Gloria Blázquez

Modeling behavioral and neuronal symptoms of Alzheimer's disease in mice: a role for intraneuronal amyloid.

The amyloid Abeta-peptide (Abeta) is suspected to play a critical role in the cascade leading to AD as the pathogen that causes neuronal and synaptic dysfunction and, eventually, cell death. Therefore, it has been the subject of a huge number of clinical and basic research studies on this disease. Abeta is typically found aggregated in extracellular amyloid plaques that occur in specific brain regions enriched in nAChRs in Alzheimers disease (AD) and Down syndrome (DS) brains. Advances in the genetics of its familiar and sporadic forms, together with those in gene transfer technology, have provided valuable animal models that complement the traditional cholinergic approaches, although modeling the neuronal and behavioral deficits of AD in these models has been challenging. More recently, emerging evidence indicates that intraneuronal accumulation of Abeta may also contribute to the cascade of neurodegenerative events and strongly suggest that it is an early, pathological biomarker for the onset of AD and associated cognitive and other behavioral deficits. The present review covers these studies in humans, in in vitro and in transgenic models, also providing more evidence that adult 3xTg-AD mice harboring PS1M146V, APPSwe, tauP301L transgenes, and mimicking many critical hallmarks of AD, show cognitive deficits and other behavioral alterations at ages when overt neuropathology is not yet observed, but when intraneuronal Abeta, synaptic and cholinergic deficits can already be described.

Combined sequence-based and genetic mapping analysis of complex traits in outbred rats

Genetic mapping on fully sequenced individuals is transforming understanding of the relationship between molecular variation and variation in complex traits. Here we report a combined sequence and genetic mapping analysis in outbred rats that maps 355 quantitative trait loci for 122 phenotypes. We identify 35 causal genes involved in 31 phenotypes, implicating new genes in models of anxiety, heart disease and multiple sclerosis. The relationship between sequence and genetic variation is unexpectedly complex: at approximately 40% of quantitative trait loci, a single sequence variant cannot account for the phenotypic effect. Using comparable sequence and mapping data from mice, we show that the extent and spatial pattern of variation in inbred rats differ substantially from those of inbred mice and that the genetic variants in orthologous genes rarely contribute to the same phenotype in both species.

A resource for the simultaneous high-resolution mapping of multiple quantitative trait loci in rats: The NIH heterogeneous stock

The laboratory rat (Rattus norvegicus) is a key tool for the study of medicine and pharmacology for human health. A large database of phenotypes for integrated fields such as cardiovascular, neuroscience, and exercise physiology exists in the literature. However, the molecular characterization of the genetic loci that give rise to variation in these traits has proven to be difficult. Here we show how one obstacle to progress, the fine-mapping of quantitative trait loci (QTL), can be overcome by using an outbred population of rats. By use of a genetically heterogeneous stock of rats, we map a locus contributing to variation in a fear-related measure (two-way active avoidance in the shuttle box) to a region on chromosome 5 containing nine genes. By establishing a protocol measuring multiple phenotypes including immunology, neuroinflammation, and hematology, as well as cardiovascular, metabolic, and behavioral traits, we establish the rat HS as a new resource for the fine-mapping of QTLs contributing to variation in complex traits of biomedical relevance.

Relationship between ethanol preference and sensation/novelty seeking

High- and low-avoidance Roman inbred rat strains (RHA-I, RLA-I) were selected for extreme differences in two-way active avoidance. RHA-I rats also express less anxiety than RLA-I rats. This study compared male Roman rats in ethanol preference and sensation/novelty seeking. Rats were first exposed in counterbalanced order to the hole-board test (forced exposure to novelty) and the Y-maze and emergence tests (free choice between novel and familiar locations). Then, rats were tested in 24-h, two-bottle preference tests with water in one bottle and ethanol (2, 4, 6, 8, or 10% in successive days). Compared to RLA-I rats, RHA-I rats showed (1) higher frequency and time in head dipping, (2) higher activity, and (3) lower frequency of rearing and grooming in the hole-board test, and (4) remained in the novel arm longer in the Y-maze test. No strain differences were observed in the emergence test. RHA-I rats exhibited higher preference for and consumed more ethanol than RLA-I rats at all concentrations. However, both strains preferred ethanol over water for 2-4% concentrations, but water over ethanol for 6-10% concentrations. Factorial analysis with all the rats pooled identified a two-factor solution, one grouping preferred ethanol concentrations (2-4%) with head dipping and grooming in the hole board, and another factor grouping the nonpreferred ethanol concentrations (6-10%) with activity in the hole board and novel-arm time in the Y-maze test. These results show that preference for ethanol is associated with different aspects of behavior measured in sensation/novelty-seeking tests.

Cognitive and emotional profiles of aged Alzheimer's disease (3 × TgAD) mice: Effects of environmental enrichment and sexual dimorphism

Alzheimers disease is a neurodegenerative disorder associated with age which represents the most common cause of dementia. It is characterized by an accelerated memory loss compared to normal aging, and deterioration of other cognitive abilities that interfere with mood, reason, judgment and language. The main neuropathological hallmarks of the disorder are β-amyloid (βA) plaques and neurofibrillary Tau tangles. Triple transgenic 3×TgAD mouse model develops βA and Tau pathologies in a progressive manner, with a specific temporal and anatomic profile mimicking the pattern that takes place in the human brain with AD, and showing cognitive alterations characteristic of the disease. Environmental enrichment treatment in mice induces behavioral and emotional reactivity changes, including cognitive improvements in some AD-related transgenic mice. The present work intended to characterize the behavioral profile of 3×TgAD mice at advanced stages of neuropathological development (12 and 15 months of age) and to investigate whether environmental enrichment administered during adulthood was able to modify some of their behavioral and cognitive alterations. Results show that, at advanced stages of the disease 3×TgAD mice show deficits of spatial learning acquisition, as well as short-term and working memory deficits, while displaying increased levels of anxiety/fearfulness and normal sensorimotor functions. 3×TgAD mice also show sexual dimorphism, as reflected by increased cognitive deficits in females and increased levels of novelty-induced behavioral inhibition in males. Environmental enrichment exerts some slight positive effects, by mainly improving the initial acquisition of the spatial learning and working memory in 12-month-old 3×TgAD mice. Such effects vary depending on the gender.

Context-dependent differences in grooming behavior among the NIH heterogeneous stock and the Roman high- and low-avoidance rats

Grooming occurs during/after stress and seems to accompany dearousal. Here, grooming was investigated under testing situations involving different levels of aversiveness, taking advantage of differences among three rat strains in fearfulness/anxiety. Inbred Roman High Avoidance (RHA-I) rats are less anxious/fearful than inbred Roman Low Avoidance (RLA-I). The outbred genetically heterogeneous stock of rats (NIH-HS), which resembles the RLA-I in many behavioral traits, was also studied. Adult male rats (RLA-I: n=9, RHA-I: n=10, NIH-HS: n=12) were observed for 30min in: a novel open-field, a novel hole-board and in the home-cage. They were also observed during two-way active avoidance training. Differences in grooming depended on test situation: (a) No differences were found in the home-cage. (b) While tested in a novel environment, RHA-I showed less grooming activity than the other rats. (c) After avoidance responses appeared, differences among the strains were opposite to the observed in novelty tests. Furthermore, results suggest that (i) grooming is mostly suppressed when assured aversive experience is under way; (ii) rostral grooming prevails when experience with aversive stimuli is unpredictable (novelty) or potential (avoidance training); (iii) body grooming increases for a period in novel environments. In general, our results support that grooming takes place during dearousal.

Prepulse inhibition predicts spatial working memory performance in the inbred Roman high- and low-avoidance rats and in genetically heterogeneous NIH-HS rats: relevance for studying pre-attentive and cognitive anomalies in schizophrenia

Animal models of schizophrenia-relevant symptoms are increasingly important for progress in our understanding of the neurobiological basis of the disorder and for discovering novel and more specific treatments. Prepulse inhibition (PPI) and working memory, which are impaired in schizophrenic patients, are among the symptoms/processes modeled in those animal analogs. We have evaluated whether a genetically-selected rat model, the Roman high-avoidance inbred strain (RHA-I), displays PPI deficits as compared with its Roman low-avoidance (RLA-I) counterpart and the genetically heterogeneous NIH-HS rat stock. We have investigated whether PPI deficits predict spatial working memory impairments (in the Morris water maze; MWM) in these three rat types (Experiment 1), as well as in a separate sample of NIH-HS rats stratified according to their extreme (High, Medium, Low) PPI scores (Experiment 2). The results from Experiment 1 show that RHA-I rats display PPI and spatial working memory deficits compared to both RLA-I and NIH-HS rats. Likewise, in Experiment 2, “Low-PPI” NIH-HS rats present significantly impaired working memory with respect to “Medium-PPI” and “High-PPI” NIH-HS subgroups. Further support to these results comes from correlational, factorial, and multiple regression analyses, which reveal that PPI is positively associated with spatial working memory performance. Conversely, cued learning in the MWM was not associated with PPI. Thus, using genetically-selected and genetically heterogeneous rats, the present study shows, for the first time, that PPI is a positive predictor of performance in a spatial working memory task. These results may have translational value for schizophrenia symptom research in humans, as they suggest that either by psychogenetic selection or by focusing on extreme PPI scores from a genetically heterogeneous rat stock, it is possible to detect a useful (perhaps “at risk”) phenotype to study cognitive anomalies linked to schizophrenia.

Heterogeneous stock rat: A unique animal model for mapping genes influencing bone fragility

Previously, we demonstrated that skeletal mass, structure and biomechanical properties vary considerably among 11 different inbred rat strains. Subsequently, we performed quantitative trait loci (QTL) analysis in four inbred rat strains (F344, LEW, COP and DA) for different bone phenotypes and identified several candidate genes influencing various bone traits. The standard approach to narrowing QTL intervals down to a few candidate genes typically employs the generation of congenic lines, which is time consuming and often not successful. A potential alternative approach is to use a highly genetically informative animal model resource capable of delivering very high resolution gene mapping such as Heterogeneous stock (HS) rat. HS rat was derived from eight inbred progenitors: ACI/N, BN/SsN, BUF/N, F344/N, M520/N, MR/N, WKY/N and WN/N. The genetic recombination pattern generated across 50 generations in these rats has been shown to deliver ultra-high even gene-level resolution for complex genetic studies. The purpose of this study is to investigate the usefulness of the HS rat model for fine mapping and identification of genes underlying bone fragility phenotypes. We compared bone geometry, density and strength phenotypes at multiple skeletal sites in HS rats with those obtained from five of the eight progenitor inbred strains. In addition, we estimated the heritability for different bone phenotypes in these rats and employed principal component analysis to explore relationships among bone phenotypes in the HS rats. Our study demonstrates that significant variability exists for different skeletal phenotypes in HS rats compared with their inbred progenitors. In addition, we estimated high heritability for several bone phenotypes and biologically interpretable factors explaining significant overall variability, suggesting that the HS rat model could be a unique genetic resource for rapid and efficient discovery of the genetic determinants of bone fragility.

Cognitive and emotional alterations in young Alzheimer's disease (3xTgAD) mice: Effects of neonatal handling stimulation and sexual dimorphism

Alzheimer disease is the most common neurodegenerative disorder and cause of senile dementia. It is characterized by an accelerated memory loss, and alterations of mood, reason, judgment and language. The main neuropathological hallmarks of the disorder are β-amyloid (βA) plaques and neurofibrillary Tau tangles. The triple transgenic 3xTgAD mouse model develops βA and Tau pathologies in a progressive manner which mimicks the pattern that takes place in the human brain with AD, and showing cognitive alterations characteristic of the disease. The present study intended to examine whether 3xTgAD mice of both sexes present cognitive, emotional and other behavioral alterations at the early age of 4 months, an age in which only some intraneuronal amyloid accumulation is found. Neonatal handling (H) is an early-life treatment known to produce profound and long-lasting behavioral and neurobiological effects in rodents, as well as improvements in cognitive functions. Therefore, we also aimed at evaluating the effects of H on the behavioral/cognitive profile of 4-month-old male and female 3xTgAD mice. The results indicate that, (1) 3xTgAD mice present spatial learning/memory deficits and emotional alterations already at the early age of 4 months, (2) there exists sexual dimorphism effects on several behavioral variables at this age, (3) neonatal handling exerts a preventive effect on some cognitive (spatial learning) and emotional alterations appearing in 3xTgAD mice already at early ages, and 4) H treatment appears to produce stronger positive effects in females than in males in several spatial learning measures and in the open field test.

Neonatal handling decreases unconditioned anxiety, conditioned fear, and improves two-way avoidance acquisition: a study with the inbred Roman high (RHA-I)- and low-avoidance (RLA-I) rats of both sexes.

The present study evaluated the long-lasting effects of neonatal handling (NH; administered during the first 21 days of life) on unlearned and learned anxiety-related responses in inbred Roman High- (RHA-I) and Low-avoidance (RLA-I) rats. To this aim, untreated and neonatally-handled RHA-I and RLA-I rats of both sexes were tested in the following tests/tasks: a novel object exploration (NOE) test, the elevated zero maze (ZM) test, a “baseline acoustic startle” (BAS) test, a “context-conditioned fear” (CCF) test and the acquisition of two-way active—shuttle box—avoidance (SHAV). RLA-I rats showed higher unconditioned (novel object exploration test -“NOE”-, elevated zero maze test -“ZM”-, BAS), and conditioned (CCF, SHAV) anxiety. NH increased exploration of the novel object in the NOE test as well as exploration of the open sections of the ZM test in both rat strains and sexes, although the effects were relatively more marked in the (high anxious) RLA-I strain and in females. NH did not affect BAS, but reduced CCF in both strains and sexes, and improved shuttle box avoidance acquisition especially in RLA-I (and particularly in females) and in female RHA-I rats. These are completely novel findings, which indicate that even some genetically-based anxiety/fear-related phenotypes can be significantly modulated by previous environmental experiences such as the NH manipulation.