Ongoing Electroencephalographic Activity Associated with Cortical Arousal in Transgenic PDAPP Mice (hAPP V717F).

BACKGROUND: It has been shown that theta (6-10 Hz) and delta (1-6 Hz) ongoing electroencephalographic (EEG) rhythms revealed variations in the cortical arousal in C57 Wild Type (WT) mice during cage exploration (active condition) compared to awake quiet behavior (passive condition; IMI PharmaCog project, www.pharmacog.eu). OBJECTIVE: The objective was to test if these EEG rhythms might be abnormal in old PDAPP mice modeling Alzheimer's disease (AD) with a hAPP Indiana V717F mutation (They show abnormal neural transmission, cognitive deficits, and brain accumulation of Aß1-42). METHODS: Ongoing EEG rhythms were recorded by a frontoparietal bipolar channel in 15 PDAPP and 23 WT C57 male mice (mean age of 22.8 months ±0.4 and 0.3 standard error, respectively). EEG absolute power (density) was calculated. Frequency and amplitude of individual delta and theta frequency (IDF and ITF) peaks were considered during passive and active states in the wakefulness. RESULTS: Compared with the WT group, the PDAPP group showed higher frequency of the IDF during the passive condition and lower frequency of the ITF during the active state. Furthermore, the WT but not PDAPP group showed significant changes in the frontoparietal EEG power (IDF, ITF) during active over passive state. CONCLUSION: PDAPP mice were characterized by less changes in the brain arousal during an active state as revealed by frontoparietal EEG rhythms. Future studies will have to cross-validate the present results on large animal groups, clarify the neurophysiological underpinning of the effect, and test if the disease modifying drugs against AD amyloidosis normalize those candiate EEG biomarkers in PDAPP mice.

Perinatal nicotine treatment induces transient increases in NACHO protein levels in the rat frontal cortex.

The nicotinic acetylcholine receptor (nAChR) regulator chaperone (NACHO) was recently identified as an important regulator of nAChR maturation and surface expression. Here we show that NACHO levels decrease during early postnatal development in rats. This decrease occurs earlier and to a greater degree in the frontal cortex (FC) compared with the hippocampus (HIP). We further show that rats exposed to nicotine during pre- and postnatal development exhibit significantly higher NACHO levels in the FC at postnatal day (PND) 21, but not at PND60. Repeated exposure to nicotine selectively during early (PND8-14) or late (PND54-60) postnatal stages did not affect NACHO protein levels in the FC or HIP, neither did exposure to high doses of the selective α7 nAChR agonists SSR180711, A-582941, or PNU-282987. However, we found significantly increased NACHO protein levels in the FC of PND36 rats after a single exposure to a combination of nicotine and the type II α7 nAChR positive allosteric modulator (PAM) PNU-120596, but not the type I PAM AVL-3288. These findings suggest that exposure to nAChR agonism affects NACHO protein levels, and that this effect is more pronounced during pre- or early postnatal development. The effect of PNU-120596 further suggests that the increase in NACHO expression is caused by activation rather than desensitization of nAChRs.

Axonal degeneration in an Alzheimer mouse model is PS1 gene dose dependent and linked to intraneuronal Aß accumulation.

Abnormalities and impairments in axonal transport are suggested to strongly contribute to the pathological alterations underlying AD. The exact mechanisms leading to axonopathy are currently unclear, but it was recently suggested that APP expression itself triggers axonal degeneration. We used APP transgenic mice and crossed them on a hemi- or homozygous PS1 knock-in background (APP/PS1KI). Depending on the mutant PS1 dosage, we demonstrate a clear aggravation in both plaque-associated and plaque-distant axonal degeneration, despite of an unchanged APP expression level. Amyloid-ß (Aß) peptides were found to accumulate in axonal swellings as well as in axons and apical dendrites proximate to neurons accumulating intraneuronal Aß in their cell bodies. This suggests that Aß can be transported within neurites thereby contributing to axonal deficits. In addition, diffuse extracellular Aß deposits were observed in the close vicinity of axonal spheroids accumulating intracellular Aß, which might be indicative of a local Aß release from sites of axonal damage.

Reduced basal and novelty-induced levels of activity-regulated cytoskeleton associated protein (Arc) and c-Fos mRNA in the cerebral cortex and hippocampus of APPswe/PS1ΔE9 transgenic mice.

Activity-regulated cytoskeletal-associated protein (Arc) and c-Fos are immediate early gene (IEG) products induced by novelty in the hippocampus and involved in the consolidation of synaptic plasticity and long-term memory. We investigated whether induction of arc and c-fos after exposure to a novel open field environment was compromised in different neocortical areas and the hippocampal formation in APP/PS1ΔE9 transgenic mice characterized by pronounced accumulation and deposition of beta amyloid (Aß). Notably, the basal level of Arc and c-fos mRNA in the neocortex was significantly lower in APP/PS1ΔE9 compared to wild-type mice. Novelty exposure induced an increase in Arc and c-Fos mRNA in the medial prefrontal cortex (mPFC), parietal cortex, and hippocampal formation in both APP/PS1ΔE9 transgenic and wild-type mice. However, novelty-induced IEG expression did not reach the same levels in APP/PS1ΔE9 as in the wild-type mice. In contrast, synaptophysin levels did not differ between mutant and wild type mice, suggesting that the observed effect was not due to a general decrease in the number of presynapses. These data suggest a reduction in basal and novelty-induced neuronal activity in a transgenic mouse model of Alzheimer's disease, which is most pronounced in cortical regions, indicating that a decreased functional response in IEG expression could be partly responsible for the cognitive deficits observed in patients with Alzheimer's disease.

Environmental enrichment fails to rescue working memory deficits, neuron loss, and neurogenesis in APP/PS1KI mice.

Environmental enrichment has been used in a variety of transgenic mouse models of Alzheimer's disease (AD), however, with conflicting results. Here we studied the influence of environmental enrichment in a severely affected AD mouse model, showing a multiplicity of pathological alterations including hippocampal neuron loss. APP/PS1KI and wild type (WT) control mice were housed under standard conditions or in enriched cages equipped with various objects and running wheels. Amyloid plaque load, motor and working memory performance, axonopathy, as well as CA1 neuron number and hippocampal neurogenesis were assessed. Although a partial improvement in motor performance was observed, 4 months of enriched housing showed no beneficial effects in terms of working memory, Aß plaque pathology, or neuron loss in APP/PS1KI mice. In addition, no changes in hippocampal neurogenesis and even an aggravation of the axonal phenotype were detected with a tendency toward a premature death. The APP/PS1KI model represents a model for mild to severe AD showing early behavioral deficits starting at 2 months of age with fast deterioration. Therefore our data might suggest that physical activity and enriched environment might be more beneficial in patients with mild cognitive impairment than in patients with incipient AD.

Activation of nicotinic α(7) acetylcholine receptor enhances long term potentation in wild type mice but not in APP(swe)/PS1ΔE9 mice.

Amyloid ß (Aß) plays a central role in Alzheimer's disease (AD) and binds to the nicotinic α(7) receptor (α(7) nAChR). Little is known about the degree to which the binding of Aß to the α(7) nAChR influences the role of this receptor in long-term potentiation (LTP), however. We have studied the effect of the partial α(7) nAChR agonist SSR180711 on hippocampal slice preparations from normal wild type (Wt) and APP(swe)/PS1ΔE9 transgenic (Tg) mice. In the hippocampal slices from the 6 months old Wt mice, the application of both nicotine (5µM) and SSR180711 (300nM) resulted in a significant enhancement of LTP expressed in area CA1. However, in the Tg mice the application of SSR180711 did not result in an increase in LTP beyond control levels. The amount of binding of the α(7) nAChR ligand 125-I-α-bungarotoxin was not different between in Tg and Wt mice. These findings indicate that the α(7) nAChR is functionally blocked in the hippocampal neurons, downstream of the α(7) nAChR, and that this is likely due to an interaction between the receptor and Aß, which leads to changes in LTP.

Repeated administration of alpha7 nicotinic acetylcholine receptor (nAChR) agonists, but not positive allosteric modulators, increases alpha7 nAChR levels in the brain.

The alpha7 nicotinic acetylcholine receptor (nAChR) is an important target for treatment of cognitive deficits in schizophrenia and Alzheimer's disease. However, the receptor desensitizes rapidly in vitro, which has led to concern regarding its applicability as a clinically relevant drug target. Here we investigate the effects of repeated agonism on alpha7 nAChR receptor levels and responsiveness in vivo in rats. Using [(125)I]-alpha-bungarotoxin (BTX) autoradiography we show that acute or repeated administration with the selective alpha7 nAChR agonist A-582941 increases the number of alpha7 nAChR binding sites in several brain regions, particularly in the prefrontal cortex. The alpha7 nAChR agonists SSR180711 and PNU-282987 also increase [(125)I]-BTX binding, suggesting that this is a general consequence of alpha7 nAChR agonism. Interestingly, the alpha7 nAChR positive allosteric modulators PNU-120596 and NS1738 do not increase [(125)I]-BTX binding. Furthermore, A-582941-induced increase in Arc and c-fos mRNA expression in the prefrontal cortex is enhanced and unaltered, respectively, after repeated administration, demonstrating that the alpha7 nAChRs remain responsive. Contrarily, A-582941-induced phosphorylation of Erk2 in the prefrontal cortex occurs following acute, but not repeated administration. Our results demonstrate that repeated agonist administration increases the number of alpha7 nAChRs in the brain, and leads to coupling versus uncoupling of specific intracellular signaling pathways. Additionally, our data suggest a fundamental difference between the sequelae of repeated administration with agonists and allosteric modulators of the alpha7 nAChR.

Accumulation of intraneuronal Abeta correlates with ApoE4 genotype.

In contrast to extracellular plaque and intracellular tangle pathology, the presence and relevance of intraneuronal Abeta in Alzheimer's disease (AD) is still a matter of debate. Human brain tissue offers technical challenges such as post-mortem delay and uneven or prolonged tissue fixation that might affect immunohistochemical staining. In addition, previous studies on intracellular Abeta accumulation in human brain often used antibodies targeting the C-terminus of Abeta and differed strongly in the pretreatments used. To overcome these inconsistencies, we performed extensive parametrical testing using a highly specific N-terminal Abeta antibody detecting the aspartate at position 1, before developing an optimal staining protocol for intraneuronal Abeta detection in paraffin-embedded sections from AD patients. To rule out that this antibody also detects the beta-cleaved APP C-terminal fragment (beta-CTF, C99) bearing the same epitope, paraffin-sections of transgenic mice overexpressing the C99-fragment were stained without any evidence for cross-reactivity in our staining protocol. The staining intensity of intraneuronal Abeta in cortex and hippocampal tissue of 10 controls and 20 sporadic AD cases was then correlated to patient data including sex, Braak stage, plaque load, and apolipoprotein E (ApoE) genotype. In particular, the presence of one or two ApoE4 alleles strongly correlated with an increased accumulation of intraneuronal Abeta peptides. Given that ApoE4 is a major genetic risk factor for AD and is involved in neuronal cholesterol transport, it is tempting to speculate that perturbed intracellular trafficking is involved in the increased intraneuronal Abeta aggregation in AD.

Intracellular Aß triggers neuron loss in the cholinergic system of the APP/PS1KI mouse model of Alzheimer's disease.

Loss of cholinergic neurons in the Nucleus Basalis of Meynert in Alzheimer's disease (AD) patients was one of the first discoveries of neuron loss in AD. Despite an intense focus on the cholinergic system in AD, the reason for this cholinergic neuron loss is yet unknown. In the present study we examined Abeta-induced pathology and neuron loss in the cholinergic system of the bigenic APP/PS1KI mouse model. Expression of the APP transgene was found in ChAT-positive neurons of motor nuclei accompanied by robust intracellular Abeta accumulation, whereas no APP expressing neurons and thus no intracellular Abeta accumulation were found in neither the forebrain or pons complexes, nor in the caudate putamen. This expression pattern was used as a model system to study the effect of intra- and extracellular Abeta accumulation on neuron loss in the cholinergic system. Stereological quantification revealed a loss of ChAT-positive neurons in APP/PS1KI mice only in the motor nuclei Mo5 and 7N accumulating intracellular Abeta. This study supports the hypothesis of intracellular Abeta accumulation as an early pathological alteration contributing to cell death in AD.

Formic acid is essential for immunohistochemical detection of aggregated intraneuronal Abeta peptides in mouse models of Alzheimer's disease.

The staining protocols so far applied to study intracellular Abeta accumulation in human tissue have been inconsistent with varying use of heat and formic acid (FA) for antigen retrieval. Microwave heat treatment has been reported to enhance the staining of intraneuronal Abeta as compared to no or enzymatic pretreatment. FA is widely used to increase the staining of plaque pathology in AD, yet the effect of FA on intraneuronal Abeta staining has been reported to be low and similar to the effect of heat or even to counteract the enhancing effect of heat pretreatment on intraneuronal Abeta immunohistochemical detection. To overcome these inconsistencies, there is a need for optimization of the staining protocol for intraneuronal Abeta detection and more knowledge is required concerning the effects of the different antigen retrieval methods. In the present work, we optimized the staining protocol for intraneuronal Abeta in paraffin-embedded sections in relation to heat and FA using four different mouse models known to accumulate intraneuronal Abeta peptides. It was found that FA is essential for the staining of highly aggregated intraneuronal Abeta peptides in AD transgenic mouse tissue.

alpha(7) Nicotinic acetylcholine receptor activation prevents behavioral and molecular changes induced by repeated phencyclidine treatment.

The core features of schizophrenia include deficits in cognitive processes, such as attention and working memory, subserved by the prefrontal cortex (PFC). These deficits are believed to involve deficient neurotransmission through NMDA receptors, particularly on parvalbumin-containing interneurons, and administration of the NMDA-antagonist phencyclidine (PCP) in rodents is a well validated model of such cognitive deficits. Here we show that repeated PCP treatment (10 mg/kg/day for 10 days) decreased the expression of parvalbumin and synaptophysin mRNA in the mouse PFC, which corresponds to changes seen in patients with schizophrenia. In addition, PCP increased the basal mRNA expression in the PFC of the activity-regulated cytoskeleton-associated protein (Arc), a molecule involved in synaptic plasticity. These molecular changes produced by PCP were accompanied by a behavioral impairment as determined in a modified Y-maze test. Polymorphisms in the alpha(7) nicotinic acetylcholine receptor (nAChR) gene have been linked to schizophrenia. Here we demonstrate that acute administration of the selective alpha(7) nAChR partial agonist SSR180711 dose-dependently reversed the behavioral impairment induced by PCP. Importantly, repeated co-administration of SSR180711 (3 mg/kg) with PCP prevented both the changes in parvalbumin, synaptophysin, and Arc mRNA expression in the PFC, and the behavioral impairment induced by PCP. These results are the first to demonstrate prevention of the deleterious effects induced by repeated PCP treatment. The behavioral and molecular effects of alpha(7) nAChR agonism in this model, particularly the prevention of a decline in parvalbumin mRNA expression, suggest an involvement of the alpha(7) nAChR not only in the symptomatic relief, but also the pathophysiology, of schizophrenia.