Postnatal development of forebrain regions in the autoimmune NZB-mouse. A model for degeneration in neuronal systems

Identification of proliferative progenitors associated with prominent postnatal growth of the pons

The pons controls crucial sensorimotor and autonomic functions. In humans, it grows sixfold postnatally and is a site of paediatric gliomas; however, the mechanisms of pontine growth remain poorly understood. We show that the murine pons quadruples in volume postnatally; growth is fastest during postnatal days 0–4 (P0–P4), preceding most myelination. We identify three postnatal proliferative compartments: ventricular, midline and parenchymal. We find no evidence of postnatal neurogenesis in the pons, but each progenitor compartment produces new astroglia and oligodendroglia; the latter expand 10- to 18-fold postnatally, and are derived mostly from the parenchyma. Nearly all parenchymal progenitors at P4 are Sox2⁺Olig2⁺, but by P8 a Sox2⁻ subpopulation emerges, suggesting a lineage progression from Sox2⁺ ‘early' to Sox2⁻ ‘late' oligodendrocyte progenitor. Fate mapping reveals that >90% of adult oligodendrocytes derive from P2–P3 Sox2⁺ progenitors. These results demonstrate the importance of postnatal Sox2⁺Olig2⁺ progenitors in pontine growth and oligodendrogenesis.

Postnatal growth of the pons is not well characterized. Here the authors show that growth of the murine pons is fastest during postnatal day 0–4, a period preceding myelination, and is primarily driven by an expansion of the oligodendrocyte population that derive from Sox2⁺Olig2⁺ progenitors.

Mapping postnatal mouse brain development with diffusion tensor microimaging

While mouse brain development has been extensively studied using histology, quantitative characterization of morphological changes is still a challenging task. This paper presents how developing brain structures can be quantitatively characterized with magnetic resonance diffusion tensor microimaging coupled with techniques of computational anatomy. High resolution diffusion tensor images of ex vivo postnatal mouse brains provide excellent contrasts to reveal the evolutions of mouse forebrain structures. Using anatomical landmarks defined on diffusion tensor images, tissue level growth patterns of mouse brains were quantified. The results demonstrate the use of these techniques to three-dimensionally and quantitatively characterize brain growth.

Neurotoxic effects of postnatal thimerosal are mouse strain dependent

The developing brain is uniquely susceptible to the neurotoxic hazard posed by mercurials. Host differences in maturation, metabolism, nutrition, sex, and autoimmunity influence outcomes. How population-based variability affects the safety of the ethylmercury-containing vaccine preservative, thimerosal, is unknown. Reported increases in the prevalence of autism, a highly heritable neuropsychiatric condition, are intensifying public focus on environmental exposures such as thimerosal. Immune profiles and family history in autism are frequently consistent with autoimmunity. We hypothesized that autoimmune propensity influences outcomes in mice following thimerosal challenges that mimic routine childhood immunizations. Autoimmune disease-sensitive SJL/J mice showed growth delay; reduced locomotion; exaggerated response to novelty; and densely packed, hyperchromic hippocampal neurons with altered glutamate receptors and transporters. Strains resistant to autoimmunity, C57BL/6J and BALB/cJ, were not susceptible. These findings implicate genetic influences and provide a model for investigating thimerosal-related neurotoxicity.

Murine models of brain aging and age-related neurodegenerative diseases

In the past, structural changes in the brain with aging have been studied using a variety of animal models, with rats and nonhuman primates being the most popular. With the rapid evolution of mouse genetics, murine models have gained increased attention in the neurobiology of aging. The genetic contribution of age-related traits as well as specific mechanistic hypotheses underlying brain aging and age-related neurodegenerative diseases can now be assessed by using genetically-selected and genetically-manipulated mice. Against this background of increased demand for aging research in mouse models, relatively few studies have examined structural alterations with aging in the normal mouse brain, and the data available are almost exclusively restricted to the C57BL/6 strain. Moreover, many older studies have used quantitative techniques which today can be questioned regarding their accuracy. Here we review the state of knowledge about structural changes with aging in outbred, inbred, genetically-selected, and genetically-engineered murine models. Moreover, we suggest several new opportunities that are emerging to study brain aging and age-related neurodegenerative diseases using genetically-defined mouse models. By reviewing the literature, it has become clear to us that in light of the rapid progress in genetically-engineered and selected mouse models for brain aging and age-related neurodegenerative diseases, there is a great and urgent need to study and define morphological changes in the aging brain of normal inbred mice and to analyze the structural changes in genetically-engineered mice more carefully and completely than accomplished to date. Such investigations will broaden knowledge in the neurobiology of aging, particularly regarding the genetics of aging, and possibly identify the most useful murine models.

Evaluation of memory, learning ability, and clinical neurologic function in pathogen-free mice with systemic lupus erythematosus

OBJECTIVE

To determine if neurologic impairment is related to progressive autoimmune disease in 3 murine models of systemic lupus erythematosus (SLE): MRL/lpr, NZB, and NZB/WF1.

METHODS

Sensorimotor function, learning, and memory were tested within strains at specific ages, before and after the appearance of SLE. These parameters were also compared between strains for young and older lupus mice and their congenic controls with reduced autoimmune disease (MRL/lpr versus MRL/+; NZB versus NZB/xid).

RESULTS

Abnormal neurologic features were present at a much higher frequency in MRL/lpr mice than in age-matched MRL/+ control mice, and sensorimotor function deficits were also seen in NZB/WF1 mice. Strains that develop lupus showed deficits on a water-escape, distal cue discrimination task and on a food-rewarded, proximal cue discrimination task, but the cognitive impairments were not global.

CONCLUSION

MRL/lpr, NZB, and NZB/WF1 mice differed in terms of which behaviors were impaired as well as when those impairments appeared.

Developmental dyslexia and animal studies: at the interface between cognition and neurology

Recent findings in autopsy studies, neuroimaging, and neurophysiology indicate that dyslexia is accompanied by fundamental changes in brain anatomy and physiology, involving several anatomical and physiological stages in the processing stream, which can be attributed to anomalous prenatal and immediately postnatal brain development. Epidemiological evidence in dyslexic families led to the discovery of animal models with immune disease, comparable anatomical changes and learning disorders, which have added needed detail about mechanisms of injury and plasticity to indicate that substantial changes in neural networks concerned with perception and cognition are present. It is suggested that the disorder of language, which is the cardinal finding in dyslexic subjects, results from early perceptual anomalies that interfere with the establishment of normal cognitive-linguistic structures, coupled with primarily disordered cognitive processing associated with developmental anomalies of cortical structure and brain asymmetry. This notion is supported by electrophysiological data and by findings of anatomical involvement in subcortical structures close to the input as well as cortical structures involved in language and other cognitive functions. It is not possible at present to determine where the initial insult lies, whether near the input or in high-order cortex, or at both sites simultaneously.

Lashley maze learning deficits in NZB mice

In a prior study we found excellent Lashley III maze learning in BXSB mice and poor learning in NZB mice, despite the fact that both strains are autoimmune and develop cortical ectopias. This prompted us to examine NZB Lashley maze performance in detail, including comparisons to other strains and attempts to improve performance by giving additional trials with or without additional intramaze visual cues. In conventional Lashley testing (10 trials), RF mice (non-autoimmune and nonectopic) and BXSBs performed well in the Lashley maze. They had high learning indices and few errors. NZB mice performed poorly, with low learning indices and many errors. Even with additional trials or additional trials plus intramaze cues, NZB performance remained poor. The number of backward and forward errors stayed high; learning indices were low. Since both BXSB and NZB mice develop autoimmune disorders and cortical ectopias, it is unlikely that differential Lashley performance is the result of the presence of these phenomena. NZB mice are known to have alterations in their hippocampal morphology, and this is a possible mediator of the Lashley deficit.