Neuropharmacology of memory consolidation and reconsolidation: Insights on central cholinergic mechanisms

The effects of long-term high-altitude exposure on cognition: A meta-analysis

Long-term high altitudes (HA) exposure's impact on cognition has yielded inconsistent findings in previous research. To address this, we conducted a meta-analysis of 49 studies (6191 individuals) to comprehensively evaluate this effect. Moderating factors such as cognitive task type, altitude (1500-2500 m, 2500-4000 m, and above 4000 m), residential type (chronic and lifelong), adaptation level and demographic factors were analyzed. Cognitive tasks were classified into eight categories: perceptual processes, psychomotor function, long-term memory, working memory, inhibitory control, problem-solving, language, and others. Results revealed a moderate negative effect of HA on cognitive performance (g = -.40, SE =.18, 95% CI = -.76 to -.05). Psychomotor function and long-term memory notably experience the most pronounced decline, while working memory and language skills show moderate decreases due to HA exposure. However, perceptual processes, inhibitory control, and problem-solving abilities remain unaffected. Moreover, residing at altitudes above 4000 m and being a HA immigrant are associated with significant cognitive impairment. In summary, our findings indicate a selective adaptation of cognitive performance to HA conditions.

A comprehensive assessment of the cholinergic-supporting and cognitive-enhancing effects of Rosa damascena Mill. (Damask rose) essential oil on scopolamine-induced amnestic rats

INTRODUCTION

Alzheimer's disease (AD) is a neurodegenerative condition characterized by gradual loss of cognitive abilities (dementia) and is a major public health problem. Here, we aimed at investigating the effects of Rosa damascena essential oil (RDEO) on learning and memory functions in a rat model of amnesia induced by scopolamine, as well as on changes in acetylcholinesterase (AChE) activity, M1 muscarinic acetylcholine receptor (mAChR) expression, and brain-derived neurotrophic factor (BDNF) levels in the extracted brain tissues.

METHODS

The control, amnesia (scopolamine, 1 mg/kg/i.p.) and treatment (RDEO, 100 μL/kg/p.o. or galantamine, 1.5 mg/kg/i.p.) groups were subjected to Morris water maze and new object recognition tests. AChE activity was assayed by ELISA, and M1 mAChR and BDNF concentration changes were determined by western blotting. Also, using computational tools, human M1 mAChR was modeled in an active conformation, and the major components of RDEO were docked onto this receptor.

RESULTS

According to our behavioral tests, RDEO was able to mitigate the learning and memory impairments caused by scopolamine in vivo. Our in vitro assays showed that the observed positive effects correlated well with a decrease in AChE activity and an increase in M1 mAChR and BDNF levels in amnestic rat brains. We also demonstrated in an in silico setting that the major components of RDEO, specifically -citronellol, geraniol, and nerol, could be accommodated favorably within the allosteric binding pocket of active-state human M1 mAChR and anchored here chiefly by hydrogen-bonding and alkyl-π interactions.

CONCLUSION

Our findings offer a solid experimental foundation for future RDEO-based medicinal product development for patients suffering from AD.

Neuroprotective effect of ranolazine improves behavioral discrepancies in a rat model of scopolamine-induced dementia

Background

Ranolazine (Rn), an antianginal agent, acts in the central nervous system and has been used as a potential treatment agent for pain and epileptic disorders. Alzheimer's disease (AD) is one of the most prevalent neurodegenerative diseases and the leading factor in dementia in the elderly.

Aim

We examined the impact of Rn on scopolamine (Sco)-induced dementia in rats.

Methods

Thirty-two albino male rats were divided into four groups: control, Rn, Sco, and Rn + Sco.

Results

A significant decrease in the escape latency in the Morris water maze test after pre-treatment with Rn explained better learning and memory in rats. Additionally, Rn significantly upregulated the activities of the antioxidant enzymes in the treated group compared to the Sco group but substantially reduced acetylcholinesterase activity levels in the hippocampus. Moreover, Rn dramatically reduced interleukin-1 β (IL-1β) and IL-6 and upregulated the gene expression of brain-derived neurotrophic factor (BDNF). Furthermore, in the Sco group, the hippocampal tissue's immunohistochemical reaction of Tau and glial factor activating protein (GFAP) was significantly increased in addition to the upregulation of the Caspase-3 gene expression, which was markedly improved by pre-treatment with Rn. The majority of pyramidal neurons had large vesicular nuclei with prominent nucleoli and appeared to be more or less normal, reflecting the all-beneficial effects of Rn when the hippocampal tissue was examined under a microscope.

Conclusion

Our findings indicated that Rn, through its antioxidative, anti-inflammatory, and anti-apoptotic effects, as well as the control of the expression of GFAP, BDNF, and Tau proteins, has a novel neuroprotective impact against scopolamine-induced dementia in rats.

Neuroprotective effect of Tiliacora triandra (Colebr.) Diels leaf extract on scopolamine-induced memory impairment in rats

Alzheimer's disease is characterized by progressive memory loss caused from alterations in the central cholinergic system. While existing medications often have adverse effects, traditional use of Tiliacora triandra in Thailand shows its potential as a revitalizing neurotonic agent. This study explores the impact of T. triandra leaf extract on cognitive behaviors, neuronal density, and oxidative stress in male rats with scopolamine-induced cognitive impairment. Experimental groups composed of a control, vehicle, positive control meditation, and T. triandra extract-treated groups (100, 200, and 400 mg/kg BW) over 14 days, with scopolamine administration (i.p.) between days 8 and 14. Results showed significant enhancements in the discrimination ratio and spontaneous alteration behavior percentage during novel object recognition (NORT) and Y-maze tests for scopolamine-administered rats treated with T. triandra extract or donepezil. In contrast, open field test (OFT)-assessed spontaneous locomotor activity displayed no significant difference. Notably, acetylcholinesterase (AChE) activity and malondialdehyde (MDA) levels reduced significantly in scopolamine-treated rats with T. triandra extract or the positive control. Moreover, neuronal density in the hippocampal CA3 region, superoxide dismutase (SOD), and glutathione peroxidase (GSH-Px) activities increased significantly. However, catalase (CAT) activity exhibited no significant difference. In conclusion, T. triandra leaf extract shows promise in mitigating scopolamine-induced memory deficits, potentially attributed to increased neuronal density, inhibited AChE activity, reduced MDA levels, and enhanced antioxidant activities. This extract has potential as a therapeutic agent for Alzheimer's disease-associated memory impairment.

Neuroprotective Effect of Saroglitazar on Scopolamine-Induced Alzheimer's in Rats: Insights into the Underlying Mechanisms

Alzheimer's disease (AD) is one of the most prevalent and progressive neurodegenerative disorders, hallmarked by increased amyloid-β deposition and enhanced oxidative load in the brain, ensuing cognitive decline. The present study is aimed at elucidating the neuroprotective effect of saroglitazar, a dual peroxisome-proliferator-activated receptor (PPARα/γ) agonist used in the treatment of diabetic dyslipidemia, against memory impairment induced by intraperitoneal scopolamine injection. 30 male Wistar rats were randomly divided into the following five groups: (A) Veh + Veh, (B) SGZ + Veh, (C) Veh + SCOP, (D) DPZ + SCOP, and (E) SGZ + SCOP. Rats of the respective groups were pretreated with saroglitazar (10 mg/kg, p.o.) and donepezil (3 mg/kg, p.o.) once daily for 16 days. During the final 9 days of the study, a daily injection of scopolamine (3 mg/kg, i.p.) was administered to the respective groups. Adjacent to the scopolamine injection, behavioral tests such as the open field, Y maze, novel object recognition test, and Morris water maze were conducted to assess learning and memory. Additionally, biochemical parameters such as acetylcholinesterase (AChE), butyrylcholinesterase (BuChE), nitric oxide (NO), malondialdehyde (MDA), reduced glutathione (GSH), superoxide dismutase (SOD), brain-derived neurotrophic factor (BDNF), β-amyloid levels, and NF-κB were measured in the hippocampus. The rats that received scopolamine injections showed significantly impaired short-term spatial and learning memory. This was associated with an increase in β-amyloid, iNOS, nitric oxide (NO), malondialdehyde, NF-κB, and TNF-α levels in the hippocampus of AD rats. On the other hand, saroglitazar has provided promising data on its protective role in cognition by protecting the BDNF, SOD, and GSH decline. As a result, saroglitazar was found to be a promising therapy in AD by upregulating the antioxidant status and cholinergic activity and preventing memory loss. Collectively, findings in the present study revealed that saroglitazar protected AD by suppressing scopolamine-mediated learning and memory deficits, oxidative stress, and cholinergic damage. Studying these mechanisms may conclude the protective role of saroglitazar against AD. However, further studies in transgenic animals will provide numerous insights into treatment mechanisms and contribute to developing a therapeutic intervention for AD.

Hippocampal cholinergic receptors and the mTOR participation in fear-motivated inhibitory avoidance extinction memory

Evidence has demonstrated the hippocampal cholinergic system and the mammalian target of rapamycin (mTOR) participation during the memory formation of aversive events. This study assessed the role of these systems in the hippocampus for the extinction memory process by submitting male Wistar rats to fear-motivated step-down inhibitory avoidance (IA). The post-extinction session administration of the nicotinic and muscarinic cholinergic receptor antagonists, mecamylamine and scopolamine, respectively, both at doses of 2 µg/µl/side, and rapamycin, an mTOR inhibitor (0.02 µg/µl/side), into the CA1 region of the dorsal hippocampus, impaired the IA extinction memory. Furthermore, the nicotinic and muscarinic cholinergic receptor agonists, nicotine and muscarine, respectively, had a dose-dependent effect on the IA extinction memory when administered intra-CA1, immediately after the extinction session. Nicotine (0.6 µg/µl/side) and muscarine (0.02 µg/µl/side), respectively, had no effect, while the higher doses (6 and 2 µg/µl/side, respectively) impaired the IA extinction memory. Interestingly, the co-administration of muscarine at the lower dose blocked the impairment that was induced by rapamycin. This effect was not observed when nicotine at the lower dose was co-administered. These results have demonstrated the participation of the cholinergic receptors and mTOR in the hippocampus for IA extinction, and that the cholinergic agonists had a dose-dependent effect on the IA extinction memory. This study provides insights related to the behavioural aspects and the neurobiological properties underlying the early stage of fear-motivated IA extinction memory consolidation and suggests that there is hippocampal muscarinic receptor participation independent of mTOR in this memory process.

Pharmacological sequestration of mitochondrial calcium uptake protects against dementia and β-amyloid neurotoxicity

All forms of dementia including Alzheimer's disease are currently incurable. Mitochondrial dysfunction and calcium alterations are shown to be involved in the mechanism of neurodegeneration in Alzheimer's disease. Previously we have described the ability of compound Tg-2112x to protect neurons via sequestration of mitochondrial calcium uptake and we suggest that it can also be protective against neurodegeneration and development of dementia. Using primary co-culture neurons and astrocytes we studied the effect of Tg-2112x and its derivative Tg-2113x on β-amyloid-induced changes in calcium signal, mitochondrial membrane potential, mitochondrial calcium, and cell death. We have found that both compounds had no effect on β-amyloid or acetylcholine-induced calcium changes in the cytosol although Tg2113x, but not Tg2112x reduced glutamate-induced calcium signal. Both compounds were able to reduce mitochondrial calcium uptake and protected cells against β-amyloid-induced mitochondrial depolarization and cell death. Behavioral effects of Tg-2113x on learning and memory in fear conditioning were also studied in 3 mouse models of neurodegeneration: aged (16-month-old) C57Bl/6j mice, scopolamine-induced amnesia (3-month-old mice), and 9-month-old 5xFAD mice. It was found that Tg-2113x prevented age-, scopolamine- and cerebral amyloidosis-induced decrease in fear conditioning. In addition, Tg-2113x restored fear extinction of aged mice. Thus, reduction of the mitochondrial calcium uptake protects neurons and astrocytes against β-amyloid-induced cell death and contributes to protection against dementia of different ethology. These compounds could be used as background for the developing of a novel generation of disease-modifying neuroprotective agents.

Oxytocin-Cholinergic Central Interaction: Implications for Non-Social Memory Formation

Oxytocin (OT) and vasopressin (AVP) are two closely related neuropeptides implicated in learning and memory processes, anxiety, nociception, addiction, feeding behavior and social information processing. Regarding learning and memory, OT has induced long-lasting impairment in different behaviors, while the opposite was observed with AVP. We have previously evaluated the effect of peripheral administration of OT or its antagonist (AOT) on the inhibitory avoidance response of mice and on the modulation of cholinergic mechanisms. Here, we replicate and validate those results, but this time through central administration of neuropeptides, considering their poor passage through the blood-brain barrier (BBB). When we delivered OT (0.10 ng/mouse) and its antagonist (0.10 ng/mouse) through intracerebroventricular (ICV) injections, the neuropeptide impaired and AOT enhanced the behavioral performance on an inhibitory avoidance response evaluated 48 h after training in a dose-dependent manner. On top of that, we investigated a possible central interaction between OT and the cholinergic system. Administration of anticholinesterases inhibitors with access to the central nervous system (CNS), the activation of muscarinic acetylcholine (Ach) receptors and the increase of evoked ACh release using linopirdine (Lino) (3-10 µg/kg, IP), reversed the impairment of retention performance induced by OT. Besides, either muscarinic or nicotinic antagonists with unrestricted access to the CNS reduced the magnitude of the performance-facilitating effect of AOT's central infusion. We suggest that OT might induce a cholinergic hypofunction state, resulting in an impairment of IA memory formation, a process for which the cholinergic system is crucially necessary.

A multi-parameter evaluation of the neuroprotective and cognitive-enhancing effects of Origanum onites L. (Turkish Oregano) essential oil on scopolamine-induced amnestic rats

Alzheimer's disease (AD) is a neurodegenerative disorder characterized by progressive deterioration of cognitive functions (dementia) and represents a growing public health concern since the population in the age groups at risk is increasing. The latter raises an urgent need to translate research findings in the basic brain and behavioral sciences into anti-AD drugs and disease-modifying therapies. Origanum onites (L.), also called Turkish oregano, is a perennial and herbaceous plant species grown for centuries for medicinal, cosmetic and culinary purposes. This is the first study to investigate the putative neuroprotective and pro-cognitive activities of O. onites essential oil (OOEO) against scopolamine-induced amnesia of AD-type in Wistar albino rats. The results of behavioral tests revealed that OOEO administration was able to significantly alleviate learning and memory impairments induced by scopolamine in vivo. The observed effects could be attributed to inhibition of acetylcholinesterase activity, attenuation of oxidative stress and prevention of neuronal apoptosis in the hippocampus and frontal cortex of AD rats. Modulation of pro-inflammatory enzymes, including cyclooxygenase-2, inducible nitric oxide synthase and myeloperoxidase, might further contribute to the neuroprotective properties of OEOO, as predicted by our in silico models. These findings offer novel insights into the therapeutic potential of OEOO in patients with AD.

Role of prediction error and the cholinergic system on memory reconsolidation processes in mice

The ability to make predictions based on stored information is a general coding strategy. A prediction error (PE) is a mismatch between expected and current events. Our memories, like ourselves, are subject to change. Thus, an acquired memory can become active and update its content or strength by a labilization-reconsolidation process. Within the reconsolidation framework, PE drives the updating of consolidated memories. In the past our lab has made key progresses showing that a blockade in the central cholinergic system during reconsolidation can cause memory impairment, while reinforcement of cholinergic activity enhances it. In the present work we determined that PE is a necessary condition for memory to reconsolidate in an inhibitory avoidance task using both male and female mice. Depending on the intensity of the unconditioned stimulus (US) used during training, a negative (higher US intensity) or positive (lower US intensity/no US) PE on a retrieval session modified the behavioral response on a subsequent testing session. Furthermore, we demonstrated that the cholinergic system modulates memory reconsolidation only when PE is detected. In this scenario administration of oxotremorine, scopolamine or nicotine after memory reactivation either enhanced or impaired memory reconsolidation in a sex-specific manner.

Going with the grain: Fiber, cognition, and the microbiota-gut-brain-axis

Healthy dietary intake has been acknowledged for decades as one of the main contributors to health. More recently, the field of nutritional psychiatry has progressed our understanding regarding the importance of nutrition in supporting mental health and cognitive function. Thereby, individual nutrients, including omega-3 fatty acids and polyphenols, have been recognized to be key drivers in this relationship. With the progress in appreciating the influence of dietary fiber on health, increasingly research is focusing on deciphering its role in brain processes. However, while the importance of dietary fiber in gastrointestinal and metabolic health is well established, leading to the development of associated health claims, the evidence is not conclusive enough to support similar claims regarding cognitive function. Albeit the increasing knowledge of the impact of dietary fiber on mental health, only a few human studies have begun to shed light onto the underexplored connection between dietary fiber and cognition. Moreover, the microbiota-gut-brain axis has emerged as a key conduit for the effects of nutrition on the brain, especially fibers, that are acted on by specific bacteria to produce a variety of health-promoting metabolites. These metabolites (including short chain fatty acids) as well as the vagus nerve, the immune system, gut hormones, or the kynurenine pathway have been proposed as underlying mechanisms of the microbiota-brain crosstalk. In this minireview, we summarize the evidence available from human studies on the association between dietary fiber intake and cognitive function. We provide an overview of potential underlying mechanisms and discuss remaining questions that need to be answered in future studies. While this field is moving at a fast pace and holds promise for future important discoveries, especially data from human cohorts are required to further our understanding and drive the development of public health recommendations regarding dietary fiber in brain health.

Neurobiological effects of phospholipids in vitro: Relevance to stress-related disorders

Nutrition is a crucial component for maintenance of brain function and mental health. Accumulating evidence suggests that certain molecular compounds derived from diet can exert neuroprotective effects against chronic stress, and moreover improve important neuronal processes vulnerable to the stress response, such as plasticity and neurogenesis. Phospholipids are naturally occurring amphipathic molecules with promising potential to promote brain health. However, it is unclear whether phospholipids are able to modulate neuronal function directly under a stress-related context. In this study, we investigate the neuroprotective effects of phosphatidylcholine (PC), lysophosphatidylcholine (LPC), phosphatidylserine (PS), phosphatidylethanolamine (PE), phosphatidylinositol (PI), phosphatidylglycerol (PG), phosphatidic acid (PA), sphingomyelin (SM) and cardiolipin (CL) against corticosterone (CORT)-induced cytotoxicity in primary cultured rat cortical neurons. In addition, we examine their capacity to modulate proliferation and differentiation of hippocampal neural progenitor cells (NPCs).

We show that PS, PG and PE can reverse CORT-induced cytotoxicity and neuronal depletion in cortical cells. On the other hand, phospholipid exposure was unable to prevent the decrease of Bdnf expression produced by CORT. Interestingly, PS was able to increase hippocampal NPCs neurosphere size, and PE elicited a significant increase in astrocytic differentiation in hippocampal NPCs. Together, these results indicate that specific phospholipids protect cortical cells against CORT-induced cytotoxicity and improve proliferation and astrocytic differentiation in hippocampal NPCs, suggesting potential implications on neurodevelopmental and neuroprotective pathways relevant for stress-related disorders.

Scopolamine-Induced Memory Impairment in Mice: Neuroprotective Effects of Carissa edulis (Forssk.) Valh (Apocynaceae) Aqueous Extract

Alzheimer's disease is first characterised by memory loss related to the central cholinergic system alteration. Available drugs provide symptomatic treatment with known side effects. The present study is aimed to evaluate the properties of Carissa edulis aqueous extract on a Scopolamine mouse model as an attempt to search for new compounds against Alzheimer's disease-related memory impairment. Memory impairment was induced by administration of 1 mg/kg (i.p.) of Scopolamine for 7 days, and mice were treated with Carissa edulis aqueous extract. Behavioural studies were performed using T-maze and novel object recognition task for assessing learning and memory and open field test for locomotion. Brain acetylcholinesterase enzyme (AChE) activity was measured to evaluate the central cholinergic system. The level of MDA, glutathione, and catalase activity were measured to evaluate the oxidative stress level. Administration of Scopolamine shows a decrease in learning and memory enhancement during behavioural studies. A significant decrease in the time spent in the preferred arm of T-maze, in the time spent in the exploration of the novel object, and in the discrimination index of the familiar object was also observed. The significant impairment of the central cholinergic system was characterised in mice by an increase of AChE activity to 2.55 ± 0.10 mol/min/g with an increase in oxidative stress. Treatment with the different doses of Carissa edulis (62.8, 157, 314, and 628 mg/kg orally administrated) significantly increased the memory of mice in T-maze and novel object recognition tests and also ameliorated locomotion of mice in the open field. Carissa edulis aqueous extract treatment also decreases the AChE activity and brain oxidative stress. It is concluded that administration of Carissa edulis aqueous extract enhances memory of mice by reducing AChE activity and demonstrating antioxidant properties. This could be developed into a novel therapy against memory impairment related to Alzheimer's disease.

Ethanolic Extract of Orthosiphon stamineus Improves Memory in Scopolamine-Induced Amnesia Model

Alzheimer’s disease (AD) is a chronic neurodegenerative brain disease which is characterized by impairment in cognitive functioning. Orthosiphon stamineus (OS) Benth. (Lamiaceae) is a medicinal plant found around Southeast Asia that has been employed as treatments for various diseases. OS extract contains many active compounds that have been shown to possess various pharmacological properties whereby in vitro studies have demonstrated neuroprotective as well as cholinesterase inhibitory effects. This study, therefore aimed at determining whether this Malaysian plant derived flavonoid can reverse scopolamine induced learning and memory dysfunction in the novel object recognition (NOR) test and the elevated plus maze (EPM) test. In the present study, rats were treated once daily with OS 50 mg/kg, 100 mg/kg, 200 mg/kg and donepezil 1 mg/kg via oral dosing and were given intraperitoneal (ip) injection of scopolamine 1 mg/kg daily to induce cognitive deficits. Rats were subjected to behavioral analysis to assess learning and memory functions and hippocampal tissues were extracted for gene expression and immunohistochemistry studies. All the three doses demonstrated improved scopolamine-induced impairment by showing shortened transfer latency as well as the higher inflexion ratio when compared to the negative control group. OS extract also exhibited memory-enhancing activity against chronic scopolamine-induced memory deficits in the long-term memory novel object recognition performance as indicated by an increase in the recognition index. OS extract was observed to have modulated the mRNA expression of CREB1, BDNF, and TRKB genes and pretreatment with OS extract were observed to have increased the immature neurons against hippocampal neurogenesis suppressed by scopolamine, which was confirmed by the DCX-positive stained cells. These research findings suggest that the OS ethanolic extract demonstrated an improving effect on memory and hence could serve as a potential therapeutic target for the treatment of neurodegenerative diseases like AD.

Neuroprotective Effects of Soy Isoflavones on Scopolamine-Induced Amnesia in Mice

In the recent years, interest in soybean as a neuroprotective nutrient in the management of Alzheimer’s disease (AD) has increased and soy isoflavones (SI), as kinds of soybean phytochemicals, are thought to be biologically active components that confer this beneficial effect against neurodegenerative diseases. However, the neuroprotective effect of SI is not well understood. Therefore, the present study (30 days) was conducted to investigate the neuroprotective effects of soy isoflavones (SI) on scopolamine (SCOP)-induced memory impairments in Institute of Cancer Research (ICR) mice (aged 4 weeks) and to elucidate its underlying mechanisms of action. SI (40 mg/kg) administration improved the cognitive performance of SCOP-treated mice in an object location recognition task and the Morris water maze test. SI (40 mg/kg) administration significantly enhanced cholinergic system function and suppressed oxidative stress levels in the hippocampus of SCOP-treated mice. Furthermore, SI (40 mg/kg) treatment markedly upregulated the phosphorylation levels of extracellular signal-regulated kinase (ERK), cAMP response element-binding protein (CREB) and brain-derived neurotrophic factor (BDNF) expression levels in the hippocampus. Taken together, these results demonstrated that soy isoflavones exerted a significant neuroprotective effect on cognitive dysfunctions induced by scopolamine, suggesting that soy isoflavones could be a good candidate for possible treatment of neurodegenerative diseases, such as Alzheimer’s disease (AD).

Molecular docking and antiamnesic effects of nepitrin isolated from Rosmarinus officinalis on scopolamine-induced memory impairment in mice

Rosmarinus officinalis has long been known as the herb of remembrance. The present study was undertaken to investigate the anti-amnesic effects of nepitrin isolated from Rosmarinus officinalis using in-vivo models of Y-maze and novel object recognition test (NORT) along with in vitro antioxidant and acetylcholinesterase (AChE) and buterylcholinesterase (BuChE) inhibition potential. Nepitrin showed a concentration dependent inhibition of AChE and BuChE enzymes with IC₅₀ values of 65 and 72μg/mL, respectively and antioxidant activity against 2,2-diphenyl-1-picrylhydrazyl (DPPH) and 2, 2'-azinobis-3-ethylbenzothiazoline-6-sulfonic acid (ABTS) with IC₅₀ values 270 and 210μg/mL, respectively. In mice, nepitrin reversed the amnesia induced by scopolamine as indicated by a dose-dependent increase in spontaneous alternation performance in the Y-maze task (p <0.05 versus scopolamine) and increase in the discrimination index in the novel object recognition test (NORT) comparable to the standard drug donepezil 2mg/kg. Molecular docking studies were performed and the GlideScore of nepitrin was consistent with its experimental AChE inhibitory activities. Nepitrin occupied the same binding site forming similar interactions to those formed by donepezil in the crystal structure. Thus, nepitrin could provide a lead for the development of therapeutic agent useful in cognition and memory disorders such as Alzheimer's disease.

Neuroprotective effect of ipriflavone against scopolamine-induced memory impairment in rats

BACKGROUND

Alzheimer's disease is an age-related neurodegenerative disorder characterized clinically by a progressive loss of memory and cognitive functions resulting in severe dementia. Ipriflavone (IPRI) is a non-hormonal, semi-synthetic isoflavone, clinically used in some countries for the treatment and prevention of postmenopausal osteoporosis. Moreover, ipriflavone is a non-peptidomimetic small molecule AChE inhibitor with an improved bioavailability after systemic administration, due to its efficient blood-brain barrier permeability in comparison with peptidomimetic inhibitors.

OBJECTIVE

The present study aimed to evaluate the possible enhancing effects of IPRI on memory impairments caused by scopolamine administration.

METHODS

Male rats were administered IPRI (50 mg/kg, oral) 2 h before scopolamine injection (2 mg/kg, intraperitoneally injected) daily for 4 weeks. Effects of IPRI on acetylcholinesterase activity, amyloid-β precursor processing, and neuroplasticity in the rats' hippocampus were investigated.

RESULTS

Daily administration of IPRI reverted memory impairment caused by scopolamine as measured by the reduction of the escape latency. IPRI significantly alleviated the oxidative stress and restored the mRNA expression of both cAMP-response element-binding protein and brain-derived neurotrophic factor in the hippocampus. Furthermore, it significantly increased the expression of ADAM10 and ADAM17 (two putative α-secretase enzymes) and phosphorylated extracellular signal-regulated kinase 1/2 (pERK1/2) that associated with decreased expression of β-secretase (BACE) in the hippocampus. Finally, both the amyloid-β (Aβ) and Tau pathologies were reduced.

CONCLUSIONS

IPRI showed promising neuroprotective effects against scopolamine-induced memory dysfunction in rats. These findings contributed to the stimulation of α-secretase enzymes, the activation of MAPK/ERK1/2, and the alleviation of oxidative stress.

Comparison of pro-amnesic efficacy of scopolamine, biperiden, and phencyclidine by using passive avoidance task in CD-1 mice

INTRODUCTION

Memory disorders accompany numerous diseases and therapies, and this is becoming a growing medical issue worldwide. Currently, various animal models of memory impairments are available; however, many of them require high financial outlay and/or are time-consuming. A simple way to achieve an efficient behavioral model of cognitive disorders is to inject defined drug that has pro-amnesic properties. Since the involvement of cholinergic and glutamatergic neurotransmission in cognition is well established, the utilization of a nonselective muscarinic receptor antagonist, scopolamine (SCOP), a selective M1 muscarinic receptor antagonist, biperiden (BIP), and a non-competitive N-methyl-d-aspartate (NMDA) receptor antagonist, phencyclidine (PCP) seems to be reliable tools to induce amnesia. As the determination of their effective doses remains vague and the active doses vary significantly in laboratory settings and in mouse species being tested, the aim of this study was to compare these three models of amnesia in CD-1 mice.

METHODS

Male Swiss Albino mice were used in passive avoidance (PA) test. All the compounds were administered intraperitoneally (ip) at doses 1mg/kg, 5mg/kg, and 10mg/kg (SCOP and BIP), and 1mg/kg, 3mg/kg, and 6mg/kg (PCP).

RESULTS

In the retention trial of the PA task, SCOP and PCP led to the reduction of step-through latency at all the tested doses as compared to control, but BIP was effective only at the dose of 10mg/kg.

CONCLUSION

This study revealed the effectiveness of SCOP, PCP, and BIP as tools to induce amnesia, with the PCP model being the most efficacious and SCOP being the only model that demonstrates a clear dose-response relationship.

Huperzine A inhibits immediate addictive behavior but not behavioral sensitization following repeated morphine administration in rats

Acetylcholinesterase inhibitors are regarded as promising therapeutic agents to treat addiction. The current study aimed to examine the effects of huperzine A, a cholinesterase inhibitor, on behavioral sensitization induced by repeated morphine administration and relapse induced by contextual conditioning. The present study also assessed whether the state-dependency hypothesis may explain the results. Adult rats were divided into four groups (n=8) and intraperitoneally injected with 0.2, 0.3 or 0.4 mg/kg huperzine A or saline (1 ml/kg, control), for 5 days. The effect of repeated huperzine A administration alone on locomotor activity was assessed. For the experiments that analyzed the development of morphine-induced sensitization, 40 rats were divided into five groups (n=8): Saline+Saline, Saline+Morphine, 0.2, 0.3 and 0.4 mg/kg huperzine A+Morphine. Following a withdrawal period of 7 days, all animals were administered saline or morphine, as appropriate. To test the state-dependency hypothesis, the rats in the Saline+Morphine group were injected with saline and morphine, while the other three groups were administered different doses of huperzine A and morphine. To examine the effect of huperzine A on the expression of morphine-induced sensitization, the rats in huperzine A+Morphine groups were injected with appropriate concentrations of huperzine A, and morphine. The current results indicated that the administration of huperzine A alone did not affect locomotor activity, while higher doses of huperzine A inhibited the addictive behavior induced by morphine at the development phase. Additionally, huperzine A administration during the expression phase of morphine sensitization did not inhibit the relapse induced by administration of saline. Furthermore, 0.4 mg/kg huperzine A inhibited the expression of morphine-induced behavioral sensitization. Therefore, the results of the current study do not support the state-dependency hypothesis.

Toward a better understanding on the role of prediction error on memory processes: From bench to clinic

Experimental psychology defines Prediction Error (PE) as a mismatch between expected and current events. It represents a unifier concept within the memory field, as it is the driving force of memory acquisition and updating. Prediction error induces updating of consolidated memories in strength or content by memory reconsolidation. This process has two different neurobiological phases, which involves the destabilization (labilization) of a consolidated memory followed by its restabilization. The aim of this work is to emphasize the functional role of PE on the neurobiology of learning and memory, integrating and discussing different research areas: behavioral, neurobiological, computational and clinical psychiatry.

Gongjin-Dan Enhances Hippocampal Memory in a Mouse Model of Scopolamine-Induced Amnesia

We evaluated the neuropharmacological effects of Gongjin-Dan (GJD) on the memory impairment caused by scopolamine injection. BALB/c mice were orally treated with GJD (100, 200, or 400 mg/kg, daily) or tacrine (THA, 10 mg/kg) for 10 days, and scopolamine (2 mg/kg) was injected intraperitoneally. The radial arm maze and passive avoidance tests were performed to evaluate the animal’s learning and memory. Scopolamine increased the task completing time, the number of total errors (reference and working memory error) in the radial arm maze task, and the latency time in the passive avoidance test, which were significantly ameliorated by treatment with GJD. The GJD treatment also attenuated the scopolamine-induced hyperactivation of acetylcholinesterase activity, and suppression of the expression of brain-derived neurotrophic factor (BDNF), nerve growth factor (NGF) and their receptors in the hippocampus. These effects of GJD were supported by both the doublecortin (DCX)-positive staining and Nissl staining, which were used to measure hippocampal neurogenesis and atrophy, respectively. These findings strongly suggest that GJD exerts a potent anti-amnesic effect, and its underlying mechanism might involve the modulation of cholinergic activity.

DADS Analogues Ameliorated the Cognitive Impairments of Alzheimer-Like Rat Model Induced by Scopolamine

The development of agents that affect two or more relevant targets has drawn considerable attention in treatment of AD. Diallyl disulfide (DADS), an active principle of garlic, has been reported to prevent APP processing by amyloidogenic pathway. Recently, we have reported a new series of DADS derivatives and our findings revealed that compound 7k and 7l could provide good templates for developing new multifunctional agents for AD treatment. Thus, the present study was constructed to investigate the neuroprotective effect of DADS analogues (7k and 7l) against Aβ-induced neurotoxicity in SH-SY5Y human neuroblastoma cells and in ameliorating the cognition deficit induced by scopolamine in rat model. The results indicated that compound 7k and 7l significantly inhibited Aβ1-42-induced neuronal cell death by inhibiting ROS generation. Moreover, they prevented apoptosis, in response to ROS, by restoring normal Bax/Bcl-2 ratio. Furthermore, it was observed that scopolamine-induced memory impairment was coupled by alterations in neurotransmitters, acetylcholinesterase activity and oxidative stress markers. Histological analysis revealed severe damaging effects of scopolamine on the structure of cerebral cortex and hippocampus. Administration of compounds 7k and 7l at 5 mg/kg significantly reversed scopolamine-induced behavioural, biochemical, neurochemical and histological changes in a manner comparable to standard donepezil. Together the present findings and previous studies indicate that compounds 7k and 7l have neuroprotective and cognition-enhancing effects, which makes them a promising multi-target candidate for addressing the complex nature of AD.

Nociceptin and the nociceptin receptor in learning and memory

There are many processes in which the neuropeptide nociceptin/orphanin FQ (N/OFQ or nociceptin) is involved in the brain. The role of nociceptin in learning and memory holds promise in modulating these processes in health and disease in the human brain. This review summarizes the body of research focused on N/OFQ and its specific receptor, the nociceptin receptor (NOP receptor), in learning and memory, and its potential mechanisms of action, in which acetylcholine, NMDA receptor, and noradrenaline may be critical. Finally, the association between NOP receptor and posttraumatic stress disorder (PTSD), a psychiatric disorder with altered fear learning, is examined as one of the potential outcomes resulting from pathological consequences of dysregulation of N/OFQ-NOP receptor in the brain.

T cell immunity to glatiramer acetate ameliorates cognitive deficits induced by chronic cerebral hypoperfusion by modulating the microenvironment

Vascular dementia (VaD) is a progressive and highly prevalent disorder. However, in a very large majority of cases, a milieu of cellular and molecular events common for multiple neurodegenerative diseases is involved. Our work focused on whether the immunomodulating effect of glatiramer acetate (GA) could restore normalcy to the microenvironment and ameliorate cognitive decline induced by chronic cerebral hypoperfusion. We assessed cognitive function by rats’ performance in a Morris water maze (MWM), electrophysiological recordings and by pathologic changes. The results suggest that GA reduced cognitive deficits by reestablishing an optimal microenvironment such as increasing expression of the brain-derived neurotrophic factor (BDNF) and modulating the Th1/Th2 cytokine balance in the hippocampus. When microenvironmental homeostasis is restored, cholinergic activity becomes involved in ameliorating cellular damage. Since vaccination with GA can boost “protective autoimmunity” in this way, a similar strategy may have therapeutic potential for alleviating VaD disease.

Nicotinic α7 and α4β2 agonists enhance the formation and retrieval of recognition memory: Potential mechanisms for cognitive performance enhancement in neurological and psychiatric disorders

Cholinergic dysfunction has been shown to be central to the pathophysiology of Alzheimer's disease and has also been postulated to contribute to cognitive dysfunction observed in various psychiatric disorders, including schizophrenia. Deficits are found across a number of cognitive domains and in spite of several attempts to develop new therapies, these remain an unmet clinical need. In the current study we investigated the efficacy of donepezil, risperidone and selective nicotinic α7 and α4β2 receptor agonists to reverse a delay-induced deficit in recognition memory. Adult female Hooded Lister rats received drug treatments and were tested in the novel object recognition (NOR) task following a 6h inter-trial interval (ITI). In all treatment groups, there was no preference for the left or right identical objects in the acquisition trial. Risperidone failed to enhance recognition memory in this paradigm whereas donepezil was effective such that rats discriminated between the novel and familiar object in the retention trial following a 6h ITI. Although a narrow dose range of PNU-282987 and RJR-2403 was tested, only one dose of each increased recognition memory, the highest dose of PNU-282987 (10mg/kg) and the lowest dose of RJR-2403 (0.1mg/kg), indicative of enhanced cognitive performance. Interestingly, these compounds were also efficacious when administered either before the acquisition or the retention trial of the task, suggesting an important role for nicotinic receptor subtypes in the formation and retrieval of recognition memory.

The effect of α7 nicotinic receptor activation on glutamatergic transmission in the hippocampus

Nicotinic acetylcholine receptors (nAChRs) are expressed widely in the CNS, and mediate both synaptic and perisynaptic activities of endogenous cholinergic inputs and pharmacological actions of exogenous compounds (e.g., nicotine and choline). Behavioral studies indicate that nicotine improves such cognitive functions as learning and memory, however the cellular mechanism of these actions remains elusive. With help from newly developed biosensors and optogenetic tools, recent studies provide new insights on signaling mechanisms involved in the activation of nAChRs. Here we will review α7 nAChR's action in the tri-synaptic pathway in the hippocampus. The effects of α7 nAChR activation via either exogenous compounds or endogenous cholinergic innervation are detailed for spontaneous and evoked glutamatergic synaptic transmission and synaptic plasticity, as well as the underlying signaling mechanisms. In summary, α7 nAChRs trigger intracellular calcium rise and calcium-dependent signaling pathways to enhance glutamate release and induce glutamatergic synaptic plasticity.

Effects of imperatorin on scopolamine-induced cognitive impairment and oxidative stress in mice

RATIONALE

Imperatorin, a naturally occurring furanocoumarin, inactivates gamma-aminobutyric acid transaminase and inhibits acetylcholinesterase activity.

OBJECTIVES

The purpose of our experiment was to examine the influence of imperatorin on cognitive impairment and oxidative stress in the brain induced by scopolamine in male Swiss mice.

METHODS

In the present studies, we used scopolamine-invoke memory deficit measured in passive avoidance (PA) paradigm as an animal model of Alzheimer disease (AD).

RESULTS

Our finding revealed that imperatorin administered acutely at the doses of 5 and 10 mg/kg prior to the injection of scopolamine (1 mg/kg) improved memory acquisition and consolidation impaired by scopolamine. Furthermore, repeatable (7 days, twice daily) administration of the highest dose of imperatorin (10 mg/kg) significantly attenuated the effects of scopolamine on memory acquisition, whereas the doses of 5 and 10 mg/kg of this furanocoumarin were effective when memory consolidation was measured. Imperatorin, administered with scopolamine, increased antioxidant enzymes activity and decreased concentration of malondiamide, an indicator of lipid peroxidation level.

CONCLUSIONS

These results demonstrate that imperatorin may offer protection against scopolamine-induced memory impairments and possesses antioxidant properties, thus after further preclinical and clinical studies this compound may provide an interesting approach in pharmacotherapy, as well as prophylactics of AD.

Acetylcholine release and inhibitory interneuron activity in hippocampal CA1

Acetylcholine release in the central nervous system (CNS) has an important role in attention, recall, and memory formation. One region influenced by acetylcholine is the hippocampus, which receives inputs from the medial septum and diagonal band of Broca complex (MS/DBB). Release of acetylcholine from the MS/DBB can directly affect several elements of the hippocampus including glutamatergic and GABAergic neurons, presynaptic terminals, postsynaptic receptors, and astrocytes. A significant portion of acetylcholine's effect likely results from the modulation of GABAergic inhibitory interneurons, which have crucial roles in controlling excitatory inputs, synaptic integration, rhythmic coordination of principal neurons, and outputs in the hippocampus. Acetylcholine affects interneuron function in large part by altering their membrane potential via muscarinic and nicotinic receptor activation. This minireview describes recent data from mouse hippocampus that investigated changes in CA1 interneuron membrane potentials following acetylcholine release. The interneuron subtypes affected, the receptor subtypes activated, and the potential outcome on hippocampal CA1 network function is discussed.