Spatial reference- (not working- or procedural-) memory performance of aged rats in the water maze predicts the magnitude of sulpiride-induced facilitation of acetylcholine release by striatal slices

Melatonin alleviates cognition impairment by antagonizing brain insulin resistance in aged rats fed a high-fat diet

Brain insulin resistance, induced by neuroinflammation and oxidative stress, contributes to neurodegeneration, that is, processes that are associated with Aβ accumulation and TAU hyperphosphorylation. Here, we tested the effect of chronic administration of melatonin (MLT) on brain insulin resistance and cognition deficits caused by a high-fat diet (HFD) in aged rats. Results showed that MLT supplementation attenuated peripheral insulin resistance and lowered hippocampal oxidative stress levels. Activated microglia and astrocytes and hippocampal levels of TNF-α in HFD-fed rats were reduced by MLT treatment. Melatonin also prevented HFD-induced increases in beta-amyloid (Aβ) accumulation and TAU phosphorylation in the hippocampus. In addition, impairments of brain insulin signaling elicited by long-term HFD were restored by MLT treatment, as confirmed by ex vivo insulin stimulation. Importantly, MLT reversed HFD-induced cognitive decline as measured by a water maze test, normalized hippocampal LTP and restored CREB activity and BDNF levels as well as cholinergic neuronal activity in the hippocampus. Collectively, these findings indicate that MLT may exhibit substantial protective effects on cognition, via restoration of brain insulin signaling.

Protective effects of chronic treatment with a standardized extract of Ginkgo biloba L. in the prefrontal cortex and dorsal hippocampus of middle-aged rats

This study assessed the effects of chronic treatment with a standardized extract of Ginkgo biloba L. (EGb) on short-term and long-term memory as well as on anxiety-like and locomotor activity using the plus-maze discriminative avoidance task (PM-DAT). Additionally, we evaluated the antioxidant and neuroprotective effects of EGb on the prefrontal cortex (PFC) and dorsal hippocampus (DH) of middle-aged rats using the comet assay. Twelve-month-old male Wistar rats were administered vehicle or EGb (0.5mgkg(-1) or 1.0gkg(-1)) for 30days. Behavioural data showed that EGb treatment improved short-term memory. Neither an anti-anxiety effect nor a change in locomotor activity was observed. Twenty-four hours after the behavioural tests, the rats were decapitated, and the PFC and DH were quickly dissected out and prepared for the comet assay. The levels of DNA damage in the PFC were significantly lower in rats that were treated with 1.0gkg(-1) EGb. Both doses of EGb decreased H2O2-induced DNA breakage in cortical cells, whereas the levels of DNA damage in the EGb-treated animals were significantly lower than those in the control animals. No significant differences in the level of DNA damage in hippocampal cells were observed among the experimental groups. EGb treatment was not able to reduce H2O2-induced DNA damage in hippocampal cells. Altogether, our data provide the first demonstration that chronic EGb treatment improved the short-term memory of middle-aged rats, an effect that could be associated with a reduction in free radical production in the PFC. These data suggest that EGb treatment might increase the survival of cortical neurons and corroborate and extend the view that EGb has protective and therapeutic properties.

Late enrichment maintains accurate recent and remote spatial memory only in aged rats that were unimpaired when middle aged

Exposure of rodents to a stimulating environment has beneficial effects on some cognitive functions that are impaired during physiological aging, and especially spatial reference memory. The present study investigated whether environmental enrichment rescues these functions in already declining subjects and/or protects them from subsequent decline. Subgroups of 17-mo-old female rats with unimpaired versus impaired performance in a spatial reference memory task (Morris water maze) were housed until the age of 24 mo in standard or enriched environment. They were then trained in a second reference memory task, conducted in a different room than the first, and recent (1 d) and remote (10 d) memory were assessed. In unimpaired subgroups, spatial memory declined from 17 to 24 mo in rats housed in standard conditions; an enriched environment during this period allowed maintenance of accurate recent and remote spatial memory. At 24 mo, rats impaired at the age of 17 mo housed in enriched environment learned the task and displayed substantial recent memory, but their performance remained lower than that of unimpaired rats, showing that enrichment failed to rescue spatial memory in already cognitively declining rats. Controls indicated carryover effects of the first water maze training, especially in aged rats housed in standard condition, and confirmed the beneficial effect of enrichment on remote memory of aged rats even if they performed poorly than young adults housed for the same duration in standard or enriched condition.

Lifelong environmental enrichment in rats: impact on emotional behavior, spatial memory vividness, and cholinergic neurons over the lifespan

We assessed lifelong environmental enrichment effects on possible age-related modifications in emotional behaviors, spatial memory acquisition, retrieval of recent and remote spatial memory, and cholinergic forebrain systems. At the age of 1 month, Long-Evans female rats were placed in standard or enriched rearing conditions and tested after 3 (young), 12 (middle-aged), or 24 (aged) months. Environmental enrichment decreased the reactivity to stressful situations regardless of age. In the water maze test, it delayed the onset of learning deficits and prevented age-dependent spatial learning and recent memory retrieval alterations. Remote memory retrieval, which was altered independently of age under standard rearing conditions, was rescued by enrichment in young and middle-aged, but unfortunately not aged rats. A protected basal forebrain cholinergic system, which could well be one out of several neuronal manifestations of lifelong environmental enrichment, might have contributed to the behavioral benefits of this enrichment.

Characterizing cognitive aging of spatial and contextual memory in animal models

Episodic memory, especially memory for contextual or spatial information, is particularly vulnerable to age-related decline in humans and animal models of aging. The continuing improvement of virtual environment technology for testing humans signifies that widely used procedures employed in the animal literature for examining spatial memory could be developed for examining age-related cognitive decline in humans. The current review examines cross species considerations for implementing these tasks and translating findings across different levels of analysis. The specificity of brain systems as well as gaps in linking human and animal laboratory models is discussed.

Age-related deficits in spatial memory and hippocampal spines in virgin, female Fischer 344 rats

Effects of aging on memory and brain morphology were examined in aged, 21-month-old, and young, 4-month-old, Fischer 344 female rats. Spatial memory was assessed using the object placement task, and dendritic spine density was determined on pyramidal neurons in the hippocampus following Golgi impregnation. Consistent with previous studies, aged females showed poorer object placement performance than young subjects. Young subjects significantly discriminated the location of objects with a 1.5-hour intertrial delay while aged subjects did not. Spine density of basal dendrites on CA1 pyramidal cells was 16% lower in the aged subjects as compared to the young subjects. No differences in spine density were found between young and aged subjects in basal dendrites of CA1 or in either dendritic field of CA3 pyramidal neurons. Thus, decreased hippocampal CA1 dendritic spine density in aged rats may contribute to poorer spatial memory as compared to young rats. The possibility that the neuroplastic changes observed in this study may pertain only to female subjects having had a specific set of life experiences is discussed. Different factors, such as reproductive status, diet, and handling may contribute to neuroplasticity of the brain during aging; however, this view requires further examination.

Rejuvenation of antioxidant and cholinergic systems contributes to the effect of procyanidins extracted from the lotus seedpod ameliorating memory impairment in cognitively impaired aged rats

The major purpose of this study was to determine the effect of procyanidins extracted from the lotus seedpod (LSPC) on the learning and memory impairments in cognitively impaired aged rats. Based on Morris water maze performance compared with young female rats, aged unimpaired (AU) and aged impaired (AI) rats were chosen from aged female rats. LSPC supplementation (50, 100 mg/kg BW, p.o.) for 7 weeks significantly improved learning and memory impairments in AI animals in the Morris water maze test, as evaluated by shortened escape latency and swimming distance. Aged rats had significantly declined antioxidant defense capacities and significantly increased lipid peroxidation and protein oxidation levels in hippocampus and cerebral cortex than young rats. Further, AI group had higher protein oxidation level compared with AU group. LSPC (50, 100 mg/kg BW, p.o.) significantly reversed the decline of antioxidant defense capacities and significantly reduced lipid peroxidation and protein oxidation levels in hippocampus and cerebral cortex of AI rats. In addition, LSPC significantly restored acetylcholine (ACh) contents and acetylcholinesterase (AChE) activities in hippocampus and cerebral cortex of AI animals. The results of this study suggest that LSPC may play a useful role in the treatment of cognitive impairment caused by Alzheimer's disease and aging.

Chronic periadolescent cannabinoid treatment enhances adult hippocampal PSA-NCAM expression in male Wistar rats but only has marginal effects on anxiety, learning and memory

Pubertal and adolescent exposure to cannabinoids is associated with enduring alterations in anxiety and memory. However, periadolescence virtually remains unexplored. Here, we measured anxiety in the Elevated Plus Maze (EPM) in adult Wistar rats treated at periadolescence (P28-P38) with the cannabinoid agonist CP 55,940 (CP) (0.4 mg/kg; 2 ml/kg i.p., 1 daily injection), and we also defined their recognition memory in the novel object paradigm and spatial learning and memory in the water maze. Additionally, we measured the expression of hippocampal PSA-NCAM (Polysialic Acid-Neural Cell Adhesion Molecule) and long-term potentiation (LTP) as well as, given their role in mnemonic processing, the levels of plasma corticosterone and estradiol. We found that CP had no robust effects on anxiety or in recognition memory. In the water maze, only a slight decreased percentage of failed trials in the reference memory task and an improvement in an indirect index of attention were observed. However, we detected an up-regulation of hippocampal PSA-NCAM expression, only in CP-males, although this effect was not related to changes in LTP. No hormonal alterations were evident. Based on our data, minimal long-term effects on anxiety, learning and memory appear to result from cannabinoid exposure during the periadolescent period.