The epidemiology of BSE in cattle herds in Great Britain. II. Model construction and analysis of transmission dynamics.

Mathematical model that describe the key processes determining the pattern of the bovine spongiform encephalopathy (BSE) epidemic in British cattle are derived that allow for infection from feed as well as maternal and direct horizontal transmission. Heterogeneous susceptibility classes are also incorporated into the analysis. Maximum likelihood methods are used to estimate parameters and to obtain confidence intervals from available experimental and epidemiological data. A comprehensive sensitivity analysis of all model parameters and distributional assumptions is presented. Additional validation is provided by fitting the model to independent data collected in Northern Ireland. Model estimates and predictions based on BSE case data for Great Britain and Northern Ireland, together with their implications, are reviewed, and future research priorities discussed.     

Match probability calculations for multi-locus DNA profiles

The paper considers aspects of the match probability calculation for multi-locus DNA profiles and a related calculation which aims to assess the probability that a pair of profiles is concordant for the presence and absence of bands. It is suggested that levels of allelism and linkage for multi-locus profiles may be higher than reported in previous studies, and that comparison of bandsharing values between different studies is problematic. Our view is that the independence assumptions which underpin the calculations have not been established. The effect of ignoring (local) heterogeneities in band frequencies may be non-conservative. Concerns thus raised about the match probability calculation could be important in practical casework. The speculative nature of some aspects of the concordance probability calculation would seem to render it inappropriate for use in court.Editor's commentsThe author continues the investigation of multilocus probes begun introduced by Curnow in this volume. He contrasts bandsharing estimates from Jeffreyset al. (1991) and the UK Forensic Science Service. Much of the difference is attributable to the greater resolving power of Jeffreys' gels (J.S. Buckleton, personal communication). Tests for independence of multilocus probe bands, and studies of the joint possession of subsets of bands within populations, were conducted by the UK Forensic Science Service, but not published (J.S. Buckleton, personal communication). In spite of the complexities of multilocus probe profiles, it is interesting to note that, just as when several single-locus probes are used, the same profiles are not found for unrelated people in large populations.     

Repeatability of LH responses by lambs to monthly challenge with synthetic gonadotrophin releasing hormone (GnRH)

The aim of this experiment with ram and ewe lambs was to test the hypothesis that there are consistent individual differences in Luteinising Hormone (LH) response to Gonadotrophin Releasing Hormone (GnRH).Pre-puberal Border-Leicester × Merino lambs (15 of each sex) aged 9 weeks were challenged with either 0, 30 or 60 μg synthetic GnRH each month for 7 months (December to June). The lambs were then rested from this monthly routine until they were challenged an eighth time in September at 48 weeks of age. Luteinising Hormone response (area under LH release curve) was measured each month and the repeatability of individual LH responses calculated.There was a significant interaction (P < 0.01) between treatment month and sex reflecting a fall in LH response by ram lambs after a peak in February, while at the same time responses by ewe lambs increased to peak again in May. LH response also increased with GnRH dose (30 vs. 60 μg; P < 0.05).Responses by individual lambs were ranked 1 to 5 each month within sex and GnRH doses (30 and 60 μg only). Highest ranked lambs had LH responses 1.4 to 7.0 times larger than lowest ranked lambs. Repeatability of rank between months was poor in all groups except ewe lambs given 60 μg GnRH, where three of the five lambs repeated a particular rank at 5 of the 8 sample months. However, the repeatability of response in this group was not considered to be sufficient to reject the null hypothesis. It was concluded that if consistent individual differences do exist they may be subtle and easily masked by factors such as GnRH dose, sex, age and season.     

Differentiation of bundle sheath,mesophyll, and distinctive cells in the C4 grass Arundinella hirta (Poaceae)

The C₄ grass Arundinella hirta is characterized by unusual leaf blade anatomy: veins are widely spaced and files of bundle-sheath-like cells, the distinctive cells, form longitudinal strands that are not associated with vascular tissue. While distinctive cells (DCs) appear to function like bundle sheath cells (BSCs), they differ developmentally in two ways: they are derived from ground meristem rather than procambium and they are formed 1–2 plastochrons later. This study describes ultrastructural features of differentiating of BSCs, DCs, and associated mesophyll cells (MCs) during leaf development. BSCs and DCs differ from adjacent MCs by undergoing earlier cell enlargement, greater rates of chloroplast enlargement, reduction of chloroplast thylakoids at late stages of differentiation, more extensive starch formation, greater wall thickening, and deposition of a suberin lamella. The precocious delimitation of the bundle sheath layer is reflected in earlier BSC enlargement and vacuole growth. Derivation of DCs from ground meristem is correlated with late developmental changes in chloroplast size, wall thickness, and plasmodesmatal density. Despite these differences in timing of events, particularly at early stages, the development of the specialized structural features of BSCs and DCs is essentially similar. Thus, proximity to vascular tissue appears to be nonessential for the coordination and regulation of BSC- and MC-specific developmental events.     

Effects of reproductive resource supplementation on space-use patterns in Dendrobates pumilio

Summary I increased the availability of tadpole-rearing sites (bromeliads) and oviposition sites (leaf litter) and examined the effects on space-use patterns in adult Dendrobates pumilio at the La Selva Biological Reserve in northeastern Costa Rica. I made 4158 observations of 986 marked adults during the seven-month study period. The addition of leaf litter did not result in increased density, but the addition of bromeliads did. The addition of leaf litter resulted in increased home-range size, but the effect depended on bromelial addition and sex. Home-range size was greater for females than males, and may be related to parental care and/or mate selection. Home-range size was not correlated with density. Spatio-temporal overlap was not affected by resource supplementation but the proportion of females captured in sites shared with males varied temporally. Dispersion was no affected by bromeliad supplementation but males on litter-addition plots were less clumped than males on other plots. These results indicate that the density increase observed on bromeliad-addition plots was accommodated by frogs utilizing previously unoccupied space. Frogs were captured more frequently at bromeliads on bromeliad-supplemented plots than on litter-addition and control plots. The size of the area defended by territorial males is smaller than home-range size indicating the absence of home-range defense.     

Inactivation of cyclic GMP-dependent protein kinase by N alpha-tosyl-L-lysine chloromethylketone

Cyclic GMP-dependent protein kinase from bovine lung and cyclic AMP-dependent protein kinase from bovine heart are inactivated by N^α-tosyl-L-lysine chloromethylketone (TLCK) in the presence of cyclic GMP and cyclic AMP, respectively. The inactivation of both protein kinases is pseudo-first order, suggesting the rate limiting step is beyond the binding of TLCK. Cyclic GMP-dependent protein kinase is inactivated less than $\text{1}\text{4}$ as rapidly as cyclic AMP-dependent protein kinase, although it shows a higher apparent affinity for TLCK. Cyclic AMP stimulated the rate of inactivation of cyclic AMP-dependent protein kinase 10-fold but cyclic GMP stimulated the rate of inactivation of cyclic GMP-dependent protein kinase only 1.5-fold. The rate of inactivation of cyclic GMP-dependent protein kinase by TLCK is sufficiently rapid (half-time of about 30 min at 37°C with 2 mM TLCK) to account for the effects of TLCK on cell growth observed by others.     

Analysis of glutathione-enhanced differentiation by microfilariae of Onchocerca lienalis (Filarioidea: Onchocercidae) in vitro

Reduced glutathione (GSH), but not its oxidized form (GSSG), stimulated development of Onchocerca lienalis microfilariae to the late first-larval stage in vitro. The degree and frequency of development was dose-related with a peak of activity at 15 mM, a concentration that is similar to known intracellular levels of GSH. To determine the mode(s) of action of this multifunctional compound, other reducing agents (L-cysteine, dithiothreitol), cysteine delivery agents (N-acetyl-L-cysteine, L-thiazolidine-4-carboxylic acid, L-2-oxothiazolidine-4-carboxylic acid), cysteine analogues (S-methyl-L-cysteine, D-glucose-L-cysteine, cysteine ethyl ester), free-component amino acids of GSH (glutamic acid, cysteine, and glycine), a specific metabolic inhibitor of gamma-glutamyl synthetase (buthionine sulfoximine), and an inhibitor of gamma-glutamyl transpeptidase (gamma-glutamyl glutamic acid) were also tested at concentrations of 0.01-50 mM in this system. N-acetyl-L-cysteine at 1-5 mM and D-glucose-L-cysteine at 2.5-10 mM significantly enhanced development. In contrast to those worms maintained in GSH-supplemented medium, microfilariae exposed to GSH for only the first 24 hr showed no enhancement by day 7 in culture. Neither buthionine sulfoximine nor gamma-glutamyl glutamic acid at 0.01-35 mM inhibited the effects of 15 mM GSH or 1 mM N-acetyl-L-cysteine. Results indicate that GSH or other cysteine analogues possessing a free sulfhydryl group must be present in the extranematodal environment to support microfilarial differentiation in vitro.