Spatial Learning Dysfunction Research Articles

Female dominance of both spatial cognitive dysfunction and neuropsychiatric symptoms in a mouse model of Alzheimer's disease.

Alzheimer’s disease (AD) is a prevalent neurological disorder affecting memory function in elderly persons. Indeed, AD exhibits abnormality in cognitive behaviors and higher susceptibility to neuropsychiatric symptoms (NPS). Various factors including aging, sex difference and NPS severity, are implicated during in development of AD. In this study, we evaluated behavioral abnormalities of AD model, PDAPP transgenic mice at young age using the Morris Water Maze test, which was established to assess hippocampal-dependent learning and memory. We found that female AD model mice exhibited spatial learning dysfunction and highly susceptible to NPS such as anxiety and depression, whereas spatial reference memory function was comparable in female PDAPP Tg mice to female wild type (WT) mice. Spatial learning function was comparable in male AD model mice to male WT mice. Multiple regression analysis showed that spatial learning dysfunction was associated with NPS severity such as anxiety and depression. Furthermore, the analysis showed that spatial reference memory function was associated with status of depression, but not anxiety. Thus, these results suggest female dominance of spatial learning dysfunction in the AD model mice accompanying increased NPS severity. The understandings of AD model may be useful for the development of therapeutic agents and methods in human AD.

Wip1 phosphatase deficiency impairs spatial learning and memory

Spatial learning and memory are typically assessed to evaluate hippocampus-dependent cognitive and memory functions in vivo. Protein phosphorylation and dephosphorylation by kinases and phosphatases play critical roles in spatial learning and memory. Here we report that the Wip1 phosphatase is essential for spatial learning, with knockout mice lacking Wip1 phosphatase exhibiting dysfunctional spatial cognition. Aberrant phosphorylation of the Wip1 substrates p38, ATM, and p53 were observed in the hippocampi of Wip1−/− mice, but only p38 inhibition reversed impairments in long-term potentiation in Wip1-knockout mice. p38 inhibition consistently ameliorated the spatial learning dysfunction caused by Wip1 deficiency. Our results demonstrate that deletion of Wip1 phosphatase impairs hippocampus-dependent spatial learning and memory, with aberrant downstream p38 phosphorylation involved in this process and providing a potential therapeutic target.

Euxanthone Attenuates Aβ1-42-Induced Oxidative Stress and Apoptosis by Triggering Autophagy.

Alzheimer's disease (AD) is the most common neurodegenerative disorder and is characterized by the deposition of β-Amyloid (Aβ) plaques which contribute to its pathology. The present study was aimed at exploring the protective effects of euxanthone against Aβ-induced neurotoxicity both in vivo and in vitro. We found that euxanthone significantly attenuated Aβ1-42-induced memory and spatial learning dysfunction and also significantly reversed Aβ1-42-induced neuronal apoptosis and autophagy in the hippocampal region. Euxanthone also protected the neuroblastic PC12 cells against Aβ1-42-induced oxidative stress and apoptosis by inducing autophagy. In conclusion, euxanthone exerts its neuroprotective effect against Aβ1-42 by inducing autophagy, indicating its potential therapeutic role in AD.

PROTECTIVE EFFECT OF IRIS GERMANICA L. IN Β-AMYLOID-INDUCED ANIMAL MODEL OF ALZHEIMER'S DISEASE.

Background:Alzheimer’s disease (AD) is the most common cause of dementia that is an irretrievable chronic neurodegenerative disease. In the current study, we have examined the therapeutic effects of Iris germanica extract on Amyloid β (Aβ) induced memory impairment.Materials and Methods:Wistar rats were divided into five groups of 8 per each. Groups were as followed: control group which were normal rats without induction of AD, Aβ group which received Aβ (50 ng/side), iris 100 group which received Aβ + Iris (100 mg/kg), iris 200 group which received Aβ + Iris (200 mg/kg), and iris 400 group which received Aβ + Iris (400 mg/kg). AD was established by intrahippocampal injection of 50 ng/μl/side Aβ1-42. The day after surgery, animals in treatment groups received different doses of the aqueous extract of Iris by gavage for 30 days. Morris water maze test (MWM) was performed to assess the effects of I. germanica on learning and memory of rats with Aβ induced AD.Results:Data from MWM tests, including escape latency and traveled distance, demonstrated that I. germanica extract could markedly improve spatial memory in comparison to control. Moreover, the plant had a significantly better effect on the performance of AD rats in the probe test.Conclusion:I. germanica extract can successfully reverse spatial learning dysfunction in an experimental model of AD. Further neuro psyco-pharmacological studies are mandatory to reveal the mechanism of action of this natural remedy in the management of AD symptoms.

Hyperammonemia induces glial activation, neuroinflammation and alters neurotransmitter receptors in hippocampus, impairing spatial learning: reversal by sulforaphane.

BackgroundPatients with liver cirrhosis and minimal hepatic encephalopathy (MHE) show mild cognitive impairment and spatial learning dysfunction. Hyperammonemia acts synergistically with inflammation to induce cognitive impairment in MHE. Hyperammonemia-induced neuroinflammation in hippocampus could contribute to spatial learning impairment in MHE. Two main aims of this work were: (1) to assess whether chronic hyperammonemia increases inflammatory factors in the hippocampus and if this is associated with microglia and/or astrocytes activation and (2) to assess whether hyperammonemia-induced neuroinflammation in the hippocampus is associated with altered membrane expression of glutamate and GABA receptors and spatial learning impairment. There are no specific treatments for cognitive alterations in patients with MHE. A third aim was to assess whether treatment with sulforaphane enhances endogenous the anti-inflammatory system, reduces neuroinflammation in the hippocampus of hyperammonemic rats, and restores spatial learning and if normalization of receptor membrane expression is associated with learning improvement.MethodsWe analyzed the following in control and hyperammonemic rats, treated or not with sulforaphane: (1) microglia and astrocytes activation by immunohistochemistry, (2) markers of pro-inflammatory (M1) (IL-1β, IL-6) and anti-inflammatory (M2) microglia (Arg1, YM-1) by Western blot, (3) membrane expression of GABA, AMPA, and NMDA receptors using the BS3 cross-linker, and (4) spatial learning using the radial maze.ResultsThe results reported show that hyperammonemia induces astrocytes and microglia activation in the hippocampus, increasing pro-inflammatory cytokines IL-1β and IL-6. This is associated with altered membrane expression of AMPA, NMDA, and GABA receptors which would be responsible for altered neurotransmission and impairment of spatial learning in the radial maze. Treatment with sulforaphane promotes microglia differentiation from pro-inflammatory M1 to anti-inflammatory M2 phenotype and reduces activation of astrocytes in hyperammonemic rats. This reduces neuroinflammation, normalizes membrane expression of glutamate and GABA receptors, and restores spatial learning in hyperammonemic rats.ConclusionsHyperammonemia-induced neuroinflammation impairs glutamatergic and GABAergic neurotransmission by altering membrane expression of glutamate and GABA receptors, resulting in impaired spatial learning. Sulforaphane reverses all these effects. Treatment with sulforaphane could be useful to improve cognitive function in cirrhotic patients with minimal or clinical hepatic encephalopathy.

Crocetin Attenuates Spatial Learning Dysfunction and Hippocampal Injury in a Model of Vascular Dementia

Chronic cerebral hypoperfusion produces brain ischemia and is associated with related memory impairment. In this study, we prepared crocetin from crocin (the main water soluble pigment in saffron stigmas) in an acidic hydrolysis and its purity was evaluated using spectrophotometry, thin layer chromatography (TLC) and high performance liquid chromatography (HPLC). The memory enhancing effect of crocetin was then studied in a rat model of chronic cerebral hypoperfusion. Different doses of crocetin were administered intraperitoneally (i.p.). The spatial learning and memory function were tested using Morris water maze, after permanent occlusion of common carotids. Finally, the animals were euthanatized in CO2 chamber and histopathological changes in cerebral cortex and hippocampus were investigated. The results indicated that the escape latency time significantly decreased in crocetin treated rats, in comparison with control animals. Also, the percentage of time spent and traveled distance in target quadrant on final test trial day increased in crocetin 8 mg/kg group, compared to control group, while no difference was observed between groups in swimming speed. All behavioral results were confirmed by histopathological analysis. According to our data, crocetin (8 mg/kg) could properly protect cerebrocortical and hippocampus neurons against ischemia. In conclusion, treatment with crocetin could effectively prevent neuropathological alterations in hippocampus thereby resulting in improvement of spatial learning memory in rats after chronic cerebral hypoperfusion.

Injection of neural progenitor cells attenuates decrease in level of connexin 43 in brain capillaries after cerebral ischemia

Although functional disruption of the cerebrovasculature, which is called the “neurovascular unit (NVU)”, may lead to amplification of ischemia-induced injury, changes in the gap junctional proteins within the NVU and their pathophysiological roles after brain injury remain controversial. We previously demonstrated that the intravenous injection of neural progenitor cells (NPCs) have therapeutic potential for improving the spatial learning dysfunction and depression-like behaviors observed after cerebral ischemia. In this study, we investigated whether severe cerebral ischemia would alter the expression of gap junctional proteins in isolated brain capillaries and examined the effect of intravenous injection of NPCs on the levels of these proteins. Cerebral ischemia induced a sustained decrease in the level of the gap junctional protein connexin 43 (Cx43) in the isolated brain capillaries, whereas the level of aquaporin 4 (AQP-4) was transiently increased. The injection of NPCs increased the level of Cx43 compared that of vehicle in the microsphere embolism (ME) rats, suggesting this decrease to be a possible mechanism for disruption of the astrocyte-endothelial cell interface within the NVU without causing any changes in the level of AQP-4 and N-cadherin. We also demonstrated that some of the intravenously injected NPCs migrated into the blood vessels in the peri-infarct area. These results suggest that the intravenous injection of the NPCs would remodel the NVU after severe cerebral ischemia, which remodeling might be associated with functional improvement following the NPC injection.

Attenuation of brain edema and spatial learning deficits by the inhibition of NADPH oxidase activity using apocynin following diffuse traumatic brain injury in rats

Diffuse brain injury (DBI) is a leading cause of mortality and disability among young individuals and adults worldwide. In specific cases, DBI is associated with permanent spatial learning dysfunction and motor deficits due to primary and secondary brain damage. Nicotinamide adenine dinucleotide phosphate (NADPH) oxidase (NOX) is a major complex that produces reactive oxygen species (ROS) during the ischemic period. The complex aggravates brain damage and cell death following ischemia/reperfusion injury; however, its role in DBI remains unclear. The present study aimed to investigate the hypothesis that levels of NOX2 (a catalytic subunit of NOX) protein expression and the activation of NOX are enhanced following DBI induction in rats and are involved in aggravating secondary brain damage. A rat model of DBI was created using a modified weight-drop device. Our results demonstrated that NOX2 protein expression and NOX activity were enhanced in the CA1 subfield of the hippocampus at 48 and 72h following DBI induction. Treatment with apocynin (50mg/kg body weight), a specific inhibitor of NOX, injected intraperitoneally 30min prior to DBI significantly attenuated NOX2 protein expression and NOX activation. Moreover, treatment with apocynin reduced brain edema and improved spatial learning function assessed using the Morris water maze. These results reveal that treatment with apocynin may provide a new neuroprotective therapeutic strategy against DBI by diminishing the upregulation of NOX2 protein and NOX activity.

Intravenous Injection of Neural Progenitor Cells Improves Cerebral Ischemia-Induced Learning Dysfunction

The ability of stem cells to enhance neurological recovery seen after cerebral ischemia has been reported. However, it remains to be clarified whether neural progenitor cells (NPCs) improve cerebral ischemia-induced learning dysfunction. We found in an earlier study that the direct injection of NPCs into the hippocampus prevents spatial learning dysfunction after cerebral ischemia. As the intravascular injection of cells represents a minimally invasive therapeutic approach, we sought to determine whether the intravenous injection of NPCs also would improve ischemia-induced spatial learning dysfunction. Cerebral ischemia was produced by the injection of 700 microspheres into the right hemisphere of rats. The injection of NPCs via a femoral vein on day 7 after the induction of ischemia improved the modified neurological severity score and reduced the prolongation of the escape latency seen in the water maze task on days 12-28 after cerebral ischemia. The intravenous injection of NPCs on day 7 did not affect the viable area of the ipsilateral hemisphere on day 28 compared with that of the non-treated ischemic rats. Furthermore, the NPCs injected via the vein were detected in the ipsilateral hemisphere; and they expressed brain-derived neurotrophic factor (BDNF) on day 28. The decrease in the BDNF level in the ipsilateral hemisphere was also inhibited by the injection of NPCs. These results suggest that the NPCs injected via the vein after cerebral ischemia improved spatial learning dysfunction, but without having any restorative effect on the damaged areas, possibly by acting as a source of neurotrophic factors.

Luteolin promotes long-term potentiation and improves cognitive functions in chronic cerebral hypoperfused rats

Processes of synaptic plasticity, such as long-term potentiation (LTP), has been considered a cellular correlate of learning and memory and many neurological disorders accompanied by cognitive deficits exhibit abnormal synaptic function. This emerging concept is exemplified by Alzheimer's disease. Mounting evidence suggests that Alzheimer's disease begins with subtle alterations of hippocampal synaptic efficacy prior to frank neuronal degeneration, which make it critical to identify LTP enhancers to slow down or stop the progression of Alzheimer's disease. In this study, we found flavonoid luteolin could enhance basal synaptic transmission and facilitate the induction of LTP by high frequency stimulation in the dental gyrus of rat hippocampus. Furthermore, we investigated the effects of luteolin on chronic cerebral hypoperfusion-induced spatial learning dysfunction and LTP impairment in rat. The results showed chronic cerebral hypoperfusion produced by 2-vessel occlusion significantly impaired spatial learning and memory, and luteolin reversed the learning and memory deficit. 2-vessel occlusion resulted in dramatic inhibition of LTP formation in the hippocampus and luteolin significantly rescued the LTP impairment. These results demonstrate that luteolin not only directly modulates LTP formation, but also protects synapses from the detrimental effects of chronic cerebral hypoperfusion on LTP formation, which may contribute to the protective effects of luteolin on learning and memory. By immunoblotting, we found the effects of luteolin on LTP and memory may due to the activation of cAMP response element-binding protein (CREB). Therefore, flavonoid luteolin shows great potential as a novel treatment agent for protecting synaptic function and enhancing memory in neurodegenerative disorders.

Delayed injection of neural progenitor cells improved spatial learning dysfunction after cerebral ischemia

Although stem cells are likely to improve neurological deficits seen after cerebral ischemia, the effects of neural progenitor cells (NPCs) on cerebral ischemia-induced learning dysfunction remain to be clarified. We tested whether the delayed injection of exogenous NPCs could prevent learning dysfunction after cerebral ischemia. Cerebral ischemia was produced by the injection of microspheres into the right hemisphere of each rat. Injection of NPCs obtained from green fluorescent protein transgenic rats into the hippocampus on Day 7 after the induction of cerebral ischemia improved the modified neurological severity score and reduced the prolongation of the escape latency seen in the water maze task. A few of the injected NPCs were positive for mature neuronal markers. In addition, the injected NPCs expressed BDNF on Day 28 after cerebral ischemia. Thus, the exogenous NPCs delivered by injection could act as a source of neurotrophic factors and prevent cerebral ischemia-induced learning dysfunction.

Targeting epileptogenesis‐associated induction of neurogenesis by enzymatic depolysialylation of NCAM counteracts spatial learning dysfunction but fails to impact epilepsy development

Polysialylation is a post-translational modification of the neural cell adhesion molecule (NCAM), which in the adult brain promotes structural changes in regions of neurogenesis and neuroplasticity. Because a variety of plastic changes including neurogenesis have been suggested to be functionally involved in the pathophysiology of epilepsies, it is of specific interest to define the impact of the polysialic acid (PSA)-NCAM system on development of this disease and associated comorbidities. Therefore, we studied the impact of transient enzymatic depolysialylation of NCAM on the pathophysiology in an electrically induced rat post-status epilepticus (SE) model. Loss of PSA counteracted the SE-induced increase in neurogenesis in a significant manner. This effect of endoneuraminidase (endoN) treatment on hippocampal neurogenesis did not impact the subsequent development of spontaneous seizures. In contrast, transient lack of PSA during SE and in the early phase of epileptogenesis exhibited a cognition sparing effect as revealed in the Morris water maze paradigm. In conclusion, our data do not support a central role of neurogenesis in the development of a hyperexcitable epileptic network. However, in view of the cognition-sparing effect, the transient modulation of the PSA-NCAM system seems to allow beneficial long-term disease modification, which might be mediated by the partial normalization of neurogenesis.

Altered mitogen-activated protein kinase signaling, tau hyperphosphorylation and mild spatial learning dysfunction in transgenic rats expressing the β-amyloid peptide intracellularly in hippocampal and cortical neurons

The pathological significance of intracellular Aβ accumulation in vivo is not yet fully understood. To address this, we have studied transgenic rats expressing Alzheimer's-related transgenes that accumulate Aβ intraneuronally in the cerebral and hippocampal cortices but do not develop extracellular amyloid plaques. In these rats, the presence of intraneuronal Aβ is sufficient to provoke up-regulation of the phosphorylated form of extracellular-regulated kinase (ERK) 2 and its enzymatic activity in the hippocampus while no changes were observed in the activity or phosphorylation status of other putative tau kinases such as p38, glycogen synthase kinase 3, and cycline-dependent kinase 5. The increase in active phospho-ERK2 was accompanied by increased levels of tau phosphorylation at S396 and S404 ERK2 sites and a decrease in the phosphorylation of the CREB kinase p90RSK. In a water maze paradigm, male transgenic rats displayed a mild spatial learning deficit relative to control littermates. Our results suggest that in the absence of plaques, intraneuronal accumulation of Aβ peptide correlates with the initial steps in the tau-phosphorylation cascade, alterations in ERK2 signaling and impairment of higher CNS functions in male rats.

Effects of nefiracetam on spatial memory function and acetylcholine and GABA metabolism in microsphere-embolized rats

The present study aimed to determine whether nefiracetam, N-(2,6-dimethylphenyl)-2-(2-oxo-1-pyrrolidinyl) acetamide, a cognition enhancer, has an effect on learning and memory function in sustained cerebral ischemia, and whether the effect, if any, may accompany modification of the cholinergic or γ-aminobutyric acid (GABA)ergic system, which are conceived to be involved in the learning and memory function, in the ischemic brain. Sustained cerebral ischemia was induced by the injection of 700 microspheres into the right hemisphere of the rat. The animals were treated once daily with 10 mg/kg nefiracetam p.o. from 15 h after the operation to either 10 days for the water maze study, or 3 or 5 days after the operation for neurochemical examination. Microsphere-embolized rats showed stroke-like symptoms 15 h after the operation and lengthened the escape latency in the water maze task on days 7–10, suggesting a spatial learning dysfunction. The delayed treatment did not reduce the stroke-like symptoms, but effectively shortened the escape latency. The animals at days 3 and 5 after the operation showed decreases in acetylcholine content and choline acetyltransferase activity, which were not prevented by nefiracetam. The microsphere-embolized rats showed decreases in GABA content and glutamic acid decarboxylase activity. The delayed treatment appreciably restored GABA content in the hippocampus on day 5 and reversed glutamic acid decarboxylase activity in both brain regions on day 5. These results suggest that the GABAergic activity rather than the cholinergic activity may be, at least in part, involved in the pharmacological effects of nefiracetam in the ischemic brain.