Vahram Haroutunian

Loss and altered spatial distribution of oligodendrocytes in the superior frontal gyrus in schizophrenia

BACKGROUNDnBrain imaging, molecular genetic, and ultrastructural evidence indicate the existence of pathologic alterations in the cortical and subcortical white matter of schizophrenic patients.nnnMETHODSnWe performed a stereologic analysis of numbers, densities, and spatial distribution of oligodendrocytes in layer III and in the gyral white matter of Brodmanns area 9 in the superior frontal gyrus to assess whether these cells are affected in schizophrenia. Counts were obtained on Nissl-stained materials and on sections immunolabeled for the oligodendrocyte marker 2,3-cyclic nucleotide-3-phosphodiesterase (CNPase) in seven schizophrenic and seven age-matched control cases.nnnRESULTSnA 28% decrease in total numbers (or densities) of cortical layer III oligodendrocytes and a 27% decrease in the white matter were detected in schizophrenic compared with control cases based on CNPase immunostaining. Nissl and CNPase immunohistochemistry yielded comparable results. The spatial distribution of oligodendrocytes in area 9 white matter exhibited a less clustered arrangement in schizophrenic cases.nnnCONCLUSIONSnThese results suggest a severe pathology of oligodendrocytes in schizophrenia and provide a quantitative cellular correlate of the white matter changes observed by brain imaging in vivo, showing reduced fractional anisotropy in schizophrenia. The data support recent evidence that several genes encoding myelin-related proteins consistently exhibit reduced expression in schizophrenia.

Dopamine Receptor mRNA Expression in Human Striatum and Neocortex

The distributions of the transcripts encoding the five dopamine receptors have been determined in the human striatum and selected regions of the neocortex. In the striatum significant levels of dopamine receptor expression are restricted to the D1, D2, and D3 receptors. D1 and D2 receptor messenger ribonucleic acids (mRNAs) are homogeneously distributed throughout the caudate, putamen, and nucleus accumbens. D3 receptor mRNA is particularly enriched in the nucleus accumbens, with moderate levels in the ventral putamen. In the prefrontal cortex D1 and D4 receptor mRNAs are the most abundant, although the other three transcripts are seen at lower levels. A similar pattern is seen in the temporal neocortex. In the occipital cortex, D1 receptor mRNA is the most abundant, D3 the rarest, while the other three transcripts are present at modest levels of expression. These data add to a growing understanding of the neuroanatomical distribution of these transcripts in the human brain. They are essential to understand in the context of the limbic circuitry of the brain, as new hypotheses of dysfunction of dopaminergic neurotransmission are advanced in psychiatry and as these receptor subtypes are targeted for development of novel pharmacological treatments.

Pharmacological alleviation of cholinergic lesion induced memory deficits in rats

The cholinergic cells of the nucleus basalis of Meynert (nbM) have recently been found to degenerate in Alzheimers disease and are thought to be at least partly responsible for the cognitive deficits which are characteristic of this disease. These experiments explored the behavioral effects of bilateral excitotoxic lesions of the nbM in adult rats. The first experiment showed that nbM lesions lead to a substantial deficit in the 24 hour retention of the habituation to a novel environment without affecting general exploratory behavior. The second experiment showed that this retention deficit is a general phenomenon reflected in the 72 hour retention of a one trial passive avoidance task. These retention deficits could be reversed by the postacquisition administration of the acetylcholinesterase inhibitor, physostigmine. These results support the hypothesis that central cholinergic systems are involved in the retention of learned responses, and suggest that cholinergic lesion induced retention deficits can be reversed by pharmacological means.

Severe cognitive impairment in elderly schizophrenic patients: A clinicopathological study ☆

The severe cognitive impairment that affects many of the elderly schizophrenic patients could represent the outcome of schizophrenia in old age for the very severe and chronically ill patients or may be the result of lengthy institutionalization and somatic treatment. Alternatively, it could be due to the presence of concurrent dementing disorders, such as Alzheimers disease (AD) or multi-infarct dementia. Using an identical neuropathological protocol, brain specimens from schizophrenic patients who showed evidence of severe cognitive impairment were compared with 12 age-matched control cases and the same number of age-matched cases of neuropathologically confirmed patients with AD. Despite their relatively advanced age (mean age 77.1 years +/- 2.8), none of the schizophrenia cases showed sufficient degree of senile plaques and neurofibrillary tangle formations to confirm a diagnosis of AD. Other neurodegenerative disorders associated with dementia were also not identified. These studies suggest that alternative explanations need to be sought for the severe cognitive impairment commonly encountered in elderly schizophrenic patients.

CNS oxidative stress associated with the kainic acid rodent model of experimental epilepsy

The role of oxidative stress in seizure-induced brain injury was investigated in a kainic acid model of experimental epilepsy. Kainic acid (12.5 mg/kg) or saline was injected intraperitoneally into 12-week-old male Fischer 344 rats and sacrificed by decapitation at 4 and 24 h after injection. Markers of oxidative stress including protein carbonyls, thiobarbituric acid reactive material (TBARs), glutathione (GSH) and glutathione disulfide (GSSG) were measured in hippocampus, cortex, cerebellum and basal ganglia. Four hours after treatment, protein carbonyls were elevated by 103, 55, 52 and 32% in cortex, hippocampus, basal ganglia and cerebellum, respectively. TBARs were increased by 30-45% in all areas. After 24 h, elevated protein and lipid oxidative markers persisted in the hippocampus and cerebellum; by contrast, in the cortex, TBARs almost normalized to control values and protein carbonyls trended downward by one-half compared with measurements at 4 h, although this reduction relative to the 4 h timepoint did not reach statistical significance. In the basal ganglia, protein carbonyls approached control values at 24 h. GSSG levels were only increased statistically in the cortex after 4 h, GSH levels in all the regions were unchanged after treatment with kainic acid. However, in cortex, GSH levels correlated negatively with increases in protein and lipid oxidation (r = -0.69, P < 0.002). In contrast, significant correlations between GSH, protein carbonyls and TBARs measured in the hippocampus or cerebellum were not observed. Our data suggests that kainic acid induced similar oxidative stress in all of the brain regions that were examined, and that GSH plays a major antioxidant role in the cerebral cortex but not the hippocampus.

Restoration of cholinomimetic activity by clonidine in cholinergic plus noradrenergic lesioned rats

The effects of combined lesions of forebrain cholinergic and noradrenergic systems on memory and responsivity to the memory enhancing effects of cholinomimetics were investigated in rats. Forebrain noradrenergic deficits produced by the injection of 6-hydroxydopamine into the ascending noradrenergic bundle (ANB) blocked the ability of cholinomimetics such as physostigmine and oxotremorine to enhance retention test performance in nucleus basalis of Meynert lesioned rats. Low doses of the noradrenergic receptor agonist clonidine, when administered in conjunction with cholinomimetics reversed this blockade. These results suggest that combined cholinergic/noradrenergic therapy may be of value in the treatment of some Alzheimers disease patients.

Using the subcortically lesioned rat cortex to understand the physiological role of amyloid precursor protein

Alzheimers disease pathology is characterized by the presence of neuritic plaques and neurofibrillary tangles and specific neurotransmitter deficits in the cortex and hippocampus. Advances in the understanding of Alzheimers disease have been hampered by the absence of appropriate animal model systems. Most in vivo rodent models have turned to aged animals, animals with experimentally induced lesions of various neurotransmitter systems, animals with pharmacologically induced neurotransmitter perturbations, and mice made transgenic for genes related to amyloid precursor protein. These models have been useful for the investigation of some discrete aspects of Alzheimers disease, including deficits in forebrain cholinergic activity and the resulting cognitive deficits. However, none of these models have led to the development of the principal neuropathological hallmarks of Alzheimers disease, neuritic plaques and neurofibrillary tangles. Furthermore, the relationship, if any, between the reduction of neurotransmitter activity and the formation of neuritic plaques and neurofibrillary tangles is unknown. The subcortically lesioned rat model system which we have used approximates the cortical neurotransmitter and the cognitive deficits of Alzheimers disease. We have recently found that these same subcortical neurotransmitter system lesions alter the expression of amyloid precursor protein, the precursor of beta amyloid peptide, which is the principal component of neuritic plaques. Loss of functional subcortical innervation by either permanent lesions or transient inhibition of cortical neurotransmitter (acetylcholine) release resulted in the induction of amyloid precursor protein in the cortex. The induction was rapid and persistent with the permanent lesions or reversible with the transient inhibition. Lesions cholinergic, serotonergic,and adrenergic neurotransmitter systems all resulted in the induction.(ABSTRACT TRUNCATED AT 250 WORDS)

Somatic Mutation Analysis of the APP and Presenilin 1 and 2 Genes in Alzheimer's Disease Brains

The molecular basis for sporadic Alzheimer disease (AD) remains largely unknown. We hypothesized that in some cases of sporadic AD, a somatic mutation in an embryonic cell committed to neuronal development within the amyloid precursor protein (APP), the presenilin 1 (PS-1) or the presenilin 2 (PS-2) genes (genes known to be involved in familial AD) may result in AD phenotype. Using PCR, denaturing gradient gel electrophoresis (DGGE), restriction enzyme digest and direct DNA sequencing, we analyzed these genes in 99 brain tissues from patients with histopathologically proven AD. One brain sample showed a mutation within the PS-1 gene, His163 Arg, later shown to be a germline mutation. No other migration abnormalities were demonstrated in any sample in exon 16 or 17 of the APP gene or the coding exons of the PS-1 gene. Restriction digest pattern was normal with regard to the predominant PS-2 gene mutation (N141I). A known mutation in the APP gene, as well as novel mutations within the PS-1 gene were easily detected by DGGE (Reznick Wolf et al. manuscript submitted). We conclude that the genes that are involved in familial AD do not display somatic mutations in the brains of sporadic AD patients, and that other molecular mechanisms are probably involved in the pathogenesis of sporadic AD.

158. Decreased vesicular monoamine transporter density in schizophrenic prefrontal cortex

A recent report has suggested decreased dopaminergic innervation to the schizophrenic prefrontal cortex, based on diminished immunocytochemical labeling of tyrosine hydroxylase-positive axons in this cortical region (Akil et al, Am J Psychiatry 156:1580–1589, 1999). To further investigate possible alterations in presynaptic aspects of dopaminergic neurotransmission in schizophrenic prefrontal cortex, we have examined the binding of the vesicular monoamine transporter (VMAT2) ligand [3H]dihydotetrabenazine by quantitative autoradiography in sections of prefrontal cortex from a group of older subjects with schizophrenia and a comparison group of non-psychiatrically ill individuals. VMAT binding was readily identifiable in prefrontal cortex, although it was present in a homogeneous pattern with no lamina-specific pattern of distribution. Dramatic reductions (30–50%) were found in multiple divisions of the prefrontal cortex in the subjects with schizophrenia. Given past reports of no changes in the level of expression of this molecule after pharmacological treatment with antipsychotic agents, it in unlikely that this effect is secondary to antipsychotic exposure, but rather is associated with the illness itself. These results suggest that there are decreased numbers of dopamine-containing secretory vesicles in presynaptic nerve terminals in the schizophrenic prefrontal cortex, and are consistent with the hypothesis of decreased dopamine afferent innervation to this cortical region. This study adds to the growing evidence for alterations of patterns of dopaminergic innervation to cortical regions in schizophrenia, and suggests that there may be presynaptic abnormalities of dopaminergic neurotransmission in this illness.

Phenserine: A Selective, Long-Acting and Brain-Directed Acetylcholinesterase Inhibitor Affecting Cognition and β-APP Processing

Alzheimer’s disease (AD) is characterized by (i) the presence of β-amyloid (Aβ) plaques and angiopathy, neurofibrillary tangles (NFTs), neuronal loss and brain atrophy; (ii) a time-course of degenerative changes; and (iii) a correlation of some measures of pathological changes with clinical course (Wisniewski and Weigel, 1994). Although the neuropathological quantification of plaques and NFTs in the Alzheimer’s brain is the basis of confirming diagnosis after death (Khachaturian, 1985), patients initially present themselves to physicians as a consequence of a time-dependent and progressive memory loss. Indeed, it is counts of neocortical synapses rather than of plaques and NFTs that correlate best to psychometric indices of cognitive performance in AD (Terry et al., 1991). The loss of cholinergic neuronal markers, specifically the enzymes choline acetyltransferase (CT) and acetylcholinesterase (AC), in selected brain regions, the forebrain and its projection sites in the cortex and hippocampus, remains one of the earliest known schedule of events leading to AD. These are markers of synaptic loss of the most affected neurotransmitter system involved in AD and in memory processing. Whereas multiple neurotransmitter deficiencies also occur in AD, these do so always in addition to, and not instead of, the cholinergic system deficiency.