Ultrastructural and behavioural changes precede amyloid deposition in a transgenic model of Alzheimer's disease.

We describe the thorough characterisation of a new transgenic mouse line overexpressing the 695-amino acid isoform of human amyloid precursor protein harbouring the Swedish double familial Alzheimer's disease mutation. This line, referred to as TAS10, exhibits neuropathological features and cognitive deficits that are closely correlated to the accumulation of Abeta in their brain and that are reminiscent of those observed in AD. Data on the TAS10 line are presented at five time points: 2, 6, 12, 18 and 24 months in a longitudinal study. The TAS10 line is characterised by the following changes: i) significant age-related increases in the levels of total and individual species (1-40, 1-42) of beta-amyloid in the brains of transgenics compared with non-transgenic littermates; ii) transgenic mice showed pronounced spatial learning deficits in the Morris water maze at 6 months and working memory deficits by 12 months; iii) amyloid plaque and associated pathologies were observed by the 12-month time point and the burden increased substantially, particularly in the cortex, by 18 months; iv) electron microscopy of the hippocampus of transgenic mice showed evidence of abnormal ultrastructural features such as dystrophic neurites and lipid deposits that developed from 6 months and increased in number and severity with age. Morphometric studies demonstrate that the synapse to neuron ratio is higher in transgenics than in control mice at 12 months, but this ratio decreases as they age and synapse size increases. Thus, this mouse model exhibits a close correlation of amyloid burden with behavioural deficits and ultrastructural abnormalities and so represents an ideal system to study the mechanisms underlying the impact of amyloid pathology on CNS function.

A survey of hantavirus antibody in small-mammal populations in selected United States National Parks.

Hantavirus activity in 39 National Parks in the eastern and central United States was surveyed by testing 1,815 small mammals of 38 species for antibody reactive to Sin Nombre virus. Antibody-positive rodents were found throughout the area sampled, and in most biotic communities. Antibody was detected in 7% of 647 deer mice (Peromyscus maniculatus), 2% of 590 white-footed mice (P. leucopus), 17% of 12 rice rats (Oryzomys palustris), 3% of 31 cotton rats (Sigmodon hispidus), and 33% of 18 western harvest mice (Reithrodontomys megalotis). Antibody was also found in three of six species of voles, and in one of 33 chipmunks (Tamias minimus). Prevalence among Peromyscus was highest in the northeast. Although few cases of hantavirus pulmonary syndrome have been identified from the eastern and central regions, widespread infection in reservoir populations indicates that potential exists for human infection throughout much of the United States.

Ticks (Acari: Ixodidae) in Bulloch County, Georgia.

An 18-mo study was conducted in Bulloch County, Georgia, to determine tick species composition, seasonal activity of individual tick species, and host-tick associations. The following 7 methods of tick collection were included: (1) live trapping of potential host animals, (2) checking wild game, (3) drag sampling, (4) carbon dioxide attraction, (5) checking livestock, road kills, nests, and burrows, (6) samples submitted from veterinarians, and (7) ticks collected by local residents and submitted for identification. Twelve tick species (Ixodidae) were identified. Blacklegged tick, Ixodes scapularis Say, and American dog tick, Dermacentor variabilis (Say), had the widest host ranges and were the most numerous. White-tailed deer, Odocoileus virginianus (Zimmermann), supported 5 tick species, the greatest number on any host. Of 55 animal species examined, 16 mammal, 5 bird, and 3 reptile species were parasitized by ticks. Opossums, Didelphis virginiana Kerr, and cotton mice, Peromyscus gossypinus (LeConte), were the most commonly examined wild animals.

Image analysis of bromodeoxyuridine (BrdU) staining for measurement of S-phase in rat and mouse liver.

We developed a system for quantifying the numbers of bromodeoxyuridine (BrdU)-labeled hepatocyte nuclei in rat and mouse liver with an automated image analysis system. We began by developing a protocol for BrdU staining that would provide consistently intense staining to facilitate identification of both labeled and unlabeled nuclei by image analysis. Preliminary studies detected and characterized hepatocyte nuclei and differentiated them from non-hepatocyte nuclei using area and form factors. The parameters were selected to optimize discrimination between the two populations, selecting 90% of hepatocyte and 5% non-hepatocyte nuclei. Finally, we developed a program for automatic counting of BrdU-labeled hepatocyte and total hepatocyte nuclei. Results obtained from this method correlated well with data collected by a microscopist over a wide range of labeling indices. The automated system reduces interobserver variation and should minimize intraobserver error, as well as reducing the tedium of measuring labeling indices in the liver. Moreover, the techniques described should be applicable to other tissues.

Establishment of the foreign partheonogenetic tick Amblyomma rotundatum (Acari: Ixodidae) in Florida.

The parthenogenetic tick Amblyomma rotundatum, a Central and South American species, has become established in southern Florida. The date of introduction is unknown, but it is suspected to be either during the 1930s, when 1 of its natural hosts, the giant or marine toad, Bufo marinus, was introduced to southern Florida as a potential biological control of pest beetles in sugar cane fields, or between 1955 and 1964 when specimens of B. marinus were accidentally or deliberately released in the greater Miami area. Several museum specimens of this toad collected in the Miami area 25 April 1979 had nymphal and adult A. rotundatum attached. Subsequent examination of living giant toads collected at another Miami area site from 1983 through 1985 revealed larval, nymphal, and adult A. rotundatum and confirmed colonization of this tick. Under laboratory conditions, another neotropical amphibian and reptile tick, Amblyomma dissimile, is capable of transmitting Cowdria ruminantium, the causative agent of heartwater, a disease present in the Caribbean area. Therefore, we suggest that A. rotundatum should also be tested for vectorial competence.

Ixodes affinis Neumann (Acari: Ixodidae): new host and distribution records, description of immatures, seasonal activities in Georgia, and laboratory rearing.

New host and distributional records, seasonal activities in Georgia, laboratory rearing data, and taxonomic description of nymphal and larval Ixodes affinis are presented. Our data expand the list of known natural hosts of this species, record for the first time several natural hosts of larvae and nymphs, provide information on feeding periods of all stages, preecdysial intervals, preovipositional, ovipositional, and incubational periods, as well as provide information on fecundity. The immatures are fully described and SEM micrographs of them are presented.

Spring shoot growth in douglas-fir may be initiated by gibberellins exported from the roots.

Trials conducted under controlled environments demonstrated that the delay of bud activity of Douglas-fir (Pseudotsuga menziesii) seedlings occasioned by low temperature of the soil could be eliminated by application of gibberellic acid. Analyses of field-grown plants showed a parallel increase in bud activity, level of gibberellin-like compounds in xylem sap, and soil temperature during February and March.