Neurodegeneration最新文献

We studied the microglial reaction in mice using the 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP)-induced model for Parkinson's disease (PD). Microglial cells were identified by means of the Griffonia simplicifolia lectin (GSA-I-B₄). Dopaminergic neurons were marked by tyrosine hydroxylase antibodies. Microglial activation was demonstrated by an increase in cellular number and changes of morphology (increased lectin staining, larger cell bodies and thicker processes) were seen in the substantia nigra from the 1st to the 14th day and in the striatum from the 1st to the 4th day after intoxication. Depletion of dopaminergic neurons was most pronounced 7 and 14 days following the treatment. The results suggest that microglial activation may be involved in the sequence of pathological changes that lead to dopaminergic neuronal damage after MPTP intoxication.

Stain sensitivity is a key factor in estimating the frequency of plaques and neurofibrillary tangles in Alzheimer's disease (AD), making it essential that the sensitivity and selectivity of detection methods for identifying these lesions is maximized. Several new, improved techniques have recently been described, although these methods have not been compared quantitatively with those techniques currently recommended for use in standardized diagnostic protocols. In the present study, eight different stains were examined for their selectivity and sensitivity in detecting plaques and tangles in serial tissue sections from AD and control brains. Techniques compared were immunohistochemistry for tau and β-amyloid, thioflavin S, nickel peroxidase method, and four silver impregnation techniques (Gallyas silver iodide, Campbell-Switzer-Martin, Garvey's modified Bielschowsky and methenamine silver methods). Among these eight staining techniques, the nickel peroxidase proved the most reliable method for the demonstration of the histopathological lesions of AD. This method labels all morphological types of plaques and tangles within a single tissue section, and provides several advantages for the analysis of lesion progression and distribution.

The loss of dopaminergic neurons from the substantia nigra in Parkinson's disease (PD) may provoke a reorganization of cellular interactions in the nigrostriatal pathway. Indeed, a plasticity of putative corticostriatal synapses has been evidenced in the striatum of rats with a 6-hydroxydopamine-induced lesion of the substantia nigra. However, to our knowledge, synaptic plasticity in the striatum has not previously been investigated in human PD. In this study, we have analysed, at electron microscope level, the morphological characteristics of the synapses formed by afferents in asymmetric contact with dendritic spines of neurons in the caudate nucleus of three patients with PD and three matched controls. The length of the postsynaptic densities and the number of perforated synapses were both significantly increased (24 and 88%, respectively) in the PD patients; the size of these afferents and the surface area occupied by their mitochondria also showed an increase (24 and 50%, respectively), although not statistically significant. The size and density of dendritic spines and the size of postsynaptic density perforations were unchanged. These data indicate the presence of plasticity of the putative corticostriatal synapses in PD and suggest a hyperactivity of cortical afferents to GABAergic neurons.

This preliminary study aimed to test the proposal that neuronal death is triggered by expression of specific genes. In rat pups, the sciatic nerve was injured unilaterally on the first day after birth and actinomycin D, an RNA synthesis inhibitor, was administered 3 days later in a lower and higher dose to rat pups just prior to onset of motoneurone death induced by the lesion. Four weeks later, sciatic motoneurones from operated and contralateral pools were counted and their size measured. Significantly fewer motoneurones (16.7% ± 2.9 SD) survived when the animals were treated with a lower dose of the inhibitor compared to saline treated controls (36.6% ± 12.7 SD). Experiments recording tension generated in soleus muscle in response to sciatic nerve stimulation, at different ages following nerve crush, suggested that the treatment with the RNA synthesis inhibitor may have delayed regeneration of motor axons back to the muscle. However, survival of motoneurones after treatment with the higher dose did not differ significantly from controls (27.5% ± 1.3 SD. Nevertheless, the higher dose significantly reduced growth of motoneurones after 4 weeks. Therefore, the higher dose, although impeding normal development of motoneurones, is less neurotoxic than a lower dose. This suggests that a balancing of conflicting effects may have occurred. The neurodegenerative effects of delayed reinnervation induced by RNA synthesis inhibition may be balanced by some neuroprotective effects at a higher dose. More extensive studies are required to validate these pilot findings.

We have examined by immunohistochemistry the parvalbumin-containing neurons of the substantia nigra in patients with Parkinson's disease and in age-matched controls. Parvalbumin, a calcium binding protein, is involved in buffering intracellular calcium and in this study was localized within the majority of non-pigmented neurons of the human pars reticulata. Previous studies have shown that the parvalbumin-immunoreactive pars reticulata neurons are GABAergic and project to the motor thalamus and tectum. Their increased output, due to the loss of dopaminergic inhibition in Parkinson's disease, decreases cortical activation via thalamic pathways, causing parkinsonian symptoms. In Parkinson's disease there was a significant loss of parvalbumin-immunoreactivity from these neurons, though there was no evidence of actual cell loss. This loss of parvalbumin-immunoreactivity was detected only in those cases with end-stage Parkinson's disease.

To gain insight into the role of microglia in the formation of senile plaques (SP), especially in the generation of the two major molecular species of amyloid β protein (Aβ) with different carboxyl (C)-termini, Aβ40 and Aβ42(43), we conducted double immunolabelling studies on tissue sections from the brains of Alzheimer's disease (AD) and non-demented aged individuals using antibodies to the C-termini of Aβ and ferritin, a marker for microglia. All SP were Aβ42(43)-positive in AD as well as in non-demented individuals, only a proportion of which were Aβ40-positive. Both in AD and in non-demented individuals, approximately 2/3 of the Aβ40-positive SP were typical SP with amyloid cores, these being almost invariably associated with microglia. Aβ40-positive, uncored SP were also frequently associated with microglia (mean, 74%), whereas only 24% of Aβ40-negative, uncored SP contained microglia. These results suggest that microglia may play a role in the maturation of SP, especially in the generation of Aβ40.

The abnormal form of the prion protein (PrP^Sc), a synthetic prion protein peptide fragment (PrP^106–126) and fragments of the Alzheimer's protein precursor, APP, have been shown to be cytotoxicin vitro.We have used synchronous, clonal cell models originally developed to study the toxicity of the Alzheimer's disease amyloid peptide, Aβ25–35, to investigate the actions of PrP peptides. We found that the cytotoxicity of the PrP^106–126depends on its state of aggregation and the cellular expression of PrP^C, and is independent of a loss of MTT reduction activity in the absence of cell death associated with the cellular effects of Aβ25–35. These factors may play a role in the lesion specificity of different pathological phenotypes of prion-protein related diseases.

Disease specific forms of a host encoded cell surface sialoglycoprotein called prion protein (PrP) accumulate during the incubation period of the transmissible spongiform encephalopathies. A 33–35 kDa disease specific form of PrP is partially resistant to protease digestion whereas the normal form of PrP can be completely digested. Proteinase K digestion of the murine disease specific form of PrP produces diverse forms of low molecular weight PrP, some of which are N-terminally truncated at amino acid residue 49 or 57 within the octapeptide repeat segment. Amyloid plaques are a pathological feature of many of the transmissible spongiform encephalopathies and are composed of PrP. Using synthetic peptide antibodies to the N-terminus of PrP (which is not present in truncated disease specific PrP) and antibodies to the protease resistant fraction of PrP we have immunostained plaques and pre-amyloid deposits in the brains of mice, experimentally infected with the 87V strain of scrapie, for examination by light and electron microscopy. Classical fibrillar amyloid deposits in plaques as well as pre-amyloid deposits were both immunostained by antibodies to the N-terminus of PrP and to the protease resistant core of the PrP molecule. This suggests that both N-terminal and core amino acid residues are present in disease specific PrP released from scrapie infected cells in vivo. The results also suggest that N-terminal truncation of PrP may not be essential for formation of amyloid fibrils.

Oxotremorine-M stimulated [³⁵S]GTPγS binding was used to assess acetylcholine muscarinic M2 receptor mediated G-protein function in superior frontal cortical, superior temporal cortical and hippocampal membranes from a series of Alzheimer's disease and matched control subjects. No significant differences were seen in basal [³⁵S]GTPγS binding between the groups. The maximal level of oxotremorine-M stimulated [³⁵S]GTPγS binding over basal was significantly increased in Alzheimer's disease superior temporal cortex, suggesting an enhanced muscarinic M2 receptor-G-protein coupling efficiency in this region. In contrast, the maximal level of oxotremorine-M stimulated [³⁵S]GTPγS binding over basal was unaltered in Alzheimer's disease superior frontal cortex and significantly reduced in Alzheimer's disease hippocampus. Western immunoblotting using antisera towards the α-subunits of those G-protein types known to couple muscarinic receptors, revealed that G_qαand G_iα, but not G_oα, levels were significantly reduced in Alzheimer's disease superior temporal cortex. Neither G_qα, G_iαnor G_oαlevels were significantly altered in Alzheimer's disease superior frontal cortex or hippocampus. These results suggest that the efficacy of muscarinic M₂receptor G-protein coupling shows regional selective changes in Alzheimer's disease postmortem brain with deficits occurring only in a region that shows severe pathology.

Enzyme activities of α-ketoglutarate dehydrogenase complex (αKGDHC) and one of its constituent subunits, dihydrolipoamide dehydrogenase (E3), are reported to be reduced in non-CNS tissues of some patients with Friedreich's ataxia (FA); however, the results are highly confliicting. To determine whether an enzyme abnormality occurs in brain, we measured immunoreactive levels of the three αKGDHC subunits, namely, α-ketoglutarate dehydrogenase (E1), dihydro-lipoamide succinyltransferase (E2) and E3 in postmortem frontal, occipital and cerebellar cortices of 18 control subjects, 9 patients with FA and, for comparison, 12 patients with spinocerebellar ataxia type 1 (SCA1). Decreased (−20 to −31%) levels of E3 were observed in all three examined areas of the patients with FA with the changes statistically significant in cerebellar and frontal cortices. The E3 reduction could be explained by a loss of αKGDHC or other dehydrogenase complexes (e.g. pyruvate dehydrogenase complex) which utilize this subunit. In SCA1, enzyme changes were limited to E2 in cerebellar (−26%) and frontal (−19%) cortices. Although the E3 and E2 reductions are only slight, and may represent secondary events, the changes in this key Krebs cycle enzyme could exacerbate degenerative processes in both of the spinocerebellar ataxia disorders.