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

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

Recent neuroradiologic and neuropathological studies indicate that at least some patients with schizophrenia have slightly enlarged cerebral ventricles and subtle anatomical abnormalities in the region of the anterior hippocampus. Using magnetic resonance imaging (MRI), we studied 15 sets of monozygotic twins who were discordant for schizophrenia (age range, 25 to 44 years; 8 male and 7 female pairs). For each pair of twins, T1-weighted contiguous coronal sections (5 mm thick) were compared blindly, and quantitative measurements of brain structures were made with a computerized image-analysis system. In 12 of the 15 discordant pairs, the twin with schizophrenia was identified by visual inspection of cerebrospinal fluid spaces. In two pairs no difference could be discerned visually, and in one the twin with schizophrenia was misidentified. Quantitative analysis of sections through the level of the pes hippocampi showed the hippocampus to be smaller on the left in 14 of the 15 affected twins, as compared with their normal twins, and smaller on the right in 13 affected twins (both P less than 0.001). In the twins with schizophrenia, as compared with their normal twins, the lateral ventricles were larger on the left in 14 (P less than 0.003) and on the right in 13 (P less than 0.001). The third ventricle also was larger in 13 of the twins with schizophrenia (P less than 0.001). None of these differences were found in seven sets of monozygotic twins without schizophrenia who were studied similarly as controls. We conclude that subtle abnormalities of cerebral anatomy (namely, small anterior hippocampi and enlarged lateral and third ventricles) are consistent neuropathologic features of schizophrenia and that their cause is at least in part not genetic. Further study is required to determine whether these changes are primary or secondary to the disease.

https://www.nejm.org/doi/pdf/10.1056/NEJM199003223221201

Anatomical abnormalities in the brains of monozygotic twins discordant for schizophrenia.

• A recent report suggested that neurons in the prefrontal, anterior cingulate, and primary motor cortex of the brains of schizophrenic subjects may be less dense than those in the brains of nonschizophrenic subjects. We have determined whether pyramidal neurons and/or interneurons are preferentially reduced in schizophrenic subjects. Twelve control subjects and 18 schizophrenic subjects were studied in a blind, quantitative analysis of the density of pyramidal cells, interneurons, and glial cells in each of the six layers of the anterior cingulate and prefrontal cortex. The results showed that numbers of small neurons (interneurons) were reduced in most layers of the cingulate cortex in schizophrenic subjects compared with nonschizophrenic subjects, with the differences being greatest in layer II. In the prefrontal area, interneuronal density was also lower in layer II and, to a lesser extent, in layer I in schizophrenic subjects compared with control subjects. In most cases, the differences were similar, although more significant, in schizophrenic subjects who had had superimposed mood disturbances than in schizophrenic subjects who had not had such comorbidity. Numbers of pyramidal neurons generally were not different between control and schizophrenic subjects, except in layer V of the prefrontal area, where schizophrenic subjects showed higher densities of these neurons. Glial numbers did not differ between the control and schizophrenic subjects, suggesting that a neurodegenerative process did not cause the reduced interneuronal density observed. Using multiple regression analysis and analysis of covariance, decreases in the density of layer II interneurons could not be adequately explained by the effects of various confounding variables, such as age, postmortem interval, duration of specimen fixation, or administration of neuroleptic agents. Two younger patients who had not received neuroleptic agents also had reduced numbers of small neurons, suggesting that reduction in numbers of small neurons is not due to the effects of antipsychotic medication. Reductions of interneurons, possibly ones that are inhibitory in nature, may occur within intrinsic cortical circuits, and may be an important aspect of the pathophysiology of schizophrenia.

Deficits in Small Interneurons in Prefrontal and Cingulate Cortices of Schizophrenic and Schizoaffective Patients

One of the most remarkable characteristics of astrocytes is their vigorous response to diverse neurologic insults, a feature that is well conserved across a variety of different species. The astroglial response occurs rapidly and can be detected within one hour of a focal mechanical trauma (Mucke et al., 1991). Prominent reactive astrogliosis is seen; in AIDS dementia; a variety of other viral infections; prion associated spongiform encephalopathies; inflammatory demyelinating diseases; acute traumatic brain injury; neurodegenerative diseases such as Alzheimer's disease. The prominence of astroglial reactions in various diseases, the rapidity of the astroglial response and the evolutionary conservation of reactive astrogliosis indicate that reactive astrocytes fulfill important functions of the central nervous system (CNS). Yet, the exact role reactive astrocytes play in the injured CNS has so far remained elusive. This chapter summaries the various experimental models and diseases that exhibit astrogliosis and increase in glial fibrillary acidic protein (GFAP). Recent in vitro studies to inhibit GFAP synthesis are also presented.

GFAP and Astrogliosis

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

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

Gliosis in schizophrenia: A survey

The location of the neuropeptides methionine-enkephalin (ME), neurotensin (NT), neuropeptide Y (NPY) and vasoactive intestinal polypeptide (VIP) within the amygdaloid complex of healthy human individuals, schizophrenics and patients suffering from Huntington's chorea was studied qualitatively by means of immunohistochemistry VIP-like immunoreactivity (IR) was present predominantly in a dense cluster of fibers and terminals in the central amygdaloid nucleus ME-IR was observed in fibers, terminals and cell bodies in the same subnucleus, exhibiting a characteristical distribution pattern NT-positive cell bodies were situated within the center of the central amygdaloid nucleus, fibers and terminals being encountered mainly at the periphery NPY-IR was found to be evenly distributed throughout the amygdala Distribution and staining intensity of ME, NPY and NT in the amygdala showed no qualitatively recognizable difference between the normal and schizophrenic specimens, whereas VIP-IR appeared to be slightly increased in the central amygdaloid nucleus of schizophrenics In the choreic cases, the considerably shrunken amygdala exhibited only very low staining intensity of the four investigated neuropeptides

M. Zech

Papers

Gliosis in schizophrenia: A survey

Neuropeptides in the amygdala of controls, schizophrenics and patients suffering from Huntington's chorea: an immunohistochemical study.