Chronic social defeat stress in prairie voles (Microtus ochrogaster): A preclinical model for the study of depression-related phenotypes

BACKGROUND

Stress-induced illnesses, like major depression, are among the leading causes of disability across the world. Consequently, there is a dire need for the validation of translationally-suited animal models incorporating social stress to uncover the etiology of depression. Prairie voles (Microtus ochrogaster) are more translationally relevant than many other rodent models as they display monogamous social and bi-parental behaviors. Therefore, we evaluated whether a novel social defeat stress (SDS) model in male prairie voles induces depression-relevant behavioral outcomes.

METHODS

Adult sexually-naïve male prairie voles experienced SDS bouts from a conspecific pair-bonded male aggressor, 10 min per day for 10 consecutive days. Non-stressed controls (same-sex siblings) were housed in similar conditions but never experienced physical stress. Twenty-four h later, voles were evaluated in social interaction, sucrose preference, and Morris water maze tests - behavioral endpoints validated to assess social withdrawal, anhedonia-related behavior, and spatial memory performance, respectively.

RESULTS

SDS-exposed voles displayed lower sociability and body weight, decreased preference for a sucrose solution, and impairment of spatial memory retrieval. Importantly, no differences in general locomotor activity were observed as a function of SDS exposure.

LIMITATIONS

This study does not include female voles in the experimental design.

CONCLUSIONS

We found that repeated SDS exposure, in male prairie voles, results in a depression-relevant phenotype resembling an anhedonia-like outcome (per reductions in sucrose preference) along with social withdrawal and spatial memory impairment - highlighting that the prairie vole is a valuable model with potential to study the neurobiology of social stress-induced depression-related outcomes.

Intermittent working memory training during adulthood protects against age-related long-term spatial reference memory decline in rats

Engagement in cognitive activity in adulthood is one of the factors that enable successful cognitive aging, both in humans and rodents. However, some studies emphasize that the beneficial effect on cognition of such an activity may reflect carry over from one test situation to another, including memory for procedural aspects of the behavioral tasks, and thus question whether this effect can be limited to the trained cognitive domain or whether it can be transferred to an untrained ones. In the current study, we assessed whether adulthood intermittent working memory training has beneficial effect on long-term memory of aged rats using two very different test situations. To this aim, rats trained in a delayed non-matching to position task in operant box at 3 and 15 months of age were tested in a place learning task in water maze when they were 24 months. The two tasks differ with regard to the cognitive domain but also in their spatial ability requirement and the nature of the reinforcer used. During the memory tests, accuracy of the platform search indicated age-related impairment only in the aged-untrained group. Thus, intermittent training during adult life in a task involving working memory protects aged animals from the deleterious effects of aging on spatial reference memory. This result highlights the long-term beneficial effects of training on a working memory task on an untrained cognitive domain.

Sex-Specific Alterations in Spatial Memory and Hippocampal AKT-mTOR Signaling in Adult Mice Pre-exposed to Ketamine and/or Psychological Stress During Adolescence

Background

Ketamine (KET) is administered to manage major depression in adolescent patients. However, the long-term effects of juvenile KET exposure on memory-related tasks have not been thoroughly assessed. We examined whether exposure to KET, psychological stress, or both results in long-lasting alterations in spatial memory in C57BL/6 mice. Furthermore, we evaluated how KET and/or psychological stress history influenced hippocampal protein kinase B-mechanistic target of rapamycin (AKT-mTOR)-related signaling.

Methods

On postnatal day 35, male and female mice underwent vicarious defeat stress (VDS), a form of psychological stress that reduces sociability in both sexes, with or without KET exposure (20 mg/kg/day, postnatal days 35-44). In adulthood (postnatal day 70), mice were assessed for spatial memory performance on a water maze task or euthanized for hippocampal tissue collection.

Results

Juvenile pre-exposure to KET or VDS individually increased the latency (seconds) to locate the escape platform in adult male, but not female, mice. However, juvenile history of concomitant KET and VDS prevented memory impairment. Furthermore, individual KET or VDS pre-exposure, unlike their combined history, decreased hippocampal AKT-mTOR signaling in adult male mice. Conversely, KET pre-exposure alone increased AKT-mTOR in the hippocampus of adult female mice. Lastly, rapamycin-induced decreases of mTOR in naïve adult female mice induced spatial memory retrieval deficits, mimicking adult male mice with a history of exposure to VDS or KET.

Conclusions

Our preclinical model shows how KET treatment for the management of adolescent psychological stress-induced sequelae does not impair spatial memory later in life. However, juvenile recreational KET misuse, like psychological stress history, results in long-term spatial memory deficits and hippocampal AKT-mTOR signaling changes in a sex-specific manner.

Xanthohumol improves cognition in farnesoid X receptor-deficient mice on a high-fat diet

Xanthohumol (XN) improves cognition of wild-type rodents on a high-fat diet (HFD). Bile acids and ceramide levels in the liver and hippocampus might be linked to these effects. XN modulates activity of the nuclear farnesoid X receptor (FXR; also known as NR1H4), the primary receptor for bile acids. To determine the role of FXR in the liver and intestine in mediating the effects of XN on cognitive performance, mice with intestine- and liver-specific FXR ablation (FXRIntestine-/- and FXRLiver-/-, respectively) on an HFD or an HFD containing XN were cognitively tested. XN improved cognitive performance in a genotype- and sex-dependent manner, with improved task learning in females (specifically wild-type), reversal learning in males (specifically wild-type and FXRIntestine-/- mutant) and spatial learning (both sexes). XN increased hippocampal diacylglycerol and sphingomyelin levels in females but decreased them in males. XN increased the ratio of shorter-chain to longer-chain ceramides and hexaceramides. Higher diacylglycerol and lower longer-chain ceramide and hexaceramide levels were linked to improved cognitive performance. Thus, the beneficial sex-dependent cognitive effects of XN are linked to changes in hippocampal diacylglycerol and ceramide levels. This article has an associated First Person interview with the first author of the paper.

Effects of Toll-like receptor 4 inhibition on spatial memory and cell proliferation in male and female adult and aged mice

Toll-like receptors (TLRs) participate in the response to infection, stress, and injury by initiating an innate immune response. In addition, these receptors are expressed in many neural cell types and under physiological conditions are implicated in modulating cognitive function and neural plasticity in the adult and aged brain. Knockout of the Toll-like receptor 4 (TLR4) subtype enhances spatial memory and adult hippocampal neurogenesis through increasing proliferation and neuronal differentiation. Currently unknown is whether pharmacological inhibition of TLR4 produces similar enhancements in cognitive function and cell proliferation. The present study evaluated water maze performance, cytokine expression, and cell proliferation in the hippocampus of young and aged male and female C57BL6/J mice following treatment with the TLR4 antagonist, TAK-242. Further, alterations in the response to an acute stressor were evaluated in TAK-242-treated mice. Results showed that TAK-242 selectively enhanced spatial learning and memory in young females. Additionally, TAK-242 treatment reduced thigmotaxis in the water maze and lowered corticosterone levels following acute stress in females. TAK-242 decreased hippocampal interleukin (IL)-1β expression but had no effect on IL-6 or tumor necrosis factor-α (TNFα). Aged mice showed decreased cell proliferation compared to young mice, but TAK-242 administration had minimal effects on estimated Ki67 positive cell numbers. Findings indicate that pharmacological inhibition of TLR4 improves cognitive function in young females likely through attenuating stress reactivity.

Role of the parental NF1 carrier in effects of pharmacological inhibition of anaplastic lymphoma kinase in Neurofibromatosis 1 mutant mice

Neurofibromatosis type 1 (NF1), a genetically determined neurodevelopmental disorder and tumor syndrome, is associated with cognitive impairments, including in executive function and sleep-related problems. Consistent with the human data, NF1 heterozygous (Het) mice show impaired spatial learning and memory in the water maze and extinction of contextual fear memory. It is not clear whether neurological phenotypes might depend on the parental carrier. In this study, we compared the behavioral and cognitive performance of NF1 Het and wild-type litter mates with either the father (PC) or the mother (MC) as the NF1 carrier on a F1 C57BL/66/129SvJ background. The behavioral and cognitive phenotypes and responsiveness to Alk inhibition in heterozygous NF1 offspring depended on whether the parental carrier was maternal or paternal. Alk inhibition (20 mg/kg) increased activity levels during the dark period in NF1 Het PC, but not MC, mice. In the water maze, NF1 Het PC, but not MC, mice showed reduced cognitive flexibility and impaired ability to locate the third hidden platform location, which was improved by Alk inhibition (3.6 mg/kg). Consistent with reduced cognitive flexibility, WT, but not NF1, mice showed better performance in the third than second water maze probe trial. Finally, Alk inhibition (10 mg/kg) increased baseline activity of NF1 MC, but not PC, mice during the fear conditioning test. Thus, the effective dose depends on the behavioral test and genotype but indicates that in NF1 patients cognitive flexibility might be particularly sensitive to Alk inhibition.

Hippocampal gray matter volume in the long-term course after transient global amnesia

•

No substantial hippocampus-dependent memory deficits in the long-term course after transient global amnesia.

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Greater hippocampal gray matter volume in patients with transient global amnesia compared to healthy controls in the long-term course.

•

Transient global amnesia might trigger neuronal and/or non-neuronal mechanisms in the hippocampus resulting in an increase of grey matter rather than atrophy.

Objective

In this retrospective, cross-sectional study we aimed to examine long-term memory deficits and gray matter volumes (GMV) in the hippocampus after transient global amnesia (TGA).

Methods

20 patients with a history of TGA (TGA+, mean 6.5 years after TGA) and 20 age-matched healthy controls (TGA-) underwent neurocognitive assessment (i.e. Mini-Mental State Examination (MMSE), visuospatial, verbal and episodic autobiographical memory and visuospatial learning/navigation [“human water maze”]) in combination with structural cerebral MRI. Voxel-based morphometry (VBM) was used to detect GMV in the hippocampus in TGA+ versus TGA-.

Results

Besides slight differences in MMSE and visuo-spatial learning/navigation measured with a human water maze in TGA+ vs. TGA-, no other tests of visuo-spatial, verbal and autobiographical long-term memory differed between groups. VBM analyses yielded a statistically significant difference in bilateral hippocampal GMV with TGA+ compared to TGA- showing greater GMV in a region corresponding to bilateral CA1. However, none of the hippocampus-dependent cognitive measures correlated with hippocampal GMV.

Conclusion

In the long-term course after TGA, only subtle neurocognitive deficits without microstructural damage of the hippocampus could be detected. Greater GMV in bilateral hippocampus in TGA+ vs. TGA- may indicate that TGA triggers hippocampal GMV increase rather than atrophy.

Decreased investigatory head scanning during exploration in learning-impaired, aged rats

"Head scanning" is an investigatory behavior that has been linked to spatial exploration and the one-trial formation or strengthening of place cells in the hippocampus. Previous studies have demonstrated that a subset of aged rats with normal spatial learning performance show head scanning rates during a novel, local-global cue-mismatch manipulation that are similar to those of young rats. However, these aged rats demonstrated different patterns of expression of neural activity markers in brain regions associated with spatial learning, perhaps suggesting neural mechanisms that compensate for age-related brain changes. These prior studies did not investigate the head scanning properties of aged rats that had spatial learning impairments. The present study analyzed head scanning behavior in young, aged-unimpaired, and aged-impaired Long Evans rats. Aged-impaired rats performed the head scan behavior at a lower rate than the young rats. These results suggest that decreased attention to spatial landmarks may be a contributing factor to the spatial learning deficits shown by the aged-impaired rats.

NavWell: A simplified virtual-reality platform for spatial navigation and memory experiments

Being able to navigate, recall important locations, and find the way home are critical skills, essential for survival for both humans and animals. These skills can be examined in the laboratory using the Morris water maze, often considered the gold standard test of animal navigation. In this task, animals are required to locate and recall the location of an escape platform hidden in a pool filled with water. Because animals can not see the platform directly, they must use various landmarks in the environment to escape. With recent advances in technology and virtual reality (VR), many tasks originally used in the animal literature can now be translated for human studies. The virtual water maze task is no exception. However, a number of issues are associated with these mazes, including cost, lack of flexibility, and lack of standardization in terms of experimental designs and procedures. Here we present a virtual water maze system (NavWell) that is readily downloadable and free to use. The system allows for the easy design of experiments and the testing of participants on a desktop computer or fully immersive VR environment. The data from four independent experiments are presented in order to validate the software. From these experiments, a set of procedures for use with a number of well-known memory tests is suggested. This potentially can help with the standardization of navigational research and with navigational testing in the clinic or in an educational environment. Finally, we discuss the limitations of the software and plans for its development and future use.

Programming effects of peripubertal stress on spatial learning

Exposure to adversity during early life can have profound influences on brain function and behavior later in life. The peripubertal period is emerging as an important time-window of susceptibility to stress, with substantial evidence documenting long-term consequences in the emotional and social domains. However, little is known about how stress during this period impacts subsequent cognitive functioning. Here, we assessed potential long-term effects of peripubertal stress on spatial learning and memory using the water maze task. In addition, we interrogated whether individual differences in stress-induced behavioral and endocrine changes are related to the degree of adaptation of the corticosterone response to repeated stressor exposure during the peripubertal period. We found that, when tested at adulthood, peripubertally stressed animals displayed a slower learning rate. Strikingly, the level of spatial orientation in the water maze completed on the last training day was predicted by the degree of adaptation of the recovery -and not the peak-of the corticosterone response to stressor exposure (i.e., plasma levels at 60 min post-stressor) across the peripubertal stress period. In addition, peripubertal stress led to changes in emotional and glucocorticoid reactivity to novelty exposure, as well as in the expression levels of the plasticity molecule PSA-NCAM in the hippocampus. Importantly, by assessing the same endpoints in another peripubertally stressed cohort tested during adolescence, we show that the observed effects at adulthood are the result of a delayed programming manifested at adulthood and not protracted effects of stress. Altogether, our results support the view that the degree of stress-induced adaptation of the hypothalamus-pituitary-adrenal axis responsiveness at the important transitional period of puberty relates to the long-term programming of cognition, behavior and endocrine reactivity.

Learning and aging affect neuronal excitability and learning

The first study that demonstrated a change in intrinsic neuronal excitability after learning in ex vivo brain tissue slices from a mammal was published over thirty years ago. Numerous other manuscripts describing similar learning-related changes have followed over the years since the original paper demonstrating the postburst afterhyperpolarization (AHP) reduction in CA1 pyramidal neurons from rabbits that learned delay eyeblink conditioning was published. In addition to the learning-related changes, aging-related enlargement of the postburst AHP in CA1 pyramidal neurons have been reported. Extensive work has been done relating slow afterhyperpolarization enhancement in CA1 hippocampus to slowed learning in some aging animals. These reproducible findings strongly implicate modulation of the postburst AHP as an essential cellular mechanism necessary for successful learning, at least in learning tasks that engage CA1 hippocampal pyramidal neurons.

Long-term cognitive impairment without diffuse axonal injury following repetitive mild traumatic brain injury in rats

Repetitive mild traumatic brain injuries (TBI) impair cognitive abilities and increase risk of neurodegenerative disorders in humans. We developed two repetitive mild TBI models in rats with different time intervals between successive weight-drop injuries. Rats were subjected to repetitive Sham (no injury), single mild (mTBI), repetitive mild (rmTBI - 5 hits, 24 h apart), rapid repetitive mild (rapTBI - 5 hits, 5 min apart) or a single severe (sTBI) TBI. Cognitive performance was assessed 2 and 8 weeks after TBI in the novel object recognition test (NOR), and 6-7 weeks after TBI in the water maze (MWM). Acute immunohistochemical markers were evaluated 24 h after TBI, and blood biomarkers were measured with ELISA 8 weeks after TBI. In the NOR, both rmTBI and rapTBI showed poor performance at 2 weeks post-injury. At 8 weeks post-injury, the rmTBI group still performed worse than the Sham and mTBI groups, while the rapTBI group recovered. In the MWM, the rapTBI group performed worse than the Sham and mTBI groups. Acute APP and RMO-14 immunohistochemistry showed axonal injury at the pontomedullary junction in the sTBI, but not in other groups. ELISA showed increased serum GFAP levels 8 weeks after sTBI, while no differences were found between the injury groups in the levels of phosphorylated-tau and S100β. Results suggest that the rmTBI protocol is the most suitable model for testing cognitive impairment after mild repetitive head injuries and that the prolonged cognitive impairment after repetitive mild TBI originates from different structural and molecular mechanisms compared to similar impairments after single sTBI.

Long-term administration of Aspalathus linearis infusion affects spatial memory of adult Sprague-Dawley male rats as well as increases their striatal dopamine content

ETHNOPHARMACOLOGICAL RELEVANCE

Everyday use of the herbal tea rooibos, produced from Aspalathus linearis (Brum.f) Dahlg. (Fabaceae) is customary in South Africa, a continuation of its historical use by indigenous people. Although evidence of its traditional indications is anecdotal, rooibos tea is regarded as a general health tea.

AIMS OF THE STUDY

Available contemporary research indicates to broad cell protective activity of rooibos focusing on its antioxidative, anti-inflammatory, anti-hyperglycaemic and antithrombotic features affecting metabolic syndrome, cardiovascular risk and neuroprotection. Nevertheless little is known about its impact on brain functions. The present experiment aimed to evaluate the possible behavioural and neurochemical effects of long-term oral administration of "fermented"" rooibos herbal tea (FRHT) infusions to adult male Sprague-Dawley rats.

MATERIALS AND METHODS

Infusions, prepared using 1, 2 and 4 g of "fermented"" (oxidised) A. linearis leaves for 100 ml of hot water, were characterised in terms of flavonoid content by ultra-high and high performance liquid chromatography (UHPLC-qTOF-MS, HPLC-DAD) and administered to rats as sole drinking fluid for 12 weeks. Spatial memory behaviour was assessed in a modified version of the Morris water maze. Dopamine, noradrenaline, serotonin and their metabolite levels (DOPAC, 3-MT, HVA, MHPG, 5-HIAA) were quantified in prefrontal cortex, hippocampus and striatum by HPLC-ECD. Body weight and blood glucose level were additionally estimated.

RESULTS

All FRHT-treated rats showed improvement of long-term spatial memory defined as increased number of crossings over the previous platform position in SE quadrant of the water maze. It was not accompanied by excessive motor activity. Striatal dopamine and its metabolite 3-MT (3-methoxytyramine) levels were increased in treated rats. There were no differences in body weight gain between control and treated animals but blood glucose level was significantly lower in the latter ones.

CONCLUSION

The improvement of long-term memory in FRHT-treated rats and stimulating impact of FRHT on their dopaminergic striatal transmission support the wellness enhancing effect of rooibos tea, contributing to a better understanding of the neurological background of traditional habitual consumption of this herbal tea.

Assessment of Cognitive Phenotyping in Inbred, Genetically Modified Mice, and Transgenic Mouse Models of Alzheimer's Disease

Genetically modified mouse models are being used predominantly to understand brain functions and diseases. Well-designed and controlled behavioral analyses of genetically modified mice have successfully led to the identification of gene functions, understanding of brain diseases, and development of treatments. Recently, complex and higher cognitive functions have been examined in mice with genetic mutations. Therefore, research strategies for cognitive phenotyping should be sophisticated and evolve to convey the exact meaning of the findings and provide robust translational tools for testing hypotheses and developing treatments. This review addresses issues of experimental design and discusses studies that have examined cognitive function using mouse strain differences, genetically modified mice, and transgenic mice for Alzheimer's disease.

Young and aged TLR4 deficient mice show sex-dependent enhancements in spatial memory and alterations in interleukin-1 related genes

Toll-like receptor-4 (TLR4) is a transmembrane receptor that initiates an immune response following a bacterial infection or host derived molecules associated with cellular distress. Beyond triggering inflammation, TLR4 has been implicated in modulating behavioral and cognitive processes in a physiologically normal state, as young adult TLR4 deficient mice show learning enhancements in select tasks. Currently unknown is whether these benefits are present in both sexes and persist with aging. The present study evaluated spatial memory, anxiety-like behavior, and central levels of pro- and anti-inflammatory molecules in young (4-5 months) and aged (18-19 months) TLR4 deficient (TLR4-/-) and wild-type (WT) male and female mice. Results confirmed that TLR4-/- mice show enhanced spatial memory compared to WT mice. These effects were age- and sex-specific, as memory retention was superior in the TLR4-/- young males and aged females. While TLR4-/- mice showed age-related changes in behavior, these changes were attenuated relative to aged WT mice. Further, aged TLR4-/- mice showed differential expression of molecules involved in interleukin (IL)-1 signaling in the hippocampus. For instance, aged TLR4-/- females showed heightened expression of IL-1 receptor antagonist (IL-1ra) and the IL-1 accessory proteins AcP and AcPb. Collectively, these data provide the initial evidence that TLR4 deficiency enhances cognitive function and modulates the inflammatory profile of the hippocampus in a sex- and age-dependent manner.

Relevance of electroencephalogram assessment in amyloid and tau pathology in rat

In order to contribute to a better knowledge on the relationship between amyloid and tau pathology, and electroencephalography (EEG) disturbances, the aim of this study was to evaluate the effects of injection of beta amyloid Abeta(1-42) peptide, tau (a recombinant AAV (Adeno-Associated Virus) containing the human transgene tau with the P301 L mutation on rats and the combination of both, on the power of brain's rhythm (delta, theta, alpha, beta and gamma waves) during the different sleep/wake states of animals by EEG recording. Currently, no preclinical studies explore the effect of the tau pathology on EEG. The experimentations were performed 3 weeks and 3 months post injections. Beta amyloid deposits and hyperphosphorylated Tau are observed by immunohistofluorescence, only in the hippocampus. Furthermore, using a radial arm water maze, the main effect was observed on working memory which was significantly impaired in Abeta-Tau group only 3 months post injections. However, on EEG, as early as the 3^rd week, an overall decrease of the EEG bands power was observed in the treated groups, particularly the theta waves during the rapid eye movement (REM) sleep. Beta amyloid was mainly involved in these perturbations. Obviously, EEG seems to be an interesting tool in the early diagnostic of amyloid and tau pathologies, with a good sensitivity and the possibility to perform a follow up during a large period.

Maternal voluntary exercise ameliorates learning deficit in rat pups exposed, in utero, to valproic acid; role of BDNF and VEGF and their receptors

In utero exposure to therapeutic doses of valproic acid (VPA) during pregnancy can produce physical malformation and CNS abnormalities in the offspring. There is evidence indicating that even lower doses of VPA during pregnancy could cause cognitive impairment in offspring. It has been demonstrated that maternal exercise has positive effects on offspring's cognitive function. In this study we evaluated the preventive potential of maternal voluntary exercise on cognitive deficits induced by in utero exposure to VPA, in rat pups. Furthermore, the alteration of hippocampal brain-derived neurotrophic factor (BDNF) and vascular endothelial growth factor (VEGF) and their respective receptors were measured. In treatment groups, pregnant rats received VPA (10 and 20 mg/kg) daily on the gestation days (GD) 7 for twelve days with or without access to a running wheel. In control groups, rats received saline with or without access to a running wheel. On postnatal day (PND) 30, learning and memory of rat pups were assessed using the Morris Water Maze (MWM) task. Also, on PND 30, hippocampal BDNF and VEGF were measured by ELISA and western blot analysis respectively. VEGFR (VEGF receptor) and TrkB (Tyrosine receptor kinase B, the receptor for BDNF) expressions were assessed using immunofluorescence staining. Results revealed that maternal voluntary exercise enhanced learning in offspring but had little effect on memory retention. Exposure to VPA during pregnancy disturbed learning and memory in rat pups. Maternal voluntary exercise could ameliorate some aspects of cognitive deficit induced by VPA. TrkB and VEGFR2 expression were enhanced in pups from running mothers. VPA, at both doses, suppressed exercise induced expression of these two receptors. Voluntary exercise and to a much greater extent VPA administration increased hippocampal BDNF. Voluntary exercise of mothers caused an enhance expression of VEGF in rat pups as did VPA administration, although to a smaller amount.

Effects of ethanol and varenicline on female Sprague-Dawley rats in a third trimester model of fetal alcohol syndrome

Perinatal ethanol exposure disrupts a variety of developmental processes in neurons important for establishing a healthy brain. These ethanol-induced impairments known as fetal alcohol spectrum disorder (FASD) are not fully understood, and currently, there is no effective treatment. Further, growing evidence suggests that adult females are more susceptible to ethanol, with the effects of perinatal ethanol exposure also being sexually divergent. Female models have been historically underutilized in neurophysiological investigations, but here, we used a third-trimester binge-ethanol model of FASD to examine changes to basal forebrain (BF) physiology and behavior in female Sprague-Dawley rats. We also tested varenicline as a potential cholinomimetic therapeutic. Rat pups were gavage-treated with binge-like ethanol, varenicline and ethanol, and varenicline alone. Using patch-clamp electrophysiology in BF slices, we observed that binge-ethanol exposure increased spontaneous post-synaptic current (sPSC) frequency. Varenicline exposure alone also enhanced sPSC frequency. Varenicline plus ethanol co-treatment prevented the sPSC frequency increase. Changes in BF synaptic transmission persisted into adolescence after binge-ethanol treatment. Behaviorally, binge-ethanol treated females displayed increased anxiety (thigmotaxis) and demonstrated learning deficits in the water maze. Varenicline/ethanol co-treatment was effective at reducing these behavioral deficits. In the open field, ethanol-treated rats displayed longer distances traveled and spent less time in the center of the open field box. Co-treated rats displayed less anxiety, demonstrating a possible effect of varenicline on this measure. In conclusion, ethanol-induced changes in both BF synaptic transmission and behavior were reduced by varenicline in female rats, supporting a role for cholinergic therapeutics in FASD treatment.

Rats with ventral hippocampal damage are impaired at various forms of learning including conditioned inhibition, spatial navigation, and discriminative fear conditioning to similar contexts

The ventral hippocampus (vHPC) has been implicated in learning and memory functions that seem to differ from its dorsal counterpart. The goal of this series of experiments was to provide further insight into the functional contributions of the vHPC. Our previous work implicated the vHPC in spatial learning, inhibitory learning, and fear conditioning to context. However, the specific role of vHPC on these different forms of learning are not clear. Accordingly, we assessed the effects of neurotoxic lesions of the ventral hippocampus on retention of a conditioned inhibitory association, early versus late spatial navigation in the water task, and discriminative fear conditioning to context under high ambiguity conditions. The results showed that the vHPC was necessary for the expression of conditioned inhibition, early spatial learning, and discriminative fear conditioning to context when the paired and unpaired contexts have high cue overlap. We argue that this pattern of effects, combined with previous work, suggests a key role for vHPC in the utilization of broad contextual representations for inhibition and discriminative memory in high ambiguity conditions.

The Neurogenesis Actuator and NR2B/NMDA Receptor Antagonist Ro25-6981 Consistently Improves Spatial Memory Retraining Via Brain Region-Specific Gene Expression

NR2B-containing NMDA (NR2B/NMDA) receptors are important in controlling neurogenesis and are involved in generating spatial memory. Ro25-6981 is a selective antagonist at these receptors and actuates neurogenesis and spatial memory. Inter-structural neuroanatomical profiles of gene expression regulating adult neurogenesis and neuroapoptosis require examination in the context of memory retrieval and reversal learning. The aim was to investigate spatial memory retrieval and reversal learning in relation to gene expression-linked neurogenetic processes following blockade of NR2B/NMDA receptors by Ro25-6981. Rats were trained in Morris water maze (MWM) platform location for 5 days. Ro25-6981 was administered (protocol days 6–7) followed by retraining (days 15–18 or 29–32). Platform location was tested (on days 19 or 33) then post-mortem brain tissue sampling (on days 20 or 34). The expression of three genes known to regulate cell proliferation (S100a6), differentiation (Ascl1), and apoptosis (Casp-3) were concomitantly evaluated in the hippocampus, prefrontal cortex, and cerebellum in relation to the MWM performance protocol. Following initial training, Ro25-6981 enhanced visuospatial memory retrieval performance during further retraining (protocol days 29–32) but did not influence visuospatial reversal learning (day 33). Hippocampal Ascl1 and Casp-3 expressions were correspondingly increased and decreased while cerebellar S100a6 and Casp-3 activities were decreased and increased respectively 27 days after Ro25-6981 treatment. Chronological analysis indicated a possible involvement of new mature neurons in the reconfiguration of memory processes. This was attended by behavioral/gene correlations which revealed direct links between spatial memory retrieval enhancement and modified gene activity induced by NR2B/NMDA receptor blockade and upregulation.

Negative transfer effects between reference memory and working memory training in the water maze in C57BL/6 mice

The water maze is one of the most widely employed spatial learning paradigms in the cognitive profiling of genetically modified mice. Oftentimes, tests of reference memory (RM) and working memory (WM) in the water maze are sequentially evaluated in the same animals. However, critical difference in the rules governing efficient escape from the water between WM and RM tests is expected to promote the adoption of incompatible mnemonic or navigational strategies. Hence, performance in a given test is likely poorer if it follows the other test instead of being conducted first. Yet, the presence of such negative transfer effects (or proactive interference) between WM and RM training in the water maze is often overlooked in the literature. To gauge whether this constitutes a serious concern, the present study determined empirically the magnitude, persistence, and directionality of the transfer effect in wild-type C57BL/6 mice. We contrasted the order of tests between two cohorts of mice. Performance between the two cohorts in the WM and RM tests were then separately compared. We showed that prior training of either test significantly reduced performance in the subsequent one. The statistical effect sizes in both directions were moderate to large. Although extended training could overcome the deficit, it could re-emerge later albeit in a more transient fashion. Whenever RM and WM water maze tests are conducted sequentially in the same animals - regardless of the test order, extra caution is necessary when interpreting the outcomes in the second test. Counterbalancing test orders between animals is recommended.

Effect of Fluoxetine on the Hippocampus of Wistar Albino Rats in Cold Restraint Stress Model

INTRODUCTION

Stress has been known to be a potential modulator of learning and memory. Long term stress can lead to depression. Fluoxetine is a selective serotonin reuptake inhibitor group of drug used in the treatment of depression.

AIM

The present study was conducted to evaluate the potential of Fluoxetine on cold restraint induced stress in the hippocampus of Wistar rats.

MATERIALS AND METHODS

A total of 18 male wistar albino rats were divided randomly into three groups (n=6). Group 1 was the control group which were kept in normal laboratory conditions. Group 2 was the negative control group which were given cold restraint stress for period of four weeks. Group 3 was the experimental group, where the animals were pretreated with fluoxetine 10 mg/kg for a period of one week followed by cold restraint stress for 30 minutes and cotreated with fluoxetine 10 mg/kg for a period of four weeks. The whole study was done for a period of five weeks followed by behavioural studies and subsequently sacrificed with removal of brain for various histological, Immunohistochemical (IHC), neurochemical and antioxidant analysis. The values were expressed as Mean±SEM. One-way analysis of variance followed by Tukey's multiple comparisons test was used for the comparison of means. A probability of 0.05 and less was taken as statistically significant using Prism Graphpad software version 6.01.

RESULTS

The results show there was significant improvement in the Morris water maze test after treatment with fluoxetine in Group 2. Similar results were also noted in the levels of neurotransmitters and antioxidant levels in brain and also in the number of cells counted in IHC and histological studies by H&E when Group 3 was compared with Group 2. The treatment reversed the damage in Group 2 which was comparable with the control group.

CONCLUSION

The results revealed that administration of fluoxetine 10 mg/kg given orally has a potential antistressor effect by improving the neurogenic and neuroprotective effect on the cold restraint stress induced hippocampal damage.

Sargassum swartzii extracts ameliorate memory functions by neurochemical modulation in a rat model

Recently, considerable attention has been paid to drug exploration from natural sources for treating memory loss, a major manifestation of various neurodegenerative diseases. Increasing evidences implicate brain serotonin metabolism in learning and memory, supporting the notion that targeting 5-HT (5-hydroxytryptamine) and its receptors would be beneficial in the treatment of cognitive disorders. In the present study, behavioral and neurochemical effects were examined following administration of Sargassum swartzii extracts in albino Wistar rats. Increase in spatial working memory and recognition memory was exhibited by the seaweed-treated rats as compared to controls. Plasma tryptophan, brain 5-HT, and 5-hydroxyindoleacetic acid levels were measured using HPLC-ECD, and a significant increase in brain 5-HT metabolism was observed in the seaweed-treated rats. The increase in memory functions following repeated administration of S. swartzii extracts is suggested to be due to the increased serotonergic neurotransmission in the brain of seaweed-treated rats.

Antioxidant and acetylcholinesterase inhibitory activities in vitro of different fraction of Huperzia squarrosa (Forst.) Trevis extract and attenuation of scopolamine-induced cognitive impairment in mice

ETHNOPHARMACOLOGICAL RELEVANCE

Huperzia squarrosa (Forst.) Trevis is used in traditional medicine for improving memory deficits. Alkaloids, triterpenoids, flavonoids are main bioactive compounds of Huperzia squarrosa (Forst.) Trevis.

AIM OF THE STUDY

This study aimed to investigate the antioxidant, AChE inhibitory activities in vitro of differents fraction of Huperzia squarrosa (Forst.) Trevis extract and neuroprotective effects of EtOAc fraction on scopolamine-induced cognitive impairment in mice.

MATERIALS AND METHODS

Antioxidant activity was measured by DPPH assay. AChE inhibitory effect in vitro and detail kinetic inhibition mechanism was evaluated by Ellman's assay. For in vivo assay, mice were administrated orally EtOAc fraction (150 and 300mg/kg) for fourteen days, and injected scopolamine at a dose of 1mg/kg intraperitoneally for four days to induce memory injured. The memory behaviors were evaluated using the Morris water maze. ACh levels were measured in brain tissue. Superoxide dismutase (SOD), glutathione peroxidase (GPx) activities, malondialdehyde and protein thiol groups were also evaluated in the brains.

RESULTS

Our data also demonstrated that EtOAc fraction had the strongest antioxidant with an IC₅₀ value of 9.35±1.68µg/mL and AChE inhibitory activity with an IC₅₀ value of 23.44±3.14μg/mL in a concentration-dependent manner. Kinetic inhibition analysis indicated that EtOAc fraction was mixed inhibition type with Ki (representing the affinity of the enzyme and inhibitor) was 34.75±1.42µg/mL. Scopolamine significantly increased the escape latency time, reduced the crossings number, and swimming time in the target quadrant, while EtOAc fraction reversed these scopolamine-induced effects. EtOAc fraction significantly increased levels of acetylcholine in the brain. EtOAc fraction also significantly decreased oxidative stress in mice.

CONCLUSION

Our data suggest that EtOAc fraction of Huperzia squarrosa extract exhibited a strong neuroprotective effect on cognitive impairment, and may be a potential candidate for the treatment of Alzheimer.

Interaction between age and perceptual similarity in olfactory discrimination learning in F344 rats: relationships with spatial learning

Emerging evidence suggests that aging is associated with a reduced ability to distinguish perceptually similar stimuli in one's environment. As the ability to accurately perceive and encode sensory information is foundational for explicit memory, understanding the neurobiological underpinnings of discrimination impairments that emerge with advancing age could help elucidate the mechanisms of mnemonic decline. To this end, there is a need for preclinical approaches that robustly and reliably model age-associated perceptual discrimination deficits. Taking advantage of rodents' exceptional olfactory abilities, the present study applied rigorous psychophysical techniques to the evaluation of discrimination learning in young and aged F344 rats. Aging did not influence odor detection thresholds or the ability to discriminate between perceptually distinct odorants. In contrast, aged rats were disproportionately impaired relative to young on problems that required discriminations between perceptually similar olfactory stimuli. Importantly, these disproportionate impairments in discrimination learning did not simply reflect a global learning impairment in aged rats, as they performed other types of difficult discriminations on par with young rats. Among aged rats, discrimination deficits were strongly associated with spatial learning deficits. These findings reveal a new, sensitive behavioral approach for elucidating the neural mechanisms of cognitive decline associated with normal aging.