The complexities of behavioural assessment in neurodegenerative disorders: A focus on Alzheimer’s disease

Effects of long-term individual housing of middle-aged female Octodon degus on spatial learning and memory in the Barnes maze task

Introduction

Prolonged social isolation is a form of passive chronic stress that has consequences on human and animal behavior. The present study was undertaken to elucidate whether the long-term isolation would precipitate age-related changes in anxiety and spatial learning and memory in degus.

Methods

We investigated the effects of long-term social isolation on anxiety levels in the light-dark test, and spatial orientation abilities in the Barnes maze. Middle-aged female Octodon degus were allocated to either group-housed (3 animals per cage) or individually-housed for 5 months.

Results

Under this experimental condition, there were no significant group differences in the anxiety level tested in the light-dark test and in the motivation to escape from the Barnes maze. There were no significant differences in cortisol levels between individually- and group-housed animals. On the last acquisition training day of spatial learning, individually- housed animals had a significantly higher number of correct responses and a smaller number of reference and working memory errors than the group-housed animals. In addition, isolated animals showed a tendency for reference and working memory impairment on the retention trial, while group-housed degus showed improvement in these parameters.

Discussion and conclusion

The present study indicates that prolonged social isolation during adulthood in female degus has a dual effect on spatial orientation. Specifically, it results in a significant improvement in acquisition skills but a slight impairment in memory retention. The obtained cognitive changes were not accompanied by modification in anxiety and cortisol levels.

A Systematic Review of the Effects of Capsaicin on Alzheimer's Disease

Alzheimer's Disease (AD) is a progressive neurodegenerative disorder characterised by cognitive impairment, and amyloid-β plaques and neurofibrillary tau tangles at neuropathology. Capsaicin is a spicy-tasting compound found in chili peppers, with anti-inflammatory, antioxidant, and possible neuroprotective properties. Capsaicin intake has been associated with greater cognitive function in humans, and attenuating aberrant tau hyperphosphorylation in a rat model of AD. This systematic review discusses the potential of capsaicin in improving AD pathology and symptoms. A systematic analysis was conducted on the effect of capsaicin on AD-associated molecular changes, cognitive and behaviour resulting in 11 studies employing rodents and/or cell cultures, which were appraised with the Cochrane Risk of Bias tool. Ten studies showed capsaicin attenuated tau deposition, apoptosis, and synaptic dysfunction; was only weakly effective on oxidative stress; and had conflicting effects on amyloid processing. Eight studies demonstrated improved spatial and working memory, learning, and emotional behaviours in rodents following capsaicin treatment. Overall, capsaicin showed promise in improving AD-associated molecular, cognitive, and behavioural changes in cellular and animal models, and further investigations are recommended to test the readily available bioactive, capsaicin, to treat AD.

Predicting conversion of patients with Mild Cognitive Impairment to Alzheimer's disease using bedside cognitive assessments

INTRODUCTION

Patients diagnosed with Mild Cognitive Impairment (MCI) often go on to develop dementia, however many do not. Although cognitive tests are widely used in the clinic, there is limited research on their potential to help predict which patients may progress to Alzheimer's disease (AD) from those that do not.

METHODS

MCI patients (n = 325) from the longitudinal Alzheimer's Disease Neuroimaging Initiative (ADNI-2) dataset were tracked across a 5 year period. Upon initial diagnosis, all patients underwent a series of cognitive tests including the Mini Mental State Examination (MMSE), Montreal Cognitive Assessment (MoCA) and Alzheimer's Disease Assessment Scale-Cognitive (ADAS-Cog 13). Twenty-five percent (n = 83) of those initially diagnosed with MCI subsequently developed AD within 5 years.

RESULTS

We showed that those individuals that progressed to AD had significantly lower scores upon baseline testing on the MMSE and MoCA, and higher scores on the ADAS-13, compared to those that did not convert. However, not all tests were equivalent. We showed that the ADAS-13 offers the best predictability of conversion (Adjusted Odds ratio (AOR) = 3.91). This predictability was higher than that offered by the two primary biomarker Amyloid-beta (Aβ, AOR = 1.99) and phospho-tau (Ptau, AOR = 1.72). Further analysis on the ADAS-13 showed that MCI patients that subsequently converted to AD performed particularly poorly on delayed-recall (AOR = 1.93), word recognition (AOR = 1.66), word finding difficulty (AOR = 1.55) and orientation (1.38) test items.

CONCLUSIONS

Cognitive testing using the ADAS-13 may offer a simpler, less invasive, more clinically relevant and a more effective method of determining those that are in danger of converting from MCI to AD.

Treatment with Autophagy Inducer Trehalose Alleviates Memory and Behavioral Impairments and Neuroinflammatory Brain Processes in db/db Mice

Autophagy attenuation has been found in neurodegenerative diseases, aging, diabetes mellitus, and atherosclerosis. In experimental models of neurodegenerative diseases, the correction of autophagy in the brain reverses neuronal and behavioral deficits and hence seems to be a promising therapy for neuropathologies. Our aim was to study the effect of an autophagy inducer, trehalose, on brain autophagy and behavior in a genetic model of diabetes with signs of neuronal damage (db/db mice). A 2% trehalose solution was administered as drinking water during 24 days of the experiment. Expressions of markers of autophagy (LC3-II), neuroinflammation (IBA1), redox state (NOS), and neuronal density (NeuN) in the brain were assessed by immunohistochemical analysis. For behavioral phenotyping, the open field, elevated plus-maze, tail suspension, pre-pulse inhibition, and passive avoidance tests were used. Trehalose caused a slight reduction in increased blood glucose concentration, considerable autophagy activation, and a decrease in the neuroinflammatory response in the brain along with improvements of exploration, locomotor activity, anxiety, depressive-like behavior, and fear learning and memory in db/db mice. Trehalose exerted some beneficial peripheral and systemic effects and partially reversed behavioral alterations in db/db mice. Thus, trehalose as an inducer of mTOR-independent autophagy is effective at alleviating neuronal and behavioral disturbances accompanying experimental diabetes.

Virtual Morris water maze: opportunities and challenges

The ability to accurately recall locations and navigate our environment relies on multiple cognitive mechanisms. The behavioural and neural correlates of spatial navigation have been repeatedly examined using different types of mazes and tasks with animals. Accurate performances of many of these tasks have proven to depend on specific circuits and brain structures and some have become the standard test of memory in many disease models. With the introduction of virtual reality (VR) to neuroscience research, VR tasks have become a popular method of examining human spatial memory and navigation. However, the types of VR tasks used to examine navigation across laboratories appears to greatly differ, from open arena mazes and virtual towns to driving simulators. Here, we examined over 200 VR navigation papers, and found that the most popular task used is the virtual analogue of the Morris water maze (VWM). Although we highlight the many advantages of using the VWM task, there are also some major difficulties related to the widespread use of this behavioural method. Despite the task's popularity, we demonstrate an inconsistency of use - particularly with respect to the environmental setup and procedures. Using different versions of the virtual water maze makes replication of findings and comparison of results across researchers very difficult. We suggest the need for protocol and design standardisation, alongside other difficulties that need to be addressed, if the virtual water maze is to become the 'gold standard' for human spatial research similar to its animal counterpart.