Neuronal and glial gene expression in neocortex of Down's syndrome and Alzheimer's disease.

The association cortex of Down's syndrome (DS) predictably and prematurely undergoes neurofibrillary degeneration of Alzheimer type. Hence studies of DS are potentially useful in defining the earliest pathogenetic events in Alzheimer's disease (AD). Previous reports have described altered expression of several mRNAs in AD cortex; but the pathogenetic stage at which expression of these mRNAs begins to deviate from the norm has not been defined. We have examined this issue in neocortex of DS. Expression of mRNAs, known to be altered in AD cortex, was studied by Northern analysis, comparing frontal cortex of DS (15-45 years) with age-matched controls and with AD. Chromosome 21- and non-21-encoded mRNAs were studied, including transcripts expressed preferentially in neurons (neurofilament light subunit and amyloid precursor transcripts) and in glia (glial fibrillary acidic protein [GFAP] and S100 beta). Chromosome 21-encoded mRNAs were increased in DS cortex as expected. Except in the DS case with extensive neurofibrillary degeneration, GFAP was expressed at levels significantly below the control, suggesting that trisomy 21 exerts a suppressive effect on GFAP gene expression. We found no instance in which AD-type changes of transcript expression preceded the appearance of neurofibrillary degeneration. The findings indicate that in trisomy 21, certain changes of mRNA prevalence previously described for AD neocortex are not a necessary antecedent to neurofibrillary degeneration.

Neurofilamentous axonal swellings as a normal finding in the spinal anterior horn of man and other primates.

To define the nature and extent of axonal swellings in the normal spinal anterior horn, we studied the spinal cords of patients five days to 83 years of age from a general autopsy population. Axonal swellings were routinely found in the anterior horn of the cervical and lumbosacral spinal cord. The swellings measure 5-50 micron in diameter and are most numerous at the anterior edge of the anterior horn. They first appear about five months of age and appear to increase in number until about 20 years of age, with no increment thereafter. Ultrastructurally, they are filled with neurofilaments and surrounded by a thin myelin sheath. Most are probably aberrant components of motor axons. Identical axonal swellings, in the same anatomical site, were found in the spinal cords of cynomolgus and rhesus monkeys. On the basis of their natural history and morphologic features, they should be distinguished from the neuroaxonal dystrophy of aging. The largest of them resemble the neurofilamentous axonal swellings of early onset motor neuron disease but occur in much smaller numbers. Moreover, location on the proximal axon could not be demonstrated for any of these swellings. An awareness of this normal phenonemon is essential for the interpretation of axonal swellings in the spinal cord.

Doxorubicin intoxication: neurofilamentous axonal changes with subacute neuronal death.

Neurofilamentous axonal swellings occur in various chronic neuronal degenerations in man and animals. The pathogenesis of these swellings in the setting of neuronal degeneration remains unclear. A toxic model of neuronal degeneration can be produced by doxorubicin. This agent impairs DNA-dependent RNA synthesis and produces subacute neuronal death. The aim of the present study was to investigate whether neurofilamentous axonal swellings occur in association with neuronal nuclear derangement and subacute neuronal death produced by doxorubicin. We investigated the evolution of changes seen in retinal ganglion cells and their axons after an intravitreous injection of doxorubicin in rats. The earliest changes were in the nuclei of the retinal ganglion cells. Later, transient axonal swellings filled with neurofilaments were prominent. These neurofilamentous swellings preceded the subacute neuronal cell death. To determine whether these changes represent a direct effect of the agent on the axon, we injected doxorubicin directly into the sciatic nerve. This local injection did not produce similar changes in the axons. These results suggest that in this model neurofilamentous axonal swellings precede neuronal cell death and may be due to a primary insult to the nerve cell body.

Gene expression in Alzheimer neocortex as a function of age and pathologic severity.

Previous studies have shown a marked decline in neuronal and an increase in glial gene expression in Alzheimer's disease (AD) neocortex. Severity of pathologic changes may be greater in presenile AD (PAD) than in senile AD (SAD). We evaluated whether changes in transcript expression were altered as a function of age or pathologic severity. Northern analysis revealed a marked (> 50%) decline in expression of transcripts for the neurofilament light subunit and the major amyloid precursor protein (APP) isoforms in both PAD and SAD. Expression of these neuronal transcripts declined as a function of age in AD and control cases. Expression of the glial fibrillary acidic protein (GFAP) transcript was increased in AD, particularly in the presenile group. AD cases with larger numbers of neurofibrillary tangles had higher levels of GFAP transcript; AD cases with larger numbers of senile plaques had higher levels of APP695 transcript. We conclude that the neuronal mRNA decrements of AD are superimposed on an age-related decline. Age-related shift in expression of certain genes may account for the differences in pathologic severity of PAD and SAD.

Aging is associated with divergent effects on Nf-L and GFAP transcription in rat brain.

We studied the effects of advancing age on the expression of several proteins important in the structure and function of the nervous system. Brains of young (3 month), middle-aged (13 month), and old (29 month) male Fischer 344 rats were examined. Run-on transcription and Northern blot hybridizations were used to determine gene-specific transcription rates and mRNA levels, respectively. With advancing age, there was a decrement in the transcription rate and mRNA levels for neurofilament-light subunit (Nf-L), but an increment in the transcription rate and mRNA levels for glial fibrillary acidic protein (GFAP). Proteolipid protein (PLP) mRNA levels were attenuated between 3 and 13 months of age, whereas amyloid precursor protein (APP) mRNA levels were attenuated in the middle-aged but not the old animals. Transcription rates for alpha-actin and fos, and mRNA levels for alpha-actin, were unaffected. These observations indicate divergent transcriptional regulation of several genes, notably Nf-L and GFAP, in the aging mammalian forebrain.

Cognitive impairment in the nondemented elderly. Results from the Canadian Study of Health and Aging.

STUDY OBJECTIVE: To describe a population that was categorized as "cognitively impaired not demented" (CIND) and to examine the utility of some of the proposed criteria for describing this degree of cognitive impairment. DESIGN: Population-based prevalence study of dementia in those subjects who were 65 years and older. SETTING: Community and institutional settings in Canada. SUBJECTS: Individuals who underwent a clinical evaluation (N = 2914). INTERVENTION: Initial screening with the Modified Mini-Mental State Examination (3MS) to identify potential cognitive impairment; the 3MS was followed by a detailed clinical examination to confirm the presence of dementia and to determine the probable cause. Clinical examinations were performed on all those subjects who were residing in institutions, those in the community with a 3MS score less than 78, and a sample of those in the community with a 3MS score of 78 or more. Neuropsychological testing was performed as part of the clinical examination when the 3MS score was 50 or more. At the conclusion of the assessment, subjects were categorized as being cognitively normal, CIND, and demented. MEASUREMENTS: Frequency of a diagnosis of CIND; demographical, cognitive, and functional characteristics of cognitively normal and CIND subjects and those with early and late dementia; and proportion of subjects who were CIND and met the proposed criteria. RESULTS: Subjects who were categorized as CIND were common and fell between cognitively normal subjects and those with dementia in terms of age, 3MS score, general intellectual function, and performance of daily activities. Because of the restrictive inclusion and exclusion criteria, the proposed criteria for cognitive impairment described only 30% of our subjects who were CIND. CONCLUSIONS: Subjects who were categorized as CIND appeared to be distinct from and intermediate between subjects with dementia and cognitively normal subjects. Most individuals did not meet the criteria that were evaluated for describing this group. While the various criteria that were evaluated may accurately define a select subset of cognitively impaired individuals, the natural history and prognosis of such groups, currently unknown, may not be generalizable to the larger population of subjects who are CIND. Further work is needed to clearly define this group, and longitudinal studies are required to determine an outcome.

Neurotoxic effects of cisplatin therapy.

Swelling of the optic disc and loss of tendon reflexes developed in a 3 1/2-year-old girl after 11 high-dose courses of cisplatin (cis-dichlorodiammine platinum [II]) therapy for recurrent sacrococcygeal teratoma. Postmortem examination demonstrated optic disc swelling; the spinal cord showed loss of myelinated fibers and gliosis of the dorsal columns. To our knowledge this case is the first in which the neuropathologic changes associated with cisplatin therapy have been demonstrated by postmortem examination.

Postinfectious leukoencephalitis complicating Mycoplasma pneumoniae infection.

Neuropathological findings in a patient with fatal neurological complications due to infection with Mycoplasma pneumoniae were similar to those seen in postinfectious encephalitis and acute hemorrhagic leukoencephalitis. This case supports the hypothesis that immune mechanisms play a role in the pathogenesis of neurological symptoms during mycoplasmal infections.

Prevalence and types of dementia in the very old: results from the Canadian Study of Health and Aging.

We report on the prevalence of dementia in Canadians age 85 years and older. The purpose of this study was to determine whether the prevalence of dementia continued to increase in the very old, and to define the types of dementia and their relative proportions in this age group. We collected data as part of the Canadian Study of Health and Aging (1990 to 1992), which consisted of a sample of 1,835 subjects from a population of 283,510 Canadians who were 85 years of age and older residing in the community or in institutions. The prevalence of dementia in the 85 years and older group was 28.5%, more than twice that of the 75- to 84-years cohort. The prevalence of dementia of 23% in the 85- to 89-years sample (n = 1,332) increased to 40% in the 90 to 94 years group (n = 371) and, in the 95 years and older sample (n = 104), reached 58%. Overall, Alzheimer's disease (AD; probable or possible) accounted for 75% of all dementias; a vascular etiology alone accounted for 13% of dementias. The proportion of clinically diagnosed AD cases to vascular dementia cases increased significantly after age 65 and was higher in the 85+ group than in a younger cohort (65 to 84 years).

The diagnosis of Huntington's disease.

We investigated all patients in Maryland reported to have Huntington's disease (HD), and found considerable diagnostic inaccuracy. Fifteen percent of cases reported as HD actually had some other diagnosable condition; 11% of cases that met diagnostic criteria for HD had been given some other diagnosis. Diagnostic errors could be reduced by documentation of the family history by systematic interviewing of relatives and by demonstration of the characteristic disorder of voluntary movement in addition to chorea.

Diaphragmatic paralysis in motor neuron disease. Report of two cases and a review of the literature.

Two patients presenting with respiratory insufficiency had diaphragmatic paralysis secondary to adult-onset motor neuron disease (progressive spinal muscular atrophy). A review of the literature discloses seven similar cases, most of them reported in non-neurological journals.

The nucleus basalis in Huntington's disease.

The nucleus basalis of Meynert (nbM) provides most of the cholinergic input to the cerebral cortex. The loss of cortical choline acetyltransferase (CAT) activity in Alzheimer's disease (AD) and senile dementia of the Alzheimer's type (SDAT) appears to be related to a severe depopulation of the nbM in this dementia. In Huntington's disease (HD), by contrast, there is no loss of cortical CAT activity. The present quantitative study indicates that (1) there is no significant loss of neurons from the nbM in HD, and (2) that the previously described cytologic changes in the neurons of this nucleus in HD patients do not differ significantly from controls. These findings are consistent with the working hypothesis that the types of dementia associated with reductions of neocortical CAT activity are characterized by dysfunction or death of neurons in the nbM, but dementing disorders with normal neocortical CAT activity manifest no major abnormalities in this cholinergic nucleus of the basal forebrain.

Beta-amyloid precursor protein gene is differentially expressed in axotomized sensory and motor systems.

The beta-amyloid precursor protein (APP) is involved in the degenerative and regenerative neural changes associated with aging and Alzheimer's disease. We studied the regulation of APP gene expression in a paradigm of degeneration and regeneration, the axotomized rat sciatic system. The sciatic nerves of rats were crushed and at intervals between 4 and 60 days, the affected dorsal root ganglia and spinal cord segments were processed for Northern analysis and in situ hybridization to evaluate various APP mRNA species. After nerve crush, dorsal root ganglia APP mRNA levels are increased for both APP695 (695 amino acids) and APPKPI (Kunitz protease inhibitor). Following reinnervation, APP695 returns to baseline but APPKPI remains elevated. In spinal cord there is a decrease of APP695, which returns to baseline following reinnervation. If regeneration is prevented, the initial phase of post-axotomy response for all APP forms persists for at least 60 days in both dorsal root ganglia and spinal cord. In situ hybridization confirms that the changes are referable to neurons. These findings indicate that neuron-target interactions are important in APP gene regulation; that the APP695 and APPKPI transcripts are differentially regulated following neuronal injury; and that different neuronal populations regulate APP expression in a cell-type specific manner.

Neuronal gene expression in amyotrophic lateral sclerosis.

To characterize neuronal gene expression in amyotrophic lateral sclerosis (ALS), we quantitated one glial and three neuronal mRNAs in spinal cords of 7 subjects with ALS and 11 controls. The ALS cases showed no loss of mRNA for the neurofilament light subunit when assessed with in situ hybridization. Northern analysis, and RNase protection assay; and no loss of mRNA for amyloid precursor protein or a growth-associated protein (GAP-43/B-50) on Northern analysis. ALS cords also showed no significant change in glial mRNA. Our findings indicate that expression of these neuronal mRNAs is well maintained in ALS-afflicted spinal cord. They do not support the hypothesis of a generalized impairment of neuronal gene transcription in the pathogenesis of this disorder.

Increase in protein and tubulin mRNA synthesis in frog sensory neurons treated with the adenylate cyclase activator, forskolin.

We are interested in the role cyclic AMP may play as a mediator of growth factor-induced gene expression in regenerating peripheral nerves. As a first step, we investigated mRNA levels and protein synthesis in intact frog dorsal root ganglia (DRG) treated with the adenylate cyclase activator, forskolin in vitro. Forskolin (10-7 M) increased intraganglionic cyclic AMP concentration 3-fold within 40 min of application and maintained this concentration through 60 min, when the drug was withdrawn. Addition of forskolin to isolated DRG neurons for 1 h increased the incorporation of [3H]leucine into TCA-insoluble material beginning 12 h after the withdrawal of forskolin. Axonally transported labeled material was increased almost 2-fold by 12 h. The effect of forskolin could be blocked by the simultaneous addition of actinomycin D, but not if actinomycin D was added 1 h later. Northern and dot-blot analysis of RNA extracted from the treated ganglia indicated that an mRNA coding for an α-subunit of tubulin was increased by treatment with forskolin. 2D PAGE also demonstrated an increase in an α-subunit of tubulin. An increase in neuronal cyclic AMP appears to selectively increase the production of specific proteins and may contribute to the production of macromolecules involved in the initiation and stimulation of axonal regeneration.

Selective interruption of axonal transport of neurofilament proteins in the visual system by beta,beta'-iminodipropionitrile (IDPN) intoxication.

Beta,beta'-iminodipropionitrile (IDPN) is an agent that produces a marked impairment in the transport of neurofilaments. Its effect on other slowly transported cytoskeletal components such as tubulin and actin is variable. Previous studies have evaluated transport of neurofilaments after IDPN intoxication in a neurofilament-rich system (sciatic motor nerves) and in a system devoid of neurofilaments (axons of the dorsal motor nucleus of the vagus). In the former, IDPN impairs the transport of tubulin and actin but to a lesser degree than it does neurofilament proteins. In the latter, tubulin and actin transport were not impaired, and neurofilament proteins were not present. In this study we evaluated the transport of the cytoskeletal components in a system with an intermediate amount of neurofilaments (the visual system). In the visual system, there is a selective and marked (50%) impairment in the transport of neurofilaments with no impairment in transport of tubulin or microtubule-associated proteins (tau group). We conclude that these different patterns of impairment in transport reflect the differences in pre-intoxication neurofilament content of the nerves examined, the effect of IDPN on the transport of the other components of slow transport being secondary to the presence of stagnated neurofilaments. This model also suggests that transport of neurofilaments can be selectively impaired without producing an effect on other major slow transport components.

Neurofilament gene expression following beta,beta'-iminodipropionitrile (IDPN) intoxication.

beta,beta'-Iminodipropionitrile (IDPN) is an agent that produces a disorganization of the axonal cytoskeleton with massive accumulation of neurofilaments in the proximal axon. Abnormalities in axonal transport of neurofilament proteins and in their phosphorylation occur in this model. In this study we evaluated the gene expression of neurofilament and other cytoskeletal components at an early, intermediate and late stage of intoxication to determine whether this neuropathy is directly due to or secondarily affects the expression of these components. Specific cytoskeletal mRNA expression was evaluated in the spinal cords of rats treated with IDPN for varying durations using Northern analysis and in situ hybridization. Our results show no qualitative or quantitative alteration in the mRNA expression of the neurofilament triplet, alpha-tubulin, alpha-actin or glial fibrillary acidic protein. We conclude that abnormalities at various stages of cytoskeletal processing such as the early disorganization of the cytoskeleton, the impairment of neurofilament transport, and the long-term redistribution of neurofilaments along the axon are not directly due to, nor do they affect the gene expression of cytoskeletal components in IDPN neuropathy.

Brainstem findings in Huntington's disease. Possible mechanisms for slow vertical saccades.

Quantitative, morphometric studies of the rostral interstitial nucleus of the medial longitudinal fasciculus (riMLF) were performed on the brains of four patients with Huntington's disease (HD) who had shown slow vertical saccades, and on the brains of three control subjects. Only one HD brain showed a statistically significant decrease in the number of larger neurons in the riMLF though all four brains showed non-specific gliosis. Taken with results from physiological and other clinical studies, the present data suggest that slow vertical saccades in HD are due, at least in part, to disordered inputs to the riMLF.

Neuropathology of the antischistosomal agent amoscanate administered in high oral doses to rats.

Amoscanate is a highly effective antischistosomal agent when administered as a 5% absorbable aqueous suspension. This preparation produces lesions in the brains of young adult rats given extremely high oral doses. Lesions are confined to areas adjacent to the lateral ventricles and are dominated by necrosis of the neuropil of the medial striatum, with relative sparing of bundles of myelinated fibers in the necrotic zone. There is a striking accumulation of calcium-containing microgranules in these areas. The ependyma survives on the ventricular wall overlying the necrotic zone, but pyknosis and increased extracellular space are apparent among ependymal and subependymal cells in the region. Occasionally, fibers of the fornix are focally damaged in immediate proximity to the lateral ventricle; the corpus callosum is rarefied, and microhemorrhages also occur. It is hypothesized that high concentration of the toxic agent in ventricular cerebrospinal fluid plays an important role in pathogenesis. The neuropil of the medial striatum is selectively vulnerable.

Expression of neuronal mRNAs in Alzheimer type degeneration of the nervous system.

There is extensive evidence for decrements of gene expression in AD, at several levels in the process. There is also evidence for increments of expression of some genes. Message for the amyloid precursor protein (APP), for example, is elevated in surviving neurons of certain subcortical populations in AD. We evaluated expression of message for APP as well as for certain neuronal and glial cytoskeletal proteins in the cortex of six cases of AD. Neuronal mRNAs, including that for APP, were significantly decreased when compared with control cortex, whereas the glial mRNA was increased. We have projected studies to determine the evolution of these mRNA decrements in Alzheimer-type degeneration. The rationale for these studies and preliminary findings are discussed.