Potentiation of cognitive enhancer effects of Alzheimer's disease medication memantine by alpha7 nicotinic acetylcholine receptor agonist PHA-543613 in the Morris water maze task

Circular eight-room maze for assessing spatial learning and memory functions in rats: An example using a traumatic brain injury model

BACKGROUND AND OBJECTIVES

This study introduced an animal cognitive function assessment system using a novel circular eight-room maze (CERM). The CERM, designed for tracking path trajectories in animal models of cognitive impairment pathologies such as traumatic brain injury (TBI), comprised a 120-cm diameter disk with eight rooms (30 cm × 25 cm × 30 cm).

METHODS

These rooms have magnetic interfaces for modular assembly and disassembly. Notably, one room remained dark and contained food, while the remaining seven rooms automatically lit up when a rat entry, facilitating the assessment of the rat's learning and spatial memory. An infrared night vision camera captured the animal's search trajectory, and binary image processing techniques were employed to eliminate noise and extract the rat's position coordinates to record the rat's path trajectories. The system automatically calculated various cognitive assessment parameters, such as latency, distance traveled, time spent in each quadrant, inner and outer area exploration times, short-term and long-term memory errors, and the number of entries to all the rooms by chance/by memory.

RESULTS

The analysis of overall path trajectories revealed increasingly erratic movement and a growing reliance on chance to enter rooms in rats with TBI over time, likely due to declining memory and the consequent inability to locate the food room. Moreover, increased trajectories in the first quadrant and inner area characterized the behavior of rats with TBI, with statistically significant differences from the sham group observed on day 7. By day 28, all cognitive parameters except short-term memory error significantly differed between the two groups.

CONCLUSION

Experimental data indicated a substantial increase in irregular search behavior in the TBI group over time, suggesting deterioration in cognitive function and an inability to accurately recall the food room. Conversely, the sham group exhibited consistent search trajectories, typically following the walls and rapidly locating the food room. Moreover, their room entries were guided by memory rather than by chance. Compared with traditional maze tests, this system's strengths lie in its ability to provide more quantitative data and vividly portray behavioral patterns. Therefore, the proposed CERM system can be used as an effective tool for cognitive assessment.

Interplay of MeCP2/REST/Synaptophysin-BDNF and intranasal oxytocin influence on Aβ-induced memory and cognitive impairments

BACKGROUND

Alzheimer's disease (AD) is linked to the accumulation of Aβ, increased tau hyperphosphorylation, persistent neuroinflammation, and a decline in neurotrophic factors, neurogenesis, and synaptic plasticity. Oxytocin (OT) has a significant impact on memory and learning. We examined the influence of intranasal (IN) OT on synaptic plasticity, neurogenesis, histone acetylation, and spatial and cognitive memories in rats.

METHODS

Aβ25-35 (5 µg/2.5 µl) was administered bilaterally in the CA1 of male Wistar rats for four consecutive days. After seven days of recovery, OT (2 µg/µl, 10 µl in each nostril) was administered IN for seven consecutive days. Working, spatial, and cognitive memories, and gene expression of neurogenesis- and synaptic plasticity-involved factors were measured in the hippocampus. Histone acetylation (H3K9 and H4K8) was also measured using western blotting.

RESULTS

IN administration of OT significantly improved working and spatial memory impairment induced by Aβ and increased the factors involved in synaptic plasticity (MeCP2, REST, synaptophysin, and BDNF) and neurogenesis (Ki67 and DCX). We also found an enhancement in the levels of H3K9ac and H4K8ac following OT administration.

CONCLUSION

These findings indicated that IN OT could improve hippocampus-related behaviors by increasing synaptic plasticity, stimulating neurogenesis, and chromatin plasticity.

Cellular Mechanisms of Cognitive Enhancement: The In Vivo Modulation of the Firing Activity and the Responsiveness of Rat Hippocampal Neurons by Memantine and Alpha7 Nicotinic Acetylcholine Receptor Ligands

Promising new pharmacological strategies for the enhancement of cognition target either nicotinic acetylcholine receptors (nAChR) or N-methyl-D-aspartate receptors (NMDAR). There is also an increasing interest in low-dose combination therapies co-targeting the above neurotransmitter systems to reach greater efficacy over the monotreatments and to reduce possible side effects of high-dose monotreatments. In the present study, we assessed modulatory effects of the α7 nAChR-selective agonist PHA-543613 (PHA), a novel α7 nAChR positive allosteric modulator compound (CompoundX) and the NMDAR antagonist memantine on the in vivo firing activity of CA1 pyramidal neurons in the rat hippocampus. Three different test conditions were applied: spontaneous firing activity, NMDA-evoked firing activity and ACh-evoked firing activity. Results showed that high but not low doses of memantine decreased NMDA-evoked firing activity, and low doses increased the spontaneous and ACh-evoked firing activity. Systemically applied PHA robustly potentiated ACh-evoked firing activity with having no effect on NMDA-evoked activity. In addition, CompoundX increased both NMDA- and ACh-evoked firing activity, having no effects on spontaneous firing of the neurons. A combination of low doses of memantine and PHA increased firing activity in all test conditions and similar effects were observed with memantine and CompoundX but without spontaneous firing activity increasing effects. Our present results demonstrate that α7 nAChR agents beneficially interact with Alzheimer's disease medication memantine. Moreover, positive allosteric modulators potentiate memantine effects on the right time and the right place without affecting spontaneous firing activity. All these data confirm previous behavioral evidence for the viability of combination therapies for cognitive enhancement.

Rosavin thwarts amyloid-β-induced macromolecular damages and neurotoxicity, exhibiting anti-Alzheimer's disease activity in Wister rat model

Lately, interest surrounding the utilization of plant-derived compounds as a viable beneficial approach for treating Alzheimer's disease (AD) has significantly increased. This study aimed to assess the defensive properties of rosavin against Alzheimer's disease induced by amyloid-β, utilizing experimental models. We found that rosavin exhibited anti-aggregation and disaggregation properties, suggesting its potential to prevent the gathering of Aβ-aggregates. In vitro experiments revealed that rosavin effectively mitigated the neurotoxicity induced by Aβ in Neuro-2a cells, showcasing its protective potential. Rosavin significantly improved the Aβ-induced cognitive deficits in Wistar rats, particularly in spatial memory. Which the pathophysiology of AD includes oxidative damage, which negatively impacts biological macromolecules. Triggers the apoptotic process, causing macromolecular destruction. Interestingly, rosavin attenuated Aβ-induced macromolecular damages, thereby preserving neuronal integrity. Furthermore, the activation of antioxidative defense enzymes by rosavin inhibited oxidative damage. The positive outcomes associated with rosavin were primarily attributed to its capacity to enhance acetylcholine-mediated effects. Finally, rosavin has the potential to alleviate Aβ-induced neurotoxicity and macromolecular damages, ultimately resulting in enhanced memorial and reasoning function in Wistar rats, offering promising prospects for the treatment of AD.

Increased brain cytokine level associated impairment of vigilance and memory in aged rats can be alleviated by alpha7 nicotinic acetylcholine receptor agonist treatment

Age-related neurocognitive disorders are common problems in developed societies. Aging not only affects memory processes, but may also disturb attention, vigilance, and other executive functions. In the present study, we aimed to investigate age-related cognitive deficits in rats and associated molecular alterations in the brain. We also aimed to test the effects of the alpha7 nicotinic acetylcholine receptor (nAChR) agonist PHA-543613 on memory as well as on the sustained attention and vigilance of aged rats. Short- and long-term spatial memories of the rats were tested using the Morris water maze (MWM) task. To measure attention and vigilance, we designed a rat version of the psychomotor vigilance task (PVT) that is frequently used in human clinical examinations. At the end of the behavioral experiments, mRNA and protein expression of alpha7 nAChRs, cytokines, and brain-derived neurotrophic factor (BDNF) were quantitatively measured in the hippocampus, frontal cortex, striatum, and cerebellum. Aged rats showed marked cognitive deficits in both the MWM and the PVT. The deficit was accompanied by increased IL-1beta and TNFalpha mRNA expression and decreased BDNF protein expression in the hippocampus. PHA-543613 significantly improved the reaction time of aged rats in the PVT, especially for unexpectedly appearing stimuli, while only slightly (non-significantly) alleviating spatial memory deficits in the MWM. These results indicate that targeting alpha7 nAChRs may be an effective strategy for the amelioration of attention and vigilance deficits in age-related neurocognitive disorders.

Small molecule ligands for α9* and α7 nicotinic receptors: a survey and an update, respectively

The α9- and α7-containing nicotinic acetylcholine receptors (nAChRs) mediate numerous physiological and pathological processes by complex mechanisms that are currently the subject of intensive study and debate. In this regard, selective ligands serve as invaluable investigative tools and, in many cases, potential therapeutics for the treatment of various CNS disfunctions and diseases, neuropathic pain, inflammation, and cancer. However, the present scenario differs significantly between the two aforementioned nicotinic subtypes. Over the past few decades, a large number of selective α7-nAChR ligands, including full, partial and silent agonists, antagonists, and allosteric modulators, have been described and reviewed. Conversely, reports on selective α9-containing nAChR ligands are relatively scarce, also due to a more recent characterization of this receptor subtype, and hardly any focusing on small molecules. In this review, we focus on the latter, providing a comprehensive overview, while providing only an update over the last five years for α7-nAChR ligands.

A Comparative Study of the Impact of NO-Related Agents on MK-801- or Scopolamine-Induced Cognitive Impairments in the Morris Water Maze

Learning and memory deficits accompany numerous brain dysfunctions, including schizophrenia and Alzheimer’s disease (AD), and many studies point to the role of nitric oxide (NO) in these processes. The present investigations constitute the follow-up of our previous research, in which we investigated the activity of NO releasers and a selective inhibitor of neuronal NO synthase (nNOS) to prevent short-term memory deficits in novel object recognition and T-maze. Here, the ability of the compounds to prevent the induction of long-term memory deficits by MK-801 or scopolamine administration was investigated. The Morris Water Maze test, a reliable and valid test of spatial learning and memory, was used, in which escape latency in the acquisition phase and nine different parameters in the retention phase were measured. A fast NO releaser (spermine NONOate), a slow NO releaser (DETA NONOate), and a nNOS inhibitor, N(ω)-propyl-L-arginine (NPLA), were used. The compounds were administered i.p. at a dose range of 0.05–0.5 mg/kg. All compounds prevented learning deficits in the acquisition phase and reversed reference memory deficits in the retention phase of the scopolamine-treated mice. Spermine NONOate was the least effective. In contrast, the drugs poorly antagonised MK-801-induced deficits, and only the administration of DETA NONOate induced some improvements in the retention trial.

Search Strategy Analysis of 5xFAD Alzheimer Mice in the Morris Water Maze Reveals Sex- and Age-Specific Spatial Navigation Deficits

Spatial disorientation and navigational impairments are not only some of the first memory deficits in Alzheimer's disease, but are also very disease-specific. In rodents, the Morris Water Maze is used to investigate spatial navigation and memory. Here, we examined the spatial memory in the commonly used 5xFAD Alzheimer mouse model in a sex- and age-dependent manner. Our findings show first spatial learning deficits in 7-month-old female 5xFAD and 12-month-old male 5xFAD mice, respectively. While the assessment of spatial working memory using escape latencies provides a global picture of memory performance, it does not explain how an animal solves a spatial task. Therefore, a detailed analysis of swimming strategies was performed to better understand the behavioral differences between 5xFAD and WT mice. 5xFAD mice used a qualitatively and quantitatively different search strategy pattern than wildtype animals that used more non-spatial strategies and showed allocentric-specific memory deficits. Furthermore, a detailed analysis of swimming strategies revealed allocentric memory deficits in the probe trial in female 3-month-old and male 7-month-old 5xFAD animals before the onset of severe reference memory deficits. Overall, we could demonstrate that spatial navigation deficits in 5xFAD mice are age- and sex-dependent, with female mice being more severely affected. In addition, the implementation of a search strategy classification system allowed an earlier detection of behavioral differences and therefore could be a powerful tool for preclinical drug testing in the 5xFAD model.

Neurotransmitters in Prevention and Treatment of Alzheimer's Disease

Alzheimer's disease (AD) is the most frequent cause of cognitive impairment in middle-aged and older populations. There is a lack of drugs that demonstrate significant efficacy in AD, so the study of the pathogenesis of AD is of great importance. More efficacious interventions are needed, as reflected by our population's fast aging. Synaptic plasticity is the capacity of neurons to adjust their connections, and it is strongly tied to learning and memory, cognitive function, and brain injury recovery. Changes in synaptic strength, such as long-term potentiation (LTP) or inhibition (LTD), are thought to represent the biological foundation of the early stages of learning and memory. The results of numerous studies confirm that neurotransmitters and their receptors play an important role in the regulation of synaptic plasticity. However, so far, there is no definite correlation between the function of neurotransmitters in aberrant neural oscillation and AD-related cognitive impairment. We summarized the AD process to understand the impact of neurotransmitters in the progression and pathogenesis of AD, including the current status of neurotransmitter target drugs, and the latest evidence of neurotransmitters' function and changes in the AD process.

Alpha7 nicotinic acetylcholine receptor agonist PHA-543613 improves memory deficits in presenilin 1 and presenilin 2 conditional double knockout mice

Cholinergic system dysfunction has been considered as a critical feature of neurodegenerative progression in Alzheimer's disease (AD). The α7 nicotinic acetylcholine receptors (α7-nAChRs) are widely expressed in the hippocampus cortex and play an important role in memory formation, considered as potential therapeutic agents targets. However, underlying mechanisms have not been fully elucidated. Here, we combine behavioral, molecular biological methods with in vitro slice and in vivo multichannel electrophysiological recording techniques to investigate the molecular, cellular synaptic and neuronal mechanisms of activating α7-nAChR by PHA-543613 (a selective α7-nAChR agonist), which influences the impaired cognitive function using presenilin 1 (PS1) and presenilin 2 (PS2) conditional double knockout (cDKO) mice. Our results demonstrated that PHA-543613 treatment significantly improved the impaired hippocampus-related memory via recovering the reduced the hippocampal synaptic protein levels of α7-nAChR, NMADAR and AMPAR, thereby restoring the impaired post-tetanic potentiation (PTP), long-term potentiation (LTP), activation of molecular signaling pathway for neuronal protection, theta power and strength of theta-gamma phase-amplitude coupling (PAC) at hippocampus in 6-month-old cDKO mice. For the first time, we systematically reveal the mechanisms by which PHA-543613 improves memory deficits at different levels. Therefore, our findings may be significant for the development of therapeutic strategies for AD.

Vitamin D3 supplementation ameliorates cognitive impairment and alters neurodegenerative and inflammatory markers in scopolamine induced rat model

A multifaceted approach can be effective for the treatment of dementia including the most common form, Alzheimer's disease (AD). However, currently, it involves only symptomatic treatment with cholinergic drugs. Beneficial effects of high Vitamin D₃ levels or its intake in the prevention and treatment of cognitive disorders have been reported. Thus, the present study examined the preventive effect of Vitamin D₃ (Calcitriol) supplementation on cognitive impairment and evaluated its impact on the accumulation or degradation of Aβ plaques. A single intraperitoneal injection of scopolamine was used to induce cognitive impairment in rats. Treatment of Vitamin D₃ was provided for 21 days after the injection. Various behavioral parameters like learning, spatial memory and exploratory behavior, biochemical alterations in the brain homogenate and histology of the hippocampus were investigated. Our results indicated that scopolamine-induced rats depicted cognitive deficits with high Aβ levels and hyperphosphorylated tau proteins in the brain tissue, while Vitamin D supplementation could significantly improve the cognitive status and lower these protein levels. These results were supported by the histopathological and immunohistochemical staining of the hippocampal brain region. Furthermore, mechanistic analysis depicted that Vitamin D supplementation improved the Aβ protein clearance by increasing the neprilysin levels. It also reduced the accumulation of Aβ plaques by lowering neuroinflammation as well as oxidative stress. The present findings indicate that Vitamin D₃ supplementation can ameliorate cognitive deficits and thereby delay AD progression by increasing Aβ plaque degradation, reducing inflammation and oxidative stress.

The effects of bilateral prostriata lesions on spatial learning and memory in the rat

Area prostriata is the primary limbic structure for rapid response to the visual stimuli in the far peripheral visual field. Recent studies have revealed that the prostriata receives inputs not only from the visual and auditory cortices but also from many structures critical for spatial processing and navigation. To gain insight into the functions of the prostriata in spatial learning and memory the present study examines the effects of bilateral lesions of the prostriata on motor ability, exploratory interest and spatial learning and memory using the open field, elevated plus-maze and Morris water maze tests. Our results show that the spatial learning and memory abilities of the rats with bilateral prostriata lesions are significantly reduced compared to the control and sham groups. In addition, the lesion rats are found to be less interested in space exploration and more anxious while the exercise capacity of the rats is not affected based on the first two behavioral tests. These findings suggest that the prostriata plays important roles in spatial learning and memory and may be involved in anxiety as well.

Anti-Inflammatory Activity of 4-(4-(Heptyloxy)phenyl)-2,4-dihydro-3H-1,2,4-triazol-3-one via Repression of MAPK/NF-κB Signaling Pathways in β-Amyloid-Induced Alzheimer's Disease Models

Alzheimer’s disease (AD) is a major neurodegenerative disease, but so far, it can only be treated symptomatically rather than changing the process of the disease. Recently, triazoles and their derivatives have been shown to have potential for the treatment of AD. In this study, the neuroprotective effects of 4-(4-(heptyloxy)phenyl)-2,4-dihydro-3H-1,2,4-triazol-3-one (W112) against β-amyloid (Aβ)-induced AD pathology and its possible mechanism were explored both in vitro and in vivo. The results showed that W112 exhibits a neuroprotective role against Aβ-induced cytotoxicity in PC12 cells and improves the learning and memory abilities of Aβ-induced AD-like rats. In addition, the assays of the protein expression revealed that W112 reversed tau hyperphosphorylation and reduced the production of proinflammatory cytokines, tumor necrosis factor-α and interleukin-6, both in vitro and in vivo studies. Further study indicated that the regulation of mitogen-activated protein kinase/nuclear factor-κB pathways played a key role in mediating the neuroprotective effects of W112 against AD-like pathology. W112 may become a potential drug for AD intervention.

Electroacupuncture Ameliorates Tibial Fracture-Induced Cognitive Dysfunction by Elevating α7nAChR Expression and Suppressing Mast Cell Degranulation in the Hippocampus of Rats

Intracerebral neuroinflammation, closely related to brain mast cell (MC) activation, performs an integral function in the pathogenic process of postoperative cognitive dysfunction (POCD). In addition to regulating cognitive activities, the alpha-7-nicotinic acetylcholine receptor (α7nAChR) engages in the progression of cognitive deficiency. In this research, we aimed to investigate how electroacupuncture (EA) affects the cognitive function in rats after tibial fracture surgery to determine whether the underlying mechanism involves the inhibition of hippocampal MC degranulation via α7nAChR. A rat model of tibial fracture surgery for inducing POCD was developed and subjected to treatment with EA or the α7nAChR antagonist α-bungarotoxin (α-BGT) and the α7nAChR agonist PHA-543613. The spatial memory tasks in the Morris Water Maze (MWM) test showed that both EA and PHA-543613-treated rats performed significantly better than untreated rats, with reduced escape latency and increased frequency of passage through the platform. However, EA and PHA-543613 intervention decreased the protein and mRNA levels of High-mobility group box-1(HMGB-1) and proinflammatory cytokines tumor necrosis factor-α (TNF-α), interleukin-1β (IL-1β) in the serum and hippocampus, respectively, by upregulating α7nAChR in the hippocampus. Furthermore, EA and PHA-543613 pretreatment reduced the number of activated MCs and suppressed neuronal apoptosis after tibial fracture surgery in the hippocampal CA1 regions, which was reversed by α-BGT. The findings indicated that EA pretreatment ameliorated POCD after tibial fracture surgery in rats by inhibiting brain MC activation and neuroinflammation mediated by the α7nAChR-dependent cholinergic anti-inflammatory system.