Choline acetyltransferase activity and [3H]quinuclidinylbenzilate binding in brains of scrapie-infected hamsters

Choline acetyltransferase (ChAT) activity and [3H]quinuclidinylbenzilate binding were studied in the brain of scrapie-infected hamsters and sham inoculated controls. Although scrapie-infected hamsters showed no reduction of ChAT activity compared to the controls, they showed a decrease in the affinity and maximum number of post-synaptic muscarinic receptors. Scrapie virus thus alters the cholinergic system at the post-synaptic rather than at the pre-synaptic level.

Monoamine abnormalities in the brain of scrapie-infected rats

The effects of the scrapie agent on the levels of monoamines and their metabolites, and on choline acetyltransferase (CAT) activity have been investigated in discrete brain areas in the rat. Two strains of scrapie (8745 from sheep brain and C506 M3 from mice brain) were inoculated. Scrapie-infected rats showed a reduction in the levels of serotonin (prefrontal cortex, hippocampus, striatum) and dopamine (striatum) and an elevation of 5-HIAA levels (cerebral cortex, striatum, thalamus). Noradrenaline levels were decreased only in the cerebral cortex and cerebellum of rats infected with the scrapie strain C506 M3. CAT activity remained unchanged. These data suggest that the scrapie agent causes a derangement of noradrenergic, serotonergic and dopaminergic systems in the rat brain.

A rapid and efficient method to enrich SAF-protein from scrapie brains of hamsters

Scrapie hamster brains contain at least 5-10 micrograms of scrapie-associated fibrils (SAF) per brain as estimated by the amount of its major constituent, a protein of about 26 000 daltons (SAF-protein). It can be extracted efficiently by a 10% solution of sarkosyl and can be enriched by differential centrifugation and buffer extraction. Scrapie infectivity, SAF, and SAF-protein copurify.

Decreased high-affinity binding of [3H]muscimol to cerebral synaptic membranes of scrapie-infected mice

Scrapie is a transmissible disease that results in progressive degeneration of the central nervous system and death. Although scrapie has been studied histopathologically, relatively little is known concerning neurotransmitter alterations. Specific [3H]muscimol binding to whole brain crude synaptic membranes (CSM) from mice clinically affected with scrapie was significantly (p less than 0.01) reduced, to approximately 73% of that of the controls. Of the brain regions examined, binding to only cerebral CSM was significantly (p less than 0.0001) decreased. Scatchard analyses of saturation curves revealed that the high-affinity (KD = 8 +/- 3 nM) site for muscimol was abolished in cerebral CSM from scrapie-infected mice, while the low-affinity site was unaffected. Binding of [3H]flunitrazepam to cerebral CSM was unaffected by scrapie and was stimulated by GABA to the same extent in both scrapie and control mice. These results suggest that scrapie agent 139A in C57BL/6J mice manifests a portion of its CNS pathology via a high-affinity GABA binding site that is unassociated with the benzodiazepine receptor.

Cerebral glucose utilization: local changes after microinoculation of scrapie agent in hamster

The effects of scrapie agent on local cerebral energy metabolism were studied by the [14C]2-deoxyglucose (2-DG) autoradiographic method of Sokoloff et al. after stereomicroinoculation (0.5 microliter, 10(-2) of scrapie suspension) in hamster left striatum. From a group of 20 hamsters inoculated, 2 animals were killed every 10 days from the 30th day after inoculation to the terminal stage of the disease. Experiments were carried out according to the qualitative 2-DG procedure and cerebral autoradiographs of inoculated animals were compared to those of 3 controls. The results show changes of local cerebral glucose utilization in some discrete brain regions, ipsilateral to the side of inoculation, and their sequential spreading to other cerebral structures with a definite order: left anterior thalamus, left posterior thalamus, then medial geniculate body (ipsilateral, then controlateral), and finally some brainstem nuclei (inferior colliculus, superior olivary nucleus); the inoculated striatum is affected very late, after clinical signs. Metabolic changes which first occur ipsilaterally to the side of inoculation precede the clinical symptoms, while their contralateral spreading is concomitant with the clinical signs. The data demonstrate a rostral--caudal sequence of the cerebral metabolic changes, ipsilateral to the side of inoculation, which may reflect in part the slow spread of agent in the central nervous system from the inoculation site.

Immunohistochemical demonstration of glial fibrillary acidic protein in scrapie

Although little is known about its metabolism, glial fibrillary acidic (GFA) protein has become widely used as a cell-specific, species-non-specific antigenic marker for normal or pathologically altered astroglia. So far there have been few investigations on GFA protein in relation to scrapie and analogous spongiform encephalopathies although there has been a need for an unequivocal method for the discrimination of different types of glia in these diseases. In the present studies, a commercially available antiserum to GFA protein incorporated in a peroxidase-antiperoxidase procedure was applied to paraffin sections of brain and spinal cord from mice affected with scrapie, avirulent Semliki forest virus and cuprizone encephalopathy, and to tissues from healthy and scrapie-affected sheep. Excellent delineation of GFA protein was obtained in astroglial cell bodies and processes and in fibrils in the glia limitans and in perivascular and subependymal sites. The method was extremely sensitive and selective. A massive increase in GFA protein in scrapie-affected mice paralleled an increase in reactive astrocytes and facilitated the construction of astroglial lesion profiles for scrapie and the other encephalopathies. In sheep, abundant GFA protein occurred in both healthy and in scrapie-affected animals and in the tissues examined the differences were not conclusive.

Serotonin concentrations in brain and blood of scrapie-infected and normal hamsters and mice

Whole brains and bloods of scrapie-infected and control mice and hamsters were assayed for serotonin content. Late clinical scrapie-infected mice showed a 20% reduction in whole-brain serotonin concentrations but no change in blood concentrations relative to controls. Late clinical scrapie-infected hamsters showed no change in whole-brain serotonin concentrations but a 2.5-fold decrease in blood concentrations relative to controls.

Neurophysin in the brain and pituitary gland of normal and scrapie-affected sheep—I

By use of an immunofluorescence histochemical technique with a cross-species reactive antiserum to porcine neurophysin-II the precise localization of neurophysin in the pituitary gland and the hypothalamic area of the brain of the sheep has been determined. Neurophysin was confined to neurosecretory pathways originating from the supraoptic and paraventricular hypothalamic nuclei. The major pathway terminates in the neurohypophysis but in addition a second neurophysin-containing pathway proceeds in the external infundibular zone of the median eminence-pituitary stalk and is associated with the presence of vasopressin. In sheep affected with the hereditary degenerative disease known as natural scrapie, this supraoptico-paraventriculo-infundibular pathway is preserved and hypertrophied, while the major pathway to the posterior lobe of the pituitary degenerates. The supraoptic and paraventricular nuclei in the sheep comprise at least two distinct but morphologically similar neuronal populations affected differently by the natural scrapie genome, one undergoing dissolution by middle-age and one surviving and becoming hyperactive. This premature ageing is probably associated with a primary biochemical lesion affecting the rate of the axonal flow of neurosecretory vesicles and of their discharge at synaptic terminals. Possible metabolic and circulatory bases for such an anomaly are considered. The presence of neurophysin in the rostral and caudal adenohypophysis supports the view that vasopressin is acting directly as a trophic-hormone releasing factor, possibly for the quick release of adrenocorticotropic hormone and of growth hormone. The relation of neurophysin-rich aggregations in the neurohypophysis to Herring bodies and the turnover of neurosecretory material are discussed.

Infectious etiology of neuritic (senile) plaques in mice

Brains of inbred female VM mice infected with scrapie agent were studied with the use of the Bodian silver impregnation method and by electron microscopy. In brains affected with scrapie, after an incubation period of between 587 and 655 days, numerous primitive, classical, and amyloid plaques were found. No plaques of any type were seen in the control mice.