Comparative epidemiology of scrapie outbreaks in individual sheep flocks

Data recording the course of scrapie outbreaks in 4 sheep flocks (2 in Cheviot sheep and 2 in Suffolks) are compared. For each outbreak the data on scrapie incidence and sheep demography and pedigrees cover periods of years or decades. A key finding is that the incidence of clinical cases peaks in sheep 2-3 years old, despite very different forces-of-infection. This is consistent with age-specific susceptibility of sheep to scrapie, as has been reported for cattle to bovine spongiform encephalopathy and for humans to variant Creutzfeldt-Jakob disease. Scrapie incidence was higher in ewes than rams and at certain times of years, though these effects were not consistent between flocks. There was no evidence for high levels of vertical transmission.

Folate binding protein from kidney brush border membranes contains components characteristic of a glycoinositol phospholipid anchor

A number of cell surface proteins have been shown to be anchored to the plasma membrane by a covalently attached glycoinositol phospholipid (GPL) in amide linkage to the C-terminus of the mature protein. We applied several criteria to establish that folate binding protein (FBP) in brush border membranes of rat kidney contains a GPL anchor. Brush border membranes were isolated and labeled with [3H]folate, and the complex of FBP and [3H]folate was shown to be released to the supernatant by incubation with purified bacterial phosphatidylinositol-specific phospholipase C (PIPLC) but not by incubation with a purified bacterial phosphatidylcholine-specific phospholipase C. The FBP-[3H]folate complex both in crude extracts and after FBP purification by ligand-directed affinity chromatography interacted with Triton X-114 micelles, and prior incubation with PIPLC prevented this detergent interaction. Individual residues characteristic of GPL anchors were found to be covalently associated with FBP following polyacrylamide gel electrophoresis in sodium dodecyl sulfate. These included glucosamine and ethanolamine, which were radiolabeled by reductive methylation and identified by chromatography on an amino acid analyzer, and inositol phosphate, which was inferred by Western blotting with an anti-CRD antisera. This antisera gave positive immunostaining only after FBP had been cleaved by PIPLC, a reliable diagnostic of a GPL anchor. The relationship between GPL-anchored FBP in biological membranes and soluble FBP in biological fluids also is discussed.

Distribution of the prion protein in sheep terminally affected with BSE following experimental oral transmission

This study has examined the distribution of PrP(Sc) in sheep by immunocytochemistry of tissues recovered from terminally affected animals following their experimental infection by the oral route with BSE. Despite a wide range of incubation period lengths, affected sheep showed a similar distribution of high levels of PrP(Sc) throughout the central nervous system. PrP(Sc) was also found in the lymphoid system, including parts of the digestive tract, and some components of the peripheral nervous system. These abundant PrP(Sc) deposits in sheep in regions outside the central nervous system are in direct contrast with cattle infected with BSE, which show barely detectable levels of PrP(Sc) in peripheral tissues. A number of genetically susceptible, challenged animals appear to have survived.

Discriminant responses of the catalytic unit and glucose 6-phosphate transporter components of the hepatic glucose-6-phosphatase system in Ehrlich ascites-tumor-bearing mice

The effect of Ehrlich ascites tumor cells, in vivo, on the hepatic glucose-6-phosphatase (G6Pase) system was examined. The V(max) for glucose 6-phosphate hydrolysis by G6Pase was reduced by 40% and a greater than 15-fold decrease in mRNA encoding the catalytic unit of the G6Pase system was observed 8 days after injection with tumor cells. Blood glucose concentration was decreased from 169 +/- 17 to 105 +/- 9 mg/dl in tumor-bearing mice. There was no change in the G6P transporter (G6PT) mRNA level. However, there was a significant decrease in G6P accumulation into hepatic microsomal vesicles derived from tumor-bearing mice. Decreased G6P accumulation was also associated with a decrease in G6Pase hydrolytic activity in the presence of vanadate, a potent catalytic-unit inhibitor. In addition, G6P accumulation was nearly abolished in microsomes treated with N-bromoacetylethanolamine phosphate, an irreversible inhibitor of the G6PT. These results demonstrate that the catalytic unit and G6PT components of the G6Pase system can be discriminantly regulated, and that microsomal glucose 6-phosphate uptake is dependent on catalytic unit activity as well as G6PT action.

Population dynamics of a scrapie outbreak

A detailed analysis of a scrapie outbreak in a flock of Cheviot sheep is described. A total of 33 cases of 1473 sheep born to the flock were reported between 1985 and 1994. The epidemiology of scrapie can only be understood with reference to sheep demography, the population genetics of susceptibility to scrapie, pathogenesis during a long incubation period, and the rate of transmission (by both horizontal and vertical routes), all of which interact in complex ways. In recent work a mathematical model incorporating these elements was developed and successfully reproduced key features of an earlier outbreak of scrapie in this flock. Here an application of the model to the second outbreak is described. The model accurately reproduces observed allele frequencies and total numbers of susceptible animals remaining at the end of the outbreak. A major difference between the two outbreaks is the very much lower force of infection in the second outbreak. This provided additional information which suggested two ways in which our existing assumptions be refined; firstly, older animals have reduced susceptibility to scrapie and secondly, homozygous and heterozygous susceptibles have different incubation periods.

Clinical signs, histopathology and genetics of experimental transmission of BSE and natural scrapie to sheep and goats

This paper compares the dinical signs, histopathology, detection of PrPSc protein and PrP genetics of the transmission of BSE to sheep and goats, with the effects of the transmission of natural scrapie from a brain homogenate from a single sheep. After intracerebral and oral inoculations there were similarities in the clinical signs due to the two sources of infection, but there were differences in pathology at the end stage of disease and in the genotypes of the sheep which succumbed to the challenges. The incubation period of BSE was associated with the sheep PrP codon 171 genotype, but the natural scrapie source, despite inducing disease only in known susceptible genotypes, showed no clear association with PrP genotype.

A centuries-long epidemic of scrapie in British sheep?

The apparent persistence of scrapie in British sheep for more than 250 years is difficult to explain. Susceptibility to scrapie is associated with particular alleles at a single locus, the PrP gene. As the only known effect of these alleles is to confer susceptibility to a fatal disease, natural selection is expected to reduce their frequency, as has been observed in practice during scrapie outbreaks in single sheep flocks. Susceptibility alleles, and hence scrapie itself, are therefore expected to become rare, yet the disease remains widespread. We suggest that the paradox of scrapie's persistence can be explained by the exceptionally long time-scales inherent in the epidemiology of the disease. It is proposed that scrapie should be regarded as epidemic in British sheep but, unlike more familiar epidemics, which have time-scales of months or years, the scrapie epidemic has a time-scale of centuries. This interpretation implies that scrapie should eventually disappear from the sheep population.

Transmission of BSE by blood transfusion in sheep

We have shown that it is possible to transmit bovine spongiform encephalopathy (BSE) to a sheep by transfusion with whole blood taken from another sheep during the symptom-free phase of an experimental BSE infection. BSE and variant Creutzfeldt-Jakob disease (vCJD) In human beings are caused by the same infectious agent, and the sheep-BSE experimental model has a similar pathogenesis to that of human vCJD. Although UK blood transfusions are leucodepleted--a possible protective measure against any risk from blood transmission--this report suggests that blood donated by symptom-free vCJD-infected human beings may represent a risk of spread of vCJD infection among the human population of the UK.

N-Bromoacetylethanolamine phosphate as a probe for the identification of a liver microsomal glucose-6-phosphate transporter peptide in rats and Ehrlich ascites tumor-bearing mice

Hepatic microsomal glucose-6-phosphatase is a multicomponent system composed of substrate/product translocases and a catalytic subunit. Previously we (Foster et al. (1996) Biochim. Biophys. Acta 12, 244-254) demonstrated that N-bromoacetylethanolamine phosphate (BAEP) is a time-dependent, irreversible inhibitor of glucose-6-phosphate hydrolysis in intact but not disrupted microsomes. We proposed that BAEP manifests its inhibitory effect by binding with a glucose-6-phosphate translocase protein of the glucose-6-phosphatase system. Here we provide additional evidence that BAEP inhibits glucose-6-phosphate transport in microsomal vesicles and utilize [(32)P]BAEP as an affinity label in the identification of a glucose-6-phosphate transport protein. In this study, we identify 51-kDa rat and mouse liver microsomal proteins involved in glucose-6-phosphate transport into and out of microsomal vesicles by utilizing (1) an Ehrlich ascites tumor-bearing mouse model, which displays a decreased sensitivity to the time-dependent inhibitory effect of BAEP, and (2) another glucose-6-phosphate translocase inhibitor, tosyl-lysine chloromethyl ketone, in conjunction with [(32)P]BAEP as an affinity label.

Mineralocorticoid receptors in the mammalian olfactory mucosa

Mineralocorticoid hormones regulate secretion and absorption in a wide variety of epithelial tissues, although specific mechanisms in the olfactory mucosa are currently unknown. Utilizing reverse transcription-polymerase chain reaction (RT-PCR) analysis, we have demonstrated the expression of mineralocorticoid (type I) receptor messenger RNA in the rodent olfactory mucosa. Amplification products of predicted size were obtained with nucleotide sequences corresponding to respective mineralocorticoid receptor (MR) kidney transcripts. Immunocytochemistry, using an antibody with known specificity for MRs, was then utilized in order to localize the cellular site(s) of MR protein expression in the olfactory mucosa. The highest levels of MR immunoreactivity were localized to the supranuclear region of sustentacular cells, as well as the acinar cells of the Bowman's glands. The respiratory regions of the nasal cavity were devoid of appreciable MR immunoreactivity. This study demonstrates both MR transcript and protein expression in the olfactory mucosa. We hypothesize that the mineralocorticoid hormones may have a role in modulation of olfactory secretion and/or sensory transduction in the peripheral olfactory system.

Regulation of glucose production by the liver

Glucose is an essential nutrient for the human body. It is the major energy source for many cells, which depend on the bloodstream for a steady supply. Blood glucose levels, therefore, are carefully maintained. The liver plays a central role in this process by balancing the uptake and storage of glucose via glycogenesis and the release of glucose via glycogenolysis and gluconeogenesis. The several substrate cycles in the major metabolic pathways of the liver play key roles in the regulation of glucose production. In this review, we focus on the short- and long-term regulation glucose-6-phosphatase and its substrate cycle counter-part, glucokinase. The substrate cycle enzyme glucose-6-phosphatase catalyzes the terminal step in both the gluconeogenic and glycogenolytic pathways and is opposed by the glycolytic enzyme glucokinase. In addition, we include the regulation of GLUT 2, which facilitates the final step in the transport of glucose out of the liver and into the bloodstream.

Population dynamics of scrapie in a sheep flock

A detailed analysis of an outbreak of natural scrapie in a flock of Cheviot sheep is described. A total of 137 cases was reported over 13 years among 1307 sheep born into the flock. The epidemiology of scrapie can only be understood with reference to sheep demography, the population genetics of susceptibility to scrapie, pathogenesis during a long incubation period, and the rate of transmission (by both vertical and horizontal routes), all of which interact in complex ways. A mathematical model incorporating these features is described, parameter values and model inputs are derived from available information from the flock and from independent sources, and model outputs are compared with the field data. The model is able to reproduce key features of the outbreak, including its long duration and the ages of cases. The analysis supports earlier work suggesting that many infected sheep do not survive to show clinical signs, that most cases arise through horizontal transmission, and that there is strong selection against susceptible genotypes. However, important aspects of scrapie epidemiology remain poorly understood, including the possible role of carrier genotypes and of an environmental reservoir of infectivity, and the mechanisms maintaining alleles giving susceptibility to scrapie in the sheep population.

Olfactory secretion and sodium, potassium-adenosine triphosphatase: regulation by corticosteroids

OBJECTIVES

To investigate the cellular distribution and relative intensity of the immunoreactivity associated with the expression of sodium, potassium-adenosine triphosphatase (Na, K-ATPase) in cells of the olfactory mucosa. Second, changes in the activity of this enzyme in the olfactory mucosa are correlated with changes in the circulating corticosteroid aldosterone.

METHODS

Combination of immunohistochemical and biochemical techniques were employed to examine the olfactory Na, K-ATPase.

RESULTS

Within the olfactory epithelium, the Na, K-ATPase immunoreactivity was greatest at the supranuclear region of sustentacular cells and/or dendrites of olfactory receptor neurons (ORNs). Cell bodies of ORNs demonstrated moderate immunoreactivity, whereas the duct cells of Bowman's gland exhibited moderate to intense immunoreactivity. Acinar cells of the Bowman's gland were the most intensely stained components of the lamina propria, exhibiting strong immunoreactivity at the basolateral plasma membrane domains of the acinar cells and less within the cytoplasm. Binding of ouabain, a specific inhibitor of Na, K-ATPase, was significantly elevated for aldosterone-injected versus sham-injected controls.

CONCLUSION

These results suggest that olfactory Na, K-ATPase is regulated by the systemic corticosteroid aldosterone. The results are consistent with the hypothesis that corticosteroids regulate olfactory secretion.

Histone II-A activates the glucose-6-phosphatase system without microsomal membrane permeabilization

Many agents have been used to release the latent portion of the activities catalyzed by the glucose-6-phosphatase (Glc-6-Pase) system. Detergents, which disrupt the microsomal membrane concomitantly with Glc-6-Pase activation, have been the most widely used of these agents. The treatment of microsomes with alamethicin or histone II-A has also been reported to activate the Glc-6-Pase system to the same extent as detergent treatment. While alamethicin reportedly permeabilizes the microsomal membrane (R. Fulceri et al., 1995, Biochem. J. 307, 391-397), conflicting ideas as to histone II-A's mechanism of activation have been described (J. St.-Denis et al., 1995, Biochem. J. 310, 221-224 and J. Blair and A. Burchell, 1988, Biochim. Biophys. Acta 964, 161-167). We further investigated whether activation of the Glc-6-Pase system by histone II-A is due to permeabilization of the microsomal membrane. We treated rat liver microsomes with Triton X-100, alamethicin, or histone II-A and found them to be equally effective in maximally activating the Glc-6-Pase system. We also examined the modifying effects of alamethicin and histone II-A on the sensitivity of Glc-6-Pase activities to inhibition by N-bromoacetylethanolamine phosphate (BAEP) and 3-mercaptopicolinate (3-MP), both thiol-directed reagents. Alamethicin, but not histone II-A, abolished the inhibitory effects of BAEP and 3-MP on activities of the Glc-6-Pase system. Our studies support previous reports of Glc-6-Pase activation by alamethicin via permeabilization of microsomal membranes and histone II-A activation without microsomal membrane permeabilization.

Expression of glucocorticoid receptor mRNA and protein in the olfactory mucosa: physiologic and pathophysiologic implications

OBJECTIVES

Define the presence and distribution of glucocorticoid receptors (GRs) within the olfactory mucosa in order to assess potential physiologic and pathophysiologic effects of these hormones on olfaction.

STUDY DESIGN

The olfactory mucosa was harvested from adult male rats and guinea pigs. Kidney tissue was utilized as a known positive control.

METHODS

The techniques of reverse transcriptase-polymerase chain reaction (RT-PCR) and immunocytochemistry were utilized to examine the expression of GR mRNA and protein. To assure the presence of olfactory mucosa in the nasal tissue samples, RT-PCR was utilized to identify the olfactory marker protein (OMP).

RESULTS

The presence of GR mRNA was confirmed in both the olfactory mucosa and kidney. GR-like immunoreactivity associated with the olfactory epithelium was greatest at the apical surface, a position corresponding to the dendrites, knobs, and cilia of olfactory receptor neurons, as well as the supranuclear region of sustentacular cells. Weaker GR-like immunoreactivity was associated with the region of the cell bodies of the olfactory receptor neurons. Within the lamina propria, acinar cells of the Bowman's glands and olfactory nerve bundles were intensely immunoreactive.

CONCLUSIONS

The presence of GR mRNA and protein within the olfactory mucosa is consistent with a functional role for glucocorticoid hormones in the systemic regulation of olfaction. Furthermore, these studies suggest that corticosteroid medications may have direct effects on the cells of the olfactory mucosa in the pathologic state. The potential mechanisms whereby these hormones may act are discussed.

Low-Km mannose-6-phosphatase as a criterion for microsomal integrity

The low-Km activity of mannose-6-phosphatase (Man-6-Pase) has been used for many years to measure the structural integrity of microsomes. Recently histone II-A has been shown to activate glucose-6-phosphatase (Glc-6-Pase) and Man-6-Pase activities. However, in contrast to detergents, this compound appears to activate without disrupting microsomal vesicles (J.-F. St-Denis, B. Annabi, H. Khoury, and G. van de Werve. 1995. Biochem. J. 310: 221-224). This suggests that Man-6-Pase latency can be abolished without disrupting microsomal integrity and that even normally microsomes may manifest some low-Km Man-6-Pase activity without being "leaky." We have studied the relationship of Man-6-Pase with microsomal integrity further by measuring the latency of several enzymes reported to reside within the lumen of endoplasmic reticulum. We have also correlated this latency with the microsomal permeability of substrates for these enzymes. We found that (i) lumenal enzymes have different degrees of latency when compared with each other, (ii) permeability, as determined via osmotically induced changes in light scattering, is not always consistent with enzymatic latency, (iii) increases in the hydrolysis of Glc-6-P and Man-6-P were not parallel when microsomes were treated with low but increasing concentrations of detergent, and (iv) kinetic studies suggest that mannose-6-phosphate is hydrolyzed by untreated microsomes by more than a single mechanism. We propose that Man-6-Pase is not a reliable index of the integrity of microsomes.

Tungstate: a potent inhibitor of multifunctional glucose-6-phosphatase

The insulin-like action of tungstate in diabetic rats (A. Barberà et al., 1994, J. Biol. Chem. 269, 20047-20053) prompted us to examine the effects of tungstate on the glucose-6-phosphatase system. Our results indicate that tungstate is a potent inhibitor of glucose-6-phosphatase, with a Ki in the 10-25 microM range determined with native microsomes and in the 1-7 microM range determined with detergent-treated microsomes. With both preparations, simple linear competitive inhibition was observed versus glucose 6-phosphate (glucose-6-P) as substrate with the glucose-6-P phosphohydrolase activity of the enzyme. Tungstate was a simple linear competitive inhibitor versus carbamyl phosphate (carbamyl-P) and a linear noncompetitive inhibitor versus glucose with the carbamyl-P:glucose phosphotransferase activity of the glucose-6-phosphatase system. These findings, in addition to the observation that tungstate protected the enzyme against thermal inactivation, indicate that tungstate binds with high affinity and competes at the active site of the enzyme where the substrates glucose-6-P and carbamyl-P bind prior to catalysis. Our results suggest that potent inhibition of glucose-6-P hydrolysis by tungstate is likely responsible, at least in part, for the normalization of glycemia and the rebound in hepatic glucose-6-P levels observed in earlier studies in which tungstate exhibited insulin-like action in diabetic rats.

Effects of ionic strength and chloride ion on activities of the glucose-6-phosphatase system: regulation of the biosynthetic activity of glucose-6-phosphatase by chloride ion inhibition/deinhibition

Certain amino acids stimulate glycogenesis from glucose. The regulatory volume decrease mechanism explaining these effects was defined by Meijer et al. (1992, J. Biol. Chem. 267, 5823-5828). It involves amino acid-induced swelling of hepatocytes resulting in loss of chloride ions which leads to deinhibition of glycogen synthase phosphatase. This results in enhanced conversion of the inactive to active form of glycogen synthase and thus enhanced glycogen synthesis. We have studied the effects of amino acids and chloride ion on the glucose-6-phosphatase system (Glc-6-Pase) with rat liver microsomal preparations, and correlated our results with those reported by others with glycogen synthase. Glc-6-Pase activities are increased by elevated ionic strength varied by increasing the concentration of various buffers or charged amino acids but are not affected by changes in osmolarity, varied with disaccharides or uncharged amino acids. With undisrupted microsomes, chloride ion competitively inhibits carbamyl phosphate: glucose phosphotransferase (KCP,t,UMi,Cl- = 19 mM) more extensively than Glc-6-P phosphohydrolase (KG6P,h,UMi,Cl- = 117 mM). Inhibition by chloride ion and activation due to ionic strength may be important considerations when assessing in vitro Glc-6-Pase activities where an attempt is made to replicate physiologic conditions. Further we propose that amino acids may play a role in increasing biosynthetic activity of Glc-6-Pase, as well as previously characterized glycogen synthase (Meijer et al., op. cit.), via the regulatory volume decrease mechanism through diminished chloride ion inhibition. Reduced concentration of chloride ion will (1) deinhibit the biosynthetic activity of Glc-6-Pase, while still inhibiting Glc-6-P hydrolysis, leading to an increased cellular concentration of Glc-6-P (an important glycogenic intermediate as well as allosteric activator of glycogen synthase) and (2) increase the active form of glycogen synthase by deinhibiting glycogen synthase phosphatase both through the previously defined mechanism (see above) and via Glc-6-P-enhanced conversion of glycogen synthase from its inactive to active form. We propose that the biosynthetic activity of Glc-6-Pase may act in concert with glycogen synthase during amino acid-induced glycogenesis from glucose.

Glucose-6-phosphatase structure, regulation, and function: an update

Work on the glucose-6-phosphatase system has intensified and diversified extensively in the past 3 years. The gene for the catalytic unit of the liver enzyme has been cloned from three species, and regulation at the level of gene expression is being studied in several laboratories worldwide. More than 20 sites of mutation in the catalytic unit protein have been demonstrated to underlie glycogenesis type 1a. inhibition of glucose-6-P hydrolysis by several newly identified competitive and time-dependent, irreversible inhibitors has been demonstrated and in several instances the predicted effects on liver glycogen formation and/or breakdown and on blood glucose production have been shown. Refinements in and additions to the presently dominant "substrate transport-catalytic unit" topological model for the glucose-6-phosphatase system have been made. A new model alternative to this, based on the "combined conformational flexibility-substrate transport" concept, has emerged. Experimental evidence for the phosphorylation of glucose in liver by high-K(m),glucose enzyme(s) in addition to glucokinase has continued to emerge, and new in vitro evidence supportive of biosynthetic functions of the glucose-6-phosphatase system in this role has appeared. High levels of multifunctional glucose-6-phosphatase have been shown present in pancreatic islet beta cells. Glucose-6-P has been established as the likely insulin secretagog in beta cells. Interesting differences in the temporal responses of glucose-6-phosphatase in kidney and liver have been demonstrated. An initial attempt is made here to meld the hepatic and pancreatic islet beta-cell glucose-6-phosphatase systems, and to a lesser extent the kidney tubular and small intestinal mucosal glucose-6-phosphatase systems into an integrated, coordinated mechanism involved in whole-body glucose homeostasis in health and disease.

Natural scrapie and PrP genotype: case-control studies in British sheep

Natural scrapie in sheep is associated with polymorphisms of the PrP gene, particularly at amino acid codons 136, 154 and 171. This paper reports the results of nine scrapie case-control studies in Bleu du Maine, Herdwick, Merino x Shetland, Poll Dorset, Scottish Halfbred, Shetland, Soay, Suffolk and Swaledale sheep from British flocks affected by scrapie. In some outbreaks, scrapie was found to occur only in animals with at least one PrP allele encoding valine at codon 136 (V136), usually a relatively rare allele in healthy controls. In other outbreaks, the V136, PrP allele was either not found or was not an absolute prerequisite for scrapie to develop. Although scrapie had a strong tendency to affect sheep with PrP genotypes homozygous for glutamine at codon 171 (QQ171), these genotypes (QQ171 but varying at other codon positions) were relatively common in healthy controls. The reliable prediction of scrapie susceptibility in previously uninvestigated sheep flocks will therefore require information at least about PrP genotypes at codons 136 and 171.

Glucocorticoid (type II) receptors in the olfactory mucosa of the guinea-pig: RU 28362

The glucocorticoid RU 28362 was employed to identify glucocorticoid receptors in the olfactory mucosa of the guinea-pig. Results demonstrate significant binding of RU 28362 and suggest that the olfactory mucosa is a target site for glucocorticoid action.

Mineralocorticoid (type I) receptors in the olfactory mucosa of the mammal: studies with [3H]aldosterone and the anti-mineralocorticoid spironolactone

High-affinity, specific binding sites to mineralocorticoids, with characteristics of mineralocorticoid (type I) receptors, have been found in the mammalian olfactory mucosa. In the presence of RU 28362, which blocks low-affinity binding of the labeled hormone to glucocorticoid (type II) receptors, Scatchard analysis of the specific [3H]aldosterone binding indicates that aldosterone binds to a single class of high-affinity (type I) sites with a dissociation constant, Kd, of 1.2 x 10(-9) M and a maximum number of binding sites, Bmax, of 63 fmol/mg dry tissue. Time course of association of [3H]aldosterone and its binding sites showed maximal binding by 30 min at 25 degrees C which remained unchanged up to 90 min. Competition studies performed with 1 x 10(-7)-1 x 10(-5) M spironolactone, a competitive mineralocorticoid antagonist, showed a dose-response reduction of [3H]aldosterone binding, implying that in the olfactory mucosa this compound behaves as an aldosterone antagonist. These results demonstrate significant [3H]aldosterone binding to receptors of high affinity and mineralocorticoid specificity and suggest that the olfactory mucosa is a target site for mineralocorticoid action.

Immunolocalisation of the prion protein (PrP) in the brains of sheep with scrapie

Cheviot sheep from the Neuropathogenesis Unit flock were examined for PrP in brain sections using immunocytochemistry in order to aid scrapie diagnosis. Brains were collected from sheep which had been naturally or experimentally infected with scrapie and fixed in periodate-lysine-paraformaldehyde or in formalin. Immunolabelling was achieved using a monoclonal antibody (FH11) raised to the N-terminus of recombinant PrP protein. Several pre-treatments were studied in an effort to enhance PrP immunolabelling such as trypsin, formic acid and hydrated autoclaving. Trypsin was successful in highlighting PrP staining in formalin-fixed tissue. PrP staining was regularly observed in the dorsal vagus nucleus of the medulla oblongata and in the thalamus. Differences in the distribution and intensity of PrP immunostaining were apparent between the scrapie sources ME7 and SSBP/I.