Objective quantification of prion protein in spinal cords of cases of Creutzfeldt-Jakob disease.

A recent investigation into prion protein (PrP) deposition in cases of Creutzfeldt-Jakob disease (CJD) has suggested that the spinal cord is affected in some cases of this disease. In an attempt to measure this phenomenon we have used quantitative image analysis techniques to assess the amount of PrP deposited in the spinal cords of three different cases of CJD. By using an automatic method of image intensity threshold setting we have measured the tissue area occupied by PrP in a non-subjective manner. The ranking of these different cases has confirmed that suggested by visual inspection. This analysis shows a substantial variation in the quantity of PrP positivity observed when a panel of different PrP antibodies was compared, confirming early findings. The distribution of PrP across the spinal cord has also been mapped using the image analysis system.

Pathology of the transmissible spongiform encephalopathies with special emphasis on ultrastructure.

The transmissible spongiform encephalopathies are a group of genetic and infectious disorders which are exemplified by scrapie in animals and Creutzfeldt-Jakob disease in humans. The spongiform encephalopathies are characterized by symmetrical vacuolation of neurons and neuropil. Amyloid plaque formation similar to that found in Alzheimer's disease is conspicuous in many, but not all, of these diseases. The sub-cellular pathology features of the spongiform encephalopathies have been studied by conventional transmission electron microscopy, scanning electron microscopy, freeze fracture, negative staining and most recently by application of immunogold labelling methods. Although these studies have revealed many unusual structures, convincing virus-like particles have not been demonstrated. Considerable data, including important transgenic mouse studies, now suggest that a single cellular protein, designated prion protein, is necessary for infection. Ultrastructural immunogold studies have shown that prion protein is released from the surface of neurons and neurites, diffuses through the extracellular space around infected cells where it accumulates and finally becomes aggregated as amyloid fibrils. It is likely that the accumulation of prion protein within the extracellular space is instrumental in causing nerve cell dysfunction and, ultimately, neurological disease.

Prion protein accumulation in the spinal cords of patients with sporadic and growth hormone associated Creutzfeldt-Jakob disease.

An immunohistological study of the spinal cord in 20 cases of sporadic and 4 iatrogenic (growth hormone) cases of Creutzfeldt-Jakob (CJD) disease patients was performed to detect the presence of disease specific prion protein using a number of different antisera. Prion protein was present in all the growth hormone recipients and in 11 of the 20 sporadic CJD cases. Plaque-like deposits of prion protein were found in all the growth hormone cases and three of the sporadic cases. This is the first demonstration of the topographic immunolocalisation of prion protein in the spinal cord of CJD patients, a feature which could help elucidate some important aspects of the pathogenesis of CJD.

Macrophage response during axonal regeneration in the axolotl central and peripheral nervous system.

We have used a monoclonal antibody (5F4) and Griffonia lectin to study the recruitment of macrophages after crushing axolotl central and peripheral axons. In both cases axonal regeneration begins within one to two days and, in the CNS, proceeds at a rate of about 0.05 mm per day. However, in the spinal cord, macrophage entry is restricted to the lesion site whilst in peripheral nerves macrophages rapidly enter the distal nerve stump after injury. These results suggest that the role (if any) played by macrophages during axonal regeneration may differ in these two situations.

Regeneration in the Xenopus tadpole optic nerve is preceded by a massive macrophage/microglial response.

Changes in the optic nerve following a crush lesion and during axonal regeneration have been studied in Xenopus tadpoles, using ultrastructural and immunohistological methods. Degeneration of both unmyelinated and myelinated axons is very rapid and leads to the formation, within 5 days, of a nerve which consists largely of degeneration debris and cells. Immunohistological analysis with monoclonal antibody 5F4 shows that there is a rapid and extensive microglial/macrophage response to crush of the nerve. Regenerating axons have begun to enter the distal stump by 5 days and grow along the outer part of the nerve in close approximation to the astrocytic glia limitans. Between 5 and 10 days after nerve crush, regenerating axons reach and pass the chiasma. Macrophages are seen in the nerve at the site of the lesion within 1 h, and the response peaks between 3-5 days, just before axonal regeneration gets under way.

Microglia in tadpoles of Xenopus laevis: normal distribution and the response to optic nerve injury.

We have studied the distribution of microglia in normal Xenopus tadpoles and after an optic nerve lesion, using a monoclonal antibody (5F4) raised against Xenopus retinas of which the optic nerves had been cut 10 days previously. The antibody 5F4 selectively recognizes macrophages and microglia in Xenopus. In normal animals microglia are sparsely but widely distributed throughout the retina, optic nerve, diencephalon and mesencephalon (other regions were not examined). After crush or cut of an optic nerve, or eye removal, there occurs an extensive microglial response along the affected optic pathway. Within 18 h an increase in the number of microglial cells in the optic tract and tectum can be detected. This response increases to peak at around 5 days after the lesion. At this time the nerve distal to the lesion contains many microglial cells; the entire optic tract is outlined by microglia, extended along the degenerating fibres; and the affected tectum shows a heavy concentration of microglia. This microglial response thereafter decreases and has mostly gone by 34 days. We conclude that the microglial response to optic nerve injury in Xenopus tadpoles starts early, peaks just before the regenerating optic nerve axons enter the brain, and is much diminished by the time the retinotectal projection is re-established. The timing is such that the microglial response could play a major role in facilitating regeneration.

Monoclonal antibody-based enzyme linked immunosorbent assay of aflatoxin B1, T-2 toxin, and ochratoxin A in barley.

Aflatoxin B1 (B1), T-2 toxin (T2), and ochratoxin A (OA) were assayed in a single extract from barley grain by using competitive enzyme linked immunosorbent assays (ELISAs) with monoclonal antibodies. B1 and T2 monoclonal antibodies were conjugated to horseradish peroxidase for direct competitive ELISA while an indirect competitive ELISA was used for OA determination. The competitive ELISA detected 0.1 ng/mL of B1, 10 ng/mL of T2, or 1 ng/mL of OA. Acetonitrile-0.5% KCl-6% H2SO4 (89 + 10 + 1) extracts of barley grain either were diluted 1:10 for direct assay or were subjected to a simple liquid-liquid cleanup procedure to concentrate the extract 10:1 before assay. For cleanup, water was added to the acetonitrile extract to partition water-soluble interfering substances, and then the mycotoxins were re-extracted with chloroform. The chloroform extract was evaporated to dryness and redissolved in Tris HCl buffer for ELISA. The mean recoveries from barley spiked with 4-60 ng/g of B1, 50-5000 ng/g of T2, and 5-500 ng/g of OA were, respectively, 93.8, 80.6, and 95.8%. The mean within-assay, inter-assay, and subsample coefficients of variation by ELISA of barley grain colonized with toxigenic fungi were less than 12% for B1 and OA but as high as 17% for T2.