Phorbol ester-induced neuritic alterations in the rat neocortex. Structural and immunocytochemical studies

Focal damage to the adult rat neocortex induces wound healing accompanied by axonal sprouting and dendritic structural plasticity

Accumulating evidence indicates that damage to the adult mammalian brain evokes an array of adaptive cellular responses and may retain a capacity for structural plasticity. We have investigated the cellular and architectural alterations following focal experimental brain injury, as well as the specific capacity for structural remodeling of neuronal processes in a subset of cortical interneurons. Focal acute injury was induced by transient insertion of a needle into the neocortex of anesthetized adult male Hooded-Wistar rats and thy1 green fluorescent protein (GFP) mice. Immunohistochemical, electron microscopy, and bromodeoxyuridine cell proliferation studies demonstrated an active and evolving response of the brain to injury, indicating astrocytic but not neuronal proliferation. Immunolabeling for the neuron-specific markers phosphorylated neurofilaments, α-internexin and calretinin at 7 days post injury (DPI) indicated phosphorylated neurofilaments and α-internexin but not calretinin immunopositive axonal sprouts within the injury site. However, quantitative studies indicated a significant realignment of horizontally projecting dendrites of calretinin-labeled interneurons at 14 DPI. This remodeling was specific to calretinin immunopositive interneurons and did not occur in a subpopulation of pyramidal neurons expressing GFP in the injured mouse cortex. These data show that subclasses of cortical interneurons are capable of adaptive structural remodeling.

Comparison of neurodegenerative pathology in transgenic mice overexpressing V717F beta-amyloid precursor protein and Alzheimer's disease

Overexpression of mutated human amyloid precursor protein (hAPP717V-->F) under control of platelet-derived growth factor promoter (PDAPP minigene) in transgenic (tg) mice results in neurodegenerative changes similar to Alzheimer's disease (AD). To clarify the pathology of these mice, we studied images derived from laser scanning confocal and electron microscopy and performed comparisons between PDAPP tg mice and AD. Similar to AD, neuritic plaques in PDAPP tg mouse contained a dense amyloid core surrounded by anti-hAPP- and antineurofilament-immunoreactive dystrophic neurites and astroglial cells. Neurons were found in close proximity to plaques in PDAPP tg mice and, to a lesser extent, in AD. In PDAPP tg mice, and occasionally in AD, neuronal processes contained fine intracellular amyloid fibrils in close proximity to the rough endoplasmic reticulum, coated vesicles, and electron-dense material. Extracellular amyloid fibrils (9-11 nm in diameter) were abundant in PDAPP tg and were strikingly similar to those observed in AD. Dystrophic neurites in plaques of PDAPP tg mouse and AD formed synapses and contained many dense multilaminar bodies and neurofilaments (10 nm). Apoptotic-like figures were present in the tg mice. No paired helical filaments have yet been observed in the heterozygote PDAPP tg mice. In summary, this study shows that PDAPP tg mice develop massive neuritic plaque formation and neuronal degeneration similar to AD. These findings show that overproduction of hAPP717V-->F in tg mice is sufficient to cause not only amyloid deposition, but also many of the complex subcellular degenerative changes associated with AD.

Neurofibrillary tangle-associated alteration of stathmin in Alzheimer's disease

Stathmin (p19), a 19-kDa cytosolic phosphorotein, plays a key role in converting extracellular signals into intracellular biochemical changes. Antibodies and cDNA specific for stathmin were used to study its levels and localization in normal and Alzheimer's disease (AD) brain tissue. The stathmin protein concentration was reduced in AD neocortex as assessed by Western blotting, whereas the concentration of its mRNA detected by both in situ hybridization and slot blot were increased in AD. The alteration of the stathmin protein concentration was negatively correlated with neurofibrillary tangle numbers but not with plaque numbers. Immunoreactivity was evenly localized to the cytoplasm of neurons in control cortical sections, whereas in AD it was preferentially localized to some of the neurofibrillary tangle-bearing neurons. Numbers of stathmin-positive neurons were inversely correlated with tangle numbers but not with plaque numbers in the frontal cortex of AD patients.