Neurobehavioral development, adult openfield exploration and swimming navigation learning in mice with a modified beta-amyloid precursor protein gene

Genetic and chemical disruption of amyloid precursor protein processing impairs zebrafish sleep maintenance

Amyloid precursor protein (APP) is a brain-rich, single pass transmembrane protein that is proteolytically processed into multiple products, including amyloid-beta (Aβ), a major driver of Alzheimer disease (AD). Although both overexpression of APP and exogenously delivered Aβ lead to changes in sleep, whether APP processing plays an endogenous role in regulating sleep is unknown. Here, we demonstrate that APP processing into Aβ40 and Aβ42 is conserved in zebrafish and then describe sleep/wake phenotypes in loss-of-function appa and appb mutants. Larvae with mutations in appa had reduced waking activity, whereas larvae that lacked appb had shortened sleep bout durations at night. Treatment with the γ-secretase inhibitor DAPT also shortened night sleep bouts, whereas the BACE-1 inhibitor lanabecestat lengthened sleep bouts. Intraventricular injection of P3 also shortened night sleep bouts, suggesting that the proper balance of Appb proteolytic processing is required for normal sleep maintenance in zebrafish.

Alternative splicing and heparan sulfation converge on neurexin-1 to control glutamatergic transmission and autism-related behaviors

Neurexin synaptic organizing proteins are central to a genetic risk pathway in neuropsychiatric disorders. Neurexins also exemplify molecular diversity in the brain, with over a thousand alternatively spliced forms and further structural heterogeneity contributed by heparan sulfate glycan modification. Yet, interactions between these modes of post-transcriptional and post-translational modification have not been studied. We reveal that these regulatory modes converge on neurexin-1 splice site 5 (S5): the S5 insert increases the number of heparan sulfate chains. This is associated with reduced neurexin-1 protein level and reduced glutamatergic neurotransmitter release. Exclusion of neurexin-1 S5 in mice boosts neurotransmission without altering the AMPA/NMDA ratio and shifts communication and repetitive behavior away from phenotypes associated with autism spectrum disorders. Thus, neurexin-1 S5 acts as a synaptic rheostat to impact behavior through the intersection of RNA processing and glycobiology. These findings position NRXN1 S5 as a potential therapeutic target to restore function in neuropsychiatric disorders.

Physiology and pharmacology of amyloid precursor protein

Amyloid precursor protein (APP) is an evolutionarily conserved transmembrane protein and a well-characterized precursor protein of amyloid-beta (Aβ) peptides, which accumulate in the brains of individuals with Alzheimer's disease (AD)-related pathologies. Aβ has been extensively investigated since the amyloid hypothesis in AD was proposed. Besides Aβ, previous studies on APP and its proteolytic cleavage products have suggested their diverse pathological and physiological functions. However, their roles still have not been thoroughly understood. In this review, we extensively discuss the evolutionarily-conserved biology of APP, including its structure and processing pathway, as well as recent findings on the physiological roles of APP and its fragments in the central nervous system and peripheral nervous system. We have also elaborated upon the current status of APP-targeted therapeutic approaches for AD treatment by discussing inhibitors of several proteases participating in APP processing, including α-, β-, and γ-secretases. Finally, we have highlighted the future perspectives pertaining to further research and the potential clinical role of APP.

Knockdown of Amyloid Precursor Protein: Biological Consequences and Clinical Opportunities

Amyloid precursor protein (APP) and its cleavage fragment Amyloid-β (Aβ) have fundamental roles in Alzheimer's disease (AD). Genetic alterations that either increase the overall dosage of APP or alter its processing to favour the generation of longer, more aggregation prone Aβ species, are directly causative of the disease. People living with one copy of APP are asymptomatic and reducing APP has been shown to lower the relative production of aggregation-prone Aβ species in vitro. For these reasons, reducing APP expression is an attractive approach for AD treatment and prevention. In this review, we will describe the structure and the known functions of APP and go on to discuss the biological consequences of APP knockdown and knockout in model systems. We highlight progress in therapeutic strategies to reverse AD pathology via reducing APP expression. We conclude that new technologies that reduce the dosage of APP expression may allow disease modification and slow clinical progression, delaying or even preventing onset.

Fe65: A Scaffolding Protein of Actin Regulators

The scaffolding protein family Fe65, composed of Fe65, Fe65L1, and Fe65L2, was identified as an interaction partner of the amyloid precursor protein (APP), which plays a key function in Alzheimer’s disease. All three Fe65 family members possess three highly conserved interaction domains, forming complexes with diverse binding partners that can be assigned to different cellular functions, such as transactivation of genes in the nucleus, modulation of calcium homeostasis and lipid metabolism, and regulation of the actin cytoskeleton. In this article, we rule out putative new intracellular signaling mechanisms of the APP-interacting protein Fe65 in the regulation of actin cytoskeleton dynamics in the context of various neuronal functions, such as cell migration, neurite outgrowth, and synaptic plasticity.

Behavioral Phenotyping for Down Syndrome in Mice

Down syndrome (DS) is the most frequent genetic cause of intellectual disability, characterized by alterations in different behavioral symptom domains: neurodevelopment, motor behavior, and cognition. As mouse models have the potential to generate data regarding the neurological basis for the specific behavioral profile of DS, and may indicate pharmacological treatments with the potential to affect their behavioral phenotype, it is important to be able to assess disease-relevant behavioral traits in animal models in order to provide biological plausibility to the potential findings. The field is at a juncture that requires assessments that may effectively translate the findings acquired in mouse models to humans with DS. In this article, behavioral tests are described that are relevant to the domains affected in DS. A neurodevelopmental behavioral screen, the balance beam test, and the Multivariate Concentric Square Field test to assess multiple behavioral phenotypes and locomotion are described, discussing the ways to merge these findings to more fully understand cognitive strengths and weaknesses in this population. New directions for approaches to cognitive assessment in mice and humans are discussed. © 2020 Wiley Periodicals LLC. Basic Protocol 1: Preweaning neurodevelopmental battery Basic Protocol 2: Balance beam Basic Protocol 3: Multivariate concentric square field test (MCSF).

Mutant MRPS5 affects mitoribosomal accuracy and confers stress-related behavioral alterations

The 1555 A to G substitution in mitochondrial 12S A‐site rRNA is associated with maternally transmitted deafness of variable penetrance in the absence of otherwise overt disease. Here, we recapitulate the suggested A1555G‐mediated pathomechanism in an experimental model of mitoribosomal mistranslation by directed mutagenesis of mitoribosomal protein MRPS5. We first establish that the ratio of cysteine/methionine incorporation and read‐through of mtDNA‐encoded MT‐CO1 protein constitute reliable measures of mitoribosomal misreading. Next, we demonstrate that human HEK293 cells expressing mutant V336Y MRPS5 show increased mitoribosomal mistranslation. As for immortalized lymphocytes of individuals with the pathogenic A1555G mutation, we find little changes in the transcriptome of mutant V336Y MRPS5 HEK cells, except for a coordinated upregulation of transcripts for cytoplasmic ribosomal proteins. Homozygous knock‐in mutant Mrps5 V338Y mice show impaired mitochondrial function and a phenotype composed of enhanced susceptibility to noise‐induced hearing damage and anxiety‐related behavioral alterations. The experimental data in V338Y mutant mice point to a key role of mitochondrial translation and function in stress‐related behavioral and physiological adaptations.

Generation of App knock-in mice reveals deletion mutations protective against Alzheimer's disease-like pathology

Although, a number of pathogenic mutations have been found for Alzheimer’s disease (AD), only one protective mutation has been identified so far in humans. Here we identify possible protective deletion mutations in the 3′-UTR of the amyloid precursor protein (App) gene in mice. We use an App knock-in mouse model carrying a humanized Aβ sequence and three AD mutations in the endogenous App gene. Genome editing of the model zygotes using multiple combinations of CRISPR/Cas9 tools produces genetically mosaic animals with various App 3′-UTR deletions. Depending on the editing efficiency, the 3′-UTR disruption mitigates the Aβ pathology development through transcriptional and translational regulation of APP expression. Notably, an App knock-in mouse with a 34-bp deletion in a 52-bp regulatory element adjacent to the stop codon shows a substantial reduction in Aβ pathology. Further functional characterization of the identified element should provide deeper understanding of the pathogenic mechanisms of AD.

To date, only one mutation in the gene for amyloid-beta precursor protein APP has been suggested to be protective against Alzheimer’s disease. Here, authors found using gene editing of a mutant App knock-in mouse line that deletion of the 3’UTR region is protective against amyloid-β accumulation in vivo, and subsequently identify a 52-bp element in the 3’UTR region that is responsible for this effect.

A Battery of Motor Tests in a Neonatal Mouse Model of Cerebral Palsy

As the sheer number of transgenic mice strains grow and rodent models of pediatric disease increase, there is an expanding need for a comprehensive, standardized battery of neonatal mouse motor tests. These tests can validate injury or disease models, determine treatment efficacy and/or assess motor behaviors in new transgenic strains. This paper presents a series of neonatal motor tests to evaluate general motor function, including ambulation, hindlimb foot angle, surface righting, negative geotaxis, front- and hindlimb suspension, grasping reflex, four limb grip strength and cliff aversion. Mice between the ages of post-natal day 2 to 14 can be used. In addition, these tests can be used for a wide range of neurological and neuromuscular pathologies, including cerebral palsy, hypoxic-ischemic encephalopathy, traumatic brain injury, spinal cord injury, neurodegenerative diseases, and neuromuscular disorders. These tests can also be used to determine the effects of pharmacological agents, as well as other types of therapeutic interventions. In this paper, motor deficits were evaluated in a novel neonatal mouse model of cerebral palsy that combines hypoxia, ischemia and inflammation. Forty-eight hours after injury, five tests out of the nine showed significant motor deficits: ambulation, hindlimb angle, hindlimb suspension, four limb grip strength, and grasping reflex. These tests revealed weakness in the hindlimbs, as well as fine motor skills such as grasping, which are similar to the motor deficits seen in human cerebral palsy patients.

Truncating mutations in APP cause a distinct neurological phenotype

Dominant missense mutations in the amyloid β (Aβ) precursor protein (APP) gene have been implicated in early onset Alzheimer disease. These mutations alter protein structure to favor the pathologic production of Aβ. We report that homozygous nonsense mutations in APP are associated with decreased somatic growth, microcephaly, hypotonia, developmental delay, thinning of the corpus callosum, and seizures. We compare the phenotype of this case to those reported in mouse models and demonstrate multiple similarities, strengthening the role of amyloid precursor protein in normal brain function and development. Ann Neurol 2016;80:456-460.

The Neuroprotective Properties of the Amyloid Precursor Protein Following Traumatic Brain Injury

Despite the significant health and economic burden that traumatic brain injury (TBI) places on society, the development of successful therapeutic agents have to date not translated into efficacious therapies in human clinical trials. Injury to the brain is ongoing after TBI, through a complex cascade of primary and secondary injury events, providing a valuable window of opportunity to help limit and prevent some of the severe consequences with a timely treatment. Of note, it has been suggested that novel treatments for TBI should be multifactorial in nature, mimicking the body's own endogenous repair response. Whilst research has historically focused on the role of the amyloid precursor protein (APP) in the pathogenesis of Alzheimer's disease, recent advances in trauma research have demonstrated that APP offers considerable neuroprotective properties following TBI, suggesting that APP is an ideal therapeutic candidate. Its acute upregulation following TBI has been shown to serve a beneficial role following trauma and has lead to significant advances in understanding the neuroprotective and neurotrophic functions of APP and its metabolites. Research has focused predominantly on the APP derivative sAPPα, which has consistently demonstrated neuroprotective and neurotrophic functions both in vitro and in vivo following various traumatic insults. Its neuroprotective activity has been narrowed down to a 15 amino acid sequence, and this region is linked to both heparan binding and growth-factor-like properties. It has been proposed that APP binds to heparan sulfate proteoglycans to exert its neuroprotective action. APP presents us with a novel therapeutic compound that could overcome many of the challenges that have stalled development of efficacious TBI treatments previously.

Better Utilization of Mouse Models of Neurodegenerative Diseases in Preclinical Studies: From the Bench to the Clinic

The major symptom of Alzheimer's disease is dementia progressing with age. Its clinical diagnosis is preceded by a long prodromal period of brain pathology that encompasses both formation of extracellular amyloid and intraneuronal tau deposits in the brain and widespread neuronal death. At present, familial cases of dementia provide the most promising foundation for modeling neurodegenerative tauopathies, a group of heterogeneous disorders characterized by prominent intracellular accumulation of hyperphosphorylated tau protein. In this chapter, we describe major behavioral hallmarks of tauopathies, briefly outline the genetics underlying familial cases, and discuss the arising implications for modeling the disease in transgenic mouse systems. The selection of tests performed to evaluate the phenotype of a model should be guided by the key behavioral hallmarks that characterize human disorder and their homology to mouse cognitive systems. We attempt to provide general guidelines and establish criteria for modeling dementia in a mouse; however, interpretations of obtained results should avoid a reductionist "one gene, one disease" explanation of model characteristics. Rather, the focus should be directed to the question of how the mouse genome can cope with the over-expression of the protein coded by transgene(s). While each model is valuable within its own constraints and the experiments performed are guided by specific hypotheses, we seek to expand upon their methodology by offering guidance spanning from issues of mouse husbandry to choices of behavioral tests and routes of drug administration that might increase the external validity of studies and consequently optimize the translational aspect of preclinical research.

Lack of parvalbumin in mice leads to behavioral deficits relevant to all human autism core symptoms and related neural morphofunctional abnormalities

Gene mutations and gene copy number variants are associated with autism spectrum disorders (ASDs). Affected gene products are often part of signaling networks implicated in synapse formation and/or function leading to alterations in the excitation/inhibition (E/I) balance. Although the network of parvalbumin (PV)-expressing interneurons has gained particular attention in ASD, little is known on PV's putative role with respect to ASD. Genetic mouse models represent powerful translational tools for studying the role of genetic and neurobiological factors underlying ASD. Here, we report that PV knockout mice (PV(-/-)) display behavioral phenotypes with relevance to all three core symptoms present in human ASD patients: abnormal reciprocal social interactions, impairments in communication and repetitive and stereotyped patterns of behavior. PV-depleted mice also showed several signs of ASD-associated comorbidities, such as reduced pain sensitivity and startle responses yet increased seizure susceptibility, whereas no evidence for behavioral phenotypes with relevance to anxiety, depression and schizophrenia was obtained. Reduced social interactions and communication were also observed in heterozygous (PV(+/-)) mice characterized by lower PV expression levels, indicating that merely a decrease in PV levels might be sufficient to elicit core ASD-like deficits. Structural magnetic resonance imaging measurements in PV(-/-) and PV(+/-) mice further revealed ASD-associated developmental neuroanatomical changes, including transient cortical hypertrophy and cerebellar hypoplasia. Electrophysiological experiments finally demonstrated that the E/I balance in these mice is altered by modification of both inhibitory and excitatory synaptic transmission. On the basis of the reported changes in PV expression patterns in several, mostly genetic rodent models of ASD, we propose that in these models downregulation of PV might represent one of the points of convergence, thus providing a common link between apparently unrelated ASD-associated synapse structure/function phenotypes.

RAB GTPases and RAB-interacting proteins and their role in the control of cognitive functions

A RAS-related class of small monomeric G proteins, the RAB GTPases, is emerging as of key biological importance in compartment specific directional control of vesicles formation, transport and fusion. Thanks to human genetic observation and to the consequent dedicated biochemical work, substantial progress has been made on the understanding of the role played by RAB GTPases and their effector proteins on neuronal development and the shaping of cognitive functions. This review is highlighting these initial elements to broaden the current scope of research on developmental cognitive deficits and take the point of view of RAB GTPases control on membrane transport in neurons and astrocytes.

Neddylation dysfunction in Alzheimer's disease

Ubiquitin-dependent proteolysis is a major mechanism that downregulates misfolded proteins or those that have finished a programmed task. In the last two decades, neddylation has emerged as a major regulatory pathway for ubiquitination. Central to the neddylation pathway is the amyloid precursor protein (APP)-binding protein APP-BP1, which together with Uba3, plays an analogous role to the ubiquitin-activating enzyme E1 in nedd8 activation. Activated nedd8 covalently modifies and activates a major class of ubiquitin ligases called Cullin-RING ligases (CRLs). New evidence suggests that neddylation also modifies Type-1 transmembrane receptors such as APP. Here we review the functions of neddylation and summarize evidence suggesting that dysfunction of neddylation is involved in Alzheimer's disease.

A ketone ester diet exhibits anxiolytic and cognition-sparing properties, and lessens amyloid and tau pathologies in a mouse model of Alzheimer's disease

Alzheimer's disease (AD) involves progressive accumulation of amyloid β-peptide (Aβ) and neurofibrillary pathologies, and glucose hypometabolism in brain regions critical for memory. The 3xTgAD mouse model was used to test the hypothesis that a ketone ester-based diet can ameliorate AD pathogenesis. Beginning at a presymptomatic age, 2 groups of male 3xTgAD mice were fed a diet containing a physiological enantiomeric precursor of ketone bodies (KET) or an isocaloric carbohydrate diet. The results of behavioral tests performed at 4 and 7 months after diet initiation revealed that KET-fed mice exhibited significantly less anxiety in 2 different tests. 3xTgAD mice on the KET diet also exhibited significant, albeit relatively subtle, improvements in performance on learning and memory tests. Immunohistochemical analyses revealed that KET-fed mice exhibited decreased Aβ deposition in the subiculum, CA1 and CA3 regions of the hippocampus, and the amygdala. KET-fed mice exhibited reduced levels of hyperphosphorylated tau deposition in the same regions of the hippocampus, amygdala, and cortex. Thus, a novel ketone ester can ameliorate proteopathic and behavioral deficits in a mouse AD model.

All in the Family: How the APPs Regulate Neurogenesis

Recent intriguing evidence suggests that metabolites of amyloid precursor protein (APP), mutated in familial forms of Alzheimer’s disease (AD), play critical roles in developmental and postnatal neurogenesis. Of note is soluble APPα (sAPPα) that regulates neural progenitor cell proliferation. The APP family encompasses a group of ubiquitously expressed and evolutionarily conserved, type I transmembrane glycoproteins, whose functions have yet to be fully elucidated. APP can undergo proteolytic cleavage by mutually exclusive pathways. The subtle structural differences between metabolites generated in the different pathways, as well as their equilibrium, may be crucial for neuronal function. The implications of this new body of evidence are significant. Miscleavage of APP would readily impact developmental and postnatal neurogenesis, which might contribute to cognitive deficits characterizing Alzheimer’s disease. This review will discuss the implications of the role of the APP family in neurogenesis for neuronal development, cognitive function, and brain disorders that compromise learning and memory, such as AD.

Preweaning sensorimotor deficits and adolescent hypersociability in Grin1 knockdown mice

Mice with knockdown of the N-methyl-D-aspartate (NMDA) receptor NR1 subunit, encoded by the gene Grin1, have been investigated as a model for the intrinsic NMDA hypofunction hypothesized for schizophrenia. Previous work has shown that adult Grin1 mutant mice have overt deficits in habituation and sensorimotor gating, exaggerated reactivity to environmental stimuli, reduced social approach, and other alterations that reflect behavioral manifestations of schizophrenia. In humans, the emergence of overt symptoms of the disorder typically occurs in adolescence or early adulthood, suggesting a role for aberrant maturation of NMDA receptor signaling in symptom onset. The following study evaluated Grin1 mutant mice for abnormal behavioral phenotypes during the preweaning, adolescent, and adult periods. Measures included open field activity, prepulse inhibition of acoustic startle responses, and social preference in a three-chamber choice task. Mice from the C57BL/6J inbred strain, one of the parental strains for the Grin1 line, were also tested. The results showed that developmental reduction of NMDA receptor function led to significant alterations in behavior during the second and third weeks of life, including exaggerated startle responses and sensorimotor gating deficits on postnatal day 13, and pronounced hypersociability in adolescence. Male Grin1 mutant mice were more susceptible than female mice to the detrimental effects of decreased NMDA signaling. Overall, these findings provide evidence that reduced Grin1 function leads to abnormal phenotypes in the preweaning period, and that deficient NMDA signaling can lead to both overt hypersociability or marked asociality, dependent upon sex and age.

APP transgenic mice for modelling behavioural and psychological symptoms of dementia (BPSD)

The discovery of gene mutations responsible for autosomal dominant Alzheimer's disease has enabled researchers to reproduce in transgenic mice several hallmarks of this disorder, notably Aβ accumulation, though in most cases without neurofibrillary tangles. Mice expressing mutated and wild-type APP as well as C-terminal fragments of APP exhibit variations in exploratory activity reminiscent of behavioural and psychological symptoms of Alzheimer dementia (BPSD). In particular, open-field, spontaneous alternation, and elevated plus-maze tasks as well as aggression are modified in several APP transgenic mice relative to non-transgenic controls. However, depending on the precise murine models, changes in open-field and elevated plus-maze exploration occur in either direction, either increased or decreased relative to controls. It remains to be determined which neurotransmitter changes are responsible for this variability, in particular with respect to GABA, 5HT, and dopamine.

Vascular endothelial growth factor induces contralesional corticobulbar plasticity and functional neurological recovery in the ischemic brain

Vascular endothelial growth factor (VEGF) is a potent angiogenic factor, which also has neuroprotective activity. In view of these dual actions on vessels and neurons, we were interested whether VEGF promotes long distance axonal plasticity in the ischemic brain. Herein, we show that VEGF promotes neurological stroke recovery in mice when delivered in a delayed way starting 3 days after middle cerebral artery occlusion. Using anterograde tract-tracing experiments that we combined with histochemical and molecular biological studies, we demonstrate that although VEGF promoted angiogenesis predominantly in the ischemic hemisphere, pronounced axonal sprouting was induced by VEGF in the contralesional, but not the ipsilesional corticobulbar system. Corticobulbar plasticity was accompanied by the deactivation of the matrix metalloproteinase MMP9 in the lesioned hemisphere and the transient downregulation of the axonal growth inhibitors NG2 proteoglycan and brevican and the guidance molecules ephrin B1/2 in the contralesional hemisphere. The regulation of matrix proteinases, growth inhibitors, and guidance molecules offers insights how brain plasticity is controlled in the ischemic brain.

Endogenous amyloid-β is necessary for hippocampal synaptic plasticity and memory

OBJECTIVE

The goal of this study was to investigate the role of endogenous amyloid-β peptide (Aβ) in healthy brain.

METHODS

Long-term potentiation (LTP), a type of synaptic plasticity that is thought to be associated with learning and memory, was examined through extracellular field recordings from the CA1 region of hippocampal slices, whereas behavioral techniques were used to assess contextual fear memory and reference memory. Amyloid precursor protein (APP) expression was reduced through small interfering RNA (siRNA) technique.

RESULTS

We found that both antirodent Aβ antibody and siRNA against murine APP reduced LTP as well as contextual fear memory and reference memory. These effects were rescued by the addition of human Aβ₄₂, suggesting that endogenously produced Aβ is needed for normal LTP and memory. Furthermore, the effect of endogenous Aβ on plasticity and memory was likely due to regulation of transmitter release, activation of α7-containing nicotinic acetylcholine receptors, and Aβ₄₂ production.

INTERPRETATION

Endogenous Aβ₄₂ is a critical player in synaptic plasticity and memory within the normal central nervous system. This needs to be taken into consideration when designing therapies aiming at reducing Aβ levels to treat Alzheimer disease.

The intracellular threonine of amyloid precursor protein that is essential for docking of Pin1 is dispensable for developmental function

Background

Processing of Aβ-precursor protein (APP) plays an important role in Alzheimer's Disease (AD) pathogenesis. Thr residue at amino acid 668 of the APP intracellular domain (AID) is highly conserved. When phosphorylated, this residue generates a binding site for Pin1. The interaction of APP with Pin1 has been involved in AD pathogenesis.

Methodology/Principal Findings

To dissect the functions of this sequence in vivo, we created an APP knock-in allele, in which Thr⁶⁶⁸ is replaced by an Ala (T⁶⁶⁸A). Doubly deficient APP/APP-like protein 2 (APLP2) mice present postnatal lethality and neuromuscular synapse defects. Previous work has shown that the APP intracellular domain is necessary for preventing early lethality and neuromuscular junctions (NMJ) defects. Crossing the T⁶⁶⁸A allele into the APLP2 knockout background showed that mutation of Thr⁶⁶⁸ does not cause a defective phenotype. Notably, the T⁶⁶⁸A mutant APP is able to bind Mint1.

Conclusions/Significance

Our results argue against an important role of the Thr⁶⁶⁸ residue in the essential function of APP in developmental regulation. Furthermore, they indicate that phosphorylation at this residue is not functionally involved in those APP-mediated functions that prevent (NMJ) defects and early lethality in APLP2 null mice.

A single tyrosine residue in the amyloid precursor protein intracellular domain is essential for developmental function

The Aβ-precursor protein (APP) intracellular domain is highly conserved and contains many potentially important residues, in particular the (682)YENPTY(687) motif. To dissect the functions of this sequence in vivo, we created an APP knock-in allele mutating Tyr(682) to Gly (Y682G). Crossing this allele to APP-like protein 2 (APLP2) knock-out background showed that mutation of Tyr(682) results in postnatal lethality and neuromuscular synapse defects similar to doubly deficient APP/APLP2 mice. Our results demonstrate that a single residue in the APP intracellular region, Tyr(682), is indispensable for the essential function of APP in developmental regulation.

Generation of conditional null alleles for APP and APLP2

Proteolytical cleavage of the beta-amyloid precursor protein (APP) generates beta-amyloid, which is deposited in the brains of patients suffering from Alzheimer's disease (AD). Despite the well-established key role of APP for AD pathogenesis, the physiological function of APP and its close homologues APLP1 and APLP2 remains poorly understood. Previously, we generated APP(-/-) mice that proved viable, whereas APP(-/-)APLP2(-/-) mice and triple knockouts died shortly after birth, likely due to deficits of neuromuscular synaptic transmission. Here, we generated conditional knockout alleles for both APP and APLP2 in which the promoter and exon1 were flanked by loxP sites. No differences in expression were detectable between wt and floxed alleles, whereas null alleles were obtained upon crossing with Cre-transgenic deleter mice. These mice will now allow for tissue and time-point controlled knockout of both genes.

Role of Nogo-A in neuronal survival in the reperfused ischemic brain

Nogo-A is an oligodendroglial neurite outgrowth inhibitor, the deactivation of which enhances brain plasticity and functional recovery in animal models of stroke. Nogo-A's role in the reperfused brain tissue was still unknown. By using Nogo-A(-/-) mice and mice in which Nogo-A was blocked with a neutralizing antibody (11C7) that was infused into the lateral ventricle or striatum, we show that Nogo-A inhibition goes along with decreased neuronal survival and more protracted neurologic recovery, when deactivation is constitutive or induced 24 h before, but not after focal cerebral ischemia. We show that in the presence of Nogo-A, RhoA is activated and Rac1 and RhoB are deactivated, maintaining stress kinases p38/MAPK, SAPK/JNK1/2 and phosphatase-and-tensin homolog (PTEN) activities low. Nogo-A blockade leads to RhoA deactivation, thus overactivating Rac1 and RhoB, the former of which activates p38/MAPK and SAPK/JNK1/2 via direct interaction. RhoA and its effector Rho-associated coiled-coil protein kinase2 deactivation in turn stimulates PTEN, thus inhibiting Akt and ERK1/2, and initiating p53-dependent cell death. Our data suggest a novel role of Nogo-A in promoting neuronal survival by controlling Rac1/RhoA balance. Clinical trials should be aware of injurious effects of axonal growth-promoting therapies. Thus, Nogo-A antibodies should not be used in the very acute stroke phase.

Understanding the molecular basis of Alzheimer's disease using a Caenorhabditis elegans model system

Alzheimer's disease (AD) is the major cause of dementia in the United States. At the cellular level, the brains of AD patients are characterized by extracellular dense plaques and intracellular neurofibrillary tangles whose major components are the beta-amyloid peptide and tau, respectively. The beta-amyloid peptide is a cleavage product of the amyloid precursor protein (APP); mutations in APP have been correlated with a small number of cases of familial Alzheimer's disease. APP is the canonical member of the APP family, whose functions remain unclear. The nematode Caenorhabditis elegans, one of the premier genetic workhorses, is being used in a variety of ways to address the functions of APP and determine how the beta-amyloid peptide and tau can induce toxicity. First, the function of the C. elegans APP-related gene, apl-1, is being examined. Although different organisms may use APP and related proteins, such as APL-1, in different functional contexts, the pathways in which they function and the molecules with which they interact are usually conserved. Second, components of the gamma-secretase complex and their respective functions are being revealed through genetic analyses in C. elegans. Third, to address questions of toxicity, onset of degeneration, and protective mechanisms, different human beta-amyloid peptide and tau variants are being introduced into C. elegans and the resultant transgenic lines examined. Here, we summarize how a simple system such as C. elegans can be used as a model to understand APP function and suppression of beta-amyloid peptide and tau toxicity in higher organisms.

Delayed melatonin administration promotes neuronal survival, neurogenesis and motor recovery, and attenuates hyperactivity and anxiety after mild focal cerebral ischemia in mice

Melatonin is a potent antioxidant with neuroprotective activity in animal models of ischemic stroke, which based on its lack of serious toxicity has raised hopes that it might be used for human stroke treatment in the future. This study investigated how subacute delivery of melatonin, starting at 24 hr after stroke onset, and continuing for 29 days (4 mg/kg/day; via drinking water), influences neuronal survival, endogenous neurogenesis, motor recovery and locomotor activity in C57Bl6/j mice submitted to 30-min middle cerebral artery occlusion. Histologic studies showed that melatonin improved neuronal survival and enhanced neurogenesis, even when applied 1 day after stroke. Cell survival was associated with a long-lasting improvement of motor and coordination deficits, evaluated by the grip strength and RotaRod tests, as well as with attenuation of hyperactivity and anxiety of the animals as revealed in open field tests. The robust functional neurologic improvements encourage proof-of-concept studies with melatonin in human stroke patients.

Functional interactions of APP with the apoE receptor family

The beta-amyloid precursor protein (APP) is central to the pathogenesis of Alzheimer's disease, but its normal functions in the brain are poorly understood. A number of APP-interacting proteins have been identified: intracellularly, APP interacts with adaptor proteins through its conserved NPXY domain; extracellularly, APP interacts with a component of the extracellular matrix, F-spondin. Interestingly, many of these APP-interacting proteins also interact with the family of receptors for apolipoprotein E (apoE), the Alzheimer's disease risk factor. apoE receptors also share with APP the fact that they are cleaved by the same secretase activities. apoE receptors are shed from the cell surface, a cleavage that is regulated by receptor-ligand interactions, and C-terminal fragments of apoE receptors are cleaved by gamma-secretase. Functionally, both APP and apoE receptors affect neuronal migration and synapse formation in the brain. This review summarizes these numerous interactions between APP and apoE receptors, which provide clues about the normal functions of APP.

Amyloid precursor protein knockout mice show age-dependent deficits in passive avoidance learning

Amyloid precursor protein (APP) is involved in the pathogenesis of Alzheimer's disease (AD), but its role in cognition has been relatively little studied. APP knockout (KO) animals have been described previously and show deficits in grip strength, reduced locomotor activity and impaired learning and memory in a conditioned avoidance test and the Morris water-maze. In order to further investigate the in vivo function of APP and its proteolytic derivatives, we tested APP KO mice and age-matched wild type controls at two different ages, 3 and 8 months, in a range of behavioural tests measuring neuromuscular, locomotor and cognitive functions. These tests included the acquisition of a passive avoidance response as a measure of long-term memory of an aversive experience, and spontaneous alternation in a Y-maze, regarded as a measure of spatial short-term memory. The absence of APP expression in APP KO mice was confirmed at the protein level using hippocampal tissue in Western blotting. APP KO mice displayed deficits in forelimb grip strength and locomotor activity in agreement with previous studies. In the Y-maze test used for spontaneous alternation behaviour, APP KO animals did not exhibit reduced alternation rates. On the other hand, in the passive avoidance test, APP KO mice showed an age-related deficit in retention of memory for an aversive experience. The results suggest that APP and/or its proteolytic derivatives may play a role in long-term memory in adult brain and/or may be required during the development and maintenance of neuronal networks involved in this type of memory.

The secreted beta-amyloid precursor protein ectodomain APPs alpha is sufficient to rescue the anatomical, behavioral, and electrophysiological abnormalities of APP-deficient mice

It is well established that the proteolytic processing of the beta-amyloid precursor protein (APP) generates beta-amyloid (Abeta), which plays a central role in the pathogenesis of Alzheimer's disease (AD). In contrast, the physiological role of APP and of its numerous proteolytic fragments and the question of whether a loss of these functions contributes to AD are still unknown. To address this question, we replaced the endogenous APP locus by gene-targeted alleles and generated two lines of knock-in mice that exclusively express APP deletion variants corresponding either to the secreted APP ectodomain (APPs alpha) or to a C-terminal (CT) truncation lacking the YENPTY interaction motif (APPdeltaCT15). Interestingly, the deltaCT15 deletion resulted in reduced turnover of holoAPP, increased cell surface expression, and strongly reduced Abeta levels in brain, likely because of reduced processing in the endocytic pathway. Most importantly, we demonstrate that in both APP knock-in lines the expression of APP N-terminal domains either grossly attenuated or completely rescued the prominent deficits of APP knock-out mice, such as reductions in brain and body weight, grip strength deficits, alterations in circadian locomotor activity, exploratory activity, and the impairment in spatial learning and long-term potentiation. Together, our data suggest that the APP C terminus is dispensable and that APPs alpha is sufficient to mediate the physiological functions of APP assessed by these tests.

The functions of mammalian amyloid precursor protein and related amyloid precursor-like proteins

It is well established that proteolytic processing of the beta-amyloid precursor protein (APP) generates beta-amyloid which plays a central role in the pathogenesis of Alzheimer's disease. In contrast, the physiological role of APP and the question of whether a loss of these functions contributes to Alzheimer's disease are still unclear. For a long time, the characterization of APP functions was markedly hampered by the high redundancy between APP and the related APP family members amyloid precursor-like proteins 1 and 2. The generation and analyses of combined gene deficiencies for APP and amyloid precursor-like proteins in mice finally marked the beginning of uncovering the in vivo roles of these proteins in mammals. In the current review, we summarize recent insights into the functions of the APP gene family from mice lacking one, two or all three family members.

Unraveling in vivo functions of amyloid precursor protein: insights from knockout and knockdown studies

The amyloid precursor protein (APP) is a widely expressed transmembrane protein that is cleaved to generate Abeta peptides in the central nervous system and is a key player in the pathogenesis of Alzheimer's disease. The precise biological functions of APP still remain unclear although various roles have been proposed. While a commonly accepted model argues that Abeta peptides are the cause of onset and early pathogenesis of Alzheimer's disease, recent discussions challenge this 'Abeta hypothesis' and suggest a direct role for APP in this neurodegenerative disease. Loss-of-function studies are an efficient way to elucidate the role of proteins and concurrently a variety of in vitro and in vivo studies has been performed for APP where protein levels have been downregulated and functional consequences monitored. Complete disruption of APP gene expression has been achieved by the generation of APP knockout animal models. Further knockdown studies using antisense and RNA interference have allowed scientists to reduce APP expression levels and have opened new avenues to explore the physiological roles of APP. In the present review, we focus on knockout and knockdown approaches that have provided insights into the physiological functions of APP and discuss their advantages and drawbacks.

Keratinocytes from APP/APLP2-deficient mice are impaired in proliferation, adhesion and migration in vitro

Growing evidence shows that the soluble N-terminal form (sAPPalpha) of the amyloid precursor protein (APP) represents an epidermal growth factor fostering keratinocyte proliferation, migration and adhesion. APP is a member of a protein family including the two mammalian amyloid precursor-like proteins APLP1 and APLP2. In the mammalian epidermis, only APP and APLP2 are expressed. APP and APLP2-deficient mice die shortly after birth but do not display a specific epidermal phenotype. In this report, we investigated the epidermis of APP and/or APLP2 knockout mice. Basal keratinocytes showed reduced proliferation in vivo by about 40%. Likewise, isolated keratinocytes exhibited reduced proliferation rates in vitro, which could be completely rescued by either exogenously added recombinant sAPPalpha, or by co-culture with dermal fibroblasts derived from APP knockout mice. Moreover, APP-knockout keratinocytes revealed reduced migration velocity resulting from severely compromised cell substrate adhesion. Keratinocytes from double knockout mice died within the first week of culture, indicating essential functions of APP-family members for survival in vitro. Our data indicate that sAPPalpha has to be considered as an essential epidermal growth factor which, however, in vivo can be functionally compensated to a certain extent by other growth factors, e.g., factors released from dermal fibroblasts.

Mouse behavioural analysis in systems biology

Molecular techniques allowing in vivo modulation of gene expression have provided unique opportunities and challenges for behavioural studies aimed at understanding the function of particular genes or biological systems under physiological or pathological conditions. Although various animal models are available, the laboratory mouse (Mus musculus) has unique features and is therefore a preferred animal model. The mouse shares a remarkable genetic resemblance and aspects of behaviour with humans. In this review, first we describe common mouse models for behavioural analyses. As both genetic and environmental factors influence behavioural performance and need to be carefully evaluated in behavioural experiments, considerations for designing and interpretations of these experiments are subsequently discussed. Finally, common behavioural tests used to assess brain function are reviewed, and it is illustrated how behavioural tests are used to increase our understanding of the role of histaminergic neurotransmission in brain function.

Lengthening of G2/mitosis in cortical precursors from mice lacking β-amyloid precursor protein

The beta-amyloid precursor protein (APP) is expressed within the nervous system, even at the earliest stages of embryonic development when cell growth and proliferation is particularly important. In order to study the function of APP at these early developmental stages, we have studied the development of the cerebral cortex in both wild type and App-/- mutant mice. Here, we demonstrate that APP mRNA is expressed in cortical precursor cells and that APP protein is concentrated within their apical domains during interphase. However, during mitosis, APP re-localizes to the peripheral space surrounding the metaphase plate. In APP-deficient cortical precursors, the duration of mitosis is increased and a higher proportion of cortical precursor cells contained nuclei in late G2. We conclude that during cortical development APP plays a role in controlling cell cycle progression, particularly affecting G2 and mitosis. These observations may have important implications for our understanding of how APP influences the progression of Alzheimer's disease, since degenerating cortical neurons have been shown to up-regulate cell cycle markers and re-enter the mitotic cycle before dying.

Cortical dysplasia resembling human type 2 lissencephaly in mice lacking all three APP family members

The Alzheimer's disease beta-amyloid precursor protein (APP) is a member of a larger gene family that includes the amyloid precursor-like proteins, termed APLP1 and APLP2. We previously documented that APLP2-/-APLP1-/- and APLP2-/-APP-/- mice die postnatally, while APLP1-/-APP-/- mice and single mutants were viable. We now report that mice lacking all three APP/APLP family members survive through embryonic development, and die shortly after birth. In contrast to double-mutant animals with perinatal lethality, 81% of triple mutants showed cranial abnormalities. In 68% of triple mutants, we observed cortical dysplasias characterized by focal ectopic neuroblasts that had migrated through the basal lamina and pial membrane, a phenotype that resembles human type II lissencephaly. Moreover, at E18.5 triple mutants showed a partial loss of cortical Cajal Retzius (CR) cells, suggesting that APP/APLPs play a crucial role in the survival of CR cells and neuronal adhesion. Collectively, our data reveal an essential role for APP family members in normal brain development and early postnatal survival.

β-Amyloid Treatment Sensitizes Mice to Amphetamine-Induced Locomotion but Reduces Response to Caffeine

BACKGROUND

Psychosis frequently occurs in Alzheimer's disease (AD), being associated with more severe cognitive decline, but the underlying mechanisms are unknown.

OBJECTIVE

To investigate the effect of centrally administered beta-amyloid peptide, a model for AD, in the locomotor response to amphetamine, caffeine and MK-801, which are psychoactive drugs related to neurochemical changes occurring in psychosis.

METHODS

Mice were intracerebroventricularly injected with beta-amyloid (25-35), and after 1 week they were tested in the passive avoidance, spontaneous alternation and locomotor tasks.

RESULTS

Besides impaired performance in inhibitory avoidance and spontaneous alternation tasks, beta-amyloid-treated mice showed increased spontaneous locomotion, augmented response to amphetamine (1.5 mg/kg), blunted response to caffeine (30 mg/kg) and no difference in MK-801 (0.25 mg/kg)-induced locomotor activation when compared to its respective control.

CONCLUSION

These results are compatible with the hypothesis that beta-amyloid peptide may predispose to psychotic symptoms of AD by increasing sensitivity of the dopaminergic system, possibly related to a decreased adenosinergic inhibitory tone.

Animal models of mental retardation: from gene to cognitive function

About 2-3% of all children are affected by mental retardation, and genetic conditions rank among the leading causes of mental retardation. Alterations in the information encoded by genes that regulate critical steps of brain development can disrupt the normal course of development, and have profound consequences on mental processes. Genetically modified mouse models have helped to elucidate the contribution of specific gene alterations and gene-environment interactions to the phenotype of several forms of mental retardation. Mouse models of several neurodevelopmental pathologies, such as Down and Rett syndromes and X-linked forms of mental retardation, have been developed. Because behavior is the ultimate output of brain, behavioral phenotyping of these models provides functional information that may not be detectable using molecular, cellular or histological evaluations. In particular, the study of ontogeny of behavior is recommended in mouse models of disorders having a developmental onset. Identifying the role of specific genes in neuropathologies provides a framework in which to understand key stages of human brain development, and provides a target for potential therapeutic intervention.

Enriched early experiences of mice underexpressing the beta-amyloid precursor protein restore spatial learning capabilities but not normal openfield behavior of adult animals

We have previously reported severely impaired spatial learning in mutant mice underexpressing a shortened variant of the beta-amyloid precursor protein (beta-APPtheta/theta). This targeted mutation is functionally equivalent to a null mutation. It also disturbs behavioral and neurological maturation with deficits emerging mainly between postnatal day (pd) 11 and 19. Such early tested mice exhibited almost no genotype-related difference in Morris water maze learning, raising the possibility that early handling might have compensated for genetic deficits. To verify this effect, we compared watermaze learning and open field behavior of 66 adult mutant and wildtype mice having been handled during pd 3-27 with that of 70 non-handled mutant and wildtype mice. Neurological testing during pd 3-27 markedly reduced time near wall and improved spatial retention of adult mutants, restoring their learning capabilities to wildtype levels. Early handling did not cure the mutation associated activity deficit in the open field, but mainly increased center field exploration in both mutants and wildtypes. In a follow-up experiment we analyzed whether an early (pd 3-10, n = 22) or middle (pd 11-19, n = 24) period of handling in form of neurological testing had differential effects on adult behavior. Mice handled during pd 11-19 had slightly shorter escape times than mice handled during pd 3-10 but were not significantly different in other behavioral measures. There were no sex related differences. Correlational and factor analysis showed that both the mutation and early handling had pleiotropic behavioral effects, resulting in differentially impaired mutants depending on the test situation. Likewise, early handling affected not only thigmotactic tendencies but also, more subtly, other behavioral components underlying water maze learning. We conclude that early postnatal stimulation can prevent mutation induced learning deficits in adult mice, but probably through other developmental mechanisms than those affected by the mutation. This implies that some behavioral impairments related to beta-APP malfunction may be corrected through simple treatments.

Assessing the behavioral and cognitive effects of seizures on the developing brain

The degree to which seizures lead to 'brain damage' is not fully known, but this question has important clinical implications. Seizure-induced brain damage can be defined in several ways: structural, physiological, and behavioral. The behavioral and cognitive effects of seizures are difficult to ascertain in patients, because it is hard to differentiate the effects of the seizures from the underlying brain pathology, anticonvulsant treatment, and developmental variables. In animal models, the ability to control seizure variables allows detailed investigation of factors that cannot be easily distinguished in clinical studies. In models of experimental epilepsy, both brief and prolonged seizures lead to brain damage. While the consequences of seizures are much more extensive in the adult brain, long-term alterations are also seen in the developing brain. This chapter focuses on the effects of seizures during development on subsequent behavior and cognition in experimental epilepsy models. The investigator must choose carefully among the various tests of behavior, learning, memory, and cognition, since the existence or extent of deficits may depend upon which test is selected and how the data are analyzed. The experimental evidence suggests that seizures early in life are associated with subtle deficits in behavior and cognition, even in the absence of overt structural neuronal damage. These deficits are dependent upon the age at which seizures occur (less severe deficits at younger ages), seizure frequency and seizure severity, but are largely independent of seizure etiology, occurring after several types of chemoconvulsants and electrical stimulation. Seizure-induced behavioral and cognitive deficits, which may not become obvious until long after the onset of the epilepsy, might be equally or more detrimental to a child's overall function than the seizures themselves.

Transgenic and knock-out mouse pups: the growing need for behavioral analysis

Few laboratories working with transgenic and knockout mice analyze the neurobehavioral consequences of genetic manipulation in early ontogeny. However, the study of behavioral endpoints during the early postnatal period in genetically modified mice is important not only to assess possible developmental abnormalities, but also to better understand and disentangle the effects of genetic manipulations in adulthood. We propose that the assessment of neurobehavioral development represents an appropriate strategy to identify possible compensatory and/or unexpected effects. Nowadays, a large number of experimental protocols that take into account the practical constraints imposed by the peculiar physiological and behavioral responses of an immature subject are available to assess the neurobehavioral profile of developing mice. While this knowledge should be applied to the field of transgenic and knock-out mice in general, it should be recommended, in particular, for the study of mouse models of neurodevelopmental disorders.

Behavioral phenotyping enhanced--beyond (environmental) standardization

It is basic biology that the phenotype of an animal is the product of a complex and dynamic interplay between nature (genotype) and nurture (environment). It is far less clear, however, how this might translate into experimental design and the interpretation of animal experiments. Animal experiments are a compromise between modelling real world phenomena with maximal validity (complexity) and designing practicable research projects (abstraction). Textbooks on laboratory animal science generally favour abstraction over complexity. Depending on the area of research, however, abstraction can seriously compromise information gain, with respect to the real world phenomena an experiment is designed to model. Behavioral phenotyping of mouse mutants often deals with particularly complex manifestations of life, such as learning, memory or anxiety, that are strongly modulated by environmental factors. A growing body of evidence indicates that current approaches to behavioral phenotyping might often produce results that are idiosyncratic to the study in which they were obtained, because the interactive nature of genotype-environment relationships underlying behavioral phenotypes was not taken into account. This paper argues that systematic variation of genetic and environmental backgrounds, instead of excessive standardization, is needed to control the robustness of the results and to detect biologically relevant interactions between the mutation and the genetic and environmental background of the animals.

Extended analysis of path data from mutant mice using the public domain software Wintrack

Animal tracking by means of videocameras has made considerable progress over the past several years and is now being used in a large number of studies. However, the precision and frequency at which xy path data can be recorded using personal computers contrast with the relative simplicity of the analyses commonly conducted with this type of data. In order to achieve more analytical power and flexibility in numerical and graphical path analysis, we have developed Wintrack, a Windows application that processes data from a variety of commercially available tracking systems. The application provides an intuitive drag-and-drop interface to increase ease and speed of standard analysis and graphical representation of data. A flexible scripting language allows the advanced user to extend the capabilities of the program by defining custom arenas and specialized parameters. For example, this permits to integrate path data with events recorded through the keyboard or to adapt the program for the processing of GPS data from outdoors experiments. A macro language allows for fully automated and database-controlled large-scale data analysis. We are using this feature to develop new analysis parameters for water maze and open-field experiments and to evaluate them retrospectively with reference data from several thousand mice tested in our laboratory. For noncommercial use, the software can be downloaded free of charge at www.dpwolfer.ch/wintrack.

Transgenic mouse models of Alzheimer's disease

Alzheimer's disease (AD) is a neurodegenerative disorder, characterized by a progressive loss of cognitive function. Despite considerable progress, a complete description of the molecular pathology of this disease has yet to be elucidated. In this respect, the need for an animal model that develops some or all aspects of this uniquely human disease in a reproducible fashion is crucial for the development and testing of potential treatments. A valid animal model for AD should exhibit (1) progressive AD-like neuropathology and (2) cognitive deficits, and (3) should be verified in several laboratories. Transgenic models should be able to (4) discern pathogenic effects of familial forms (FAD) mutations from those of transgene overexpression. Models derived from microinjection of FAD mutant alleles should (5) encompass more than one Tg line. At present, however, no model that replicates all of these desirable features exists. In this review, we discuss transgenic mouse models with well-characterized AD-like neuropathology that show some form of cognitive impairment. We argue that conclusions drawn from a limited selection of cross-sectional experiments should be verified in longitudinally designed experiments. Future studies should attempt to establish a closer relationship between molecular pathology and the degree of cognitive impairment. While exact replication of AD in mice may not attainable (due to phylogenetic differences and fundamental differences in behavioral ecology), rigorous comparative analysis of cognitive behavior observed in various mouse models of AD should provide a framework for better understanding of molecular mechanisms underlying cognitive impairment observed in AD patients.

Learning deficits in mice with persistent Borna disease virus infection of the CNS associated with elevated chemokine expression

Borna disease virus (BDV) is a highly neurotropic RNA virus that causes a CD8(+) T cell-mediated neurological disease in certain mouse strains. We established asymptomatic persistent central nervous system (CNS) infections in mutant C57BL/10J mice that lack functional CD8(+) T cells. When analyzed at adult age for spatial learning abilities in a water maze, BDV-infected mice showed slightly impaired escape performance while their exploratory behavior in an openfield test was indistinguishable from uninfected control mice. Histological and molecular biological analysis revealed extensive viral spread throughout the CNS of infected animals. Most neurons of the hippocampus contained viral antigen, but there was no overt loss of neurons from this structure. We found almost unchanged levels of the proinflammatory cytokines IL-1beta and TNF-alpha, but clearly increased levels of the chemokines IP-10 and RANTES in brains of infected mice. Re-examination of water maze data revealed that only infected mice with IP-10 transcript levels above a certain threshold showed impaired performance, whereas the performance of infected mice with lower IP-10 levels was indistinguishable from uninfected controls. This suggests that BDV infection can disturb the function of the mammalian CNS without causing overt neuronal loss, and that the magnitude of virus-induced chemokine production in the CNS correlates with the degree of impairment.