PKR downregulation prevents neurodegeneration and ß-amyloid production in a thiamine-deficient model.

Brain thiamine homeostasis has an important role in energy metabolism and displays reduced activity in Alzheimer's disease (AD). Thiamine deficiency (TD) induces regionally specific neuronal death in the animal and human brains associated with a mild chronic impairment of oxidative metabolism. These features make the TD model amenable to investigate the cellular mechanisms of neurodegeneration. Once activated by various cellular stresses, including oxidative stress, PKR acts as a pro-apoptotic kinase and negatively controls the protein translation leading to an increase of BACE1 translation. In this study, we used a mouse TD model to assess the involvement of PKR in neuronal death and the molecular mechanisms of AD. Our results showed that the TD model activates the PKR-eIF2α pathway, increases the BACE1 expression levels of Aß in specific thalamus nuclei and induces motor deficits and neurodegeneration. These effects are reversed by PKR downregulation (using a specific inhibitor or in PKR knockout mice).

Bcl2, a transcriptional target of p38alpha, is critical for neuronal commitment of mouse embryonic stem cells.

Mouse embryonic stem (ES) cells remain pluripotent in vitro when grown in the presence of leukemia inhibitory factor (LIF) cytokine. LIF starvation leads to cell commitment, and part of the ES-derived differentiated cells die by apoptosis together with caspase3-cleavage and p38alpha activation. Inhibition of p38 activity by chemical compounds (PD169316 and SB203580), along with LIF withdrawal, leads to different outcomes on cell apoptosis, giving the opportunity to study the influence of apoptosis on cell differentiation. By gene profiling studies on ES-derived differentiated cells treated or not with these inhibitors, we have characterized the common and specific set of genes modulated by each inhibitor. We have also identified key genes that might account for their different survival effects. In addition, we have demonstrated that some genes, similarly regulated by both inhibitors (upregulated as Bcl2, Id2, Cd24a or downregulated as Nodal), are bona fide p38alpha targets involved in neurogenesis and found a correlation with their expression profiles and the onset of neuronal differentiation triggered upon retinoic acid treatment. We also showed, in an embryoid body differentiation protocol, that overexpression of EGFP (enhanced green fluorescent protein)-BCL2 fusion protein and repression of p38alpha are essential to increase formation of TUJ1-positive neuronal cell networks along with an increase in Map2-expressing cells.

Unraveling substantia nigra sequential gene expression in a progressive MPTP-lesioned macaque model of Parkinson's disease.

Taking advantage of a progressive nonhuman primate model mimicking Parkinson's disease (PD) evolution, we monitored transcriptional fluctuations in the substantia nigra using Affymetrix microarrays in control (normal), saline-treated (normal), 6 days-treated (asymptomatic with 20% cell loss), 12 days-treated (asymptomatic with 40% cell loss) and 25 days-treated animals (fully parkinsonian with 85% cell loss). Two statistical methods were used to ascertain the regulation and real-time quantitative PCR was used to confirm their regulation. Surprisingly, the number of deregulated transcripts is limited at all time points and five clusters exhibiting different profiles were defined using a hierarchical clustering algorithm. Such profiles are likely to represent activation/deactivation of mechanisms of different nature. We briefly speculate about (i) the existence of yet unknown compensatory mechanisms is unraveled, (ii) the putative triggering of a developmental program in the mature brain in reaction to progressing degeneration and finally, (iii) the activation of mechanisms leading eventually to death in final stage. These data should help development of new therapeutic approaches either aimed at enhancing existing compensatory mechanisms or at protecting dopamine neurons.

Alzheimer pathology disorganizes cortico-cortical circuitry: direct evidence from a transgenic animal model.

It has been proposed that Alzheimer disease (AD) is associated with a "disconnection syndrome" due to the gradual loss of morphological and functional integrity of cortico-cortical pathways. This hypothesis derives from indirect neuropathological observations, but definitive evidence that AD primarily targets cortico-cortical networks is still lacking. By means of neuroanatomical anterograde tracing methods, we have investigated, in a murine transgenic model of AD, the impact of the amyloid burden on axonal terminals in different neural systems. Axonal tracings revealed, in accordance with the "disconnection syndrome" hypothesis, that cortico-cortical fibers are significantly disorganized. Terminal fields in local and distant cortical areas contained numerous swollen dystrophic neurites often grouped in grape-like clusters at the plaque periphery. In contrary to fibers of cortical origin, those originating from subcortical brain structures only showed limited signs of degeneration upon reaching their cortical targets. These observations suggest a selective disruption of cortico-cortical connections induced by AD brain pathology.

Increased tau phosphorylation but absence of formation of neurofibrillary tangles in mice double transgenic for human tau and Alzheimer mutant (M146L) presenilin-1.

Neurofibrillary tangles, composed of tau proteins, are a key lesion observed in sporadic forms of Alzheimer's disease and in familial forms associated with mutations of presenilin-1 (PS1). We have generated a double transgenic mouse line expressing a human tau isoform and a mutated form of PS1 (M146L) in neurons. Increased expression of the PS1 holoprotein was observed in the tau/PS1 transgenic mice and the proteolytic fragments of PS1 did not appear to be modified. A somatodendritic accumulation of the transgenic tau and an increase in tau phosphorylation were observed in both tau- and tau/PS1 transgenic mice. Neurofibrillary tangles were not observed in animals analyzed up to 17 months. Immunoprecipitation of tau from brain homogenates demonstrated its binding with active glycogen synthase kinase-3beta in control, tau- and tau/PS1 transgenic lines. These results suggest that overexpression of this Alzheimer mutant PS1 in vivo is not by itself sufficient to induce the formation of neurofibrillary tangles, even in neurons co-expressing and accumulating a human tau isoform.

Reelin in plaques of beta-amyloid precursor protein and presenilin-1 double-transgenic mice.

There is circumstantial evidence that the reelin signaling pathway may contribute to neurodegeneration in the adult brain and could be linked to Alzheimer's disease (AD). In the present immunohistochemical report we studied the reelin expression profile in double-transgenic mice that express both human mutant beta-amyloid precursor protein (APP) and human mutant presenilin-1. We were able to demonstrate that reelin immunostaining was found together with human APP in the neuritic component of many AD-typical plaques in both hippocampus and neocortex. This observation gives the first evidence for the association of reelin with amyloid deposits.

The caspase-derived C-terminal fragment of betaAPP induces caspase-independent toxicity and triggers selective increase of Abeta42 in mammalian cells.

During its physiopathological maturation, the beta-amyloid precursor protein undergoes several distinct proteolytic events by activities called secretases. In Alzheimer's disease, the main histological hallmark called senile plaque is clearly linked to the overproduction of the amyloid peptides Abeta40 and Abeta42, two highly aggregable betaAPP-derived fragments generated by combined cleavages by beta- and gamma-secretases. Recently, an alternative hydrolytic pathway was described, involving another category of proteolytic activities called caspases, responsible for the production of a 31 amino acids betaAPP C-terminal fragment called C31. C31 was reported to lower the viability of N2a cells but the exact mechanisms mediating C31-toxicity remained to be established. Here we show that the transient transfection of pSV2 vector encoding C31 lowers by about 80% TSM1 neuronal cells viability. Arguing against a C31-stimulated apoptotic response, we demonstrate by combined enzymatic and immunological approaches that C31 expression did not modulate basal or staurosporine-induced caspase 3-like activity and pro-caspase-3 activation. Furthermore, C31 did not modify Bax and p53 expressions, poly-(ADP-ribose)-polymerase cleavage and cytochrome c translocation into the cytosol. However, we established that C31 overexpression triggers selective increase of Abeta42 but not Abeta40 production by HEK293 cells expressing wild-type betaAPP751. Altogether, our data demonstrate that C31 induces a caspase-independent toxicity in TSM1 neurons and potentiates the pathogenic betaAPP maturation pathway by increasing selectively Abeta42 species in wild type-betaAPP-expressing human cells.

Neurofibrillary tangles and tau phosphorylation.

Neurofibrillary tangles (NFTs) are a characteristic neuropathological lesion of Alzheimer's disease (AD). They are composed of a highly-phosphorylated form of the microtubule-associated protein tau. We are investigating the relationship between NFTs and microtubule stability and how tau phosphorylation and function is affected in transgenic models and by co-expression with beta-amyloid precursor protein and presenilins. In most NFT-bearing neurons, we observed a strong reduction in acetylated alpha-tubulin immunoreactivity (a marker of stable microtubules) and a reduction of the in situ hybridization signal for tubulin mRNA. In transfected cells, mutated tau forms (corresponding to tau mutations identified in familial forms of frontotemporal dementias linked to chromosome 17) were less efficient in their ability to sustain microtubule growth. These observations are consistent with the hypothesis that destabilization of the microtubule network is an important mechanism of cell dysfunction in Alzheimer's disease. The glycogen synthase kinase-3 beta (GSK-3 beta) generates many phosphorylated sites on tau. We performed a neuroanatomical study of GSK-3 beta distribution showing that developmental evolution of GSK-3 beta compartmentalization in neurons paralleled that of phosphorylated tau. Studies on transfected cells and on cultured neurons showed that GSK-3 beta activity controls tau phosphorylation and tau functional interaction with microtubules. Tau phosphorylation was not affected in neurons overexpressing beta-amyloid precursor protein. Transgenic mice expressing a human tau isoform and double transgenic animals for tau and mutated presenilin 1 have been generated; a somatodendritic accumulation of phosphorylated transgenic tau proteins, as observed in the pretangle stage in AD, has been observed but NFTs were not found, suggesting that additional factors might be necessary to induce their formation.

Intraneuronal Abeta accumulation precedes plaque formation in beta-amyloid precursor protein and presenilin-1 double-transgenic mice.

beta-Amyloid peptides are key molecules that are involved in the pathology of Alzheimer's disease (AD). The source and place of the neurotoxic action of Abeta, however, is still a matter of controversial debates. In the present report, we studied the neuropathological events in a transgenic mouse model expressing human mutant beta-amyloid precursor protein and human mutant presenilin-1 in neurons. Western blot and immunohistochemical analysis revealed that intracellular Abeta staining preceded plaque deposition, which started in the hippocampal formation. At later stages, many neuritic Abeta positive plaques were found in all cortical, hippocampal and many other brain areas. Interestingly, intraneuronal Abeta staining was no longer detected in the brain of aged double-transgenic mice, which correlates with the typical neuropathology in the brain of chronic AD patients.

FE65 in Alzheimer's disease: neuronal distribution and association with neurofibrillary tangles.

FE65, a protein expressed in the nervous system, has the ability to bind the C-terminal domain of the amyloid precursor protein. This suggests a role for FE65 in the pathogenesis of Alzheimer's disease (AD). The present study was conducted to find out if the distribution of FE65 immunoreactivity was affected during the course of AD, and to determine the degree of co-localization of FE65 with other proteins known to be involved in AD. Single immunoperoxidase-labeling experiments, conducted on six sporadic AD patients and six nondemented age-matched controls, showed that the proportion of volume occupied by FE65 immunoreactivity was not modified in the isocortex of AD patients. However, in hippocampal area CA4, increased FE65 immunoreactivity seemed to be associated with the severity of the disease. Double-immunofluorescent labeling did not show any clear co-localization of FE65 with the amyloid precursor protein. FE65 immunoreactivity was also absent from focal and diffuse deposits of the beta-amyloid peptide. Unexpectedly double labeling experiments showed a co-localization of FE65 and tau proteins in intracellular tangles. Ultrastructural observations confirmed that FE65 was associated with paired helical filaments.

Parkin immunoreactivity in the brain of human and non-human primates: an immunohistochemical analysis in normal conditions and in Parkinsonian syndromes.

The etiology of Parkinson's disease is unknown, but the gene involved in an autosomic recessive form of the disease with early onset has recently been identified. It codes for a protein with an unknown function called parkin. In the present study we produced a specific polyclonal antiserum against human parkin. Immunohistochemical analysis showed that parkin is expressed in neuronal perikarya and processes but also in glial and blood vessels in the primate brain (human and monkey). Electron microscopy indicated that parkin immunoreactivity is mostly located in large cytoplasmic vesicles and at the level of the endoplasmic reticulum. Parkin was expressed heterogeneously in various structures of the brain. It was detectable in the dopaminergic systems at the level of the perikarya in the mesencephalon but also in the striatum. However, parkin was also expressed by numerous nondopaminergic neurons. The staining intensity of parkin was particularly high in the hippocampal formation, the pallidal complex, the red nucleus, and the cerebellum. Comparison of control subjects with patients with Parkinson's disease and control animals with 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP)-intoxicated animals revealed a loss of parkin-immunoreactive neurons only in the substantia nigra pars compacta. Furthermore, the surviving dopaminergic neurons in the parkinsonian state continued to express parkin at a level similar to that observed in the control situation. These data indicate that parkin is a widely expressed protein. Thus, the degeneration of dopaminergic neurons in familial cases of Parkinson's disease with autosomal recessive transmission cannot be explained solely in terms of an alteration of this protein.

Overexpression of Rab11 or constitutively active Rab11 does not affect sAPPalpha and Abeta secretions by wild-type and Swedish mutated betaAPP-expressing HEK293 cells.

Presenilins 1 and 2 are two homologous proteins which, when mutated, appear responsible for most of the early-onset familial forms of Alzheimer's disease. Among various functional aspects, presenilins appear to behave as chaperoning partners of a series of proteins including the beta-amyloid precursor protein. Recently, presenilins were shown to interact with Rab11, a GTPase involved in intracellular transport. This suggested that Rab11-presenilin interaction could influence the routing of betaAPP and thereby modulate its maturation. In this context, we examined whether overexpression of Rab11 or its constitutively active mutant Rab11Q70L could affect betaAPP maturation in human HEK293 cells. We show here that the overexpression of both Rab11-related proteins does not modify the recovery of secreted sAPPalpha or Abeta in HEK293 cells expressing wild-type betaAPP or betaAPP harboring the Swedish double mutation. These data indicate that Rab11 does not influence betaAPP processing in HEK293 cells. However, it does not preclude the possibility for Rab11 to modulate other presenilin-mediated functions in human cells.

Differential screening of mutated SOD1 transgenic mice reveals early up-regulation of a fast axonal transport component in spinal cord motor neurons.

In the present study we analyze the molecular mechanisms underlying motor neuron degeneration in familial amyotrophic lateral sclerosis (FALS). For this, we used a transgenic mouse model expressing the Cu/Zn superoxide dismutase (SOD1) gene with a Gly(86) to Arg (G86R) mutation equivalent to that found in a subset of human FALS. Using an optimized suppression subtractive hybridization method, a cDNA specifically up-regulated during the asymptomatic phase in the lumbar spinal cord of G86R mice was identified by sequence analysis as the KIF3-associated protein (KAP3), a regulator of fast axonal transport. RT-PCR analysis revealed that KAP3 induction was an early event arising long before axonal degeneration. Immunohistochemical studies further revealed that KAP3 protein predominantly accumulates in large motor neurons of the ventral spinal cord. We further demonstrated that KAP3 up-regulation occurs independent of any change in the other components of the kinesin II complex. However, since the ubiquitous KIF1A motor is up-regulated, our results show an early and complex rearrangement of the fast axonal transport machinery in the course of FALS pathology.

Laminar specific loss of isocortical presenilin 1 immunoreactivity in Alzheimer's disease. Correlations with the amyloid load and the density of tau-positive neurofibrillary tangles.

Presenilin 1 has been shown to be mutated in a high proportion of cases of familial Alzheimer's disease. Immunoreactive epitopes of the protein have been found mainly in neurones devoid of neurofibrillary tangles - an observation that has led to the conclusion that presenilin 1 could have a protective role. In this study, the relationship between deposits of Abeta peptide (both the 40 and 42 isoforms), tau positive neurofibrillary tangles and presenilin 1-positive neuronal profiles were analysed in three cases of presenilin 1 mutation, four cases of sporadic Alzheimer's disease and five controls. Immunohistochemistry was performed in a sample from the supramarginal gyrus. The proportion of volume occupied by the Abeta1-40 and Abeta1-42 deposits (amyloid load) was evaluated by a point-counting technique. Tau-positive neurofibrillary tangles, and presenilin 1-positive neuronal profiles were directly counted. The location of the lesions in the thickness of the cortex was recorded. The density of PS1-positive neuronal profiles in Alzheimer's disease cases was lower than in the controls. The deficit was significant only in the upper layers of the cortex. The density of presenilin 1 neuronal profiles was negatively correlated with Abeta1-40 and Abeta1-42 loads, and with the density of tau-positive neurofibrillary tangles. Multivariate analysis showed that the Abeta1-42 load was the best determinant of the decrease in presenilin 1-positive neuronal profiles. Presenilin 1-positive neurones appear to be lost rather than protected in the course of Alzheimer disease.

Cloning of rat parkin cDNA and distribution of parkin in rat brain.

The rat parkin cDNA sequence was characterized after screening a rat hypothalamus cDNA library with a 32P-labeled probe containing the entire open reading frame of the human parkin cDNA. This sequence encompasses 1,576 bp and contains a single open reading frame that encodes a 465-amino acid protein. The rat parkin amino acid sequence exhibits a very striking homology to the human and mouse parkin, with 85 and 95% identity, respectively. Both the N-terminal ubiquitin and the ring-IBR (in between ring)-ring finger domains appear to be highly conserved among rat, human, and mouse parkin. An affinity-purified polyclonal antibody (ASP5p) was generated with a synthetic peptide corresponding to amino acids 295-311 of the parkin sequence, which is identical in the three species. Western blotting revealed that ASP5p recognizes a single 52-kDa band, which corresponds to the molecular mass of the parkin protein. Immunostaining with ASP5p showed that parkin is principally located in the cytoplasm of neurons that are widely distributed in the rat brain. Parkin-immunoreactive neurons abound in structures that are specifically targeted in Parkinson's disease, e.g., subtantia nigra, but are also present in unaffected structures, e.g., cerebellum. Furthermore, parkin-enriched glial cells can be detected in various nuclei of the rat brain. Thus, the role of parkin may be much more global than previously thought on the basis of genetic findings gathered in cases of early-onset parkinsonism.

Presenilins and Alzheimer's disease: biological functions and pathogenic mechanisms.

Alzheimer's disease (AD) is the most common cause of dementia in the elderly population. Dementia is associated with massive accumulation of fibrillary aggregates in various cortical and subcortical regions of the brain. These aggregates appear intracellularly as neurofibrillary tangles, extracellularly as amyloid plaques and perivascular amyloid in cerebral blood vessels. The causative factors in AD etiology implicate both, genetic and environmental factors. The large majority of early-onset familial Alzheimer's disease (FAD) cases are linked to mutations in the genes coding for presenilin 1 (PS1) and presenilin 2 (PS2). The corresponding proteins are 467 (PS1) and 448 (PS2) amino-acids long, respectively. Both are membrane proteins with multiple transmembrane regions. Presenilins show a high degree of conservation between species and a presenilin homologue with definite conservation of the hydrophobic structure has been identified even in the plant Arabidopsis thaliana. More than 50 missense mutations in PS1 and two missense mutations in PS2 were identified which are causative for FAD. PS mutations lead to the same functional consequence as mutations on amyloid precursor protein (APP), altering the processing of APP towards the release of the more amyloidogenic form 1-42 of Abeta (Abeta42). In this regard, the physical interaction between APP and presenilins in the endoplasmic reticulum has been demonstrated and might play a key role in Abeta42 production. It was hypothesized that PS1 might directly cleave APP. However, extracellular amyloidogenesis and Abeta production might not be the sole factor involved in AD pathology and several lines of evidence support a role of apoptosis in the massive neuronal loss observed. Presenilins were shown to modify the apoptotic response in several cellular systems including primary neuronal cultures. Some evidence is accumulating which points towards the beta-catenin signaling pathways to be causally involved in presenilin mediated cell death. Increased degradation of beta-catenin has been shown in brain of AD patients with PS1 mutations and reduced beta-catenin signaling increased neuronal vulnerability to apoptosis in cell culture models. The study of presenilin physiological functions and the pathological mechanisms underlying their role in pathogenesis clearly advanced our understanding of cellular mechanisms underlying the neuronal cell death and will contribute to the identification of novel drug targets for the treatment of AD.

Apolipoprotein E-deficient mice are not more susceptible to the biochemical and memory deficits induced by nucleus basalis lesion.

We investigated whether the nucleus basalis lesion induced by quisqualic acid was associated with a more severe impairment of spatial navigation in a water maze, a greater reduction in frontal choline acetyltransferase activity and decrease in the number of choline acetyltransferase-positive neurons in the nucleus basalis in apolipoprotein E-deficient mice than in control mice. We also studied the effect of ageing on water maze spatial navigation and cortical choline acetyltransferase activity in 16-month-old control and apolipoprotein E-deficient mice. We found that the lesion decreased choline acetyltransferase-positive neurons in the nucleus basalis and frontal choline acetyltransferase activity equally in control and apolipoprotein E-deficient mice. The nucleus basalis lesion had no effect on the initial acquisition in the water maze in control and apolipoprotein E-deficient mice after 25 or 106 days of recovery. However, the nucleus basalis lesion impaired the reversal learning in the water maze similarly in both strains after 25 days of recovery, but had no effect after 106 days of recovery. Finally, water maze spatial navigation and cortical choline acetyltransferase activity were similar in old control and apolipoprotein E-deficient mice. These results suggest that young and old apolipoprotein E-deficient mice do not have impairments in cholinergic activity or spatial navigation. Furthermore, apolipoprotein E deficiency does not increase the sensitivity to cholinergic and spatial navigation deficits induced by lesioning of the nucleus basalis with an excitatory amino acid and does not slow down the behavioral recovery.

Impaired recovery of noradrenaline levels in apolipoprotein E-deficient mice after N-(2-chloroethyl)-N-ethyl-2-bromobenzylamine lesion.

We investigated the effect of the noradrenergic neurotoxin, N-(2-chloroethyl)-N-ethyl-2-bromobenzylamine (DSP-4) (1 or 3 x 50 mg/kg, intraperitoneally), on hippocampal, cortical and cerebellar noradrenaline levels after recovery of one, five and 11 months in control and apolipoprotein E-deficient mice. Apolipoprotein E-deficient mice had lower hippocampal noradrenaline levels than control mice. DSP-4-lesioned control mice had a more extensive recovery of hippocampal and cortical noradrenaline levels than DSP-4-lesioned apoE-deficient mice after five months' survival. Furthermore, the hippocampal noradrenaline levels after five and 11 months and cortical noradrenaline levels after five months of recovery had slightly recovered in control but not in apolipoprotein E-deficient mice treated with a single dose of DSP-4 compared with mice treated with three doses of DSP-4. These results show that apolipoprotein E-deficient mice have impaired recovery capacity in their locus coeruleus neurons.

Brain-derived neurotrophic factor-mediated protection of striatal neurons in an excitotoxic rat model of Huntington's disease, as demonstrated by adenoviral gene transfer.

Huntington's disease (HD) is a genetic disorder leading to the degeneration of striatal GABA-ergic output neurons. No treatment is currently available for this devastating disorder, although several neurotrophic factors, including brain-derived neurotrophic factor (BDNF), have been shown to be beneficial for striatal neuron survival. We analyzed the effect of adenovirus-mediated transfer of the BDNF gene in a model of HD. Using a stereological procedure, three groups of rats were given an intrastriatal injection of adenovirus encoding BDNF, beta-galactosidase, or sham surgery. Two weeks after treatment, the animals were lesioned with quinolinic acid (QUIN), a toxin that induces striatal neuron death by an excitotoxic process. One month after the lesion, histological study revealed that striatal neurons were protected only in rats treated with the BDNF adenovirus. Volume measurements showed that the QUIN-induced lesions were 55% smaller in the BDNF adenovirus-treated group than in the beta-galactosidase adenovirus-treated group (p < 0.05), and the sham-treated group (p < 0.05). To determine the survival of striatal GABA-ergic output neurons after the QUIN-induced lesion, we immunostained brain sections with DARPP-32, an antibody specific for striatal output neurons. Prior treatment with the BDNF adenovirus resulted in a cell survival of 64%, whereas that after beta-galactosidase treatment was 46% (p < 0.05), showing that the BDNF adenovirus protected the striatal neurons. These results indicate that transfer of the BDNF gene is of therapeutic value for Huntington's disease.

Moderate cortical EEG changes in apolipoprotein E-deficient mice during ageing and scopolamine treatment but not after nucleus basalis lesion.

RATIONALE: Recent studies suggest that apoE-deficient mice may have impaired central cholinergic function and neuronal recovery capacity. OBJECTIVE: We investigated whether apoE-deficient mice are more susceptible to the biochemical and EEG defects induced by ageing or nucleus basalis (NB) lesion. METHODS: ApoE-deficient and control mice were used. The baseline EEG activity and EEG response to a muscarinic acetylcholine receptor antagonist, scopolamine (0.05 and 0.2 mg/kg) and a benzodiazepine receptor agonist, diazepam (0.5 and 2.0 mg/kg), were studied during ageing. In addition, the cortical and hippocampal ChAT activities were measured in aged mice. The baseline EEG activity and EEG response to scopolamine (0.05 and 0.2 mg/kg), and cortical ChAT activity, were studied after quisqualic acid-induced unilateral NB lesion. RESULTS: The baseline EEG fast wave activity (relative alpha and beta) was higher in apoE-deficient mice. Ageing decreased relative alpha activity similarly in both strains. The scopolamine induced EEG slowing was less prominent in apoE-deficient than in control mice, and the difference between the strains became slightly clearer during ageing. The NB lesion failed to produce more severe changes in cortical EEG and ChAT activity in apoE-deficient mice. Cortical and hippocampal ChAT activity was equal in young and aged apoE-deficient and control mice. The EEG response to diazepam in young and aged mice was similar in both strains. CONCLUSIONS: The regulation of cortical EEG activity of apoE-deficient mice was somewhat altered during ageing and the response to scopolamine treatment was blunted. However, the cholinergic cells of the NB of apoE-deficient mice were not more sensitive to lesion or to ageing, suggesting that apoE does not have to be present to preserve the viability of cholinergic neurons.