A developmental perspective on the pathology and neurochemistry of the temporal lobe in schizophrenia

Disrupted prefrontal interhemispheric structural coupling in schizophrenia related to working memory performance

BACKGROUND

Prominent regional cortical thickness reductions have been shown in schizophrenia. In contrast, little is known regarding alterations of structural coupling between regions in schizophrenia and how these alterations may be related to cognitive impairments in this disorder.

METHODS

T1-weighted magnetic resonance images were acquired in 54 patients with schizophrenia and 68 healthy control subjects aged 18-55 years. Cortical thickness was compared between groups using a vertex-wise approach. To assess structural coupling, seeds were selected within regions of reduced thickness, and brain-wide cortical thickness correlations were compared between groups. The relationships between identified patterns of circuit structure disruption and cognitive task performance were then explored.

RESULTS

Prominent cortical thickness reductions were found in patients compared with controls at a 5% false discovery rate in a predominantly frontal and temporal pattern. Correlations of the left dorsolateral prefrontal cortex (DLPFC) with right prefrontal regions were significantly different in patients and controls. The difference remained significant in a subset of 20 first-episode patients. Participants with stronger frontal interhemispheric thickness correlations had poorer working memory performance.

CONCLUSIONS

We identified structural impairment in a left-right DLPFC circuit in patients with schizophrenia independent of illness stage or medication exposure. The relationship between left-right DLPFC thickness correlations and working memory performance implicates prefrontal interhemispheric circuit impairment as a vulnerability pathway for poor working memory performance. Our findings could guide the development of novel therapeutic interventions aimed at improving working memory performance in patients with schizophrenia.

Effect of isolation rearing on the expression of AMPA glutamate receptors in the hippocampal formation

Reduced glutamatergic signaling may contribute to cognitive dysfunction in schizophrenia. Glutamatergic synapses might be the site of primary abnormalities in this disorder with the dopaminergic changes being secondary to altered glutamatergic transmission. Isolation rearing of rats from weaning has been used as an experimental model for affective disorders like schizophrenia. In this immunohistochemistry study we evaluate the changes in the expression of GluR1 and GluR2 AMPA receptors in the hippocampus, amygdala and entorhinal cortex induced by isolation rearing. Two groups of Wistar rats (grouped and isolated, n = 6/each) were used. Isolation rearing induced a significant decrease in GluR1- and GluR2-immunopositive cells in the hippocampus. For GluR1 the reduction was 31% in the hilus of dentate gyrus (p = 0.02) and 47% in CA3 (p = 0.002). For GluR2 the reduction was 52% in the hilus of dentate gyrus (p < 0.0001) and 29% in CA1 (p = 0.002). Isolation rearing induced a non-significant decrease in GluR1-immunopositive cells in the basolateral amygdala (p = 0.066) while no alteration was found in the lateral nucleus (p = 0.657). For GluR2 no changes were induced by isolation in both nuclei of the amygdala. In the entorhinal cortex no apparent difference was seen in GluR1- or GluR2-immunopositive cells when isolated reared rats were compared to grouped rats. The results suggest that isolation rearing from weaning induces changes on the expression of AMPA glutamate receptors in the hippocampus similar to those reported for postmortem human brains with schizophrenia. These findings also contribute to additional evidence for using isolation rearing of rats from weaning as an animal model for schizophrenia.

Estimation of baseline dopamine D2 receptor occupancy in striatum and extrastriatal regions in humans with positron emission tomography with [18F] fallypride

BACKGROUND

This study examined whether positron emission tomography (PET) studies with [18F] fallypride performed before and after alpha-methyl-para-tyrosine (AMPT) administration can be used to estimate baseline dopamine (DA) D2 receptor occupancy in striatal and extrastriatal regions.

METHODS

Six normal subjects underwent PET with [18 F] fallypride before and after administration of AMPT. The DA D2 receptor binding potentials (bp) were calculated with the reference region method. Percent changes in bp in striatal and extrastriatal regions were calculated with both region-of-interest analysis and on a voxel by voxel basis with parametric images of DA D2 receptor levels.

RESULTS

The results of the current study indicate that AMPT treatment significantly increased the bp in the caudate, putamen, ventral striatum, and substantia nigra. A trend level increase was seen in the medial thalamus.

CONCLUSIONS

This study demonstrates that PET with [18F] fallypride can be used to estimate baseline DA D2 receptor occupancy in striatal and extrastriatal regions.

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

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

METHODS

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

RESULTS

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

DISCUSSION

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

Amphetamine-induced displacement of [18F] fallypride in striatum and extrastriatal regions in humans

This study examined D-amphetamine (D-AMPH)-induced displacements of [18F] fallypride in striatal and extrastriatal regions and the correlations of these displacements with cognition, affect, and sensation-seeking behavior. In all, 14 normal subjects, six females and eight males (ages 21-32, mean age 25.9 years), underwent positron emission tomography (PET) with [18F]fallypride before and 3 h after a 0.43 mg/kg oral dose of D-AMPH. Levels of dopamine (DA) D2 receptor density were calculated with the reference region method of Lammerstma. Percent displacements in striatal and extrastriatal regions were calculated for the caudate, putamen, ventral striatum, medial thalamus, amygdala, substantia nigra, and temporal cortex. Correlations of changes in cognition, affect, and sensation seeking with parametric images of D-AMPH-induced DA release were computed. Significant displacements were seen in the caudate, putamen, ventral striatum substantia nigra, and temporal cortex with a trend level change in the amygdala. Greatest displacements were seen in striatal subdivisions-5.6% in caudate, 11.2% in putamen, 7.2% in ventral striatum, and 6.6% in substantia nigra. Lesser decrements were seen in amygdala-4.4%, temporal cortex-3.7%, and thalamus-2.8%. Significant clusters of correlations of regional DA release with cognition and sensation-seeking behavior were observed. The current study demonstrates that [18F]fallypride PET studies using oral D-AMPH (0.43 mg/kg) can be used to study D-AMPH-induced DA release in the striatal and extrastriatal regions in humans, and their relationship with cognition and sensation-seeking behavior.

Decreased levels of brain-derived neurotrophic factor in serum of chronic schizophrenic patients

Neurotrophic factors regulate neuronal development as well as synaptic plasticity, and their impairment is often implicated as a cause of schizophrenia. Among various neurotrophic molecules, brain-derived neurotrophic factor (BDNF) levels have been found to be increased in the corticolimbic regions of patients' brains. In the present study, we assessed peripheral BDNF levels in whole blood as well as in the serum of two independent groups of schizophrenic patients (n = 34 in each group) and healthy volunteers (n = 35 and n = 27, respectively). BDNF protein levels in fresh serum and blood of the patients and volunteers were measured using a two-site enzyme immunoassay and correlated with the number and decay of platelets. In addition to the studies of patients and volunteers, neuroleptic effects on BDNF levels were assessed by administering haloperidol to adult rats for 2 weeks or 5 months. The major findings were as follows: BDNF levels were significantly reduced in the serum of schizophrenic patients (P < 0.005, Mann-Whitney U-test) but not in their whole blood. Antipsychotic dose did not correlate with serum BDNF levels. Moreover, chronic administration of haloperidol failed to decrease serum BDNF levels in adult rats. Abnormal levels of BDNF are evident not only in the brain of schizophrenic patients, but also in their peripheral blood. The BDNF reduction in serum but not in whole blood suggests a potential deficit in neurotrophic factor release in patients with schizophrenia.

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

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

Regional cerebral blood flow in schizophrenia using stable xenon-enhanced computed tomography

To investigate the regional cerebral blood flow (rCBF) and the factors affecting the rCBF in schizophrenia, we measured the rCBF using stable xenon-enhanced computed tomography in 118 schizophrenic patients and 21 healthy subjects. A multiple regression analysis was applied to assess the potential affecting factors, i.e. age, gender, duration of illness, dose of antipsychotics and usage of antiparkinsonism and antianxiety drugs. The rCBF of the schizophrenic patients was significantly lower than that of the healthy subjects in all regions except for the occipital region. The rCBF was decreased with increasing age in both groups to the same extent. The dosage of antipsychotic drugs taken had a significant regression relationship with the rCBF in the bilateral thalamus.

PET mapping of extrastriatal D2-like dopamine receptors in the human brain using an anatomic standardization technique and [11C]FLB 457

The Computerized Brain Atlas (CBA) transforms PET images of individual subjects into a standard brain anatomy. We have previously applied this to PET images with [(11)C]raclopride and confirmed that the D2 dopamine receptors in the striatum can be evaluated accurately with a standard brain anatomy. There is growing evidence that extrastriatal D2 receptors, in spite of their low density, have pathophysiological significance for schizophrenia. We used the CBA to explore the extrastriatal distribution of D2 receptors in 13 healthy subjects using [11C]FLB 457, a substituted benzamide with very high affinity for D2 and D3 receptors. There was good agreement between the specific binding ratios from CBA quantification of standardized images and those from region-of-interest analyses of original images. The highest levels of binding were observed in the putamen and caudate nucleus, followed by the globus pallidus and nucleus accumbens. Besides the basal ganglia, the hypothalamus and nucleus ruber also showed high levels of binding. Intermediate levels were found in the substantia nigra, nucleus subthalami, amygdala, and thalamus. Interestingly, there was very heterogeneous binding among the thalamic nuclei. The anterior and mediodorsal nuclei showed relatively high binding. The cerebral cortices showed lower levels with significant regional differences. Binding was highest in the temporal cortex and hippocampus followed by the anterior cingulate gyrus, and the parietal and frontal cortices, but was lowest in the occipital cortex. The use of CBA for analysis of [11C]FLB 457 binding makes it possible to build a normal database for the extrastriatal D2 receptors in the living human brain. The heterogeneous distribution of D2 receptors provides an attractive opportunity for new research on the pathophysiology and drug treatment of schizophrenia.

Hippocampal volume reduction in schizophrenia: effects of genetic risk and pregnancy and birth complications

BACKGROUND

Hippocampal volume reduction has been repeatedly demonstrated in schizophrenia. The relative contribution of genetic and environmental factors to this is unclear.

METHODS

To address this question, we compared volumetric measurements of the left and right hippocampus, obtained using stereological methods from brain MRI scans, from two groups of patients with schizophrenia as well as healthy controls (n = 26). Patients (n = 27) in the first group, had no family history of schizophrenia and had experienced severe pregnancy and birth complications (PBCs). The second group comprised of patients (n = 21) without a history of severe PBCs from families multiply affected with schizophrenia.

RESULTS

Reduction of the left hippocampal volume was associated with the diagnosis of schizophrenia but was present only in patients with a history of severe PBCs; in this group the smaller hippocampal volume, the earlier the onset of psychosis.

CONCLUSIONS

Our findings suggest that environmental factors, in this case severe PBCs, make a significant contribution to hippocampal abnormalities in schizophrenia.

Dementia praecox to schizophrenia: the first 100 years

The historical roots of dementia praecox and schizophrenia are described in the context of current nosology and continuing controversies surrounding this nosology. Relevant books and journal articles were reviewed. The information was obtained through computer searches and cross-references from previously published papers. If English translations of foreign language articles were available, they were used; if not, the cross-references were consulted. The psychoses have existed as diagnostic categories from ancient times although their names have changed. Initially, these disorders were considered diseases of the brain, a concept that was swept aside in the United States, influenced by European-derived psychodynamic theories. American clinicians and investigators simply accepted these theories, showing little interest in testing their underlying principles. In contrast, a narrower Kraepelinian approach was adopted outside the United States, and attempts were made to refine its nosology. Because current data supports a central nervous system aetiology for schizophrenia, the concept of dementia praecox warrants resurrection. The authors suggest abandoning the term schizophrenia in favour of the more broad and generic term dementia praecox. Replacing 'schizophrenia' with 'dementia praecox' in the 21st century will facilitate further research and help clarify the nosology of various brain disorders currently included in the schizophrenias.

Comparison of the effects of dopamine D1 and D2 receptor antagonists on nerve growth factor mRNA expression

Regulation of the expression of the nerve growth factor (NGF) gene has been reported previously to be mediated by the interaction of c-fos with an activator protein-1 (AP-1) binding site present in the first intron on the NGF gene. Using an RNase protection assay and in situ hybridization, we examined the effects of dopamine D1 and D2 receptor antagonists on NGF mRNA. Haloperidol (0.1-8 mg/kg) and (-)-sulpiride (10-100 mg/kg), induced NGF mRNA in a dose-dependent fashion in the hippocampus, piriform cortex, striatum and nucleus accumbens. The haloperidol (1 mg/kg)- and (-)-sulpiride (20 mg/kg)-induced NGF mRNA expression attained a maximum level 120 min after injection and returned to control levels 24 h later. Prior administration of the protein synthesis inhibitor cycloheximide blocked the haloperidol- and (-)-sulpiride-mediated induction of NGF mRNA. In contrast, R-(-)-8-chloro-2,3,4,5-tetrahydro-3,1-methyl-5-phenyl-11-3-benzyoepin e-7-ol (SCH23390) did not induce NGF mRNA expression in either a dose-dependent or time-dependent manner. Our previous studies have shown that haloperidol and (-)-sulpiride induce the expression of c-fos and c-jun mRNAs and increase their AP-1 DNA binding activities. Thus, the data suggest that neuroleptics induce NGF gene expression by increasing AP-1 DNA binding activity.

A decrease of reelin expression as a putative vulnerability factor in schizophrenia

Postmortem prefrontal cortices (PFC) (Brodmann's areas 10 and 46), temporal cortices (Brodmann's area 22), hippocampi, caudate nuclei, and cerebella of schizophrenia patients and their matched nonpsychiatric subjects were compared for reelin (RELN) mRNA and reelin (RELN) protein content. In all of the brain areas studied, RELN and its mRNA were significantly reduced (approximately 50%) in patients with schizophrenia; this decrease was similar in patients affected by undifferentiated or paranoid schizophrenia. To exclude possible artifacts caused by postmortem mRNA degradation, we measured the mRNAs in the same PFC extracts from gamma-aminobutyric acid (GABA)A receptors alpha1 and alpha5 and nicotinic acetylcholine receptor alpha7 subunits. Whereas the expression of the alpha7 nicotinic acetylcholine receptor subunit was normal, that of the alpha1 and alpha5 receptor subunits of GABAA was increased when schizophrenia was present. RELN mRNA was preferentially expressed in GABAergic interneurons of PFC, temporal cortex, hippocampus, and glutamatergic granule cells of cerebellum. A protein putatively functioning as an intracellular target for the signal-transduction cascade triggered by RELN protein released into the extracellular matrix is termed mouse disabled-1 (DAB1) and is expressed at comparable levels in the neuroplasm of the PFC and hippocampal pyramidal neurons, cerebellar Purkinje neurons of schizophrenia patients, and nonpsychiatric subjects; these three types of neurons do not express RELN protein. In the same samples of temporal cortex, we found a decrease in RELN protein of approximately 50% but no changes in DAB1 protein expression. We also observed a large (up to 70%) decrease of GAD67 but only a small decrease of GAD65 protein content. These findings are interpreted within a neurodevelopmental/vulnerability "two-hit" model for the etiology of schizophrenia.

Alteration of dopamine metabolites in CSF and behavioral impairments induced by neonatal hippocampal lesions

Alterations of monoamine metabolites in CSF and behavioral abnormalities were studied in rats with neonatal hippocampal lesions and controls. Lesions of the ventral hippocampus were produced bilaterally by ibotenic acid on postnatal day 7. Lesion-induced neurochemical alterations and behavioral impairments were examined concurrently when rats were 12 weeks old. CSF from the cisterna magna was sampled repeatedly from freely moving rats. The levels of free 3,4-dihydroxyphenylacetic acid (DOPAC), homovanillic acid (HVA), and 5-hydroxyindoleacetic acid (5-HIAA) in CSF were determined. An exposure to a novel environment induced hyperexploratory behavior and elevated the level of free DOPAC in CSF in lesioned rats. Although a swim stress increased the levels of free DOPAC and 5-HIAA in CSF in both control and lesioned groups, rats with hippocampal lesions had a further elevation of free DOPAC in CSF and greater spontaneous activity relative to controls shortly after stress. Amphetamine (1.5 mg/kg, i.p.) induced hyperlocomotion in lesioned rats compared to controls. For the control group, the levels of the three monoamine metabolites in CSF were not significantly influenced by amphetamine. However, for the lesioned group, the level of DOPAC significantly decreased compared to preinjection of amphetamine. The results indicate that neonatal hippocampal lesion-induced impairments can be manifested by behavioral and neurochemical abnormalities. Alterations of monoamine metabolites in CSF may be determined quantitatively and used as indices for monitoring lesion-impaired monoaminergic function in the central nervous system.

VASE-containing N-CAM isoforms are increased in the hippocampus in bipolar disorder but not schizophrenia

The neural cell adhesion molecule (N-CAM) is a cell recognition molecule that is involved in cellular migration, synaptic plasticity, and CNS development. In schizophrenia, a 105- to 115-kDa N-CAM protein is increased in CSF and in the hippocampus and prefrontal cortex. The variable alternatively spliced exon (VASE) of N-CAM is developmentally regulated and can be spliced into any of the major 120-, 140-, and 180-kDa N-CAM isoforms. We determined that the variable alternative spliced exon of N-CAM (VASE) also is increased in bipolar disorder by quantitative Western immunoblot. VASE immunoreactive proteins (triplet bands around 140 kDa and a single band around 145 kDa) were identified in soluble and membrane brain extracts and quantified in the hippocampus. Soluble VASE 140 kDa was increased in the hippocampus of patients with bipolar disorder as compared to controls, patients with schizophrenia, and suicide cases. Membrane-extracted VASE 140 and 145 kDa were unchanged in the same groups. Multiple 145-kDa VASE-immunoreactive proteins that also reacted to an N-CAM antibody were separated by isoelectric focusing and electrophoresis followed by western immunoblotting; however, the VASE 140-kDa proteins were only weakly N-CAM immunoreactive. By immunohistochemistry, VASE colocalized with GFAP-positive astrocytes in the hippocampus. VASE immunostaining was also observed in the cytoplasm of CA4 pyramidal neurons that were positive for phosphorylated high molecular weight neurofilament and synaptophysin terminals. Thus no differences in VASE were found in patients with schizophrenia, but there was a marked increase of VASE immunoreactive proteins in bipolar disorder. It is possible that abnormal regulation of N-CAM proteins results in differing patterns of abnormal expression in neuropsychiatric disorders.

Does dysplasia cause anatomical dysconnectivity in schizophrenia?

Evidence is reviewed that dysplastic brain development in the second half of pregnancy predisposes to schizophrenia. We suggest that an important corollary of aberrant development at this stage of ontogenesis is abnormal afferentation of the cortical plate, and that this may be macroscopically measurable in terms of abnormal correlational structure in adult brain imaging data. This prediction is tested by analysis of multiple cortical volume measures on magnetic resonance imaging data acquired from 35 male right-handed schizophrenics and 35 matched controls. There are no significant differences between groups in global, intra-hemispheric or inter-hemispheric correlational structure; but schizophrenics are shown to have significantly reduced dependencies between frontal and temporal lobe volumes, and frontal and hippocampal volumes, in the left hemisphere. We conclude that anatomical dysconnectivity (between frontal and temporal cortex) in schizophrenia may be caused by dysplasia.

The dysplastic net hypothesis: an integration of developmental and dysconnectivity theories of schizophrenia

Two separate theories that attempt to explain different aspects of schizophrenia have recently attracted much attention. The first, the neurodevelopmental hypothesis, postulates that deviations in early development establish a neuronal phenotype that predisposes to, or, in some versions, determines the later onset of schizophrenia. The second theory proposes that schizophrenic symptoms arise from abnormalities in neuronal connectivity. Here, we suggest that the findings from these two separate lines of inquiry can be integrated into a unitary framework: the dysplastic net hypothesis. In essence, this proposes that anatomical and physiological dysconnectivity of the adult schizophrenic brain is determined by dysplastic fetal brain development. We also indicate how abnormal connectivity between brain regions constituting large-scale neurocognitive networks is expressed in both the prepsychotic and psychotic phases of schizophrenia, and we examine possible risk factors (genetic and environmental) for dysplastic formation of these networks.

Schizophrenia: developmental disturbance of brain and mind?

Schizophrenia is the most severe of the mental illnesses and affects approximately 0.8% of the population in Western societies. Postmortem and neuroimaging studies show that patients with schizophrenia have slightly larger cerebral ventricles than normal and a decrease in cortical volume, most markedly in the left temporal lobe. These changes are present at diagnosis and appear to show little change over extended periods of follow-up. Associated findings such as lack of normal cerebral asymmetry and cytoarchitectonic changes suggestive of impaired migration of cortical neurons implicate aberrant neurodevelopment. Schizophrenics also show an excess of pregnancy and birth complications, and an association with prenatal exposure to maternal influenza. These and reports of abnormal psychological development in pre-schizophrenic children add further support to the theory that the disorder has neurodevelopmental origins.

Distribution of kainate receptor subunit mRNAs in human hippocampus, neocortex and cerebellum, and bilateral reduction of hippocampal GluR6 and KA2 transcripts in schizophrenia

The mRNAs encoding kainic acid (KA) preferring glutamate receptor subunits (GluR5-7, KA1 and KA2) are differentially expressed in rat brain. We have used regional and cellular in situ hybridization histochemistry with subunit-specific 35S-labelled oligodeoxyribonucleotides to examine these mRNAs in adult human hippocampus, neocortex and cerebellum. GluR5 mRNA was detected only in Purkinje cells and a few scattered hippocampal neurons. GluR6 mRNA was relatively abundant in all areas, notably in dentate gyrus, pyramidal neurons of CA3, and cerebellar granule cells, as well as being present in superficial and deep laminae of the neocortex. Moderate signal for GluR7 mRNA was seen in deep laminae of the neocortex with a weak signal in the dentate gyrus; in dipped sections GluR7 mRNA was also apparent over some pyramidal and non-pyramidal cells in hippocampus and over putative cerebellar stellate/basket cells. KA1 mRNA was detected in the dentate gyrus but not reliably elsewhere. The expression profile and abundance of KA2 mRNA was similar to that of GluR6 mRNA. For all five transcripts, concurrent hybridization of rat brain sections produced the anticipated distribution of signal. The data indicate that the regional and cellular distribution of KA receptor subunit mRNAs in human hippocampus, neocortex and cerebellum largely parallels that in the corresponding areas of rat brain, albeit at lower levels, especially with regard to GluR5 and KA1 transcripts. In schizophrenia there is a partial loss of hippocampal non-NMDA receptors, but there are no data concerning KA receptor subunit expression. KA2 and GluR6 mRNAs were sufficiently abundant for a comparison in the left and right hippocampus between 11 schizophrenics and 13 controls. Using film autoradiography, both mRNAs were significantly reduced in the schizophrenics, having controlled for the effects of brain pH, post mortem interval and age. GluR6 mRNA was also quantitated in cerebellum, wherein no differences were found between cases and controls. In conjunction with earlier findings of reduced hippocampal GluR1 and GluR2 expression and a loss of [3H]KA binding sites, these data show that schizophrenia is associated with impaired expression of both AMPA- and KA-preferring ionotropic glutamate receptors. These deficits are likely to contribute to the glutamatergic component of the disease pathophysiology.

Kainic acid lesions enhance locomotor responses to novelty, saline, amphetamine, and MK-801

Intracerebroventricular (i.c.v.) administration of kainic acid (KA) to rats produces neuronal loss in the hippocampus and other areas of the limbic system. The present study demonstrates that i.c.v. KA enhances the locomotor response to novelty and saline injection, as well as to amphetamine and MK-801. Sixteen to 18 days after i.c.v. administration of KA or vehicle, lesioned and control rats were placed in a novel cage, and locomotor activity and grooming were recorded for 30 min prior to and 60 min following a subcutaneous injection of saline, D-amphetamine, or MK-801. In response to the novel cage and after each injection, KA rats exhibited increased locomotor activity relative to controls. Grooming behavior was found to be elevated in the KA rats when compared to controls, but only in response to the novel cage and saline injection. The possibility that damage to the limbic system disrupts dopaminergic regulation of locomotor behavior is discussed, as well as implications for neuropathology in schizophrenia.

Substantia innominata: a notion which impedes clinical-anatomical correlations in neuropsychiatric disorders

Comparative neuroanatomical investigations in primates and non-primates have helped disentangle the anatomy of the basal forebrain region known as the substantia innominata. The most striking aspect of this region is its subdivision into two major parts. This reflects the fundamental organizational scheme for this portion of the forebrain. According to this scheme, two major subcortical telencephalic structures, i.e. the striatopallidal complex and extended amygdala, form large diagonally oriented bands. The rostroventral extension of the pallidum accounts for a large part of the rostral subcommissural substantia innominata, while the sublenticular substantia innominata is primarily occupied by elements of the extended amygdala. Also dispersed across this region is the basal nucleus of Meynert, which is part of a more or less continuous collection of cholinergic and non-cholinergic corticopetal and thalamopetal cells, which stretches from the septum diagonal band rostrally to the caudal globus pallidus. The basal nucleus of Meynert is especially prominent in the primate, where it is sometimes inappropriately applied as a synonym for the substantia innominata, thereby tacitly ignoring the remaining components. In most mammals, the extended amygdala presents itself as a ring of neurons encircling the internal capsule and basal ganglia. The extended amygdala may be further subdivided, i.e. into the central extended amygdala (related to the central amygdaloid nucleus) and the medial extended amygdala (related to the medial amygdaloid nucleus), which generally form separate corridors both in the sublenticular region and along the supracapsular course of the stria terminalis. The extended amygdala is directly continuous with the caudomedial shell of the accumbens, and to some extent appears to merge with it. Together the accumbens shell and extended amygdala form an extensive forebrain continuum, which establishes specific neuronal circuits with the medial prefrontal-orbitofrontal cortex and medial temporal lobe. This continuum is particularly characterized by a prominent system of long intrinsic association fibers, and a variety of highly differentiated downstream projections to the hypothalamus and brainstem. The various components of the extended amygdala, together with the shell of the accumbens, are ideally structured to generate endocrine, autonomic and somatomotor aspects of emotional and motivational states. Behavioral observations support this proposition and demonstrate the relevance of these structures to a variety of functions, ranging from the various elements of the reproductive cycle to drug-seeking behavior. The neurochemical and connectional features common to the accumbens shell and the extended amygdala are especially relevant to understanding the etiology and treatment of neuropsychiatric disorders. This is discussed in general terms, and also in specific relation to the neurodevelopmental theory of schizophrenia and to the neurosurgical treatment of neuropsychiatric disorders.

GluR2 glutamate receptor subunit flip and flop isoforms are decreased in the hippocampal formation in schizophrenia: a reverse transcriptase-polymerase chain reaction (RT-PCR) study

GluR2 is the key subunit of heteromeric AMPA-preferring glutamate receptors. GluR2 mRNA has been shown by in situ hybridization histochemistry to be decreased in the hippocampal formation in schizophrenics. Here, a quantitative reverse transcriptase-polymerase chain reaction (RT-PCR) method was used to investigate GluR2 expression further and to examine the relative abundance of its alternatively spliced mRNA isoforms ('flip' and 'flop') in 11 schizophrenics and 11 matched controls. Compared to the controls, schizophrenics showed reduced expression of both isoforms relative to cyclophilin mRNA, but a greater loss of the flop isoform led to a higher flip:flop ratio. These differences were observed having controlled for the confounding effects of brain pH and age upon the mRNAs. We also found that the abundance of GluR2 mRNA correlates with that of the encoded subunit. This study has confirmed that, in schizophrenia, hippocampal GluR2 mRNA is reduced, and indicates that GluR2 subunits are composed of a higher proportion of the flip variant. These data extend the evidence for glutamatergic dysfunction in the disease. They suggest that signal transduction through hippocampal AMPA receptors is impaired in schizophrenia both by an overall loss of GluR2 expression, and by the change in flip:flop ratio which is predicted to alter the desensitization kinetics of the remaining GluR2 subunits.

Neonatal hippocampal lesions induced hyperresponsiveness to amphetamine: behavioral and in vivo microdialysis studies

The effect of neonatal hippocampal lesions on behavioral sensitivity to amphetamine (AMPH) and dopamine (DA) release in the nucleus accumbens (NAc) were examined. The ventral hippocampus was damaged bilaterally by ibotenic acid on postnatal day 7 (PD7). Spontaneous exploration and AMPH-stimulated locomotor activity were examined on postnatal day 35 (PD35) and day 56 (PD56). Extracellular DA, dihydroxyphenylacetic acid (DOPAC), homovanillic acid (HVA), and 5-hydroxyindoleacetic acid (5-HIAA) were sampled using in vivo microdialysis while simultaneously AMPH-stimulated locomotion was examined in freely moving rats on PD56. Spontaneous exploration increased in rats with hippocampal lesions relative to controls on PD56 but not PD35. AMPH (0, 0.187, 0.375, 0.75, 1.5, and 3 mg/kg) enhanced locomotion dose-dependently in both control and lesioned groups. Locomotor activity was higher in lesioned rats than controls following AMPH at the dose of 0.75 mg/kg on PD35 and at the doses of 1.5 and 3.0 mg/kg on PD56. The basal level of DA in the NAc was not different between the hippocampal and control groups. AMPH (1.5 mg/kg) induced hyperlocomotion in lesioned rats relative to controls. DA release in the NAc for both groups was enhanced following injections of AMPH. However, neonatal hippocampal lesions had no further enhancement on AMPH-stimulated release of DA as compared to the control group. The levels of DOPAC and HVA in the NAc were altered by AMPH but not lesions. The level of 5-HIAA was not influenced by either lesions or AMPH. The results of neonatal lesion-induced hyperlocomotion suggest that an emergence of behavioral hyperresponsiveness to AMPH was dependent on an interaction of lesions, age of examination, and dose of the drug. A dissociation between the effect of AMPH on lesion-enhanced hyperlocomotion and a lack of a lesion-enhanced DA release in the NAc suggest that presynaptic release of DA had no major contribution to lesion-enhanced DA transmission in the mesolimbic DA system.

Dopamine receptor gene expression in hippocampus is differentially regulated by the NMDA receptor antagonist MK-801

Glutamate agonists have been shown to stimulate the release of dopamine in the striatum, while the NMDA receptor antagonist MK-801 has been shown to cause an increase in extracellular dopamine in the hippocampus. The effects of MK-801 treatment on dopamine receptor gene expression in the hippocampus are largely unknown. To begin to address this question, we treated rats with 0.3, 1.0, and 3.0 mg/kg of MK-801 daily for 1 week, and measured the mRNAs encoding all five of the dopamine receptors in the hippocampus. MK-801 caused changes in dopamine D1, D2, D3, and D4 receptor gene expression in a complex manner that suggests that dopamine receptor gene expression in the hippocampus may be differentially regulated by glutamate, via the NMDA receptor. These findings may have implications both for understanding the pathophysiology and modifying treatment of schizophrenia.

Fetal brain development of twins assessed in utero by ultrasound: implications for schizophrenia

There is evidence that some forms of schizophrenia are due to alterations of in utero brain development. Given the concordance rate for schizophrenia in monozygotic twins is approx. 45%, it is not clear how a shared genetic predisposition for schizophrenia and a shared in utero environment might selectively lead to schizophrenia in one but not the other twin in a monozygotic twin pair. This study was undertaken to test the hypothesis that there is a difference in brain development between twins in a monozygotic twin pair that may contribute to the observed concordance rates for schizophrenia. Fetal ultrasound measures of brain (biparietal diameter, head circumference, ventricular width) and body size (femur length, abdominal circumference) obtained during the second trimester of fetal development were retrospectively analyzed in 41 monozygotic and 103 dizygotic twin pairs. In monozygotic twin pairs, there was a significant difference in measures of biparietal diameter, head circumference, and ventricular width, as well as in femur length and abdominal circumference, between twins. There was a similar difference in dizygotic twin pairs. These results indicate that in monozygotic twins, brain development is not identical. This difference in brain development may contribute to the observed concordance rates in monozygotic twins with schizophrenia.

Decreased expression of mRNAs encoding non-NMDA glutamate receptors GluR1 and GluR2 in medial temporal lobe neurons in schizophrenia

Schizophrenia is associated with a complex pattern of alterations in the glutamatergic system of the brain. Previous studies have shown a reduced density of some hippocampal non-N-methyl-D-aspartate (non-NMDA) receptors which is accompanied by a loss of encoding receptor mRNA. We have extended this work using in situ hybridization histochemistry with oligonucleotide probes specific for two non-NMDA receptor transcripts, GluR1 and GluR2, in right and left medial temporal lobe sections from 9 schizophrenics and 14 matched normal controls. Both mRNAs were found to be decreased bilaterally and to a similar degree in the hippocampal formation in schizophrenia. Analysis of autoradiograms showed a regional loss of GluR1 and GluR2 mRNAs in dentate gyrus, CA4, CA3 and subiculum. GluR2 mRNA was also reduced in parahippocampal gyrus. These reductions ranged from 25% to 70% in terms of 35S nCi/g tissue equivalents. Additionally we measured grain density for the mRNAs over individual pyramidal neurons in each area. GluR1 and GluR2 mRNAs were less abundant per neuron in CA4 and CA3 in schizophrenia than in controls. GluR2 mRNA was also reduced significantly in parahippocampal gyrus neurons, with an increase in the proportion of GluR1 mRNA to GluR2 mRNA in this cell population. No asymmetries in expression of GluR1 and GluR2 were found in normal or schizophrenic brains. These data further the evidence for reduced non-NMDA receptor expression in the medial temporal lobe in schizophrenia. They confirm the decrease in GluR1 mRNA and show that there are similar losses of GluR2 mRNA in the hippocampal formation. The pattern of changes in the two mRNAs suggests a common mechanism which is unknown but which may be a correlate of the neurodevelopmental abnormalities postulated to underlie the disease. The reduction of GluR2 mRNA but not GluR1 mRNA in parahippocampal gyrus neurons in schizophrenia may have functional consequences given the calcium permeability of non-NMDA receptors lacking the GluR2 subunit.

Disturbances in cell recognition molecules (N-CAM and L1 antigen) in the CSF of patients with schizophrenia

Although the pathogenesis of schizophrenia is unknown, there are data which indicate that the disease may be due to neurodevelopmental disturbances. Cell recognition molecules such as N-CAM and L1 antigen are involved in cell-cell interactions during development and in plasticity of the nervous system and could therefore be altered in relation to ongoing or established pathological processes. Using the Western blot technique, we found significant increases in N-CAM immunoreactive proteins and decreases in L1 antigen in the CSF of schizophrenic patients as compared to normal controls. The decrease in L1 antigen was observed in the 140-kDa band, and N-CAM was increased only in the 120-kDa band. The 120-kDa band of N-CAM and the 140-kDa band of L1 antigen were prominent components of CSF, but in serum these bands were minor or not detectable. Neuroleptic treatment did not significantly change either N-CAM or L1 antigen concentrations in CSF. It is possible that these CSF proteins are derived from CNS cells as secreted soluble N-CAM isoforms and L1 peptides. Our results suggest the possibility of a specific pattern of abnormal cellular function in the CNS in schizophrenia.

Lack of effect of antipsychotic and antidepressant drugs on glutamate receptor mRNA levels in rat brains

By employing multiprobe oligonucleotide solution hybridisation (MOSH) we have measured the levels of mRNA encoding the NMDA receptor subtypes (R1, R2A, R2B and R2C) and the non-NMDA glutamate receptor subtypes (GluR1, 2, 3, and 4) within rat brain following, 1-32 days of antipsychotic or antidepressant drug administration. The results suggest that the drugs studied do not significantly alter rat glutamatergic system mRNA levels when compared to controls.

Differential changes in glutamate receptor subunit messenger RNAs in rat brain after haloperidol treatment

Glutamate receptors are implicated in several neuropsychiatric disorders and in the actions of neuroleptic drugs used to treat them. To help clarify how these drugs impinge upon the glutamatergic system, we have studied the effects of 2 weeks' haloperidol (2 mg kg(-1) d(-1)) upon the distribution and abundance of glutamate receptor mRNAs in rat brain. The mRNAs detected were those encoding the glutamate-binding protein (GBP), the N-methyl D-aspartate (NMDA) receptor (NR1 subunit) and the flip and flop isoforms of α-amino-3-hydroxy- 5-methyl-4-isoxazolpropionate (AMPA)-preferring non-NMDA receptors gluR1 and gluR2. The mRNAs were studied using in situ hybridization histochemistry in dorsolateral striatum, nucleus accumbens, frontal cortex and hippocampus. Haloperidol led to an increase in GBP mRNA in striatum and frontal cortex but not in hippocampus. AMPA receptor mRNAs showed gene- and isoform-specific alterations in treated animals, with a significant increase in the proportion of gluR2 flip compared to gluR2 flop. The gluR1 flop:gluR2 flop ratio also increased. No differences were observed for NR1 mRNA in any area. Thus, subchronic administration of haloperidol has a molecularly and spatially specific effect upon expression of glutamate receptor-related transcripts. The data have several implications. Firstly, the enhanced expression of GBP mRNA may contribute to the alterations in other glutamatergic parameters observed after neuroleptics. Secondly, the pattern of changes for the NMDA and AMPA receptor mRNAs suggests that the alterations in density of these receptors and their mRNAs reported in schizophrenia are not an artefact of neuroleptic treatment. Finally, the specific increase in flip:flop mRNA ratio for gluR2, together with the increased proportion of gluR1 flop:gluR2 flop mRNA, is likely to affect the properties of the encoded AMPA receptors. Such changes may be relevant to the desired or undesired effects of these drugs.

Significant reductions in synapsin but not synaptophysin specific activity in the brains of some schizophrenics

The levels of the synaptic vesicle-associated proteins, synapsin and synaptophysin, were examined in human postmortem hippocampus from the brains of schizophrenics and age-matched controls using a quantitative western blot analysis. The schizophrenic samples had significantly lower levels of synapsin I than controls. In individual data, five of the seven schizophrenic samples had extremely low levels of synapsin, whereas two of the schizophrenic samples had normal levels of synapsin. This deficit in synapsin does not appear to be due to some non-specific neuronal loss as the levels of the other synaptic vesicle marker, synaptophysin, were near normal in all seven schizophrenics. Given that synapsin is thought to regulate neurotransmitter release, it is possible that this deficit in synapsin could result in abnormal processing of neuronal information as is seen in various sensory processing abnormalities associated with schizophrenia.

A case for changing the way schizophrenia is conceptualised, using a questionnaire to relatives

In view of dissatisfaction among philosophers and many doctors with the DSM III criteria for schizophrenia a new conceptualization is needed. Recent research results showing the complex influences on the development and functions of the brain suggest that the primary problem is a reduced capacity for information processing and not the more obvious symptoms of acute episodes. An analysis of a questionnaire to relatives (members of the National Schizophrenia Fellowship) has been used to illustrate how data from relatives can provide useful indicators of some of the factors such as possible metabolic abnormalities and immune system deficiencies which may contribute to this problem. It is suggested that a broad data-base is needed to study such contributory factors and point the way to forms of treatment which might make lower levels of maintenance neuroleptic medication possible.

Expression of alternatively-spliced glutamate receptors in human hippocampus

Rat glutamate receptors have been shown to be expressed as two developmentally regulated, alternatively spliced isoforms. We have investigated the expression of these isoforms of GluRA and GluRB in the human hippocampus. The expression pattern of the mRNAs coding for these subunits does not correspond to that in the rat hippocampus, both isoforms being preferentially expressed in the dentate gyrus and CA1 regions, with lower expression in CA3, with the exception of GluRB flop, where hybridization in CA3 is only lower than in dentate gyrus. Cloning of cDNA from human frontal cortex has also revealed that the two isoforms of human GluRB have virtual nucleotide sequence identity with the alternative exons in the rat, confirming the usefulness of oligonucleotides complementary to the rat cDNAs as probes for these receptor subunits in human neuropsychiatric disorders.

Genes, viruses and neurodevelopmental schizophrenia

Recent neuroimaging and neuropathological studies suggest a developmental origin for schizophrenia. Some cases may, therefore, be caused by a genetic defect in the specification of brain development. Early environmental hazards such as obstetric complications, and maternal exposure during pregnancy to influenza epidemics, have also been found to increase the risk of later schizophrenia. The relationship between the prevalence of influenza and birth date has been found more consistently for female than male schizophrenics. Female schizophrenia is also associated with a higher risk of schizophrenia in first degree relatives. This raises the question of whether part of the genetic predisposition to schizophrenia may comprise an abnormal reaction to maternal influenza.