Cholesterol and tau protein--findings in Alzheimer's and Niemann Pick C's disease

Niemann Pick C (NPC), a fatal autosomal-recessive neurovisceral lipid storage disorder, is a juvenile dementia with massive nerve-cell loss and cytoskeletal abnormalities in cerebral neurons. These abnormalities consist of tangles of tau protein, which is otherwise highly soluble and usually stabilizes the microtubules. Immunologically and ultrastructurally similar tangles are seen some decades later in patients with Alzheimer's disease (AD). There is evidence that tangle-bearing cells in both diseases show higher levels of free (i. e. filipin-positive) cholesterol than adjacent tangle-free nerve cells. The cholesterol accumulates either in a more diffuse way (mainly in AD) or in granule-like accumulations (mainly in NPC). In NPC, neuron cholesterol may originate from sources other than the alimentary tract. Experiments with a NPC mouse model revealed that even in pure neuron cultures, the NPC -/- neurons accumulate free cholesterol in contrast to NPC-wt littermates, suggesting that the cholesterol is either synthesized by the neurons or liberated from degenerated ones before being taken up by the endosomal/lysosomal pathway. The accumulation of free cholesterol in the somata of NPC neurons is associated with a decrease of cholesterol levels in myelin sheaths. In terms of tau protein, NPC -/- mice exhibit higher levels of AT8-positive tau, suggesting that the phosphorylation-dependent mAb AT8 has detected a tau-epitope in a state considered to represent early stages of tangle formation. Concomitantly to the increase in free intracellular cholesterol, the rate-limiting enzyme in cholesterol and isoprenoid biosynthesis, HMG-CoA reductase, was found to be significantly reduced. Experimental blockade of the enzyme's activity by application of the lipid-lowering drug lovastatin showed subcellular shifts in tau phosphorylation as monitored with mAbs AT8, 12E8 and others. In summary, the data showed interesting similarities between NPC and AD suggesting some pathological metabolic pathway in common.

Transneuronally altered dendritic processing of tangle-free neurons in Alzheimer's disease

In Alzheimer's disease (AD), changes in dendritic morphology can be regarded as a result of an inherent disease-specific process associated with the formation of neurofibrillary tangles. Using three-dimensional morphometrical techniques and neuropatholologically staged tissue (Braak classification) of 32 cases, we demonstrate alterations in the dendritic length, branch order and number of segments of a tangle-free neuronal population in the AD-afflicted hippocampus, i.e. parvalbumin-containing cells of the fascia dentata. These alterations occurred primarily on the apical dendritic tree, the target of the entorhinal input. Mean of relative dendritic length, branch order and number of dendritic segments of apical dendrites decreased significantly, by 40-70% comparing stage V to stages 0 or I. In contrast, basal dendrites receiving no entorhinal input did not show significant changes. Entorhinal neurons projecting to the hippocampus are the first to be affected in AD and the first to die, resulting in hippocampal deafferentation. Therefore, this input-specific dendritic alteration of tangle-free neurons suggests that AD is confounded with a transneuronal component resulting from deafferentation. Experiments showed that deafferentation results in altered dendritic geometry causing an impaired signal integration. Thus, transneuronally altered dendritic signal integration might occur in neurons devoid of the major intraneuronal hallmark of AD, i.e. the neurofibrillary tangle.

Anorexia nervosa and sudden death in childhood: clinical data and results obtained from quantitative neurohistological investigations of cortical neurons

A crude rate of mortality of 5.9% has been quoted for Anorexia nervosa (AN) in recent studies. There are different causes of death ranging from suicide to sudden death. Autopsy data are extremely rare about brain alterations in deceased AN patients. Reported in this study is a female patient, aged 13.5 years, who died of acute AN. Quantitative neurohistological investigation post mortem was performed on her brain. Results were compared with data obtained from a girl of the same age with no contributory neuropsychiatric findings. In the cortex of the anorexia case beside typical pyramidal neurons, a slim neuron type with one extremely long basal dendritic field was found to occur more frequently than normal. In the neurons of the AN case, the ramification pattern of single basal dendritic fields was found to be reduced and changes in the spine morphology, as well as reduction in spine density, were observed. However, a simultaneous lengthening of the terminal dendrites of higher order gave some evidence for repair mechanisms and neuronal plasticity. The AN-specific implications of these findings are discussed. The conclusion is that all AN deaths should be reported together with descriptions of causes and cerebral alterations.

[Quantitative studies in lamina V-pyramidal neurons of the frontal brain after infantile brain damage]

Cortical pyramidal neurons (lamina V, Area 10) were investigated in brain autopsy material obtained from 8 patients with serious bodily and mental retardation, aged between 3 and 24 years. Quantitative neuromorphological estimations of the ramification degree, length and spine density of apical or basal single dendritic fields (SDF) of these neurons were carried out using the impregnation technique of GOLGI and a computer-assisted quantification method. The results were compared with related data found in the prefrontal cortex (Area 10 according to Brodmann) of patients in the same age without neuropathological or psychiatric disturbances. During the normal maturation period the development of dendritic length and spine density reflects the diminution of the relative excess of growth during the early postnatal phase. When comparing the dendritic length or spine density of a SDF in children with that of juvenile adolescents or young adults, the length is reduced by 40%, the spine density by 15%. In the brains of mentally retarded children we found the dendritic length reduced by 30% (apical) or 40% (basal), and a further elongation and ramification of the dendritic tree (especially nonramified terminal dendrites) in juvenile adolescents. However, the spine density showed a significant deficit of about 30% in children as well as in juvenile adolescents. This spine loss may be morphologically related to the symptoms of mental retardation. In these cases, the genetically controlled spine distribution pattern along the dendritic orders was not changed. The results obtained are discussed by taking into consideration data from animal experiments as well in view of the normal or disturbed neuronal development.

[Correlation of neuronal parameters of cingulate lamina V and lamina III pyramidal neurons in the rat]

The data obtained by quantitative neuromorphological investigations of pyramidal cells from the cingulate cortex of 3 month old rats gave evidence for significant statistical correlation between different parameters of lamina III- as well as lamina V-pyramids. The spine-number counted in single apical dendritic fields (EDF) was highly positive correlated to the total apical spine-sum and the some correlation existed in the basal dendritic tree; i.e. the data obtained in a basal EDF were representative for the whole basal dendritic tree, respectively. In the fully developed pyramids the parameters of the apical dendritic tree were considered to be of stronger importance for the data collected from the whole dendritic tree of the neuron. However, in more primitive pyramids the parameters of the apical and basal dendritic tree were found to be of the same significance for the data of the whole neuron. The development of the apical dendritic tree when compared with the basal one gave never positive correlations in their sum parameters. Significant correlation was obtained between the length of the dendrites and the volumes of their distribution area. In fully developed regular pyramids the statistical analysis gave evidence for a higher importance of distal parts of the dendritic tree as representative for the sum parameters, in contrast to primitive pyramids with higher significance of the perikaryon-near parts. These primitive pyramids are quite abundant in the phylogenetically older mesoarchicortical and mesoneocortical parts of the cingular cortex.