Use of a preclinical test in the control of classical scrapie.

Scrapie control in Great Britain (GB) was originally based on the National Scrapie Plan's Ram Genotyping scheme aimed at reducing the susceptibility of the national flock. The current official strategy to control scrapie in the national flock involves culling susceptible genotypes in individual, known affected flocks (compulsory scrapie flock scheme or CSFS). However, the recent development of preclinical test candidates means that a strategy based on disease detection may now be feasible. Here, a deterministic within-flock model was used to demonstrate that only large flocks with many home-bred ewes are likely to be a significant risk for flock-to-flock transmission of scrapie. For most other flocks, it was found that the CSFS could be replaced by a strategy using a currently available live test without excessive risk to other farmers, even if the proportion of susceptible genotypes in the flock is unusually large. Even for flocks that represent a high risk of harbouring a high prevalence of infection, there would be limited probability of onward transmission if scrapie is detected soon after disease introduction (typically less than 5 years). However, if detection of disease is delayed, the existing CSFS strategy may be the most appropriate control measure in these cases.

HLA-associated clinical progression correlates with epitope reversion rates in early human immunodeficiency virus infection.

Human immunodeficiency virus type 1 (HIV-1) can evade immunity shortly after transmission to a new host but the clinical significance of this early viral adaptation in HIV infection is not clear. We present an analysis of sequence variation from a longitudinal cohort study of HIV adaptation in 189 acute seroconverters followed for up to 3 years. We measured the rates of variation within well-defined epitopes to determine associations with the HLA-linked hazard of disease progression. We found early reversion across both the gag and pol genes, with a 10-fold faster rate of escape in gag (2.2 versus 0.27 forward mutations/1,000 amino acid sites). For most epitopes (23/34), variation in the HLA-matched and HLA-unmatched controls was similar. For a minority of epitopes (8/34, and generally associated with HLA class I alleles that confer clinical benefit), new variants appeared early and consistently over the first 3 years of infection. Reversion occurred early at a rate which was HLA-dependent and correlated with the HLA class 1-associated relative hazard of disease progression and death (P = 0.0008), reinforcing the association between strong cytotoxic T-lymphocyte responses, viral fitness, and disease status. These data provide a comprehensive overview of viral adaptation in the first 3 years of infection. Our findings of HLA-dependent reversion suggest that costs are borne by some escape variants which may benefit the host, a finding contrary to a simple immune evasion paradigm. These epitopes, which are both strongly and frequently recognized, and for which escape involves a high cost to the virus, have the potential to optimize vaccine design.

The role of polysialic acid and other carbohydrate polymers in neural structural plasticity.

Polysialic acid (PSA) fulfills several criteria for a molecule involved in structural plasticity, including expression in regions capable of plasticity, re-expression in structures undergoing synaptic rearrangement in the adult, downregulation following innervation, and regulation by activity. In addition, removal of PSA reduces the capacity for structural plasticity. PSA may be paradigmatic for other large polymeric carbohydrates, such as glycosaminoglycans and proteoglycans, which also are highly charged and can be extensively hydrated. These carbohydrates may affect structural plasticity by altering cell-cell and/or cell-matrix interactions by increasing intermolecular spacing through hydration.

Early postmitotic neurons transiently express TOAD-64, a neural specific protein.

To identify proteins involved in the early development of the mammalian cerebral cortex, we previously used two-dimensional gels to compare proteins synthesized at different stages in corticogenesis in the embryonic rat at embryonic day 14 (E14), E17, and E21. During this period, the cortex develops from a morphologically homogeneous population of proliferative precursor cells into a complex structure containing a diverse array of terminally differentiated neurons. Several proteins are up-regulated coincident with the generation of postmitotic neurons. Here we describe the purification, partial amino acid sequencing, and characterization of one of these proteins, TOAD-64 (Turned On After Division; 64 kDa), using polyclonal antisera to two synthetic peptides from the protein. This analysis reveals that TOAD-64 is a 64,000 Da protein that increases in abundance over the period of corticogenesis and then subsequently decreases to very low levels in the adult. The protein is neural specific and is expressed by postmitotic neurons as they begin their migration out of the ventricular zone into the developing cortical plate. It is expressed in advance of most other neuronal proteins. Progenitor cells do not express TOAD-64. Therefore, this protein is a marker for postmitotic cells that have made a commitment to a neuronal phenotype. The extremely early expression, the relative abundance in newly born neurons, as well as the restriction in expression to the period of initial neuronal differentiation suggest that TOAD-64 may be a key structural protein for early neuronal function.

Identification and characterization of novel developmentally regulated proteins in rat spinal cord.

We previously used 2-dimensional (2-D) gel electrophoresis to identify novel proteins that may be involved in the genesis of the mammalian nervous system [1]. Several novel proteins that were up- or down-regulated coincident with neurogenesis and neuronal migration in rat neocortex were identified. To further investigate the expression of some of these developmentally regulated proteins during a comparable period in spinal cord development, 2-D electrophoresis is used to study their regulation in the crude membrane and soluble fractions of spinal cord at embryonic day 12 (E12) and embryonic day 21 (E21). This analysis indicates that 7 of the proteins that exhibited large changes in their synthesis in cerebral cortex between embryonic day 14 (E14) and embryonic day 21 (E21) demonstrate similar up- or down-regulation during spinal cord neurogenesis. However, two proteins are restricted in their expression or developmental regulation. One of these, 667-800, appears cortex-specific, while the up-regulation of protein SC.1 appears to be spinal cord specific. Several of these proteins also appear to be enriched in both the cortex and spinal cord relative to non-neural tissues (117, 162, 182, 310 [TOAD-64], 667-800) and may be neural specific. To further characterize its expression, one of these neural-specific, up-regulated proteins, TOAD-64 (protein 310) [2-4], is studied throughout embryonic and postnatal spinal cord development using peptide-specific polyclonal antibodies. As suggested by the 2-D gel analysis and the previously reported expression pattern in cerebral cortex [3], TOAD-64 is transiently expressed in postmitotic spinal cord neurons early in their development and sharply down-regulated after the second postnatal week. In the adult spinal cord, TOAD-64 expression is remarkably restricted to a subset of primary afferents to the spinal cord. This expression pattern, coupled with its recently discovered homology to two proteins implicated in axon pathfinding in the chick and nematode [5,3], suggests that TOAD-64 may have a fundamental role in axon pathfinding.

Effects of skim milk, skim milk yogurt, orotic acid, and uric acid on lipid metabolism in rats.

The effects of feeding two milk products (skim milk and skim milk yogurt) and two proposed hypocholesterolemic factors (orotic acid and uric acid) on serum cholesterol (HDL, LDL, total, HDL/Total and HDL/LDL), liver lipids (total liver lipids and liver cholesterol), and aortal cholesterol were studied. Ten groups, of nine rats each, were fed isocaloric Chow-based diets containing water, 45% skim milk (SM), 45% skim milk yogurt (SMY), and 0.0025% orotic acid (OA) or 0.001% uric acid (UA), without or with cholesterol. The SM diet (with cholesterol) resulted not only in lower total cholesterol (P < 0.10), LDL cholesterol (P < 0.05), aortal cholesterol (P < 0.01), and liver cholesterol (P < 0.10), but also in increased HDL (P < 0.05) and HDL/LDL (P < 0.10) cholesterol ratio. The SMY diet, on the other hand, resulted in lowered total serum cholesterol (P < 0.05) and aortal cholesterol (P < 0.01) and in higher LDL (P < 0.05) cholesterol. The hypocholesterolemic effects were more marked for SM than for SMY. Addition of OA and UA to diets increased serum cholesterol, LDL cholesterol, and total liver lipids; the OA diet also increased liver cholesterol. Neither OA nor UA alone was the factor responsible for the hypocholesterolemic effects seen with SM and SMY feeding.

Nutritional knowledge and attitudes of dental students.

The nutritional knowledge and attitudes of 230 dental students were studied. The students answered 68.6% of the nutritional knowledge questions currectly, but the test scores were low because they were adversely affected by the degree of certainty. First-year students scored significantly higher than fourth-year students. There was no significant difference between scores of men and women. Knowledge scores were highest for questions on nutrition and oral health and lowest for those on nutritional assessment. Dental students generally expressed favorable attitudes toward nutrition and nutritional care of patients. They agreed that dentists were vital members of the health team and had a responsibility to become involved in health screening and nutrition education of patients. Dietitians were seen as valuable resources to be consulted about nutrition education of the dental patient. More first-year students supported the idea that dentists should prescribe nutritoinal supplements for patients, whereas more fourth-year students were undecided about this matter. There were no differences in nutrition attitude scores attributable to gender of the student or year in dental school. In this study, nutritional knowledge scores did not correlate with nutrition attitude scores.

Haematological and serum chemistry profiles of ferrets (Mustela putorius furo).

Female, male and castrated male ferrets were studied. Weight gain plateaued at 28 weeks of age with males about 500 g heavier than females. No statistically significant differences in haematology were observed with age, but alkaline phosphatase and alanine aminotransferase levels fell while glucose increased. Haemolysis led to various changes including marked increases in total protein, albumin, inorganic phosphate and sorbitol dehydrogenase.

Neutral sterol excretions in rats fed skim milk and skim milk yogurt diets.

Acceleration of cholesterol catabolism (through feces) has been proposed as one of the mechanisms for the hypocholesterolemic effect of dairy products. This study examined the effects of feeding two milk products (skim milk and skim milk yogurt) on fecal neutral sterol excretions in rats. Six groups of nine rats each were fed iso-caloric Chow-based diets containing water, 45% skim milk (SM), or 45% skim milk yogurt (SMY), without or with cholesterol. The results indicate that both SM and SMY increased the excretion of total neutral sterols under hyperlipemic conditions. The SMY diet (with cholesterol) also increased the excretion of coprostanol, a bacterial metabolite.

Identification of proteins downregulated during the postnatal development of the cat visual cortex.

To identify proteins that play a role in the development of the mammalian visual cortex, we have used an immunosuppression and rapid immunization strategy to generate monoclonal antibodies to antigens that are present in area 17 of the cat during the peak of cortical plasticity but are downregulated near the end of the plastic period. We report here the immunohistochemical and immunobiochemical characterization of six monoclonal antibodies that identify antigens preferentially expressed in the cat visual cortex at 5 weeks of age. Monoclonal antibodies Cat-305 and Cat-306 detect three immunoreactive elements that are not present at birth but are present at 5 weeks. The majority of immunoreactivity is associated with a population of cells in the white matter that are absent at 15 weeks of age. At both 5 and 15 weeks, a very small number of neurons show intense immunoreactivity throughout all processes, resembling that achieved with a Golgi stain. In addition, a diffuse band of immunoreactivity in layer IV is largely restricted to cortical areas 17 and 18. Cat-307 recognizes a 150 kDa soluble protein present in small cytoplasmic inclusions. These cytoplasmic "dot" are present in all layers, but are most prominent in layer V. Cat-307 immunoreactivity is present at birth and is completely downregulated by 15 weeks. Cat-104 and Cat-105 recognize a 200 kDa insoluble protein present at birth and at 5 weeks, but markedly downregulated by 15 weeks. At birth, the white matter, subplate, and layer I are most densely labeled, while at 5 weeks labeling is densest in layers II, III, and V. Cat-402 recognizes a number of high-molecular-weight antigens that are differentially expressed at 5 and 15 weeks of age. Stained non-neuronal cells that resemble protoplasmic astrocytes are present in all layers at both 5 and 15 weeks. At 5 weeks, but not at birth or 15 weeks, darkly immunoreactive radial processes are observed that run through the full depth of the cortex. We show here that immunoreactivity for several different monoclonal antibodies is detected selectively during the period of maximal developmental plasticity. The results demonstrate that the cat visual cortex at 5 weeks of age is molecularly distinct from the cortex at 15 weeks.

Effects of dietary fiber, carbohydrate, lipid and protein levels on serum and liver lipids in rats.

Response-surface regression analysis was used to study dietary levels of fiber, carbohydrate, lipid and protein to minimize serum and liver cholesterol and triglyceride levels and maximize serum high-density lipoprotein-cholesterol levels of male weanling rats. Because the dietary components were not statistically independent, they were studied in combinations of three variables. The three-variable combinations were the most useful in locating the desired maximum or minimum lipid responses in terms of the proportions of the dietary components. These analyses indicated that dietary carbohydrate, lipid and protein were better than dietary fiber for predicting the serum and liver lipid response levels. Response-surface contours and three-dimensional plots were developed for each lipid response except serum triglycerides, which were not predictable. The contours and three-dimensional plots were used to help determine those combinations of the diet components that would produce the desired maximum or minimum lipid responses. The statistical analyses indicated that the desired lipid response levels could be attained with a diet consisting of 3-5% neutral detergent bran fiber, 6-10% lipid, 54-55% carbohydrate, 26-30% protein and 4.7% vitamins and minerals.

Lowry protein assay using an automatic microtiter plate spectrophotometer.

The method of protein determination reported by Lowry et al. (1951, J. Biol. Chem. 193, 265-275) has been adapted for use with 96-well microtiter plates and an automatic microplate spectrophotometer. The spectrophotometer has been interfaced with a computer which plots the standard curve and calculates the protein content of each sample. The adapted method offers advantages over previously reported methods in that it is more rapid and uses a smaller sample volume (100 microliters) for samples containing 3-300 micrograms/ml (0.3-30 micrograms/assay) of protein. The method of Bensadoun and Weinstein (1976, Anal. Biochem. 70, 241-252) for precipitating microgram amounts of protein away from substances which interfere with the Lowry assay has also been adapted to this microplate procedure. These techniques should be particularly useful for laboratories where large numbers of samples containing a wide range of protein concentrations are assayed.

The high molecular weight Cat-301 chondroitin sulfate proteoglycan from brain is related to the large aggregating proteoglycan from cartilage, aggrecan.

Monoclonal antibodies Cat-301 and Cat-304 recognize a neuronal cell surface-associated chondroitin sulfate proteoglycan (CSPG), which is expressed during critical periods of postnatal development in the mammalian central nervous system (CNS). In the present study we show that the CNS CSPG identified by Cat-301/304 is similar to aggrecan, the high molecular weight CSPG from cartilage. By Western blot analysis, cartilaginous tissues, which are rich sources of aggrecan, have a high concentration of a high molecular weight CSPG which is immunoreactive with Cat-301 and 304. The Cat-301 and 304 epitopes, however, are partially masked by chondroitin sulfate glycosamino-glycan and are unmasked by digestion of the antigen with chondroitinase ABC. Although the antigen from both cartilage and CNS can be purified by CsCl buoyant density gradient centrifugation, a standard technique for purifying aggrecan, most of the antigen from the CNS has a lower buoyant density than that of cartilage. This may be due, in part, to the paucity of keratan sulfate substitution on the CNS antigen compared with that of the cartilage antigen. Both the CNS and cartilage antigens bind to hyaluronic acid, a feature characteristic of aggrecan. The physiochemical, biochemical, and functional properties of the Cat-301/304 antigen from cartilage are identical to aggrecan. The CNS antigen is similar, but not identical, to the cartilage antigen, and may thus represent another member of the family of high molecular weight CSPGs which bind to and aggregate with hyaluronic acid.

Phospholipase C-beta1 is present in the botrysome, an intermediate compartment-like organelle, and Is regulated by visual experience in cat visual cortex.

Monoclonal antibody Cat-307 identifies a 165 kDa neuronal protein expressed in the cat visual cortex during the period of sensitivity to alterations in visual experience (). Dark-rearing, which prolongs the sensitive period, also prolongs the expression of the Cat-307 protein. The Cat-307 protein localizes to an organelle, here called the botrysome (from the Greek botrys, cluster of grapes), that is located between the endoplasmic reticulum (ER) and Golgi apparatus. The botrysome is composed of small ring-shaped profiles with electron-dense coats. The size and morphology of the rings and their coats are similar to those described for ER to Golgi transport vesicles. Biochemically, the Cat-307 protein cofractionates with microsomes and partitions with subunits of the coatomer proteins that coat ER-to-Golgi transport vesicles. Partial amino acid sequencing reveals that the Cat-307 protein is phospholipase C-beta1, the G-protein-dependent phosphodiesterase that hydrolyses phosphatidylinositol 4,5 biphosphate into inositol 1,4,5 triphosphate and diacylglycerol after the stimulation of a variety of neurotransmitter receptors at the cell surface. These results suggest a role for phospholipase C-beta1 and the botrysome in developmental plasticity and provide a possible link between receptor activation at the cell surface and protein transport during neuronal development.

TOAD-64, a gene expressed early in neuronal differentiation in the rat, is related to unc-33, a C. elegans gene involved in axon outgrowth.

Using two-dimensional gel electrophoresis we previously identified membrane-associated proteins that are upregulated over the course of neurogenesis. One of these, TOAD-64 (Turned On After Division, 64 kDa), is expressed immediately after neuronal birth and is dramatically downregulated in the adult. The gene encoding TOAD-64 has now been cloned, and its sequence shows homology to the unc-33 gene from C. elegans, mutations in which lead to aberrations in axon outgrowth. Northern and in situ hybridization show that TOAD-64 mRNA is enriched in the nervous system and is developmentally regulated in parallel with the protein. The expression of the TOAD-64 protein and gene coincident with initial neuronal differentiation and the downregulation when the majority of axon growth is complete suggests a role in axon elaboration. Three additional lines of evidence support this possibility: TOAD-64 is upregulated following neuronal induction of P19 and PC12 cells; the protein is found in lamellipodia and filopodia of growth cones; and axotomy of the sciatic nerve induces reexpression. While the sequence of TOAD-64 lacks a signal sequence and therefore is likely to encode a cytoplasmic protein, biochemical experiments demonstrate that the protein is tightly, but noncovalently, associated with membranes. The data presented here suggest that TOAD-64 could be a central element in the machinery underlying axonal outgrowth and pathfinding, perhaps playing a role in the signal transduction processes that permit growing axons to choose correct routes and targets.

Excitotoxic death of a subset of embryonic rat motor neurons in vitro.

We have used cultures of purified embryonic rat spinal cord motor neurons to study the neurotoxic effects of prolonged ionotropic glutamate receptor activation. NMDA and non-NMDA glutamate receptor agonists kill a maximum of 40% of the motor neurons in a concentration- and time-dependent manner, which can be blocked by receptor subtype-specific antagonists. Subunit-specific antibodies stain all of the motor neurons with approximately the same intensity and for the same repertoire of subunits, suggesting that the survival of the nonvulnerable population is unlikely to be due to the lack of glutamate receptor expression. Extracellular Ca2+ is required for excitotoxicity, and the route of entry initiated by activation of non-NMDA, but not NMDA, receptors is L-type Ca2+ channels. Ca2+ imaging of motor neurons after application of specific glutamate receptor agonists reveals a sustained rise in intracellular Ca2+ that is present to a similar degree in most motor neurons, and can be blocked by appropriate receptor/channel antagonists. Although the lethal effects of glutamate receptor agonists are seen in only a subset of cultured motor neurons, the basis of this selectivity is unlikely to be simply the glutamate receptor phenotype or the level/pattern of rise in agonist-evoked intracellular Ca2+.

Reduction of functional N-methyl-D-aspartate receptors in neurons by RNase P-mediated cleavage of the NR1 mRNA.

One approach to studying the functional role of individual NMDA receptor subunits involves the reduction in the abundance of the protein subunit in neurons. We have pursued a strategy to achieve this goal that involves the use of a small guide RNA which can lead to the destruction of the mRNA for a specific receptor subunit. We designed a small RNA molecule, termed 'external guide sequence' (EGS), which binds to the NR1 mRNA and directs the endonuclease RNase P to cleave the target message. This EGS has exquisite specificity and directed the RNase P-dependent cleavage at the targeted location within the NR1 mRNA. To improve the efficiency of this EGS, an in vitro evolution strategy was employed which led to a second generation EGS that was 10 times more potent than the parent molecule. We constructed an expression cassette by flanking the EGS with self-cleaving ribozymes and this permitted generation of the specified EGS RNA sequence from any promoter. Using a recombinant Herpes simplex virus (HSV), we expressed the EGS in neurons and showed the potency of the EGS to reduce NR1 protein within neurons. In an excitotoxicity assay, we showed that expression of the EGS in cortical neurons is neuroprotective. Our results demonstrate the utility of EGSs to reduce the expression of any gene (and potentially any splice variant) in neurons.

Immune responses of dairy cattle to parainfluenza-3 virus in intranasal infectious bovine rhinotracheitis-parainfluenza-3 virus vaccines.

Two hundred and fifty dairy heifers were vaccinated at three to six months of age with an intranasal infectious bovine rhinotracheitis-parainfluenza-3 vaccine. Eighteen additional heifers were tested prior to vaccination and again three to four weeks after vaccination. Neither cell-mediated nor humoral immunity was significantly raised to parainfluenza-3 virus in either group of cattle.

Brain-derived neurotrophic factor induces excitotoxic sensitivity in cultured embryonic rat spinal motor neurons through activation of the phosphatidylinositol 3-kinase pathway.

Neurotrophic factors (NTFs) can protect against or sensitize neurons to excitotoxicity. We studied the role played by various NTFs in the excitotoxic death of purified embryonic rat motor neurons. Motor neurons cultured in brain-derived neurotrophic factor, but not neurotrophin 3, glial-derived neurotrophic factor, or cardiotrophin 1, were sensitive to excitotoxic insult. BDNF also induces excitotoxic sensitivity (ES) in motor neurons when BDNF is combined with these other NTFs. The effect of BDNF depends on de novo protein and mRNA synthesis. Reagents that either activate or inhibit the 75-kDa NTF receptor p75NTR do not affect BDNF-induced ES. The low EC50 for BDNF-induced survival and ES suggests that TrkB mediates both of these biological activities. BDNF does not alter glutamate-evoked rises of intracellular Ca2+, suggesting BDNF acts downstream. Both wortmannin and LY294002, which specifically block the phosphatidylinositol 3-kinase (PI3K) intracellular signaling pathway in motor neurons, inhibit BDNF-induced ES. We confirm this finding using a herpes simplex virus (HSV) that expresses the dominant negative p85 subunit of PI3K. Infecting motor neurons with this HSV, but not a control HSV, blocks activation of the PI3K pathway and BDNF-induced ES. Through the activation of TrkB and the PI3K signaling pathway, BDNF renders developing motor neurons susceptible to glutamate receptor-mediated cell death.