Active microglia, sick astroglia and Alzheimer type dementias

New Paradigm in Cell Therapy Using Sperm Head to Restore Brain Function and Structure in Animal Model of Alzheimer’s Disease: Support for Boosting Constructive Inflammation vs. Anti-Inflammatory Approach

Alzheimer’s is characterized by accumulation of amyloid-β (Aβ) associated with insufficient clearance of toxicants from the brain establishing a chronic inflammation and other abnormalities in the brain. Inflammatory microglia and astrocytes along with abnormal lymphatics associated with insufficient clearance of Aβ and other toxicants from the brain establish a chronic inflammation. This causes abnormal choroid plexus, leukocyte trafficking, and hypoxic condition along with high levels of regulatory T cells (Tregs). There is no consensus among researchers regarding decreasing or increasing Tregs to achieve therapeutic effects. Different opposing studies tried to suppress or boost inflammation to treat AD. Based on reproductive immunology, sperm induces constructive inflammatory response and seminal-vesicle-fluid (SVF) suppresses inflammation leading to uterus remodeling. It prompted us to compare therapeutic efficiency of inflammatory or anti-inflammatory approaches in AD model based on reproductive immunology. To do so, SVF, sperm, or sperm head (from Wistar rat) was administered via intra-cerebro-ventricular route to Sprague Dawley rat AD model. Behavioral and histological examination were made and treatment groups were compared with control AD model and normal groups. Therapeutic efficacy was in the order of sperm head>sperm>SVF. Sperm head returned learning memory, Aβ, lymphatics, neural growth factors, choroid plexus function, Iba-1/GFAP, MHC II/CD86/CD40, CD38/IL-10, and hypoxia levels back to normal level. However, SVF just partially ameliorated the disease. Immunologic properties of sperm/sperm head to elicit constructive inflammation can be extended to organs other than reproductive. This nature-based approach overcomes genetic difference as an important obstacle and limitation in cell therapy, and is expected to be safe or with least side effects.

The Role of Glial Adenosine Receptors in Neural Resilience and the Neurobiology of Mood Disorders

Adenosine receptors were classified into A1- and A2-receptors in the laboratory of Bernd Hamprecht more than 25 years ago. Adenosine receptors are instrumental to the neurotrophic effects of glia cells. Both microglia and astrocytes release after stimulation via adenosine receptors factors that are important for neuronal survival and growth. Neuronal resilience is now considered as of pivotal importance in the neurobiology of mood disorders and their treatment. Both sleep deprivation and electroconvulsive therapy, two effective therapeutic measures in mood disorders, are associated with an increase of adenosine and upregulation of adenosine A1-receptors in the brain. Parameters closely related to adenosine receptor activation such as cerebral metabolic rate and delta power in the sleep EEG provide indirect evidence that adenosinergic signaling may be associated with the therapeutic response to these measures. Thus, neurotrophic effects evoked by adenosine receptors might be important in the mechanism of action of ECT and perhaps also sleep deprivation.

Astroglial regulation of apolipoprotein E expression in neuronal cells. Implications for Alzheimer's disease

Although apolipoprotein (apo) E is synthesized in the brain primarily by astrocytes, neurons in the central nervous system express apoE, albeit at lower levels than astrocytes, in response to various physiological and pathological conditions, including excitotoxic stress. To investigate how apoE expression is regulated in neurons, we transfected Neuro-2a cells with a 17-kilobase human apoE genomic DNA construct encoding apoE3 or apoE4 along with upstream and downstream regulatory elements. The baseline expression of apoE was low. However, conditioned medium from an astrocytic cell line (C6) or from apoE-null mouse primary astrocytes increased the expression of both isoforms by 3-4-fold at the mRNA level and by 4-10-fold at the protein level. These findings suggest that astrocytes secrete a factor or factors that regulate apoE expression in neuronal cells. The increased expression of apoE was almost completely abolished by incubating neurons with U0126, an inhibitor of extracellular signal-regulated kinase (Erk), suggesting that the Erk pathway controls astroglial regulation of apoE expression in neuronal cells. Human neuronal precursor NT2/D1 cells expressed apoE constitutively; however, after treatment of these cells with retinoic acid to induce differentiation, apoE expression diminished. Cultured mouse primary cortical and hippocampal neurons also expressed low levels of apoE. Astrocyte-conditioned medium rapidly up-regulated apoE expression in fully differentiated NT2 neurons and in cultured mouse primary cortical and hippocampal neurons. Thus, neuronal expression of apoE is regulated by a diffusible factor or factors released from astrocytes, and this regulation depends on the activity of the Erk kinase pathway in neurons.

DNA damage and activated caspase-3 expression in neurons and astrocytes: evidence for apoptosis in frontotemporal dementia

Frontotemporal dementia (FTD) is a neurodegenerative disease which affects mainly the frontal and anterior temporal cortex. It is associated with neuronal loss, gliosis, and microvacuolation of lamina I to III in these brain regions. In previous studies we have described neurons with DNA damage in the absence of tangle formation and suggested this may result in tangle-independent mechanisms of neurodegeneration in the AD brain. In the present study, we sought to examine DNA fragmentation and activated caspase-3 expression in FTD brain where tangle formation is largely absent. The results demonstrate that numerous nuclei were TdT positive in all FTD brains examined. Activated caspase-3 immunoreactivity was detected in both neurons and astrocytes and was elevated in FTD cases as compared to control cases. A subset of activated caspase-3-positive cells were also TdT positive. In addition, the cell bodies of a subset of astrocytes showed enlarged, irregular shapes, and vacuolation and their processes appeared fragmented. These degenerating astrocytes were positive for activated caspase-3 and colocalized with robust TdT-labeled nuclei. These findings suggest that a subset of astrocytes exhibit degeneration and that DNA damage and activated caspase-3 may contribute to neuronal cell death and astrocyte degeneration in the FTD brain. Our results suggest that apoptosis may be a mechanism of neuronal cell death in FTD as well as in AD (228).

Glial reaction in aging and Alzheimer's disease

It is well-established that glial cells play an important role during injury and neurodegenerative processes in the central nervous system. In normal aging, no global glia proliferation is found morphologically, but reactive gliosis has been described in specific areas of the limbic system and neocortex that undergo selective neuronal or synaptic degeneration in nondemented elderly persons. In addition, there is an age-associated increase in the metabolic turnover of cellular proteins, such as glial fibrillary acidic protein, in human brain tissue, even without detectable signs of neurodegeneration. In contrast to the relatively moderate overall glial changes in normal aging, the close association of activated astrocytes and microglial cells with neuritic plaques and cells undergoing neurofibrillary degeneration in Alzheimer's disease (AD), the expression of receptors for complement by glial cells, and the release of soluble cytokines strongly suggest that inflammatory processes may play an important part in the complex pathophysiological interactions that occur in AD. Understanding the role of glia in age-associated neurodegenerative disorders may provide new insights into the neurobiology of glia-neuronal interaction and may allow the development of strategies to alter the disease process. This review aims to summarize some of the important aspects of glial cells in aging and dementia.

Interaction of presenilins with the filamin family of actin-binding proteins

Mutations in presenilin genes PS1 and PS2 account for approximately 50% of early-onset familial Alzheimer's disease (FAD). The PS1 and PS2 genes encode highly homologous transmembrane proteins related to the Caenorhabditis elegans sel-12 and spe-4 gene products. A hydrophilic loop region facing the cytoplasmic compartment is likely to be functionally important because at least 14 mutations in FAD patients have been identified in this region. We report here that the loop regions of PS1 and PS2 interact with nonmuscle filamin (actin-binding protein 280, ABP280) and a structurally related protein (filamin homolog 1, Fh1). Overexpression of PS1 appears to modify the distribution of ABP280 and Fh1 proteins in cultured cells. A monoclonal antibody recognizing ABP280 and Fh1 binds to blood vessels, astrocytes, neurofibrillary tangles, neuropil threads, and dystrophic neurites in the AD brain. Detection of ABP280/Fh1 proteins in these structures suggests that these presenilin-interacting proteins may be involved in the development of AD and that interactions between presenilins and ABP280/Fh1 may be functionally significant. The ABP280 gene is located on the human X chromosome, whereas the newly identified Fh1 gene maps to human chromosome 3. These results provide a new basis for understanding the function of presenilin proteins and further implicate cytoskeletal elements in AD pathogenesis.

Astrocytes regulate microglial phagocytosis of senile plaque cores of Alzheimer's disease

We have developed an in vitro model in which isolated senile plaque (SP) cores are presented to rat microglial cells in culture. Microglia rapidly phagocytosed, broke apart, and cleared SP cores. However, when cocultured with astrocytes, microglial phagocytosis was markedly suppressed, allowing the SPs to persist. Suppression of phagocytosis by astrocytes appears to be a general phenomena since microglia in the presence of astrocytes showed reduced capacity to phagocytose latex beads as well. The astrocyte effect on microglia is related in part to a diffusible factor(s) since astrocyte- but not fibroblast-conditioned media also reduced phagocytosis. These results suggest that while microglia have the capacity to phagocytose and remove SPs, astrocytes which lie in close association to microglia may help prevent the efficient clearance of SP material allowing them to persist in Alzheimer's disease.

The progression of beta-amyloid deposition in the frontal cortex of the aged canine

Brains from 41 aged canines (> or = 10 years of age) were examined immunohistochemically to characterize the laminar distribution and age-related progression of beta-amyloid (A beta) in frontal cortex. We classified the A beta patterns into four distinct types. Type I was characterized by small, faint deposits of A beta in deep cortical layers. Type II consisted of diffuse deposits of A beta mainly in layers V and VI. Type III had both dense plaques in superficial layers, and diffuse deposits in deep layers. Finally, Type IV had solely dense plaques throughout all layers of cortex. We compared the A beta distribution pattern between the Old canines (10-15 years, n = 22) and the Very Old canines (> 15 years, n = 19). The Old group primarily had negative staining, or Type I and Type II patterns of amyloid deposition (73%). Conversely, the Very Old group had predominantly Types II, III and IV deposits (89.5%), a difference that was significant (P < 0.05). We suggest that A beta deposition in canine frontal cortex is a progressive age-related process beginning with diffuse deposits in the deep cortical layers followed by the development of deposits in outer layers. In support of this hypothesis, the deeper layer diffuse plaques in the Very Old group of dogs also contain the largest proportion of beta-amyloid with an isomerized aspartic acid residue at position 7, indicating that these deposits had been present for some time. We also observed fiber-like A beta immunoreactivity within regions of diffuse A beta deposits. These fibers appeared to be degenerating neurites, which were negative for hyperphosphorylated tau. Therefore, these fibers may represent a very early form of neuritic change that precede tau hyperphosphorylation or develop by an alternative pathway.

Brain-derived neurotrophic factor is reduced in Alzheimer's disease

Alzheimer's disease may be due to a deficiency in neurotrophin protein or receptor expression. Consistent with this hypothesis, a reduction in BDNF mRNA expression has been observed in human post-mortem Alzheimer's disease hippocampi. To further investigate this observation, we examined whether the alteration in BDNF expression also occurred at the protein level in human post-mortem Alzheimer's disease hippocampi and temporal cortices using immunohistochemical techniques. We observed a reduction in the intensity and number of BDNF-immunoreactive cell bodies within both the Alzheimer's disease hippocampus and temporal cortex when compared to normal tissue. These results support and extend previous findings that BDNF mRNA is reduced in the human Alzheimer's disease hippocampus and temporal cortex, and suggest that a loss of BDNF may contribute to the progressive atrophy of neurons in Alzheimer's disease.

Neurite outgrowth inhibitor of gliotic brain tissue. Mode of action and cellular localization, studied with specific monoclonal antibodies

Membranes from injured adult rat brain express a heparan/chondroitin sulphate proteoglycan that inhibits neurite outgrowth in vitro. We have developed monoclonal antibodies (Mabs) against this proteoglycan, two of which were characterized and used for the study of the inhibitor mode of action and localization in normal and injured adult brain. The antibodies recognized a molecule of apparent molecular weight 200 kDa in Western blots of injured brain membranes. One of the Mabs blocked both the inhibition of neurite outgrowth and the growth cone collapse activity, associated with the proteoglycan. In adult brain, inhibitor immunoreactivity was found predominantly in neurons but, after a lesion, it was associated mainly with reactive glial cells. The localization of neurite outgrowth inhibitors in reactive glia supports the idea that gliotic tissue is largely responsible for the failure of axonal regeneration in mammalian CNS.

Okadaic acid stimulates nerve growth factor production via an induction of interleukin-1 in primary cultures of cortical astroglial cells

Neonatal rat cortical astroglial cells in primary culture synthesize and secrete interleukin-1 beta (IL-1) and nerve growth factor (NGF). Treatment of astrocytes with okadaic acid (OA), an inhibitor of phosphoprotein phosphatases, dramatically increased both IL-1 and NGF mRNA content (about 50-fold) with maximal induction seen at 20-30 nM OA. The induction of IL-1 mRNA preceded that of NGF mRNA and was maximal after 9 h of treatment. OA increased IL-1 mRNA half-life by about 10-fold similar to the reported stabilization of the NGF mRNA. Addition of an IL-1 receptor antagonist dose-dependently inhibited the secretion of NGF stimulated by OA and IL-1. The results indicate that OA profoundly stimulates IL-1 expression in glial cells by enhancing IL-1 mRNA stability and that glial cell-derived IL-1 acts in a paracrine/autocrine manner to stimulate NGF production.

Influence of advanced glycation end-products and AGE-inhibitors on nucleation-dependent polymerization of beta-amyloid peptide

Nucleation-dependent polymerization of beta-amyloid peptide, the major component of plaques in patients with Alzheimer's disease, is significantly accelerated by crosslinking through Advanced Glycation End-products (AGEs) in vitro. During the polymerization process, both nucleus formation and aggregate growth are accelerated by AGE-mediated crosslinking. Formation of the AGE-crosslinked amyloid peptide aggregates could be attenuated by the AGE-inhibitors Tenilsetam, aminoguanidine and carnosine. These experimental data, and clinical studies, reporting a marked improvement in cognition and memory in Alzheimer's disease patients after Tenilsetam treatment, suggest that AGEs might play an important role in the etiology or progression of the disease. Thus AGE-inhibitors may generally become a promising drug class for the treatment of Alzheimer's disease.

Early activation of microglia in the pathogenesis of fatal murine cerebral malaria

Microglia are pluripotent members of the macrophage/monocyte lineage that can respond in several ways to pathological changes in the central nervous system. To determine their role in the pathogenesis of fatal murine cerebral malaria (FMCM) we have conducted a detailed study of the changes in morphology and distribution of retinal microglia during the progression of the disease. Adult CBA/T6 mice were inoculated with Plasmodium berghei ANKA. These mice died 7 days post inoculation (p.i.) with the parasite while exhibiting cerebral symptoms, increased permeability of the blood-brain barrier, and monocyte adherence to the vascular endothelium. Mice were injected i.v. with Monastral blue 2 h prior to sacrifice to identify "activated" monocytes, and their isolated retinae were incubated with the Griffonia simplicifolia (GS) lectin or reacted for the nucleoside diphosphatase enzyme to visualize microglia and the vasculature. Changes in microglial morphology were seen within 2-3 days p.i., that is, at least 3 days prior to the onset of cerebral symptoms and 4 days before death. Morphological changes included retraction of ramified processes, soma enlargement, an increasingly amoeboid appearance, and vacuolation. There was also increased staining intensity and redistribution of "activated" microglia toward retinal vessels, but no increase in density of NDPase-positive cells. The GS lectin only labeled a small population of microglia in the uninfected adult mouse retina. However, there was a striking increase in the focal density of GS-positive microglia during the progression of the disease. Extravasation of monocytes also was observed prior to the onset of cerebral symptoms. These results provide the first evidence that microglial activation is a critical component of the pathological process during FMCM.

Trk receptor alterations in Alzheimer's disease

The expression of trk receptors in postmortem normal, Huntington's disease and Alzheimer's disease human brains was investigated using immunohistochemistry, in-situ hybridisation and Western blotting. Alzheimer's disease hippocampi displayed an increase in trkA receptor levels in astrocytes in the CA1 region, some of which were associated with beta-amyloid-positive plaques. Truncated trkB receptors were found in high levels in senile plaques, while the full-length receptor was expressed in glial-like cells in the hippocampus of Alzheimer's disease brains. In-situ hybridisation studies indicated that trk receptor mRNA was also elevated in Alzheimer's. The appearance of trkA and trkB receptors in astrocytes and plaques in Alzheimer's disease might be related to beta-amyloid deposition and could be implicated in the development of Alzheimer's disease.

Neurotoxicity induced by interleukin-2: involvement of infiltrating immune cells

Interleukin-2 (IL-2), a key regulator of immune functions, also has potent effects on neurons and glia. IL-2 modulates neural cell growth and survival and transmitter and hormone releases and is thought to mediate neuroimmune interactions. Investigating the neuroendocrine consequences of chronically elevated central nervous system (CNS) levels of IL-2, we recently observed marked neurotoxicity [Hanisch et al. (1994) Endocrinology 135:2465-2472]. In the present study, we characterize in detail the modifications in brain tissue architecture as they result in Sprague-Dawley rats from intracerebroventricular (i.c.v.) administration of low amounts of IL-2 (5 and 15 U/h, respectively, delivered by means of osmotic minipumps for up to 14 days). Histological inspection of the brains revealed massive cellular infiltrates in the ipsilateral hemisphere. The infiltrates were associated with pronounced angiogenesis and changes in the composition of the extracellular matrix. These anatomical changes apparently developed between day 7 and 14. They were specific for IL-2 and were not seen in animals treated, for example, with heat-inactivated IL-2 (controls). We further show that chronic central administration of IL-2 let to T and B lymphocyte invasion of the brain and an intracranial agglomeration of large numbers of MHC class II-positive cells. Immunocytochemistry revealed a widespread inundation of CNS tissue and a decoration of glial cells and neurons by endogenous antibodies. Tissue regions around the IL-2-induced infiltrates showed myelin destruction and neuronal cell loss. Chronically elevated CNS levels of IL-2 may, thus, not only interfere with neurotransmission and endocrine functions but also severely disturb tissue homeostasis. Therefore, the present findings could be relevant to brain injuries, CNS disorders, and clinical treatments associated with increased IL-2 levels or involving an immune component.

Amyloid beta-peptide and oxidative cellular injury in Alzheimer's disease

Alzheimer's disease is a progressive neurodegenerative disorder that affects primarily learning and memory functions. There is significant neuronal loss and impairment of metabolic functioning in the temporal lobe, an area believed to be crucial for learning and memory tasks. Aggregated deposits of amyloid beta-peptide may have a causative role in the development and progression of AD. We review the cellular actions of A beta and how they can contribute to the cytotoxicity observed in AD. A beta causes plasma membrane lipid peroxidation, impairment of ion-motive ATPases, glutamate uptake, uncoupling of a G-protein linked receptor, and generation of reactive oxygen species. These effects contribute to the loss of intracellular calcium homeostasis reported in cultured neurons. Many cell types other than neurons show alterations in the Alzheimer's brain. The effects of A beta on these cell types is also reviewed.

Chromogranin A triggers a phenotypic transformation and the generation of nitric oxide in brain microglial cells

Chromogranin A is an ubiquitous 48,000 mol. wt secretory protein stored and released from many neuroendocrine cells and neurons. In human brain, chromogranin A is a common feature of regions that are known to be affected by various neurodegenerative pathologies such as Alzheimer's, Parkinson's and Pick's diseases. Brain degenerative areas are generally infiltrated by activated microglial cells, the resident macrophage cell population within the central nervous system. Here, we report that both recombinant human chromogranin A and chromogranin A purified from bovine chromaffin granules trigger drastic morphological changes in rat microglial cells maintained in culture. Microglial cells exposed to chromogranin A adopted a flattened amoeboid shape and, this change was associated with an accumulation of actin in the subplasmalemmal region, as observed by immunocytochemistry and confocal laser microscopy. In single microglial cells loaded with indo-1, chromogranin A elicited a rapid and transient increase in [Ca2+]i which preceded the reorganization of actin cytoskeleton. The activity of nitric oxide synthase was estimated by measuring the accumulation of nitrite in the culture medium. Both recombinant human chromogranin A and bovine chromogranin A triggered an important accumulation of nitrite comparable to that induced by lipopolysaccharide, a well-known activator of microglia. The effect of chromogranin A was dose dependent, inhibited by N omega-nitro-L-arginine methyl ester, a competitive inhibitor of nitric oxide synthase, and by cycloheximide, an inhibitor of protein synthesis. These findings suggest that chromogranin A induces an activated phenotype of microglia, and thus may have a role in the pathogenesis of neuronal degeneration in the brain.

Removal of cobalt-labeled neurons and nerve fibers by microglia from the frog's brain and spinal cord

We investigated the microglial reaction around cobalt-labeled degenerating neurons and nerve fibers in the frog central nervous system. The aim of these studies was to reveal the routes of migrating microglial cells during debris removal and the effect of seasonal changes on this process in a cold-blooded animal. Oculomotor and spinal motoneurons were filled with cobaltous-lysine complex through their axons. In the torus semicircularis and the isthmic nucleus, neurons were labeled with iontophoretically applied cobaltous-lysine complex through their injured dendrites and axons. The animals were left to survive for 1 to 50 days. During the summer, oculomotor neurons disintegrated by the seventh postoperative day. The debris from the neurons were phagocytosed by microglia-like cells identified by the presence of cobalt in their cytoplasm. Some of these cells were wedged between ependymoglial cells of the cerebral aqueduct, others appeared at the pial surface of the mesencephalon. The speed of this process was twice as fast during the summer as during the winter. Part of cobalt-labeled microglial cells in the torus semicircularis and the isthmic nucleus moved toward the ependyma of the optic ventricle and the cerebral aqueduct, respectively. Cobalt-loaded microglial cells did not move toward the surface in the spinal cord and the deep part of mesencephalic tegmentum, and left the brain probably via blood vessels. We conclude that microglial cells loaded with phagocytosed tissue debris may leave the brain tissue via three routes and their activity depends on the environmental temperature.

Interleukin-2 as a neuroregulatory cytokine

Interleukin-2 (IL-2), the cytokine also known as T-cell growth factor, has multiple immunoregulatory functions and biological properties not only related to T-cells. In the past decade, substantial evidence accumulated to suggest that IL-2 is also a modulator of neural and neuroendocrine functions. First, extremely potent effects of IL-2 on neural cells were discovered, including activities related to cell growth and survival, transmitter and hormone release and the modulation of bioelectric activities. IL-2 may be involved in the regulation of sleep and arousal, memory function, locomotion and the modulation of the neuroendocrine axis. Second, the concept that IL-2 could act as a neuroregulatory cytokine has been supported by reports on the presence in rodent and human brain tissues of IL-2-like bioactivity, IL-2-like immunoreactivity, IL-2-like mRNA, IL-2 binding sites, IL-2 receptor (IL-2R alpha) and beta chain mRNA and IL-2R immunoreactivity. IL-2 and/or IL-2R molecules mainly localize to the frontal cortex, septum, striatum, hippocampal formation, hypothalamus, locus coeruleus, cerebellum, the pituitary and fiber tracts, such as the corpus callosum, where they are likely expressed by both neuronal and glial cells. Although the molecular biology of the brain IL-2/IL-2R system (including its relation to IL-15/IL-15R alpha) is not yet fully established by cloning and complete sequencing of all respective components, similarities (and to some extent differences) to peripheral counterparts are now apparent. The ability of IL-2 to readily penetrate the blood-brain barrier further suggests that this cytokine could regulate interactions between peripheral tissues and the central nervous system. Taken together, these data suggest that IL-2 of either immune and CNS origin can have access to functional IL-2R molecules on neurons and glia under normal conditions. Additionally, dysregulation of the IL-2/IL-2 receptor system could lead or contribute to functional and pathological alterations in the brain as in the immune system. Understanding the neurobiology of the IL-2/IL-2 receptor system should also help to explain neurologic, neuropsychiatric and neuroendocrine side effects occurring during IL-2 treatment of peripheral and brain tumors. Immunopharmacological manipulation either aiming at the activation or suppression of IL-2 signaling should consider functional interference with constitutive and inducible IL-2 receptors on brain cells in order to fulfil the high expectations associated with the use of this cytokine as a promising agent in immunotherapies, especially of brain tumors.

Beta amyloid is neurotoxic in hippocampal slice cultures

We examined the neurotoxicity of the 40 amino acid fragment of beta amyloid peptide (A beta 1-40) in cultured hippocampal slices. When injected into area CA3, A beta 1-40 produced widespread neuronal damage. Injection of the reverse sequence peptide, A beta 40-1, or vehicle alone produced little damage. The distribution A beta 1-40 was highly correlated with the area of neuronal damage. Thioflavine S and electron microscopic analysis confirmed that injected A beta 1-40 formed 7-9 nm AD type amyloid fibrils in the cultures. A beta 1-40 also altered the number of GFAP immunoreactive astrocytes and ED-1 immunoreactive microglia/macrophages within and around the A beta 1-40 deposit. The observed neurotoxicity of A beta 1-40 in hippocampal slice cultures provides evidence that this peptide may be responsible for the neurodegeneration observed in AD.

Alterations of Müller (glial) cells in dystrophic retinae of RCS rats

We have carried out a light microscopical study of Müller cells in the retinae of rats with inherited retinal dystrophy (Royal College of Surgeons rats). Isolated retinae of both control and Royal College of Surgeons rats were exposed to a Procion Yellow solution which is taken up selectively into Müller cells. The shape of the cells was then studied by confocal microscopy. Enzymatically isolated Müller cells were studied immunocytochemically with antibodies against glial fibrillary acidic protein, cathepsin D, beta-amyloid precursor protein, bcl-2 protooncogene product, and glutamine synthetase. Müller cells from RCS retinae were shorter than those from control retinae, and showed a coarse hypertrophy of their distal (sclerad) processes. In Müller cells isolated from the retinae of Royal College of Surgeon's rats, the expression of glial fibrillary acidic protein, cathepsin D, beta-amyloid precursor protein and bcl-2 protooncogene product was increased, and the expression of glutamine synthetase was reduced. Obviously, loss of neighbouring neurons leads to major alterations of both the shape and metabolism of Müller cells. The expression of enzymes that serve functional glio-neuronal interactions, such as glutamine synthetase, seems to be down-regulated, whereas proteins involved in cell reconstruction (cathepsin D), cell repair (possibly beta-amyloid precursor protein), and protection against apoptotic cell death (bcl-2 protooncogene product), are up-regulated, together with the 'pathological marker' glial fibrillary acidic protein.