Search

Adult hippocampal neurogenesis has been implicated in a number of disorders where reward processing is disrupted but whether new neurons regulate specific aspects of reward-related decision making remains unclear. Given the role of the hippocampus in future-oriented cognition, here we tested whether adult neurogenesis regulates preference for future, advantageous rewards in a delay discounting paradigm for rats. Indeed, blocking neurogenesis caused a profound aversion for delayed rewards, and biased choice behavior toward immediately available, but smaller, rewards. Consistent with a role for the ventral hippocampus in impulsive decision making and future-thinking, neurogenesis-deficient animals displayed reduced activity in the ventral hippocampus. In intact animals, delay-based decision making restructured dendrites and spines in adult-born neurons and specifically activated adult-born neurons in the ventral dentate gyrus, relative to dorsal activation in rats that chose between immediately-available rewards. Putative developmentally-born cells, located in the superficial granule cell layer, did not display task-specific activity. These findings identify a novel and specific role for neurogenesis in decisions about future rewards, thereby implicating newborn neurons in disorders where short-sighted gains are preferred at the expense of long-term health.

During immature stages, adult-born neurons pass through critical periods for survival and plasticity. It is generally assumed that by 2 months of age adult-born neurons are mature and equivalent to the broader neuronal population, raising questions of how they might contribute to hippocampal function in old age when neurogenesis has declined. However, few have examined adult-born neurons beyond the critical period, or directly compared them to neurons born in infancy. Here, we used a retrovirus to visualize functionally-relevant morphological features of 2- to 24-week-old adult-born neurons in male rats. From 2-7 weeks neurons grew and attained a relatively mature phenotype. However, several features of 7-week-old neurons suggested a later wave of growth: these neurons had larger nuclei, thicker dendrites and more dendritic filopodia than all other groups. Indeed, between 7-24 weeks, adult-born neurons gained additional dendritic branches, grew a 2nd primary dendrite, acquired more mushroom spines and had enlarged mossy fiber presynaptic terminals. Compared to neonatally-born neurons, old adult-born neurons had greater spine density, larger presynaptic terminals, and more putative efferent filopodial contacts onto inhibitory neurons. By integrating rates of cell birth and growth across the lifespan, we estimate that adult neurogenesis ultimately produces half of the cells and the majority of spines in the dentate gyrus. Critically, protracted development contributes to the plasticity of the hippocampus through to the end of life, even after cell production declines. Persistent differences from neonatally-born neurons may additionally endow adult-born neurons with unique functions even after they have matured.SIGNIFICANCE STATEMENTNeurogenesis occurs in the hippocampus throughout adult life and contributes to memory and emotion. It is generally assumed that new neurons have the greatest impact on behavior when they are immature and plastic. However, since neurogenesis declines dramatically with age, it is unclear how they might contribute to behavior later in life when cell proliferation has slowed. Here we find that newborn neurons mature over many months in rats, and end up with distinct morphological features compared to neurons born in infancy. Using a mathematical model, we estimate that a large fraction of neurons is added in adulthood. Moreover, their extended growth produces a reserve of plasticity that persists even after neurogenesis has declined to low rates.

Adult neurogenesis modifies hippocampal circuits and behavior, but removing newborn neurons does not consistently alter spatial processing, a core function of the hippocampus. Additionally, little is known about sex differences in neurogenesis since few studies have compared males and females. Since adult-born neurons regulate the stress response, we hypothesized that spatial functions may be more prominent under aversive conditions and may differ between males and females given sex differences in stress responding. We therefore trained intact and neurogenesis-deficient rats in the spatial water maze at temperatures that vary in their degree of aversiveness. In the standard water maze, ablating neurogenesis did not alter spatial learning in either sex. However, in cold water, ablating neurogenesis had divergent sex-dependent effects: relative to intact rats, male neurogenesis-deficient rats were slower to escape the maze and female neurogenesis-deficient rats were faster. Neurogenesis promoted temperature-related changes in search strategy in females, but it promoted search strategy stability in males. Females displayed greater recruitment (Fos expression) of the dorsal hippocampus than males, particularly in cold water. However, blocking neurogenesis did not alter Fos expression in either sex. Finally, morphologic analyses revealed greater experience-dependent plasticity in males. Adult-born neurons in males and females had similar morphology at baseline but training increased spine density and reduced presynaptic terminal size, specifically in males. Collectively, these findings indicate that adult-born neurons contribute to spatial learning in stressful conditions and they provide new evidence for sex differences in their behavioral functions.

The central amygdala (CEA) has been richly studied for interpreting function and behavior according to specific cell types and circuits. Such work has typically defined molecular cell types by classical inhibitory marker genes; consequently, whether marker-gene-defined cell types exhaustively cover the CEA and co-vary with connectivity remains unresolved. Here, we combined single-cell RNA sequencing, multiplexed fluorescent

Adult hippocampal neurogenesis has been implicated in the spatial processing functions of the hippocampus but ablating neurogenesis does not consistently lead to behavioral deficits in spatial tasks. Parallel studies have shown that adult-born neurons also regulate behavioral responses to stressful and aversive stimuli. We therefore hypothesized that spatial functions of adult-born neurons may be more prominent under conditions of stress, and may differ between males and females given established sex differences in stress responding. To test this we trained intact and neurogenesis-deficient rats in the spatial water maze at temperatures that vary in their degree of aversiveness. At standard temperatures (25°C) ablating neurogenesis did not alter learning and memory in either sex, consistent with prior work. However, in cold water (16°C), ablating neurogenesis had divergent sex-dependent effects: relative to intact rats, male neurogenesis-deficient rats were slower to escape and female neurogenesis-deficient rats were faster. Neurogenesis promoted temperature-related changes in search strategy in females, but it promoted search strategy stability in males. Females displayed greater recruitment of the dorsal hippocampus than males, particularly at 16°C. However, blocking neurogenesis did not alter activity-dependent immediate-early gene expression in either sex. Finally, morphological analyses of retrovirally-labelled neurons revealed greater experience-dependent plasticity in new neurons in males. Neurons had comparable morphology in untrained rats but 16°C training increased spine density, and 25°C training caused shrinkage of mossy fiber presynaptic terminals, specifically in males. Collectively, these findings indicate that neurogenesis functions in memory are prominent under conditions of stress, they provide the first evidence for sex differences in the behavioral function of newborn neurons, and they suggest possibly distinct roles for neurogenesis in cognition and mental health in males and females.

The basolateral amygdala complex (BLA), extensively connected with both local amygdalar nuclei as well as long-range circuits, is involved in a diverse array of functional roles. Understanding the mechanisms of such functional diversity will be greatly informed by understanding the cell-type-specific landscape of the BLA. Here, beginning with single-cell RNA sequencing, we identified both discrete and graded continuous gene-expression differences within the mouse BLA. Via in situ hybridization, we next mapped this discrete transcriptomic heterogeneity onto a sharp spatial border between the basal and lateral amygdala nuclei, and identified continuous spatial gene-expression gradients within each of these regions. These discrete and continuous spatial transformations of transcriptomic cell-type identity were recapitulated by local morphology as well as long-range connectivity. Thus, BLA excitatory neurons are a highly heterogenous collection of neurons that spatially covary in molecular, cellular, and circuit properties. This heterogeneity likely drives pronounced spatial variation in BLA computation and function.

Insulin dysregulation independently underlies diabetes and Alzheimer’s Disease (AD) pathology. However, the former has also been shown to be a risk factor for the latter. The ancestral insulin gene (Ins2), but not the pancreas-specific Ins1gene, is transcribed locally within the brain in mice. We confirmed that neuronal expression of Ins2 is most prominent within the hippocampus, a brain region with established roles in learning and memory, and that it was reduced by a diet known to promote neuronal dysfunction. It is not yet clear, however, how insulin produced locally within the brain influences hippocampal function, learning and memory. To eliminate brain-derived insulin, we used young and old mice with germline Ins2knockout (Ins2-/-) and their normal complement of wildtype Ins1 alleles, which had equivalent pancreatic insulin and normal glucose homeostasis. Using the Morris water maze, we found that learning and memory performance of female Ins2-/-mice was significantly impaired relative to wild-type mice, whereas the performance of male Ins2-/-and wild-type mice did not differ. During acquisition training, the swim-speed in female Ins2-/-was faster than wild-type mice, suggesting increased stress reactivity and motivation to escape from water. Indeed, anxiety-like behavior was increased in female mice as assessed by the open-field test. Using RNA sequencing to profile isolated hippocampi, we found that femaleIns2-/-mice had a significant reduction in Cyclin D1 (Ccnd1) compared with littermate controls. This observation points to a possible defect in hippocampal neurogenesis, a physiological hallmark of impaired memory and emotionality implicated in both, diabetes and AD. Together these data suggest that Ins2plays sex- and brain region-specific roles in neuronal function and perhaps adult neurogenesis.

The APPswe/PS1dE9 mouse (line 85) is a double transgenic model of Alzheimer's disease (AD) with familial amyloid precursor protein and presenilin-1 mutations. These mice develop age-related behavioral changes reflective of the neuropsychiatric symptoms (altered anxiety-like behaviour, hyperactivity) and cognitive dysfunction (impaired learning and memory) observed in AD. The APPswe/PS1dE9 mouse has been used to examine the efficacy of therapeutic interventions on behaviour, despite previous difficulties in replicating behavioural phenotypes. Therefore, the purpose of this study was to establish the reliability of these phenotypes by further characterizing the behaviour of male APPswe/PS1dE9 and wild-type mice between 7 and 14 months of age. Mice were tested on the open-field over 5-days to examine emotionality, locomotor activity and inter-session habituation. Mice were also tested on the repeated-reversal water maze task and spontaneous alternation on the Y-maze to assess working memory. Sensori-motor gating was examined with acoustic startle and pre-pulse inhibition. Lastly contextual and cued (trace) memory was assessed with fear conditioning. The results show that among non-cognitive behaviours, APPswe/PS1dE9 mice have normal locomotor activity, anxiety-like behavior, habituation and sensori-motor gating. However, APPswe/PS1dE9 mice show impaired working memory on the repeated-reversal water-maze and impaired memory in contextual but not trace-cued fear conditioning. These results indicate that the APPswe/PS1dE9 (line 85) mice have deficits in some types of hippocampal-dependent learning and memory and, at the ages tested, APPswe/PS1dE9 mice model cognitive dysfunction but not neuropsychiatric symptoms.

Motor problems occur early in some patients with Alzheimer's disease (AD) and as the disease progresses many patients develop motor dysfunction. Motor dysfunction has been reported in some mouse models of AD, including the 5xFAD mouse, thus this model may be particularly useful for studying motor dysfunction in AD. In order to determine the extent of motor dysfunction in these mice, we tested 11-13 month old female 5xFAD and wildtype (WT) control mice in a battery of motor behaviour tasks. The 5xFAD mice showed hind limb clasping, weighed less and had slower righting reflexes than WT mice. In the open field, the 5xFAD mice travelled a shorter distance than the WT mice, spent less time moving and had a slower movement speed. The 5xFAD mice fell faster than the WT mice from the balance beam, wire suspension, grid suspension and rotarod tasks, indicating dysfunctions in balance, grip strength, motor co-ordination and motor learning. The 5xFAD mice had a short, shuffling gait with a shorter stride length than WT mice and had a slower swim speed. The 5xFAD mice also failed to show an acoustic startle response, likely due to motor dysfunction and previously reported hearing impairment. The 5xFAD mice did not show deficits in the ability of peripheral motor nerves to drive muscle output, suggesting that motor impairments are not due to dysfunction in peripheral motor nerves. These results indicate that the aged 5xFAD mice are deficient in numerous motor behaviours, and suggest that these mice may prove to be a good model for studying the mechanisms of motor dysfunction in AD, and motor behaviour might prove useful for assessing the efficacy of AD therapeutics. Motor dysfunction in 5xFAD mice must also be considered in behavioural tests of sensory and cognitive function so that performance is not confounded by impaired locomotor or swimming behaviour.

Hearing dysfunction has been associated with Alzheimer's disease (AD) in humans, but there is little data on the auditory function of mouse models of AD. Furthermore, characterization of hearing ability in mouse models is needed to ensure that tests of cognition that use auditory stimuli are not confounded by hearing dysfunction. Therefore, we assessed acoustic startle response and pre-pulse inhibition in the double transgenic 5xFAD mouse model of AD from 3-4 to 16 months of age. The 5xFAD mice showed an age-related decline in acoustic startle as early as 3-4 months of age. We subsequently tested auditory brainstem response (ABR) thresholds at 4 and 13-14 months of age using tone bursts at frequencies of 2-32 kHz. The 5xFAD mice showed increased ABR thresholds for tone bursts between 8 and 32 kHz at 13-14 months of age. Finally, cochleae were extracted and basilar membranes were dissected to count hair cell loss across the cochlea. The 5xFAD mice showed significantly greater loss of both inner and outer hair cells at the apical and basal ends of the basilar membrane than wild-type mice at 15-16 months of age. These results indicate that the 5xFAD mouse model of AD shows age-related decreases in acoustic startle responses, which are at least partially due to age-related peripheral hearing loss. Therefore, we caution against the use of cognitive tests that rely on audition in 5xFAD mice over 3-4 months of age, without first confirming that performance is not confounded by hearing dysfunction.

Spatial navigation is a universal behavior that varies depending on goals, experience and available sensory stimuli. Spatial navigational tasks are routinely used to study learning, memory and goal-directed behavior, in both animals and humans. One popular paradigm for testing spatial memory is the Morris water maze, where subjects learn the location of a hidden platform that offers escape from a pool of water. Researchers typically express learning as a function of the latency to escape, though this reveals little about the underlying navigational strategies. Recently, a number of studies have begun to classify water maze search strategies in order to clarify the precise spatial and mnemonic functions of different brain regions, and to identify which aspects of spatial memory are disrupted in disease models. However, despite their usefulness, strategy analyses have not been widely adopted due to the lack of software to automate analyses. To address this need we developed Pathfinder, an open source application for analyzing spatial navigation behaviors. In a representative dataset, we show that Pathfinder effectively characterizes the development of highly-specific spatial search strategies as male and female mice learn a standard spatial water maze. Pathfinder can read data files from commercially- and freely-available software packages, is optimized for classifying search strategies in water maze paradigms, but can also be used to analyze 2D navigation by other species, and in other tasks, as long as timestamped xy coordinates are available. Pathfinder is simple to use, can automatically determine pool and platform geometry, generates heat maps, analyzes navigation with respect to multiple goal locations, and can be updated to accommodate future developments in spatial behavioral analyses. Given these features, Pathfinder may be a useful tool for studying how navigational strategies are regulated by the environment, depend on specific neural circuits, and are altered by pathology.

Glucocorticoids (GCs) are secreted into the blood by the adrenal glands and are also locally-produced by organs such as the lymphoid organs (bone marrow, thymus, and spleen). Corticosterone is the primary circulating GC in many species, including mice, rats and birds. Within lymphoid organs, corticosterone can be locally produced from the inactive metabolite, 11-dehydrocorticosterone (DHC). However, very little is known about endogenous DHC levels, and no immunoassays are currently available to measure DHC. Here, we developed an easy-to-use and inexpensive immunoassay to measure DHC that is accurate, precise, sensitive, and specific. The DHC immunoassay was validated in multiple ways, including comparison with a mass spectrometry assay. After assay validations, we demonstrated the usefulness of this immunoassay by measuring DHC (and corticosterone) in mice, rats and song sparrows. Overall, corticosterone levels were higher than DHC levels across species. In Study 1, using mice, we measured steroids in whole blood and lymphoid organs at postnatal day (PND) 5, PND23, and PND90. Corticosterone and DHC showed distinct tissue-specific patterns across development. In Studies 2 and 3, we measured circulating corticosterone and DHC in adult rats and song sparrows, before and after restraint stress. In rats and song sparrows, restraint stress rapidly increased circulating levels of both steroids. This novel DHC immunoassay revealed major changes in DHC concentrations during development and in response to stress, which have important implications for understanding GC physiology, effects of stress on immune function, and regulation of local GC levels.

In addition to cognitive decline, patients with Alzheimer's disease (AD) exhibit sensory, motor, and neuropsychiatric deficits. Many AD patients also show weight loss, suggesting that AD may involve a metabolic syndrome. The 5xFAD mouse model shows age-related weight loss compared to wildtype controls, and thus may exhibit metabolic dysfunction. This longitudinal study measured age-related weight loss in female 5xFAD and B6SJL/JF2 wild-type mice from 3 to 12 months of age, and examines some of the behavioural and physiological phenotypes in these mice that have been proposed to contribute to this weight loss. Because some mice had to be singly housed during the study, we also examined genotype by housing interactions. The 5xFAD mice weighed less and ate less than WT littermates starting at 6 months of age, exhibited less home cage activity, had higher frailty scores, less white adipose tissue, and lower leptin expression. At 9 and 12 months of age, heavier 5xFAD mice performed better on the rotarod, suggesting that metabolic deficits which begin between 6 and 9 months of age may exacerbate the behavioural deficits in 5xFAD mice. These results indicate that the 5xFAD mouse is a useful model to study the behavioural and metabolic changes in AD.

Alzheimer's disease (AD) is an age-related neurodegenerative disorder that causes profound cognitive dysfunction. Deficits in olfactory memory occur in early stages of AD and may be useful in AD diagnosis. The 5xFAD mouse is a commonly used model of AD, as it develops neuropathology, cognitive and sensori-motor dysfunctions similar to those seen in AD. However, olfactory memory dysfunction has not been studied adequately or in detail in 5xFAD mice. Furthermore, despite sex differences in AD prevalence and symptom presentation, few studies using 5xFAD mice have examined sex differences in learning and memory. Therefore, we tested olfactory memory in male and female 5xFAD mice from 3 to 15 months of age using a conditioned odour preference task. Olfactory memory was not impaired in male or female 5xFAD mice at any age tested, nor were there any sex differences. Because early-onset impairments in very long-term (remote) memory have been reported in 5xFAD mice, we trained a group of mice at 3 months of age and tested olfactory memory 90 days later. Very long-term olfactory memory in 5xFAD mice was not impaired, nor was their ability to perform the discrimination task with new odourants. Examination of brains from 5xFAD mice confirmed extensive Aβ-plaque deposition spanning the olfactory memory system, including the olfactory bulb, hippocampus, amygdala and piriform cortex. Overall this study indicates that male and female 5xFAD mice do not develop olfactory memory deficits, despite extensive Aβ deposition within the olfactory-memory regions of the brain.

Alzheimer's disease (AD) is a neurodegenerative disorder that leads to age-related cognitive and sensori-motor dysfunction. There is an increased understanding that motor dysfunction contributes to overall AD severity, and a need to ameliorate these impairments. The 5xFAD mouse develops the neuropathology, cognitive and motor impairments observed in AD, and thus may be a valuable animal model to study motor deficits in AD. Therefore, we assessed age-related changes in motor ability of male and female 5xFAD mice from 3 to 16 months of age, using a battery of behavioral tests. At 9-10 months, 5xFAD mice showed reduced body weight, reduced rearing in the open-field and impaired performance on the rotarod compared to wild-type controls. At 12-13 months, 5xFAD mice showed reduced locomotor activity on the open-field, and impaired balance on the balance beam. At 15-16 months, impairments were also seen in grip strength. Although sex differences were observed at specific ages, the development of motor dysfunction was similar in male and female mice. Given the 5xFAD mouse is commonly on a C57BL/6 × SJL hybrid background, a subset of mice may be homozygous recessive for the Dysf im mutant allele, which leads to muscular weakness in SJL mice and may exacerbate motor dysfunction. We found small effects of Dysf im on motor function, suggesting that Dysf im contributes little to motor dysfunction in 5xFAD mice. We conclude that the 5xFAD mouse may be a useful model to study mechanisms that produce motor dysfunction in AD, and to assess the efficacy of therapeutics on ameliorating motor impairment.

Brain glucose hypometabolism has been observed in Alzheimer’s disease (AD) patients, and is detected with 18 F radiolabelled glucose, using positron emission tomography. A pathological hallmark of AD is deposition of brain β - amyloid plaques that may influence cerebral glucose metabolism. The five times familial AD (5XFAD) mouse is a model of brain amyloidosis exhibiting AD-like phenotypes. This study examines brain β -amyloid plaque deposition and 18 FDG uptake, to search for an early biomarker distinguishing 5XFAD from wild-type mice. Thus, brain 18 FDG uptake and plaque deposition was studied in these mice at age 2, 5 and 13 months. The 5XFAD mice demonstrated significantly reduced brain 18 FDG uptake at 13 months relative to wild-type controls but not in younger mice, despite substantial β - amyloid plaque deposition. However, by comparing the ratio of uptake values for glucose in different regions in the same brain, 5XFAD mice could be distinguished from controls at age 2 months. This method of measuring altered glucose metabolism may represent an early biomarker for the progression of amyloid deposition in the brain. We conclude that brain 18 FDG uptake can be a sensitive biomarker for early detection of abnormal metabolism in the 5XFAD mouse when alternative relative uptake values are utilized.

We examined measures of locomotor and anxiety-like behavior in male and female mice of 15 inbred strains on the elevated-plus maze, light/dark transition box and open field. Strain differences were found on all measures of locomotor activity and anxiety. Strain means for measures of locomotor activity on the three apparatus were significantly correlated, but strain means for commonly used measures of anxiety were not correlated. Principal component analysis revealed a common locomotor activity factor, which accounted for 28.6 % of the variance, but no common anxiety factor. Species-typical behaviors (defecations, stretch-attend postures, grooming) accounted for smaller proportions (

The Barnes maze is a visuo-spatial learning and memory test originally designed for use with rats, and later adapted for use with mice. The Barnes maze design and test procedure vary across studies using mice, but the effects of variation in Barnes maze design and test procedure on learning and memory in mice have not yet been investigated. Therefore the present experiment investigates whether test procedures, such as the number of habituation trials and parameters of the probe trial (correct zone size and trial length) influence learning and memory performance on three Barnes maze designs that differed in size and the presence of a wall with intra-maze visual cues. Performance was compared across the three mazes to determine how apparatus design influences visuo-spatial cue use. The number of habituation trials and parameters of the probe trial had small effects on learning and memory performance. Apparatus design, had little effect on acquisition performance but had a significant effect on memory performance. Mice on a maze with a small diameter, external wall and intra-maze visual cues had very poor visuo-spatial memory relative to mice tested on small and large diameter mazes without a wall or intra-maze visual cues. Assessment of visuo-spatial cue use indicated that mice do not rely on visuo-spatial cues to locate the escape hole on the small-diameter maze with a wall and intra-maze visual cues, but show reliable visuo-spatial cue use on small or large diameter mazes with no wall. These results indicate that apparatus design influences search strategy use and memory performance on the Barnes maze, and that including a wall around the edge of the Barnes maze decreases visuo-spatial cue use.

Hygrothermal assessment is the combined analysis of heat, air and moisture transfer through the building fabric. The two approaches are covered by conventions known as the IS EN 5250:2011 (Glaser method) and IS EN 15026:2007 which differs from Glaser by solving the equations numerically using computer software. Results for hygrothermal analysis provide valuable information for surface and interstitial condensation risk assessment and the impact of energy upgrades. For traditional solid walled structures, conditions such as wind driven rain (WDR) and rising ground water can have a significant impact on the environmental behaviour and in particular the moisture behaviour of the building envelope. The convention IS EN 5250:2011 is still widely used to assess the moisture performance of buildings and their components, even though it is not a comprehensive assessment methodology as it fails to include the movement of liquid water and for solid wall structures in particular, it is imperative that all forms of moisture movement are assessed. This research sets out a design methodology, to establish the hygrothermal performance of rendered solid brick wall constructions to ultimately establish the optimum and most appropriate retrofit intervention. The methodology chosen establishes all material properties of a monitored wall. A weather station is used to establish all weather data for the site. The building, will be monitored initially for a 12 month period to determine its hygrothermal condition. The data logged monitoring will establish the temperature and RH profile through the wall. The data from this monitoring will be inputted to software which meets the IS EN15026:2007 convention-a dynamic model which assesses the movement of water both as a vapour and as a liquid.

We have previously shown that apparatus design can affect visual–spatial cue use and memory performance of mice on the Barnes maze. The present experiment extends these findings by determining the optimal behavioral measures and test procedure for analyzing visuo-spatial learning and memory in three different Barnes maze designs. Male and female C57BL/6J mice were trained with a stable or random escape hole location and the sensitivities (statistical power) of four commonly used measures of learning and three measures of memory to detect differences between these training procedures were compared on each maze design. A maze design with a large diameter and no wall was optimal, because mice showed a reliable use of extra-maze visual cues, visuo-spatial search strategies, and spatial memory. A maze design with a small diameter, surrounding wall, and intra-maze visual cues was the least sensitive for determining visuo-spatial learning and memory, because mice showed little evidence of extra-maze cue use. Errors, distance traveled, and hole deviation scores were more sensitive measures of learning than latency to find the escape hole. Measures based on locating the escape hole (primary measures) were more sensitive than measures based on entering the escape hole (total measures). Measures of memory had similar levels of sensitivity on each maze. This experiment demonstrates that both apparatus design and the behavioral measures used as indicators of learning and memory can influence the ability of the Barnes maze to detect visuo-spatial learning and memory impairments in mice.

Rodent self-grooming is an important, evolutionarily conserved behavior, highly sensitive to pharmacological and genetic manipulations. Mice with aberrant grooming phenotypes are currently used to model various human disorders. Therefore, it is critical to understand the biology of grooming behavior, and to assess its translational validity to humans. The present in-silico study used publicly available gene expression and behavioral data obtained from several inbred mouse strains in the open-field, light-dark box, elevated plus- and elevated zero-maze tests. As grooming duration differed between strains, our analysis revealed several candidate genes with significant correlations between gene expression in the brain and grooming duration. The Allen Brain Atlas, STRING, GoMiner and Mouse Genome Informatics databases were used to functionally map and analyze these candidate mouse genes against their human orthologs, assessing the strain ranking of their expression and the regional distribution of expression in the mouse brain. This allowed us to identify an interconnected network of candidate genes (which have expression levels that correlate with grooming behavior), display altered patterns of expression in key brain areas related to grooming, and underlie important functions in the brain. Collectively, our results demonstrate the utility of large-scale, high-throughput data-mining and in-silico modeling for linking genomic and behavioral data, as well as their potential to identify novel neural targets for complex neurobehavioral phenotypes, including grooming.

Postnatal development of the mammalian geniculostriate visual pathway is partly guided by visually driven activity. Disruption of normal visual input during certain critical periods can alter the structure of neurons, as well as their connections and functional properties. Within the layers of the dorsal lateral geniculate nucleus (dLGN), a brief early period of monocular deprivation can alter the structure and soma size of neurons within deprived-eye-receiving layers. This modification of structure is accompanied by a marked reduction in labeling for neurofilament protein, a principle component of the stable cytoskeleton. This study examined the extent of neurofilament recovery in monocularly deprived cats that either had their deprived eye opened (binocular recovery), or had the deprivation reversed to the fellow eye (reverse occlusion). The loss of neurofilament and the reduction of soma size caused by monocular deprivation were ameliorated equally and substantially in both recovery conditions after 8 days. The degree to which this recovery was dependent on visually driven activity was examined by placing monocularly deprived animals in complete darkness. Though monocularly deprived animals placed in darkness showed recovery of soma size in deprived layers, the manipulation catalyzed a loss of neurofilament labeling that extended to non-deprived layers as well. Overall, these results indicate that both recovery of soma size and neurofilament labeling is achieved by removal of the competitive disadvantage of the deprived eye. However, while the former occurred even in the absence of visually driven activity, recovery of neurofilament did not. The finding that a period of darkness produced an overall loss of neurofilament throughout the dLGN suggests that this experiential manipulation may cause the visual pathways to revert to an earlier more plastic developmental stage. It is possible that short periods of darkness could be incorporated as a component of therapeutic measures for treatment of deprivation-induced disorders such as amblyopia.

Visuo-spatial learning and memory were assessed in male and female mice of 13 inbred strains on a small diameter mouse version of the Barnes maze surrounded by a wall and intra-maze visual cues. Mice completed acquisition and reversal training to assess learning, followed by a probe test to assess memory for the spatial location of the escape hole. The C57BL/6J and CAST/EiJ strains showed better learning performance than the other strains. A/J and 129/SvImJ strains showed poor learning performance, which may be due to their low rates of exploration. No differences in memory were found between strains in the probe test. Males showed better learning performance than females in the DBA/2J and C3H/HeJ strains, but there were no sex differences in the other strains. However, mice may not have used visuo-spatial cues to locate the escape hole in this maze, as (1) all strains primarily used the non-spatial serial/thigmotaxic search strategy, (2) no strains showed a reversal effect when the escape hole location was moved, and (3) learning and memory performance were not correlated with measures of visual ability. Multivariate and univariate analyses of variance indicated that mice with good visual ability performed better than mice with poor visual ability, but the effect sizes were small. The small diameter of the maze and the presence of a wall around the edge of the maze may promote thigmotaxis in mice, increasing the use of a non-visual search strategy, thereby reducing the influence of vision on performance and decreasing the sensitivity of this maze design to detect strain differences in visuo-spatial learning and memory. These results indicate that the design of the Barnes maze has a significant effect on learning and memory processes.

Batteries of tests that are thought to measure different aspects of anxiety-related behaviour are used to characterise mice after genetic or pharmacological manipulation. However, because of the potentially confounding effects of repeated testing and natural intra-individual variations in behaviour over time, subjecting mice to a succession of tests is not ideal.The aim of this study was to investigate, in mice, the utility of an integrated apparatus that combines three classical tests of anxiety, the open field, elevated plus maze (EPM) and light/dark box.Mice from four different strains (CD-1, BALB/cJ, DBA/2J, C57BL/6J) were used in a series of five experiments where their behaviour was observed for 15 min in the integrated apparatus. Responses to anxiety-modulating drugs and 2-day repeated testing were evaluated.CD-1 mice explored the apparatus thoroughly, providing measures from all areas throughout the entire testing session. Factor analysis showed that measures of locomotion and anxiety-related behaviour were dissociable. BALB/cJ, DBA/2J and C57BL/6J showed markedly different behavioural profiles, largely consistent with previous studies examining individual tests. Avoidance of aversive environments did not increase with repeated testing. In CD-1 mice, the anxiolytics diazepam and alprazolam (4 and 2 mg/kg, respectively) increased the approach towards the EPM open arms. Alprazolam also had sedative effects, whereas the anxiogenic pentylenetetrazole had no effects.These findings suggest that the triple test is sensitive to genetic/pharmacological influences on anxiety and locomotion and that, by providing quasi-simultaneous measures from three different apparatuses, it may represent an alternative to the use of test batteries.

The APPswe/PS1dE9 mouse is a double transgenic model of Alzheimer's disease, which harbors mutant mouse/human amyloid precursor protein (Swedish K594N/M595L) and presenilin-1 genes (PS1-dE9). These mice develop beta-amyloid plaques and exhibit visuo-spatial learning and memory impairment in the Morris water maze (MWM) at 8-12 and 16-18 months of age. To extend these findings, we tested visuo-spatial learning and memory of male and female APPswe/PS1dE9 mice at 16 months of age on the Barnes maze. APPswe/PS1dE9 mice showed impaired acquisition learning using measures of latency, distance traveled, errors and hole deviation scores, and were less likely to use the spatial search strategy to locate the escape hole than wild-type mice. APPswe/PS1dE9 mice also showed a deficit in memory in probe tests on the Barnes maze relative to wild-type mice. Learning and memory deficits, however, were not found during reversal training and reversal probe tests. Sex differences were observed, as male APPswe/PS1dE9 mice had smaller reversal effects than male wild-type mice, but females of each genotype did not differ. Overall, these results replicate previous findings using the MWM, and indicate that APPswe/PS1dE9 mice have impaired visuo-spatial learning and memory at 16 months of age.