Notes from the graveyard: neuropathology and schizophrenia

Basal-Forebrain Cholinergic Nuclei Alterations are Associated With Medication and Cognitive Deficits Across the Schizophrenia Spectrum

BACKGROUND AND HYPOTHESIS

The cholinergic system is altered in schizophrenia. Particularly, patients' volumes of basal-forebrain cholinergic nuclei (BFCN) are lower and correlated with attentional deficits. It is unclear, however, if and how BFCN changes and their link to cognitive symptoms extend across the schizophrenia spectrum, including individuals with at-risk mental state for psychosis (ARMS) or during first psychotic episode (FEP).

STUDY DESIGN

To address this question, we assessed voxel-based morphometry (VBM) of structural magnetic resonance imaging data of anterior and posterior BFCN subclusters as well as symptom ratings, including cognitive, positive, and negative symptoms, in a large multi-site dataset (n = 4) comprising 68 ARMS subjects, 98 FEP patients (27 unmedicated and 71 medicated), 140 patients with established schizophrenia (SCZ; medicated), and 169 healthy controls.

RESULTS

In SCZ, we found lower VBM measures for the anterior BFCN, which were associated with the anticholinergic burden of medication and correlated with patients' cognitive deficits. In contrast, we found larger VBM measures for the posterior BFCN in FEP, which were driven by unmedicated patients and correlated at-trend with cognitive deficits. We found no BFCN changes in ARMS. Altered VBM measures were not correlated with positive or negative symptoms.

CONCLUSIONS

Results demonstrate complex (posterior vs. anterior BFCN) and non-linear (larger vs. lower VBM) differences in BFCN across the schizophrenia spectrum, which are specifically associated both with medication, including its anticholinergic burden, and cognitive symptoms. Data suggest an altered trajectory of BFCN integrity in schizophrenia, influenced by medication and relevant for cognitive symptoms.

Hippocampal Pathophysiology: Commonality Shared by Temporal Lobe Epilepsy and Psychiatric Disorders

Accumulating evidence points to the association of epilepsy, particularly, temporal lobe epilepsy (TLE), with psychiatric disorders, such as schizophrenia. Among these illnesses, the hippocampus is considered the regional focal point of the brain, playing an important role in cognition, psychosis, and seizure activity and potentially suggesting common etiologies and pathophysiology of TLE and schizophrenia. In the present review, we overview abnormal network connectivity between the dentate gyrus (DG) and the Cornus Ammonis area 3 (CA3) subregions of the hippocampus relative to the induction of epilepsy and schizophrenia. In light of our recent finding on the misguidance of hippocampal mossy fiber projection in the rodent model of schizophrenia, we discuss whether ectopic mossy fiber projection is a commonality in order to evoke TLE as well as symptoms related to schizophrenia.

Neuroplasticity and the brain connectome: what can Jean Talairach’s reflections bring to modern psychosurgery?

Contrary to common psychosurgical practice in the 1950s, Dr. Jean Talairach had the intuition, based on clinical experience, that the brain connectome and neuroplasticity had a role to play in psychosurgery. Due to the remarkable progress of pharmacology at that time and to the technical limits of neurosurgery, these concepts were not put into practice. Currently, these concepts are being confirmed by modern techniques such as neuroimaging and computational neurosciences, and could pave the way for therapeutic innovation in psychiatry.

Psychosurgery commonly uses a localizationist approach, based on the idea that a lesion to a specific area is responsible for a deficit opposite to its function. To psychosurgeons such as Walter Freeman, who performed extensive lesions causing apparently inevitable deficit, Talairach answered with clinical data: complex psychic functions cannot be described that simply, because the same lesion does not provoke the same deficit in different patients. Moreover, cognitive impairment did not always follow efficacious psychosurgery. Talairach suggested that selectively destructing part of a network could open the door to a new organization, and that early psychotherapy could encourage this psychoplasticity. Talairach did not have the opportunity to put these concepts into practice in psychiatric diseases because of the sudden availability of neuroleptics, but connectomics and neuroplasticity gave rise to major advances in intraparenchymal neurosurgery, from epilepsy to low-grade glioma. In psychiatry, alongside long-standing theories implicating focal lesions and diffuse pathological processes, neuroimaging techniques are currently being developed. In mentally healthy individuals, combining diffusion tensor imaging with functional MRI, magnetoencephalography, and electroencephalography allows the determination of a comprehensive map of neural connections in the brain on many spatial scales, the so-called connectome. Ultimately, global neurocomputational models could predict physiological activity, behavior, and subjective feeling, and describe neuropsychiatric disorders.

Connectomic studies comparing psychiatric patients with controls have already confirmed the early intuitions of Talairach. As a striking example, massive dysconnectivity has been found in schizophrenia, leading some authors to propose a “dysconnection hypothesis.” Alterations of the connectome have also been demonstrated in obsessive-compulsive disorder and depression. Furthermore, normalization of the functional dysconnectivity has been observed following clinical improvement in several therapeutic interventions, from psychotherapy to pharmacological treatments. Provided that mental disorders result from abnormal structural or functional wiring, targeted psychosurgery would require that one be able: 1) to identify the pathological network involved in a given patient; 2) to use neurostimulation to safely create a reversible and durable alteration, mimicking a lesion, in a network compatible with neuroplasticity; and 3) to predict which functional lesion would result in adapted neuronal plasticity and/or to guide neuronal plasticity to promote recovery. All these conditions, already suggested by Talairach, could now be achievable considering modern biomarkers and surgical progress.

Immune involvement in the pathogenesis of schizophrenia: a meta-analysis on postmortem brain studies

Although the precise pathogenesis of schizophrenia is unknown, genetic, biomarker and imaging studies suggest involvement of the immune system. In this study, we performed a systematic review and meta-analysis of studies investigating factors related to the immune system in postmortem brains of schizophrenia patients and healthy controls. Forty-one studies were included, reporting on 783 patients and 762 controls. We divided these studies into those investigating histological alterations of cellular composition and those assessing molecular parameters; meta-analyses were performed on both categories. Our pooled estimate on cellular level showed a significant increase in the density of microglia (P=0.0028) in the brains of schizophrenia patients compared with controls, albeit with substantial heterogeneity between studies. Meta-regression on brain regions demonstrated this increase was most consistently observed in the temporal cortex. Densities of macroglia (astrocytes and oligodendrocytes) did not differ significantly between schizophrenia patients and healthy controls. The results of postmortem histology are paralleled on the molecular level, where we observed an overall increase in expression of proinflammatory genes on transcript and protein level (P=0.0052) in patients, while anti-inflammatory gene expression levels were not different between schizophrenia and controls. The results of this meta-analysis strengthen the hypothesis that components of the immune system are involved in the pathogenesis of schizophrenia.

What are the similarities and differences between schizophrenia and schizophrenia-like psychosis of epilepsy? A neuropathological approach to the understanding of schizophrenia spectrum and epilepsy

Temporal lobe epilepsy (TLE) and psychosis coexist more frequently than chance would predict. In this short review, clinical and neuropathological findings of schizophrenia, TLE, and psychosis of epilepsy are described to enhance our understanding of the noncoincidental association between these conditions. In addition, psychosis of epilepsy was included for the first time in the Diagnostic and Statistical Manual of Mental Disorders (DSM), in the recently launched 5th edition, and improvement in diagnostic criteria was highlighted. Since the hippocampus has long been considered an anatomical area involved in the pathophysiology of TLE and schizophrenia, neuropathological studies of psychoses of epilepsy may contribute to our understanding of the pathophysiology of psychosis in general. The discovery of shared mechanisms and/or affected neurochemicals in TLE and schizophrenia might disclose important clues on the vulnerability of patients with TLE to psychotic symptoms and be an opportunity for new treatment development.

Differential aberrant sprouting in temporal lobe epilepsy with psychiatric co-morbidities

Psychiatric co-morbidities in epilepsy are common in patients with temporal lobe epilepsy (TLE). Pathological alterations in TLE are well characterised; however, neuropathologic data are relatively scale regarding the association between psychiatric diseases and epilepsy. Our objective was to evaluate the clinical data of 46 adult TLE patients with and without psychiatric co-morbidities and to correlate the data with hippocampal neuronal density and mossy fiber sprouting. Accordingly, patients were grouped as follows: TLE patients without history of psychiatric disorder (TLE, n=16), TLE patients with interictal psychosis (TLE+P, n=14), and TLE patients with major depression (TLE+D, n=16). Hippocampi from autopsies served as non-epileptic controls (n=10). TLE+P exhibited significantly diminished mossy fiber sprouting and decreased neuronal density in the entorhinal cortex when compared with TLE. TLE+P showed significantly poorer results in verbal memory tasks. TLE+D exhibited significantly increased mossy fiber sprouting length when compared with TLE and TLE+P. Further, a higher proportion of TLE+D and TLE+P presented secondarily generalised seizures than did TLE. Our results indicate that TLE patients with psychiatric disorders have distinct features when compared with TLE patients without psychiatric co-morbidities and that these changes may be involved in either the manifestation or the maintenance of psychiatric co-morbidities in epilepsy.

Cortical development and neuropathology in schizophrenia

Epidemiological studies suggest that perturbations occurring during pregnancy can increase the incidence of schizophrenia among offspring. Examination of the neuropathology of the brains of some schizophrenics suggests that a defect in the later phases of cerebral cortical development, notably the last phases of neuronal migration and the establishment and refinement of patterns of cortical connections, may be involved. Most of these studies are conjectural, and the relationship between primary lesions and potential secondary retrograde and anterograde effects in the circuitry linking the prefrontal cortex, basal forebrain, mediodorsal thalamus and medial temporal cortex is unknown. Our hypothesis, based on neuromorphological and gene expression studies, is that a disturbance of migration or in the pattern of preprogrammed cell death in the subplate zone of the developing cerebral cortex causes a failure to establish normal patterns of connections in the overlying cortex. This compromised circuitry subsequently decompensates, leading to schizophrenic symptoms and activity-dependent manifestations of altered gene expression for neurotransmitter- and receptor-related molecules.

Schizophrenia seen as a deficit in the modulation of cortical minicolumns by monoaminergic systems

The highly evolved architecture of the cerebral cortex is organized across hierarchical levels that maximize functional repertoires (emergent properties) and expedite information processing. Minicolumns are nested within this multiscale architecture as the smallest module capable of processing information. Signals are transmitted within minicolumns through massive ion-gated connections and modulated through slower onset second messenger systems. The terminal zones of the modulatory second messenger systems comprise the laminae of the cortex. A comprehensive review of the literature suggests that schizophrenia results from widely distributed changes at the level of the cerebral cortex and little, if any, neuronal somatic changes: (Esiri & Crow, 2002). Concordant with this observation recent studies indicate that schizophrenic patients have an alteration of neuronal connectivity according to both lamina and brain region examined. One possible explanation for this deficit is an alteration in the modulatory system of cortical minicolumns. This ontogenetic deficit propitiates a cascade of neurochemical changes resulting in varying abnormalities relating information processing to behavioural states.

Variations in differential gene expression patterns across multiple brain regions in schizophrenia

Large-scale gene expression studies in schizophrenia (SZ) have generally focused on the dorsolateral prefrontal cortex. Despite a wealth of evidence implicating multiple other brain regions in the disease, studies of other brain regions have been less frequent and have rarely been performed in the same subjects. We analyzed postmortem gene expression in the frontal, cingulate, temporal, parietal and occipital cortices (Brodmann areas 8, 10, 44, 46, 23/31, 24/32, 20, 21, 22, 36/28, 7 and 17, respectively) as well as in the hippocampus, caudate nucleus and putamen of persons with schizophrenia and control subjects (N's = 13) using Affymetrix GeneChip microarrays. Under identical data filtering conditions, the superior temporal cortex (BA22) of schizophrenia subjects showed the maximal number of altered transcripts (approximately 1200) compared to controls. Anterior and posterior cingulate cortices (BA23/31, 24/32) and the hippocampus followed the superior temporal cortex with two-times lower numbers of altered transcripts. The dorsolateral prefrontal cortex (BA46), a frequent target of SZ-associated studies, showed substantially fewer altered transcripts (approximately 33). These regional differences in differentially expressed genes could not be accounted for by factors such as total numbers of genes expressed or the filtering conditions and criteria used for identification of differentially expressed genes. These findings suggest that the temporal and cingulate cortices and the hippocampal formation represent brain regions of particular abnormality in SZ and may be more susceptible to the disease process(es) than other regions thus far studied.

Gene expression of metabotropic glutamate receptor 5 and excitatory amino acid transporter 2 in the schizophrenic hippocampus

A disturbance in glutamatergic transmission has been suggested to contribute to the pathophysiology of schizophrenia and recent studies on ionotropic glutamate receptors are consistent with altered glutamatergic function in the hippocampus of schizophrenics. In order to investigate this hypothesis further, the expression of two 'glutamatergic' markers, the mRNAs of metabotropic glutamate receptor 5 (mGluR5) and human excitatory amino acid transporter (EAAT2) were compared in the hippocampus of control subjects and schizophrenics. We examined the regional/cellular mRNA expression of mGluR5 and EAAT2 in postmortem hippocampal sections from schizophrenics and control subjects, using in situ hybridization. Regions of interests were dentate gyrus, cornu ammonis 4, 3, 1 and parahippocampal gyrus. The regional/cellular mGluR5 mRNA content was not different between the two groups. The cellular EAAT2 mRNA content was significantly decreased in schizophrenic parahippocampal gyrus, but not in other hippocampal regions. Furthermore, only in the parahippocampal gyrus, schizophrenics had a significantly increased mGluR5/EAAT2 ratio at both the regional and cellular mRNA level. The results suggest that a disturbance of glutamatergic neurotransmission in schizophrenia was not apparent using these indices in the hippocampus, but 'hypo-glutamatergic' neurotransmission may be present in the schizophrenic parahippocampal gyrus.

Subnucleus-specific loss of neurons in medial thalamus of schizophrenics

The hypoactivity of dorsolateral prefrontal cortex in schizophrenics is well known. One cause of this hypoactivity may be defective corticocortical or thalamocortical connections. Recent imaging studies of the thalamus suggest reductions in volume of the whole thalamus and reduced activity in the medial group of thalamic nuclei, which may indicate loss of functional input to the cortex. Using stereological techniques in six pairs of individually matched brains from schizophrenics and controls, we measured the volumes and obtained estimates of the number of neurons in the three subnuclei (parvocellular, pc; densocellular, dc; magnocellular, mc) of the mediodorsal nucleus (MD) and from the ventral posterior medial nucleus. There was a significant reduction in total neuron number in MD as a whole but this neuron loss was largely restricted to MDpc and MDdc [-30.9 and -24.5%, respectively (P </= 0.01)]. MDmc and the control ventral posterior medial nucleus showed no significant changes in cell number. Because the subnuclei of MD have different connections and project to different areas of the frontal cortex, the specific loss of neurons in MDpc and MDdc has implications for the functional defects observed in schizophrenia.

Underconstrained perception: a theoretical approach to the nature and function of verbal hallucinations

We do not see the world as it is. Perception forms a subjective image of the world in a language that has proven to be adaptive to our interaction with the external world. Perception is mainly determined by current needs of the organism and goals of behavior. Sensory processing itself does not culminate in perception and is not essential for perception, since perception derives from representations of internal symbols and their features. The current stimulation of sensory organs does, however, constrain our perception. Perception might be less constrained by the external world in cases of (1) increased attention, (2) decreased sensory stimulation, or (3) facilitated formation of cortical associations between representations of expectations and internal symbols. Hallucinations are perceptions that are underconstrained by external sensory stimulation. Verbal hallucinations that allow the patient to infer about his self-image might constitute the core psychopathology in a subset of schizophrenia. Commenting and discussing voices might be perceived under the pressure of increased attention to environmental factors that relate to the patient's social fears and wishes. Secondarily, delusions about the possession of thoughts and disorders of self-experience may develop.

Ventricular dilation over several weeks following induction of excitotoxic (systemic lithium/pilocarpine) lesions: potential role of damage to the substantia nigra reticulata

Time-dependent atrophy of cerebral space and enlargement of the lateral ventricles were noted in healthy rats 1 to 100 days after the induction of seizures by a single systemic injection of lithium and pilocarpine. The rate of atrophy was most strongly correlated (0.90) with the log (base 10) of the time in days. Most of the degeneration had occurred within about 20 to 30 days after the seizure-induced brain trauma. Concomitant reduction in the area of the substantia nigra reticulata was the most powerful predictor of ventricular enlargement at the level of the caudate-putamen.

The human striatum in schizophrenia. I. Increase in overall relative striatal volume in schizophrenics

Postmortem volumetry of the human striatum and its subdivisions (putamen, n.caudatus, n.accumbens) was performed on serial coronal sections of complete hemispheres. Both hemispheres of 9 male schizophrenic patients younger than 65 years were closely matched in age with the hemispheres of 9 male control individuals. All obtained values were corrected with individual and region-specific shrinkage factors; the intrarater reliability was 1% difference in volume. The absolute striatal volume was significantly correlated with the volume of the hemisphere (r = 0.931; P = 0.0003***). Reflecting differences in the hemispheric volumes of the schizophrenic and the control group, the absolute striatal volume consequently did not differ between both groups (P > 0.55). However, we found a clear increase in the volume density (i.e. the relative striatal portion of the hemisphere; the relative striatal volume) in the schizophrenic group, highly significant on both sides (P = 0.003** for the right striatum, P = 0.002** for the left striatum). The increase in volume density concerned both the putamen (P = 0.003** for the right side) and the n.caudatus/n.accumbens (P = 0.01* for the right side). Discrepant volumetric results of previous authors who compared only absolute volume values in samples not matched for identical hemispheric volume could thus be explained by this high positive correlation with the hemispheric volume. Since exact matching for identical hemispheric volume is not feasible and examined groups will never be large enough to rule out the influence of the hemispheric volume, the determination of relative volumes (i.e. volume densities) seems to be advantageous for future volumetric studies.

Could schizophrenia be reasonably explained by Dohan's hypothesis on genetic interaction with a dietary peptide overload?

1. Dohan has proposed that schizophrenia is a genetic disposition which interacts with an overload of dietary proteins such as casein and gluten or gliadin. 2. A systematic attempt is made to see if this hypothesis is possible faced with aspects of schizophrenia that must be accounted for. 3. The authors conclusion is that it is possible, but more serious work in this field is urgently needed.

Electroencephalography in schizophrenic patients: comparison between neuroleptic-naive state and after treatment

Electroencephalography of 12 schizophrenic patients was recorded in a neuroleptic-naive state and after 6.2 +/- 1.1 months of treatment, when they were on medication and in partial remission. Compared with age- and sex-matched controls, the neuroleptic-naive schizophrenics had less alpha 2 power. In the medicated state, alpha 2 power and slow-wave power were reduced as compared with the neuroleptic-naive state. The reduction in alpha 2 power may occur from the early stage of the disease and progress even though the patients are medicated and clinically improved.

Neonatal insult to the hippocampal region and schizophrenia: a review and a putative animal model

OBJECTIVE

To review the mounting evidence implicating early hippocampal dysfunction in the pathogenesis and the pathophysiology of schizophrenia. An account is made of recent neurodevelopmental hypotheses indicating how an early dysfunction of the hippocampal region disrupts maturational events in brain systems connected to that structure, thus inducing dysfunctional connectional development. Finally, an animal model is presented.

METHOD

Socioemotional behaviour of monkeys (Macaca mulatta) with selective neonatal hippocampal lesions was assessed by analyzing their interactions with their age-matched controls at 2 months, 6 months, and 5 to 8 years of age and by comparing the social interactions at each age with those of normal controls paired together.

RESULTS

At 2 months of age, monkeys with neonatal hippocampal lesions presented minor disturbances in initiation of social interactions. These subtle changes of behaviour were less evident at 6 months, although by that age, the operated monkeys displayed more withdrawals in response to an increase in aggressive responses from their unoperated peers. In adulthood, the amount of time spent by the hippocampectomized monkeys in social contacts with their normal peers decreased markedly. In addition, operated monkeys exhibited more locomotor stereotypies than normal controls.

CONCLUSION

These experimental findings indicate that the time-course and nature of the behavioural disturbances resulting from early trauma to the hippocampal region have some similarities with the clinical symptoms of schizophrenic patients and the typical time-course of the disease.

Neurophysiology of converging synaptic inputs from the rat prefrontal cortex, amygdala, midline thalamus, and hippocampal formation onto single neurons of the caudate/putamen and nucleus accumbens

Neurophysiological responses mediated by projections from five telencephalic and diencephalic regions (the infra- and prelimbic portions of the prefrontal cortex, amygdala, midline and intralaminar thalamic nuclei, entorhinal cortex and subiculum/CA1) to the caudate/putamen (CPu) and nucleus accumbens (Acb) of the dorsal and ventral striatum were studied in chloral-hydrate-anesthetized rats. Both extra- and intracellular in vivo recording techniques were used. A retrograde tracer (wheatgerm agglutinin-apo-horseradish peroxidase-5 nm colloidal Gold) was deposited in some animals in the vicinity of recording sites to confirm that stimulating electrodes were located near cells that projected to the striatum. Electrical stimulation of these five regions, respectively, evoked excitatory responses in 60%, 22%, 51%, 25%, and 17% of striatal neurons. Some responses, particularly with thalamic stimulation, showed short-term frequency potentiation in which 5/s stimulation increased the probability of spike firing. About half of responsive cells showed convergent excitation to more than one stimulating site. It was possible with convergent excitatory responses to show synaptic interactions: simultaneous activation of more than one site produced spatial and temporal summation to increase the probability of spike firing. Up to 5-way convergence onto single striatal neurons and up to 3-way interactions could be shown. These results indicate that functional influences from the hippocampal formation can converge with other excitatory input onto single striatal neurons to effect synaptic integration.

Neuropsychological principia brevita: an application to traumatic (acquired) brain injury

The concepts and discoveries of modern neuroscience now challenge many of the presumptions that influence diagnostic decisions within neurology, psychiatry, and clinical neuropsychology. Many of these presumptions are derived from archaic bivariate models such as the mind-body argument, organic-functional dichotomy, and single lesion-single behaviour causality. Thirteen basic principles which may be useful for inferring more reliable and accurate relationships between microstructural function an clinical manifestations are developed.

Hippocampal synaptic plasticity as a biological substrate underlying episodic psychosis

Structural change in the hippocampal formation has become popular as a proposed neurobiological substrate for schizophrenic disorders. It is postulated that behavioral plasticity in the form of long-term potentiation of hippocampal synaptic transmission is an attractive putative mechanism for the mediation of transient psychosis. Moreover, the disturbed hippocampal neuroarchitecture found in schizophrenic brain may be susceptible to potentiation and dysfunctional to the degree that delusions and hallucinations develop. Partial and selective blockade of the receptors mediating potentiation may prove to be an efficient means of preventing psychotic episodes and avoiding further damage to the involved network. Basic research, utilizing experimental models such as intraventricular kainic acid injection, may help to clarify the anatomical and physiological substrate of psychosis.

Neurophysiology and neuropharmacology of projections from entorhinal cortex to striatum in the rat

We studied projections from the entorhinal cortex (Ent) to the striatum in anesthetized rats using extra- and intracellular recording and multibarrel iontophoresis. The majority of recording were from the caudate-putamen (CPu) and core of the nucleus accumbens (AcbC). Electrical stimulation of the Ent evoked synaptic responses in 77% of tests with AcbC neurons and 48% of tests with CPu neurons. In the case of AcbC neurons, 61% of these tests proved to be excitatory and were often followed by inhibitory phases. In contrast to this, only 18% of tests from CPu neurons were excitatory. Intracellular HRP labeling showed that responsive cells were medium spiny neurons. During iontophoretic experiments, application of the glutamatergic AMPA antagonist DNQX could selectively decrease or block excitatory responses. The GABAA antagonist bicuculline methiodide increased cellular firing rates and could reveal excitatory responses, suggesting block of a short-latency, short-duration inhibitory component. Ejection of the GABAB antagonist CGP-35348 could attenuate a later, longer-duration component of inhibition. The results indicate that the Ent excites striatal neurons at least in part by glutamatergic receptors and suggest that this excitation is followed by secondary prolonged GABAergic inhibition.

Increased prevalence of antibrain antibodies in the sera from schizophrenic patients

The pathogenesis of schizophrenia is still unknown. In a previous study we found antibrain antibodies in the sera of schizophrenic patients, but not in normal controls. Therefore we have further examined the sera of schizophrenic patients versus normal controls, increasing the number of brain areas, to explore whether certain areas were involved more often than others in the antibody binding process. The sera of 50 patients suffering from an acute episode of schizophrenia (classified by DSM III-criteria) were tested. 70% of the patients showed antibody binding, while only 12% of the age- and sex-matched controls were positive. The binding was mediated by IgG- as well as IgM-antibodies. Amygdala, frontal cortex, cingulate gyrus, and septal area were the prominent targets, while hippocampus, parahippocampal gyrus, entorhinal cortex, putamen, mamillary bodies and head of the caudate nucleus were involved to a lesser degree. Binding was not present to nucleus olivaris, to the thyroid gland or to HEp-2 cells, which we included to test for unspecific antinuclear factors. Longterm studies of schizophrenic patients and biochemical analyses of the antigen(s) involved are in progress.

Regional neuropathology in schizophrenia: where are we? Where are we going?

This paper presents a neurologic formulation for the clinical features of the schizophrenic syndrome, and tests it against a systematic, region by region review of available postmortem neuroanatomical and neuropharmacological data. Based on this review a model is proposed that postulates a developmental lesion affecting the midline neurotransmitter-specific ascending projection systems. Due to the facilitatory role these systems play in the development of the brain regions to which they project, such a lesion is one parsimonious, and testable, explanation for virtually all the clinical, laboratory, and pathological findings reported to date in schizophrenia research. A case is made for establishing a global antemortem-postmortem collaboration using a Latin square design; the alternative may be that, as has happened in the past, the best efforts of dilligent researchers around the world may lead to little improvement in our understanding of schizophrenia.

Cortical regulation of subcortical dopamine systems and its possible relevance to schizophrenia

A unique model of DA system regulation is presented, in which tonic steady-state DA levels in the ECF act to down-regulate the response of the system to pulsatile DA released by DA cell action potential generation. This type of regulation is similar in many respects to the phenomenon proposed to mediate the action of norepinephrine on target neurons; i.e., an increase in the "signal-to-noise" ratio as measured by postsynaptic cell firing (Freedman et al., 1977; Woodward et al., 1979). However, in this model the signal and the noise are neurochemical rather than electrophysiological. Furthermore, the "noise" (tonic DA in the ECF) actually down-regulates the "signal" (phasic DA release) directly, and thereby provides a "signal" of its own that affects the system over a longer time-course. Therefore, the difference between signal and noise may also depend on the time frame under which such determinations are made.

The depolarization block hypothesis of neuroleptic action: implications for the etiology and treatment of schizophrenia

Antipsychotic drugs are known to block dopamine receptors soon after their administration, resulting in an increase in dopamine neuron firing and dopamine turnover. Nonetheless, antipsychotic drugs must be administered repeatedly to schizophrenics before therapeutic benefits are produced. Recordings from dopamine neurons in rats have revealed that chronic antipsychotic drug treatment results in the time-dependent inactivation of dopamine neuron firing via over-excitation, or depolarization block. Furthermore, the clinical profile of the response to antipsychotic drugs appears to correspond to the dopamine system affected: antipsychotic drugs that exert therapeutic actions in schizophrenics inactivate dopamine neuron firing in the limbic-related ventral tegmental area, whereas drugs that precipitate extrapyramidal side effects cause depolarization block of the motor-related substantia nigra dopamine cells. One factor that remains unresolved with regard to the actions of antipsychotic drugs is the relationship between dopamine turnover and depolarization block--i.e., why does a significant level of dopamine release or turnover remain after antipsychotic drug treatment if dopamine cells are no longer firing? We addressed this question using an acute model of neuroleptic-induced depolarization block. In this model, dopamine cells recorded in rats one month after partial dopamine lesions could be driven into depolarization block by the acute administration of moderate doses of haloperidol. However, similar doses of haloperidol, which were effective at increasing dopamine levels in the striatum of intact rats, failed to change dopamine levels in lesioned rats. This is consistent with a model in which neuroleptic drugs exert their therapeutic effects in schizophrenics by causing depolarization block in DA cells, thereby preventing further activation of dopamine neuron firing in response to external stimuli. Thus, attenuating the responsivity of the dopamine system to stimuli may be more relevant to the therapeutic actions of antipsychotic drugs than receptor blockade or decreases in absolute levels of dopamine, which could presumably be circumvented by homeostatic adaptations in this highly plastic system.

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

Neuropathological, neuroimaging, clinical and epidemiological evidence suggests that many cases of schizophrenia are developmental in origin. Dysplastic changes in the medial temporal lobes appear to be of particular importance. However, research implicating a neurodevelopmental origin for schizophrenia has proceeded largely in isolation from knowledge concerning the neurochemistry of the disorder. This paper attempts to integrate these disparate lines of research, and examines the role of trophic mechanisms in the formation of the hippocampus. Those neurotransmitters which have been most consistently found to be abnormal in the temporal lobes of schizophrenics (excitatory amino acids and CCK), are involved in the control of hippocampal development. We suggest that these neurotransmitter findings are the residue of abnormalities in their role as trophic factors in foetal or neonatal life, and that the latter contribute to the developmental aberrations considered fundamental to schizophrenia.

Distribution of CCK binding sites in the human hippocampal formation and their alteration in schizophrenia: a post-mortem autoradiographic study

The distribution of cholecystokinin binding sites has been visualized and quantified by quantitative autoradiography in the human hippocampus from post-mortem brains of 11 controls and 11 schizophrenics. CCK receptors were localized to subiculum and parahippocampal gyrus. In the cortical areas there was a particularly dense lamination of receptors. In the schizophrenic material a similar overall pattern was seen, but there were significant losses of receptors in CA1 subiculum and cortex. These findings confirm the distribution of CCK receptors in the retrohippocampal areas in man and also provide further support for earlier homogenate studies which have also shown a loss of CCK binding sites in schizophrenia. This effect was localized primarily to parahippocampal gyrus suggesting that CCK plays some role in the genesis of developmental abnormalities in this region.

Merck, Sharp & Dohme Prize for Young Psychopharmacologists: A history of frontal and temporal lobe aspects of the neuropharmacology of schizophrenia

In the past two decades neurobiological research into schizophrenia has seen a shift of emphasis from the dopaminergic pharmacology of subcortical systems to areas of abnormality inferred from direct studies, i.e. frontal cortex and medial temporal lobe. Recent research has tried to integrate morphological abnormalities with neurochemical and pharmacological data. These integrated approaches have uncovered neurochemical systems other than dopamine which are of importance. This approach has led to greater understanding of neurochemical mechanisms associated with these abnormalities and may provide novel approaches for therapeutic intervention.

Partial hippocampal pyramidal cell loss alters behavior in rats: implications for an animal model of schizophrenia

A putative biological substrate of schizophrenia involves cellular pathology within the hippocampus. While hippocampal dysfunction is associated with impaired learning and memory, schizophrenics have been observed to acquire simple conditioned reflexes at rates superior to controls. The present study evaluates the acquisition of shuttlebox avoidance responses in animals with partial damage to hippocampus. Intraventricular microinjections of kainic acid (0.5 or 1.5 nM) were utilized to partially destroy the pyramidal cell population. Animals in the high dosage group acquired the response at rates superior to controls; the low dosage group performed at an intermediate level. Consequently, partial loss of pyramidal neurons may be sufficient to significantly alter simple acquisition. Results are discussed in reference to the "embryological hypothesis" of schizophrenia and mechanisms for induction of schizophrenic behavior in intractable seizure disorders are considered.

G proteins (Gi, Go) in the medial temporal lobe in schizophrenia: preliminary report of a neurochemical correlate of structural change

We have measured the amount of Gi (the inhibitory G-protein) or Go (a similar G-protein of unknown function) in 5 areas of the medial temporal lobe of control and schizophrenic brains utilizing pertussis toxin-catalyzed ADP ribosylation. The material used has previously been shown to have asymmetrical structural abnormalities of the ventricular system. The amount of Gi or Go was reduced on the left side in the hippocampus, amygdala and parahippocampal gyrus, the difference reaching significance in the hippocampus. This data is the first report of a neurochemical correlate of the structural change in the brains of patients with schizophrenia. Decreased Gi or Go in hippocampus may relate to other reported neurochemical deficits or other transmembrane signalling abnormalities. Further investigations of these indices of secondary messenger function in relation to structural changes are indicated.

Phasic versus tonic dopamine release and the modulation of dopamine system responsivity: a hypothesis for the etiology of schizophrenia

A novel mechanism for regulating dopamine activity in subcortical sites and its possible relevance to schizophrenia is proposed. This hypothesis is based on the regulation of dopamine release into subcortical regions occurring via two independent mechanisms: (1) transient or phasic dopamine release caused by dopamine neuron firing, and (2) sustained, "background" tonic dopamine release regulated by prefrontal cortical afferents. Behaviorally relevant stimuli are proposed to cause short-term activation of dopamine cell firing to trigger the phasic component of dopamine release. In contrast, tonic dopamine release is proposed to regulate the intensity of the phasic dopamine response through its effect on extracellular dopamine levels. In this way, tonic dopamine release would set the background level of dopamine receptor stimulation (both autoreceptor and postsynaptic) and, through homeostatic mechanisms, the responsivity of the system to dopamine in these sites. In schizophrenics, a prolonged decrease in prefrontal cortical activity is proposed to reduce tonic dopamine release. Over time, this would elicit homeostatic compensations that would increase overall dopamine responsivity and thereby cause subsequent phasic dopamine release to elicit abnormally large responses.

Schizophrenia: a neuropathological perspective

It is probable that all schizophrenics have abnormalities in the medial temporal lobe, which differ in degree but not in kind. The structures of the medial temporal lobe are believed to have a crucial role in the integration and processing of the output from the association cortex. Dysfunction of this system could result in the clinical symptoms that form the core of the schizophrenia syndrome. The structural differences appear to fit the profile of a disturbance in the normal pattern of brain development. The asymmetrical patterns of normal brain development explain how such a disturbance simultaneously affecting both hemispheres could, disproportionately, affect the left (dominant) hemisphere. Epidemiological and pathological evidence points to aberrant genetic mechanisms as being the cause of the developmental anomaly in the majority of cases; environmental factors probably play a minor role. Despite the great progress made in solving the enigma of the structural changes in the brains of schizophrenics, the cause(s) of the changes--the aberrant genetic mechanism controlling brain development--may prove difficult to define.

Astrocytosis in the molecular layer of the dentate gyrus: a study in Alzheimer's disease and schizophrenia

Recently, several authors have claimed prominent abnormalities in the entorhinal cortex of both patients with Alzheimer's disease (AD) and schizophrenia. The entorhinal cortex is the origin of the perforant pathway, a major input to granule cells of the dentate gyrus of the hippocampus. The present study explored the possibility of a lesion in the entorhinal cortex of both AD and schizophrenic patients by quantitating astrocytic markers within the terminal fields of the perforant pathway. An increase in fibrillary astrocytes was found in half (3/6) of the AD patients while none of the schizophrenic (n = 6) or control (n = 7) brains exhibited gliosis. Since the redistribution and hyperplasia of astrocytes within the molecular layer of the partially deafferented dentate gyrus depend on the chronicity of the entorhinal lesion, the abnormalities observed in AD patients are consistent with the progressive course of the illness. Furthermore, the presence of gliosis in the subiculum of three out of six AD patients suggested pathology secondary to projections from the entorhinal region, amygdala, or prepyriform cortex. The absence of similar changes in schizophrenic patients does not disprove previous claims of entorhinal pathology but suggests that the lesion, if it exists, is either static in nature or occurred long before death.

Schizophrenia: the cellular biology of a functional psychosis

Structural abnormalities are found in the brains of schizophrenics. They affect preferentially, but not exclusively, medial temporal lobe structures (parahippocampal gyrus, hippocampus and amygdala), and can be found in all sub-types of schizophrenia. The structures of the medial temporal lobe are believed to have a crucial role in the integration and processing of the output from association cortex. It is probable that all schizophrenics have abnormalities in the medial temporal lobe that differ in degree but not in kind. Dysfunction of this system could result in the clinical symptoms that form the core of the schizophrenia syndrome. The changes in brain structure are not the result of neurodegenerative processes or destructive lesions but suggest a disturbance in the normal pattern of brain development.