Part II. Clinical diagnosis and course of Alzheimer's disease

Acetylcholine from the nucleus basalis magnocellularis facilitates the retrieval of well-established memory

Retrieval deficit of long-term memory is a cardinal symptom of dementia and has been proposed to associate with abnormalities in the central cholinergic system. Difficulty in the retrieval of memory is experienced by healthy individuals and not limited to patients with neurological disorders that result in forgetfulness. The difficulty of retrieving memories is associated with various factors, such as how often the event was experienced or remembered, but it is unclear how the cholinergic system plays a role in the retrieval of memory formed by a daily routine (accumulated experience). To investigate this point, we trained rats moderately (for a week) or extensively (for a month) to detect a visual cue in a two-alternative forced-choice task. First, we confirmed the well-established memory in the extensively trained group was more resistant to the retrieval problem than recently acquired memory in the moderately trained group. Next, we tested the effect of a cholinesterase inhibitor, donepezil, on the retrieval of memory after a long no-task period in extensively trained rats. Pre-administration of donepezil improved performance and reduced the latency of task initiation compared to the saline-treated group. Finally, we lesioned cholinergic neurons of the nucleus basalis magnocellularis (NBM), which project to the entire neocortex, by injecting the cholinergic toxin 192 IgG-saporin. NBM-lesioned rats showed severely impaired task initiation and performance. These abilities recovered as the trials progressed, though they never reached the level observed in rats with intact NBM. These results suggest that acetylcholine released from the NBM contributes to the retrieval of well-established memory developed by a daily routine.

Curcumin-Loaded BSA Nanoparticles Protect More Efficiently Than Natural Curcumin Against Scopolamine-Induced Memory Retrieval Deficit

Introduction:

There is evidence indicating that the rate of AD is lower in curry consuming populations. Then, there is an effort to elucidate if curcumin -as the main ingredient of turmeric-might affect the process of AD. However, in clinical trials of AD, a six-month curcumin treatment failed to show any progress, which might be attributable to its low bioavailability. In this line, a recent human study revealed that a more bioavailable solid lipid curcumin enhances cognition in aged adults. By the application of Bovine Serum Albumin (BSA), the current study aimed at converting curcumin to nano sizes and assessing its protective effects against scopolamine-induced passive avoidance memory retrieval deficit.

Methods:

Nanocurcumin was prepared via dissolution method. Male NMRI mice (20–25 g body weight) were used. The effective doses of nanocurcumin were selected according to the initial pilot test. The mice were treated with nanocurcumin 15 or 20 mg/kg/p.o or distilled water for 10 days. The animals were habituated and trained in passive avoidance apparatus on the day 10. The retention test was performed 24 hours later. Scopolamine (1 mg/kg/i.p.) or saline was injected 30 minutes before memory retention trial.

Results:

The findings indicated that nanocurcumin in doses 15 or 20 mg/kg/p.o prevented the retrieval deficit induced by scopolamine while natural curcumin in its equivalent doses did not have such an effect. Furthermore, nanocurcumin by itself improved memory retention comparing with the control group.

Conclusion:

These findings implied that the potential anti-amnesic effects of curcumin might be observed by producing and using its nanoformulation form.

Curcumin ameliorates scopolamine-induced mice memory retrieval deficit and restores hippocampal p-Akt and p-GSK-3β

The loss of cholinergic neurons has been a major issue in researches on Alzheimer's disease (AD) for about 40 years. Therefore, the scopolamine model of amnesia has been widely used in AD researches. Recently, it was reported that the early stage amnesia of AD is related to memory retrieval deficit. Curcumin, as the main ingredient of turmeric, has been suggested to decrease the prevalence of AD in human population. This study was conducted to assess if curcumin prevents retrieval deficit induced by scopolamine in passive avoidance task. Moreover, according to the proposed link between cholinergic system and Akt/GSK-3β (Glycogen synthase kinase 3 beta) signaling, the hippocampal contents of these proteins were determined. Male NMRI mice (20-25 g body weight) were treated with 50 or 100 mg/kg/po curcumin or its vehicle for 10 days. On day 10, the animals were trained in passive avoidance apparatus. The retention trial was performed 24 h later. Scopolamine (1 mg/kg/i.p.) or its vehicle was administered 30 min before retention test. At the completion of behavioral studies, the hippocampi were removed and western blot analysis was performed to determine hippocampal phosphorylated and total Akt and GSK-3β and beta actin contents. The results showed that curcumin treatment at 50 and 100 mg/kg doses prevented scopolamine-induced memory retrieval deficit and restored Akt and GSK dephosphorylation caused by scopolamine. Overall, these findings showed that pre-test scopolamine administration disrupts memory retrieval along with the diminished Akt and GSK-3β phosphorylation in hippocampus while curcumin administration prevented those changes.

Scopolamine-induced passive avoidance memory retrieval deficit is accompanied with hippocampal MMP2, MMP-9 and MAPKs alteration

Alzheimer's disease (AD) is a neurodegenerative disorder characterized by progressive loss of memory and cognitive deficit. The observed amnesia in the early stages of AD is suggested to be a retrieval problem, rather than encoding and consolidation deficit. According to the cholinergic hypothesis of AD, scopolamine is used to induce an animal model of amnesia. Howbeit the effect of scopolamine on memory retrieval is contradictory. This study aimed to assess the effect of scopolamine on passive avoidance memory retrieval. Additionally according to the reported changes of MMP-2, MMP-9 and MAPKs (ERK, P38 and JNK) in AD pathology the hippocampal contents of these proteins were determined. Male NMRI mice weighing 20-25g were trained in passive avoidance apparatus. The drug or its vehicle was injected 24h after training (30min before retention test). The hippocampal tissue was isolated and western blot analysis was done for MMP-2, MMP-9 and MAPKs (ERK, P38 and JNK). The results indicated that scopolamine (1mg/kg) disrupts passive avoidance memory retrieval. This scopolamine treatment resulted in hippocampal MMP-2 and MMP-9 decline while increased MAPKs in the hippocampus. These results suggest that cholinergic system has an important role in learnt memory retrieval. It might also suggest the positive role of MMP-2 and MMP-9 in this phase of memory while propose that MAPKs affect negatively the reactivation of memory which is compatible with MAPKs activation in AD.

Blockade of muscarinic receptors impairs the retrieval of well-trained memory

Acetylcholine (ACh) is known to play an important role in memory functions, and its deficit has been proposed to cause the cognitive decline associated with advanced age and Alzheimer's disease (the cholinergic hypothesis). Although many studies have tested the cholinergic hypothesis for recently acquired memory, only a few have investigated the role of ACh in the retrieval process of well-trained cognitive memory, which describes the memory established from repetition and daily routine. To examine this point, we trained rats to perform a two-alternative forced-choice visual detection task. Each trial was started by having the rats pull upward a central-lever, which triggered the presentation of a visual stimulus to the right or left side of the display monitor, and then pulling upward a stimulus-relevant choice-lever located on both sides. Rats learned the task within 10 days, and the task training was continued for a month. Task performance was measured with or without systemic administration of a muscarinic ACh receptor (mAChR) antagonist, scopolamine (SCOP), prior to the test. After 30 min of SCOP administration, rats stopped manipulating any lever even though they explored the lever and surrounding environment, suggesting a loss of the task-related associative memory. Three hours later, rats were recovered to complete the trial, but the rats selected the levers irrespective of the visual stimulus, suggesting they remembered a series of lever-manipulations in association with a reward, but not association between the reward and visual stimulation. Furthermore, an m1-AChR, but not nicotinic AChR antagonist caused a similar deficit in the task execution. SCOP neither interfered with locomotor activity nor drinking behavior, while it influenced anxiety. These results suggest that the activation of mAChRs at basal ACh levels is essential for the recall of well-trained cognitive memory.

Nutritional determinants of cognitive aging and dementia

The objective of this review is to provide an overview of nutritional factors involved in cognitive aging and dementia with a focus on nutrients that are also important in neurocognitive development. Several dietary components were targeted, including antioxidant nutrients, dietary fats and B-vitamins. A critical review of the literature on each nutrient group is presented, beginning with laboratory and animal studies of the underlying biological mechanisms, followed by prospective epidemiological studies and randomised clinical trials. The evidence to date is fairly strong for protective associations of vitamin E from food sources, the n-3 fatty acid, DHA, found in fish, a high ratio of polyunsaturated to saturated fats, and vitamin B12 and folate. Attention to the level of nutrient intake is crucial for interpreting the literature and the inconsistencies across studies. Most of the epidemiological studies that observe associations have sufficient numbers of individuals who have both low and adequate nutrient status. Few of the randomised clinical trials are designed to target participants who have low baseline status before randomising to vitamin supplement treatments, and this may have resulted in negative findings. Post-hoc analyses by some of the trials reveal vitamin effects in individuals with low baseline intakes. The field of diet and dementia is a relatively young area of study. Much further work needs to be done to understand dietary determinants of cognitive aging and diseases. Further, these studies must be particularly focused on the levels of nutrient intake or status that confer optimum or suboptimal brain functioning.

Loss of motor function in preclinical Alzheimer's disease

Accumulating evidence suggests that Alzheimer's disease (AD) has a long preclinical phase, during which time its characteristic pathology accumulates and patient function declines, but symptoms are insufficient to warrant a clinical diagnosis of dementia. There have been increasing reports of noncognitive symptoms, including loss of motor function, reported to be associated with incident AD. To understand the link between motor function and preclinical AD, this article examines: our understanding of motor function and its clinical assessment in cohort studies; the relationship of motor function and loss of cognition in older persons; risk factors for cognitive and motor decline; and the relation of post-mortem indices of AD and motor function prior to death. Together, these data suggest that age-related cognitive and motor decline may share a common causation. Furthermore, individuals with a clinical diagnosis of AD may represent the 'tip of the iceberg', since AD pathology may also account for a substantial proportion of cognitive and motor dysfunction currently considered 'normal aging' in older persons without dementia. Thus, AD may have a much larger impact on the health and wellbeing of our aging population.

Gene expression changes in children with autism

The objective of this study was to identify gene expression differences in blood differences in children with autism (AU) and autism spectrum disorder (ASD) compared to general population controls. Transcriptional profiles were compared with age- and gender-matched, typically developing children from the general population (GP). The AU group was subdivided based on a history of developmental regression (A-R) or a history of early onset (A-E without regression). Total RNA from blood was processed on human Affymetrix microarrays. Thirty-five children with AU (17 with early onset autism and 18 with autism with regression) and 14 ASD children (who did not meet criteria for AU) were compared to 12 GP children. Unpaired t tests (corrected for multiple comparisons with a false discovery rate of 0.05) detected a number of genes that were regulated more than 1.5-fold for AU versus GP (n=55 genes), for A-E versus GP (n=140 genes), for A-R versus GP (n=20 genes), and for A-R versus A-E (n=494 genes). No genes were significantly regulated for ASD versus GP. There were 11 genes shared between the comparisons of all autism subgroups to GP (AU, A-E, and A-R versus GP) and these genes were all expressed in natural killer cells and many belonged to the KEGG natural killer cytotoxicity pathway (p=0.02). A subset of these genes (n=7) was tested with qRT-PCR and all genes were found to be differentially expressed (p<0.05). We conclude that the gene expression data support emerging evidence for abnormalities in peripheral blood leukocytes in autism that could represent a genetic and/or environmental predisposition to the disorder.