Selective neuronal vulnerability is involved in cerebellar lesions of Guinea pigs infected with bovine spongiform encephalopathy (BSE) prions: Immunohistochemical and electron microscopic investigations

The cerebellar lesions of bovine spongiform encephalopathy (BSE)-infected guinea pigs were characterized as severe atrophy of the cerebellar cortex associated with the loss of granule cells, decrease in the width of the molecular layer, and intense protease-resistant prion protein (PrP^Sc ) accumulations that are similar to cerebellar lesions in kuru and the VV2 type of sporadic Creutzfeldt-Jakob disease. The aim of this study is to assess the relationships between the distribution and localization of PrP^Sc and synapses expressing neurotransmitter transporters in order to reveal the pathogenesis of the disease. We used cell-type-specific immunohistochemical makers recognizing glutamatergic and γ-aminobutylic acid (GABA)ergic terminals to identify terminals impaired with PrP^Sc accumulations. The distribution of PrP^Sc accumulations and immunoreactivity of synaptic vesicles were studied throughout the neuroanatomical pathways in cerebellar lesions. Time course study demonstrated that PrP^Sc accumulation showed a tendency to spread from granular layer to molecular layer. The immunoreactivity of vesicular glutamate transporter 1 (VGluT1) was localized in axon terminals of cerebellar granule cells, and decreased in association with the severity of PrP^Sc accumulations and loss of granule cells. Immunoreactivities of vesicular glutamate transporter 2 (VGluT2) and vesicular GABA transporter (VGAT) that exist in axon terminals of inferior olivary neurons and GABAergic synapses of Purkinje cells, respectively, were preserved well in these lesions. In brainstem, VGluT1 immunoreactivity decreased selectively in pontine nuclei that are a component of the pontocerebellar pathway, although other neurotransmitter immunoreactivities were preserved well. Our findings suggest that the selective loss of VGluT1-immunoreactive synapses subsequent to PrP^Sc accumulations can contribute to the pathogenesis of cerebellar lesions of BSE-infected guinea pigs.

Mapping of neurotrophins and their receptors in the adult mouse brain and their role in the pathogenesis of a transgenic murine model of bovine spongiform encephalopathy

Neurotrophins are a family of growth factors that act on neuronal cells. The neurotrophins include nerve growth factor (NGF), brain-derived neurotrophic factor (BDNF) and neurotrophin (NT)-3, -4 and -5. The action of neurotrophins depends on two transmembrane-receptor signalling systems: (1) the tropomyosin-related kinase (Trk) family of tyrosine kinase receptors (Trk A, Trk B and Trk C) and (2) the p75 neurotrophin receptor (p75(NTR)). The interaction between neurotrophic factors and their receptors may be involved in the mechanisms that regulate the differential susceptibility of neuronal populations in neurodegenerative diseases. The aim of the present study was to evaluate the role of neurotrophins in the pathogenesis of bovine spongiform encephalopathy (BSE) using a transgenic mouse overexpressing bovine prnp (BoTg 110). Histochemistry for Lycopersicum esculentum agglutinin, haematoxylin and eosin staining and immunohistochemistry for the abnormal isoform of the prion protein (PrP(d)), glial fibrillary acidic protein (GFAP), NGF, BDNF, NT-3 and the receptors Trk A, Trk B, Trk C and p75(NTR) was performed. The lesions and the immunolabelling patterns were assessed semiquantitatively in different areas of the brain. No significant differences in the immunolabelling of neurotrophins and their receptors were observed between BSE-inoculated and control animals, except for p75(NTR), which showed increased expression correlating with the distribution of lesions, PrP(d) deposition and gliosis in the BSE-inoculated mice.