Comprehensive Evaluation of the 5XFAD Mouse Model for Preclinical Testing Applications: A MODEL-AD Study

The ability to investigate therapeutic interventions in animal models of neurodegenerative diseases depends on extensive characterization of the model(s) being used. There are numerous models that have been generated to study Alzheimer's disease (AD) and the underlying pathogenesis of the disease. While transgenic models have been instrumental in understanding AD mechanisms and risk factors, they are limited in the degree of characteristics displayed in comparison with AD in humans, and the full spectrum of AD effects has yet to be recapitulated in a single mouse model. The Model Organism Development and Evaluation for Late-Onset Alzheimer's Disease (MODEL-AD) consortium was assembled by the National Institute on Aging (NIA) to develop more robust animal models of AD with increased relevance to human disease, standardize the characterization of AD mouse models, improve preclinical testing in animals, and establish clinically relevant AD biomarkers, among other aims toward enhancing the translational value of AD models in clinical drug design and treatment development. Here we have conducted a detailed characterization of the 5XFAD mouse, including transcriptomics, electroencephalogram, in vivo imaging, biochemical characterization, and behavioral assessments. The data from this study is publicly available through the AD Knowledge Portal.

Comprehensive Evaluation of the 5XFAD Mouse Model for Preclinical Testing Applications: A MODEL-AD Study

The ability to investigate therapeutic interventions in animal models of neurodegenerative diseases depends on extensive characterization of the model(s) being used. There are numerous models that have been generated to study Alzheimer's disease (AD) and the underlying pathogenesis of the disease. While transgenic models have been instrumental in understanding AD mechanisms and risk factors, they are limited in the degree of characteristics displayed in comparison with AD in humans, and the full spectrum of AD effects has yet to be recapitulated in a single mouse model. The Model Organism Development and Evaluation for Late-Onset Alzheimer's Disease (MODEL-AD) consortium was assembled by the National Institute on Aging (NIA) to develop more robust animal models of AD with increased relevance to human disease, standardize the characterization of AD mouse models, improve preclinical testing in animals, and establish clinically relevant AD biomarkers, among other aims toward enhancing the translational value of AD models in clinical drug design and treatment development. Here we have conducted a detailed characterization of the 5XFAD mouse, including transcriptomics, electroencephalogram, in vivo imaging, biochemical characterization, and behavioral assessments. The data from this study is publicly available through the AD Knowledge Portal.

Alpha and beta subunits of CaM-kinase II are localized in different neurons in chick ciliary ganglion

The ciliary ganglion of the chicken contains only two types of neurons. Using monoclonal antibodies against the alpha and the beta subunits of Ca2+/calmodulin-stimulated protein kinase II (CaMPK-II) we found that the alpha-subunit was localized to the choroid neurons while beta subunit was associated with the ciliary neurons. As both neurons receive their inputs from the oculomotor nerve, while their postganglionic axons leave via different nerves, the ciliary ganglion of the chicken is a neuronal system in which the functional differences between alpha and beta CaMPK-II homopolymers in the regulation of synaptic transmission can be investigated.

Cryo-immunogold ultrastructural localization of laminin in adult rat peripheral nerve

Elucidation of the functional roles of the extracellular matrix component laminin in adult peripheral nerve has been hindered by differing accounts of its ultrastructural localization. This is the first report applying the advantages of the cryo-immunogold technique to laminin localization in peripheral nerve. Laminin labelling was found over the basal lamina and possibly over the immediately subjacent Schwann cell plasma membrane, but specific labelling appeared to be absent from other membranes (including those of non-myelinated axon/Schwann cell clusters) and from endoneurial collagen fibrils. It would appear that the functional roles played by laminin in normal adult peripheral nerve are likely to be mediated via its localization in the basal lamina, rather than through a more widespread distribution within the endoneurium.

Imaging myelinated nerve fibres by confocal fluorescence microscopy: individual fibres in whole nerve trunks traced through multiple consecutive internodes

Current methods of morphological analysis do not permit detailed imaging of individual myelinated fibres over substantial lengths without disruption of neighbouring, potentially significant, cellular and extracellular relationships. We report a new method which overcomes this limitation by combining aldehyde-induced fluorescence with confocal microscopy. Myelin fluorescence was intense relative to that from other tissue components, enabling individual myelinated nerve fibres to be traced for distances of many millimeters in whole PNS nerve trunks. Image obtained with a Bio-Rad MRC-600 confocal laser scanning microscope clearly displayed features of PNS and CNS myelinated fibres including nodes of Ranvier; fibre diameter; sheath thickness and contour; branch points at nodes; as well as (in the PNS) Schmidt-Lanterman incisures and the position of Schwann cell nuclei. Direct comparisons using the same specimens (whole nerve trunks; also teased fibres) showed confocal imaging to be markedly superior to conventional fluorescence microscopy in terms of contrast, apparent resolution and resistance to photobleaching. Development of the fluorophore was examined systemically in sciatic nerves of young adult rats. In separate experiments, animals were perfused systemically using (1) 5% glutaraldehyde; (2) Karnovsky's solution; (3) 4% paraformaldehyde; buffered with either 0.1 M sodium phosphate or sodium cacodylate (pH 7.4). The concentration of glutaraldehyde in the fixative solution was the principal determinant of fluorescence intensity. Confocal imaging was achieved immediately following perfusion with 5% glutaraldehyde or Karnovsky's. Fluorescence intensity increased markedly during overnight storage in these fixatives and continued to increase during subsequent storage in buffer alone. The fluorophore was stable and resistant to fading during storage (15 months at least), enabling data collection over extended periods. To demonstrate application of the method in neuropathology, individual fibres in transected sciatic nerve trunks were traced through multiple successive internodes: Classical features of Wallerian degeneration (axonal swelling and debris; ovoid formation and incisure changes; variation among fibres in the extent of degeneration) were displayed. The method is compatible with subsequent ultrastructural examination and will complement existing methods of investigation of myelinated fibre anatomy and pathology, particularly where preservation of 3-dimensional relationships or elucidation of spatial gradients are required.

Morphometric analysis of axons myelinated during adult life in the mouse superior cervical ganglion

In experimental studies addressing the regulation of myelin formation and maintenance by Schwann cells, the sympathetic nervous system of young adult rodents has served a key role as an essentially nonmyelinated yet modifiable control tissue. Nevertheless there is clear evidence of substantial myelination in the superior cervical ganglion (SCG) of normal mice and rats of more advanced age. Against this background, interpretation of experimental outcomes in particular sympathetic tissues will require detailed quantitative control data taking account of animal age. To provide a baseline for future investigations on myelin remodelling, an ultrastructural morphometric study of myelinated fibres in the SCG was undertaken in 4 strains (QS, Balb/C, C57 and CBA) of adult male mice aged 32-72 wk. Numbers of myelinated fibres in SCG cross-sections varied substantially between individual animals, and the mean numbers for QS (132), Balb/C (165) and CBA (254) were significantly higher than that for C57 (32). Both axonal and fibre diameter were distributed unimodally (means for the 4 strains ranged from 2.3-2.4 microns and 3.2-3.6 microns respectively). Myelin spiral length was distributed unimodally and skewed to the right (range of means = 227-357 microns) and was significantly greater in QS mice as compared with the other 3 strains. While the mean g ratio (axonal diameter/fibre diameter) was significantly lower in QS mice than in the other 3 strains, the range for mean g ratio was 0.64-0.73, indicating that myelination had proceeded appropriately even though late in onset in this tissue. The index of circularity was high in all strains, both for axons (range of means = 0.80-0.88) and fibres (range of means = 0.84-0.89). The small axonal and fibre diameter and unimodal distribution are consistent with the characteristics of autonomic myelinated fibres and it is probable that most are postganglionic sympathetic fibres arising within the SCG. In terms of providing a sufficient population of myelinated fibres for future experimental studies, the QS, Balb/C and CBA strains would be preferable to C57 mice.

Thyroid morphology and function and its role in thermoregulation in the newborn southern elephant seal (Mirounga leonina) at Macquarie Island

The thyroid gland of the newborn southern elephant seal pup exhibits markedly increased secretory activity during the first 24 hours after birth. Thyroid epithelial cell height is cuboidal to columnar for pups from birth to 48 hours postpartum after which it decreases by five days of age. Ultrastructurally the thyroid epithelial cells show pseudopodia protruding into the lumen at zero, two and six hours after birth. After 24 hours postpartum pseudopodia are rarely observed in thyroid follicles from two to 20 days old pups. The number of colloid droplets increases by six hours after birth and they are distributed throughout the cytoplasm. At 24 hours and two days, few colloid droplets are observed. Plasma T4 concentration increases three-fold from birth, to peak at six hours postpartum after which it steadily declines. Plasma concentration of T3 increases eight-fold between birth and 24 hours postpartum. T3 levels remain high until five days to seven days, then decrease to 20 days. The observed changes in thyroid epithelial cell height and ultrastructure is strongly suggestive of increased secretion of thyroid hormones during the first six hours of postnatal life. This pattern of thyroid activity is similar to that in other newborn mammals which have been examined. The thyroid gland of the southern elephant seal is markedly active at birth and is responsible for the elevated levels of T4 and T3, thus playing a vital role in maintaining the body temperature of the newborn seal when it enters the harsh environment of the sub-Antarctic.

The pineal gland in newborn southern elephant seals, Mirounga leonina

In the newborn southern elephant seal the pineal gland is very large, and both pineal and plasma melatonin concentration is elevated. The pineal gland was investigated during the first 24 h, and up to 20 days of age, in elephant seal pups. A primary aim of this investigation was to determine whether there are obvious ultrastructural characteristics of pinealocytes that are exhibiting extraordinarily high levels of activity. Blood and pineal glands were collected from thirty seven pups of known age which were sampled at random from early September to early November (1985) at Macquarie Island. The pineal gland is large (mean weight, 4.71 +/- 0.35 gm, range 1-9.3 gm) and actively secreting melatonin at birth. Melatonin concentrations were extremely variable, yet very high in pups during the first 24 h post-partum. Mean melatonin plasma concentration for pups 0-24 h was 17632.8 +/- 5723.8 pmol/l (4090.8 +/- 1327.9 pg/ml), ranging from 126 pmol/l (29 pg/ml) to 297000 pmol/l (68904 pg/ml). Electron microscopic examination did not reveal any marked changes in pinealocyte ultrastructure suggestive of increased secretory activity during this period. The large and extremely active pineal gland in newborn southern elephant seal suggests that it is actively involved in thermoregulation.

Microwave irradiation as a form of fixation for dental pulp

This study investigated developments in microwave energy fixation and the general applicability of microwave fixation to studies of dental pulp. Rat mandibles with incisors were dissected out and immersed in various solutions before and after exposure to microwave energy. Histological examination showed no combination with microwave fixation to be equal in quality to control tissues fixed in formalin. Inferior but satisfactory results could be achieved by immersion of tissues in formalin after microwave irradiation, a step thought to protect the microwave fixed tissue from subsequent damage caused by decalcification. Good fixation of tissues outside the pulp was achieved using microwave energy. Further investigation is required to perfect microwave fixation of pulpal tissue.

Growth From Birth to 20 Days in the Elephant Seal, Mirounga-Leonina, at Macquarie-Island

Recent investigations by members of Australian National Antarctic Research Expeditions to Macquarie I. have revealed a decrease in the elephant seal population there of approximately 50% over the last 36 years. Lower birth weights and/or slower growth during the lactation period might explain this decrease. To test this hypothesis, growth of pups was studied from birth to 20 days during the 1984 and 1985 breeding seasons; these results were compared as far as possible with similar results for the 1956 and 1965 seasons. Average birth weight has not changed significantly over the last 20 years; it is suggested that if food supply were a major factor in the reduction of the elephant seal population, then birth weights in 1985 would have been lower than those in 1956. At birth, male pups were 7% (3 kg) heavier than female pups in 1985. Results from previous years suggest that this is probably normal in this seal. The weight of pups near weaning (20 or 21 days old) is shown to be significantly less in 1984 and 1985 than 1965, but this may be explained by differences in methodology. It is concluded that, on the evidence available, the pattern of pup growth on Macquarie I. has not altered significantly with time, but more work is needed to reach a clear conclusion.

The structure of the lung of the newborn marsupial bandicoot, Isoodon macrourus

In bandicoots, implantation takes place 9.5 days after mating and birth occurs 3 days later. It is therefore of interest to examine the lungs of newborn marsupials to ascertain the stage of lung development with respect to other organs and other mammals in view of the short period of time allowed for maturation of lung tissue. The newborn bandicoot lung is composed of a primitive system of branching airways which terminate in large blind sacs; alveolar ducts or alveoli are not present. The terminating sacs, which are delineated by thick connective-tissue septae, have a highly vascularised internal lining. Thin squamous cells and numerous type-II "surfactant"-secreting cells constitute the air interface of the sac. Corticosteroids influence the development of the eutherian fetal lung by accelerating pulmonary maturation and increasing the synthesis of surfactant. Since recent evidence indicates that the adrenal of the bandicoot is active at, or before birth, it is possible that this organ also plays an important role in preparing the lungs of the marsupial for extra-uterine life in the pouch.