Assessment of spatial memory in mice

The retinoic acid receptor agonist Am80 increases hippocampal ADAM10 in aged SAMP8 mice

The retinoic acid (RA, a vitamin A metabolite) receptor (RAR) is a transcription factor. Vitamin A/RA administration improves the Alzheimer's disease (AD)- and age-related attenuation of memory/learning in mouse models. Recently, a disintegrin and metalloproteinase domain-containing protein 10 (ADAM10) was identified as a key molecule in RA-mediated anti-AD mechanisms. We investigated the effect of chronic administration of the RAR agonist Am80 (tamibarotene) on ADAM10 expression in senescence-accelerated mice (SAMP8). Moreover, we estimated changes in the expression of the amyloid precursor protein (APP), amyloid beta (Aβ), and hairy/enhancer of split (Hes), which are mediated by ADAM10. Spatial working memory and the levels of a hippocampal proliferation marker (Ki67) were also assessed in these mice. ADAM10 mRNA and protein expression was significantly reduced in the hippocampus of 13-month-old SAMP8 mice; their expression improved significantly after Am80 administration. Further, after Am80 administration, the expression levels of Hes5 and Ki67 were restored and the deterioration of working memory was suppressed, whereas APP and Aβ levels remained unchanged. Our results suggest that Am80 administration effectively improves dementia by activating the hippocampal ADAM10-Notch-Hes5 proliferative pathway.

Pharmacological characterization of memoquin, a multi-target compound for the treatment of Alzheimer's disease

Alzheimer's disease (AD) is characterized by progressive loss of cognitive function, dementia and altered behavior. Over 30 million people worldwide suffer from AD and available therapies are still palliative rather than curative. Recently, Memoquin (MQ), a quinone-bearing polyamine compound, has emerged as a promising anti-AD lead candidate, mainly thanks to its multi-target profile. MQ acts as an acetylcholinesterase and β-secretase-1 inhibitor, and also possesses anti-amyloid and anti-oxidant properties. Despite this potential interest, in vivo behavioral studies with MQ have been limited. Here, we report on in vivo studies with MQ (acute and sub-chronic treatments; 7–15 mg/kg per os) carried out using two different mouse models: i) scopolamine- and ii) beta-amyloid peptide- (Aβ-) induced amnesia. Several aspects related to memory were examined using the T-maze, the Morris water maze, the novel object recognition, and the passive avoidance tasks. At the dose of 15 mg/kg, MQ was able to rescue all tested aspects of cognitive impairment including spatial, episodic, aversive, short and long-term memory in both scopolamine- and Aβ-induced amnesia models. Furthermore, when tested in primary cortical neurons, MQ was able to fully prevent the Aβ-induced neurotoxicity mediated by oxidative stress. The results support the effectiveness of MQ as a cognitive enhancer, and highlight the value of a multi-target strategy to address the complex nature of cognitive dysfunction in AD.

Forced mastication increases survival of adult neural stem cells in the hippocampal dentate gyrus

In this study, we examined the effect of forced mastication on neurogenesis in the hippocampal dentate gyrus (DG) of adult mice. Six-week-old mice were subjected to either a hard or normal diet for 13 weeks. They received a daily injection of bromodeoxyuridine (BrdU) for 12 consecutive days beginning at 14 weeks of age. The number of BrdU-positive cells in the DG was counted 1 day after and 5 weeks after the final BrdU injection. The number of BrdU-positive cells 1 day after injection did not differ between the 2 diet groups. However, the number of BrdU-positive cells in the group fed the hard diet was significantly increased 5 weeks after BrdU injection compared to the group fed the normal diet. The results of the Morris water maze test showed that mice fed a hard diet required significantly less time to reach the platform than the control mice when tested at 10 days. Moreover, mice in the group fed the hard diet spent significantly more time in the former platform area than the group fed the normal diet, indicating that hard diet feeding improved spatial memory compared to normal diet feeding. Real-time PCR analysis showed that the expression of glutamate receptor 1 mRNA was significantly increased in the group fed the hard diet compared with the group fed the normal diet. These results suggest that mastication increases the survival of adult neural stem cells in the hippocampal DG.

Electro-acupuncture combined with transcranial magnetic stimulation improves learning and memory function of rats with cerebral infarction by inhibiting neuron cell apoptosis

This study examined the effect of electro-acupuncture (EA) combined with transcranial magnetic stimulation (TMS) therapy at different time windows on learning and memory ability of rats with cerebral infarction and the underlying mechanism. Two hundred SD rats were randomly divided into four groups: normal group, sham-operated group, model group and EA+TMS group, and each group was then divided into five sub-groups in terms of the different time to start treatment post operation: 6, 12, 24, 48 and 72 h. Cerebral infarction models were established in the model and the EA+TMS groups by left middle cerebral artery occlusion/reperfusion (MCAO/R). After treatment for 14 d, the Morris water maze test was applied to examine the spatial learning and memory abilities of rats. In infarcted area, the expression of caspase-3 was immunohistochemically detected, and real-time fluorescent quantitative PCR was used to measure the expression of Bcl-2 mRNA. The results showed that in EA+TMS group compared with model group at the same treatment time windows, the escape latency was substantially shortened, the expression of caspase-3 was considerably decreased and the expression level of Bcl-2 mRNA significantly increased (P<0.05). In the EA+TMS sub-groups, the escape latency was shortest, the expression level of caspase-3 lowest, and the expression level of Bcl-2 mRNA highest at the treatment time window of 24 h. It was concluded that EA combined with TMS can promote neurological function of rats with cerebral infarction by increasing the expression level of Bcl-2 mRNA and decreasing the expression of caspase-3. The best time window is 24 h after perfusion treatment to ischemia.

Chronic activation of corticotropin-releasing factor type 2 receptors reveals a key role for 5-HT1A receptor responsiveness in mediating behavioral and serotonergic responses to stressful challenge

BACKGROUND

The corticotropin-releasing factor type 2 receptor (CRFR2) is suggested to play an important role in aiding recovery from acute stress, but any chronic effects of CRFR2 activation are unknown. CRFR2 in the midbrain raphé nuclei modulate serotonergic activity of this key source of serotonin (5-HT) forebrain innervation.

METHODS

Transgenic mice overexpressing the highly specific CRFR2 ligand urocortin 3 (UCN3OE) were analyzed for stress-related behaviors and hypothalamic-pituitary-adrenal axis responses. Responses to 5-HT receptor agonist challenge were assessed by local cerebral glucose utilization, while 5-HT and 5-hydroxyindoleacetic acid content were quantified in limbic brain regions.

RESULTS

Mice overexpressing urocortin 3 exhibited increased stress-related behaviors under basal conditions and impaired retention of spatial memory compared with control mice. Following acute stress, unlike control mice, they exhibited no further increase in these stress-related behaviors and showed an attenuated adrenocorticotropic hormone response. 5-HT and 5-hydroxyindoleacetic acid content of limbic nuclei were differentially regulated by stress in UCN3OE mice as compared with control mice. Responses to 5-HT type 1A receptor challenge were significantly and specifically reduced in UCN3OE mice. The distribution pattern of local cerebral glucose utilization and 5-HT type 1A receptor messenger RNA expression levels suggested this effect was mediated in the raphé nuclei.

CONCLUSIONS

Chronic activation of CRFR2 promotes an anxiety-like state, yet with attenuated behavioral and hypothalamic-pituitary-adrenal axis responses to stress. This is reminiscent of stress-related atypical psychiatric syndromes such as posttraumatic stress disorder, chronic fatigue, and chronic pain states. This new understanding indicates CRFR2 antagonism as a potential novel therapeutic target for such disorders.

Cognitive enhancement by omega-3 fatty acids from child-hood to old age: findings from animal and clinical studies

Omega-(n)-3 polyunsaturated fatty acids (PUFAs), including docosahexaenoic acid (DHA) and eicosapentaenoic acid (EPA) are major components of neuronal membranes and have a wide range of functions, from modulating synaptic plasticity and neurochemistry, to neuroimmune-modulation and neuroprotection. Thus, it is not surprising that n-3 PUFA are widely acknowledged to have cognitive-enhancing effects. Although clinical evidence is somewhat conflicting, probably in large part due to methodological issues, animal studies have consistently demonstrated that n-3 PUFA are indispensable for proper brain development, may enhance cognitive function in healthy, adult individuals and attenuate cognitive impairment in aging and age-related disorders, such as dementia. This review discusses and integrates up to date evidence from clinical and animal studies investigating the cognitive-enhancing effects of n-3 PUFA during development, child- and adult-hood, as well as old-age with associated neurodegenerative diseases, such as Alzheimer's disease. Furthermore, we cover the major underlying biochemical and neurophysiological mechanisms by which n-3 PUFA mediate these effects on cognition. This article is part of a Special Issue entitled 'Cognitive Enhancers'.

Liraglutide improves hippocampal synaptic plasticity associated with increased expression of Mash1 in ob/ob mice

OBJECTIVE

Consumption of high-fat diet exerts adverse effects on learning and memory formation, which is linked to impaired hippocampal function. Activation of glucagon-like peptide-1 (GLP-1) signalling ameliorates detrimental effects of obesity-diabetes on cognitive function; however, mechanisms underlying these beneficial actions remain unclear. This study examined effects of daily subcutaneous treatment with GLP-1 mimetic, Liraglutide, on synaptic plasticity, hippocampal gene expression and metabolic control in adult obese diabetic (ob/ob) mice.

RESULTS

Long-term potentiation (LTP) induced by area CA1 was completely abolished in ob/ob mice compared with lean controls. Deleterious effects on LTP were rescued (P<0.001) with Liraglutide. Indeed, Liraglutide-treated mice exhibited superior LTP profile compared with lean controls (P<0.01). Expression of hippocampal brain-derived neurotropic factor and neurotrophic tyrosine kinase receptor-type 2 were not significantly different, but synaptophysin and Mash1 were decreased in ob/ob mice. Treatment with Liraglutide over 21 days increased expression of Mash1 in ob/ob mice (2.0-fold; P<0.01). These changes were associated with significantly reduced plasma glucose (21% reduction; P<0.05) and markedly improved plasma insulin concentrations (2.1- to 3.3-fold; P<0.05 to P<0.01). Liraglutide also significantly reduced the glycaemic excursion following an intraperitonal glucose load (area under curve (AUC) values: 22%; P<0.05) and markedly enhanced the insulin response to glucose (AUC values: 1.6-fold; P<0.05). O2 consumption, CO2 production, respiratory exchange ratio and energy expenditure were not altered by Liraglutide therapy. On day 21, accumulated food intake (32% reduction; P<0.05) and number of feeding bouts (32% reduction; P<0.05) were significantly reduced but simple energy restriction was not responsible for the beneficial actions of Liraglutide.

CONCLUSION

Liraglutide elicits beneficial effects on metabolic control and synaptic plasticity in mice with severe obesity and insulin resistance mediated in part through increased expression of Mash1 believed to improve hippocampal neurogenesis and cell survival.

Less efficient pattern separation may contribute to age-related spatial memory deficits

Spatial memory deficits have been well-documented in older adults and may serve as an early indicator of mild cognitive impairment (MCI) or Alzheimer's disease (AD) in some individuals. Pattern separation is a critical mechanism for reducing potential interference among similar memory representations to enhance memory accuracy. A small but growing literature indicates that spatial pattern separation may become less efficient as a result of normal aging, possibly due to age-related changes in subregions of the hippocampus. This decreased efficiency in spatial pattern separation may be a critical processing deficit that could be a contributing factor to spatial memory deficits and episodic memory impairment associated with aging. The present paper will review recently published studies in humans, non-human primates, and rodents that have examined age-related changes in spatial pattern separation. The potential basic science, translational, and clinical implications from these studies are discussed to illustrate the need for future research to further examine the relationship between spatial pattern separation and brain changes associated with aging and neurodegenerative disease.

LMN diet, rich in polyphenols and polyunsaturated fatty acids, improves mouse cognitive decline associated with aging and Alzheimer's disease

We examined whether LMN diet, reported to induce neurogenesis in adult mice, was able to antagonize the age-related behavioural impairment and neuropathology in wild type (WT) mice and Tg2576 mice, a mouse model of Alzheimer's disease (AD). Thirteen-month-old mice (once the amyloid (Aβ) plaques were formed) were fed with the LMN diet for 5 months, and in the last 2 months of the regimen they received a battery of behavioural tests. In general, both aging and (to a higher extent) Tg2576 genotype deteriorated sensorimotor reflexes, exploratory behaviour in the hole board, activity (but not anxiety) in the elevated plus-maze, ambulation in the home cage during the dark phase, and spatial learning in the Morris water maze. LMN diet did not affect the detrimental effects observed in sensorimotor reflexes, but clearly reversed the effects of both aging and Tg2576 genotype. This behavioural amelioration was correlated with a 70% increase in cellular proliferation in subventricular zone (SVZ) of the brain, but did not correlate with a decrease of amyloid plaques. In contrast, administration of LMN diet to 10 months old mice (before the plaques are formed) strongly suggested a putative delay in the formation of plaques, as indicated by a decreasing tendency of soluble and fibrillar Aβ levels in hippocampus which correlated with a decrease in Aβ (1-40, 1-42) plasma content. Herein we describe for the first time that LMN diet rich in polyphenols, dry fruits and cocoa, was able to decrease behavioural deterioration caused by aging and Tg2576 genotype and to delay the Aβ plaque formation. These results corroborate the increasing importance of polyphenols as human dietary supplements in amelioration of the cognitive impairment during aging and neurological disorders such as AD.

Aging impairs hippocampus-dependent long-term memory for object location in mice

The decline in cognitive function that accompanies normal aging has a negative impact on the quality of life of the elderly and their families. Studies in humans and rodents show that spatial navigation and other hippocampus-dependent functions are particularly vulnerable to the deleterious effects of aging. However, reduced motor activity and alterations in the stress response that accompany normal aging can hinder the ability to study certain cognitive behaviors in aged animals. In an attempt to circumvent these potential confounds, we used a hippocampus-dependent object-place recognition task to show that long-term spatial memory is impaired in aged mice. Aged animals performed similarly to young adult mice on an object recognition task that does not rely on hippocampal function.

What we have learnt about PIKE from the knockout mice

Phosphoinositide 3-kinase enhancer (PIKE) is a group of GTPase that belongs to the centaurin superfamily. These proteins have been discovered for more than a decade but our understandings on their functions are still limited. Studies from our research group and others have revealed some of their functions in a cellular context but their roles in organ development or systemic homeostasis just begin to unveil. The generation of PIKE knockout mice thus provides the valuable model to delineate the physiological roles of PIKE. In addition to being a PI3K/Akt enhancer, phenotypic characterization of the PIKE knockout mice demonstrates that the proteins are involved in multiple signaling cascades including Janus kinase (JAK)/ Signal Transducer and Activator of Transcription (STAT), AMP-activated protein kinase (AMPK)/Acetyl-CoA carboxylase (ACC) and insulin receptor (IR)/Akt. In this article, we will review the current findings from the PIKE knockout mice studies and will discuss how these in vivo observations lead to the identifications of novel signaling cascades regulated by PIKE.