Molecular correlates of cortical network modulation by long-term sensory experience in the adult rat barrel cortex.

Modulation of cortical network connectivity is crucial for an adaptive response to experience. In the rat barrel cortex, long-term sensory stimulation induces cortical network modifications and neuronal response changes of which the molecular basis is unknown. Here, we show that long-term somatosensory stimulation by enriched environment up-regulates cortical expression of neuropeptide mRNAs and down-regulates immediate-early gene (IEG) mRNAs specifically in the barrel cortex, and not in other brain regions. The present data suggest a central role of neuropeptides in the fine-tuning of sensory cortical circuits by long-term experience.

Chronic partial sleep deprivation reduces brain sensitivity to glutamate N-methyl-D-aspartate receptor-mediated neurotoxicity.

It has been hypothesized that insufficient sleep may compromise neuronal function and contribute to neurodegenerative processes. While sleep loss by itself may not lead to cell death directly, it may affect the sensitivity to a subsequent neurodegenerative insult. Here we examined the effects of chronic sleep restriction (SR) on the vulnerability of the brain to N-methyl-d-aspartate (NMDA)-induced excitotoxicity. Animals were kept awake 20 h per day and were only allowed to rest during the first 4 h of the light phase, i.e. their normal circadian resting phase. After 30 days of SR all rats received a unilateral injection with a neurotoxic dose of NMDA into the nucleus basalis magnocellularis (NBM). Brains were collected for assessment of damage. In the intact non-injected hemisphere, the number of cholinergic cells in the NBM and the density of their projections in the cortex were not affected by SR. In the injected hemisphere, NMDA caused a significant loss of cholinergic NBM cells and cortical fibres in all animals. However, the loss of cholinergic cells was attenuated in the SR group as compared with the controls. These data suggest that, if anything, SR reduces the sensitivity to a subsequent excitotoxic insult. Chronic SR may constitute a mild threat to the brain that does not lead to neurodegeneration by itself but prepares the brain for subsequent neurotoxic challenges. These results do not support the hypothesis that sleep loss increases the sensitivity to neurodegenerative processes.

The basal forebrain cholinergic system in aging and dementia. Rescuing cholinergic neurons from neurotoxic amyloid-ß42 with memantine.

The dysfunction and loss of basal forebrain cholinergic neurons and their cortical projections are among the earliest pathological events in the pathogenesis of Alzheimer's disease (AD). The evidence pointing to cholinergic impairments come from studies that report a decline in the activity of choline acetyltransferase (ChAT) and acetylcholine esterase (AChE), acetylcholine (ACh) release and the levels of nicotinic and muscarinic receptors, and loss of cholinergic basal forebrain neurons in the AD brain. Alzheimer's disease pathology is characterized by an extensive loss of synapses and neuritic branchings which are the dominant scenario as compared to the loss of the neuronal cell bodies themselves. The appearance of cholinergic neuritic dystrophy, i.e. aberrant fibers and fiber swelling are more and more pronounced during brain aging and widely common in AD. When taking amyloid-ß (Aß) deposition as the ultimate causal factor of Alzheimer's disease the role of Aß in cholinergic dysfunction should be considered. In that respect it has been stated that ACh release and synthesis are depressed, axonal transport is inhibited, and that ACh degradation is affected in the presence of Aß peptides. ß-Amyloid peptide 1-42, the principal constituent of the neuritic plaques seen in AD patients, is known to trigger excess amount of glutamate in the synaptic cleft by inhibiting the astroglial glutamate transporter and to increase the intracellular Ca(2+) level. Based on the glutamatergic overexcitation theory of AD progression, the function of NMDA receptors and treatment with NMDA antagonists underlie some recent therapeutic applications. Memantine, a moderate affinity uncompetitive NMDA receptor antagonist interacts with its target only during states of pathological activation but does not interfere with the physiological receptor functions. In this study the neuroprotective effect of memantine on the forebrain cholinergic neurons against Aß42 oligomers-induced toxicity was studied in an in vivo rat dementia model. We found that memantine rescued the neocortical cholinergic fibers originating from the basal forebrain cholinergic neurons, attenuated microglial activation around the intracerebral lesion sides, and improved attention and memory of Aß42-injected rats exhibiting impaired learning and loss of cholinergic innervation of neocortex.

Braak staging in mouse models of Alzheimer's disease.

In the present paper by David E. Hurtado and colleagues report on a new mouse model for AD bearing Aß and MAPT pathology by crossing PS19 and PDAPP Tg mice. Here, we tried to highlight the importance and necessity of the critical and systematic analysis of models such as the Braak like staging in AD mouse models.

Calpain inhibition prevents amyloid-beta-induced neurodegeneration and associated behavioral dysfunction in rats.

Amyloid-beta (Abeta) is toxic to neurons and such toxicity is - at least in part - mediated via the NMDA receptor. Calpain, a calcium dependent cystein protease, is part of the NMDA receptor-induced neurodegeneration pathway, and we previously reported that inhibition of calpain prevents excitotoxic lesions of the cholinergic nucleus basalis magnocellularis of Meynert. The present study reveals that inhibition of calpain is also neuroprotective in an in vivo model of Abeta oligomer-induced neurodegeneration in rats. Abeta-induced lesions of the nucleus basalis induced a significant decrease in the number of cholinergic neurons and their projecting fibers, as determined by analysis of choline-acetyltransferase in the nucleus basalis magnocellularis and cortical mantle of the lesioned animals. Treatment with the calpain inhibitor A-705253 significantly attenuated cholinergic neurodegeneration in a dose-dependent manner. Calpain inhibition also significantly diminished the accompanying neuroinflammatory response, as determined by immunohistochemical analysis of microglia activation. Administration of beta-amyloid markedly impaired performance in the novel object recognition test. Treatment with the calpain inhibitor, A-705253, dose-dependently prevented this behavioral deficit. In order to determine whether pre-treatment with the calpain inhibitor is necessary to exhibit its full protective effect on neurons we induced Abeta toxicity in primary neuronal cultures and administered A-705253 at various time points before and after Abeta oligomer application. Although the protective effect was higher when A-705253 was applied before induction of Abeta toxicity, calpain inhibition was still beneficial when applied up to 1h post-treatment. We conclude that inhibition of calpains may represent a valuable strategy for the prevention of Abeta oligomer-induced neuronal decline and associated cognitive deterioration.

LPYFDa neutralizes amyloid-beta-induced memory impairment and toxicity.

Misfolding, oligomerization, and aggregation of the amyloid-beta (Abeta) peptide is widely recognized as a central event in the pathogenesis of Alzheimer's disease (AD). Recent studies have identified soluble Abeta oligomers as the main pathogenic agents and provided evidence that such oligomeric Abeta aggregates are neurotoxic, disrupt synaptic plasticity, and inhibit long-term potentiation. A promising therapeutic strategy in the battle against AD is the application of short synthetic peptides which are designed to bind to specific Abeta-regions thereby neutralizing or interfering with the devastating properties of oligomeric Abeta species. In the present study, we investigated the neuroprotective properties of the amyloid sequence derived pentapeptide LPYFDa in vitro as well as its memory preserving capacity against Abeta(42)-induced learning deficits in vivo. In vitro we showed that neurons in culture treated with LPYFDa are protected against Abeta (42) -induced cell death. Moreover, in vivo LPYFDa prevented memory impairment tested in a contextual fear conditioning paradigm in mice after bilateral intrahippocampal Abeta (42) injections. We thus showed for the first time that an anti-amyloid peptide like LPYFDa can preserve memory by reverting Abeta (42) oligomer-induced learning deficits.

Expression of CXCL10 in cultured cortical neurons.

Chemokines expressed in neurons are important mediators in neuron-neuron and neuron-glia signaling. One of these chemokines is CCL21 that activates microglia via the chemokine receptor CXCR3. As neurons also express CXCL10, a main ligand for CXCR3, we have thus investigated in detail the expression pattern of CXCL10 in neurons. We show that CXCL10 is constitutively expressed by neurons, is stored in large dense-core vesicles and is not regulated by neuronal injury or stress. Neuronal CXCL10 release occurred constitutively at low level. In vivo CXCL10 expression was found in the developing brain at various embryonic stages and its peak expression correlates with the presence of CD11b- and GFAP-positive cells expressing CXCR3. These results suggest a possible role of neuronal CXCL10 in recruitment and homing of glial cells during embryogenesis.

Pretreatment with lovastatin prevents N-methyl-D-aspartate-induced neurodegeneration in the magnocellular nucleus basalis and behavioral dysfunction.

Besides a beneficial cardiovascular effect, it was recently suggested that statins can also exert neuroprotective actions. In a previous study, we provided in vitro evidence that lovastatin treatment abates excitotoxic cell death in primary cortical neurons. Here, we investigated the neuroprotective effect of lovastatin in an in vivo mouse model. We found that administration of lovastatin (20 mg/kg) significantly protects cholinergic neurons and their cortical projections against N-methyl-D-aspartate (60 nmol)-induced cell death in the magnocellular nucleus basalis, a neuronal cell group that is characteristically affected in Alzheimer's disease. Furthermore, lovastatin-mediated neuroprotection was shown to be dependent on protein kinase B (PKB)/Akt signaling since treatment with the PKB/Akt inhibitor LY294002 blocked the lovastatin-induced neuroprotective effect. The loss of cholinergic neurons after the lesion in the magnocellular nucleus basalis resulted in memory impairment as tested in a passive avoidance paradigm. This was reverted by pre-lesion lovastatin treatment. From these studies we conclude that treatment with lovastatin may provide protection against neuronal injury in excitotoxic conditions associated with neurodegenerative diseases including Alzheimer's disease.

Inflammation and NF-kappaB in Alzheimer's disease and diabetes.

Inflammatory processes are a hallmark of many chronic diseases including Alzheimer's disease and diabetes mellitus. Fairly recent statistical evidence indicating that type 2 diabetes increases the risk of developing Alzheimer's disease has led to investigations of the potential common processes that could explain this relation. Here, we review the literature on how inflammation and the inducible nuclear factor NF-kappaB might be involved in both diabetes mellitus and Alzheimer's disease and whether these factors can link both diseases.

TNF-alpha-mediates neuroprotection against glutamate-induced excitotoxicity via NF-kappaB-dependent up-regulation of K2.2 channels.

Previous studies have shown that tumor necrosis factor-alpha (TNF-alpha) induces neuroprotection against excitotoxic damage in primary cortical neurons via sustained nuclear factor-kappa B (NF-kappaB) activation. The transcription factor NF-kappaB can regulate the expression of small conductance calcium-activated potassium (K(Ca)) channels. These channels reduce neuronal excitability and as such may yield neuroprotection against neuronal overstimulation. In the present study we investigated whether TNF-alpha-mediated neuroprotective signaling is inducing changes in the expression of small conductance K(Ca) channels. Interestingly, the expression of K(Ca)2.2 channel was up-regulated by TNF-alpha treatment in a time-dependent manner whereas the expression of K(Ca)2.1 and K(Ca)2.3 channels was not altered. The increase in K(Ca)2.2 channel expression after TNF-alpha treatment was shown to be dependent on TNF-R2 and NF-kappaB activation. Furthermore, activation of small conductance K(Ca) channels by 6,7-dichloro-1H-indole-2,3-dione 3-oxime or cyclohexyl-[2-(3,5-dimethyl-pyrazol-1-yl)-6-methyl-pyrimidin-4-yl]-amine-induced neuroprotection against a glutamate challenge. Treatment with the small conductance K(Ca) channel blocker apamin or K(Ca)2.2 channel siRNA reverted the neuroprotective effect elicited by TNF-alpha. We conclude that treatment of primary cortical neurons with TNF-alpha leads to increased K(Ca)2.2 channel expression which renders neurons more resistant to excitotoxic cell death.

Inhibition of Calpain Prevents N-Methyl-D-aspartate-Induced Degeneration of the Nucleus Basalis and Associated Behavioral Dysfunction.

N-Methyl-D-aspartate (NMDA) receptor-mediated excitotoxicity is thought to underlie a variety of neurological disorders, and inhibition of either the NMDA receptor itself, or molecules of the intracellular cascade, may attenuate neurodegeneration in these diseases. Calpain, a calcium-dependent cysteine protease, has been identified as part of such an NMDA receptor-induced excitotoxic signaling pathway. The present study addressed the question of whether inhibition of calpain can prevent neuronal cell death and associated behavioral deficits in a disease-relevant animal model, which is based on excitotoxic lesions of the cholinergic nucleus basalis magnocellularis of Meynert. Excitotoxic lesions of the nucleus basalis with NMDA induced a markedly impaired performance in the novel object recognition test. Treatment with the calpain inhibitor, N-(1-benzyl-2-carbamoyl-2-oxoethyl)-2-[E-2-(4-diethlyaminomethylphenyl) ethen-1-yl]benzamide (A-705253), dose-dependently prevented the behavioral deficit. Subsequent analysis of choline acetyltransferase in the cortical mantle of the lesioned animals revealed that application of A-705253 dose-dependently and significantly attenuated cholinergic neurodegeneration. Calpain inhibition also significantly diminished the accompanying gliosis, as determined by immunohistochemical analysis of microglia activation. Finally, inhibition of calpain by A-705253 and the peptidic calpain inhibitor N-acetyl-Leu-Leu-Nle-CHO did not impair long-term potentiation in hippocampal slices, indicating that calpain inhibition interrupts NMDA excitotoxicity pathways without interfering with NMDA receptor-mediated signaling involved in cognition. We conclude that inhibition of calpains may represent a valuable strategy for the prevention of excitotoxicity-induced neuronal decline without interfering with the physiological neuronal functions associated with learning and memory processes. Thus, calpain inhibition may be a promising and novel approach for the treatment of various neurodegenerative disorders.