Behavioural profiles of inbred mouse strains used as transgenic backgrounds. II: cognitive tests

Strains and stressors: an analysis of touchscreen learning in genetically diverse mouse strains

Touchscreen-based systems are growing in popularity as a tractable, translational approach for studying learning and cognition in rodents. However, while mouse strains are well known to differ in learning across various settings, performance variation between strains in touchscreen learning has not been well described. The selection of appropriate genetic strains and backgrounds is critical to the design of touchscreen-based studies and provides a basis for elucidating genetic factors moderating behavior. Here we provide a quantitative foundation for visual discrimination and reversal learning using touchscreen assays across a total of 35 genotypes. We found significant differences in operant performance and learning, including faster reversal learning in DBA/2J compared to C57BL/6J mice. We then assessed DBA/2J and C57BL/6J for differential sensitivity to an environmental insult by testing for alterations in reversal learning following exposure to repeated swim stress. Stress facilitated reversal learning (selectively during the late stage of reversal) in C57BL/6J, but did not affect learning in DBA/2J. To dissect genetic factors underlying these differences, we phenotyped a family of 27 BXD strains generated by crossing C57BL/6J and DBA/2J. There was marked variation in discrimination, reversal and extinction learning across the BXD strains, suggesting this task may be useful for identifying underlying genetic differences. Moreover, different measures of touchscreen learning were only modestly correlated in the BXD strains, indicating that these processes are comparatively independent at both genetic and phenotypic levels. Finally, we examined the behavioral structure of learning via principal component analysis of the current data, plus an archival dataset, totaling 765 mice. This revealed 5 independent factors suggestive of "reversal learning," "motivation-related late reversal learning," "discrimination learning," "speed to respond," and "motivation during discrimination." Together, these findings provide a valuable reference to inform the choice of strains and genetic backgrounds in future studies using touchscreen-based tasks.

Impact of anxiety profiles on cognitive performance in BALB/c and 129P2 mice

It has been suggested over the decades that dysfunctional anxiety may be caused by distinct alterations in cognitive processing. To learn more about the relation between anxiety and cognitive functioning, two mouse strains that display either adaptive (BALB/c) or nonadaptive (129P2) anxiety, as reflected by their ability to habituate when repeatedly exposed to a novel environment, were tested for their cognitive performance in the modified hole board (mHB) task. In general, both strains showed successful acquisition of the task. The initially more anxious BALB/c mice revealed rapid habituation to the test setup, followed by decreased long-term and short-term memory errors across the experimental period and fast relearning after reversal of the task. By contrast, the nonadaptive 129P2 mice made more short-term memory errors and performed worse than the BALB/c animals after reversal of the test. The results confirm the proposed interaction of anxiety and cognition: In BALB/c mice, adaptive characteristics of anxiety were paralleled by more successful cognitive performance, while in 129P2 mice nonadaptive anxiety-related behaviour was accompanied by a higher level of short-term memory errors and less cognitive flexibility. Moreover, these results support our hypothesis that the nonadaptive anxiety phenotype in 129P2 mice may be the result of impaired cognitive control of emotional processes, resulting in impaired behavioural flexibility, for example in response to novelty.

Mood and memory-associated behaviors in neuropeptide Y5 knockout mice

Recent data led to suggest that in addition to Y1 and Y2 subtypes, Y5 receptors may be involved in mood-related behaviors (Morales-Medina et al., 2010). In the present study, using a battery of behavioral tests to assess anxiety and depression-like paradigms, as well as memory function, we evaluated the potential behavioral changes induced in mice devoid of Y5 receptors. Those paradigms were assessed using the open field (OF), elevated plus maze (EPM), forced swim test (FST), social interaction test (SI), object recognition test (ORT) and Morris water maze (MWM) in Y5 knockout (KO) mice and wild type (WT) animals. In the tests associated to anxiety related behaviors (OF, EPM and SI), no difference for locomotion and time spent in the lateral area of open field were observed between Y5 KO and WT mice. Similar results were observed for time and number of entries in open arms in EPM. Additionally, in SI test, Y5 KO mice spent same amount of time and number of entries in the stranger chamber as compared to WT animals. In the FST, as compared to WT mice, Y5 KO mice had similar immobility time on day 1. No memory dysfunction was observed in the MWM and ORT in Y5 KO mice, as compared to WT. Altogether these data suggest that under basal conditions Y5 KO and WT mice display similar mood behaviors and memory functions. However, as compared to WT, Y5 KO mice display increased grooming and rearing in the OF, lower ratio entries in open arms in the EPM and increased immobility time on the second day of the FST.

The roles of oxytocin and CD38 in social or parental behaviors

The nine amino acid peptide oxytocin (OXT) has been directly associated with different types of behavioral reactions. The formation and maintenance of social relationships in youth and middle age are important components of human mental health. A deficit in healthy behavioral formation leads to social isolation and limitation of well-being. Mice are social animals and are therefore useful for investigating the neurobiological mechanisms of cognitive process control, including the development of social relationships and social skills. Studies in mice may broaden our understanding of the human condition. The multifunctional protein CD38/ADP-ribosyl cyclase is highly expressed in the brain, plays an important role in central OXT release, and regulates social memory. In this review article, we discuss the mechanisms of social behavior affected by the dysregulation of brain OXT function as a consequence of a lack of CD38. OXT bound to OXT receptors initiates autoregulatory positive feedback of OXT release in the hypothalamus and posterior pituitary. OXT bio-behavioral positive feedback is usually implicated in female reproductive systems, but can also be observed in social behavior. Exogenous stimuli (OXT treatment in vitro, OXT intravenous or intraventricular administration, and nasal OXT delivery) initiate activation of OXT neurons via PKC-CD38/ADP-ribosyl cyclase cascades and result in the modulation of social behavior in humans and mice. Based on these findings, we reviewed the functions of OXT and its properties with respect to the development of therapies for human social behavior impairments in psychological diseases. In addition, preliminary studies of continuous nasal OXT administration on subjects with autism spectrum disorders are described.

Mouse models of polyglutamine diseases: review and data table. Part I

Polyglutamine (polyQ) disorders share many similarities, such as a common mutation type in unrelated human causative genes, neurological character, and certain aspects of pathogenesis, including morphological and physiological neuronal alterations. The similarities in pathogenesis have been confirmed by findings that some experimental in vivo therapy approaches are effective in multiple models of polyQ disorders. Additionally, mouse models of polyQ diseases are often highly similar between diseases with respect to behavior and the features of the disease. The common features shared by polyQ mouse models may facilitate the investigation of polyQ disorders and may help researchers explore the mechanisms of these diseases in a broader context. To provide this context and to promote the understanding of polyQ disorders, we have collected and analyzed research data about the characterization and treatment of mouse models of polyQ diseases and organized them into two complementary Excel data tables. The data table that is presented in this review (Part I) covers the behavioral, molecular, cellular, and anatomic characteristics of polyQ mice and contains the most current knowledge about polyQ mouse models. The structure of this data table is designed in such a way that it can be filtered to allow for the immediate retrieval of the data corresponding to a single mouse model or to compare the shared and unique aspects of many polyQ models. The second data table, which is presented in another publication (Part II), covers therapeutic research in mouse models by summarizing all of the therapeutic strategies employed in the treatment of polyQ disorders, phenotypes that are used to examine the effects of the therapy, and therapeutic outcomes.

Characterization of an alcohol addiction-prone phenotype in mice

Human studies indicate that high impulsivity, novelty seeking and anxiety predispose individuals to alcohol abuse. Unclear, however, is whether the same phenotypes can be observed in laboratory animals prone to uncontrolled alcohol drinking. To characterize a novelty-seeking trait, anxiety, impulsivity, compulsivity and the motivation for natural rewards in mice, numerous tests were performed in the automated IntelliCage learning system. The same mice then had extended access to alcohol for 70 days, followed by the evaluation of addiction-like behaviors, including (1) the motivation for alcohol in a progressive-ratio schedule of reinforcement; (2) persistent and compulsive alcohol seeking and taking during signaled 'no alcohol' periods and (3) when subjected to punishment; and (4) the intensity of relapse after alcohol withdrawal. Our data suggest that high levels of anxiety-related traits (i.e. low novelty seeking, low resistance to punishment and a high level of compulsive behaviors) and high impulsivity predict addiction-like alcohol drinking in mice. Future studies are, however, warranted to create a valid model of alcohol addiction in mice in the IntelliCage system.

Differential long term effects of early diisopropylfluorophosphate exposure in Balb/C and C57Bl/J6 mice

The long-term effect of postnatal administration of a sub-toxic dose of the irreversible acetylcholinesterase inhibitor diisopropylfluorophosphate (DFP) on depression and anxiety behavior was compared in two strains of inbred mice. C57BL/6J and Balb/C mice were injected for 7 consecutive days with either 1 mg/kg DFP or saline on postnatal days 14-20. Mice were tested at age 3-4 months for initial and learned anxiety using double-exposure elevated plus maze and to a novel enclosed environment. Depression was assayed using the sweet preference model of anhedonia and the forced swim test for despair. Postnatal DFP pretreatment led to less activity and more immobility in the elevated plus maze in both mouse strains in the first session. The effect was attenuated in the second session in the C57BL/6J strain but not the Balb/C strain. DFP did not affect the sweet preference or forced swim tests, suggesting a dissociation between the long-term effects of DFP on immobility in the context of approach-avoidance conflict (elevated plus maze) versus despair (forced swim).

Effects of low-dose D-serine on recognition and working memory in mice

RATIONALE

D -Serine is an endogenous co-agonist of the N-methyl-D: -aspartate (NMDA) receptor and has been suggested to improve cognitive deficits in schizophrenia.

OBJECTIVES

The present study investigates the effects of treatment with D -serine in mice on tasks that require recognition learning and working memory, two cognitive domains that are impaired in schizophrenia.

METHODS

We studied the effects of various regimens of systemic administration of D -serine (50 mg/kg/day) on BALB/c mice performing object recognition, T-maze alternation, and open-field exploration tasks. For the object recognition task, we also contrasted the effects of D -serine and D -cycloserine and investigated whether D -serine could reverse alterations induced by subchronic injections of the NMDA antagonist MK-801. D -Serine levels after injections were measured by high-performance liquid chromatography.

RESULTS

In the object recognition task, pre-training treatment with D -serine or D -cycloserine significantly enhanced recognition memory 24 h after training. A single administration of D -serine 30 min (but not 6 h) after training produced similar enhancement, suggesting an effect on memory consolidation. Daily treatment with D: -serine enhanced both object recognition and T-maze performance over multiple days and improved short-term memory in MK-801-treated mice. D -Serine treatment did not alter open-field exploration. Behavioral effects were accompanied by increased levels of D -serine in the hippocampus of treated animals.

CONCLUSIONS

Our results show that treatment with D -serine can improve performance in tasks related to recognition learning and working memory, suggesting that this agent can be useful for the treatment of disorders involving declines in these cognitive domains.

The gene or not the gene--that is the question: understanding the genetically engineered mouse phenotype

Embryonic stem cells have had a significant impact on understanding gene function and gene interactions through the use of genetically engineered mice. However, the genetic context (ie, mouse strain) in which these modifications in alleles are made may have a considerable effect on the phenotypic changes identified in these mice. In addition, tissue- and time-specific gene expression systems may generate unanticipated outcomes. This article discusses the history of embryonic stem cells, reviews how mouse strain can affect phenotype (using specific examples), and examines some of the caveats of conditional gene expression systems.

Reduction of endogenous kynurenic acid formation enhances extracellular glutamate, hippocampal plasticity, and cognitive behavior

At endogenous brain concentrations, the astrocyte-derived metabolite kynurenic acid (KYNA) antagonizes the alpha 7 nicotinic acetylcholine receptor and, possibly, the glycine co-agonist site of the NMDA receptor. The functions of these two receptors, which are intimately involved in synaptic plasticity and cognitive processes, may, therefore, be enhanced by reductions in brain KYNA levels. This concept was tested in mice with a targeted deletion of kynurenine aminotransferase II (KAT II), a major biosynthetic enzyme of brain KYNA. At 21 days of age, KAT II knock-out mice had reduced hippocampal KYNA levels (-71%) and showed significantly increased performance in three cognitive paradigms that rely in part on the integrity of hippocampal function, namely object exploration and recognition, passive avoidance, and spatial discrimination. Moreover, compared with wild-type controls, hippocampal slices from KAT II-deficient mice showed a significant increase in the amplitude of long-term potentiation in vitro. These functional changes were accompanied by reduced extracellular KYNA (-66%) and increased extracellular glutamate (+51%) concentrations, measured by hippocampal microdialysis in vivo. Taken together, a picture emerges in which a reduction in the astrocytic formation of KYNA increases glutamatergic tone in the hippocampus and enhances cognitive abilities and synaptic plasticity. Our studies raise the prospect that interventions aimed specifically at reducing KYNA formation in the brain may constitute a promising molecular strategy for cognitive improvement in health and disease.

Strain and regional dependence of alternate splicing of acetylcholinesterase in the murine brain following stress or treatment with diisopropylfluorophosphate

Induction of the rare readthrough variant of acetylcholinesterase (AChE-R) by an acetylcholinesterase (AChE) inhibitor or by stress was tested in four mouse strains that differ in their behavioural profiles on tests of anxiety and depression. BALB/C, C57Bl/6, C3H/He and CD-1 mouse strains were tested in the elevated plus maze in two sessions, separated by 48h. All strains, except CD-1, showed the expected reduction in open arm exploration on the second session. BALB/C and C3H mice spent a greater proportion of the time in the open arms on the first exposure, but spent more time immobile in the maze compared to the CD1 and C57 strains. Immobility was attenuated upon the second exposure in all strains, except the BALB/C mice. Real-time PCR was used to investigate regional and strain differences in induction of AChE-R mRNA following four daily injections of diisopropylfluorophosphate (DFP) (.1mg/kg). AChE-R induction was found in the frontal cortex, but not in amygdala, hippocampus or striatum of CD-1 mice. Nor was there AChE-R induction in the brains of the inbred strains. Four daily sessions of swim stress were used to investigate stress-induced induction of AChE-R. BALB/C mice showed significantly more immobility in the forced swim test (FST) compared to the other strains. FST did not induce AChE-R mRNA in any brain region tested; however, AChE-R mRNA expression in the frontal cortex was negatively correlated with immobility in the FST.

Housing conditions and stimulus females: a robust social discrimination task for studying male rodent social recognition

Social recognition (SR) enables rodents to distinguish between familiar and novel conspecifics, largely through individual odor cues. SR tasks utilize the tendency for a male to sniff and interact with a novel individual more than a familiar individual. Many paradigms have been used to study the roles of the neuropeptides oxytocin and vasopressin in SR. However, inconsistencies in results have arisen within similar mouse strains, and across different paradigms and laboratories, making reliable testing of SR difficult. The current protocol details a novel approach that is replicable across investigators and in different strains of mice. We created a protocol that uses gonadally intact, singly housed females presented within corrals to group-housed males. Housing females singly before testing is particularly important for reliable discrimination. This methodology will be useful for studying short-term social memory in rodents, and may also be applicable for longer term studies.

Anatomical and electrophysiological comparison of CA1 pyramidal neurons of the rat and mouse

The study of learning and memory at the single-neuron level has relied on the use of many animal models, most notably rodents. Although many physiological and anatomical studies have been carried out in rats, the advent of genetically engineered mice has necessitated the comparison of new results in mice to established results from rats. Here we compare fundamental physiological and morphological properties and create three-dimensional compartmental models of identified hippocampal CA1 pyramidal neurons of one strain of rat, Sprague-Dawley, and two strains of mice, C57BL/6 and 129/SvEv. We report several differences in neuronal physiology and anatomy among the three animal groups, the most notable being that neurons of the 129/SvEv mice, but not the C57BL/6 mice, have higher input resistance, lower dendritic surface area, and smaller spines than those of rats. A surprising species-specific difference in membrane resonance indicates that both mouse strains have lower levels of the hyperpolarization-activated nonspecific cation current I(h). Simulations suggest that differences in I(h) kinetics rather than maximal conductance account for the lower resonance. Our findings indicate that comparisons of data obtained across strains or species will need to account for these and potentially other physiological and anatomical differences.

Identifying emotional adaptation: behavioural habituation to novelty and immediate early gene expression in two inbred mouse strains

Normal anxiety is an adaptive emotional response. However, when anxiety appears to lack adaptive value, it might be defined as pathological. Adaptation in animals can be assessed for example by changes in behavioural responses over time, i.e. habituation. We hypothesize that non-adaptive anxiety might be reflected by impaired habituation. To test our hypothesis, we repeatedly exposed male mice from two inbred strains to a novel environment, the modified hole board. BALB/cJ mice were found to be initially highly anxious, but subsequently habituated to the test environment. In contrast, 129P3/J mice initially showed less anxiety-related behaviour compared with the BALB/cJ mice but no habituation in anxiety-related behaviour was observed. Notably, anxiety-related behaviour even increased during the experimental period. Complementary, 129P3/J mice did not show habituation in other parameters such as locomotor and exploratory activity, whereas significant changes appeared in these behaviours in BALB/c mice. Finally, the expression of the immediate early gene c-fos differed between the two strains in distinct brain areas, known to regulate the integration of emotional and cognitive processes. These results suggest that 129P3/J mice might be a promising (neuro)-behavioural animal model for non-adaptive, i.e. pathological anxiety.

Functional outcome is impaired following traumatic brain injury in aging Nogo-A/B-deficient mice

Increasing age is associated with a poor prognosis following traumatic brain injury (TBI). CNS axons may recover poorly following TBI due to expression of myelin-derived inhibitors to axonal outgrowth such as Nogo-A. To study the role of Nogo-A/B in the pathophysiological response of the elderly to TBI, 1-year-old mice deficient in Nogo-A/B (Nogo-A/B homozygous(-/-) mice), Nogo-A/B heterozygous(-/+) mice, and age-matched wild-type (WT) littermate controls were subjected to a controlled cortical impact (CCI) TBI. Sham-injured WT mice (7 months old) and 12 month old naïve Nogo-A/B(-/-) and Nogo-A/B(-/+) served as controls. Neurological motor function was evaluated up to 3 weeks, and cognitive function, hemispheric tissue loss, myelin staining and hippocampal beta-amyloid (A beta) immunohistochemistry were evaluated at 4 weeks post-injury. In WT littermates, TBI significantly impaired learning ability at 4 weeks and neurological motor function up to 2 weeks post-injury and caused a significant loss of hemispheric tissue. Following TBI, Nogo-A/B(-/-) mice showed significantly less recovery from neurological motor and cognitive deficits compared to brain-injured WT mice. Naïve Nogo-A/B(-/-) and Nogo-A/B(-/+) mice quickly learned the MWM task in contrast to brain-injured Nogo-A/B(-/-) mice who failed to learn the MWM task at 4 weeks post-injury. Hemispheric tissue loss and cortical lesion volume were similar among the brain-injured genotypes. Neither TBI nor the absence of NogoA/B caused an increased A beta expression. Myelin staining showed a reduced area and density in the corpus callosum in brain-injured Nogo-A/B(-/-) animals compared to their littermate controls. These novel and unexpected behavioral results demonstrate that the absence of Nogo-A/B may negatively influence outcome, possibly related to hypomyelination, following TBI in mice and suggest a complex role for this myelin-associated axonal growth inhibitor following TBI.

Social approach in genetically engineered mouse lines relevant to autism

Profound impairment in social interaction is a core symptom of autism, a severe neurodevelopmental disorder. Deficits can include a lack of interest in social contact and low levels of approach and proximity to other children. In this study, a three-chambered choice task was used to evaluate sociability and social novelty preference in five lines of mice with mutations in genes implicated in autism spectrum disorders. Fmr1(tm1Cgr/Y)(Fmr1(-/y)) mice represent a model for fragile X, a mental retardation syndrome that is partially comorbid with autism. We tested Fmr1(-/y)mice on two genetic backgrounds, C57BL/6J and FVB/N-129/OlaHsd (FVB/129). Targeted disruption of Fmr1 resulted in low sociability on one measure, but only when the mutation was expressed on FVB/129. Autism has been associated with altered serotonin levels and polymorphisms in SLC6A4 (SERT), the serotonin transporter gene. Male mice with targeted disruption of Slc6a4 displayed significantly less sociability than wild-type controls. Mice with conditional overexpression of Igf-1 (insulin-like growth factor-1) offered a model for brain overgrowth associated with autism. Igf-1 transgenic mice engaged in levels of social approach similar to wild-type controls. Targeted disruption in other genes of interest, En2 (engrailed-2) and Dhcr7, was carried on genetic backgrounds that showed low levels of exploration in the choice task, precluding meaningful interpretations of social behavior scores. Overall, results show that loss of Fmr1 or Slc6a4 gene function can lead to deficits in sociability. Findings from the fragile X model suggest that the FVB/129 background confers enhanced susceptibility to consequences of Fmr1 mutation on social approach.

Genetic models of the endocannabinoid system

The endocannabinoid (ECB) system comprises cannabinoid receptors, ECBs and the whole machinery for the synthesis and degradation of ECBs. It has emerged as an important signalling system in the nervous system, controlling numerous physiological processes, including synaptic transmission, learning and memory, reward, feeding, neuroprotection, neuroinflammation, and neural development. This system is also implicated in various diseases of the nervous system, and thus has become a promising therapeutic target. The use of genetically modified mice has contributed crucially to our rapidly expanding knowledge of the ECB system. In this chapter, the existing mouse mutants targeting the ECB system will be discussed in detail. The use of conditional mutants has given an additional dimension to the analysis of the system, and, it is hoped, will finally enable us to understand this widespread and complex system in the context of intricate networks where different brain regions and neurotransmitter systems interact tightly with each other.

Pitfalls in the interpretation of genetic and pharmacological effects on anxiety-like behaviour in rodents

Over the last 15 years, genetically modified mice have added important data to our knowledge on psychiatric diseases including anxiety. This has produced many behavioural publications, partially by non-behaviourists, in which differences between mutants and normal wild-type animals were described. The popularity of these novel tools allowing the study of new mechanisms also, however, led to observations that could not be confirmed. This review attempts to summarize various factors that can lead to difficult and partially incorrect interpretation of data collected in anxiety-related paradigms. These pitfalls are explained by using virtual data. Our analysis illustrates that determining anxiety in rodents is more complicated than measuring a single parameter in a particular paradigm. It is important to use proper controls such as additional measures in the same or other procedures, as well as a conservative estimation of the chance of finding an actual effect. In this way, it is possible to enhance confidence in the findings. Alternative explanations for findings, like side effects or main effects in a different domain, such as cognition, should always be taken into account. Finally, several examples from the literature are presented as illustrations of the theoretical issues discussed. We believe that considering the pitfalls presented here will help researchers to design optimized experiments that can be more readily interpreted and replicated across laboratories.

Age dependence of motor activity and sensitivity to dopamine receptor 1 agonist, SKF82958, of inbred AKR/J, BALB/c, C57BL/6J, SAMR1, and SAMP6 strains

Motor activity is a key component in many behavioral tests. To assess the relationship between aging and activity, we recorded motor activity for 72 consecutive hours for C57BL/6J (B6J), BALB/c, AKR/J, senescence-accelerated mouse prone 6 (SAMP6), and senescence-accelerated mouse resistant 1 (SAMR1) strains at the ages of 6 and 12 months. Further, to examine whether the dopamine receptor 1 (D1) signaling system is associated with the age-related alteration of activity, we evaluated the motor activity of the mice treated with SKF82958 (6-chloro-7,8-dihydroxy-3-allyl-1-phenyl-2,3,4,5-tetrahydro-1-phenyl-1H-3-benzazepine hydrobromide), a D1 agonist. Twelve-month-old B6J showed higher activity on day 1 and higher D1 sensitivity than 6-month-old mice. Twelve-month-old BALB/c showed higher activity on day 3 and a slightly lower threshold of D1 than 6-month-old mice. Twelve-month-old AKR/J, SAMR1 and SAMP6 strains showed lower motor activity than 6-month-old mice. The D1 sensitivities in 12-month-old AKR/J and SAMR1 were similar to those of corresponding 6-month-old mice, whereas the D1 sensitivity of 12-month-old SAMP6 was significantly lower than that of 6-month-old SAMP6. SKF82958 significantly increased the motor activity of 6-month-old SAMP6 compared with age-matched, AKR/J and SAMR1. Our results indicate that D1 contributes substantially to the age-related increase of activity in B6J, but not to that in BALB/c. In AKR/J, SAMR1, and SAMP6, an age-related decrease of activity was observed. The contribution of D1 to this appeared to be small in AKR/J and SAMR1, but substantial in SAMP6. Thus, the contribution of D1 to age-related changes of motor activity is strongly strain-dependent.

Comparing memory-forming capabilities between laboratory-reared and wildLymnaea: learning in the wild, a heritable component of snail memory

We set out to determine whether the ability to form long-term memory (LTM)is influenced by laboratory rearing. We investigated the ability of four populations of Lymnaea stagnalis to form LTM following operant conditioning both in the freely behaving animal and at the electrophysiological level in a neuron, RPeD1, which is a necessary site for LTM. We hypothesized that laboratory rearing results in a decreased ability to form LTM because rearing does not occur in an `enriched environment'. Of the four populations examined, two were collected in the wild and two were reared in the laboratory – specifically, (1) wild Dutch snails; (2) their laboratory-reared offspring; (3) wild Southern Alberta snails (Belly); and (4)their laboratory-reared offspring. We found that Belly snails had an enhanced capability of forming LTM compared with Dutch laboratory-reared snails. That is, the Belly snails, which are much darker in colour than laboratory-reared snails (i.e. blonds), were `smarter'. However, when we tested the offspring of Belly snails reared in the laboratory we found that these snails still had the enhanced ability to form LTM, even though they were now just as `blond' as their laboratory-reared Dutch cousins. Finally, we collected wild Dutch snails, which are also dark, and found that their ability to form LTM was not different to that of their laboratory-reared offspring. Thus, our hypothesis was not proved. Rather, we now hypothesize that there are strain differences between the Belly and Dutch snails, irrespective of whether they are reared in the wild or in the laboratory.

The stop null mice model for schizophrenia displays [corrected] cognitive and social deficits partly alleviated by neuroleptics

Recently evidence has accumulated that schizophrenia can arise from primary synaptic defects involving structural proteins particularly, microtubule associated proteins. Previous experiments have demonstrated that a STOP (stable tubule only peptide) gene deletion in mice leads to a phenotype mimicking some aspects of positive symptoms classically observed in schizophrenic patients. In the current study, we determined if STOP null mice demonstrate behavioral abnormalities related to the social and cognitive impairments of schizophrenia. Compared with wild-type mice, STOP null mice exhibited deficits in the non-aggressive component of social recognition, short term working memory and social and spatial learning. As described in humans, learning deficits in STOP null mice were poorly sensitive to long term treatment with typical neuroleptics. Since social and cognitive dysfunction have consistently been considered as central features of schizophrenia, we propose that STOP null mice may provide a useful model to understand the neurobiological correlates of social and cognitive defects in schizophrenia and to develop treatments that better target these symptoms.

Hybridizing behavioral models: a possible solution to some problems in neurophenotyping research?

The use of batteries of single-domain tests for neurophenotyping research is a common strategy to achieve higher data density and explore different behavioral domains. This approach, however, is accompanied by several methodological challenges, briefly discussed here. As an alternative, this paper advocates the wider use of extensive "hybrid" protocols that assess multiple domains in parallel, or logically/logistically combine experimental paradigms, in a way that disproportionately maximizes the number of tested phenotypes per experimental manipulation. Several examples of this approach are given in this paper, demonstrating the potential to reduce time, cost and subject requirements for the experiments. Offering behavioral analyses that are lacking in the standard single-domain tests, such "hybrid" models enable innovative modeling of neuropsychiatric disorders by more thorough and broader investigation of complex phenotypical characteristics.

Learning strategy selection in the water maze and hippocampal CREB phosphorylation differ in two inbred strains of mice

Learning strategy selection was assessed in two different inbred strains of mice, C57BL/6 and DBA/2, which are used for developing genetically modified mouse models. Male mice received a training protocol in a water maze using alternating blocks of visible and hidden platform trials, during which mice escaped to a single location. After training, mice were required to choose between the spatial location where the platform had been during training (a place strategy) and a visible platform presented in a new location (a cued/response strategy). Both strains of mice had similar escape performance on the visible and hidden platform trials during training. However, in the strategy preference test, C57BL/6 mice selected a place strategy significantly more often than DBA/2 mice. Because much evidence implicates the hippocampus and striatum as important neural substrates for spatial/place and cued/response learning, respectively, the engagement of the hippocampus was then assessed after either place or cue training by determining levels of cAMP response element-binding protein (CREB) and phosphorylated CREB (pCREB) in these two mouse strains. Results revealed that hippocampal CREB levels in both strains of mice were significantly increased after place in comparison to cued training. However, the relation of hippocampal pCREB levels to training was strain dependent; pCREB was significantly higher in C57BL/6 mice than in DBA/2 mice after place training, while hippocampal pCREB levels did not differ between strains after cued training. These findings indicate that pCREB, specifically associated with place/spatial training, is closely tied to differences in spatial/place strategy preference between C57BL/6 and DBA/2 mice.

Evaluation of exploration and risk assessment in pre-weaning mice using the novel cage test

Exploration and risk behaviour (risk assessment/risk taking) are critical to enable mice to cope with novel situations and gain control over their environment. Evaluation of those behaviours would therefore be a useful part of early phenotypic characterization of genetically modified mice, allowing early detection of behavioural phenotypes that require special attention and/or are of scientific interest. This study aimed to evaluate exploration and risk behaviour in pre-weaning mice using the novel cage test, which consists in exploration of a novel, clean, Makrolon type III cage. The results of this test were compared with those obtained in more complex and established tests to which the same mice were subjected as adolescents and young adults. Mice of two inbred strains (129S6/Bkl, n=10; C57BL/6Bkl, n=10) and one hybrid (B6CBAF1/Bkl, n=10) were used for validation of the test. The animals were tested in the novel cage (at weaning), the open field test (at 5 weeks), and from 9 weeks of age in three other tests: the elevated plus-maze, the concentric square field and the rat exposure test. The novel cage test effectively detected strain differences in pre-weaning mice as regards exploration and risk behaviour and the results were largely consistent with those obtained in the established tests later in life. In all tests 129S6 displayed a low locomotion and high risk assessment, while C57BL/6 and B6CBAF1 showed high locomotion and exploration. In addition high levels of risk taking were observed in C57BL/6. The novel cage test is rapid, requires no special equipment and is as discriminatory as more complex tests in detecting strain/genotype differences. This suggests that the novel cage test is a valuable tool for evaluation of exploration, risk assessment and risk taking in juvenile mice.

Cosegregation of CD14 locus and polymorphic alleles of glucocorticoid receptor and protocadherins into CD14 knockout mouse genome

Targeted mutagenesis technology has been used to investigate the biological characteristics of genes. We incidentally observed a discrepancy in the size of the glucocorticoid receptor (GCR) between CD14 knockout (KO) mice and backcross controls. The CD14 KO mice were generated using 129S4/SvJae-derived J1 embryonic stem cells, C57BL/ 6J donor blastocysts, and C57BL/6J backcross strain. In this study, the extent of genomic heterogeneity of the CD14 KO mice, potentially affecting their phenotype, was characterized in comparison to C57BL/6J controls. There were polymorphic alleles of the GCR gene in CD14 KO and C57BL/6J mice: a tandem repeat of 8 CAGs and 17 CAGs in the transactivation domain, respectively. The subsequent finding of eight CAGs in all 129 substrains examined and colocalization of CD14 and GCR genes on the same contig on chromosome 18 suggested that the GCR allele in the J1 embryonic stem cell genome cosegregated with the targeted CD14 locus. Interestingly, all three clusters of the protocadherin family, central genes in determining neuronal networks, were mapped between the CD14 and GCR loci. Further analyses revealed numerous nonsynonymous coding single-nucleotide polymorphisms within the protocadherin family between CD14 KO and C57BL/6J mice. In addition, heterogeneous profiles of endogenous retroviruses, which constitute approximately 10% of the genome, were observed between them. These findings suggest that cosegregation of genes flanking the targeted locus leads to a substantial level of genetic heterogeneity in CD14 KO mice compared with their backcross controls. Phenotypic changes observed in some KO mice may not be as definitive as expected.

Progression of multiple behavioral deficits with various ages of onset in a murine model of Hurler syndrome

Mucopolysaccharidosis type I (MPS I) is one of the most common lysosomal storage diseases with progressive neurological dysfunction. To characterize the chronological behavioral profiles and identify the onset of functional deficits in a MPS I mouse model (IDUA(-/-)), we evaluated anxiety, locomotor behavior, startle, spatial learning and memory with mice at 2, 4, 6 and 8 months of age. In automated open-field test, IDUA(-/-) mice showed hypoactivity as early as 2 months of age and altered anxiety starting from 6 months of age during the initial exploratory phase, even though normal habituation was observed at all ages. In the marble-burying task, the anxiety-like compulsive behavior was normal in IDUA(-/-) mice at almost all tested ages, but significantly reduced in 8-month old male IDUA(-/-) mice which coincided with the rapid death of IDUA(-/-) males starting from 7 months of age. In the Morris water maze, IDUA(-/-) mice exhibited impaired proficient learning only at 4 months of age during the acquisition phase. Spatial memory deficits were observed in IDUA(-/-) mice during both 1 and 7 days probe trials at 4 and 8 months of age. The IDUA(-/-) mice performed normally in a novel object recognition task at younger ages until 8 months old when reduced visual cognitive memory retention was noted in the IDUA(-/-) mice. In addition, 8-month-old IDUA(-/-) mice failed to habituate to repeated open-field exposure, suggesting deficits in non-aversive and non-associative memory. In acoustic startle assessment, significantly more non-responders were found in IDUA(-/-) mice, but normal performance was seen in those that did show a response. These results presented a temporal evaluation of phenotypic behavioral dysfunctions in IDUA(-/-) mice from adolescence to maturity, indicating the impairments, with different ages of onset, in locomotor and anxiety-like compulsive behaviors, spatial learning and memory, visual recognition and short-term non-associative memory retention. This study would also provide guidelines for the experimental designs of behavioral evaluation on innovative therapies for the treatment of MPS type I.

Strain specificity and cholinergic modulation of visuospatial attention in three inbred mouse strains

The tremendous increase in the use of mouse inbred strains and mutant mice to study the molecular basis of psychiatric disorders urges for a better understanding of attentional performance in mice. To this aim, we investigated possible strain differences in performance and cholinergic modulation of visuospatial attention in three widely used mouse inbred strains (129S2/SvHsd, C57BL/6JOlaHsd and DBA/2OlaHsd) in the five-choice serial reaction time task. Results indicated that after extended training, performance of 129S2/SvHsd mice was superior to that of C57BL/6JOlaHsd and DBA/2OlaHsd mice in terms of attention, omission errors, inhibitory control and latencies to correct choice. Increasing the attentional load resulted in comparable decrements in attention in all strains and inhibitory control impairments that were most pronounced in DBA/2OlaHsd mice. Further pharmacological evaluation indicated that all strains showed attentional impairments after treatment with the muscarinic and nicotinic antagonists scopolamine and mecamylamine, respectively. 129S2/SvHsd mice were less sensitive, whereas DBA/2OlaHsd mice appeared more sensitive to the detrimental effects of mecamylamine. In addition, subchronic, but not acute, nicotine treatment slightly improved attentional performance in all strains to the same extent. In conclusion, our data indicate strain specificity with particularly good performance of 129S2/SvHsd mice and strong cholinergic involvement in visuospatial attention in mice.

Effects of selective dopamine D1-like and D2-like agonists on prepulse inhibition of startle in inbred C3H/HeJ, SPRET/EiJ, and CAST/EiJ mice

RATIONALE

Prepulse inhibition (PPI) and locomotor activity have been used to investigate the effects of antipsychotic and stimulant drugs and their underlying dopaminergic mechanisms. Whereas D2-like agonists consistently decreased PPI and increased locomotion in rats in previous studies, we recently reported that these hallmark behavioral effects were not observed in several mouse strains. Nevertheless, we recently identified three mouse strains (C3H/HeJ, SPRET/EiJ, and CAST/EiJ) that exhibited locomotor hyperactivity after administration of a selective D2-like agonist.

OBJECTIVES

We hypothesized that, similar to rats, C3H/HeJ, SPRET/EiJ, and CAST/EiJ mice would exhibit decreased PPI after administration of a D2-like agonist.

RESULTS

Administration of the D2-like agonist quinelorane dose-dependently decreased PPI in C3H/HeJ and SPRET/EiJ mice. In agreement with previous reports in rats and other strains of mice, the D1-like agonist R-6-Br-APB also decreased PPI in C3H/HeJ and SPRET/EiJ mice. In contrast, CAST/EiJ mice had low levels of baseline PPI in our standard test session and quinelorane and R-6-Br-APB had no effect on PPI under those conditions. Through the optimization of session parameters, we obtained higher baseline PPI in CAST/EiJ mice and found that quinelorane but not R-6-Br-APB decreased PPI. In summary, similar to rats and unlike previous published reports on several strains of mice, we have now identified three strains of mice in which a D2-like agonist decreased PPI.

CONCLUSIONS

The C3H/HeJ, SPRET/EiJ, and CAST/EiJ mice may more closely mirror the Sprague Dawley rat than most other mouse strains and may confer advantages in cross-species behavioral pharmacology studies related to D2 receptor function.

The influence of visual ability on learning and memory performance in 13 strains of mice

We calculated visual ability in 13 strains of mice (129SI/Sv1mJ, A/J, AKR/J, BALB/cByJ, C3H/HeJ, C57BL/6J, CAST/EiJ, DBA/2J, FVB/NJ, MOLF/EiJ, SJL/J, SM/J, and SPRET/EiJ) on visual detection, pattern discrimination, and visual acuity and tested these and other mice of the same strains in a behavioral test battery that evaluated visuo-spatial learning and memory, conditioned odor preference, and motor learning. Strain differences in visual acuity accounted for a significant proportion of the variance between strains in measures of learning and memory in the Morris water maze. Strain differences in motor learning performance were not influenced by visual ability. Conditioned odor preference was enhanced in mice with visual defects. These results indicate that visual ability must be accounted for when testing for strain differences in learning and memory in mice because differences in performance in many tasks may be due to visual deficits rather than differences in higher order cognitive functions. These results have significant implications for the search for the neural and genetic basis of learning and memory in mice.

The pharmacology, neuroanatomy and neurogenetics of one-trial object recognition in rodents

Rats and mice are attracted by novel objects. They readily approach novel objects and explore them with their vibrissae, nose and forepaws. It is assumed that such a single explorative episode leaves a lasting and complex memory trace, which includes information about the features of the object explored, as well as where and even when the object was encountered. Indeed, it has been shown that rodents are able to discriminate a novel from a familiar object (one-trial object recognition), can detect a mismatch between the past and present location of a familiar object (one-trial object-place recognition), and can discriminate different objects in terms of their relative recency (temporal order memory), i.e., which one of two objects has been encountered earlier. Since the novelty-preference paradigm is very versatile and has some advantages compared to several other memory tasks, such as the water maze, it has become a powerful tool in current neurophamacological, neuroanatomical and neurogenetical memory research using both rats and mice. This review is intended to provide a comprehensive summary on key findings delineating the brain structures, neurotransmitters, molecular mechanisms and genes involved in encoding, consolidation, storage and retrieval of different forms of one-trial object memory in rats and mice.

Mouse behavioral tasks relevant to autism: phenotypes of 10 inbred strains

Three defining clinical symptoms of autism are aberrant reciprocal social interactions, deficits in social communication, and repetitive behaviors, including motor stereotypies and insistence on sameness. We developed a set of behavioral tasks designed to model components of these core symptoms in mice. Male mice from 10 inbred strains were characterized in assays for sociability, preference for social novelty, and reversal of the spatial location of the reinforcer in T-maze and Morris water maze tasks. Six strains, C57BL/6J, C57L/J, DBA/2J, FVB/NJ, C3H/HeJ, and AKR/J, showed significant levels of sociability, while A/J, BALB/cByJ, BTBR T(+)tf/J, and 129S1/SvImJ mice did not. C57BL/6J, C57L/J, DBA/2J, FVB/NJ, BALB/cByJ, and BTBR T(+)tf/J showed significant preference for social novelty, while C3H/HeJ, AKR/J, A/J, and 129S1/SvImJ did not. Normal scores on relevant control measures confirmed general health and physical abilities in all strains, ruling out artifactual explanations for social deficits. Elevated plus maze scores confirmed high anxiety-like behaviors in A/J, BALB/cByJ, and 129S1/SvImJ, which could underlie components of their low social approach. Strains that showed high levels of performance on acquisition of a T-maze task were also able to reach criterion for reversal learning. On the Morris water maze task, DBA/2J, AKR/J, BTBR T(+)tf/J, and 129S1/SvImJ failed to show significant quadrant preference during the reversal probe trial. These results highlight a dissociation between social task performance and reversal learning. BTBR T(+)tf/J is a particularly interesting strain, displaying both low social approach and resistance to change in routine on the water maze, consistent with an autism-like phenotype. Our multitask strategy for modeling symptoms of autism will be useful for investigating targeted and random gene mutations, QTLs, and microarray analyses.

Stability of inbred mouse strain differences in behavior and brain size between laboratories and across decades

If we conduct the same experiment in two laboratories or repeat a classical study many years later, will we obtain the same results? Recent research with mice in neural and behavioral genetics yielded different results in different laboratories for certain phenotypes, and these findings suggested to some researchers that behavior may be too unstable for fine-scale genetic analysis. Here we expand the range of data on this question to additional laboratories and phenotypes, and, for the first time in this field, we formally compare recent data with experiments conducted 30-50 years ago. For ethanol preference and locomotor activity, strain differences have been highly stable over a period of 40-50 years, and most strain correlations are in the range of r = 0.85-0.98, as high as or higher than for brain weight. For anxiety-related behavior on the elevated plus maze, on the other hand, strain means often differ dramatically across laboratories or even when the same laboratory is moved to another site within a university. When a wide range of phenotypes is considered, no inbred strain appears to be exceptionally stable or labile across laboratories in any general sense, and there is no tendency to observe higher correlations among studies done more recently. Phenotypic drift over decades for most of the behaviors examined appears to be minimal.

Impaired long-term memory and long-term potentiation in N-type Ca2+ channel-deficient mice

Voltage-dependent N-type Ca(2+) channels, along with the P/Q-type, have a crucial role in controlling the release of neurotransmitters or neuromodulators at presynaptic terminals. However, their role in hippocampus-dependent learning and memory has never been examined. Here, we investigated hippocampus-dependent learning and memory and synaptic plasticity at hippocampal CA3-CA1 synapses in mice deficient for the alpha(1B) subunit of N-type Ca(2+) channels. The mutant mice exhibited impaired learning and memory in the Morris water maze and the social transmission of food preference tasks. In particular, long-term memory was impaired in the mutant mice. Interestingly, among activity-dependent long-lasting synaptic changes, theta burst- or 200-Hz-stimulation-induced long-term potentiation (LTP) was decreased in the mutant, compared with the wild-type mice. This type of LTP is known to require brain-derived neurotrophic factor (BDNF). It was found that both BDNF-induced potentiation of field excitatory postsynaptic potentials and facilitation of the frequency of miniature excitatory postsynaptic currents (mEPSCs) were reduced in the mutant. Taken together, these results demonstrate that N-type Ca(2+) channels are required for hippocampus-dependent learning and memory, and certain forms of LTP.

Animal models of behavioral dysfunctions: Basic concepts and classifications, and an evaluation strategy

In behavioral neurosciences, such as neurobiology and biopsychology, animal models make it possible to investigate brain-behavior relations, with the aim of gaining insight into normal and abnormal human behavior and its underlying neuronal and neuroendocrinological processes. Different types of animal models of behavioral dysfunctions are reviewed in this article. In order to determine the precise criteria that an animal model should fulfill, experts from different fields must define the desired characteristics of that model at the neuropathologic and behavioral level. The list of characteristics depends on the purpose of the model. The phenotype-abnormal behavior or behavioral dysfunctions-has to be translated into testable measures in animal experiments. It is essential to standardize rearing, housing, and testing conditions, and to evaluate the reliability, validity (primarily predictive and construct validity), and biological or clinical relevance of putative animal models of human behavioral dysfunctions. This evaluation, guided by a systematic strategy, is central to the development of a model. The necessity of animal models and the responsible use of animals in research are discussed briefly.

Controlled and localized genetic manipulation in the brain

Brain structure and function are determined in part through experience and in part through our inherited genes. A powerful approach for unravelling the balance between activity-dependent neuronal plasticity and genetic programs is to directly manipulate the genome. Such molecular genetic studies have been greatly aided by the remarkable progress of large-scale genome sequencing efforts. Sophisticated mouse genetic manipulations allow targeted point-mutations, deletions and additions to the mouse genome. These can be regulated through inducible promoters expressing in genetically specified neuronal cell types. However, despite significant progress it remains difficult to target specific brain regions through transgenesis alone. Recent work suggests that transduction vectors, like lentiviruses and adeno-associated viruses, may provide suitable additional tools for localized and controlled genetic manipulation. Furthermore, studies with such vectors may aid the development of human genetic therapies for brain diseases.

Strain-dependent regulation of neurotransmission and actin-remodelling proteins in the mouse hippocampus

Individual mouse strains differ significantly in terms of behaviour, cognitive function and long-term potentiation. Hippocampal gene expression profiling of eight different mouse strains points towards strain-specific regulation of genes involved in neuronal information storage. Protein expression with regard to strain- dependent expression of structures related to neuronal information storage has not been investigated yet. Herein, a proteomic approach based on two-dimensional gel electrophoresis coupled with mass spectrometry (MALDI-TOF/TOF) has been chosen to address this question by determining strain-dependent expression of proteins involved in neurotransmission and activity-induced actin remodelling in hippocampal tissue of five mouse strains. Of 31 spots representing 16 different gene products analysed and quantified, N-ethylmaleimide-sensitive fusion protein, N-ethylmaleimide-sensitive factor attachment protein-alpha, actin-like protein 3, profilin and cofilin were expressed in a strain-dependent manner. By treating protein expression as a phenotype, we have shown significant genetic variation in brain protein expression. Further experiments in this direction may provide an indication of the genetic elements that contribute to the phenotypic differences between the selected strains through the expressional level of the translated protein. In view of this, we propose that proteomic analysis enabling to concomitantly survey the expression of a large number of proteins could serve as a valuable tool for genetic and physiological studies of central nervous system function.