Loss of proteins regulating synaptic plasticity in normal aging of the human brain and in Alzheimer disease.

Recent studies suggest that the cognitive impairment associated with normal aging is due to neuronal dysfunction rather than to loss of neurons or synapses. To characterize this dysfunction, molecular indices of neuronal function were quantified in autopsy samples of cerebral cortex. During normal aging, the most dramatic decline was found in levels of synaptic proteins involved in structural plasticity (remodeling) of axons and dendrites. Alzheimer disease, the most common cause of dementia in the elderly, was associated with an additional 81% decrease in levels of drebrin, a protein regulating postsynaptic plasticity. Disturbed mechanisms of plasticity may contribute to cognitive dysfunction during aging and in Alzheimer disease.

No association between Alzheimer plaques and decreased levels of cytochrome oxidase subunit mRNA, a marker of neuronal energy metabolism.

It has been proposed that neuritic plaques or toxic substances diffusing from them contribute to neurodegeneration in Alzheimer disease. We examined this hypothesis by looking for evidence of decreased neuronal energy metabolism in the proximity of neuritic plaques. Levels of mitochondrial DNA-encoded mRNA for subunit III of cytochrome oxidase, a marker of neuronal energy metabolism, were determined in post mortem brain samples. Consistent with earlier results, overall cytochrome oxidase subunit III mRNA levels were decreased in Alzheimer midtemporal cortex compared with controls. However, this reduction did not correlate with plaque density. In Alzheimer brains, cytochrome oxidase subunit III mRNA levels in neurons bearing neurofibrillary tangles were lower than in tangle-free neurons. However, neuronal cell bodies in close proximity of neuritic plaques showed no decrease in cytochrome oxidase subunit III mRNA or total polyadenylated mRNA compared with more distant neurons. Cytochrome oxidase enzyme activity in neuronal processes also showed no local reduction around neuritic plaques. These results suggest that neuritic plaques do not contribute to reduced neuronal energy metabolism in Alzheimer disease.

Downregulation of oxidative phosphorylation in Alzheimer disease: loss of cytochrome oxidase subunit mRNA in the hippocampus and entorhinal cortex.

Messenger RNA (mRNA) for cytochrome oxidase subunit II (COX II) was localized by in situ hybridization in the entorhinal cortex and hippocampal formation of postmortem brain tissue from normal human subjects and from patients with Alzheimer disease (AD). In the control entorhinal cortex, COX II mRNA was detected mainly in neuronal cell bodies of layers II and IV. In control hippocampal formation, highest levels were localized in neuronal cell bodies of the dentate gyrus and the CA3 and CA1 regions, neurons that are involved in the major input and output pathways of the hippocampal formation. In AD brain, COX II mRNA was markedly reduced in the entorhinal cortex and the hippocampal formation compared with control brain. In the AD hippocampal formation, reductions were in regions severely affected by AD pathology as well as in regions that were relatively spared. These results are consistent with the hypothesis that reduced mitochondrial energy metabolism reflects loss of neuronal connections in AD.

A magnetic resonance imaging study of planum temporale asymmetry in men with developmental dyslexia.

BACKGROUND: Imaging studies have suggested anomalous anatomical asymmetries in language-related regions of the temporal and parietal lobes in individuals with developmental dyslexia. Autopsy studies have reported unusual symmetry of the planum temporale (PT) in patients with dyslexia. Methodological limitations characterize much of this literature, however. OBJECTIVE: To examine the size and asymmetry of the PT and its extension into the parietal lobe (planum parietale [PP]) in men with well-characterized, persistent dyslexia by using magnetic resonance imaging and 3-dimensional surface rendering techniques. METHODS: The brains of 16 right-handed dyslexic men aged 18 to 40 years and 14 matched control subjects were studied with magnetic resonance imaging. Most of these subjects were previously studied with positron emission tomography, which demonstrated functional abnormalities in temporal and parietal brain regions in the dyslexic group. The area of the PT was determined with the aid of 3-dimensional surface-rendering techniques. The size of the PP was estimated by measuring the length of the posterior ascending ramus on 3 parasagittal slices. RESULTS: Approximately 70% to 80% of both groups showed equivalent leftward (left > right) asymmetries of the PT; approximately 50% to 60% showed equivalent rightward (right > left) asymmetries of the PP. These asymmetries showed equivalent moderate inverse correlations with each other in both groups. CONCLUSIONS: These results challenge the notion that anomalous asymmetry of the PT is strongly associated with developmental dyslexia. Given the heterogeneity of the dyslexic population, some subgroup of dyslexic individuals (i.e., those with developmental language disorders) may show unusual symmetry or reversed asymmetry in this region. However, anomalous asymmetry of the planum did not contribute to functional abnormalities demonstrated in these patients by positron emission tomography.

Parvalbumin-immunoreactive neurons in the hippocampal formation of Alzheimer's diseased brain.

The number and topographic distribution of immunocytochemically stained parvalbumin interneurons was determined in the hippocampal formation of control and Alzheimer's diseased brain. In control hippocampus, parvalbumin interneurons were aspiny and pleomorphic, with extensive dendritic arbors. In dentate gyrus, parvalbumin cells, as well as a dense plexus of fibers and puncta, were associated with the granule cell layer. A few cells also occupied the molecular layer. In strata oriens and pyramidale of CA1-CA3 subfields, parvalbumin neurons gave rise to dendrites that extended into adjacent strata. Densely stained puncta and beaded fibers occupied stratum pyramidale, with less dense staining in adjacent strata oriens and radiatum. Virtually no parvalbumin profiles were observed in stratum lacunosum-moleculare or the alveus. Numerous polymorphic parvalbumin neurons and a dense plexus of fibers and puncta characterized the deep layer of the subiculum and the lamina principalis externa of the presubiculum. In Alzheimer's diseased hippocampus, there was an approximate 60% decrease in the number of parvalbumin interneurons in the dentate gyrus/CA4 subfield (P<0.01) and subfields CA1-CA2 (P<0.01). In contrast, parvalbumin neurons did not statistically decline in subfields CA3, subiculum or presubiculum in Alzheimer's diseased brains relative to controls. Concurrent staining with Thioflavin-S histochemistry did not reveal degenerative changes within parvalbumin-stained profiles. These findings reveal that parvalbumin interneurons within specific hippocampal subfields are selectively vulnerable in Alzheimer's disease. This vulnerability may be related to their differential connectivity, e.g., those regions connectionally related to the cerebral cortex (dentate gyrus and CA1) are more vulnerable than those regions connectionally related to subcortical loci (subiculum and presubiculum).

Three-dimensional cortical morphometry of the planum temporale in childhood-onset schizophrenia.

OBJECTIVE: Anomalous planum temporale asymmetry has been linked to both schizophrenia and dyslexia. The authors examined the planum temporale of adolescents with childhood-onset schizophrenia who had a high rate of prepsychotic language disorders. METHOD: Planum temporale area and asymmetry were measured in 16 right-handed adolescent patients with schizophrenia who had experienced onset of psychosis by age 12. The same measures were made in 16 healthy adolescents matched for age, sex, and handedness. RESULTS: No differences between the healthy adolescents and those with schizophrenia in planum temporale area or asymmetry were observed. Prepsychotic language disorder predicted abnormal planum temporale asymmetry in the adolescents with schizophrenia. CONCLUSIONS: These findings do not support anomalous planum temporale asymmetry as a basis for psychopathology in childhood-onset schizophrenia.

Association of premorbid intellectual function with cerebral metabolism in Alzheimer's disease: implications for the cognitive reserve hypothesis.

OBJECTIVE: Clinical heterogeneity in Alzheimer's disease has been widely observed. One factor that may influence the expression of dementia in Alzheimer's disease is premorbid intellectual ability. It has been hypothesized that premorbid ability, as measured by educational experience, reflects a cognitive reserve that can affect the clinical expression of Alzheimer's disease. The authors investigated the relation between estimates of premorbid intellectual function and cerebral glucose metabolism in patients with Alzheimer's disease to test the effect of differing levels of premorbid ability on neurophysiological dysfunction. METHOD: In a resting state with eyes closed and ears occluded, 46 patients with Alzheimer's disease were evaluated with positron emission tomography and [18F]-2-fluoro-2-deoxy-D-glucose to determine cerebral metabolism. Premorbid intellectual ability was assessed by a demographics-based IQ estimate and performance on a measure of word-reading ability. RESULTS: After the authors controlled for demographic characteristics and dementia severity, both estimates of premorbid intellectual ability were inversely correlated with cerebral metabolism in the prefrontal, pre-motor, and left superior parietal association regions. In addition, the performance-based estimate (i.e., reading ability) was inversely correlated with metabolism in the anterior cingulate, paracentral, right orbitofrontal, and left thalamic regions, after demographic and clinical variables were controlled for. CONCLUSIONS: The results suggest that higher levels of premorbid ability are associated with greater pathophysiological effects of Alzheimer's disease among patients of similar dementia severity levels. These findings provide support for a cognitive reserve that can alter the clinical expression of dementia and influence the neurophysiological heterogeneity observed in Alzheimer's disease.

Decreased expression of nuclear and mitochondrial DNA-encoded genes of oxidative phosphorylation in association neocortex in Alzheimer disease.

We recently reported 50% decreases in mRNA levels of mitochondrial DNA (mtDNA)-encoded cytochrome oxidase (COX) subunits I and III in Alzheimer disease (AD) brains. The decreases were observed in an association neocortical region (midtemporal cortex) affected in AD, but not in the primary motor cortex unaffected in AD. To investigate whether the decreases are specific to mtDNA-encoded mRNA, we extended this analysis to nuclear DNA (nDNA)-encoded subunits of mitochondrial enzymes of oxidative phosphorylation (OXPHOS). Brains from five AD patients showed 50-60% decreases in mRNA levels of nDNA-encoded subunit IV of COX and the beta-subunit of the F0F1-ATP synthase in midtemporal cortex compared with mRNA levels from midtemporal cortex of control brains. In contrast, these mRNAs were not reduced in primary motor cortices of the AD brains. The amount of nDNA-encoded beta-actin mRNA and the amount of 28S rRNA were not altered in either region of the AD brain. The results suggest that coordinated decreases in expression of mitochondrial and nuclear genes occur in association cortex of AD brains and are a consequence of reduced neuronal activity and downregulation of OXPHOS machinery.

Brain energy metabolism, cognitive function and down-regulated oxidative phosphorylation in Alzheimer disease.

Reduced brain glucose utilization in early stages of Alzheimer disease, as measured with in vivo positron emission tomography, reflects potentially reversible down-regulation of gene expression for oxidative phosphorylation within neuronal mitochondria. Such down-regulation may occur when neuronal energy demand is first reduced by synaptic dysfunction or loss.

Evidence for physiological down-regulation of brain oxidative phosphorylation in Alzheimer's disease.

In vivo imaging of patients with Alzheimer's disease using positron emission tomography (PET) demonstrates progressive reductions in brain glucose metabolism and blood flow in relation to dementia severity, more so in association than primary cortical regions. These reductions likely follow regional synaptic loss or dysfunction and reflect physiological down-regulation of gene expression for glucose delivery, oxidative phosphorylation (OXPHOS), and energy consumption in brain. Indeed, the pattern of down-regulation of expression for both mitochondrial and nuclear genes coding for subunits of OXPHOS enzymes in the Alzheimer brain resembles the pattern of down-regulation in normal brain caused by chronic sensory deprivation. In both cases, down-regulation likely is mediated by changes in transcriptional and posttranscriptional regulatory factors. Physiological down-regulation of OXPHOS gene expression in Alzheimer's is consistent with PET evidence that cognitive or psychophysical activation of mildly to moderately demented Alzheimer's patients can augment brain-blood flow and glucose metabolism to the same extent as in control subjects. If the primary neuronal defect that leads to reduced brain energy demand in Alzheimer's disease could be prevented or treated, brain glucose transport and OXPHOS enzyme activities might recover to normal levels.

Neuronal activity and early neurofibrillary tangles in Alzheimer's disease.

We studied neuronal activity and its relation to the accumulation of neurofibrillary tangles in Alzheimer's disease (AD) neurons by in situ hybridization to cytochrome oxidase subunit III messenger RNA, a marker of mitochondrial energy metabolism. In AD midtemporal cortex, levels of cytochrome oxidase subunit III messenger RNA were decreased by 26% in neurons bearing early-stage neurofibrillary tangles as compared to tangle-free neurons (p < 0.01). However, levels of 12S ribosomal RNA, also encoded by mitochondrial DNA, and of total messenger RNA were decreased only in later stages of tangle development. Comparing tangle-free neurons of 4 AD brains to tangle-free neurons of 3 control brains, levels of cytochrome oxidase subunit III messenger RNA were found to be 25% lower (p < 0.001) in AD tangle-free neurons. Because energy metabolic needs of neurons are mainly determined by synaptic input, the observed decreases in cytochrome oxidase subunit III messenger RNA likely reflect downregulation due to impaired synaptic function in AD. Thus, a failure in synaptic transmission may precede tangle formation. A further decline in neuronal activity is seen as tangle formation progresses. However, these results can also be viewed as showing the viability and continuing activity, albeit at a lower level, of neurons in the early stages of neurofibrillary pathology.

Comparison of positron emission tomography, cognition, and brain volume in Alzheimer's disease with and without severe abnormalities of white matter.

OBJECTIVES: To examine cerebral metabolism, cognitive performance, and brain volumes in healthy controls and two groups of patients with probable Alzheimer's disease, one group with severe abnormalities of white matter (DAT+) and the other group with none, or minimal abnormalities (DAT-). METHODS: Neuropsychological tests, CT, MRI, quantitative MRI, and PET studies were carried out to allow comparison between the DAT+ and DAT- groups and the healthy controls. RESULTS: Compared with the healthy controls, both demented groups had significantly reduced global and regional cerebral metabolism, significant brain atrophy, and significantly lower scores on neuropsychological testing. The DAT- patient group showed a pattern of parietal-temporal cerebral metabolic reductions and neuropsychological performance deficits typical of Alzheimer's disease. In addition, metabolism in the association neocortex (AD ratio) and measures of neuropsychological task performance were significantly correlated in the DAT- patient group. Comparison of DAT+ with DAT- patients showed a significantly higher ratio of parietal to whole brain glucose utilisation for the DAT+ group. Moreover, when comparing group z score differences from the healthy controls, the DAT+ group had, on average, smaller differences from controls in the frontal, parietal, and temporal regions than did the DAT- group. Discriminant analysis using metabolic ratios of the frontal, parietal, and temporal regions showed cerebral metabolic patterns to be significantly different among the DAT+, the DAT-, and the healthy controls. These differences were due primarily to relatively higher frontal, parietal, and temporal metabolic ratios in the DAT+ group which resulted in discriminant scores for the DAT+ group between the healthy controls and the DAT- group. Group mean scores on tests of neuropsychological performance were not significantly different between the DAT- and DAT+ patients. By contrast with the DAT- group, however, no significant correlations between the AD ratio and any neuropsychological task were seen in the DAT+ group. Multiple regression analysis showed significant between group differences in the relation between the AD ratio and neuropsychological scores on three tasks. The slopes of the relations between the AD ratio and memory scores (memory and freedom from distractability deviation quotient of the Wechsler adult intelligence scale (WMDQ)) also were significantly different for the two groups. CONCLUSIONS: Although multiple causes for abnormalities of white matter exist in patients with Alzheimer's disease, these data suggest that the presence of severe abnormalities of white matter indicate a second pathological process in the DAT+ patients. The DAT- patients showed the parietal-temporal metabolic deficits and correlations between association neocortical metabolism and neuropsychological task performance typical of patients with Alzheimer's disease. By contrast, the DAT+ group had a pattern of cerebral metabolism significantly different from healthy controls and DAT+ patients, as well as no significant correlations between metabolism in the association neocortex and neuropsychological performance. These differences probably reflect the superimposed pathology of the abnormalities of white matter which may exert their affect through disruption of long corticocortical pathways.

Development and application of a modified monoclonal hybridoma technique for isolating monoclonal antibodies to human brain regions.

We developed a modified monoclonal hybridoma technique that combines two conventional methods: a conventional immunosuppression method with cyclophosphamide treatment and an in vitro immunization method. This technique is advantageous over conventional methodologies because it requires a shorter period for immunization of mice and a smaller quantity of antigen, and gives rise to antibody-secreting hybridomas with higher efficiency. One monoclonal hybridoma line, designated as BG5, was established by this technique after activation of lymphocytes with muramyl dipeptide and with the immunogen obtained from human entorhinal cortex. Western blot analysis showed a relatively high expression of BG5 antigen in human entorhinal cortex. Our results suggest that this hybridoma technique may rapidly facilitate the acquisition of brain region-specific antibodies. We call this technique 'suppression immunization followed by in vitro stimulation procedure' (SOFISTIC).

Development and application of a modified monoclonal hybridoma technique for isolating monoclonal antibodies to human brain regions.

We developed a modified monoclonal hybridoma technique that combines two conventional methods: a conventional immunosuppression method with cyclophosphamide treatment and an in vitro immunization method. This technique is advantageous over conventional methodologies because it requires a shorter period for immunization of mice and a smaller quantity of antigen, and gives rise to antibody-secreting hybridomas with higher efficiency. One monoclonal hybridoma line, designated as BG5, was established by this technique after activation of lymphocytes with muramyl dipeptide and with the immunogen obtained from human entorhinal cortex. Western blot analysis showed a relatively high expression of BG5 antigen in human entorhinal cortex. Our results suggest that this modified hybridoma technique may rapidly facilitate the acquisition of brain region-specific antibodies. We call this technique 'suppression immunization followed by in vitro stimulation procedure' (SOFISTIC).

Evidence for apoptotic cell death in Alzheimer's disease.

We provide evidence for apoptosis in Alzheimer's disease using the in situ labeling technique TUNEL (terminal transferase-mediated dUTP-biotin nick end labeling). The technique specifically detects apoptotic cells by utilizing terminal transferase to incorporate biotinylated nucleotides into the fragmented DNA of apoptotic cells. The labeled cells are visualized by reaction with avidin peroxidase and a suitable substrate. Sections from the hippocampus of Alzheimer-diseased (AD) brains and non-AD brains were examined for apoptosis. While considerable variation in the quantity of apoptotic cells was observed among individual samples, the incidence of apoptosis in AD brains was elevated in comparison to age-matched, non-AD brains in specific regions of the hippocampal formation. Immunostaining indicated that both neurons and astrocytes were undergoing apoptosis, although the majority of the TUNEL-positive cells appeared to be glial, based on the location of the stained cells. These data suggest that apoptosis may be involved in both the primary neuronal cell loss and in the glial response that is a component of AD.

Impairment in mitochondrial cytochrome oxidase gene expression in Alzheimer disease.

Brains from 5 patients with Alzheimer's disease (AD) showed a 50%-65% decrease in mRNA levels of the mitochondrial-encoded cytochrome oxidase (COX, a marker of oxidative metabolism) subunits I and III in the middle temporal association neocortex, but not in the primary motor cortex, as compared to 5 control brains. The amount of mitochondrial-encoded 12S rRNA was not altered, nor was the amount of nuclear-encoded lactate dehydrogenase B mRNA (a marker of glycolytic metabolism). These data suggest that the decrease in COX I and III subunits mRNA in affected brain regions may contribute to reduced brain oxidative metabolism in AD.

Evidence that transmitter-containing dystrophic neurites precede paired helical filament and Alz-50 formation within senile plaques in the amygdala of nondemented elderly and patients with Alzheimer's disease.

Immunocytochemical techniques were employed to examine the temporal ordering whereby amyloid beta-protein (A beta P) and neuronal elements collectively come together to form senile plaques in Alzheimer's disease (AD). Specifically, we addressed three questions: (1) whether A beta P deposition precedes or follows neuritic changes; (2) whether paired helical filament (PHF) formation is an early or late event in the genesis of the dystrophic neurites which participate in plaque formation; and (3) whether the density of senile plaques displays any relationship with the prevalence of PHF or Alz-50 containing neurons. To address these questions we studied the amygdala from a group of patients with AD, a group of nondemented age-matched individuals exhibiting a sufficient number of senile plaques to be classified by neuropathological criteria as AD, and a group of age-matched controls without AD pathology. Amyloid-bearing plaques were demonstrated by A beta P immunolabeling and thioflavine-S staining. Neuritic changes in the form of dystrophic neurites were observed with the aid of antibodies against PHF, Alz-50, as well as antibodies against several neuropeptides (i.e., substance P, somatostatin, and neurotensin) and the acetylcholine biosynthetic enzyme, choline acetyltransferase. By using a graded range of pathologic changes both within and across the patient population to provide us with a means of evaluating plaque deposition from its earliest to most advanced stages of development, we observed in patients and/or regions of the amygdala displaying a mild degree of pathologic change A beta P deposition in the absence of any neuritic changes. With increasing density of A beta P, however, we began to observe dystrophic neurites within plaques. In regions of relatively few plaques, the dystrophic neurites were immunolabeled only with antibodies against the various neurotransmitters and they lacked evidence of cytoskeletal pathology (i.e., Alz-50 or PHF). Only as the density of A beta P increased further within a region, were dystrophic neurites observed that exhibited Alz-50 or PHF. In no instance did we observe a relationship between the density of A beta P deposition and the density of Alz-50 or PHF-immunoreactive neurons. Collectively, our data suggest that the deposition of A beta P is an early pathologic event in senile plaque formation. Thereafter, swollen neurites can be seen in the vicinity of A beta P. This early neuritic response, which can first be visualized by immunolabeling for one or another transmitter substance, is followed by alterations in the cytoskeleton as recognized initially by antibodies to Alz-50 and subsequently by the presence of PHF.

Evidence that transmitter-containing dystrophic neurites precede those containing paired helical filaments within senile plaques in the entorhinal cortex of nondemented elderly and Alzheimer's disease patients.

Within the amygdala of elderly subjects and patients with Alzheimer's disease (AD), we recently found evidence suggesting amyloid beta-protein (A beta P) deposition occurs before the appearance of dystrophic neurites. Moreover, these data suggested dystrophic neurites initially lack evidence of cytoskeletal pathology although with time and further maturation, the dystrophic neurites display an altered cytoskeleton as evidenced by their immunoreactivity to Alz-50 and paired-helical filaments (PHF). These findings are of particular relevance to our understanding of the sequence of pathologic events in AD and thus it has become important to determine whether these events are unique to the amygdala or are representative of a more general pattern which can be found throughout the brain. Using a battery of antibodies to markers that are characteristic of AD pathology (i.e., A beta P, PHF, and Alz-50), three peptidergic neurotransmitters (neurotensin, somatostatin, and substance P), and one neurotransmitter biosynthetic enzyme (choline acetyltransferase), we examined the entorhinal cortex (EC) of three groups of subjects (AD, normal elderly, and a group of nondemented elderly with numerous senile plaques). The EC was studied, in part, because it is well recognized as a brain region displaying severe and, most importantly, early pathologic changes. Like the amygdala, we found evidence that amyloid beta-protein immunoreactive (A beta P-IR) and thioflavine-S-positive senile plaques occur within the EC prior to the appearance of transmitter-, Alz-50-, or PHF-immunoreactive dystrophic neurites. We also observed transmitter-immunoreactive dystrophic neurites in the absence of Alz-50 or PHF-immunolabeled dystrophic neurites and transmitter- and Alz-50-IR dystrophic neurites in the absence of those containing PHF. Collectively, these findings were similar to those seen within the amygdala and thus reinforced the concept that A beta P deposition is the primary event in plaque pathology, and this deposition is subsequently followed by the appearance of dystrophic neurites which retain their transmitter phenotype yet lack an altered cytoskeleton. With time, these dystrophic neurites develop cytoskeletal alterations and become immunoreactive to Alz-50 and PHF.

Localization of cytochrome oxidase (COX) activity and COX mRNA in the perirhinal and superior temporal sulci of the monkey brain.

Cytochrome oxidase (COX) activity and COX II mRNA expression were localized in the perirhinal and superior temporal sulci of the rhesus monkey brain. In both regions, a laminar distribution of COX activity and COX II mRNA was observed. COX activity was intense in layers I and IV and were localized to the neuropil. In contrast, COX II mRNA was localized to neuronal cell bodies. In the prorhinal region, highest levels of COX II mRNA was detected in cell bodies of layers II and IV, and in the perirhinal region, in cell bodies of layers III and V-VI. In the superior temporal sulcus, COX II mRNA was detected in cell bodies of layers III and V-VI. Thus, COX II mRNA and COX activity are uniquely localized in the cortical layers and to those neurons that support cortico-cortical connections.

Differential expression of cytochrome oxidase (COX) genes in different regions of monkey brain.

A frontal pole cDNA library from monkey (Macaca mulatta) brain was screened to identify mRNAs that are expressed more in frontal pole as compared to primary visual cortex. Three cDNA clones, whose greater expression was confirmed by Northern blot analysis, were identified as cytochrome oxidase (COX) subunits I, II, and III (COX I, II, and III). Each clone showed higher levels of mRNA in the frontal pole, dorsal lateral prefrontal cortex, and hippocampus than in the primary visual or somatosensory cortices. COX histochemistry of prefrontal, visual, and somatosensory cortical regions demonstrated heterogeneous distributions, with highest activity in dendrite-rich neuropil of the cortex. A laminar distribution of COX mRNA expression also was demonstrated with in situ hybridization. mRNA was detected in cell bodies and in apical dendrites. These results indicate region specific differences in the distribution of COX activity and in the corresponding mRNA for three of its subunits within the monkey brain. Such differences may be related to differences in the distribution of neuropil as compared with cell bodies among the brain regions studied, and may be relevant to selective vulnerability in Alzheimer's disease.