Reduced risk aversion and impaired short-term memory in juvenile rats with malformation of cortical development

Malformation of cortical developments (MCDs) is currently an incurable disease and is associated with significant neuropsychological problems, such as intellectual disability, epilepsy, and anxiety disorders from a young age. Development of a suitable animal model and pathophysiological study is therefore necessary to better understand and treat MCDs from being an incurable disease. The Y-maze, open field, and fear conditioning studies were performed at postnatal days 40-44 to validate the behavioral phenotypes of the existing rat model of MCD with prenatal methylazoxymethanol exposure at their developmental period. The study results show that juvenile rats with MCD spent significantly less time inside the novel arms in Y-maze and less time in the peripheral zones of the open field. Additionally, the rats with MCDs showed attenuated freezing behavior to sound and light cues as well as to context after fear conditioning. This comprehensive behavioral analysis of rats with MCDs at the juvenile period indicate a lack of spatial memory, decreased anxiety, and learning disability in these rats, which is compatible with the human behavioral phenotype of MCDs and can be used as the behavioral biomarkers for future translational research.

Sex differences in recovery from cognitive and metabolic impairments induced by supplementary sucrose in rats

Consumption of beverages containing around 10% sucrose contributes to worldwide obesity. Studies using rats can increase understanding of the consequences of such consumption. The present experiment aimed to compare male and female rats, first, in terms of cognitive and metabolic impairments produced by excessive intakes of 10% sucrose solution (Stage 1:8 weeks) and, second, with regard to recovery once access to sucrose ceased (Stage 2:4 weeks). All animals had unrestricted access to chow and water throughout. The primary cognitive outcome was performance on a place recognition task. The primary metabolic outcome was retroperitoneal fat pad mass/kg bodyweight at cull, with body weight and glucose tolerance as secondary outcomes. In a 3 × 2 between-subject factorial design the first factor was whether rats had: (1) unlimited access to a 10% sucrose solution and water throughout both stages (Suc-Suc); (2) were switched from sucrose in the 8-week Stage 1 to water only in the 4-week Stage 2 (Suc-Water); or (3) had no access to sucrose in either stage (Water-Water). The second factor was sex. A major metabolic outcome was that of persistent adiposity in both males and females in the Suc-Water condition. As for place recognition, females in the Suc-Suc condition showed greater long-term resistance than males to the impact of excessive sucrose on spatial memory impairment. Overall, few sex differences were found in secondary metabolic outcomes.

Bright light exposure induces dynamic changes of spatial memory in nocturnal rodents

Bright light has been reported to improve spatial memory of diurnal rodents, yet how it will influence the spatial memory of nocturnal rodents is unknown. Here, we found that dynamic changes in spatial memory and anxiety were induced at different time point after bright light treatment. Mice maintained in brighter light exhibited impaired memory in Y maze at one day after bright light exposure, but showed significantly improved spatial memory in the Y maze and Morris water maze at four weeks after bright light exposure. We also found increased anxiety one day after bright light exposure, which could be the reason of impaired memory. However, no change of anxiety was detected after four weeks. Thus, we further explore the underlying mechanism of the beneficial effects of long term bright light on spatial memory. Golgi staining indicated that the structure of dendritic spines changed, accompanied by increased expression of synaptophysin and postsynaptic density 95 in the hippocampus. Further research has found that bright light treatment leads to elevated CaMKII/CREB phosphorylation levels in the hippocampus, which are associated with synaptic function. Moreover, higher expression of brain-derived neurotrophic factor (BDNF) was followed by increased phosphorylated TrkB levels in the hippocampus, indicating that BDNF/TrkB signaling is also activated during this process. Taken together, these findings revealed that bright light exposure with different duration exert different effects on spatial memory in nocturnal rodents, and the potential molecular mechanism by which long term bright light regulates spatial memory was also demonstrated.

Endurance exercise improves avoidance learning and spatial memory, through changes in genes of GABA and relaxin-3, in rats

Different exercise patterns, neurotransmitters, and some genes have numerous effects on learning and memory. This research aims to investigate the long-term effects of submaximal aerobic exercise on spatial memory (SM), passive avoidance learning (PAL), levels of serum relaxin-3, gamma-aminobutyric acid (GABA), RLN3 gene, and glutamic acid decarboxylase (GAD65/67 genes) in the brainstem of adult male Wistar rats. Fifty male Wistar rats were randomly divided into five groups: aerobic exercise groups, performed on a treadmill running (TR), for 5 weeks (Ex_5, n = 10), 10 weeks (Ex_10, n = 10), involuntary running wheel group for 5 weeks (IRW₅, n = 10), sham (Sh, n = 10) and control (Co, n = 10). Consequently, SM, PAL, serum relaxin-3, GABA, and GAD65/67 and RLN3 genes were measured by ELISA and PCR. Ex_5, Ex₁₀ and IRW₅ improved significantly SM (p ≤ 0.05), PAL (p ≤ 0.001) and decreased significantly relaxin-3 (p ≤ 0.001). RLN3 in the brain also decreased. However, it was not significant. GABA and GAD65/GAD67 increased significantly (p ≤ 0.05) in Ex₅, Ex₁₀ compared to Sh and Co. Aerobic exercise enhanced SM and PAL in Ex compared to Co and Sh. However, duration and type of exercise affected the level of enhancement. The serum relaxin-3 and RLN3 gene displayed reverse functions compared to GABA and GAD65/67 genes in Ex. Therefore, the changes of neurotransmitters in serum relaxin-3, GABA, and their genes: RLN3 and GAD65/67 respectively, influenced learning and memory meaningfully.

Aneurysmal subarachnoid hemorrhage survivors show long-term deficits in spatial reference memory in a pilot study of a virtual water maze paradigm

BACKGROUND

Limited data exists on the long-term effects of aneurysmal subarachnoid hemorrhage (SAH) on spatial memory. Herein, we used a computerized virtual water maze to evaluate the feasibility of spatial memory testing in pilot cohort of ten patients who survived previous SAH.

METHODS

Ten SAH survivors (5.8 ± 5.1 years after initial hemorrhage) and 7 age-matched controls underwent testing in a virtual water maze computer program. Additional subgroup analyses were performed to evaluate spatial reference memory correlation for ventricular size on admission, placement of an external ventricular drain and placement of a shunt.

RESULTS

With respect to the spatial memory acquisition phase, there was no significant difference of pathway length traveled to reach the platform between SAH survivors and control subjects. During the probe trial, control subjects spent significantly longer time in target quadrants compared to SAH survivors (F_{(3, 24)} = 10.32, p = 0.0001; Target vs. Right: Mean percent difference 0.16 [0-0.32], p = 0.045; Target vs. Across: Mean percent difference 0.35 [0.19-0.51], p < 0.0001; Target vs. Left: Mean percent difference 0.21 [0.05-0.37], p = 0.0094). Furthermore, patients who initially presented with smaller ventricles performed worse that those patients who had ventriculomegaly and/or required surgical management of hydrocephalus.

CONCLUSIONS

Our data demonstrate that SAH survivors have persistent spatial reference memory deficits years after the hemorrhage. Hydrocephalus at presentation and external ventricular drainage were not found to be associated with poor spatial memory outcomes in this pilot cohort. Therefore, other causes such as global cerebral edema or magnitude of initial ICP spike, need to be considered to be examined as root cause as well in subsequent studies. The protocol described in this manuscript is able to demonstrate a spatial reference memory deficit and can be used to study risk factors for spatial memory impairment on a larger scale.

No explicit memory for individual trial display configurations in a visual search task

Previous evidence demonstrated that individuals can recall a target's location in a search display even if location information is completely task-irrelevant. This finding raises the question: does this ability to automatically encode a single item's location into a reportable memory trace extend to other aspects of spatial information as well? We tested this question using a paradigm designed to elicit attribute amnesia (Chen & Wyble, Psychological Science, 26(2) 203-210, 2015a). Participants were initially asked to report the location of a target letter among digits with stimuli arranged to form one of two or four spatial configurations varying randomly across trials. After completing numerous trials that matched their expectations, participants were surprised with a series of unexpected questions probing their memory for various aspects of the display they had just viewed. Participants had a profound inability to report which spatial configuration they had just perceived when the target's location was not unique to a specific configuration (i.e., orthogonal). Despite being unable to report the most recent configuration, answer choices on the surprise trial were focused around previously seen configurations, rather than novel configurations. Thus, there were clear memories of the set of configurations that had been viewed during the experiment but not of the specific configuration from the most recent trial. This finding helps to set boundary conditions on previous findings regarding the automatic encoding of location information into memory.

Folic Acid Supplementation in the Gestational Phase of Female Rats Improves Age-Related Memory Impairment and Neuroinflammation in Their Adult and Aged Offspring

Folic acid (FA) supplementation is important during pregnancy to avoid malformations in the offspring. However, it is unknown if it can affect the offspring throughout their lives. To evaluate the offspring, female mother rats (dams) were separated into 5 groups: Four groups received the AIN-93 diet, divided into control and FA (5, 10, and 50 mg/kg), and an additional group received a FA-deficient diet, and the diet was performed during pregnancy and lactation. We evaluated the female offspring of these dams (at 2 and 18 months old). The aged offspring fed with FA-deficient diet presented habituation, spatial and aversive memory impairment and the FA maternal supplementation prevented this. The natural aging caused an increase in the TNF-α and IL-1β levels in the hippocampus from 18-month-old offspring. FA maternal supplementation was able to prevent the increase of these cytokines. IL-4 levels decreased in the prefrontal cortex from aged control rats and FA prevented it. FA deficiency decreased the levels of IL-4 in the hippocampus of the young offspring. In addition, natural aging and FA deficiency decreased brain-derived neurotrophic factor levels in the hippocampus and nerve growth factor levels in the prefrontal cortex and FA supplementation prevented it. Thus, the present study shows for the first time the effect of FA maternal supplementation on memory, cytokines, and neurotrophins in the aged offspring.

Spatial and latent memory data in PS2Tg2576 alzheimer's disease mouse model after memantine treatment

We herein present behavioral data on whether memantine, an adamantane derivative and medical NMDA-receptor antagonist, improves spatial and latent learning deficits in amyloid precursor protein/presenilin 2 double-transgenic mice (PS2Tg2576 mice). In PS2Tg2576 mice, early amyloid-β protein (Aβ) deposition at 2-3 months of age and progressive accumulation at about 5 months of age has been shown. Thus, PS2Tg2576 mice were subjected to Morris water maze (MWM) test for spatial memory and the water-finding test for latent memory testing at ages 3 and 5-6 months. In addition, memantine (30 mg/kg/day, p.o.) was administered 3-4 weeks before commencing the behavioral tasks to check for effects on cognitive function. The information provided in this paper adds to the literature and can be used for the selection of animal models and behavioral paradigms for Alzheimer's disease (AD) research.

Distractor filtering is affected by local and global distractor probability, emerges very rapidly but is resistant to extinction

Effects of statistical learning (SL) of distractor location have been shown to persist when the probabilities of distractor occurrence are equalized across different locations in a so-called extinction phase. Here, we asked whether lingering effects of SL are still observed when a true extinction phase, during which the distractor is completely omitted, is implemented. The results showed that, once established, the effects of SL of distractor location do survive the true extinction phase, indicating that the pattern of suppression in the saliency map is encoded in a form of long-lasting memory. Quite unexpectedly, we also found that the amount of filtering implemented at a given location is not only dictated by the specific rate of distractor occurrence at that location, as previously found, but also by the global distractor probability. We therefore suggest that the visual attention system could be more or less (implicitly) prone to suppression as a function of how often the distractor is encountered overall, and that this suppressive bias affects the degree of suppression at the specific distractor-probability location. Finally, our results showed that the effects of SL of distractor location can appear much more rapidly than has been previously documented, requiring a few trials to become manifest. Hence, SL of distractor location appears to have an asymmetrical rate of learning during acquisition and extinction, while the amount of suppression exerted at a specific distractor location is modulated by distractor contextual probabilistic information.

Tumor necrosis factor α negatively regulates the retrieval and reconsolidation of hippocampus-dependent memory

Neural inflammation is associated with cognitive decline, especially learning and memory. Tumor necrosis factor α (TNFα) is a major cytokine generated during neuroinflammation. Previous studies indicated that TNFα impairs hippocampus-dependent memory including contextual fear and spatial memories. However, it is unknown which memory processes are impaired by TNFα. Here, we show that TNFα blocked the retrieval and reconsolidation of contextual fear and spatial memories. Micro-infusion of TNFα into the dorsal hippocampus at 6-18 h before retrieval impaired the retrieval of contextual fear memory, although micro-infusion before contextual fear conditioning had no effect on memory formation. Interestingly, hippocampal TNFα micro-infusion before memory retrieval decreased freezing responses, even at 24 h after retrieval, suggesting that TNFα impairs the reconsolidation of contextual fear memory. Similarly, hippocampal TNFα micro-infusion impaired the retrieval and reconsolidation of spatial memory in the Morris water maze. Consistent with these observations, hippocampal TNFα micro-infusion before retrieval blocked the induction of c-fos expression in the hippocampus, which is a marker of neural activation, in response to the retrieval of contextual fear memory. Collectively, our findings indicate that TNFα negatively regulates the retrieval and reconsolidation of hippocampus-dependent memory.

Catecholaminergic stimulation restores high-sucrose diet-induced hippocampal dysfunction

Increasing evidence suggests that long-term consumption of high-caloric diets increases the risk of developing cognitive dysfunctions. In the present study, we assessed the catecholaminergic activity in the hippocampus as a modulatory mechanism that is altered in rats exposed to six months of a high-sucrose diet (HSD). Male Wistar rats fed with this diet developed a metabolic disorder and showed impaired spatial memory in both water maze and object location memory (OLM) tasks. Intrahippocampal free-movement microdialysis showed a diminished dopaminergic and noradrenergic response to object exploration during OLM acquisition compared to rats fed with normal diet. In addition, electrophysiological results revealed an impaired long-term potentiation (LTP) of the perforant to dentate gyrus pathway in rats exposed to a HSD. Local administration of nomifensine, a catecholaminergic reuptake inhibitor, prior to OLM acquisition or LTP induction, improved long-term memory and electrophysiological responses, respectively. These results suggest that chronic exposure to HSD induces a hippocampal deterioration which impacts on cognitive and neural plasticity events negatively; these impairments can be ameliorated by increasing or restituting the affected catecholaminergic activity.

Losing balance: Kainate receptors and psychiatric disorders comorbidities

Cognition and behavior are tightly linked to synaptic function. A growing body of evidence suggests that aberrant neurotransmission, caused by changes in synaptic protein expression levels, may be a major cause underlying different brain disorders. These changes in expression result in abnormal synaptic organization or function, leading to impaired neurotransmission and unbalanced circuit operations. Here, we review the data supporting the involvement of mutations in genes coding for kainate receptor (KAR) subunits in the pathogenesis of psychiatric disorders and Down syndrome (DS). We show that most of these mutations do not affect the biophysical properties or the receptors, but rather alter subunit expression levels. On the basis of reports studying KAR genes mutations in mouse models of autism spectrum disorders and DS, we illustrate how deviations from the physiological regulatory role that these receptors play in neurotransmitter release and plasticity give rise to synaptic alterations that lead to behavioral and cognitive deficits underlying these disorders.

Lack of the peroxiredoxin 6 gene causes impaired spatial memory and abnormal synaptic plasticity

Peroxiredoxin 6 (PRDX6) is expressed dominantly in the astrocytes and exerts either neuroprotective or neurotoxic effects in the brain. Although PRDX6 can modulate several signaling cascades involving cognitive functions, its physiological role in spatial memory has not been investigated yet. This study aims to explore the function of the Prdx6 gene in spatial memory formation and synaptic plasticity. We first tested Prdx6-/- mice on a Morris water maze task and found that their memory performance was defective, along with reduced long-term potentiation (LTP) in CA3-CA1 hippocampal synapses recorded from hippocampal sections of home-caged mice. Surprisingly, after the probe test, these knockout mice exhibited elevated hippocampal LTP, higher phosphorylated ERK1/2 level, and decreased reactive astrocyte markers. We further reduced ERK1/2 phosphorylation by administering MEK inhibitor, U0126, into Prdx6-/- mice before the probe test, which reversed their spatial memory deficit. This study is the first one to report the role of PRDX6 in spatial memory and synaptic plasticity. Our results revealed that PRDX6 is necessary for maintaining spatial memory by modulating ERK1/2 phosphorylation and astrocyte activation.

Neurobehavioral, neurochemical and synaptic plasticity perturbations during postnatal life of rats exposed to chloroquine in-utero

Despite reports that quinoline antimalarials including chloroquine (Chq) exhibit idiosyncratic neuropsychiatric effects even at low doses, the drug continues to be in widespread use during pregnancy. Surprisingly, very few studies have examined the potential neurotoxic action of Chq exposure at different points of gestation or how this phenomenon may affect neurophysiological well-being in later life. We therefore studied behavior, and the expression of specific genes and neurochemicals modulating crucial neural processes in offspring of rats exposed to prophylactic dose of Chq during different stages of gestation. Pregnant rats were injected 5 mg/kg/day (3 times) of Chq either during early- (first week), mid- (second week), late- (third week), or throughout- (all weeks) gestation, while controls received PBS injection. Behavioral characterization of offspring between postnatal days 15-20 in the open field, Y-maze, elevated plus and elevated zero mazes revealed that Chq evoked anxiogenic responses and perturbed spatial memory in rats, although locomotor activity was generally unaltered. In the prefrontal cortex (PFC), hippocampus and cerebellum of rats prenatally exposed to Chq, RT-qPCR analysis revealed decreased mRNA expression of presynaptic marker synaptophysin, which was accompanied by downregulation of postsynaptic marker PSD95. Synaptic marker PICK1 expression was also downregulated in the hippocampus but was unperturbed in the PFC and cerebellum. In addition to recorded SOD downregulation in cortical and hippocampal lysates, induction of oxidative stress in rats prenatally exposed to Chq was corroborated by lipid peroxidation as evinced by increased MDA levels. Offspring of rats infused with Chq at mid-gestation and weekly treatment throughout gestation were particularly susceptible to neurotoxic changes, especially in the hippocampus. Interestingly, Chq did not cause histopathological changes in any of the brain areas. Taken together, our findings causally link intrauterine exposure to Chq with postnatal behavioral impairment and neurotoxic changes in rats.

Training level reveals a dynamic dialogue between stress and memory systems in birds

Chronic stress profoundly affects forms of declarative memory, such as spatial memory, while it may spare non-declarative memory, such as cue-based memory. It is known, however, that the effects of chronic stress on memory systems may vary according to the level of training of an individual was submitted. Here, we investigated, in birds, how chronic stress impact spatial and cue-based memories according to training level. For that, control and chronically stressed Japanese quail were trained in a task that could be solved using spatial and cue-based memory and tested for their memory performance after 5 and 15 training days (initial training and overtraining, respectively) and following an emotional challenge (exposure to an open field). Our results showed that, compared to control quail, chronic stress impacted negatively spatial memory performances in stressed birds after initial training, but these differences were lowered after overtraining. Control birds seemed to shift from spatial to cue-based memory to solve the task across overtraining. However, an emotional challenge before testing reinstated the negative impact of chronic stress on spatial memory performances between the groups, revealing that chronic stress/overtraining did not eliminate the spatial memory and differences caused by stressors can reemerge depending on the individual's immediate psychological state. Contrary to spatial memory, cue-based memory was not affected in chronically stressed birds compared to control birds in any test occasion, confirming its resistance against the negative effects of chronic stress. Altogether these findings reveal a dynamic dialogue between stress, training level, and memory systems in birds.

Urtica dioica extracts abolish scopolamine-induced neuropathies in rats

Alzheimer's disease (AD) is characterized by alterations in monoamines, oxidative stress, and metabolic dysfunctions. We aim to assess the therapeutic impacts of roots or leaf extract from Urtica dioica (UD; stinging nettle) against scopolamine (SCOP)-induced memory dysfunction, amnesia, and oxidative stress in rats. Spatial memory was assessed by Y maze test. Tissue analyses of norepinephrine (NE), dopamine (DA), serotonin (5-HT), malondialdehyde (MDA), nitric oxide (NO), glutathione (GSH, GSSG), AMP, ADP, and ATP were assessed by HPLC. mRNA levels of Tau and Hsp70 were estimated by PCR. UD extracts particularly nettle root (NR) significantly normalized the SCOP-induced memory deficits even more potent than sermion (SR) and donepezil (DON). Similarly, NR had potent therapeutic impacts on the levels of cortical and hippocampal monoamines e.g. DA, NE, and 5-HT. SCOP induced a dramatic oxidative stress as measured by MDA, NO, and GSSG levels; however, UD extracts showed significant anti-oxidative stress impacts. Additionally, UD extracts restored ATP levels and reduced the levels of AMP and ADP compared to SCOP-treated rats. Furthermore, cortical Tau and hippocampal Hsp70 were modulated by UD extracts particularly NR compared to the SCOP group. In conclusion, UD extracts particularly roots have potential therapeutic impacts against SCOP-induced neuroinflammatory and/or Alzheimer-like phenotype in rats.

A computational cognitive model of judgments of relative direction

In the past several decades, considerable theoretical progress has been made in understanding the role of reference frames in the encoding and retrieval of spatial information about the environment. Many of these insights have come from participants making judgments of relative direction using their memories of spatial layouts. In this task, participants are asked to imagine standing at a given location and facing a certain direction, and to point to a target location. Although this task has been widely and productively used, a computational cognitive model of judgments of relative direction has yet to be introduced. Computational modeling of judgments of relative direction is a critical next step to formulating and testing hypotheses about the cognitive processes involved in establishing and using spatial reference frames. We present an initial attempt to model judgments of relative direction and fit the model to two datasets exhibiting behavioral patterns commonly observed in the spatial memory literature. The model was able to predict many important features of these data, most notably alignment effects. We discuss directions for future modeling efforts.

Perspective taking and systematic biases in object location memory

The aim of the current study was to develop a novel task that allows for the quick assessment of spatial memory precision with minimal technical and training requirements. In this task, participants memorized the position of an object in a virtual room and then judged from a different perspective, whether the object has moved to the left or to the right. Results revealed that participants exhibited a systematic bias in their responses that we termed the reversed congruency effect. Specifically, they performed worse when the camera and the object moved in the same direction than when they moved in opposite directions. Notably, participants responded correctly in almost 100% of the incongruent trials, regardless of the distance by which the object was displaced. In Experiment 2, we showed that this effect cannot be explained by the movement of the object on the screen, but that it relates to the perspective shift and the movement of the object in the virtual world. We also showed that the presence of additional objects in the environment reduces the reversed congruency effect such that it no longer predicts performance. In Experiment 3, we showed that the reversed congruency effect is greater in older adults, suggesting that the quality of spatial memory and perspective-taking abilities are critical. Overall, our results suggest that this effect is driven by difficulties in the precise encoding of object locations in the environment and in understanding how perspective shifts affect the projected positions of the objects in the two-dimensional image.

The chemical chaperon 4-phenyl butyric acid restored high-fat diet- induced hippocampal insulin content and insulin receptor level reduction along with spatial learning and memory deficits in male rats

This study assessed the effect of a chronic high-fat diet (HFD) on plasma and hippocampal insulin and corticosterone levels, the hippocampus insulin receptor amount, and spatial learning and memory with or without receiving 4-phenyl butyric acid (4-PBA) in male rats. Rats were divided into high-fat and normal diet groups, then each group was subdivided into dimethyl sulfoxide (DMSO) and 4-PBA groups. After weaning, the rats were fed with HFD for 20 weeks. Then, 4-PBA or DMSO were injected for 3 days. Subsequently, oral glucose tolerance test was done. On the following day, spatial memory tests were performed. Then the hippocampus Bip, Chop, insulin, corticosterone, and insulin receptor levels were determined. HFD increased plasma glucose, leptin and corticosterone concentrations, hippocampus Bip, Chop and corticosterone levels, food intake, abdominal fat weight and body weight along with impaired glucose tolerance. It decreased plasma insulin, and insulin content, and its receptor amount in hippocampus. HFD lengthened escape latency and shortened the duration spent in target zone. 4-PBA administration improved the HFD- induced adverse changes. Chronic HFD possibly through the induction of endoplasmic reticulum (ER) stress and subsequent changes in the levels of hippocampal corticosterone, insulin and insulin receptor along with possible leptin resistance caused spatial learning and memory deficits.

Conjugated Linoleic Acid-Curcumin Attenuates Cognitive Deficits and Oxidative Stress Parameters in the Ethidium Bromide-Induced Model of Demyelination

Oxidative stress has been shown to play an important role in the pathogenesis of multiple sclerosis (MS). Curcumin (CUR), an antioxidant compound, can be a potent treatment for neurodegenerative diseases, such as MS. CUR has poor bioavailability; therefore, it is used in nanoforms to increase its bioavailability. In the present study, the effects of CUR and conjugated linoleic acid-CUR (Lino-CUR) on spatial memory and oxidative stress in a putative animal model of MS were investigated. Forty-nine adult male Wistar rats (250 ± 50 g) were randomly divided into seven groups (n = 7): control, sham, ethidium bromide (EB), CUR (20 and 40 μg/kg) + EB, and Lino-CUR (20 and 40 μg/kg) + EB groups. Following MS induction, the groups were treated for 5 consecutive days. Finally, spatial memory and levels of oxidative stress parameters were assessed. Treatment with CUR and Lino-CUR at two doses significantly improved spatial memory and reduced oxidative stress parameters in the experimental models of MS. Furthermore, the effects of high dose (40 μg/kg) of Lino-CUR were more remarkable. These findings suggest that the microinjection of CUR in its synthetic form Lino-CUR significantly ameliorated spatial memory, through the reduction of oxidative stress markers in the brain of studied animals as a rat model of MS.

Spatial movement with distributed memory

Diffusion has been widely applied to model animal movement that follows Brownian motion. However, animals typically move in non-Brownian ways due to their perceptual judgment. Spatial memory and cognition recently have received much attention in characterizing complicated animal movement behaviours. Explicit spatial memory is modeled via a distributed delayed diffusion term in this paper. The distributed time represents the memory growth and decay over time, and the spatial nonlocality reflects the dependence of spatial memory on location. When the temporal delay kernel is weak under the assumption that animals can immediately acquire knowledge and memory decays over time, the equation is equivalent to a Keller-Segel chemotaxis model. For the strong kernel with learning and memory decay stages, rich spatiotemporal dynamics, such as Turing and checker-board patterns, appear via spatially non-homogeneous steady-state and Hopf bifurcations.

Improved spatial memory, neurobehavioral outcomes, and neuroprotective effect after progesterone administration in ovariectomized rats with traumatic brain injury: Role of RU486 progesterone receptor antagonist

OBJECTIVES

The contribution of classic progesterone receptors (PR) in interceding the neuroprotective efficacy of progesterone (P4) on the prevention of brain edema and long-time behavioral disturbances was assessed in traumatic brain injury (TBI).

MATERIALS AND METHODS

Female Wistar rats were ovariectomized and apportioned into 6 groups: sham, TBI, oil, P4, vehicle, and RU486. P4 or oil was injected following TBI. The antagonist of PR (RU486) or DMSO was administered before TBI. The brain edema and destruction of the blood-brain barrier (BBB) were determined. Intracranial pressure (ICP), cerebral perfusion pressure (CPP), and beam walk (BW) task were evaluated previously and at various times post-trauma. Long-time locomotor and cognitive consequences were measured one day before and on days 3, 7, 14, and 21 after the trauma.

RESULTS

RU486 eliminated the inhibitory effects of P4 on brain edema and BBB leakage (P<0.05, P<0.001, respectively). RU486 inhibited the decremental effect of P4 on ICP as well as the increasing effect of P4 on CPP (P<0.001) after TBI. Also, RU486 inhibited the effect of P4 on the increase in traversal time and reduction in vestibulomotor score in the BW task (P<0.001). TBI induced motor, cognitive, and anxiety-like disorders, which lasted for 3 weeks after TBI; but, P4 prevented these cognitive and behavioral abnormalities (P<0.05), and RU486 opposed this P4 effect (P<0.001).

CONCLUSION

The classic progesterone receptors have neuroprotective effects and prevent long-time behavioral and memory deficiency after brain trauma.

17β-estradiol activation of dorsal hippocampal TrkB is independent of increased mature BDNF expression and is required for enhanced memory consolidation in female mice

The potent estrogen 17β-estradiol (E₂) is known to enhance hippocampal memory and plasticity, however the molecular mechanisms underlying these effects remain unclear. Brain derived neurotrophic factor (BDNF) and its receptor tropomyosin receptor kinase B (TrkB) are regulated by E₂, but the potential mechanistic roles of neurotrophic signaling in E₂-induced enhancement of memory are not well understood. Here, we examined the effects of hippocampal TrkB signaling on E₂-induced enhancement of memory consolidation in the object placement and recognition tasks. Bilateral infusion of the TrkB antagonist ANA-12 into the dorsal hippocampus of ovariectomized female mice blocked E₂-induced enhancement of memory consolidation, supporting a role for TrkB-mediated signaling in estrogenic regulation of memory. Although dorsal hippocampal E₂ infusion increased levels of phospho-TrkB and mature BDNF (mBDNF) in the dorsal hippocampus within 4-6 h, E₂-induced increases in hippocampal mBDNF expression were not required for hippocampal TrkB activation and were not inhibited by TrkB antagonism. Thus, E₂ regulates TrkB signaling to facilitate memory consolidation in a manner independent of mBDNF expression. Together these results provide the first direct evidence that E₂ modulation of hippocampal TrkB signaling is required for its beneficial effects on memory consolidation and provide additional characterization of the ways in which TrkB/BDNF signaling is regulated by E₂ in the hippocampus.

Neonatal Sevoflurane Exposure Impairs Learning and Memory by the Hypermethylation of Hippocampal Synaptic Genes

Sevoflurane anesthesia is widely used in pediatric patients. Clinical studies report memory impairment in those exposed to general anesthesia early in life. DNA methylation is essential for the modulation of synaptic plasticity through regulating the transcription of synaptic genes. Therefore, we tested whether neonatal sevoflurane exposure affects learning and memory underlying the hippocampal DNA methylation of synaptic genes. Male Sprague-Dawley rats were exposed to 3% sevoflurane or air for 2 h daily from postnatal day 7 (P7) to P9. 5-aza-2-deoxycytidine (5-AZA), an inhibitor of DNA methyltransferases (DNMTs), was intraperitoneally injected 30 min before sevoflurane or air exposure on P7-9. The rats were euthanized 6, 12, 24 h, and 28 days after the last sevoflurane exposure, followed by the determination of global and gene-specific DNA methylation. The expression of synaptic proteins and synaptic density and the transcription of Dnmts and ten eleven translocations (Tets) in the hippocampus were measured. The ability of learning and memory was assessed using Morris water maze, novel object recognition, and intruder tests. Repeated neonatal sevoflurane exposure impaired cognitive, social, and spatial memory. The memory impairment was associated with the increased Dnmt1, Dnmt3a, and 5-methylcytosine level and the decreased Tet1 and 5-hydromethylcytosine level. Sevoflurane subsequently induced hypermethylation of Shank2, Psd95, Syn1, and Syp gene and down-regulated the expression of synaptic proteins, which finally led to the decrease of synaptic density in a time-dependent manner. Notably, 5-AZA pretreatment ameliorated learning and memory in sevoflurane-treated rats. In conclusion, neonatal exposure to sevoflurane can impair learning and memory through DNA methylation of synaptic genes.

Hippocampus and cortex are involved in the retrieval of a spatial memory under full and partial cue availability

Retaking routes after a period of time usually occurs in an environment which has suffered from spatial configuration modifications. Thus, the original visual stimuli that allowed us to establish cognitive mapping using an allocentric strategy during the acquisition phase may not remain physically identical at the time of retrieval. However, in the standard experimental paradigms the cues are typically maintained constant. In this study, we explored memory retrieval with spatial modifications from learning in the Morris Water Maze. We trained rats on a reference memory protocol with five cues placed on black curtains that surrounded the pool, and seven days later, we tested memory retrieval under different conditions: maintenance of the five cues, removal of two and four of them, and the addition of three extra ones. Under full-cue and partial cue-conditions, rats showed successful memory retrieval, whereas adding extra cues resulted in impaired retrieval. Furthermore, we assessed brain oxidative metabolism through cytochrome c oxidase (CCO) histochemistry and found that, under full- and partial-cue conditions, there is an enhancement of the hippocampal, prefrontal, retrosplenial, parietal, and rhinal cortex metabolism. Rats that failed to retrieve spatial information in the extra cues condition showed similar or lower CCO activity than controls across many limbic areas. It is suggested that the presence of a partial portion of visual stimuli from learning makes it possible to reactivate the entire memory trace, but extra spatial information hinders retrieval, making it difficult to disengage the novel information from the older knowledge and establish a contextual generalization.

Contribution of the hippocampus to performance on the traveling salesperson problem in rats

The Traveling Salesman Problem (TSP) is an optimization problem in which the subject attempts to find the shortest possible route that passes through a set of fixed locations exactly once. The TSP is used in cognitive and behavioral research to study problem solving and spatial navigation. While the TSP has been studied in some depth from this perspective, the biological mechanisms underlying the behavior have not yet been explored. The hippocampus is a structure in the brain that is known to be involved in tasks that require spatial memory. Because the TSP requires spatial problem solving, we designed the current study to determine whether the hippocampus is required to find efficient solutions to the TSP, and if so, what role the hippocampus serves. Rats were pretrained on the TSP, which involved learning to retrieve bait from targets in a variety of spatial configurations. Matched for performance, rats were then divided into two groups, receiving either a hippocampal lesion or a control sham surgery. After recovering from surgery, the rats were tested on eight new configurations. A variety of behavioral measures were recorded, including distance travelled, number of revisits, memory span, and latency. The results showed that the sham group outperformed the lesion group on most of these measures. Based on the behavioral data and histological tissue analysis of each group, we determined that the hippocampus is involved in successful performance in the TSP, particularly regarding memory for which targets have already been visited.

Spatial learning and memory impaired after infection of non-neurotropic influenza virus in BALB/c male mice

During the influenza pandemic or seasonal influenza outbreak, influenza infection can cause acute influenza-associated encephalopathy/encephalitis (IAE), even death. Patients with severe IAE will also have severe neurological sequelae. Neurologic disorders have been demonstrated in the mice treated with peripheral influenza viruses infection, whether neurotropic or non-neurotropic viruses. However, previous studies focused on the acute phase of infection, and rarely paid attention to a longer range of observations. Therefore, the long-term effect of non-neurotropic virus infection on the host is not very clear. In this study, adult mice were infected with influenza virus H1N1/PR8. Then, spontaneous behavior, body weight, expression of cytokines in brain, spatial learning ability and spatial memory ability were observed, until the complete recovery period. The results showed that cytokines in the brain were highly expressed in the convalescent phase (14 day post inoculation, dpi), especially BDNF, IBA1, CX3CL1 and CD200 were still highly expressed in the recovery phase (28 dpi). Otherwise the emotional and spatial memory ability of mice were impacted in the convalescent phase (14 dpi) and the recovery phase (28 dpi). In brief, BALB/c mice infected with non-neurotropic influenza virus H1N1, the weight and motor ability decreased in acute stage. During the recovery period, the body weight and activity ability were completely restored, whereas the emotion disordered, and the ability of spatial learning and memory were impacted in the infected mice. This long-term behavior impact may be the lag injury caused by non-neurotropic influenza infection.

Endogenous variation in estradiol in women affects the weighting of metric and categorical information in spatial location memory

Recent work has suggested that sex differences may exist in the strategies or types of cues that are utilized by men and women to remember discrete spatial locations or routes through a visual environment. The current study investigated the effects of circulating estradiol levels in women on the relative weighting of categorical versus fine-grained 'metric' information in a test of short-term memory for spatial locations, either presented within a simple geometric surround (a circular enclosure) or within more visually complex landscape scenes. Patterns of displacement error in the point location estimates made by men and women were analyzed. Results confirmed a sex difference in the weighting of metric versus categorical cues. Relative to men, women's estimates of locations were more strongly biased toward the center of the surrounding category (i.e., toward the category 'prototype'). Furthermore, objective measures of estradiol via saliva collected at the time of memory testing showed that, among naturally-cycling women, estradiol concentrations correlated in a positive, graded, fashion with the degree of emphasis that women placed on categorical information when estimating point locations. No associations were found for progesterone. These findings are consistent with a wider body of research showing that biological sex and reproductive hormone levels, including 17β-estradiol, can subtly influence performance on certain spatial tasks. This is the first study to show that circulating estradiol levels may influence the relative emphasis placed on categorical versus metric cues when remembering simple point locations.

Inhibition of monoamine oxidase attenuates social defeat-induced memory impairment in goldfish, (Carassius auratus): A possible involvement of synaptic proteins and BDNF

Social defeat (SD) has been implicated in different modulatory effects of physiology and behaviour including learning and memory. We designed an experiment to test the functional role of monoamine oxidase (MAO) in regulation of synaptic transmission, synaptic plasticity and memory in goldfish Carassius auratus. To test this, individuals were divided into three groups: (i) control; (ii) social defeat (SD) group (individuals were subjected to social defeat for 10 min by Pseudotropheus demasoni) and (iii) SD + MAO inhibitor pre-treated group. All experimental groups were subjected to spatial learning and then memory. Our results suggest that SD affects a spatial learning and memory, whereas SD exerts no influence on MAOI pre-treated group. In addition, we noted that the expression of monoamine oxidase-A (MAO-A) was up-regulated and level of serotonin (5-hydroxytryptamine; 5-HT), expression of serotonin transporter (SERT), synaptophysin (SYP), synaptotagmin -1 (SYT-1), N-methyl-D-asparate (NMDA) receptors subunits (NR2A and NR2B), postsynaptic density-95 (PSD-95) and brain-derived neurotrophic factor (BDNF) were reduced by SD, while MAOIs pretreatment protects the effect of SD. Taken together, our results suggest that MAO is an essential component in the serotonergic system that finely tunes the level of 5-HT, which further regulates the molecules involving in synaptic transmission, synaptic plasticity and memory.

The neuroprotective effect of betanin in trimethyltin-induced neurodegeneration in mice

Betanin, a natural food colorant with powerful antioxidative properties, has not been studied in terms of neurodegenerative disease intervention. Therefore, the present study aimed to investigate the neuroprotective effects of betanin against trimethyltin chloride (TMT) -induced neurodegeneration in mice. Forty male ICR mice were randomly divided into four groups: Sham-veh, TMT-veh, TMT-Bet50 and TMT-Bet100. In the TMT groups, neurodegeneration was induced with a one-time intraperitoneal injection of 2.6 mg/kg TMT. Betanin-treated groups (Bet) were given oral doses of 50 or 100 mg/kg dissolved in normal saline solution. Administrations were started 24 h prior to TMT injection and continued for 2 weeks. Anxious behavior and spatial cognition were evaluated, respectively. After behavioral tests, brain oxidative status, hippocampal histology and choline acetyltransferase (ChAT) activity were evaluated. Results showed that TMT significant induce anxious behavior and spatial learning and memory deficits (p < 0.05). These were found concurrently with significant decreases in CA1 ChAT activity, brain tissue catalase (CAT) and superoxide dismutase (SOD) activities with significant increase in hippocampal CA1 degeneration (p < 0.05). Betanin 100 mg/kg exhibited significant anxiolytic effect, preventive effect on CA1 degeneration and CA1 ChAT activity alteration as well as improvement of spatial learning and memory deficits (p < 0.05). These were found concurrently with significant increases of reduced glutathione, CAT and SOD activities as well as the decrease in malondialdehyde (p < 0.05). We conclude that betanin 100 mg/kg exhibits neuroprotective effects against TMT-induced neurodegeneration in mice via its anti-oxidative properties, protective against hippocampal CA1 degeneration and ChAT activity alteration. Therefore, betanin is interesting in further neurodegenerative therapeutic study and applications.

The anterior thalamic nuclei and nucleus reuniens: So similar but so different

Two thalamic sites are of especial significance for understanding hippocampal - diencephalic interactions: the anterior thalamic nuclei and nucleus reuniens. Both nuclei have dense, direct interconnections with the hippocampal formation, and both are directly connected with many of the same cortical and subcortical areas. These two thalamic sites also contain neurons responsive to spatial stimuli while lesions within these two same areas can disrupt spatial learning tasks that are hippocampal dependent. Despite these many similarities, closer analysis reveals important differences in the details of their connectivity and the behavioural impact of lesions in these two thalamic sites. These nuclei play qualitatively different roles that largely reflect the contrasting relative importance of their medial frontal cortex interactions (nucleus reuniens) compared with their retrosplenial, cingulate, and mammillary body interactions (anterior thalamic nuclei). While the anterior thalamic nuclei are critical for multiple aspects of hippocampal spatial encoding and performance, nucleus reuniens contributes, as required, to aid cognitive control and help select correct from competing memories.

Egocentric and allocentric spatial representations in a patient with Bálint-like syndrome: A single-case study

Previous studies suggested that egocentric and allocentric spatial representations are supported by neural networks in the occipito-parietal (dorsal) and occipito-temporal (ventral) streams, respectively. The present study aimed to explore the integrity of ego- and allo-centric spatial representations in a patient (GP) who presented bilateral occipito-parietal damage consistent with the picture of a Bálint-like syndrome. GP and healthy controls were asked to provide memory-based spatial judgments on triads of objects after a short (1.5sec) or long (5sec) delay. The results showed that GP's performance was selectively impaired in the Ego/1.5sec delay condition. As a whole, our findings suggest that GP's spared ventral stream could generate short- and long-term allocentric representations. Furthermore, the stored perceptual representation processed within the ventral stream might have been used to generate long-term egocentric representation. Conversely, the generation of short-term egocentric representation appeared to be selectively undermined by the damage of the dorsal stream.

Acute ethanol administration produces larger spatial and nonspatial memory impairments in 29-33 month old rats compared to adult and 18-24 month old rats

The average age of the population in many countries is continuing to increase. Older people continue to consume alcohol, often in a binge like fashion. Previous research has demonstrated that older human subjects and aged animal subjects have an increased sensitivity to the effects of ethanol on a variety of behaviors. However, it has yet to be determined if acute ethanol exposure impairs spatial and/or nonspatial memory to a greater extent in aged rats compared to adult rats. In the current studies we trained male rats ranging in age from young adult (2 months of age) to aged rats (29-33 months of age) in the standard nonspatial task followed by the standard spatial task in the Morris water maze. Only animals deemed "cognitively-spared", that is aged animals that learn as well as young animals, were administered one of two doses of moderate ethanol and had their memory tested 30 min later. Acute ethanol administration produced similar performance impairments in spatial and nonspatial memory in all cognitively-spared animals except for the 29-33 month old animals which showed a significantly greater cognitive impairment in both tasks. In addition, blood ethanol levels were similar across all ages. The present work adds to the growing literature on the selective effects of acute ethanol exposure in aged animals.

The modulation of the spatial reference memory by the orexinergic system of the dorsal raphe nucleus

The dorsal raphe nucleus (DRN) is a brainstem nucleus involved in the pathophysiology of the depression, through its serotoninergic innervation. Furthermore, depressive symptoms in patients are also associated with some memory and sleep complaints. Anatomical evidence confirmed the presence of projections from the lateral hypothalamus to serotonergic neurons of the dorsal raphe nucleus (DRN). These projection fibers release orexin neuropeptides which play roles in the spatial memory. Both of the orexinergic receptors are widely distributed in dorsal raphe nucleus. Therefore, the present work was aimed to assess the probable roles of orexin 1 and 2 receptors using an orexin 1 receptor antagonist, SB-334867-A, and an orexin 2 receptor antagonist, TCS-OX2-29 in the DRN on the retrieval, and consolidation phases of spatial reference memory in the Morris water maze (MWM) task. The results demonstrated that blocking orexin 1 receptors in the DRN impairs the process of memory consolidation in the spatial MWM via increasing in the time of the escape latency of the probe day. Blocking these receptors did not affect the retrieval phase of MWM learning. Furthermore, blocking of the orexin 2 receptors in this area did not affect neither consolidation nor retrieval phases of the memory. In conclusion, orexin 1 receptors in the DRN play major roles in the consolidation of the spatial reference memory in rats.

Modular, Circuit-Based Interventions Rescue Hippocampal-Dependent Social and Spatial Memory in a 22q11.2 Deletion Syndrome Mouse Model

BACKGROUND

22q11.2 deletion syndrome (22qDS) manifests with myriad symptoms, including multiple neuropsychiatric disorders. Complications associated with the polygenic haploinsufficiency make 22qDS symptoms particularly difficult to manage with traditional therapeutic approaches. However, the varying mechanistic consequences often culminate to generate inappropriate regulation of neuronal circuit activity. We explored whether managing this aberrant activity in adults could be a therapeutically beneficial strategy.

METHODS

To assess and dissect hippocampal circuit function, we performed functional imaging in acute slices and targeted eloquent circuits (specific subcircuits tied to specific behavioral tasks) to provide relevant behavioral outputs. For example, the ventral and dorsal CA1 regions critically support social and spatial discrimination, respectively. We focally introduced chemogenetic constructs in 34 control and 24 22qDS model mice via adeno-associated viral vectors, driven by excitatory neuron-specific promoter elements, to manipulate circuit recruitment in an on-demand fashion.

RESULTS

22qDS model mice exhibited CA1 excitatory ensemble hyperexcitability and concomitant behavioral deficits in both social and spatial memory. Remarkably, acute chemogenetic inhibition of pyramidal cells successfully corrected memory deficits and did so in a regionally specific manner: ventrally targeted constructs rescued only social behavior, while those expressed dorsally selectively affected spatial memory. Additionally, manipulating activity in control mice could recapitulate the memory deficits in a regionally specific manner.

CONCLUSIONS

These data suggest that retuning activity dysregulation can rescue function in disease-altered circuits, even in the face of a polygenetic haploinsufficiency with a strong developmental component. Targeting circuit excitability in a focal, modular manner may prove to be an effective therapeutic for treatment-resistant symptoms of mental illness.

Dose-dependent effects of testosterone on spatial learning strategies and brain-derived neurotrophic factor in male rats

Studies suggest that males outperform females on some spatial tasks. This may be due to the effects of sex steroids on spatial strategy preferences. Past experiments with male rats have demonstrated that low doses of testosterone bias them toward a response strategy, whereas high doses of testosterone bias them toward a place strategy. We investigated the effect of different testosterone doses on the ability of male rats to effectively employ these two spatial learning strategies. Furthermore, we quantified concentrations of brain-derived neurotrophic factor (pro-, mature-, and total BDNF) in the prefrontal cortex, hippocampus, and striatum. All rats were bilaterally castrated and assigned to one of three daily injection doses of testosterone propionate (0.125, 0.250, or 0.500 mg/rat) or a control injection of the drug vehicle. Using a plus-maze protocol, we found that a lower testosterone dose (0.125 mg) significantly improved rats' performance on a response task, whereas a higher testosterone dose (0.500 mg) significantly improved rats' performance on a place task. In addition, we found that a low dose of testosterone (0.125 mg) increased total BDNF in the striatum, while a high dose (0.500 mg) increased total BDNF in the hippocampus. Taken altogether, these results suggest that high and low levels of testosterone enhance performance on place and response spatial tasks, respectively, and this effect is associated with changes in BDNF levels within relevant brain regions.

Rho Guanine Nucleotide Exchange Factor 4 (Arhgef4) Deficiency Enhances Spatial and Object Recognition Memory

Guanine nucleotide exchange factors (GEFs) play multiple functional roles in neurons. In a previous study, we reported that Arhgef4 (Rho guanine nucleotide exchange factor 4) functioned as a negative regulator of the excitatory synaptic function by sequestering postsynaptic density protein 95 (PSD-95). However, the role of Arhgef4 in behavior has not been examined. We performed comprehensive behavioral tests in knockout (KO) mice to investigate of the effects of Arhgef4 deficiency. We found that the expressed PSD-95 particle size was significantly increased in hippocampal neuronal cultures from Arhgef4 KO mice, which is consistent with the previous in vitro findings. Arhgef4 KO mice exhibited general motor activity and anxiety-like behavior comparable to those of the wild type littermates. However, spatial memory and object recognition memory were significantly enhanced in the Arhgef4 KO mice. Taken together, these data confirm the role of Arhgef4 as a negative synaptic regulator at the behavioral level.

DTI-identified microstructural changes in the gray matter of mice overexpressing CRF in the forebrain

Increased corticotroping releasing factor (CRF) contributes to brain circuit abnormalities associated with stress-related disorders including posttraumatic stress disorder. However, the causal relationship between CRF hypersignaling and circuit abnormalities associated with stress disorders is unclear. We hypothesized that increased CRF exposure induces changes in limbic circuit morphology and functions. An inducible, forebrain-specific overexpression of CRF (CRFOE) transgenic mouse line was used to longitudinally investigate its chronic effects on behaviors and microstructural integrity of several brain regions. Behavioral and diffusion tensor imaging studies were performed before treatment, after 3-4 wks of treatment, and again 3 mo after treatment ended to assess recovery. CRFOE was associated with increased perseverative movements only after 3 wks of treatment, as well as reduced fractional anisotropy at 3 wks in the medial prefrontal cortex and increased fractional anisotropy in the ventral hippocampus at 3 mo compared to the control group. In the dorsal hippocampus, mean diffusivity was lower in CRFOE mice both during and after treatment ended. Our data suggest differential response and recovery patterns of cortical and hippocampal subregions in response to CRFOE. Overall these findings support a causal relationship between CRF hypersignaling and microstructural changes in brain regions relevant to stress disorders.

The CBP KIX domain regulates long-term memory and circadian activity

Background

CREB-dependent transcription necessary for long-term memory is driven by interactions with CREB-binding protein (CBP), a multi-domain protein that binds numerous transcription factors potentially affecting expression of thousands of genes. Identifying specific domain functions for multi-domain proteins is essential to understand processes such as cognitive function and circadian clocks. We investigated the function of the CBP KIX domain in hippocampal memory and gene expression using CBP^KIX/KIX mice with mutations that prevent phospho-CREB (Ser133) binding.

Results

We found that CBP^KIX/KIX mice were impaired in long-term memory, but not learning acquisition or short-term memory for the Morris water maze. Using an unbiased analysis of gene expression in the dorsal hippocampus after training in the Morris water maze or contextual fear conditioning, we discovered dysregulation of CREB, CLOCK, and BMAL1 target genes and downregulation of circadian genes in CBP^KIX/KIX mice. Given our finding that the CBP KIX domain was important for transcription of circadian genes, we profiled circadian activity and phase resetting in CBP^KIX/KIX mice. CBP^KIX/KIX mice exhibited delayed activity peaks after light offset and longer free-running periods in constant dark. Interestingly, CBP^KIX/KIX mice displayed phase delays and advances in response to photic stimulation comparable to wildtype littermates. Thus, this work delineates site-specific regulation of the circadian clock by a multi-domain protein.

Conclusions

These studies provide insight into the significance of the CBP KIX domain by defining targets of CBP transcriptional co-activation in memory and the role of the CBP KIX domain in vivo on circadian rhythms.

Graphical abstract

E2-BSA and G1 exert neuroprotective effects and improve behavioral abnormalities following traumatic brain injury: The role of classic and non-classic estrogen receptors

The role of classical and non-classical estrogen receptors (ERs) in mediating the neuroprotective effects of this hormone on brain edema and long-term behavioral disorders was evaluated after traumatic brain injury (TBI). Ovariectomized rats were divided as follows: E2 (17 β-estradiol), E2-BSA (E2 conjugated to bovine serum albumin), G1 [G-protein-coupled estrogen receptor agonist (GPER)] or their vehicle was injected following TBI, whereas ICI (classical estrogen receptor antagonist), G15 (GPER antagonist), ICI + G15, and their vehicle were injected before the induction of TBI and the injection of E2 and E2-BSA. Brain water (BWC) and Evans blue (EB) contents were measured 24 h and 5 h after TBI, respectively. Intracranial pressure (ICP) and cerebral perfusion pressure (CPP) were measured before and at different times after TBI. Locomotor activity, anxiety-like behavior, and spatial memory were assessed on days 3, 7, 14, and 21 after injury. E2, E2-BSA, and G1 prevented the increase of BWC and EB content after TBI, and these effects were inhibited by ICI and G15. ICI and G15 also inhibited the beneficial effects of E2, E2-BSA on ICP, as well as CPP, after trauma. E2, E2-BSA, and G1 prevented the cognitive deficiency and behavioral abnormalities induced by TBI. Similar to the above parameters, ICI and G15 also reversed this E2 and E2-BSA effects on days 3, 7, 14, and 21. Our findings indicated that the beneficial effects of E2-BSA and E2 were inhibited by both ICI and G15, suggesting that GPER and classic ERs were involved in mediating the long-term effects of E2.

α2-Antiplasmin as a potential regulator of the spatial memory process and age-related cognitive decline

α2-Antiplasmin (α2AP), a principal physiological plasmin inhibitor, is mainly produced by the liver and kidneys, but it is also expressed in several parts of the brain, including the hippocampus and cerebral cortex. Our previous study demonstrated that α2AP knockout mice exhibit spatial memory impairment in comparison to wild-type mice, suggesting that α2AP is necessary for the fetal and/or neonatal development of the neural network for spatial memory. However, it is still unclear whether α2AP plays a role in the memory process. The present study demonstrated that adult hippocampal neurogenesis and remote spatial memory were enhanced by the injection of an anti-α2AP neutralizing antibody in WT mice, while the injection of α2AP reduced hippocampal neurogenesis and impaired remote spatial memory, suggesting that α2AP is a negative regulator in memory processing. The present study also found that the levels of α2AP in the brains of old mice were higher than those in young mice, and a negative correlation between the α2AP level and spatial working memory. In addition, aging-dependent brain oxidative stress and hippocampal inflammation were attenuated by α2AP deficiency. Thus, an age-related increase in α2AP might cause cognitive decline accompanied by brain oxidative stress and neuroinflammation. Taken together, our findings suggest that α2AP is a key regulator of the spatial memory process, and that it may represent a promising target to effectively regulate healthy brain aging.

Alignment in spatial memory: Encoding of reference frames or of relations?

A common assumption about spatial memory is that it is organized along one or more reference directions such that access to memory is easier along directions aligned with the reference direction(s). This assumption rests to no small part on frequently replicated alignment effects arising in judgment of relative direction. In this contribution, we report an experiment designed to investigate a possible alternative explanation of alignment effects. By contrasting performance in a judgment of relative direction task with performance in an ego perspective taking task, we tested to what extent alignment effects arise from encoding of relations in addition to or instead of from organization along reference directions. Experimental results suggest little if any contribution of relation encoding on alignment effects, thus lending further support to the assumption of reference directions in spatial memory. Data from both tasks yielded the same alignment effects and provided evidence for a single direction being encoded in memory. Moreover, our results shed new light on and raise questions concerning differential sensorimotor and cognitive influence on spatial memory use. While both influence memory use, systematic bias seems to arise solely from reference directions, along which memory is organized.

Modulation of spatial memory and expression of hippocampal neurotransmitter receptors by selective lesion of medial septal cholinergic and GABAergic neurons

The medial septum (MS) is an important modulator of hippocampal function. The degree of damage in which the particular set of septo-hippocampal projections contributes to the deficits of spatial memory with concomitant changes of hippocampal receptors expression has not been studied till present. Therefore, we investigated spatial memory and the expression level of cholinergic (α7 nACh and M1), GABAergic (α1 subunit of GABAA) and glutamatergic (NR2B subunit of NMDA and GluR 1 subunit of AMPA) receptors in the hippocampus following selective lesions of cholinergic and GABAergic septo-hippocampal projection. Learning process and long-term spatial memory were assessed using a Morris water maze. The obtained results revealed that in contrast to cholinergic lesions, rats with MS GABAergic lesions exhibit a retention deficit in 3 days after training. Western blot analyses revealed the MS cholinergic lesions have significant effect on the expression level of the M1 mACh receptors, while MS GABAergic lesions induce dramatic modulations of hippocampal glutamatergic, cholinergic and GABAergic receptors expression. These results for the first time demonstrated that selective lesions of MS cholinergic and GABAergic neurons differentially affect long-term spatial memory and the memory deficit after MS GABAergic lesion is paralleled with significant changes of hippocampal glutamate, GABA and acetylcholine receptors expression.

Sex differences in the use of spatial cues in two avian brood parasites

Shiny and screaming cowbirds are avian interspecific brood parasites that locate and prospect host nests in daylight and return from one to several days later to lay an egg during the pre-dawn twilight. Thus, during nest location and prospecting, both location information and visual features are available, but the latter become less salient in the low-light conditions when the nests are visited for laying. This raises the question of how these different sources of information interact, and whether this reflects different behavioural specializations across sexes. Differences are expected, because in shiny cowbirds, females act alone, but in screaming cowbirds, both sexes make exploratory and laying nest visits together. We trained females and males of shiny and screaming cowbird to locate a food source signalled by both colour and position (cues associated), and evaluated performance after displacing the colour cue to make it misleading (cues dissociated). There were no sex or species differences in acquisition performance while the cues were associated. When the colour cue was relocated, individuals of both sexes and species located the food source making fewer visits to non-baited wells than expected by chance, indicating that they all retained the position as an informative cue. In this phase, however, shiny cowbird females, but not screaming, outperformed conspecific males, visiting fewer non-baited wells before finding the food location and making straighter paths in the search. These results are consistent with a greater reliance on spatial memory, as expected from the shiny cowbird female's specialization on nest location behaviour.

Effects of post-training administration of LY341495, as an mGluR2/3 antagonist on spatial memory deficit in rats fed with high-fat diet

High-fat diets (HFDs) adversely influence glutamate metabolism and neurotransmission. The precise role of the group II metabotropic glutamate receptors (mGluR2/3) antagonist on spatial memory deficit following consumption of HFD has not yet been clarified. Therefore, in this study, we examined the effects of post-training administration of mGluR2/3 antagonism; LY341495 on spatial memory in rats fed with HFD (for 10 weeks) by using Morris Water Maze (MWM) task. The training session for testing memory acquisition in MWM consisted of 4 trials per day for 4 consecutive days. Twenty-four hours after the last training session the spatial probe test (retention) was given. Intraperitoneal injection (i.p) injection of LY341495 was done 30 min before probe test. Our results showed that 10 weeks consumption of HFD had no significant effect on escape latency and swimming distance in memory acquisition. Our finding showed that consumption of a HFD leads to reference memory impairment in the probe test. HFD animals spent less time in the target zone in compare with control animals. Also, LY341495 improved HFD-induced reference memory (retention) impairment. HFD animals treated with LY341495 spent more time in the target zone in compare with HFD animals. Escape latencies to find the visible platform during visual task were same in all experimental groups, indicating no visual impairment in the animals. We propose that a HFD may act through mGluR2/3 within the brain to reduce synaptic plasticity, which impairs memory retrieval, and post-training administration of LY341495 can reduce HFD-induced reference memory impairment.

Usnic acid improves memory impairment after cerebral ischemia/reperfusion injuries by anti-neuroinflammatory, anti-oxidant, and anti-apoptotic properties

Objective(s):

Cerebral ischemia/reperfusion causes complex pathological mechanisms that lead to brain tissue damage. Usnic acid is a lichen secondary metabolite that has many different biological properties including anti-inflammatory and anti-oxidant activities. Therefore, the objective of the current study was to investigate the neuroprotective effects of usnic acid on apoptotic cell death, neuroinflammation, anti-oxidant enzyme activities, and oxidative stress levels after transient cerebral ischemia/reperfusion.

Materials and Methods:

Forty-two male Wistar rats were randomly assigned to three groups (sham, ischemia/reperfusion, and ischemia/reperfusion+usnic acid). Ischemia was induced by 20 min occlusion of common carotid arteries. Injection of usnic acid (25 mg/kg, intraperitoneally) and saline was done at the beginning of reperfusion time. Morris water maze was applied to assess spatial memory. The protein expression amount was measured using immunohistochemical and immunofluorescence staining. Spectrophotometric assay was performed to determine the levels of anti-oxidant enzymes.

Results:

Usnic acid significantly reduced caspase-3, glial fibrillary acidic protein- positive and ionized calcium-binding adaptor molecule 1-positive cells (P<0.001) and enhanced spatial memory disorders (P<0.05) due to brain ischemia. In addition, treatment with usnic acid improves effects in the antioxidant system following cerebral ischemia (P<0.05).

Conclusion:

Our findings indicate that usnic acid has neuroprotective properties, which possibly is applicable as a promising candidate for cerebral injuries caused by ischemia.

Paw preference is associated with behavioural despair and spatial reference memory in male rats

Paw preference, one of the well-studied behavioural markers of asymmetry, has been associated with affective states and pathologies such as behavioural despair, a rodent model of clinical depression. However, a consistent differential effect of paw preference has not been observed for cognitive functions. In order to investigate the affective properties of paw preference together with its potential cognitive effects, we grouped male Wistar rats as left- or right-pawed, and tested them in the forced swim test and Morris water maze for behavioural despair and spatial memory performance, respectively. We found that left-pawed rats were significantly more susceptible to behavioural despair, while spatial learning performance of the two groups were not different over a five-day Morris water maze task. Left-pawed rats, however, displayed a better reference memory than the right-pawed ones on the subsequent probe trial when the hidden platform of the maze was removed. These findings indicate paw preference as a vulnerability factor for behavioural despair and reveal a previously unknown association between left-paw preference and reference memory performance as assessed in the probe trial of the Morris water maze.

Orally Administered Cinnamon Extract Attenuates Cognitive and Neuronal Deficits Following Traumatic Brain Injury

The present paper shows how cinnamon extract (CE) consumption mitigates neuronal loss and memory impairment following traumatic brain injury (TBI), one of the world's most common neurodegenerative diseases. TBI patients suffer short- and long-term behavioral, cognitive, and emotional impairments, including difficulties in concentration, memory loss, and depression. Research shows that CE application can mitigate cognitive and behavioral impairments in animal models for Alzheimer's and Parkinson's disease, whose pathophysiology is similar to that of TBI. This study builds on prior research by showing similar results in TBI mice models. After drinking CE for a week, mice were injured using our 70-g weight drop TBI device. For 2 weeks thereafter, the mice continued drinking CE alongside standard lab nutrition. Subsequently, the mice underwent behavioral tests to assess their memory, motor activity, and anxiety. The mice brains were harvested for immunohistochemistry staining to evaluate overall neuronal survival. Our results show that CE consumption almost completely mitigates memory impairment and decreases neuronal loss after TBI. Mice that did not consume CE demonstrated impaired memory. Our results also show that CE consumption attenuated neuronal loss in the temporal cortex and the dentate gyrus. Mice that did not consume CE suffered a significant neuronal loss. There were no significant differences in anxiety levels and motor activity between all groups. These findings show a new therapeutic approach to improve cognitive function and decrease memory loss after TBI.

Heat stress induced oxidative damage and perturbation in BDNF/ERK1/2/CREB axis in hippocampus impairs spatial memory

Heat exposure is an environmental stress that causes diverse heat related pathophysiological changes under extreme conditions. The brain including hippocampal region which is associated with learning and memory is significantly affected by heat stress resulting in memory impairment. However, the effect of heat on the spatial memory remains unclear. The present study aimed to explore the effect of heat stress on hippocampus and spatial memory in rats. Rat model of acute heat stress was used which was divided into two groups, viz. moderate heat stress (MHS) and severe heat stress (SHS). Redox parameters evaluation revealed that MHS and SHS exposure markedly increase the production of malondialdehyde (MDA), oxidised glutathione (GSSG), reactive oxidative species (ROS), protein oxidation level and decrease the reduced glutathione (GSH) levels in the hippocampal tissue. Furthermore, Cresyl Violet (CV) staining of hippocampal region showed higher pyknosis in rats exposed to SHS. Pronounced increase of caspase3 expression and Fluoro Jade-C (FJ-C) positive cells were observed in SHS resulting in neuronal injury and apoptosis in CA3 region of hippocampus culminating in spatial memory deficit. Our data also suggest that heat stress induces phospho Extracellular signal-regulated kinases (pERK)1/2 activation induced by Brain-derived neurotrophic factor (BDNF) leading to further activation of phospho cAMP-response element binding protein (pCREB) under MHS. However, during SHS, BDNF and pCREB expression were completely dysregulated and not sufficient to rescue cognitive decline in rats. In conclusion, SHS induces pathological alterations that include oxidative damage and apoptosis of hippocampal neurons, disturbing BDNF/ERK1/2/CREB axis that may affect spatial memory.

Social housing enhances acquisition of task set independently of environmental enrichment: A longitudinal study in the Barnes maze

Human studies suggest that healthy social relationships benefit cognition, yet little is known about the underlying neural mechanisms of this protective effect. In rodents, studies on acute isolation and environmental enrichment (EE) confirm the importance of social exposure. Despite the widely recognized importance of sociality, however, rodent models have yet to explore the independent contributions of social housing divorced of other forms of enrichment. This study dissociates the effects of social and physical enrichment on spatial learning and memory from adulthood to old age. Rats were placed in either single or group housing, provided with ample enrichment, and tested at three time points on several phases/versions of the Barnes maze (BM) (standard, retention probes, variable location, and reversal). We found that sustained social housing enhanced cognitive flexibility, as evidenced by superior acquisition of task set (standard BM), adaptability to a new task set (variable BM), and improved reversal learning (reversal BM). Long-term retention (BM retention probes) of spatial memory was unaffected by housing conditions. Recent studies from our lab, including this report, are the first to show that social housing confers cognitive benefits beyond those of physical enrichment. Importantly, our experimental design is ideal for exploring the neural underpinnings of this socially induced cognitive protection. Understanding how sociality influences cognition will be invaluable to translational models of aging, neuropsychiatric disease, and neurological injury.