Novel mimetic tissue standards for precise quantitative mass spectrometry imaging of drug and neurotransmitter concentrations in rat brain tissues

Understanding the relationship between the concentration of a drug and its therapeutic efficacy or side effects is crucial in drug development, especially to understand therapeutic efficacy in central nervous system drug, quantifying drug-induced site-specific changes in the levels of endogenous metabolites, such as neurotransmitters. In recent times, evaluation of quantitative distribution of drugs and endogenous metabolites using matrix-assisted laser desorption/ionization (MALDI)-mass spectrometry imaging (MSI) has attracted much attention in drug discovery research. However, MALDI-MSI quantification (quantitative mass spectrometry imaging, QMSI) is an emerging technique, and needs to be further developed for practicable and convenient use in drug discovery research. In this study, we developed a reliable QMSI method for quantification of clozapine (antipsychotic drug) and dopamine and its metabolites in the rat brain using MALDI-MSI. An improved mimetic tissue model using powdered frozen tissue for QMSI was established as an alternative method, enabling the accurate quantification of clozapine levels in the rat brain. Furthermore, we used the improved method to evaluate drug-induced fluctuations in the concentrations of dopamine and its metabolites. This method can quantitatively evaluate drug localization in the brain and drug-induced changes in the concentration of endogenous metabolites, demonstrating the usefulness of QMSI.

Neuromodulation of the anterior thalamus: Current approaches and opportunities for the future

The role of thalamocortical circuits in memory has driven a recent burst of scholarship, especially in animal models. Investigating this circuitry in humans is more challenging. And yet, the development of new recording and stimulation technologies deployed for clinical indications has created novel opportunities for data collection to elucidate the cognitive roles of thalamic structures. These technologies include stereoelectroencephalography (SEEG), deep brain stimulation (DBS), and responsive neurostimulation (RNS), all of which have been applied to memory-related thalamic regions, specifically for seizure localization and treatment. This review seeks to summarize the existing applications of neuromodulation of the anterior thalamic nuclei (ANT) and highlight several devices and their capabilities that can allow cognitive researchers to design experiments to assay its functionality. Our goal is to introduce to investigators, who may not be familiar with these clinical devices, the capabilities, and limitations of these tools for understanding the neurophysiology of the ANT as it pertains to memory and other behaviors. We also briefly cover the targeting of other thalamic regions including the centromedian (CM) nucleus, dorsomedial (DM) nucleus, and pulvinar, with associated potential avenues of experimentation.

Treatment effects on neurometabolite levels in schizophrenia: A systematic review and meta-analysis of proton magnetic resonance spectroscopy studies

BACKGROUND

Although there is growing evidence of alterations in the neurometabolite status associated with the pathophysiology of schizophrenia, how treatments influence these metabolite levels in patients with schizophrenia remains poorly studied.

METHODS

We conducted a literature search using Embase, Medline, and PsycINFO to identify proton magnetic resonance spectroscopy studies that compared neurometabolite levels before and after treatment in patients with schizophrenia. Six neurometabolites (glutamate, glutamine, glutamate + glutamine, gamma-aminobutyric acid, N-acetylaspartate, myo-inositol) and six regions of interest (frontal cortex, temporal cortex, parieto-occipital cortex, thalamus, basal ganglia, hippocampus) were investigated.

RESULTS

Thirty-two studies (n = 773 at follow-up) were included in our meta-analysis. Our results demonstrated that the frontal glutamate + glutamine level was significantly decreased (14 groups; n = 292 at follow-up; effect size = -0.35, P = 0.0003; I² = 22%) and the thalamic N-acetylaspartate level was significantly increased (7 groups; n = 184 at follow-up; effect size = 0.47, P < 0.00001; I² = 0%) after treatment in schizophrenia patients. No significant associations were found between neurometabolite changes and age, gender, duration of illness, duration of treatment, or baseline symptom severity.

CONCLUSIONS

The current results suggest that glutamatergic neurometabolite levels in the frontal cortex and neuronal integrity in the thalamus in schizophrenia might be modified following treatment.

From the microscope to the magnet: Disconnection in schizophrenia and bipolar disorder

White matter (WM) abnormalities have implicated schizophrenia (SZ) and bipolar disorder (BD) as disconnection syndromes, yet the extent to which these abnormalities are shared versus distinct remains unclear. Diffusion tensor imaging (DTI) studies yield a putative measure of WM integrity while neuropathological studies provide more specific microstructural information. We therefore systematically reviewed all neuropathological (n = 12) and DTI (n = 11) studies directly comparing patients with SZ and BD. Most studies (18/23) reported no difference between patient groups. Changes in oligodendrocyte density, myelin staining and gene, protein and mRNA expression were found in SZ and/or BD patients as compared to healthy individuals, while DTI studies showed common alterations in thalamic radiations, uncinate fasciculus, corpus callosum, longitudinal fasciculus and corona radiata. Altogether, findings suggest shared disconnectivity in SZ and BD, which are likely related to their considerable overlap. Above all, neuroimaging findings corroborated neuropathological findings in the prefrontal cortex, demonstrating the utility of integrating multiple methodologies. Focusing on clinical dimensions over disease entities will advance our understanding of disconnectivity and help inform preventive medicine.

Altered Global Signal Topography in Schizophrenia

Schizophrenia (SCZ) is a disabling neuropsychiatric disease associated with disruptions across distributed neural systems. Resting-state functional magnetic resonance imaging has identified extensive abnormalities in the blood-oxygen level-dependent signal in SCZ patients, including alterations in the average signal over the brain-i.e. the "global" signal (GS). It remains unknown, however, if these "global" alterations occur pervasively or follow a spatially preferential pattern. This study presents the first network-by-network quantification of GS topography in healthy subjects and SCZ patients. We observed a nonuniform GS contribution in healthy comparison subjects, whereby sensory areas exhibited the largest GS component. In SCZ patients, we identified preferential GS representation increases across association regions, while sensory regions showed preferential reductions. GS representation in sensory versus association cortices was strongly anti-correlated in healthy subjects. This anti-correlated relationship was markedly reduced in SCZ. Such shifts in GS topography may underlie profound alterations in neural information flow in SCZ, informing development of pharmacotherapies.

Increases in Intrinsic Thalamocortical Connectivity and Overall Cognition Following Cognitive Remediation in Chronic Schizophrenia

BACKGROUND

Thalamic projections to the prefrontal cortex (PFC) are critical for cognition, and disruptions in these circuits are thought to underlie the pathophysiology of schizophrenia. Cognitive remediation (REM) is a behavioral intervention that holds promise for improving cognition and functioning in schizophrenia, however the extent to which it affects thalamo-prefrontal connections has not been researched. This study sought to determine whether patients with schizophrenia who undergo a placebo-controlled trial of REM show increased functional connectivity between the thalamus and PFC, and whether these changes correspond to improvements in cognition.

METHODS

Twenty-six patients with chronic schizophrenia were randomized to either 48 hours (over 16 weeks) of a drill-and-practice working memory-focused REM or an active placebo condition. All participants underwent cognitive assessment (MATRICS Consensus Cognitive Battery), as well as both resting and task-based fMRI before and after their respective intervention. All clinicians, technicians, and raters were blind to participant condition.

RESULTS

We observed changes in resting-state connectivity in the PFC for the REM group but not the placebo group. Increased intrinsic connectivity between the thalamus and right middle frontal gyrus correlated with improvements in overall cognition. Additionally, lower baseline cognition correlated with greater increases in connectivity between the thalamus and PFC. Similar findings were observed when patients were scanned during a working memory task.

CONCLUSIONS

These results suggest that increases in thalamo-prefrontal circuitry correspond with training-related improvements of the cognitive deficits associated with schizophrenia.

Nonfunctional Glial Proteins in Tripartite Synapses: A Pathophysiological Model of Schizophrenia

A model for the pathophysiology of schizophrenia is proposed that focuses on an unbalance of transmission in tripartite synapses. Synaptically associated astrocytes should be viewed as integral modulatory elements of tripartite synapses consisting of the presynapse, the postsynapse, and the glial element. Astrocytes may secrete glial binding protein into the synaptic cleft, thus binding free neurotransmitters and thereby reducing the levels of neurotransmitters available for stimulating the postsynapse. Astrocytes also have membrane-bound receptors for neurotransmitters, and when these bind neurotransmitters, the astrocytes upregulate the amount of binding protein secreted into the synapse, resulting in a negative feedback to the presynaptic terminal. The hypothesis presented here is that glia lose their negative feedback function due to loss of function mutations in the genes encoding the binding proteins and glial receptors. The mutations generate proteins that cannot be occupied by their cognate substances of the neuronal system, primarily neurotransmitters. Therefore, the glial-neuronal interaction in tripartite synapses affected becomes totally unbalanced, and the glia lose their inhibitory or boundary-setting function. As a result, neural flux is unconstrained by normal glial boundaries, also the flux of thought on the phenomenological level. Schizophrenia may be caused by the inability to delimit conceptual boundaries.

Effect of MK-801 and Clozapine on the Proteome of Cultured Human Oligodendrocytes

Separate lines of evidence have demonstrated the involvement of N-methyl-D-aspartate (NMDA) receptor and oligodendrocyte dysfunctions in schizophrenia. Here, we have carried out shotgun mass spectrometry proteome analysis of oligodendrocytes treated with the NMDA receptor antagonist MK-801 to gain potential insights into these effects at the molecular level. The MK-801 treatment led to alterations in the levels of 68 proteins, which are associated with seven distinct biological processes. Most of these proteins are involved in energy metabolism and many have been found to be dysregulated in previous proteomic studies of post-mortem brain tissues from schizophrenia patients. Finally, addition of the antipsychotic clozapine to MK-801-treated oligodendrocyte cultures resulted in changes in the levels of 45 proteins and treatment with clozapine alone altered 122 proteins and many of these showed opposite changes to the MK-801 effects. Therefore, these proteins and the associated energy metabolism pathways should be explored as potential biomarkers of antipsychotic efficacy. In conclusion, MK-801 treatment of oligodendrocytes may provide a useful model for testing the efficacy of novel treatment approaches.

Functional hierarchy underlies preferential connectivity disturbances in schizophrenia

Schizophrenia may involve an elevated excitation/inhibition (E/I) ratio in cortical microcircuits. It remains unknown how this regulatory disturbance maps onto neuroimaging findings. To address this issue, we implemented E/I perturbations within a neural model of large-scale functional connectivity, which predicted hyperconnectivity following E/I elevation. To test predictions, we examined resting-state functional MRI in 161 schizophrenia patients and 164 healthy subjects. As predicted, patients exhibited elevated functional connectivity that correlated with symptom levels, and was most prominent in association cortices, such as the fronto-parietal control network. This pattern was absent in patients with bipolar disorder (n = 73). To account for the pattern observed in schizophrenia, we integrated neurobiologically plausible, hierarchical differences in association vs. sensory recurrent neuronal dynamics into our model. This in silico architecture revealed preferential vulnerability of association networks to E/I imbalance, which we verified empirically. Reported effects implicate widespread microcircuit E/I imbalance as a parsimonious mechanism for emergent inhomogeneous dysconnectivity in schizophrenia.

DISC1 Ser704Cys impacts thalamic-prefrontal connectivity

The Disrupted-in-Schizophrenia 1 (DISC1) gene has been thought as a putative susceptibility gene for various psychiatric disorders, and DISC1 Ser704Cys is associated with variations of brain morphology and function. Moreover, our recent diffusion magnetic resonance imaging (dMRI) study reported that DISC1 Ser704Cys was associated with information transfer efficiency in the brain anatomical network. However, the effects of the DISC1 gene on functional brain connectivity and networks, especially for thalamic-prefrontal circuit, which are disrupted in various psychiatric disorders, are largely unknown. Using a functional connectivity density (FCD) mapping method based on functional magnetic resonance imaging data in a large sample of healthy Han Chinese subjects, we first investigated the association between DISC1 Ser704Cys and short- and long-range FCD hubs. Compared with Ser homozygotes, Cys-allele individuals had increased long-range FCD hubs in the bilateral thalami. The functional and anatomical connectivity of the thalamus to the prefrontal cortex was further analyzed. Significantly increased thalamic-prefrontal functional connectivity and decreased thalamic-prefrontal anatomical connectivity were found in DISC1 Cys-allele carriers. Our findings provide consistent evidence that the DISC1 Ser704Cys polymorphism influences the thalamic-prefrontal circuits in humans and may provide new insights into the neural mechanisms that link DISC1 and the risk for psychiatric disorders.

Characterizing thalamo-cortical disturbances in schizophrenia and bipolar illness

Schizophrenia is a devastating neuropsychiatric syndrome associated with distributed brain dysconnectivity that may involve large-scale thalamo-cortical systems. Incomplete characterization of thalamic connectivity in schizophrenia limits our understanding of its relationship to symptoms and to diagnoses with shared clinical presentation, such as bipolar illness, which may exist on a spectrum. Using resting-state functional magnetic resonance imaging, we characterized thalamic connectivity in 90 schizophrenia patients versus 90 matched controls via: (1) Subject-specific anatomically defined thalamic seeds; (2) anatomical and data-driven clustering to assay within-thalamus dysconnectivity; and (3) machine learning to classify diagnostic membership via thalamic connectivity for schizophrenia and for 47 bipolar patients and 47 matched controls. Schizophrenia analyses revealed functionally related disturbances: Thalamic over-connectivity with bilateral sensory-motor cortices, which predicted symptoms, but thalamic under-connectivity with prefrontal-striatal-cerebellar regions relative to controls, possibly reflective of sensory gating and top-down control disturbances. Clustering revealed that this dysconnectivity was prominent for thalamic nuclei densely connected with the prefrontal cortex. Classification and cross-diagnostic results suggest that thalamic dysconnectivity may be a neural marker for disturbances across diagnoses. Present findings, using one of the largest schizophrenia and bipolar neuroimaging samples to date, inform basic understanding of large-scale thalamo-cortical systems and provide vital clues about the complex nature of its disturbances in severe mental illness.

Deep brain stimulation of the mediodorsal thalamic nucleus yields increases in the expression of zif-268 but not c-fos in the frontal cortex

This study explores the regions activated by deep brain stimulation of the mediodorsal thalamic nucleus through examination of immediate early genes as markers of neuronal activation. Stimulation was delivered unilaterally with constant current 100 μs duration pulses at a frequency of 130 Hz delivered at an amplitude of 200 μA for 3h. Brains were removed, sectioned and radio-labelled for the IEGs zif-268 and c-fos. In anaesthetised rats, deep brain stimulation of mediodorsal thalamic nucleus produced robust increases in the expression of zif-268 but not c-fos localised to regions that are reciprocally connected with the mediodorsal thalamic nucleus, including the prelimbic and orbitofrontal cortices, and the premotor cortex indicating an increase in synaptic activity in these regions. These findings map those brain regions that are persistently, rather than transiently, activated by high frequency electrical stimulation of the mediodorsal thalamic nucleus by a putatively antidromic mechanism which may be relevant to neuropsychiatric disorders such as schizophrenia in which thalamocortical systems are disrupted and in which DBS protocols are being considered.

Deep brain stimulation of the ventral hippocampus restores deficits in processing of auditory evoked potentials in a rodent developmental disruption model of schizophrenia

Existing antipsychotic drugs are most effective at treating the positive symptoms of schizophrenia but their relative efficacy is low and they are associated with considerable side effects. In this study deep brain stimulation of the ventral hippocampus was performed in a rodent model of schizophrenia (MAM-E17) in an attempt to alleviate one set of neurophysiological alterations observed in this disorder. Bipolar stimulating electrodes were fabricated and implanted, bilaterally, into the ventral hippocampus of rats. High frequency stimulation was delivered bilaterally via a custom-made stimulation device and both spectral analysis (power and coherence) of resting state local field potentials and amplitude of auditory evoked potential components during a standard inhibitory gating paradigm were examined. MAM rats exhibited alterations in specific components of the auditory evoked potential in the infralimbic cortex, the core of the nucleus accumbens, mediodorsal thalamic nucleus, and ventral hippocampus in the left hemisphere only. DBS was effective in reversing these evoked deficits in the infralimbic cortex and the mediodorsal thalamic nucleus of MAM-treated rats to levels similar to those observed in control animals. In contrast stimulation did not alter evoked potentials in control rats. No deficits or stimulation-induced alterations were observed in the prelimbic and orbitofrontal cortices, the shell of the nucleus accumbens or ventral tegmental area. These data indicate a normalization of deficits in generating auditory evoked potentials induced by a developmental disruption by acute high frequency, electrical stimulation of the ventral hippocampus.

Three-way (N-way) fusion of brain imaging data based on mCCA+jICA and its application to discriminating schizophrenia

Multimodal fusion is an effective approach to better understand brain diseases. However, most such instances have been limited to pair-wise fusion; because there are often more than two imaging modalities available per subject, there is a need for approaches that can combine multiple datasets optimally. In this paper, we extended our previous two-way fusion model called "multimodal CCA+joint ICA", to three or N-way fusion, that enables robust identification of correspondence among N data types and allows one to investigate the important question of whether certain disease risk factors are shared or distinct across multiple modalities. We compared "mCCA+jICA" with its alternatives in a 3-way fusion simulation and verified its advantages in both decomposition accuracy and modal linkage detection. We also applied it to real functional Magnetic Resonance Imaging (fMRI)-Diffusion Tensor Imaging (DTI) and structural MRI fusion to elucidate the abnormal architecture underlying schizophrenia (n=97) relative to healthy controls (n=116). Both modality-common and modality-unique abnormal regions were identified in schizophrenia. Specifically, the visual cortex in fMRI, the anterior thalamic radiation (ATR) and forceps minor in DTI, and the parietal lobule, cuneus and thalamus in sMRI were linked and discriminated between patients and controls. One fMRI component with regions of activity in motor cortex and superior temporal gyrus individually discriminated schizophrenia from controls. Finally, three components showed significant correlation with duration of illness (DOI), suggesting that lower gray matter volumes in parietal, frontal, and temporal lobes and cerebellum are associated with increased DOI, along with white matter disruption in ATR and cortico-spinal tracts. Findings suggest that the identified fractional anisotropy changes may relate to the corresponding functional/structural changes in the brain that are thought to play a role in the clinical expression of schizophrenia. The proposed "mCCA+jICA" method showed promise for elucidating the joint or coupled neuronal abnormalities underlying mental illnesses and improves our understanding of the disease process.

Discriminating schizophrenia and bipolar disorder by fusing fMRI and DTI in a multimodal CCA+ joint ICA model

Diverse structural and functional brain alterations have been identified in both schizophrenia and bipolar disorder, but with variable replicability, significant overlap and often in limited number of subjects. In this paper, we aimed to clarify differences between bipolar disorder and schizophrenia by combining fMRI (collected during an auditory oddball task) and diffusion tensor imaging (DTI) data. We proposed a fusion method, "multimodal CCA+ joint ICA", which increases flexibility in statistical assumptions beyond existing approaches and can achieve higher estimation accuracy. The data collected from 164 participants (62 healthy controls, 54 schizophrenia and 48 bipolar) were extracted into "features" (contrast maps for fMRI and fractional anisotropy (FA) for DTI) and analyzed in multiple facets to investigate the group differences for each pair-wised groups and each modality. Specifically, both patient groups shared significant dysfunction in dorsolateral prefrontal cortex and thalamus, as well as reduced white matter (WM) integrity in anterior thalamic radiation and uncinate fasciculus. Schizophrenia and bipolar subjects were separated by functional differences in medial frontal and visual cortex, as well as WM tracts associated with occipital and frontal lobes. Both patients and controls showed similar spatial distributions in motor and parietal regions, but exhibited significant variations in temporal lobe. Furthermore, there were different group trends for age effects on loading parameters in motor cortex and multiple WM regions, suggesting that brain dysfunction and WM disruptions occurred in identified regions for both disorders. Most importantly, we can visualize an underlying function-structure network by evaluating the joint components with strong links between DTI and fMRI. Our findings suggest that although the two patient groups showed several distinct brain patterns from each other and healthy controls, they also shared common abnormalities in prefrontal thalamic WM integrity and in frontal brain mechanisms.

Converging evidence of blood-based biomarkers for schizophrenia: an update

This chapter has carried out a review of the literature and combined this with the results of in-house studies to identify candidate blood-based biomarkers for schizophrenia and antipsychotic drug response. Literature searches retrieved 185 publications describing a total of 273 schizophrenia biomarkers identified in serum and/or plasma. Examination of seven in-house multicenter studies resulted in the identification of 137 serum/plasma biomarkers. Taken together, the findings suggested an ongoing immunological and inflammatory process in schizophrenia. This was accompanied by altered cortisol levels which suggested activated stress response and altered hypothalamic-pituitary-adrenal axis function in these patients. The authors conclude that such biomarkers may prove useful as additional parameters for characterizing specific immune and/or metabolic or hormonal subsystems in schizophrenia and might, therefore, facilitate the development of future patient stratification and personalized medicine strategies.

White matter tractography in bipolar disorder and schizophrenia

BACKGROUND

Abnormalities of white matter integrity have been repeatedly demonstrated in both schizophrenia and bipolar disorder with voxel based methods. Because these methods are limited in their ability to localize deficits to specific tracts, we sought to investigate alterations in fractional anisotropy (FA) in the uncinate fasciculus and anterior thalamic radiation with probabilistic tractography.

METHODS

Individuals with schizophrenia (n = 25) or bipolar disorder (n = 40) were recruited from families with two or more affected members and age-matched to a control group (n = 49). All participants underwent diffusion tensor magnetic resonance imaging that was subsequently analyzed with probabilistic tractography. Mean FA was calculated bilaterally for the uncinate and anterior thalamic radiation and compared between groups with repeated measures analysis of variance.

RESULTS

Patients with schizophrenia or bipolar disorder showed common reductions in the uncinate fasciculus and anterior thalamic radiation. These reductions were unrelated to age, duration of illness, current medication, or current psychiatric symptoms in all patients or the lifetime presence of psychotic symptoms in bipolar subjects.

CONCLUSIONS

Patients with schizophrenia or bipolar disorder show common abnormalities in the uncinate fasciculus and anterior thalamic radiation that fail to respect traditional diagnostic boundaries. These deficits might be related to shared risk factors and disease mechanisms common to both disorders.

Membrane phospholipid composition, alterations in neurotransmitter systems and schizophrenia

This review addresses the relationship between modifications in membrane phospholipid composition (MPC) and alterations in dopaminergic, serotonergic and cholinergic neurotransmitter systems in schizophrenia. The main evidence in support of the MPC hypothesis of schizophrenia comes from post-mortem and platelet studies, which show that in schizophrenia, certain omega-3 and omega-6 polyunsaturated fatty acid (PUFA) levels are reduced. Furthermore, examination of several biochemical markers suggests abnormal fatty acid metabolism may be present in schizophrenia. Dietary manipulation of MPC with polyunsaturated fatty acid diets has been shown to affect densities of dopamine, serotonin and muscarinic receptors in rats. Also, supplementation with omega-3 fatty acids has been shown to improve mental health rating scores, and there is evidence that the mechanism behind this involves the serotonin receptor complex. This suggests that a tight relationship exists between essential fatty acid status and normal neurotransmission, and that altered PUFA levels may contribute to the abnormalities in neurotransmission seen in schizophrenia.

The loss of self-boundaries: towards a neuromolecular theory of schizophrenia

I start out with the hypothesis that the basic symptoms of schizophrenia are caused by a loss of self-boundaries. Phenomenologically, schizophrenic symptoms are based on the inability of the brain to delimit conceptual boundaries. At the cellular level in the brain, I have in previous work attributed a spatio-temporal boundary setting function to the glial cells such that glial cells determine the grouping of neurons into functional units. Mutations in genes that result in non-splicing of introns can produce aberrant versions of neurotransmitter receptors that lack protein domains encoded by entire exons and can also have protein sequence encoded by introns that have not been properly spliced out. I propose that such "chimeric" receptors are generated in glial cells and that they cannot interact properly with their cognate neurotransmitters. The glia will then lose their inhibitory function with respect to the information processing within neuronal networks. The loss of glial boundary-setting may result in a 'borderless' generalization of information processing such that the structuring of the brain in functional domains is almost completely lost. This loss of glial boundary setting could be an explanation of the loss of self-boundaries in schizophrenia.

Stereological analysis of the mediodorsal thalamic nucleus in schizophrenia: volume, neuron number, and cell types

The mediodorsal thalamic nucleus (MD) is the principal relay nucleus for the prefrontal cortex, a brain region thought to be dysfunctional in schizophrenia. Several, but not all, postmortem studies of the MD in schizophrenia have reported decreased volume and total neuronal number. However, it is not clear whether the findings are specific for schizophrenia nor is it known which subtypes of thalamic neurons are affected. We studied the left MD in 11 subjects with schizophrenia, 9 control subjects, and 12 subjects with mood disorders. Based on morphological criteria, we divided the neurons into two subclasses, presumably corresponding to projection neurons and local circuit neurons. We estimated MD volume and the neuron number of each subclass using methods based on modern unbiased stereological principles. We also estimated the somal volumes of each subclass using a robust, but biased, approach. In addition, we investigated the left MD in four cynomolgus monkeys chronically exposed to haloperidol and in four control monkeys in order to assess the possible effects of antipsychotic medications. The three human subject groups did not differ in any of the measures. In addition, no differences were observed between the two groups of monkeys. Thus, these findings do not support the hypothesis that the MD is a locus of pathology in schizophrenia, although they cannot rule out important functional or structural changes in parameters not measured. Like other studies, this investigation is subject to the limitations involved in sampling from a heterogeneous population emphasizing the need to continue to improve the application of robust, unbiased techniques to quantitative studies of this complex brain disorder.

Altered cortical glutamate neurotransmission in schizophrenia: evidence from morphological studies of pyramidal neurons

Multiple lines of evidence from pharmacological, neuroimaging, and postmortem studies implicate disturbances in cortical glutamate neurotransmission in the pathophysiology of schizophrenia. Given that pyramidal neurons are the principal source of cortical glutamate neurotransmission, as well as the targets of the majority of cortical glutamate-containing axon terminals, understanding the nature of altered glutamate neurotransmission in schizophrenia requires an appreciation of both the types of pyramidal cell abnormalities and the specific class(es) of pyramidal cells that are affected in the illness. In this chapter, we review evidence indicating that a subpopulation of pyramidal neurons in the dorsolateral prefrontal cortex exhibits reductions in dendritic spine density, a marker of the number of excitatory inputs, and in somal volume, a measure correlated with a neuron's dendritic and axonal architecture. Specifically, pyramidal neurons located in deep layer 3 of the dorsolateral prefrontal cortex and that lack immunoreactivity for nonphosphorylated neurofilament protein may be particularly involved in the pathophysiology of schizophrenia. The presence of similar changes in pyramidal neurons located in deep layer 3 of auditory association cortex suggests that a shared property, which remains to be determined, confers cell type-specific vulnerability to a subpopulation of cortical glutamatergic neurons in schizophrenia.

Meta-analysis of brain weight in schizophrenia

Brain weight is often said to be decreased in schizophrenia, but a reduction has only been found in a minority of studies. We have therefore carried out a meta-analysis to answer this basic neuropathological question. Data were identified from literature searches and from contacting researchers in the field who were invited to submit unpublished data. Inclusion criteria were: an operational diagnosis of schizophrenia, or comparison subjects with no neurological or psychiatric history, aged 18 or over, for whom brain weight, age and sex were known. Exclusion criteria were: a history of head injury, epilepsy, substance dependence or leucotomy; neuropathological evidence of neurodegenerative disorder or focal brain lesion. Results were analysed by multilevel modelling. Brain weight was, as expected, related to age and sex (both p<0.0001). After control for these factors, there was an effect of diagnosis, with brains from the 540 schizophrenia subjects being 2% lighter than from the 794 controls (weighted mean difference=24 g [95% confidence interval, 1-47 g]; p=0.04). The difference was similar in male and female patients. There was no correlation with duration of illness. In conclusion, brain weight is slightly but significantly reduced in schizophrenia, consistent in direction and magnitude with MRI volumetric findings. The result encourages a continuing search for the histological and molecular correlates of schizophrenia.

The distribution and morphology of prefrontal cortex pyramidal neurons identified using anti-neurofilament antibodies SMI32, N200 and FNP7. Normative data and a comparison in subjects with schizophrenia, bipolar disorder or major depression

Alterations in the density and size of pyramidal neurons in the prefrontal cortex have been described in schizophrenia and mood disorder. However, the changes are generally modest and have not always been replicated. We investigated the possibility that specific pyramidal neuron sub-populations, defined by their immunoreactivity with the anti-neurofilament antibodies SMI32, N200, and FNP7, are differentially affected in these disorders. First, we assessed the distribution and characteristics of pyramidal neurons labelled by the antibodies in the human dorsolateral prefrontal cortex (Brodmann areas 9, 32, 46), using single and double label immunocytochemistry and immunofluorescence. Three largely separate sub-populations of pyramidal neurons were identified, although with more substantial overlap between SMI32- and FNP7-positive neurons in lamina V. We then determined the density, size and shape of the three pyramidal neuron sub-populations in area 9 in patients with schizophrenia, bipolar disorder, or major depressive disorder, compared to controls (n=15 in each group). We found a lower density of lamina III N200-positive neurons in major depressive disorder than in schizophrenia or bipolar disorder. There were no other overall differences in neuronal density, or in neuronal size or shape, although a planned secondary analysis supported the previously reported decrease of neuronal size in lamina V in bipolar disorder. In summary, our study illustrates a conceptual and methodological approach which may be of value for investigating the differential neuropathological involvement of pyramidal neuron sub-populations. However, we found no clear evidence that the prefrontal neuropathology of schizophrenia or mood disorders preferentially affects SMI32-, N200- or FNP7-immunoreactive pyramidal neurons.

A postmortem study of the mediodorsal nucleus of the thalamus in schizophrenia

Four studies have reported that the mediodorsal nucleus of the thalamus (MD) is smaller and contains fewer neurons in schizophrenia. The MD is a key node in a circuit proposed to be dysfunctional in the disorder. However, one study did not find a MD volume loss in schizophrenia, and all the studies to date are relatively small. Given the importance of establishing unequivocally the presence of MD pathology, we have carried out a study of the volume and number of neurons in the left and right MD in 21 patients with schizophrenia and 27 healthy comparison subjects. We also measured the size of MD neurons, and estimated total thalamic volume. We found no difference in the volume of the MD, the number of MD neurons, or the size of MD neurons in either hemisphere in schizophrenia. Neither was total thalamic volume altered. There are no obvious methodological or clinical factors to explain our failure to replicate the finding of MD involvement in schizophrenia. Hence our negative observations, in the largest sample yet investigated, cast doubt on the robustness and/or the generalisability of MD neuropathology in schizophrenia.

Schizophrenia, neurodevelopment and corpus callosum

The Zeitgeist favors an interpretation of schizophrenia as a condition of abnormal connectivity of cortical neurons, particularly in the prefrontal and temporal cortex. The available evidence points to reduced connectivity, a possible consequence of excessive synaptic pruning in development. A decreased thalamic input to the cerebral cortex appears likely, and developmental studies predict that this decrease should entail a secondary loss of both long- and short-range cortico-cortical connections, including connections between the hemispheres. Indeed, morphological, electrophysiological and neuropsychological studies over the last two decades suggest that the callosal connections are altered in schizophrenics. However, the alterations are subtle and sometimes inconsistent across studies, and need to be investigated further with new methodologies.

Schizophrenia as a disorder of neurodevelopment

A combination of genetic susceptibility and environmental perturbations appear to be necessary for the expression of schizophrenia. In addition, the pathogenesis of the disease is hypothesized to be neurodevelopmental in nature based on reports of an excess of adverse events during the pre- and perinatal periods, the presence of cognitive and behavioral signs during childhood and adolescence, and the lack of evidence of a neurodegenerative process in most individuals with schizophrenia. Recent studies of neurodevelopmental mechanisms strongly suggest that no single gene or factor is responsible for driving a highly complex biological process. Together, these findings suggest that combinatorial genetic and environmental factors, which disturb a normal developmental course early in life, result in molecular and histogenic responses that cumulatively lead to different developmental trajectories and the clinical phenotype recognized as schizophrenia.

Neural and behavioral substrates of mood and mood regulation

A review of behavioral and neurobiological data on mood and mood regulation as they pertain to an understanding of mood disorders is presented. Four approaches are considered: 1) behavioral and cognitive; 2) neurobiological; 3) computational; and 4) developmental. Within each of these four sections, we summarize the current status of the field and present our vision for the future, including particular challenges and opportunities. We conclude with a series of specific recommendations for National Institute of Mental Health priorities. Recommendations are presented for the behavioral domain, the neural domain, the domain of behavioral-neural interaction, for training, and for dissemination. It is in the domain of behavioral-neural interaction, in particular, that new research is required that brings together traditions that have developed relatively independently. Training interdisciplinary clinical scientists who meaningfully draw upon both behavioral and neuroscientific literatures and methods is critically required for the realization of these goals.

Decreased [(3)H]spiperone binding in the anterior cingulate cortex of schizophrenia patients: an autoradiographic study

Abnormalities in the anterior cingulate cortex have been reported in patients with schizophrenia, and have been implicated in the pathophysiology of this disorder. In the present study, we have examined antipsychotic-sensitive binding sites in the left anterior cingulate cortex of schizophrenia patients and controls. Using quantitative autoradiography and [(3)H]spiperone as a ligand, both saturation and competition experiments were performed in post-mortem brain tissue obtained from six schizophrenia and six control cases. Saturation experiments revealed that the maximum number of [(3)H]spiperone binding sites was significantly reduced by 31% in the schizophrenia group as compared to the control group (65.3+/-5.6 fmol/mg tissue versus 94.2+/-7.3 fmol/mg tissue). Increased dissociation constant was also observed in the schizophrenia group (2.2+/-0.4 nM versus 1.3+/-0.2 nM), but was not statistically significant (P=0.07). Competition experiments were performed in order to examine the pharmacological profile of [(3)H]spiperone binding, and revealed that: (i) displacement of [(3)H]spiperone binding by clozapine and mianserin was significantly reduced in the schizophrenia group as compared to the control group (-26% and -16% respectively); (ii) the order of displacement potency of the drugs tested was: haloperidol>mianserin>butaclamol approximately risperidone>clozapine>2-amino-6,7-dihydroxy-1,2,3,4-tetrahydronaphthalene. Our results suggest a reduction of antipsychotic-sensitive binding sites in the anterior cingulate cortex of patients with schizophrenia. Such abnormality could lead to an imbalance in neurotransmitter regulation in the anterior cingulate cortex which may contribute to the emergence of some symptoms of schizophrenia.

A major role for thalamocortical afferents in serotonergic hallucinogen receptor function in the rat neocortex

Activation of 5-hydroxytryptamine(2A) (5-HT(2A)) receptors by hallucinogenic drugs is thought to mediate many psychotomimetic effects including changes in affect, cognition and perception. Conversely, blockade of 5-HT(2A) receptors may mediate therapeutic effects of many atypical antidepressant and antipsychotic drugs. The purpose of the present study was to determine the source of subcortical glutamatergic afferents, which would project widely throughout the anterior-posterior axis of the rat brain to the apical dendrites of layer V pyramidal cells of the medial prefrontal cortex, from which serotonin induces transmitter release via activation of 5-HT(2A) receptors. Fiber-sparing chemical lesions of the medial thalamus selectively decreased the frequency of serotonin-induced excitatory postsynaptic currents recorded from layer V pyramidal cells in the prelimbic region of the medial prefrontal cortex by 60%. In contrast, large bilateral lesions of the amygdala did not alter the serotonin response. These thalamic lesions significantly decreased the amount of binding to either mu-opioid or metabotropic glutamate 2/3 receptors in the prelimbic region of the medial prefrontal cortex as expected from previous evidence that these agonists for these receptors suppress serotonin-induced excitatory postsynaptic currents by a presynaptic mechanism. Surprisingly, the amount of specific binding to cortical 5-HT(2A) receptors was significantly increased by the medial thalamic lesions. Thus, these experiments demonstrate that activation of cortical 5-HT(2A) receptors modulates transmitter release from thalamocortical terminals. Unexpectedly, lesioning the thalamocortical terminals also alters 5-HT(2A) receptor binding in the prefrontal cortex. These findings are of interest with respect to understanding therapeutic effects of antidepressant/antipsychotic drugs and the known behavioral effects of thalamic lesions in humans.

The changing roles and targets for animal models of schizophrenia

Unlike disorders of other fields of medicine (eg., diabetes, heart disease), schizophrenia has been only marginally impacted by the study of animal models. This gap reflects the incomplete understanding of the causes and mechanisms of schizophrenia and the resulting lack of defined targets for model development. However, prior attempts at modeling in animals the complex symptoms of schizophrenia have given way to more promising component models. This review will address the evolving field of animal models of schizophrenia with a focus on models of errors in neurotransmission, and of psychophysiological deficits, with a concluding discussion of the present and future promise of genetic-based models. Evolving models based on the long-held conceptualization of schizophrenia as being based on errors in neurotransmission are discussed as regards the integration of newer findings implicating alterations in dopamine, glutamate and neurotensin function in the pathophysiology and pharmacotherapy of schizophrenia. The case for the more recent conceptualization of schizophrenia as a core deficit in information processing and stimulus filtering is discussed. Animal behavioral paradigms that model psychophysiologic constructs of stimulus processing deficits related to schizophrenia include prepulse inhibition (PPI), a model of sensorimotor gating, or latent inhibition (LI), a model of salience learning. These models represent both better supported associations with schizophrenia and more productive targets and are providing important new information regarding the psychopharmacology of schizophrenia. Genetic models of schizophrenia are based on the demonstrated heritability of the disorder and more recent pharmacogenetic findings for antipsychotic medications. Genetic-based animal models use behavioral or molecular genetic techniques to manipulate behaviors related to schizophrenia by altering the frequencies of related genes. The future development of increasingly informative animal models of schizophrenia will be dependent on a more complete understanding of schizophrenia, an integration of findings across animal models and refinements in the criteria used to assess model "validity" that better reflect the changing nature and roles of animal models of schizophrenia.

Dopamine transporter-immunoreactive axons in the mediodorsal thalamic nucleus of the macaque monkey

The reciprocal connections between the mediodorsal thalamic nucleus and the prefrontal cortex participate in a circuit that is essential to a number of higher cognitive processes. Projections from the dopamine-containing cells of the ventral mesencephalon to the prefrontal cortex are also critical for these cognitive abilities. It is unclear, however, whether dopamine axons innervate the mediodorsal thalamic nucleus in primates. In order to address this question, we examined the distribution of dopamine transporter-immunoreactive axons in the mediodorsal thalamic nucleus of macaque monkeys. Labeled axons were distributed quite heterogeneously in this nucleus, and did not strictly follow cytoarchitectonic subdivision boundaries. The ventral and lateral portions of the mediodorsal thalamic nucleus, which include parts of the parvicellular and multiform subdivisions, had the highest density of dopamine transporter-immunoreactive axons. In contrast, the dorsomedial portion, which included primarily the magnocellular subdivision, had the lowest density of labeled axons. In both lightly and densely innervated portions of the nucleus, small, dense clusters of dopamine transporter-immunoreactive axons were present. Axons immunoreactive for tyrosine hydroxylase were distributed in a pattern very similar to that of dopamine transporter-labeled axons. In contrast, noradrenergic axons, as revealed by dopamine beta-hydroxylase immunoreactivity, were present in higher density and were more evenly distributed throughout the mediodorsal thalamic nucleus. This dopamine innervation of the mediodorsal thalamic nucleus reveals another possible anatomical substrate through which dopamine may influence the cognitive functions mediated by thalamo-prefrontal circuitry.

Disease-specific changes in regulator of G-protein signaling 4 (RGS4) expression in schizophrenia

Complex defects in neuronal signaling may underlie the dysfunctions that characterize schizophrenia. Using cDNA microarrays, we discovered that the transcript encoding regulator of G-protein signaling 4 (RGS4) was the most consistently and significantly decreased in the prefrontal cortex of all schizophrenic subjects examined. The expression levels of ten other RGS family members represented on the microarrays were unchanged and hierarchical data analysis revealed that as a group, 274 genes associated with G-protein signaling were unchanged. Quantitative in situ hybridization verified the microarray RGS4 data, and demonstrated highly correlated decreases in RGS4 expression across three cortical areas of ten subjects with schizophrenia. RGS4 expression was not altered in the prefrontal cortex of subjects with major depressive disorder or in monkeys treated chronically with haloperidol. Interestingly, targets for 70 genes mapped to the major schizophrenia susceptibility locus 1q21--22 were present on the microarrays, of which only RGS4 gene expression was consistently altered. The combined data indicate that a decrease in RGS4 expression may be a common and specific feature of schizophrenia, which could be due either to genetic factors or a disease- specific adaptation, both of which could affect neuronal signaling.

Molecular characterization of schizophrenia viewed by microarray analysis of gene expression in prefrontal cortex

Microarray expression profiling of prefrontal cortex from matched pairs of schizophrenic and control subjects and hierarchical data analysis revealed that transcripts encoding proteins involved in the regulation of presynaptic function (PSYN) were decreased in all subjects with schizophrenia. Genes of the PSYN group showed a different combination of decreased expression across subjects. Over 250 other gene groups did not show altered expression. Selected PSYN microarray observations were verified by in situ hybridization. Two of the most consistently changed transcripts in the PSYN functional gene group, N-ethylmaleimide sensitive factor and synapsin II, were decreased in ten of ten and nine of ten subjects with schizophrenia, respectively. The combined data suggest that subjects with schizophrenia share a common abnormality in presynaptic function. We set forth a predictive, testable model.