Behavioral responses to novelty and structural variation of the hippocampus in mice. I. Quantitative-genetic analysis of behavior in the open-field

Analysis of the cognitive and functional behavior of female rats in the periestropause after hormone therapy with estrogen

Perimenopause is a critical period, with severe cycle irregularity and lower estrogen secretion altering redox state biomarkers, leading to behavioral changes. The estrogen hormonal therapy (EHT) being commonly used to alleviate climacteric effects. Therefore, the aim of this study was to analyze anxiolytic profile, recognition memory (short and long term), ambulation, redox status, cell synaptic activity in locus coeruleus and hippocampus of Wistar rats in the periestropause after EHT. Forty rats participated in the study; 20 were treated with corn oil (group 21Mo/Veh; corn oil/0.2 mL/sc; 2x/week) and 20 were submitted to EHT (group 21Mo/E2; 17β-estradiol/15 μg/Kg/sc; 2x/week) for 120 days. Open field, elevated plus maze, object recognition (RO), and footprint tests were performed immediately before and at the end of the treatment period. From the decapitated brains, isolated hippocampus were destined for biochemical analysis, in turn, perfused brains were destined for histological analysis. The 21Mo/E2 group had a significantly greater total time in the central region and a significantly greater number of entries into the open arms compared to the 21Mo/Veh group, as in crossing, rearing and grooming behaviors, evidencing an anxiolytic profile. In the RO test, the 21Mo/Veh group decreased long-term memory, and the 21Mo/E2 group maintained the same index as at 17 months of age, in addition to a better balance of the hippocampal redox state, prevention of neuronal cell loss and better gait. Based on the results, it appears that exogenous E2 supplementation during periestropause may help preserve neurological functions and potentially prevent neuropsychological and neurodegenerative disorders.

Something new and something blue: Responses to novelty in a rodent model of depression and epilepsy comorbidity

A bidirectional comorbidity exists between depression and epilepsy such that patients with epilepsy are at higher risk for developing depression, and vice versa. Each of these conditions individually can be complicated by behavioral effects that worsen quality of life, but less is known about these interactions within the comorbidity of depression and epilepsy. The SwLo rat has been selectively bred for depression-relevant behaviors and exhibits enhanced limbic seizure susceptibility. This study sought to characterize the effects of novelty and stress on the SwLo rodent model of this comorbidity. It was hypothesized that SwLo rats would exhibit altered responses to novelty, reflected in hyperactivity-, anxiety-, sensation seeking-, and/or compulsive behaviors, and that this would be exacerbated with stress. Compared to the SwHi rat (their depression- and epilepsy-resistant counterparts), SwLo rats showed increased entries in all areas of the Open Field Test and spent significantly more time in the light compartment of the Light-Dark Box. SwLo rats also had a significantly higher number of rearing behaviors in the inner squares of the Open Field Test, the closed arms of the Elevated Plus Maze, and both areas of the Light-Dark Box. They demonstrated increased Nestlet shredding but showed no difference in a marble burying task or in latency to consume food in a novelty suppressed feeding task. Interestingly, restraint stress showed little effect on these behaviors, despite increasing corticosterone levels. Combined, these results suggest an increase in exploratory sensation seeking and hypervigilant information-gathering behaviors in the SwLo rat that are not dependent on corticosterone levels. This shows the utility of this model for studying behavioral effects of comorbid depression and epilepsy and allows for their use in identifying underlying mechanisms or screening treatment strategies for this complex comorbidity.

Evaluation of neuroprotective effects of alpha-tocopherol in cuprizone-induced demyelination model of multiple sclerosis

BACKGROUND AND PURPOSE

Multiple sclerosis (MS) is an autoimmune disorder characterized by demyelination and axonal loss. Quantitative estimation of behavioral, locomotor, and histological changes following the use of alpha-tocopherol (AT) in the animal model of MS have not been reported. The present study was planned to evaluate whether AT can improve sensorimotor dysfunction and reduce demyelination in the cuprizone (CPZ)-induced rat model of MS.

EXPERIMENTAL APPROACH

Female Sprague-Dawley rats (8 weeks) were fed with cuprizone diet for 5 weeks followed by intraperitoneal injections of alpha-tocopherol (100 mg/Kg) or PBS for 2 weeks (groups E1 and E2, n = 8). Group C (n = 8) was fed with normal pellets followed by intraperitoneal doses of PBS. Open-field test and beam walking were carried out on every 10th day. The mean area of demyelination in the corpus callosum was quantified in Luxol® fast blue (LFB) stained histological sections of the forebrain. Qualitative grading for relative changes in the stains of myelinated fibers was also done.

FINDINGS/RESULTS

During withdrawal of CPZ, AT treatment increased the average speed by 22% in group E1, compared to group E2 (P < 0.05). The mean time to walk the beam was reduced in group E1 by 2.6% compared to group E2 (P < 0.05). The rearing frequency was increased in group E1 during week 6-7 compared to that in the period of CPZ treatment. The mean area of demyelination in the corpus callosum showed a 12% reduction in group E1 compared to group E2 (P < 0.05).

CONCLUSION AND IMPLICATIONS

Short-term AT therapy showed improvement in motor dysfunction and reduction of demyelination in the animal model of MS.

Deep learning-based behavioral analysis reaches human accuracy and is capable of outperforming commercial solutions

To study brain function, preclinical research heavily relies on animal monitoring and the subsequent analyses of behavior. Commercial platforms have enabled semi high-throughput behavioral analyses by automating animal tracking, yet they poorly recognize ethologically relevant behaviors and lack the flexibility to be employed in variable testing environments. Critical advances based on deep-learning and machine vision over the last couple of years now enable markerless tracking of individual body parts of freely moving rodents with high precision. Here, we compare the performance of commercially available platforms (EthoVision XT14, Noldus; TSE Multi-Conditioning System, TSE Systems) to cross-verified human annotation. We provide a set of videos-carefully annotated by several human raters-of three widely used behavioral tests (open field test, elevated plus maze, forced swim test). Using these data, we then deployed the pose estimation software DeepLabCut to extract skeletal mouse representations. Using simple post-analyses, we were able to track animals based on their skeletal representation in a range of classic behavioral tests at similar or greater accuracy than commercial behavioral tracking systems. We then developed supervised machine learning classifiers that integrate the skeletal representation with the manual annotations. This new combined approach allows us to score ethologically relevant behaviors with similar accuracy to humans, the current gold standard, while outperforming commercial solutions. Finally, we show that the resulting machine learning approach eliminates variation both within and between human annotators. In summary, our approach helps to improve the quality and accuracy of behavioral data, while outperforming commercial systems at a fraction of the cost.

Selective increases in inter-individual variability in response to environmental enrichment in female mice

One manifestation of individualization is a progressively differential response of individuals to the non-shared components of the same environment. Individualization has practical implications in the clinical setting, where subtle differences between patients are often decisive for the success of an intervention, yet there has been no suitable animal model to study its underlying biological mechanisms. Here we show that enriched environment (ENR) can serve as a model of brain individualization. We kept 40 isogenic female C57BL/6JRj mice for 3 months in ENR and compared these mice to an equally sized group of standard-housed control animals, looking at the effects on a wide range of phenotypes in terms of both means and variances. Although ENR influenced multiple parameters and restructured correlation patterns between them, it only increased differences among individuals in traits related to brain and behavior (adult hippocampal neurogenesis, motor cortex thickness, open field and object exploration), in agreement with the hypothesis of a specific activity-dependent development of brain individuality.

Translation in Tobacco and Drug Abuse Prevention Research

The purpose of this article is to describe the translation of research on tobacco and drug abuse prevention from basic science to program development to large-scale program dissemination, and from animal to human studies. Where relevant, continuity of translation is discussed by referring to two variables that have been studied for their potential relationship to drug use risk in both animals and humans: sensation and novelty seeking and low impulse control. Review of the research indicates relatively slow translation until the early 1990s. The authors recommend several mechanisms to promote more rapid translation across types of research that encourage reciprocal rather than unidirectional transmission of knowledge to expedite the development and diffusion of more timely, targeted drug abuse prevention programs.

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.

Effects of the mGluR5 antagonist MPEP on ethanol withdrawal induced anxiety-like syndrome in rats

Abstinence from chronic ethanol consumption leads to the manifestation of a variety of symptoms attributed to central nervous system hyperexcitability, such as increased irritability, anxiety, and restlessness. Recent studies have demonstrated the importance of metabotropic glutamate receptor 5 (mGluR5) in addictive behaviours. This study investigates the effects of the mGluR5 antagonist 2-methyl-6-(phenylethynyl)-pyridine (MPEP) on ethanol withdrawal induced anxiety using two behavioural paradigms. Male Wistar rats were fed a Modified Liquid Diet (MLD) containing low fat cow milk, sucrose, and maltodextrin with a gradual introduction of 2.4%, 4.8% and 7.2% ethanol for 20 days. Six hours into ethanol withdrawal, the rats were intraperitoneally injected with normal saline and MPEP (2.5, 5.0, 10, 20, 30 mg/kg) and were assessed for ethanol withdrawal induced anxiety-like syndrome using an automated elevated plus maze and an open field. MPEP at 10 mg/kg significantly attenuated ethanol withdrawal induced anxiety without any compromising effects on locomotor activities. Despite reversing several indices of ethanol withdrawal induced anxiety in both the elevated plus maze and the open field, low doses of MPEP (2.5, 5 mg/kg) significantly compromised the locomotor activities of ethanol withdrawn rats. High doses of MPEP (20 and 30 mg/kg) significantly attenuated withdrawal anxiety when tested in the elevated plus maze but not in the open field. Administration of MPEP (2.5, 5, 10, 20, 30 mg/kg) has no significant compromising effect on the locomotor activities of ethanol naïve rats. Despite significantly reducing withdrawal anxiety in both behavioural paradigms at 10 mg/kg, the compromising effects of low and high doses of MPEP must be further explored along with the therapeutic efficiency of this drug for relieving withdrawal induced anxiety.

Optogenetic inhibition of Purkinje cell activity reveals cerebellar control of blood pressure during postural alterations in anesthetized rats

The cerebellar uvula (lobule IX), a part of the vestibulocerebellum, is extensively connected to the areas of the brainstem that participate in cardiovascular regulation and vestibular signal processing. This suggests that the uvula regulates blood pressure (BP) during postural alterations. Previous studies showed that lesions of the uvula affected the baroreceptor reflex and cardiovascular responses during postural alterations. To investigate the mechanisms underlying this BP regulation, it is necessary to have a method to selectively modulate the activity of Purkinje cells (PCs), the sole output neurons from the cerebellar cortex, without affecting other neuronal types such as local interneurons or nonlocal neurons that send their axons to the cerebellar cortex. We recently developed a novel technique using optogenetics to manipulate PC activity and showed that activation and inhibition of PCs in the uvula either decreased or increased the resting BP, respectively. This technique was employed in the current study to examine the roles of the uvula in BP regulation during postural alterations in anesthetized rats. Enhanced Natronomonas pharaonis halorhodopsin (eNpHR), a light-driven chloride ion pump, was selectively expressed in uvular PCs using a lentiviral vector containing the PC-specific L7 promoter. The eNpHR-expressing PCs were then illuminated by orange laser (593 nm) either during 30° head-up or 30° head-down tilts. The eNpHR-mediated photoinhibition of the uvula attenuated the extent of BP recovery after a BP increase induced by postural changes during head-down tilts. By contrast, photoinhibition had no statistically significant effect on BP recovery during head-up tilts. The effects of photoinhibition on BP during tilts were significantly different from those observed during the resting condition, indicating that cerebellar control of BP during tilts is dynamic rather than static. Taken together, these results suggest that PCs in the uvula dynamically regulates BP maintenance during postural alterations.

Adult hippocampal neurogenesis and plasticity in the infrapyramidal bundle of the mossy fiber projection: I. Co-regulation by activity

Besides the massive plasticity at the level of synapses, we find in the hippocampus of adult mice and rats two systems with very strong macroscopic structural plasticity: adult neurogenesis, that is the lifelong generation of new granule cells, and dynamic changes in the mossy fibers linking the dentate gyrus to area CA3. In particular the anatomy of the infrapyramidal mossy fiber tract (IMF) changes in response to a variety of extrinsic and intrinsic stimuli. Because mossy fibers are the axons of granule cells, the question arises whether these two types of plasticity are linked. Using immunohistochemistry for markers associated with axonal growth and pro-opiomelanocortin (POMC)–GFP mice to visualize the post-mitotic maturation phase of adult hippocampal neurogenesis, we found that newly generated mossy fibers preferentially but not exclusively contribute to the IMF. The neurogenic stimulus of an enriched environment increased the volume of the IMF. In addition, the IMF grew with a time course consistent with axonal outgrowth from the newborn neurons after the induction of neurogenic seizures using kainate. These results indicate that two aspects of plasticity in the adult hippocampus, mossy fiber size and neurogenesis, are related and may share underlying mechanisms. In a second part of this study, published separately (Krebs et al., 2011) we have addressed the question of whether there is a shared genetics underlying both traits.

Adult Hippocampal Neurogenesis and Plasticity in the Infrapyramidal Bundle of the Mossy Fiber Projection: II. Genetic Covariation and Identification of Nos1 as Linking Candidate Gene

The hippocampus of adult rodents harbors two systems exhibiting structural plasticity beyond the level of synapses and dendrites. First, the persistent generation of granule cells (adult neurogenesis); second, dynamic changes in the mossy fibers (MF), in particular in the infrapyramidal mossy fiber (IMF) tract. Because MFs are the axons of granule cells, the question arises whether these two types of plasticity are linked. In the first part of this study (Römer et al., 2011) we have asked how both traits are regulated in relation to each other. In the present part, we asked whether, besides activity-dependent co-regulation, there would also be signs of genetic co-regulation and co-variance. For this purpose we used the BXD panel of recombinant inbred strains of mice, a unique genetic reference population that allows genetic association studies. In 31 BXD strains we did not find correlations between the traits describing the volume of the MF subfields and measures of adult neurogenesis. When we carried out quantitative trait locus mapping for these traits, we found that the map for IMF volume showed little overlap with the maps for the other parts of the projection or for adult neurogenesis, suggesting that to a large degree the IMF is regulated independently. The highest overlapping peak in the genome-wide association maps for IMF volume and the number of new neurons was on distal chromosome 5 (118.3-199.2 Mb) with an LRS score of 5.5 for IMF and 6.0 for new neurons. Within this interval we identified Nos1 (neuronal nitric oxide synthase) as a cis-acting (i.e., presumably autoregulatory) candidate gene. The expression of Nos1 is has been previously linked with both IMF and adult neurogenesis, supporting our findings. Despite explaining on its own very little of the variance in the highly multigenic traits studied, our results suggest Nos1 may play a part in the complex genetic control of adult neurogenesis and IMF morphology.

Comt1 genotype and expression predicts anxiety and nociceptive sensitivity in inbred strains of mice

Catechol-O-methyltransferase (COMT) is a ubiquitously expressed enzyme that maintains basic biologic functions by inactivating catechol substrates. In humans, polymorphic variance at the COMT locus has been associated with modulation of pain sensitivity and risk for developing psychiatric disorders. A functional haplotype associated with increased pain sensitivity was shown to result in decreased COMT activity by altering mRNA secondary structure-dependent protein translation. However, the exact mechanisms whereby COMT modulates pain sensitivity and behavior remain unclear and can be further studied in animal models. We have assessed Comt1 gene expression levels in multiple brain regions in inbred strains of mice and have discovered that Comt1 is differentially expressed among the strains, and this differential expression is cis-regulated. A B2 short interspersed nuclear element (SINE) was inserted in the 3'-untranslated region (3'-UTR) of Comt1 in 14 strains generating a common haplotype that correlates with gene expression. Experiments using mammalian expression vectors of full-length cDNA clones with and without the SINE element show that strains with the SINE haplotype (+SINE) have greater Comt1 enzymatic activity. +SINE mice also exhibit behavioral differences in anxiety assays and decreased pain sensitivity. These results suggest that a haplotype, defined by a 3'-UTR B2 SINE element, regulates Comt1 expression and some mouse behaviors.

Systematic analysis of emotionality in consomic mouse strains established from C57BL/6J and wild-derived MSM/Ms

Consomic strains have recently attracted attention as an advantageous method to screen for genes related to developmental, physiological, and behavioral phenotypes. Recently, a new set of consomic strains was established from the Japanese wild-derived mouse strain MSM/Ms and C57BL/6JJcl. By analyzing the entire consomic panel, we were able to identify a number of chromosomes associated with anxiety-like behaviors in the open-field (OF) test, a light-dark box and an elevated plus maze. Detailed observation of the OF behavior allowed us to identify chromosomes associated with those ethological traits, such as stretch attend, rearing, and jumping. Repeated OF test trials have different meanings for animals, and we found that some chromosomes responded to only the first or second trial, while others were consistent across both trials. By examining both male and female mice, sex-dependent effects were found in several measurements. Principal component analysis of anxiety-like behaviors extracted five factors: 'general locomotor activity', 'thigmotaxis', 'risk assessment', 'open-arm exploration' and 'autonomic emotionality'. We mapped chromosomes associated with these five factors of emotionality.

Post-traumatic stress behavioural responses in inbred mouse strains: can genetic predisposition explain phenotypic vulnerability?

Clinical studies of twin pairs and families of post-traumatic stress disorder (PTSD) patients raise questions as to possible genetic predisposition to PTSD. Studies using isogenic animal populations exposed to a stress paradigm could elucidate the relative contributions of genotype and environment to endophenotypic expression. The prevalence of individuals displaying severely compromised behavioural responses to predator scent stress (PSS) was assessed in six inbred strains of mice in an animal model of PTSD that classifies individuals into groups according to the degree of their behavioural response. The choice of strains was based on the frequent use of these mice in transgenic research. The prevalence of extreme behavioural response in the elevated plus maze and the acoustic startle response paradigms, performed in sequence, was assessed at baseline and 7 d after PSS exposure between and within strains, and compared to differences in circulating corticosterone levels. Narrow-sense trait heritability was determined by comparing the between-strain variance to the total variance. Although strain-specific differences in anxiety-like behaviours were demonstrated, the results revealed a significant degree of individual variability in response patterns within each of the inbred strains, yielding a baseline heritability factor for anxiety-like behaviours of 30%, but only 10% for response to stress exposure. Baseline anxiety-like behaviours were found not to be predictive of post-exposure behavioural responses. The response of the individual to stress is multifactorial and environmental factors play a predominant role in characterizing the individual response to stress exposure, although there are significant genetic underpinnings.

Hippocampus modulates the behaviorally-sensitizing effects of nicotine in a rat model of novelty-seeking: potential role for mossy fibers

Present experiments investigate interactions between a rat model of the novelty-seeking phenotype and psychomotor sensitization to nicotine (NIC) in adolescence, and the potential role of hippocampal mossy fibers in mediating the behaviorally-sensitizing effects of NIC. Outbred rats were phenotype-screened as high-responders (HR; locomotor reactivity to novelty score ranking in the upper third of the population) or low-responders (LR; locomotor reactivity to novelty score ranking in the lower third of the population). In Experiment 1, both phenotypes were trained with four NIC injections (at 3-d intervals on postnatal days 33-44), and lidocaine microinfusion was used to temporarily inactivate the hippocampal hilus at each NIC injection. Systemic saline and microinjection of artificial cerebral spinal fluid (CSF) were used as controls. During NIC training, lidocaine inactivation caused augmented locomotor response to NIC in HRs compared to LRs irrespective of injection days. Following 1 week of abstinence, all animals were challenged with a low dose of NIC. During challenge, previously NIC/CSF trained LRs and HRs were divided into two; one half receiving lidocaine inactivation of the hippocampal hilus and the other half receiving CSF control microinjection. Only HRs showed behavioral sensitization to the challenge dose of NIC, which was enhanced with lidocaine inactivation. In Experiment 2, a single NIC exposure was found sufficient to induce sensitization to the challenge dose of NIC in HRs, and concurrently an enlarged supra-pyramidal mossy fiber (SP-MF) terminal field. The increase in the SP-MF volume in HRs was greater with repeated NIC training. In both single and repeated NIC training cases, a significant positive morphobehavioral correlation was observed between challenge NIC-induced locomotion and the SP-MF terminal field volume. These findings suggest that the HR hippocampal mossy fibers are vulnerable to neuroadaptive alterations induced by NIC, which may be a substrate for the observed behavioral vulnerability to NIC.

Reduced reactivity to novelty, impaired social behavior, and enhanced basal synaptic excitatory activity in perforant path projections to the dentate gyrus in young adult mice deficient in the neural cell adhesion molecule CHL1

The neural cell adhesion molecule CHL1 is implicated in neural development in the mouse and has been related to psychiatric disorders in humans. Here we report that mice constitutively deficient for CHL1 display reduced reactivity to environmental stimuli and reduced expression of social behaviors, whereas cognitive, motor and olfactory functions are normal. Basal synaptic transmission and plasticity in seven major excitatory connections in the hippocampus were analyzed to test whether dysfunctions in this brain region, which controls complex behaviors, correlate with the behavioral alterations of CHL1 deficient mice. We found that basal synaptic transmission in lateral and medial perforant path projections to the dentate gyrus is elevated in CHL1-deficient mice. Taking in consideration the function of these synapses in processing information from cortical areas, we hypothesize that constitutive ablation of CHL1 leads to reduced capability to react to external stimuli due to dysfunctions in the dentate gyrus.

Environmental enrichment decreases responding for visual novelty

Previous research has demonstrated that rats reared in an enriched condition (EC) with novel objects and social partners self-administer less amphetamine compared to rats raised in an isolated condition (IC). However, it is unclear if the enrichment-induced decrease in stimulant self-administration generalizes to non-drug rewards such as those provided by novel environmental stimuli. In the current study, EC, IC, and social condition (SC) rats were raised from 21 to 51 days of age before being tested in a two-lever operant conditioning chamber in which responding on one lever (active lever) resulted in illumination of a cue light. In Experiment 1, rats were initially assessed for baseline responding (no contingency) and then the contingent light was introduced. EC rats responded less than IC rats for the contingent light stimulus; however, EC rats also displayed a lower rate of baseline responding. In Experiment 2, rats were trained initially to lever press for a sucrose reward to decrease differences in baseline responding. While sucrose pretraining decreased baseline response differences between groups, EC rats still responded less for the contingent light stimulus than IC or SC rats. These results suggest that environmental enrichment decreases the incentive value of visual novelty.

Inheritance of Behavioral and Neuroanatomical Phenotypical Variance: Hybrid Mice Are Not Always More Stable Than Inbreds

Many investigators have attempted to confirm the prediction that increased levels of heterozygosity entail greater developmental stability, manifesting itself through decreased phenotypical variation. The evidence presented so far is equivocal. The predicted relationship has been found in some morphological studies, but not in others. I propose that the variability of a character should be seen as different from the character itself. For most morphological characters, natural selection promotes strong canalization of development but, to facilitate responses to environmental changes, the organism needs to retain malleability of physiological and behavioral traits. These different types of selection should lead to distinct genetic architectures for these phenotypes. I report on the results of a diallel cross between four inbred mouse strains. Qualitatively different genetic architectures were in fact revealed for variation in behaviors in the open-field. In a second study, variances of inbred and hybrid populations for hippocampal morphometry were studied. Again, hybrids were not always less variable than inbreds and sometimes even more variable. It follows that there exists no one-to-one relation between heterozygosity and developmental stability.

Multivariate Analysis of Temporal Descriptions of Open-field Behavior in Wild-derived Mouse Strains

The open-field test is a commonly used apparatus in many behavioral studies. However, in most studies, temporal changes of details of behavior have been ignored. We thus examined open-field behavior as measured by both conventional indices and 12 ethograms supported by detailed temporal observation. To obtain a broader understanding, we used genetically diverse mouse strains: 10 wild-derived mouse strains (PGN2, BFM/2, HMI, CAST/Ei, NJL, BLG2, CHD, SWN, KJR, MSM), one strain derived from the so-called fancy mouse (JFI), and one standard laboratory strain, C57BL/6. Conventional measurements revealed a variety of relationships: some strains did not show the hypothesized association between high ambulation, longer stay in the central area, and low defecation. Our ethological approach revealed that some behaviors, such as freezing and jumping, were not observed in C57BL/6 but were seen in some wild-derived strains. Principal component analysis which included temporal information indicated that these strains had varied temporal patterns of habituation to novelty.

The impact of genetic background on neurodegeneration and behavior in seizured mice

We used pilocarpine-induced seizures in mice to determine the impact of genetic background on the vulnerability of hippocampal neurons and associated changes of behavioral performance. The susceptibility of hippocampal neurons to seizure-induced cell death paralleled the severity of the seizures and depended on genetic background. Hippocampal neurons in C57BL/6 mice were most resistant to cell death, whereas they were highly vulnerable in FVB/N mice. The degree of neuronal degeneration in F1 hybrid mice obtained by crossing the two strains was at an intermediate level between the parent strains. Two weeks after the severe seizures, performance in a water-maze place navigation task showed a bimodal distribution. Seventeen of 19 (90%) F1 mice were completely unable to learn while the other two learned reasonably well. Of 28 C57BL/6 mice with similarly severe seizures, six were as strongly impaired as their F1 counterparts (22%). The remaining 22 performed normally, indicating a much lower probability of C57BL/6 mice to be affected. Treated mice showed a deficit of open-field exploration which was strongly correlated with the impairment in the place navigation task and was again more severe in F1 mice. Our results show that the vulnerability of hippocampal neurons to pilocarpine-induced seizures, as well as the associated behavioral changes, depended on genetic background. Furthermore, they confirm and extend our earlier finding that a relatively modest reduction of hippocampal cell death can be associated with dramatic changes of behavioral performance and emphasize the importance of tightly-controlled genetic backgrounds in biological studies.

Hippocampal mossy fibre terminal field size is differentially affected in a rat model of risk-taking behaviour

Individual differences in novelty-induced exploratory activity identify rats which can serve as a model of human sensation-seeking, risk-taking behaviour. Experimentally naïve rats, when exposed to mild stress of a novel environment, exhibit variability in their exploratory activity. Some rats display high rates of locomotor reactivity to novelty (high responders (HR)), and others display low rates (low responders (LR)). The LRHR phenotype is a reliable predictor of drug-taking behaviour and is linked to differences in hippocampal glucocorticoid receptor mRNA expression. In this study, we investigated whether the LRHR phenotype is associated with differences in the quantitative morphology of the hippocampal field CA3, dentate gyrus molecular layer, granule cell layer and mossy fibres. LRs and HRs showed no significant differences in the volumes of CA3 and dentate molecular layer volume or the number of dentate granule cells. However, LRs had a significantly larger suprapyramidal mossy fibre terminal field volume when compared to HRs. The infrapyramidal mossy fibres did not differ between phenotypes. Also, we found a LRHR phenotype-independent significant negative correlation between molecular layer volume per granule cell and the total number of granule cells. These findings implicate the SP-MF in vulnerability for risk-taking behaviour, and we propose that LR and HR hippocampi may differ in the way novelty information is processed.

Physical defeat reduces the sensitivity of murine splenocytes to the suppressive effects of corticosterone

Social disruption (SDR) in male mice reduces the sensitivity of their splenocytes to the actions of glucocorticoids. To determine whether physical defeat is necessary for the development of this reduced sensitivity, a modification of the SDR paradigm was employed in which mice were exposed to fighting conspecifics in the presence or absence of physical contact. This was accomplished by dividing a cage of 5 resident male C57BL/6 mice in half with a wire mesh partition so that 2 of the mice in the cage (SDR Physical Contact mice) fought and were defeated by an aggressive male C57BL/6 intruder that was placed into the cage for 2h for up to 6 days, while the remaining 3 resident mice (SDR Sensory Contact mice) were on the opposite side of the partition and thus prevented from physically interacting with the intruder. Although both the SDR Physical Contact and the SDR Sensory Contact mice had significantly elevated corticosterone levels and displayed submissive postures toward the intruder, only the SDR Physical Contact animals developed functional glucocorticoid resistance. The viability of LPS-stimulated splenocytes cultured from the SDR Physical Contact mice was not affected by pharmacological doses of corticosterone, whereas splenocyte viability was significantly reduced by corticosterone in cultured cells from SDR Sensory Contact and control mice. This study indicates that exposure to a stressful environment in the absence of physical attack does not reduce the sensitivity of murine splenocytes to the suppressive effects of corticosterone.

Exploration, emotionality, and hippocampal mossy fibers in nonaggressive AB/Gat and congenic highly aggressive mice

AB/Gat mice and congenic mice bred for high aggressiveness (CS/ag) were tested for exploratory behavior in novel situations and anxiety-related behavior, using an open-field test and the elevated plus-maze test. Subsequently, the size of hippocampal mossy fiber terminal fields was evaluated. Considerably higher exploratory activity was found in nonaggressive mice, whereas aggressive mice exhibited more anxiety-related behavior. Larger intra- and infrapyramidal mossy fiber terminal fields (IIP-MF) and a larger hilus were found in the highly aggressive strain. Within the nonaggressive AB/Gat strain, larger IIP-MF were correlated with higher exploratory behavior and lower anxiety in the plus-maze test. Within the aggressive strain, no individual correlations between hippocampal morphometry and behavior were found. The results corroborate the "ecotype hypothesis," which suggests that mice of subpopulations with highly aggressive males tend to display reduced exploratory behavior. The findings support the view that genetic factors involved in aggressive behavior also affect hippocampal connectivity. However, our results do not support the hypothesis that a higher level of aggressiveness is necessarily related to smaller IIP-MF.

Differential involvement of the mu and kappa opioid receptors in spatial learning

In order to test the role of mu and kappa opioid receptors (Mu opioid receptor (MOR) and Kappa opioid receptor (KOR)) in hippocampal-dependent spatial learning, we analyzed genetically engineered null mutant mice missing the functional MOR or KOR gene. Compared to wild-type mice, the homozygous MOR null mutants exhibited an impairment in the ultimate level of spatial learning as shown in two distinct tasks, the 8-arm radial-maze and the Morris water-maze. Control behaviors were normal. The learning impairment could be associated with the impairment we found in the maintenance of long-term potentiation in mossy fibers in CA3. In comparison, there was no impairment in spatial learning in our KOR mutants or in mossy fibers (mf) in CA3 region long-term potentiation (LTP). Our work suggests that the MOR may play a positive role in learning and memory by increasing LTP in CA3 neurons.

Prenatal elevation of endocannabinoids corrects the unbalance between dopamine systems and reduces activity in the Naples High Excitability rats

Several evidences suggest that endocannabinoids exert a neurotrophic effect on developing mesencephalic dopamine neurons. Since an altered mesocorticolimbic system seems to underlie hyperactivity and attention deficit in clinical and animal studies of attention deficit hyperactivity disorder (ADHD), prenatal elevation of anandamide has been induced in Naples high excitability (NHE) rats by inhibition of its reuptake. To this aim, pregnant NHE and random-bred females received a subcutaneous injection of AM-404 (1 mg/kg) or vehicle daily from E11 until E20. Young adult male offsprings were exposed to a spatial novelty (Làt-maze) for 30 min and the behavior was videotaped and analysed for indices of activity (travelled distance, rearing frequency) and attention (rearing duration). Moreover, morphological analysis of the brains was carried out that pertained to cytochrome oxydase as marker of metabolic activity and thyrosine hydroxylase as marker of the dopamine systems. The results indicate that prenatal AM-404 treatment significantly reduces activity by about 20% during the entire testing period and modifies the distribution of scanning times towards short duration episodes in the first part of the test only in NHE-treated rats. In addition, image analysis revealed a significant increase in relative optical density of TH+terminals in the dorsal striatum and substantia nigra of AM-404 treated NHE rats and minor changes in the dorsal cortex of AM-404 treated NRB rats. The data suggest a corrected unbalance between the two dopamine systems that apparently leads to reduced hyperactivity and modified scanning times in this animal model of ADHD. This, in turn, might open new strategies in the treatment of a subset of ADHD cases.

Molecular genetic approaches to investigate individual variations in behavioral and neuroendocrine stress responses

A large response range can be observed in both behavioral and neuroendocrine responses to environmental challenges. This variation can arise from central mechanisms such as those involved in the shaping of general response tendencies (temperaments) or involves only one or the other output system (behavioral vs. endocrine response). The participation of genetic factors in this variability is demonstrated by family and twin studies in humans, the comparison of inbred strains and selection experiments in animals. Those inbred strains diverging for specific traits of stress reactivity are invaluable tools for the study of the molecular bases of this genetic variability. Until recently, it was only possible to study biological differences between contrasting strains, such as neurotransmitter pathways in the brain or hormone receptor properties, in order to suggest structural differences in candidate genes. The increase of the power of molecular biology tools allows the systematic screening of significant genes for the search of molecular variants. More recently, it was possible to search for genes without any preliminary functional hypothesis (mRNA differential expression, nucleic acid arrays, QTL search). The approach known as quantitative trait loci (QTL) analysis is based on the association between polymorphic anonymous markers and the phenotypical value of the trait under study in a segregating population (such as F2 or backcross). It allows the location of chromosomal regions involved in trait variability and ultimately the identification of the mutated gene(s). Therefore, in a first step, those studies skip the 'black box' of intermediate mechanisms, but the knowledge of the gene(s) responsible for trait variability will point out to the pathway responsible for the phenotypical differences. Since variations in stress-related responses may be related to numerous pathological conditions such as behavioral and mood disorders, drug abuse, cardiovascular diseases or obesity, and production traits in farm animals, these studies can be expected to bring significant knowledge for new therapeutic approaches in humans and improved efficiency of selection in farm animals.

Activity, non-selective attention and emotionality in dopamine D2/D3 receptor knock-out mice

In order to assess the role of dopamine (DA) D2 and D3 receptors in the modulation of behaviour, we analysed exploration in a spatial novelty in mouse model systems. Genetically engineered mice mutants have been used that carry normal, partial or no expression of D2R, D3R, or both D2R/D3R (double mutants) DA receptor subtypes. Adult male mice were exposed for 30 min to a Làte-maze. The behaviour was analysed for indices of activity, orienting (rearing frequency), scanning times (rearing duration) and defecation score (emotionality). D2R - / - and + / - as well as the D2R/D3R double homozygous mutants were less active than wild-type (WT) controls in travelled distance. In contrast D3R + / - were more active than WT mice in the first part of the test. As to orienting frequency, the D2R - / - were less active than WT during the entire test-period, whereas the D2 + / - mutants were less active than WT only in the second part of the test. Moreover, the D3R - / - and + / - mutants showed less and more rearing frequency than WT, respectively, during the entire test. Finally, the D2/D3R - / - double mutants were also less active than WT during the entire test period. As to scanning times, D2R + / - and - / - mutants were higher than WT during the entire test or only in the second part, respectively. The D3R + / - and - / - were not different from WT, whereas the D2/D3R - / - double mutants showed shorter scanning times only in the first part of the test. As to emotionality index, the defecation score, was lower only in D3R + / - mutants. Thus, the dopamine D2 and D3 receptor subtypes appear to be differentially involved in the modulation of activity, orienting and scanning phases of attention. Lastly double mutation experiments reveal an interaction between D2R and D3R with the former prevailing on the latter.

Genetic dissection of mouse exploratory behaviour

A large variety of apparatus and procedures are being employed to measure mouse exploratory behaviour. Definitions of what constitutes exploration also vary widely. The present article reviews two studies whose results permit a genetic dissection of behaviour displayed in an open-field situation. The results agree that factors representing exploration and stress/fear underlie this type of behaviour. Both factors appear to be linked to neuroanatomical variation in the sizes of the hippocampal intra- and infrapyramidal mossy fibre terminal fields. Multivariate analysis of genetic correlations may render important insights into the structure of behaviour and its relations with neuroanatomical and neurophysiological systems.

Behavioral tests of hippocampal function: simple paradigms complex problems

Behavioral tests have become important tools for the analysis of functional effects of induced mutations in transgenic mice. However, depending on the type of mutation and several experimental parameters, false positive or negative findings may be obtained. Given the fact that molecular neurobiologists now make increasing use of behavioral paradigms in their research, it is imperative to revisit such problems. In this review three tests, T-maze spontaneous alternation task (T-CAT), Context dependent fear conditioning (CDFC), and Morris water maze (MWM) sensitive to hippocampal function, serve as illustrative examples for the potential problems. Spontaneous alternation tests are sometimes flawed because the handling procedure makes the test dependent on fear rather than exploratory behavior leading to altered alternation rates independent of hippocampal function. CDFC can provide misleading results because the context test, assumed to be a configural task dependent on the hippocampus, may have a significant elemental, i.e. cued, component. MWM may pose problems if its visible platform task is disproportionately easier for the subjects to solve than the hidden platform task, if the order of administration of visible and hidden platform tasks is not counterbalanced, or if inappropriate parameters are measured. Without attempting to be exhaustive, this review discusses such experimental problems and gives examples on how to avoid them.

Heregulin, but not ErbB2 or ErbB3, heterozygous mutant mice exhibit hyperactivity in multiple behavioral tasks

Genetic redundancy is a problem in gene targeting studies because functionally relevant sister proteins can compensate for the lack of protein product of a targeted gene. A molecular system is chosen in which it is hoped to demonstrate both the lack and presence of compensation after disruption of particular single genes. Mammals may not be able to compensate for the lack of heregulin, a single ligand for multiple ErbB receptors, however, compensation is expected when a single ErbB receptor is knocked out. To investigate this the heregulin-1, ErbB2, or ErbB3 locus was disrupted in a targeted manner and mice heterozygous for the mutation were analyzed. Heregulin and its receptors were shown to be involved in embryonic brain development and, more recently, in plastic changes associated with adult brain function in rodents. Although they have never been shown to play roles in mammalian behavior, it was decided to characterize the mice behaviorally using a battery of simple tests. Heregulin mutant mice exhibited elevated activity levels in the open field, showed improved rotorod performance, and finished T-maze spontaneous alternation task faster compared to control wild type littermates, findings that suggest a consistent hyperactivity across tests. ErbB2 and ErbB3 mutant mice, whose strain origin was identical to that of heregulin mutants, showed no sign of the behavioral alterations. It is suggested that the abnormalities seen in heregulin mutant mice are due to mutation at that locus and the lack of alterations seen in ErbB2 and ErbB3 mutant mice is the result of compensation by unaltered sister receptors.

An assessment of novelty-seeking behavior in alcohol-preferring and nonpreferring rats

This study examined novelty-seeking behavior in rat populations selectively bred for high and low alcohol-drinking behavior. In Experiment 1, and "odor-enhanced" novel environment produced greater behavioral activation in P compared to NP rats. In Experiment 2, the activity of high alcohol-drinking P and HAD rats was enhanced to a greater extent following the presentation of novel odors in a familiar arena, compared to the NP and LAD rats. The results suggest that, when measuring locomotor activity, alcohol-preferring rats are more reactive to novelty than their nonpreferring counterparts. Experiments 3 and 4, however, did not support the hypothesis that novelty seeking is associated with genetic vulnerability to high alcohol-drinking behavior. When measuring nose-poking behavior in response to novel odors and preference for a novel vs. a familiar chamber, behavior of the preferring lines did not differ from that of the nonpreferring lines, although P rats were more active in the place-preference paradigm. The overall results indicate that the relationship between novelty and alcohol drinking is only modestly associated, and is observed under specific conditions. Moreover, this study underscores the importance of using multiple measures when assessing complex behaviors such as novelty seeking.

Non-selective attention in a rat model of hyperactivity and attention deficit: subchronic methylphenydate and nitric oxide synthesis inhibitor treatment

The involvement of dopamine (DA) and nitric oxide (NO) in the process of non-selective attention (NSA) to environmental stimuli has been investigated in the juvenile Spontaneously Hypertensive rat (SHR). To this aim the frequency and duration of rearing episodes in a novelty situation, which is thought to monitor NSA, have been measured in male SHR and Wistar-Kyoto (WKY) control rats following subchronic treatment with methylphenidate (MP; 3 mg/kg) or the nitric oxide synthase (NOS) inhibitor L-Nitro-arginine-methylester (L-NAME; 1 mg/kg) or vehicle daily for two weeks. Different groups were tested at 0.5 h or 24 h after the last injection in a Làt-maze. Tests were repeated twice at a 24 h interval and lasted 10 min each. Upon first exposure, there was a differential drug effect only in the SHR. In fact, MP and L-NAME yielded a shift to the left and to the right, i.e. towards episodes of lower or higher duration, respectively. This shift was more pronounced in the group tested 0.5 h after the last injection. In contrast, both drugs produced a significant lengthening of the rearing episodes in the SHR only in comparison with the vehicle-treated rats over days of testing. Therefore both MP and L-NAME appear to shear a similar effect on non-selective attention, although the effect of L-NAME is somewhat paradoxical. The latter is likely to be due to increased arginine selective uptake due to negative feedback with the NO production. The consequent increased arginine availability displaces the NOS inhibitor, thus leading to increased NO production. In conclusion, dopamine and nitric oxide play a role in non-selective attention by synaptic and extrasynaptic mechanisms, respectively, in a rat model of hyperactivity and attention-deficits.

Behavioural trait of reactivity to novelty is related to hippocampal neurogenesis

The hippocampal formation is one of the brain areas where neurogenesis persists during adulthood, with new neurons being continuously added to the population of dentate granule cells. However, the functional implications of this neurogenesis are unknown. On the other hand, the hippocampal formation is particularly concerned with the detection of novelty, and there are indications that dentate granule cells play a significant role in this function. Recently, the existence of inter-individual differences in behavioural reactivity to novelty has been evidenced, related to differences in the reactivity of the hypothalamic-pituitary-adrenal axis (HPA). Rats that are highly reactive to novelty (HR) exhibit a prolonged corticosterone secretion in response to novelty and to stress when compared with low reactive rats (LR). Taking advantage of the existence of these inter-individual differences, we investigated whether neurogenesis in the dentate gyrus is correlated with the behavioural trait of reactivity to novelty. Rats were first selected according to their locomotor reactivity to a novel environment. Two weeks later, cell proliferation, evaluated by the incorporation of 5-bromo-2'-deoxyuridine (BrdU) in progenitors, was studied by immunohistochemistry. We found that cell proliferation in the dentate gyrus was negatively correlated with locomotor reactivity to novelty. Indeed, cell proliferation in LR rats was twice that observed in HR rats. In contrast, survival of nascent neurons was not influenced by the behavioural trait of reactivity to novelty. Using an unbiased stereology, we show that LR rats had more cells within the granule cell layer of the dentate gyrus than did HR rats. These results demonstrate the existence of inter-individual differences in neurogenesis and total granule cell number within the dentate gyrus. These differences in hippocampal plasticity can be predicted by the behavioural trait of reactivity to novelty.

Variation in hippocampal dynorphin b-immunoreactive mossy fiber terminal fields of apomorphine-(un)susceptible rats

The size of distinct hippocampal sub-fields were measured in the apomorphine-susceptible and apomorphine-unsusceptible rat lines. Mossy fiber terminal fields were delineated using dynorphin B immunoreactivity and area measurements were taken from (1) the supra-pyramidal mossy fiber terminal field; (2) the intra- and infra-pyramidal mossy fiber terminal field; (3) the hilus of the fascia dentata (4) the non dynorphin B immunoreactive area of the regio inferior and fascia dentata and (5) the total area of regio inferior and fascia dentata. The data indicate that statistically significant differences in the morphometry of the hippocampal subfields of the apomorphine susceptible and unsusceptible rats are confined to the intra- and infra terminal field: the relative size of the left and right intra- and infra terminal field of apomorphine unsusceptible rats are significantly larger than those of the apomorphine susceptible rats. These data explain at least in part the differential response of these rats to novelty.

The gene encoding proline dehydrogenase modulates sensorimotor gating in mice

Hemizygous cryptic deletions of the q11 band of human chromosome 22 have been associated with a number of psychiatric and behavioural phenotypes, including schizophrenia. Here we report the isolation and characterization of PRODH, a human homologue of Drosophila melanogaster sluggish-A (slgA), which encodes proline dehydrogenase responsible for the behavioural phenotype of the slgA mutant. PRODH is localized at chromosome 22q11 in a region deleted in some psychiatric patients. We also isolated the mouse homologue of slgA (Prodh), identified a mutation in this gene in the Pro/Re hyperprolinaemic mouse strain and found that these mice have a deficit in sensorimotor gating accompanied by regional neurochemical alterations in the brain. Sensorimotor gating is a neural filtering process that allows attention to be focused on a given stimulus, and is affected in patients with neuropsychiatric disorders. Furthermore, several lines of evidence suggest that proline may serve as a modulator of synaptic transmission in the mammalian brain. Our observations, in conjunction with the chromosomal location of PRODH, suggest a potential involvement of this gene in the 22q11-associated psychiatric and behavioural phenotypes.

Contextual learning and cue association in fear conditioning in mice: a strain comparison and a lesion study

Fear conditioning with electric shock (unconditioned stimulus, US) paired with tone cue (conditioned stimulus, CS) has been extensively applied in recent molecular neurobiological analysis of hippocampal dysfunction in mice because the context-dependent test phase of this learning paradigm is claimed to detect hippocampal impairment in a specific manner, whereas the cue-dependent test serves as a control situation independent of hippocampal function. These claims are based on hippocampal lesion studies performed with rats and have not been conclusively confirmed with mice with specific hippocampal lesion. Therefore, I investigated how hippocampal ibotenic acid lesion affects conditioned fear in mice. I confirm that extensive lesions localized to the hippocampus impair context-dependent learning but also show that, unlike in the original rat studies, the behavioral impairment is only partial. Furthermore, studying two inbred strains of mice (C57BL/6 and DBA/2) with highly different hippocampal function, I show that the presence or absence of CS during training may influence the mouse's ability to learn complex multiple contextual stimuli in a genotype-dependent manner. I conclude that performance at the 'context' test may be based on complex configural (hippocampal) learning but it can also be based on a more simple elemental (non-hippocampal) learning thus leading to potentially false-negative findings in the analysis of hippocampal dysfunction.

Combination of open field and elevated plus-maze: a suitable test battery to assess strain as well as treatment differences in rat behavior

1. A test battery consisting of a standard open field, an enriched open field and an elevated plus maze was used to study behavior in rats. 2. Male rats of the strains PVG/OlaHsd (PVG) and Sprague-Dawley-Hsd (SPRD) (150-200 g body wt) were used to assess interstrain differences as well as handling effects. In a subsequent experiment an other set of male PVG rats (150-200 g body wt) treated either with diazepam or zolpidem was used to evaluate the test battery for pharmacological purposes. 3. SPRD rats displayed higher motor activity levels and also higher levels of exploratory behavior than the PVG rats. In contrast plus-maze activity indicated more anxiety of SPRD than PVG rats. One week pre-test handling increased the activity of both strains but it increased explorative behavior in the enriched open field only in SPRD rats. Diazepam had a substantial anxiolytic effect. Zolpidem enhanced the explorative activity in a differently to diazepam and exerted only minor anxiolytic properties. 4. We concluded that the test battery used here enables to reveal differentially strain, and treatment effects in rats.

Non-selective attention and nitric oxide in putative animal models of Attention-Deficit Hyperactivity Disorder

Non-selective attention (NSA) to environmental stimuli has been measured in putative animal models of Attention-Deficit Hyperactivity Disorder (ADHD), such as the Spontaneously Hypertensive (SHR) and the Naples High-Excitability (NHE) rat lines. A series of experiments has been carried out on male juvenile SHR and Wistar-Kyoto (WKY) controls (experiment 1) and on the NHE and two controls, i.e. the Naples Low-Excitability (NLE) and a random-bred (NRB) line (experiment 2). It was done under basal conditions or following a single injection of the nitric oxide synthase (NOS) inhibitor L-nitro-arginine-methylester (L-NAME: 0.1-10 mg/kg, i.p.), or vehicle, 30 min before testing on day 1 and vehicle alone before testing on days 2 and 3 in SHR/WKY (experiment 3) and the Naples lines (experiment 4). The behavior in a Lát maze during three consecutive 10-min exposures at 24-h intervals was monitored by a CCD video camera and analyzed off-line for frequency and duration of rearings on hindlimbs per 1-min blocks. The results demonstrated that both SHR and NHE rats showed a higher frequency of rearings of shorter duration than controls. With time of testing, the duration of rearings tended to increase in the WKY but not the SHR. In the Naples lines the duration tended to increase in all but mostly in the NHE rats. The acute inhibition of NOS by L-NAME significantly increased the duration of rearing episodes both in SHR and NHE rats only at 10 mg/kg in the second part of the testing period. Therefore, NSA, as indexed by the duration of rearings, is defective in both hyperactivity models against different genetic backgrounds. In addition, this impairment is dependent upon nitric oxide (NO), which appears to play a significant role in these processes.

A new continuous alternation task in T-maze detects hippocampal dysfunction in mice. A strain comparison and lesion study

The mammalian hippocampus has been the focus of several neurobiology studies because of its important behavioral function and because long-term potentiation (LTP) is a prominent feature of this brain region. Converging evidence suggests that hippocampal function is associated with learning multiple relationships of environmental cues. In this paper a novel behavioral test procedure is introduced, a modified T-maze continuous alternation task (T-CAT), that may serve as a simple, automatable, and quick test of hippocampal function in addition to the frequently applied water maze and fear conditioning paradigms. A comparison is made between mice (strain C57BL/6) with ibotenic acid lesioned or vehicle injected hippocampus, two transgenic strains (on CD1 background) overexpressing a calcium binding protein, S100beta, and inbred (C57BL/6, DBA/2, 129/SV and 129/SVEV) and outbred (CD1) strains of mice. This study shows that hippocampal lesioning led to a significant impairment in T-CAT. Furthermore, overexpression of S100beta, which impairs hippocampal LTP, also led to an impairment demonstrating that T-CAT is sensitive to detect hippocampal dysfunction. Analysis of the mouse strains revealed that C57BL/6 and CD1 mice performed well in T-CAT, whereas 129/SV, 129/SVEV and DBA/2 were significantly impaired, a finding that underscores the importance of strain differences in pharmacological or single gene manipulation studies of hippocampal function in mice.

Neuronal and behavioral differences between Mus musculus domesticus (C57BL/6JBy) and Mus musculus castaneus (CAST/Ei)

Previous studies have demonstrated that classical inbred strains of laboratory mice do not exhibit large genetic distances when simple sequence repeats (SSRs) are used to test for their polymorphisms whereas mice from wild origin exhibit high polymorphisms (more than 90%) for these sequence when compared with classical inbred strains of laboratory mice. The difference between Mus musculus castaneus and C57BL/6J reaches 98% and F1s male and female are fertile. These two properties pave the way for gene mapping derivating segregating generations between these strains. The phenotypical characteristics of Mus musculus castaneus have not been investigated, unfortunately. The first screening of Mus musculus castaneus and C57BL/6By was carried out for sensorial and motor development, spontaneous behavior in new environment, paw preference, maternal behavior, aggression in two different situations and time to learn escape in a water maze. Morphometry of hippocampus and weight of the male reproductive organs for measures that have been reported to be correlated with several of the examined behavior are also reported. The authors tested also reactivity to one drug (beta-CCM) revealing seizure proneness. The two strains differ for 69% of the reported measures. Comparison to other strains for the same measures obtained in the laboratory for identical tests with mice reared in identical situations provided the mean to compare Mus musculus castaneus with a large set of more or less traditional mice. This strain has the most extreme position for 80% of the comparisons.

Multiple behavioral anomalies in GluR2 mutant mice exhibiting enhanced LTP

We have previously disrupted the ionotropic glutamate receptor type 2 gene (GluR2) using gene targeting in embryonic stem cells and generated mice which lacked the GluR2 gene product. Neurophysiological analyses of these mice showed a markedly enhanced long-term potentiation (LTP) and a 9-fold increase in kainate induced Ca2+ permeability in the hippocampus. Here, we analyze the behavioral and neuroanatomical consequences of GluR2 deficiency in homozygous null mutant and age-matched littermate control mice. We show that despite unaltered gross brain morphology, several aspects of behavior were abnormal in the mutants. Object exploration, rearing, grooming and locomotion were altered in the novel arena. Eye-closure reflex, motor performance on the rotating rod and spatial and non-spatial learning performance in the water maze were also abnormal in the mutants. These abnormalities together with the widespread expression pattern of GluR2 in most excitatory CNS pathways suggest that the absence of GluR2 leads to neurological phenotypes associated with not only the hippocampus but several other brain regions potentially including the cortex and cerebellum. We speculate that GluR2 mutant mice suffer from an overall non-specifically increased excitability that may alter cognitive functions ranging from stimulus processing to motivation and learning.

Catechol-O-methyltransferase-deficient mice exhibit sexually dimorphic changes in catecholamine levels and behavior

Catechol-O-methyltransferase (COMT) is one of the major mammalian enzymes involved in the metabolic degradation of catecholamines and is considered a candidate for several psychiatric disorders and symptoms, including the psychopathology associated with the 22q11 microdeletion syndrome. By means of homologous recombination in embryonic stem cells, a strain of mice in which the gene encoding the COMT enzyme has been disrupted was produced. The basal concentrations of brain catecholamines were measured in the striatum, frontal cortex, and hypothalamus of adult male and female mutants. Locomotor activity, anxiety-like behaviors, sensorimotor gating, and aggressive behavior also were analyzed. Mutant mice demonstrated sexually dimorphic and region-specific changes of dopamine levels, notably in the frontal cortex. In addition, homozygous COMT-deficient female (but not male) mice displayed impairment in emotional reactivity in the dark/light exploratory model of anxiety. Furthermore, heterozygous COMT-deficient male mice exhibited increased aggressive behavior. Our results provide conclusive evidence for an important sex- and region-specific contribution of COMT in the maintenance of steady-state levels of catecholamines in the brain and suggest a role for COMT in some aspects of emotional and social behavior in mice.

Mice lacking ataxin-1 display learning deficits and decreased hippocampal paired-pulse facilitation

Spinocerebellar ataxia type 1 (SCA1) is a neurodegenerative disorder characterized by ataxia, progressive motor deterioration, and loss of cerebellar Purkinje cells. To investigate SCA1 pathogenesis and to gain insight into the function of the SCA1 gene product ataxin-1, a novel protein without homology to previously described proteins, we generated mice with a targeted deletion in the murine Sca1 gene. Mice lacking ataxin-1 are viable, fertile, and do not show any evidence of ataxia or neurodegeneration. However, Sca1 null mice demonstrate decreased exploratory behavior, pronounced deficits in the spatial version of the Morris water maze test, and impaired performance on the rotating rod apparatus. Furthermore, neurophysiological studies performed in area CA1 of the hippocampus reveal decreased paired-pulse facilitation in Sca1 null mice, whereas long-term and post-tetanic potentiations are normal. These findings demonstrate that SCA1 is not caused by loss of function of ataxin-1 and point to the possible role of ataxin-1 in learning and memory.

Purkinje cell expression of a mutant allele of SCA1 in transgenic mice leads to disparate effects on motor behaviors, followed by a progressive cerebellar dysfunction and histological alterations

Spinocerebellar ataxia type 1 (SCA1) is an autosomal dominant neurological disorder caused by the expansion of a CAG repeat encoding a polyglutamine tract. Work presented here describes the behavioral and neuropathological course seen in mutant SCA1 transgenic mice. Behavioral tests indicate that at 5 weeks of age mutant mice have an impaired performance on the rotating rod in the absence of deficits in balance and coordination. In contrast, these mutant SCA1 mice have an increased initial exploratory behavior. Thus, expression of the mutant SCA1 allele within cerebellar Purkinje cells has divergent effects on the motor behavior of juvenile animals: a compromise of rotating rod performance and a simultaneous enhancement of initial exploratory activity. With age, these animals develop incoordination with concomitant progressive Purkinje neuron dendritic and somatic atrophy but relatively little cell loss. Therefore, the eventual development of ataxia caused by the expression of a mutant SCA1 allele is not the result of cell death per se, but the result of cellular dysfunction and morphological alterations that occur before neuronal demise.

Dissociation of spatial reference memory, spatial working memory, and hippocampal mossy fiber distribution in two rat strains differing in emotionality

Rats of the inbred strains DA/Han and BDE/Han were compared on two complex spatial learning tasks, a spatial reference memory task in a 16-unit multiple T-maze and a spatial working memory task in an eight-arm radial-maze. In addition, sizes of hippocampal mossy fiber terminal fields were measured. BDE rats showed marked superiority in multiple T-maze learning whereas DA rats outperformed BDE rats on the radial-maze task. DA rats had significantly larger intra- and infrapyramidal mossy fiber terminal fields (IIP-MF). This is consistent with findings from other studies suggesting that large IIP-MF are related to excellent spatial radial-maze learning, but it also indicates that size of IIP-MF is correlated with processing of a specific type of spatial information rather than with overall spatial abilities. BDE rats had more extended suprapyramidal mossy fiber projections (SP-MF) and a larger hilus. Rats of both strains differed in exploratory behaviour and emotionality: DA rats revealed little freezing and had a high rearing activity, whereas BDE rats showed frequent freezing and reared rarely. Results suggest that IIP-MF are involved with flexible expression of memory, updating environmental information and parallel processing whereas SP-MF might be linked to processing of familiar information. Presumably, emotional factors contribute to performance differences.

Genetic and environmental control of variation in retinal ganglion cell number in mice

How much of the remarkable variation in neuron number within a species is generated by genetic differences, and how much is generated by environmental factors? We address this problem for a single population of neurons in the mouse CNS. Retinal ganglion cells of inbred and outbred strains, wild species and subspecies, and F1 hybrids were studied using an unbiased electron microscopic method with known technical reliability. Ganglion cell numbers among diverse types of mice are highly variable, ranging from 32,000 to 87,000. The distribution of all cases (n = 252) is close to normal, with a mean of 58,500 and an SD of 7800. Genetic factors are most important in controlling this variation; 76% of the variance is heritable and up to 90% is attributable to genetic factors in a broad sense. Strain averages have an unanticipated bimodal distribution, with distinct peaks at 55,500 and 63,500 cells. Three pairs of closely related strains have ganglion cell populations that differ by > 20% (10,000 cells). These findings indicate that different alleles at one or two genes have major effects on normal variation in ganglion cell number. Nongenetic factors are still appreciable and account for a coefficient of variation that averages approximately 3.6% within inbred strains and isogenic F1 hybrids. Age- and sex-related differences in neuron number are negligible. Variation within isogenic strains appears to be generated mainly by developmental noise.

Conspecific exploration in the T-maze: abnormalities in S100 beta transgenic mice

S100 beta, a calcium binding brain protein expressed by astrocytes, has been shown to be involved in higher neural processes, including hippocampal-dependent behavioral traits and hippocampal neuronal long-term potentiation (LTP) and depression (LTD), neurophysiological phenomena that may be involved in exploring, learning and remembering novel stimuli. In the present study, the exploratory behavior of previously generated transgenic mice overexpressing the protein are compared to that of normal control mice of identical genetic background and age in a T-maze. The test mice encountered a normal control and an S100 beta transgenic mouse (the choice mice) in the goal arms of the T-maze. We show that no test mice exhibited any preference for either genotype of choice mouse. However, there was a significant difference in the spatial and temporal exploratory pattern between control and S100 beta test mice, demonstrating that S100 beta overexpression significantly altered the behavior of the transgenic mice. We suggest that one probable factor underlying the abnormalities observed is impaired short-term memory.