1H NMR metabolomic signatures in five brain regions of the AβPPswe Tg2576 mouse model of Alzheimer's disease at four ages

In the quest for biomarkers of onset and progression of Alzheimer's disease, a 1H NMR-based metabolomic study was performed on the simple single-transgenic Tg2576 mouse model. These mice develop a slow cognitive decline starting by 6 months and express amyloid plaques from 10 months of age. The metabolic profiles of extracts from five brain regions (frontal cortex, rhinal cortex, hippocampus, midbrain, and cerebellum) of Tg2576 male mice were compared to those of controls, at 1, 3, 6 and 11 months of age. The most obvious differences were due to brain regions. Age was also a discriminating parameter. Metabolic perturbations were already detected in the hippocampus and the rhinal cortex of transgenic mice as early as 1 month of age with decreased concentrations of glutamate (Glu) and N-acetylaspartate (NAA) compared to those in wild-type animals. Metabolic changes were more numerous in the hippocampus and the rhinal cortex of 3 month-old transgenic mice and involved Glu, NAA, myo-inositol, creatine, phosphocholine, and γ-aminobutyric acid (only in the hippocampus) whose concentrations decreased. A metabolic disruption characterized by an increase in the hippocampal concentrations of Glu, creatine, and taurine was detected in 6 month-old transgenic mice. At this time point, the chemical profile of the cerebellum was slightly affected. At 11 months, all the brain regions analyzed (except the frontal cortex) were metabolically altered, with mainly a marked increase in the formation of the neuroprotective metabolites creatine and taurine. Our findings demonstrate that metabolic modifications occur long before the onset of behavioral impairment.

Neurogenetic basis of cognition: Facts and hypotheses

In the natural setting, cognitive processes direct behavioural adjustments and sometimes result in behavioural novelties which allow the organism to cope with environmental pressures. The resulting behavioural changes exhibit various forms which are dependent upon different causal factors and cognitive processes. Under long-lasting environmental changes, these behavioural adaptations can become hereditary either through the process of cultural transmission or through genetic mechanisms sensitive to selective forces acting on genotypes. In the last few years, neuroethology and behavioural neurosciences have produced an increasing amount of precise knowledge about brain-behaviour relationships, neurobiological bases of cognitive processes and their development. Unfortunately, the approach to these phenomena is basically normative and does not tell us much about non-pathological determinants of individual variation in cognitive and behavioural competences. In contrast, the differential approach has provided some cases of structural variations in the brain which are under genetic control and thus liable to evolve under selective pressures. Brain size, the ratio of various brain structures to the total brain, the number and density of neurons in various parts of the brain and the variations of neuronal circuitry are potential candidates. This paper reviews them and examines their possible behavioural and cognitive outcomes. The issue here is to examine if and where in the brain potential conditions occur that would allow the genetic evolution of cognitive processes.

Spontaneous exploration, response plus position learning and hippocampal mossy fibre distribution: A correlational study

Forty-eight mice from twelve isogenic groups were tested in two different behavioral tests. The first test was a non-reinforced exploration of a Y-maze and the second was a response plus position learning followed by reversal learning in a T-maze. Behavioral results were correlated with the size of the area occupied by the various mossy fibre synaptic sub-fields in the hippocampus as revealed by Timm staining. The analysis of results showed that mice with a large suprapyramidal mossy fibre area tended to use a somewhat rigid motor response strategy during the initial exploration of the Y-maze, that they easily learned the response plus position task in the T-maze, but proved unable to quickly inhibit that learned response during the reversal task. On the other hand, mice with a large intra-infrapyramidal synaptic field displayed greater ability to cope with a situation including novelty or constraint elements.

Modifications of hippocampal circuits and early disruption of adult neurogenesis in the tg2576 mouse model of Alzheimer's disease

At advanced stages of Alzheimer's disease, cognitive dysfunction is accompanied by severe alterations of hippocampal circuits that may largely underlie memory impairments. However, it is likely that anatomical remodeling in the hippocampus may start long before any cognitive alteration is detected. Using the well-described Tg2576 mouse model of Alzheimer's disease that develops progressive age-dependent amyloidosis and cognitive deficits, we examined whether specific stages of the disease were associated with the expression of anatomical markers of hippocampal dysfunction. We found that these mice develop a complex pattern of changes in their dentate gyrus with aging. Those include aberrant expression of neuropeptide Y and reduced levels of calbindin, reflecting a profound remodeling of inhibitory and excitatory circuits in the dentate gyrus. Preceding these changes, we identified severe alterations of adult hippocampal neurogenesis in Tg2576 mice. We gathered converging data in Tg2576 mice at young age, indicating impaired maturation of new neurons that may compromise their functional integration into hippocampal circuits. Thus, disruption of adult hippocampal neurogenesis occurred before network remodeling in this mouse model and therefore may account as an early event in the etiology of Alzheimer's pathology. Ultimately, both events may constitute key components of hippocampal dysfunction and associated cognitive deficits occurring in Alzheimer's disease.

Central locomotor and cognitive effects of a NPFF receptor agonist in mouse

NPFF receptors are expressed in several brain regions directly or indirectly involved in cognition and behavior. However, the cognitive effects of the NPFF system have been poorly studied. Therefore, the aim of our study was to analyze the effects of i.c.v. injections of 1 DMe, a stable agonist of NPFF receptors, on behavioral and cognitive performances in C57BL/6J mice. We measured locomotor activity, and an open field with objects was used to estimate the ability of mice to react to spatial changes and to measure short-term retention of information. The Morris navigation task was used to evaluate the acquisition, as well as long-term retention of a hippocampo-dependent spatial memory with a distributed training procedure. Finally, 1 DMe was tested in a contextual fear conditioning paradigm to study its effect on long-term memory of contextual information acquired in a single training session. Altogether, our results demonstrate a small but complex influence of the NPFF system on mouse behavior. 1 DMe injected i.c.v. induces a delayed hyperlocomotion and mildly impairs both short-term and long-term spatial memory processing without affecting contextual fear memory.

A preliminary study of the effects of handling type on horses' emotional reactivity and the human-horse relationship

Handling is a crucial component of the human-horse relationship. Here, we report data from an experiment conducted to assess and compare the effect of two training methods. Two groups of six Welsh mares were trained during four sessions of 50 min, one handled with traditional exercises (halter leading, grooming/brushing, lifting feet, lunging and pseudo-saddling (using only girth and saddle pad) and the second group with natural horsemanship exercises (desensitization, yielding to body pressure, lunging and free-lunging). Emotional reactivity (ER) and the human-horse relationship (HHR) were assessed both prior to and following handling. A social isolation test, a neophobia test and a bridge test were used to assess ER. HHR was assessed through test of spontaneous approach to, and forced approach by, an unknown human. Horses' ER decreased after both types of handling as indicated by decreases in the occurrence of whinnying during stressful situations. Head movement (jerk/shake) was the most sensitive variable to handling type. In the spontaneous approach tests, horses in the traditional handling group showed higher latencies to approach a motionless person after handling than did the natural horsemanship group. Our study suggests that natural horsemanship exercises could be more efficient than traditional exercises for improving horses' HHR.

A neuropeptide FF agonist blocks the acquisition of conditioned place preference to morphine in C57Bl/6J mice

Neuropeptide FF behaves as an opioid-modulating peptide that seems to be involved in morphine tolerance and physical dependence. Nevertheless, the effects of neuropeptide FF agonists on the rewarding properties of morphine remain unknown. C57BL6 mice were conditioned in an unbiased balanced paradigm of conditioned place preference to study the effect of i.c.v. injections of 1DMe (D-Tyr1(NMe)Phe3]NPFF), a stable agonist of the neuropeptide FF system, on the acquisition of place conditioning by morphine or alcohol (ethanol). Morphine (10 mg/kg, i.p.) or ethanol (2 g/kg, i.p.) induced a significant place preference. Injection of 1DMe (1-20 nmol), given 10 min before the i.p. injection of the reinforcing drug during conditioning, inhibited the rewarding effect of morphine but had no effect on the rewarding effect of ethanol. However, a single injection of 1DMe given just before place preference testing was unable to inhibit the rewarding effects of morphine. By itself, 1DMe was inactive but an aversive effect of this agonist could be evidenced if the experimental procedure was biased. These results suggest that neuropeptide FF, injected during conditioning, should influence the development of rewarding effects of morphine and reinforce the hypothesis of strong inhibitory interactions between neuropeptide FF and opioids.

Encoding, consolidation, and retrieval of contextual memory: differential involvement of dorsal CA3 and CA1 hippocampal subregions

Studies on human and animals shed light on the unique hippocampus contributions to relational memory. However, the particular role of each hippocampal subregion in memory processing is still not clear. Hippocampal computational models and theories have emphasized a unique function in memory for each hippocampal subregion, with the CA3 area acting as an autoassociative memory network and the CA1 area as a critical output structure. In order to understand the respective roles of the CA3- and CA1-hippocampal areas in the formation of contextual memory, we studied the effects of the reversible inactivation by lidocaine of the CA3 or CA1 areas of the dorsal hippocampus on acquisition, consolidation, and retrieval of a contextual fear conditioning. Whereas infusions of lidocaine never impaired elementary tone conditioning, their effects on contextual conditioning provided interesting clues about the role of these two hippocampal regions. They demonstrated first that the CA3 area is necessary for the rapid elaboration of a unified representation of the context. Secondly, they suggested that the CA1 area is rather involved in the consolidation process of contextual memory. Third, they showed that CA1 or CA3 inactivation during retention test has no effect on contextual fear retrieval when a recognition memory procedure is used. In conclusion, our findings point as evidence that CA1 and CA3 subregions of the dorsal hippocampus play important and different roles in the acquisition and consolidation of contextual fear memory, whereas they are not required for context recognition.

The Collaborative Cross, a community resource for the genetic analysis of complex traits

The goal of the Complex Trait Consortium is to promote the development of resources that can be used to understand, treat and ultimately prevent pervasive human diseases. Existing and proposed mouse resources that are optimized to study the actions of isolated genetic loci on a fixed background are less effective for studying intact polygenic networks and interactions among genes, environments, pathogens and other factors. The Collaborative Cross will provide a common reference panel specifically designed for the integrative analysis of complex systems and will change the way we approach human health and disease.

Disruption of hippocampal CA3 network: effects on episodic-like memory processing in C57BL/6J mice

Lesion studies have demonstrated the prominent role of the hippocampus in spatial and contextual learning. To better understand how contextual information is processed in the CA3 region during learning, we focused on the CA3 autoassociative network hypothesis. We took advantage of a particularity of the mossy fibre (MF) synapses, i.e. their high zinc concentration, to reversibly disrupt the afferent MF pathway by microinfusions of an intracellular (DEDTC) or an extracellular (CaEDTA) zinc chelator into the CA3 area of the dorsal hippocampus of mice. Disruption of the CA3 network significantly impaired the acquisition and the consolidation of contextual fear conditioning, whereas contextual retrieval was unaffected. These results also suggest a heterogeneity between the cognitive processes underlying spatial and contextual memory that might be linked to the specific involvement of free zinc in contextual information processing.

Siah-1b is a direct transcriptional target of p53: identification of the functional p53 responsive element in the siah-1b promoter

Siah proteins are E3 ubiquitin ligases. They are homologues of the Drosophila seven in absentia (Sina), a protein required for the R7 photoreceptor development. We have previously found that the expression of human siah-1 and its mouse homologue siah-1b are induced by p53 during apoptosis and tumor reversion. So far, no evidence that the siah-1b gene is a direct transcriptional target of p53 has been provided. In the present study we investigate this issue. Northern blot analysis with a specific probe demonstrates an increase in siah-1b transcription on activation of endogenous and inducible exogenous p53. To explore whether this effect is directly mediated by p53 we analyzed 20 kb of chromosome X DNA, containing the siah-1b locus. A p53-binding site was identified in the siah-1b promoter, located at nucleotides -2155/-2103 relative to the translational start site. This site is composed of two half-sites, conforming to the p53-binding consensus sequence but separated by a nonclassical 33-bp spacer. In luciferase assays, p53 induces a substantial increase in siah-1b promoter activity. Gel shift and DNase-I-footprinting studies, combined with mutational analysis and chromatin immunoprecipitation, indicate that p53 effectively binds the siah-1b promoter in vitro and in vivo. Thus, the siah-1b gene is a direct transcriptional target of p53.

Two QTLs located on chromosomes 1 and 5 modulate different aspects of the performance of mice of the B x D Ty RI strain series in the Morris navigation task

The Morris navigation task is widely used to study spatial abilities in rodents; namely, to analyze the effects of mutations in genetically engineered mice. Although quantitative and Mendelian genetic studies have shown that the variation of these abilities is partly under genetic control, little is known about these genetic factors. In order to analyze the genetic architecture of spatial navigation in mice, a wide genome scan was performed to map the QTLs that control various aspects of the performance, using the RI strain methodology. Latencies to locate the submerged platform across learning sessions and performance to the spatial probe test were analyzed in the 26 strains of the B x D RI series. Both cluster analysis of behavioral measurements and QTL mapping confirmed previous data showing that the escape latencies and the spatial bias rely on two distinct components of the task, controlled by different loci. A QTL on chromosome 1 influenced escape latencies during the four training sessions, whereas another QTL, located on chromosome 5, was shown to control spatial performance at the probe trial and also exhibited epistatic interactions with two other QTLs on chromosomes 2 and 13. The function of these QTLs is examined in the broader context of hippocampal-dependent learning processes and in relation to QTLs already found in similar positions in other behavioral traits.

Behavioral alterations associated with apoptosis and down-regulation of presenilin 1 in the brains of p53-deficient mice

Presenilin 1 (PS1) expression is repressed by the p53 tumor suppressor. As shown herein, wild-type PS1 is an effective antiapoptotic molecule capable of significantly inhibiting p53-dependent and p53-independent cell death. We analyzed, at the functional and molecular levels, the brains of p53 knockout mice. Surprisingly, we found that lack of p53 expression induces apoptotic brain lesions, accompanied by learning deficiency and behavioral alterations. p53-deficient mice show an unexpected overexpression of p21(waf1) with subsequent down-regulation of PS1 in their brains. This process is progressive and age-dependent. These data indicate that the p53 pathway, besides affecting tumor suppression, may play a major role in regulating neurobehavioral function and cell survival in the brain.

Reversible inactivation of the hippocampal mossy fiber synapses in mice impairs spatial learning, but neither consolidation nor memory retrieval, in the Morris navigation task

The role played by hippocampal mossy fibers in the learning and memory processes implemented in the Morris swimming navigation task has been studied in C57BL/6 mice by selective and reversible inactivation of mossy fiber synaptic fields by diethyldithiocarbamate. The functional integrity of the mossy fibers proved essential for the storage of the spatial representation on the modifiable synapses of the recurrent collaterals of the CA3 pyramidal cells, whereas it is not necessary for the consolidation and recall of spatial memories. The results suggest that mossy fibers are preferentially involved in new learning. They are consistent with the hypothesis that the hippocampal CA3 region might act as an autoassociation memory.

Radial maze learning using exclusively distant visual cues reveals learners and nonlearners among inbred mouse strains

Spatial working memory on the radial maze was studied in 8 groups of isogenic mice. The device and procedure were specially designed to prevent the mice from using a response strategy or taking advantage of olfactory trails or other proximal cues. The results showed that the strains of mice were clearly split between those which succeeded (C57BL/6, DBA/2, CB6F1, B6D2F1) and those which failed (NZB, CBA, C3H/HE, BALB/c) to learn the task. A second experiment established that when more extended training was given, the four strains which had performed poorly in experiment 1 still did not improve their performance. In the conclusion, we discuss the possible reasons for the deficits of nonlearners and emphasize the importance of using proper tools to ensure the unambiguous assessment of the cognitive processes underlying behavioral adaptation.

Ontogeny of orientation and spatial learning on the radial maze in mice

The development of the orientation capacities of C57BL/6 mice has been studied on the radial maze in several procedures allowed to dissociate the different types of cues used by the mouse for solving the task with two intersession delays (2 and 24 hr). The results of the first two studies show that performance is independent of intersession delay regardless of the age of the subject. Mice as early as 23 days old obtain good performances when they can develop an algorithmic strategy or when they dispose of both proximal and distal cues during learning. At 37 days of age, however, mice can efficiently solve the radial maze task with distal cues alone. However, in the third experiment, 23-day-old mice were able to use distal cues for orientation at the end of the learning session if, at the onset, they also had access to proximal cues. These results suggest that, on weaning, mice use several types of information for task performance and that, as they mature, they turn more often to distal cues for orientation.

Analysis of behavioral and hippocampal variation in congenic albino and pigmented BALB mice

Mice of the BALB/c strain are widely used in behavioral research in spite of the albino condition, which can obscure brain-behavior relationships. We have developed a pigmented BALB strain, congenic to BALB/c, which could be more appropriate for neurogenetic studies that aim at identifying the effects of neurological mutations on behavior. Comparison of inbred albino and pigmented congenic BALB arising from the same litters provides a valuable tool for detecting the consequences of the albino mutation on behavioral performances. Preliminary results presented here show that the albino condition does not interfere with the development and patterns of connectivity of mossy fibers in the hippocampus. On the other hand, obvious coat color-linked differences appear for locomotor activity and defecation scores in the open field, pigmented mice being unexpectedly less active and more reactive than albino, as if better vision increased their reactions to a novel, anxiogenic environment. Finally, pigmented mice do not show better performances in the radial maze, which confirms that the inability of BALB mice for spatial learning in a highly demanding version of this task cannot be attributed to their inability to process visual information.

A study of behavioral and sensorial bases of radial maze learning in mice

In order to analyze the various sensorial and behavioral modes implied in learning on a radial maze, three isogenic mice groups (BALB/C, C57BL/6, and CB6F1) were subjected to four different learning procedures, each ending with a probe test. These four procedures examined the use of radial strategies and allowed to dissociate the use of olfactory and spatial cues. Results showed that all mice preferred to use a radial strategy. When the confinement procedure rendered the use of a radial strategy impossible, BALB/C mice were incapable of establishing spatial orientation but were able to learn the task by using olfactory cues. C57BL/6 mice, on the other hand, seemed to use spatial cues exclusively, while the CB6F1 hybrids showed a high degree of plasticity, using either type of information. These strain-specific differences point out the heterogeneity of the processes called into play during radial maze learning and show that unless olfactory cues are carefully controlled they can account for choice accuracy in some mice.

Behavioural strategies, sensorial processes and hippocampal mossy fibre distribution in radial maze performance in mice

Eight isogenic mice groups (6 inbred strains and 2 F1 hybrid generations) were tested on an eight-arm radial maze, using either a procedure of confinement (C) or a non-confinement (NC) to the central platform between trials, in order to control for the use of response strategies in learning. On the 6th day of training, the spatial surrounding was impoverished by removing the most salient visual cues of the room; thus allowing testing for the effective use of spatial cues during learning. Results showed that learning profiles and performance levels varied between strains within each procedure. These variations could correspond to a heterogeneity of the underlying perceptual processes involved in learning, since only some strains in each procedure were disturbed by the removal of spatial cues. Correlations between behavioural results and the distribution of mossy fibres in the hippocampus were analysed. The intercorrelation matrix revealed that correlations between the size of the infra-intrapyramidal synaptic field (IIP-MF) and some behavioural indices occurred only during the first trial on the maze, whatever the procedure. Learning performances on the 5th day of training did not correlate with any hippocampal measure. When the spatial surrounding was impoverished, on the 6th day of training, correlations with mossy fibres appeared only in the confinement procedure.

Genetic variation, hippocampal mossy fibres distribution, novelty reactions and spatial representation in mice

It is now well established that variation in hippocampal circuitry correlates with various behavioural measures. In order to formulate more precise hypotheses about the functional role of the supra (SP-MF) and intra-infra mossy fibres (IIP-MF) layers, we investigated their covariation with a large number of behavioural measures in the classic and the spatial open-field taken from a genetically heterogeneous population composed of subjects from 12 isogenic mice groups (9 inbred strains and 3 F1's). The hippocampus-behaviour intercorrelation matrix reveals that behavioural reactions and inferred psychological processes only correlate with IIP-MF. Detailed analysis of correlates shows that IIP-MF positively correlate with locomotor activity, rearings and central sector crossings in the classic open-field and correlate negatively with the short-term habituation index to the objects in the spatial open-field. Surprisingly the memory of the spatial arrangement of a set of objects does not correlate with any hippocampal measure.

Measurements of the behavioral effects of albino mutation in mice (Mus musculus): comparisons of coisogenic inbred and hybrid lines

The effects of the albino gene on mouse behavior were examined, in particular its possible interactions with nonallelic genes (epistasis). More generally, the possible effects of genetic background (inbreeding depression or hybrid vigor) on the effects of the mutation were also considered. Tasks requiring either predominantly motor or predominantly cognitive capacity were studied for coisogenic albino and pigmented mice from either an inbred strain (C57BL/6 c/c vs. C57BL/6 +/c) or an F1 heterozygous generation (F1 c/c vs. F1 +/c) from a BALB/c X C57BL/6 +/c cross. The results showed a clear albino gene effect in the two lines and provide further evidence that the gene is the effective factor. On the other hand, there was no significant interaction between the mutation and the genotypic group (C57BL/6 or F1), which indicates that the effects of the mutation act approximately in an additive fashion between loci in these groups.

Differential effects of the albino gene on behavior according to task, level of inbreeding, and genetic background

Different generations from a Mendelian crossing schedule and two inbred recombinant albino strains were compared in a water-escape and a locomotor task under dim red-orange light. The results revealed deleterious effects of the albino gene. Although seriously altering cognitive-capacities, they did not affect locomotor tasks. The degree of expression of these effects was greater in the inbred albino mice than in the albinos from heterozygous generations. Differences in the genetic background may also affect the degree of expression of the albino gene effects in various albino strains. The visual system is unlikely to mediate the pleiotropic effects of the albino gene discussed in this report.

Maternal effects in mice: influence of parents' and offspring's genotypes

Different backcrosses between the F1 and two inbred parental strains (C and B6) were compared for swimming speed in water escape task and for swimming ability in a water channel. Results showed maternal effects, mice from an F1 dam swimming faster than mice from an inbred dam. Albino mice appear to be more sensitive to these effects could also be related to the inbreeding level of the offspring, the reciprocal backcrosses showing differences, whereas the two reciprocal F1's did not. Maternal effects appear to be greater in the water escape task than in the water channel situation.

Hoarding behavior of AKR, C57BL/6 mice and their F1 in their home living space: an automatic recording technique

Earlier genetic analysis of food hoarding behavior in mice used test situations in which animals were allowed to hoard food only during short time periods. This paper describes a technique to measure food hoarding over long time periods. Small discs of standard food are equipped with a steel clip and each passage of a mouse bringing such a food disc from the food search enclosure to the nest is detected by an electromagnetic sounding lead connected to a pen recorder. Preliminary results show that female mice begin to hoard earlier than males; one of the two reciprocal F1 has a shorter latency to hoard than the other one. Results also show differences between two parental inbred strains and their reciprocal F1 for the light-dark distribution of hoarding.

A case of behavioral heterosis in mice: quantitative and qualitative aspects of performance in a water-escape task

Fourteen hundred and four mice from two inbred strains (Balb/c and C57BL/6), F1, F2, and backcrosses were subjected to four trials in a water-escape task and to a swimming test. Detailed analysis of mice behavior in these situations showed that the "F1 hybrid vigor" affected behavioral characters not directly related to physical vigor but of potential adaptive value. Their superiority was mainly due to more frequent adoption of an efficient behavioral tactic (direct or edge escape paths toward the exit) and more rapid progress with experience in this respect than other generations exhibited. These results clearly show that heterosis is not limited to physical vigor but may extend to behavioral and even psychological characters.