exhibited significantly higher omission levels compared to WT mice on increasing the attentional load, with HT mice performing at an intermediate level. Furthermore, alpha7-nAChR KO mice were significantly impaired in the odour span task when compared to WT mice, in a pattern consistent with impaired attention. These behavioural deficits were associated with the loss of alpha7-nAChRs, as alpha4beta2-nAChR density was unaltered in these mice. Thus these studies intimate that the attentional impairment in alpha7-nAChR transgenic mice maybe core to other deficits in cognition.

Limited influence of olanzapine on adult forebrain neural precursors in vitro

We evaluated the activity of the atypical antipsychotic drug olanzapine on differentiation and gene expression in adult neural precursor cells in vitro. Neural precursors obtained from forebrain subventricular zone (SVZ)-derived neurospheres express a subset (13/24) of receptors known to bind olanzapine at high to intermediate affinities; in contrast, all 24 are expressed in the SVZ. In the presence of 10 nM, 100 nM or 1 microM olanzapine, there is no significant change in the frequency of oligodendrocytes, neurons, GABAergic neurons and astrocytes generated from neurosphere precursors. In parallel, there is no apparent change in cell proliferation in response to olanzapine, based upon bromodeoxyuridine incorporation. There are no major changes in cytological differentiation in response to the drug; however, at one concentration (10 nM) there is a small but statistically significant increase in the size of glial fibrillary acidic protein-labeled astrocytes derived from neurosphere precursors. In addition, olanzapine apparently modulates expression of one serotonin receptor -- 5HT2A -- in differentiating neurosphere cultures; however, it does not modify expression of several other receptors or schizophrenia vulnerability genes. Thus, olanzapine has a limited influence on differentiation and gene expression in adult neural precursor cells in vitro.

Delayed onset of prepulse inhibition deficits following kainic acid treatment on postnatal day 7 in rats

Abnormal activity in corticolimbic circuits during development may be a predisposing factor for schizophrenia. Permanent or temporary lesions of limbic structures such as the ventral hippocampus and basolateral amygdala in rats on postnatal day (PND) 7 result in functional changes similar to some behavioural and cognitive signs of schizophrenia. The present experiments tested whether transient increases in the neural activity of corticolimbic circuits on PND 7 would result in similar behavioural changes. Long-Evans rats were treated with either kainic acid (KA, 1.5 mg/kg, i.p.) or saline on PND 7 and tested for prepulse inhibition (PPI) of the acoustic startle response and spontaneous locomotor activity both in a novel environment and following amphetamine treatment before puberty (PND 35) and in early adulthood (PND 56). In subgroups of animals PPI was also measured following apomorphine administration (0.2 mg/kg) and spatial learning and memory were tested in the water maze. Rats treated with KA were indistinguishable from saline-treated animals on PND 35. However, on PND 56, KA-treated animals showed a subtle consistent decrease in PPI relative to control animals, but did not show increased sensitivity to the disruptive effects of a low dose of apomorphine on PPI. Locomotor responses to novelty or amphetamine were not reliably altered in the KA-treated animals. KA- and saline-treated animals performed similarly in the water maze. These results support the hypothesis that neural hyperactivity on PND 7 in rats causes behavioural changes in early adulthood that resemble some symptoms of schizophrenia. These pharmacological data suggest that the changes are not mediated by postsynaptic alterations in mesolimbic dopamine transmission.

Impaired hippocampal function during the detection of novel words in schizophrenia

BACKGROUND

Patients with schizophrenia have smaller hippocampal volumes and perform abnormally on most declarative memory tasks. Although these findings are likely related, the impact of hippocampal pathology on cognitive performance in schizophrenia remains unclear. This study examined this relationship by measuring the volume of the hippocampus and its activation during memory task performance.

METHODS

Participants included 15 patients with schizophrenia and 16 age-matched control subjects. Hippocampal volume was determined via three-dimensional volumetric analysis of high-resolution magnetic resonance images. Hippocampal activity was assessed by measuring changes in blood oxygen level-dependent signal during a recognition memory task.

RESULTS

Patients with schizophrenia had smaller hippocampal volumes bilaterally and demonstrated poorer performance on the recognition memory task, largely because of a heightened rate of false alarms to novel stimuli. Both groups showed robust hippocampal activity to old and new items when compared with a low-level baseline task; however, direct comparison of hippocampal activity during recognition task performance revealed that healthy control, but not the schizophrenia, subjects showed significant right anterior hippocampal activation during the evaluation of novel items.

CONCLUSIONS

The impaired ability to classify new items as previously not experienced is associated with decreased recruitment and smaller volume of the hippocampus in schizophrenia.

Expression of disrupted-in-schizophrenia-1, a schizophrenia-associated gene, is prominent in the mouse hippocampus throughout brain development

DISC1 (Disrupted-In-Schizophrenia 1) has been associated with schizophrenia in multiple genetic studies. Studies from our laboratory have shown that Disc1, the mouse ortholog of DISC1, is highly expressed in the dentate gyrus of the hippocampus in the adult mouse brain. Because developmental dysfunction of the hippocampus is thought to play a major role in schizophrenia pathogenesis, and the dentate gyrus is a major locus for adult neurogenesis in the mouse, we investigated Disc1 expression during mouse brain development. Strikingly, Disc1 is strongly expressed in the hippocampus during all stages of hippocampal development, from embryonic day 14 through adulthood. Disc1 mRNA was detected in the dentate gyrus at all stages in which this structure was identifiable, as well as in the cornu ammonis (CA) fields of the hippocampus, the subiculum and adjacent entorhinal cortex, and the developing cerebral neocortex, hypothalamus, and olfactory bulbs, all of which also express Disc1 in the adult mouse brain. In addition, Disc1 mRNA was seen in regions of the developing mouse brain which do not express Disc1 during adulthood, regions including the bed nucleus of the stria terminalis, reticular thalamic nucleus and reuniens thalamic nucleus. These results demonstrate that Disc1 marks the hippocampus from its earliest stages, and suggest that developmental Disc1 dysfunction may lead to defects in hippocampal function that are associated with schizophrenia.

Forebrain dopamine systems--can they help us to understand psychosis?

Under normal circumstances, emotional and affective signals within the brain are tempered by signals from higher brain centres, including the forebrain. These control systems ensure that responses to emotional and affective stimuli are appropriate for the environment within which they are generated. In patients with schizophrenia, these control systems are dysfunctional causing the patients to become oversensitive to such emotional stimuli and leading to the exaggerated reactions that are symptomatic of the disease [7,19].

A non-invasive method for observing hippocampal function

A non-invasive method for observing the functioning of the hippocampus could be invaluable in understanding the role of hippocampal abnormalities in many brain disorders. Transverse patterning, a hippocampal-dependent memory task, was used in an attempt to study the functioning hippocampus. Subjects performed transverse patterning while whole-head MEG data were collected. The MEG data were analyzed using a spatial-temporal multiple-dipole approach. Controls showed right hippocampal activation. Patients with unilateral hippocampal damage showed activation in undamaged hippocampus. MEG during transverse patterning performance is a promising, non-invasive tool for assessing hippocampal function.

Selective deficit of hippocampal N-acetylaspartate in antipsychotic-naive patients with schizophrenia

BACKGROUND

Studies using proton magnetic resonance spectroscopy in schizophrenia have demonstrated abnormality of N-acetylaspartate but are confounded by the effects of phase of illness and medication. There is mounting evidence that antipsychotic medication influences N-acetylaspartate.

METHODS

A group of first-episode patients who had received no, or minimal, antipsychotic medication was examined at baseline and after 3 months treatment. Normal comparison subjects were examined at the same interval. Ratios of N-acetylaspartate, creatine plus phosphocreatine, and choline-containing compounds in the left prefrontal cortex, hippocampus, and basal ganglia were measured.

RESULTS

The mean duration of symptoms for all patients was 31.6 (SD 26.1) weeks. A significant reduction of hippocampal N-acetylaspartate/creatine plus phosphocreatine was found in the antipsychotic-naive group relative to those previously treated and to controls at baseline (F = 7.3, p <.002). No group differences were found at follow-up.

CONCLUSIONS

Hippocampal N-acetylaspartate/creatine plus phosphocreatine appears to be selectively affected early in the course of illness. The finding of neurochemical differences between treatment naive and previously treated patients confirms the relevance of medication status in proton magnetic resonance spectroscopy studies. Further investigation of the influence of medication at this stage of illness is warranted.

Hippocampal modulation of sensorimotor processes

While the hippocampus makes unique contributions to memory, it has also long been associated with sensorimotor processes, i.e. innate processes involving control of motor responses to sensory stimuli. Moreover, hippocampal dysfunction has been implicated in neuropsychiatric diseases, such as schizophrenia and anxiety disorders, primarily characterized by non-mnemonic deficits in the processing of and responding to sensory information. This review is concerned with the hippocampal modulation of three sensorimotor processes in rats-locomotor activity, prepulse inhibition (PPI) of the startle reflex, and the startle reflex itself-whose alterations are related to human psychosis or anxiety disorders. Its main purpose is to present and discuss the picture emerging from studies examining the effects of pharmacological manipulations of the dorsal and ventral hippocampus by local drug microinfusions. While a role of the hippocampus in regulating locomotor activity, PPI, and startle reactivity has also been suggested based on the effects of hippocampal lesions, the microinfusion studies have revealed additional important details of this role and suggest modifications of notions based on lesion studies. In summary, the microinfusion studies corroborate that hippocampal mechanisms can directly influence locomotor activity, PPI, and startle reactivity, and that aberrant hippocampal function may contribute to neuropsychiatric diseases, in particular psychosis. The relation between different sensorimotor processes and hippocampal neurotransmission, the role of ventral and dorsal hippocampus, and the extrahippocampal mechanisms mediating the hippocampal modulation of different sensorimotor processes can partly be dissociated. Thus, the hippocampal modulation of these sensorimotor processes appears to reflect multiple operations, rather than one unitary operation.

Reduced hippocampal anisotropy related to anteriorization of alpha EEG in schizophrenia

Dysfunctions of the hippocampus have been suggested to be related to schizophrenia, and reduced connectivity with other brain regions may be a key for the pathophysiology. The aim of this study was to investigate the effect of white matter anomalies in the hippocampus, as a sign of altered connectivity, on the brain electrical activity. We investigated seven first episode schizophrenic patients and seven age, gender and education-matched controls with diffusion tensor imaging and resting EEG. Fractional anisotropy was computed based on diffusion tensor imaging data for the right and left hippocampus for both groups. No group differences were found in hippocampal fractional anisotropy, EEG spectral power and topography. However a significant correlation was found between more anterior alpha activity and lower fractional anisotropy of both hippocampi in schizophrenics, but not in controls. More anterior alpha activity has been described in schizophrenia. We conclude that this feature might depict a group of schizophrenic patients with reduced hippocampal connectivity.