Inhibition of central angiotensin converting enzyme ameliorates scopolamine induced memory impairment in mice: role of cholinergic neurotransmission, cerebral blood flow and brain energy metabolism

Novel Substituted Pyrimidine Derivatives as Potential Anti-Alzheimer's Agents: Synthesis, Biological, and Molecular Docking Studies

The most frequent type of age-related dementia is Alzheimer's disease. To discover novel therapeutic agents for Alzheimer's disease, a series of substituted pyrimidine derivatives were synthesized and evaluated for anti-Alzheimer's activity. All the synthesized compounds were validated by 1HNMR, 13CNMR, and HRMS to assess the structural conformance of the newly synthesized compounds. The synthesized compounds were then evaluated for their in vivo acute toxicity study. Evaluation of acute toxicity showed that none of the synthesized compounds showed toxicity up to 1000 mg/kg. After in vivo acute toxicity studies, the compounds were subjected to behavioral and biochemical studies. Compound N4-(4-chlorophenyl)-N2-(2-(piperidin-1-yl)ethyl)pyrimidine-2,4-diamine 5b (SP-2) displayed an excellent anti-Alzheimer's profile, while the rest of the compounds showed satisfactory results in comparison to donepezil. Docking studies confirmed the results obtained through in vivo experiments and showed that 5b (SP-2) showed a similar interaction to that of donepezil. Further, in silico molecular property predictions showed that 5b (SP-2) possesses favorable drug-likeness and ADME properties for CNS activity. These results implied that 5b could serve as an appropriate lead molecule for the development of anti-Alzheimer's agent.

Investigation, scaffold hopping of novel donepezil-based compounds as anti-Alzhiemer's agents: synthesis, in-silico and pharmacological evaluations

Alzheimer's disease (AD) is a multifaceted neurodegenerative condition. The pathogenesis of AD is highly intricate and the disease is apparent in the aged population ~ 50-70 years old. Even after > 100 years of research, the root origin of AD and its pathogenesis is unclear, complex and multifaceted. Herein, we have designed and synthesized 9 novel molecules with three different heterocyclic scaffolds namely pyrrolidone-2-one, quinoline & indoline-2-one to imitate and explore the novel chemical space around donepezil. The synthesized molecules were evaluated for their potential as anti-Alzheimer's agents through in-vitro and in-vivo studies in appropriate animal models. To further understand their interaction with acetylcholinesterase enzyme (AChE), extra-precision docking, and molecular dynamics simulation studies were carried out. As the number of compounds was limited to thoroughly explore the structure-activity relationship, atom-based 3D-quantitative structure-activity relationships (QSAR) studies were carried out to get more insights. All the designed compounds were found to inhibit AChE with IC50 in the micromolar range. From pyrrolidone-2-one series, 6-chloro-N-(1-(1-(3,4-dimethoxybenzyl)-2-oxopyrrolidin-3-yl)piperidin-4-yl)pyridine-3-sulfonamide (9), 2-(1-benzylpiperidin-4-yl)-6,7-dimethoxy-4-(4-methoxyphenyl)quinoline (18) from quinoline series and N-(1-benzylpiperidin-4-yl)-2-(2-oxoindolin-3-yl)acetamide (23) from indolin-2-one series inhibited AChE with an IC50 value of 0.01 µM. Based on other biochemical studies like lipid peroxidation, reduced glutathione, superoxide dismutase, catalase, nitrite, and behavioural studies (Morris water maze), compound 9 was found to be a potent AChE inhibitor which can be further explored as a lead molecule to design more potent and effective anti-Alzheimer's agents.

Effects of Goldblatt hypertension on rats’ hippocampal cholinergic system

Background

The classical renin-angiotensin system (RAS) has an important role in the cardiovascular system and water homeostasis in the body. Recently, the existence of RAS with all of its components has been shown in the mammalian brain. RAS participates in many brain activities, including memory acquisition and consolidation. Since the cholinergic neurotransmission in the hippocampus is crucial for these functions, this study aims to evaluate the hippocampal angiotensin receptors (ATs) and choline acetyltransferase (ChAT) mRNA in the renovascular hypertensive rats in captopril- and losartan-treated hypertensive rats.

Methods

The rats were randomly divided into four groups of eight animals; sham, Goldblatt two kidney one clip (2K1C) hypertensive rats and Goldblatt 2K1C hypertensive rats received 5 mg/kg captopril and Goldblatt 2K1C hypertensive rats received 10 mg/kg losartan. After 8 days of treatment, the rats were sacrificed and angiotensin-converting enzyme (ACE), ChAT, AT1, and AT2 receptor mRNAs in the hippocampus of rats were assessed by real-time PCR. The Morris water maze test was applied to measure the cognitive functioning of the rats.

Results

Hypertensive rats showed impaired acquisition and memory function in the Morris water maze test. Treatment with ACE inhibitor (captopril) and AT1 receptor antagonist (losartan) reversed the observed acquisition and memory deficit in hypertensive rats. Overexpression of AChE, AT1, and AT2 and low expression of ChAT were noted in the hippocampus of rats with Goldblatt hypertension compared with that of the sham group. Treatment with captopril significantly reversed these changes, while treatment with losartan slightly reduced the mentioned effects.

Conclusion

The memory-enhancing effect of captopril in renovascular hypertensive rats might lead to increased hippocampal ChAT expression.

Long-Term Effect of Porcine Brain Enzyme Hydrolysate Intake on Scopolamine-Induced Memory Impairment in Rats

No study has revealed the effect of porcine brain enzyme hydrolysate (PBEH) on memory impairment. We aimed to examine the hypothesis that PBEH intake modulates memory deficits and cognitive behavior in scopolamine (SC)-induced amnesia rats, and its mechanism, including gut microbiota changes, was determined. Sprague–Dawley male rats had intraperitoneal injections of SC (2 mg/kg body weight/day) at 30 min after daily feeding of casein (MD-control), PBEH (7 mg total nitrogen/mL) at 0.053 mL (Low-PBEH), 0.159 mL (Medium-PBEH), 0.478 mL (High-PBEH), or 10 mg donepezil (Positive-control) per kilogram body weight per day through a feeding needle for six weeks. The Normal-control rats had casein feeding without SC injection. PBEH dose-dependently protected against memory deficits determined by passive avoidance test, Y-maze, water-maze, and novel object recognition test in SC-induced rats compared to the MD-control. The High-PBEH group had a similar memory function to the Positive-control group. Systemic insulin resistance determined by HOMA-IR was lower in the PBEH groups than in the Normal-control but not the Positive-control. In parallel with systemic insulin resistance, decreased cholesterol and increased glycogen contents in the hippocampus in the Medium-PBEH and High-PBEH represented reduced brain insulin resistance. PBEH intake prevented the increment of serum TNF-α and IL-1β concentrations in the SC-injected rats. Hippocampal lipid peroxide and TNF-α contents and mRNA TNF-α and IL-1β expression were dose-dependently reduced in PBEH and Positive-control. PBEH decreased the hippocampal acetylcholinesterase activity compared to the MD-control, but not as much as the Positive-control. PBEH intake increased the α-diversity of the gut microbiota compared to the MD-control, and the gut microbiota community was separated from MD-control. In metagenome function analysis, PBEH increased the energy metabolism-related pathways of the gut microbiota, including citric acid cycle, oxidative phosphorylation, glycolysis, and amino acid metabolism, which were lower in the MD-control than the Normal-control. In conclusion, alleviated memory deficit by PBEH was associated potentially with not only reducing acetylcholinesterase activity but also improving brain insulin resistance and neuroinflammation potentially through modulating gut microbiota. PBEH intake (1.5–4.5 mL of 7 mg total nitrogen/mL for human equivalent) can be a potential therapeutic agent for improving memory impairment.

Urtica dioica extracts abolish scopolamine-induced neuropathies in rats

Alzheimer's disease (AD) is characterized by alterations in monoamines, oxidative stress, and metabolic dysfunctions. We aim to assess the therapeutic impacts of roots or leaf extract from Urtica dioica (UD; stinging nettle) against scopolamine (SCOP)-induced memory dysfunction, amnesia, and oxidative stress in rats. Spatial memory was assessed by Y maze test. Tissue analyses of norepinephrine (NE), dopamine (DA), serotonin (5-HT), malondialdehyde (MDA), nitric oxide (NO), glutathione (GSH, GSSG), AMP, ADP, and ATP were assessed by HPLC. mRNA levels of Tau and Hsp70 were estimated by PCR. UD extracts particularly nettle root (NR) significantly normalized the SCOP-induced memory deficits even more potent than sermion (SR) and donepezil (DON). Similarly, NR had potent therapeutic impacts on the levels of cortical and hippocampal monoamines e.g. DA, NE, and 5-HT. SCOP induced a dramatic oxidative stress as measured by MDA, NO, and GSSG levels; however, UD extracts showed significant anti-oxidative stress impacts. Additionally, UD extracts restored ATP levels and reduced the levels of AMP and ADP compared to SCOP-treated rats. Furthermore, cortical Tau and hippocampal Hsp70 were modulated by UD extracts particularly NR compared to the SCOP group. In conclusion, UD extracts particularly roots have potential therapeutic impacts against SCOP-induced neuroinflammatory and/or Alzheimer-like phenotype in rats.

Conventional cardiovascular risk factors in Transient Global Amnesia: Systematic review and proposition of a novel hypothesis

Transient Global Amnesia (TGA) is an enigmatic amnestic syndrome. We conducted a systematic review to investigate the relationship between the conventional cardiovascular risk factors and TGA. MEDLINE, CENTRAL, EMBASE and PsycINFO were comprehensively searched and 23 controlled observational studies were retrieved. The prevalence of hypertension, diabetes mellitus, dyslipidemia and smoking was lower among patients with TGA compared to Transient Ischemic Attack. Regarding the comparison of TGA with healthy individuals, there was strong evidence suggesting a protective effect of diabetes mellitus on TGA and weaker evidence for a protective effect of smoking. Hypertension was associated with TGA only in more severe stages, while dyslipidemia was not related. In view of these findings, a novel pathophysiological hypothesis is proposed, in which the functional interactions of Angiotensin-II type-1 and N-methyl-D-aspartate receptors are of pivotal importance. The whole body of clinical evidence (nature of precipitating events, associations with migraine, gender-based association patterns) was integrated.

Lacidipine Prevents Scopolamine-Induced Memory Impairment by Reducing Brain Oxido-nitrosative Stress in Mice

Cholinergic deficits and oxido-nitrosative stress are consistently associated with Alzheimer's disease (AD). Previous findings indicate that acetylcholine subdues Ca²⁺ current in the brain. Cholinergic antagonists (e.g., scopolamine) can instigate Ca²⁺-induced redox imbalance, inflammation, and cell-death pathways leading to AD-type memory impairment. Earlier, several Ca²⁺-channel blockers (CCB, e.g., dihydropyridine type) or cholinergic enhancers showed promising results in animal models of AD. In the present research, pretreatment effects of lacidipine (L-type CCB) on learning and memory functions were investigated using the scopolamine mouse model of AD. Swiss albino mice (20-25 g) were administered lacidipine (1 and 3 mg/kg) for 14 days. Scopolamine, an anti-muscarinic drug, was given (1 mg/kg) from days 8 to 14. The mice were subjected to elevated plus maze (EPM) and passive-avoidance (PA) paradigms. Bay-K8644 (a Ca²⁺-channel agonist) was administered before behavioral studies on days 13 and 14. Biochemical parameters of oxidative stress and acetylcholinesterase (AChE) activity were quantified using the whole brain. Behavioral studies showed an increase in transfer latency (TL) in the EPM test and a decrease in step-through latency (STL) in the PA test in scopolamine-administered mice. Scopolamine enhanced the AChE activity and oxidative stress in the brain of mice which resulted in memory impairment. Lacidipine prevented the amnesia against scopolamine and reduced the oxidative stress and AChE activity in the brain of mice. Bay-K8644 attenuated the lacidipine-induced improvement in memory and redox balance in scopolamine-administered mice. Lacidipine can prevent the oxidative stress and improve the cholinergic function in the brain. These properties of lacidipine can mitigate the pathogenesis of AD-type dementia.

Effect of Perindopril/Indapamide on Cerebral Blood Flow in Middle-Aged, Treatment-Naïve Patients with Hypertension

INTRODUCTION

The relationship between blood pressure (BP) and cerebral blood flow (CBF) is not fully understood. This study evaluated the impact of a perindopril arginine/indapamide (Pa/I) single-pill combination (SPC) on CBF in middle-aged patients.

METHODS

A total of 22 treatment-naïve patients with essential hypertension and at least one hypertension-mediated organ damage and 41 healthy controls were enrolled. At baseline, all participants underwent brain magnetic resonance imaging (MRI); patients with hypertension underwent an additional MRI at end of follow-up. Arterial spin labeling (ASL) was used to calculate CBF in the frontal lobe cortical plate. Patients with hypertension received once-daily Pa/I 5 mg/1.25 mg SPC, which could be increased to Pa/I 10 mg/2.5 mg at 2 weeks if necessary. Patients with hypertension underwent 24-h ambulatory BP monitoring (ABPM) at baseline and end of follow-up.

RESULTS

Mean baseline BP values were 146.2/93.1 and 119.1/76.1 mmHg in the hypertension and control groups, respectively. Patients with hypertension had significantly (p < 0.001) lower CBF in the cortical plate of both left (36.2 ± 8.3 vs. 45.3 ± 3.5 ml/100 g/min) and right (37.9 ± 7.9 vs. 45.8 ± 3.2 ml/100 g/min) frontal lobes compared to normotensive controls. At the end of follow-up, there was a statistically significant (p < 0.001) increase in CBF in the cortical plate of both left (from 36.2 ± 8.3 to 47.5 ± 9.8 ml/100 g/min) and right frontal lobes (from 37.9 ± 7.9 to 47.4 ± 10.1 ml/100 g/min) compared to baseline. No significant difference was found between end of follow-up CBF levels in frontal lobes of patients with hypertension and those of healthy controls at baseline. Office BP decreased by 24.2/15.5 mmHg and 24-h ABPM from 145.5/95.3 to 120.8/79.3 mmHg.

CONCLUSION

In middle-aged, treatment-naïve patients with hypertension, Pa/I SPC was associated with increased CBF in the cortical plate of the frontal lobes, which achieved levels of normotensive controls. The increase in CBF had no clear association with observed BP changes.

REGISTRATION NUMBER

ISRCTN67799751.

Novel Benzylated (Pyrrolidin-2-one)/(Imidazolidin-2-one) Derivatives as Potential Anti-Alzheimer's Agents: Synthesis and Pharmacological Investigations

A series of N-benzylated (pyrrolidin-2-one)/(imidazolidin-2-one) derivatives were synthesized and evaluated for anti-Alzheimer's activity. The analogs were designed and synthesized on the basis of lead compound donepezil, which is currently prescribed as a major drug for the management of mild to severe Alzheimer's disease. Considering the structure activity relationship (SAR) of the lead compound, we first replaced the 5,6-dimethoxy-1-indanone moiety with N-benzylated (pyrrolidin-2-one)/(imidazolidin-2-one) (head) without depriving the key functionality interactions like carbonyl and dimethoxyphenyl and second substituted the spacer linkage (tail) in donepezil. The newly synthesized compounds were characterized by structural conformity and purity using various techniques. The compounds were then subjected to in vivo (behavioral studies) and in vitro (biochemical assays) evaluation using appropriate animal models against the standard drug. Compounds 3-(4-(4-fluorobenzoyl)-piperidin-1-yl)-1-(4-methoxybenzyl)-pyrrolidin-2-one (10b) and 1-(3,4-dimethoxybenzyl)-3-((1-(2-(trifluoromethyl)-benzyl)-piperidin-4-yl)-methyl)-imidazolidin-2-one (18c) displayed an excellent anti-Alzheimer's profile, while the rest of the compounds showed satisfactory results in comparison to donepezil.

Sattar MA, Kamel FO, Ramadan WS, Alzahrani YA. Possible combined effect of perindopril and Azilsartan in an experimental model of dementia in rats

Renin-angiotensin system exerted deleterious effects on learning and cognitive functions through different mechanisms. The present study has been designed to evaluate the protective effect of perindopril and azilsartan as monotherapy or in combination on aluminum chloride (AlCl3) induced neurobehavioral and pathological changes in Alzheimeric rats. Male Wistar rats were divided into nine groups (n = 6); negative control, AlCl3 treated, vehicle, AlCl3 and Azilsartan (3.5 mg/kg, 7 mg/kg) co-treated, AlCl3 and perindopril (0.5 mg/kg, 1 mg/kg) co-treated, AlCl3 and (Azilsartan 3.5 mg/kg + perindopril 0.5 mg/kg), and AlCl3 and (Azilsartan 7 mg/kg + perindopril 1 mg/kg), all groups were treated for consecutive 60 days. Then, memory function was evaluated by the Y- maze test. Amyloid Peptide - 42 (Aβ-42), Acetylcholinesterase (AChE), Malondialdehyde (MDA), Tumor necrosis factor (TNF-α) and Nitric Oxide (NO) levels in the hippocampus were assessed with (ELISA) kits. The histopathological studies of the hippocampal dentate gyrus (DG) and Cornu Ammonis-3 (CA3) were also performed. Oral administration of either azilsartan and perindopril alone or in combined for 60 days have shown; improvement of cognitive function, significant reduction in the hippocampal levels of Aβ-42, Acetylcholinesterase, Malondialdehyde (MDA), Tumor necrosis factor (TNF-α) and reserved most of histopathological changes in dentate gyrus (DG) and Cornu Ammonis-3 (CA3) that mediated by Alcl3. Our behavioral, biochemical, and histopathological studies indicate that perindopril and azilsartan have neuroprotective effects on the AD model of rats induced by AlCl3, suggesting that perindopril and azilsartan may be a candidate drugs for the treatment of AD.

Ameliorative effect of methanol stem extract of Parquetina nigrescens (Afzel) bullock on scopolamine-induced sub-chronic cognitive deficit in mice

Background Parquetina nigrescens (Afzel) Bullock is a commonly used medicinal plant in African traditional medicine. The powdered roots and stems of the plant are taken with pap as a memory enhancer among the Yorubas of southwestern Nigeria. The mechanism by which scopolamine induces cognitive deficit mimics the pathogenesis of neurodegeneration in cognitive impairment. This study therefore, aimed at investigating the effect of the methanol stem extract of P. nigrescens on sub-chronically scopolamine-induced cognitive deficit in mice. Method Phytochemical screening was carried out on the extract using standard protocols. The oral median lethal dose (LD50) was estimated according to the Organisation for Economic Cooperation and Development (OECD) 425 limit test guideline. Doses of 250, 500, and 1000 mg/kg of the extract were used for the study. The elevated plus maze (EPM) and novel object recognition tests (NORT) were used to assess cognitive function. The brain tissue was assayed for the level of malondialdehyde (MDA), reduced glutathione (GSH), superoxide dismutase (SOD) and acetylcholinesterase (AChE) activity. Results The plant extract contains phenolics, carbohydrates, tannins, saponins, and unsaturated sterols.The extract decreased the transfer latencies on days 7 and 8 against the scopolamine group in EPM and increased the discrimination index decreased by scopolamine in NORT. The methanol stem extract of P. nigrescens significantly (p ≤ 0.01) reduced MDA level;  significantly  (p ≤ 0.01) increased SOD activity;  non-significantly increased GSH activity and the activity of AChE apeared not altered. Conclusion The methanol stem extract of P. nigrescens ameliorated sub-chronically scopolamine-induced cognitive deficit via antioxidant mechanism.

Role of brain renin angiotensin system in neurodegeneration: An update

Renin angiotensin system (RAS) is an endocrine system widely known for its physiological roles in electrolyte homeostasis, body fluid volume regulation and cardiovascular control in peripheral circulation. However, brain RAS is an independent form of RAS expressed locally in the brain, which is known to be involved in brain functions and disorders. There is strong evidence for a major involvement of excessive brain angiotensin converting enzyme (ACE)/Angiotensin II (Ang II)/Angiotensin type-1 receptor (AT-1R) axis in increased activation of oxidative stress, apoptosis and neuroinflammation causing neurodegeneration in several brain disorders. Numerous studies have demonstrated strong neuroprotective effects by blocking AT1R in these brain disorders. Additionally, the angiotensin converting enzyme 2 (ACE2)/Angiotensin (1–7)/Mas receptor (MASR), is another axis of brain RAS which counteracts the damaging effects of ACE/Ang II/AT1R axis on neurons in the brain. Thus, angiotensin II receptor blockers (ARBs) and activation of ACE2/Angiotensin (1–7)/MASR axis may serve as an exciting and novel method for neuroprotection in several neurodegenerative diseases. Here in this review article, we discuss the expression of RAS in the brain and highlight how altered RAS level may cause neurodegeneration. Understanding the pathophysiology of RAS and their links to neurodegeneration has enormous potential to identify potentially effective pharmacological tools to treat neurodegenerative diseases in the brain.

The effects of captopril on lipopolysaccharide-induced sickness behaviors in rats

Neuro-immune mediators play an important role in the development of sickness behaviors. In the present study, the effect of captopril on sickness behaviors caused by lipopolysaccharide (LPS) was studied in the rats. The animals were randomized into the following groups: control, sham, 10 mg kg^-1 captopril - LPS (Capto 10-LPS), 50 mg kg^-1 captopril - LPS (Capto 50-LPS), and 100 mg kg^-1 captopril - LPS (Capto 100-LPS). Behavioral tests including open-field (OF), elevated plus maze (EPM) and forced swimming (FS) test were performed, and the serum level of interleukin-6 (IL-6) was assessed. In OF, the number of crossings in the central zone in Capto 10-LPS, Capto 50-LPS, and Capto 100-LPS groups was higher than that of the sham group. In EPM, the open arm entry numbers in the sham group were lower compared to the control group. Furthermore, pretreatment by captopril increased the entries to the open arms. In FS test, the immobility time of the sham group was longer than that of the control group. In Capto 10-LPS, Capto 50-LPS, and Capto 100-LPS groups, immobility was shorter compared to the sham group. In addition, the IL-6 level was higher in the sham group compared to the control group, and treatment with 50 and 100 mg kg^-1 of captopril restored the IL-6 level in comparison with the sham group. Results confirmed that pretreatment with captopril ameliorated LPS-caused sickness behaviors and attenuated IL-6 as an inflammatory marker in the rats.

Comparison of scopolamine-induced cognitive impairment responses in three different ICR stocks

Cognitive impairment responses are important research topics in the study of degenerative brain diseases as well as in understanding of human mental activities. To compare response to scopolamine (SPL)-induced cognitive impairment, we measured altered parameters for learning and memory ability, inflammatory response, oxidative stress, cholinergic dysfunction and neuronal cell damages, in Korl:ICR stock and two commercial breeder stocks (A:ICR and B:ICR) after relevant SPL exposure. In the water maze test, Korl:ICR showed no significant difference in SPL-induced learning and memory impairment compared to the two different ICRs, although escape latency was increased after SPL exposure. Although behavioral assessment using the manual avoidance test revealed reduced latency in all ICR mice after SPL treatment as compared to Vehicle, no differences were observed between the three ICR stocks. To determine cholinergic dysfunction induction by SPL exposure, activity of acetylcholinesterase (AChE) assessed in the three ICR stocks revealed no difference of acetylcholinesterase activity. Furthermore, low levels of superoxide dismutase (SOD) activity and high levels of inflammatory cytokines in SPL-treated group were maintained in all three ICR stocks, although some variations were observed between the SPLtreated groups. Neuronal cell damages induced by SPL showed similar response in all three ICR stocks, as assessed by terminal deoxynucleotidyl transferase dUTP nick end labeling (TUNEL) assay, Nissl staining analysis and expression analyses of apoptosis-related proteins. Thus, the results of this study provide strong evidence that Korl:ICR is similar to the other two ICR. Stocks in response to learning and memory capacity.

Conjugation to Ascorbic Acid Enhances Brain Availability of Losartan Carboxylic Acid and Protects Against Parkinsonism in Rats

Identification of renin-angiotensin system in the interplay of hypertension and neurodegeneration has paved the way for the repurposing of antihypertensive drugs against Parkinsonism. Losartan carboxylic acid (LCA), the potent AT1 blocker metabolite of losartan, suffers from poor bioavailability and brain access. Since ascorbate transporters have earlier shown enough flexibility as carriers, we have conjugated losartan carboxylic acid to ascorbic acid with the aim of achieving higher oral/brain availability. Ester of LCA and ascorbic acid (FED) was developed keeping in view the substrate specificity of ascorbate transporters. Oral/brain bioavailability was assessed using in vivo pharmacokinetic model. Effect on central nervous system (CNS) and protection against Parkinsonism was evaluated using in vivo models. FED enhanced bioavailability of LCA. The higher brain availability of LCA enabled CNS protection as evident from the increase in locomotor activity, improved motor coordination, and protection against drug-induced catatonia. In conclusion, FED offers an approach to repurpose LCA against Parkinsonism. This can encourage further investigation to simultaneously address hypertension and neurodegeneration.

Cerebral Perfusion Enhancing Interventions: A New Strategy for the Prevention of Alzheimer Dementia

Cardiovascular and cerebrovascular diseases are major risk factors in the development of cognitive impairment and Alzheimer's disease (AD). These cardio-cerebral disorders promote a variety of vascular risk factors which in the presence of advancing age are prone to markedly reduce cerebral perfusion and create a neuronal energy crisis. Long-term hypoperfusion of the brain evolves mainly from cardiac structural pathology and brain vascular insufficiency. Brain hypoperfusion in the elderly is strongly associated with the development of mild cognitive impairment (MCI) and both conditions are presumed to be precursors of Alzheimer dementia. A therapeutic target to prevent or treat MCI and consequently reduce the incidence of AD aims to elevate cerebral perfusion using novel pharmacological agents. As reviewed here, the experimental pharmaca include the use of Rho kinase inhibitors, neurometabolic energy boosters, sirtuins and vascular growth factors. In addition, a compelling new technique in laser medicine called photobiomodulation is reviewed. Photobiomodulation is based on the use of low level laser therapy to stimulate mitochondrial energy production non-invasively in nerve cells. The use of novel pharmaca and photobiomodulation may become important tools in the treatment or prevention of cognitive decline that can lead to dementia.

Effect of walnut protein hydrolysate on scopolamine-induced learning and memory deficits in mice

A walnut protein hydrolysate (WPH) was prepared by using a mixture of pancreatin and viscozyme L from industrially available defatted walnut meal. The antioxidant effects of WPH were confirmed and quantified by reducing power, oxygen radical absorbance capacity, hydroxyl radical radical-scavenging activity and ABTS⁺· radical-scavenging activity assays. The protective effects of WPH on scopolamine-induced learning and memory deficits in mice were also evaluated based on in vivo behavioral tests. Results showed that WPH administration would lead to significantly decreased latencies while increased crossing times and target times in the spatial probe test, and increased escape latency and decreased error times in the step-down avoidance test for the scopolamine-induced dementia mice. Biochemical results indicated that the ameliorative effects of WPH on scopolamine-induced dementia mice could be attributed to the significantly increased amount of acetylcholine receptors. Therefore, WPH may be a potential therapeutic agent against Alzheimer's disease.

Associations of centrally acting ACE inhibitors with cognitive decline and survival in Alzheimer's disease

BACKGROUND

Cognitive improvement has been reported in patients receiving centrally acting angiotensin-converting enzyme inhibitors (C-ACEIs).

AIMS

To compare cognitive decline and survival after diagnosis of Alzheimer's disease between people receiving C-ACEIs, non-centrally acting angiotensin-converting enzyme inhibitors (NC-ACEIs), and neither.

METHOD

Routine Mini-Mental State Examination (MMSE) scores were extracted in 5260 patients receiving acetylcholinesterase inhibitors and analysed against C-/NC-ACEI exposure at the time of Alzheimer's disease diagnosis.

RESULTS

In the 9 months after Alzheimer's disease diagnosis, MMSE scores significantly increased by 0.72 and 0.19 points per year in patients on C-ACEIs and neither respectively, but deteriorated by 0.61 points per year in those on NC-ACEIs. There were no significant group differences in score trajectories from 9 to 36 months and no differences in survival.

CONCLUSIONS

In people with Alzheimer's disease receiving acetylcholinesterase inhibitors, those also taking C-ACEIs had stronger initial improvement in cognitive function, but there was no evidence of longer-lasting influence on dementia progression.

DECLARATION OF INTEREST

R.S. has received research funding from Pfizer, Lundbeck, Roche, Janssen and GlaxoSmithKline.

COPYRIGHT AND USAGE

© The Royal College of Psychiatrists 2017. This is an open access article distributed under the terms of the Creative Commons Non-Commercial, No Derivatives (CC BY-NC-ND) license.

Kidney–brain axis inflammatory cross-talk: from bench to bedside

Epidemiologic data suggest that individuals at all stages of chronic kidney disease (CKD) have a higher risk of developing neuropsychiatric disorders, cognitive impairment, and dementia. This risk is generally explained by the high prevalence of both symptomatic and subclinical ischemic cerebrovascular lesions. However, other potential mechanisms, including cytokine/chemokine release, production of reactive oxygen species (ROS), circulating and local formation of trophic factors and of renin–angiotensin system (RAS) molecules, could also be involved, especially in the absence of obvious cerebrovascular disease. In this review, we discuss experimental and clinical evidence for the role of these mechanisms in kidney–brain cross-talk. In addition, we hypothesize potential pathways for the interactions between kidney and brain and their pathophysiological role in neuropsychiatric and cognitive changes found in patients with CKD. Understanding the pathophysiologic interactions between renal impairment and brain function is important in order to minimize the risk for future cognitive impairment and to develop new strategies for innovative pharmacological treatment.

Toxin-Induced Experimental Models of Learning and Memory Impairment

Animal models for learning and memory have significantly contributed to novel strategies for drug development and hence are an imperative part in the assessment of therapeutics. Learning and memory involve different stages including acquisition, consolidation, and retrieval and each stage can be characterized using specific toxin. Recent studies have postulated the molecular basis of these processes and have also demonstrated many signaling molecules that are involved in several stages of memory. Most insights into learning and memory impairment and to develop a novel compound stems from the investigations performed in experimental models, especially those produced by neurotoxins models. Several toxins have been utilized based on their mechanism of action for learning and memory impairment such as scopolamine, streptozotocin, quinolinic acid, and domoic acid. Further, some toxins like 6-hydroxy dopamine (6-OHDA), 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) and amyloid-β are known to cause specific learning and memory impairment which imitate the disease pathology of Parkinson's disease dementia and Alzheimer's disease dementia. Apart from these toxins, several other toxins come under a miscellaneous category like an environmental pollutant, snake venoms, botulinum, and lipopolysaccharide. This review will focus on the various classes of neurotoxin models for learning and memory impairment with their specific mechanism of action that could assist the process of drug discovery and development for dementia and cognitive disorders.

Attenuation in rats of impairments of memory by scopolamine, a muscarinic receptor antagonist, by mecamylamine, a nicotinic receptor antagonist

RATIONALE

Scopolamine, a muscarinic antagonist, impairs learning and memory for many tasks, supporting an important role for the cholinergic system in these cognitive functions. The findings are most often interpreted to indicate that a decrease in postsynaptic muscarinic receptor activation mediates the memory impairments. However, scopolamine also results in increased release of acetylcholine in the brain as a result of blocking presynaptic muscarinic receptors.

OBJECTIVES

The present experiments assess whether scopolamine-induced increases in acetylcholine release may impair memory by overstimulating postsynaptic cholinergic nicotinic receptors, i.e., by reaching the high end of a nicotinic receptor activation inverted-U dose-response function.

RESULTS

Rats tested in a spontaneous alternation task showed dose-dependent working memory deficits with systemic injections of mecamylamine and scopolamine. When an amnestic dose of scopolamine (0.15 mg/kg) was co-administered with a subamnestic dose of mecamylamine (0.25 mg/kg), this dose of mecamylamine significantly attenuated the scopolamine-induced memory impairments. We next assessed the levels of acetylcholine release in the hippocampus in the presence of scopolamine and mecamylamine. Mecamylamine injections resulted in decreased release of acetylcholine, while scopolamine administration caused a large increase in acetylcholine release.

CONCLUSIONS

These findings indicate that a nicotinic antagonist can attenuate impairments in memory produced by a muscarinic antagonist. The nicotinic antagonist may block excessive activation of nicotinic receptors postsynaptically or attenuate increases in acetylcholine release presynaptically. Either effect of a nicotinic antagonist-to decrease scopolamine-induced increases in acetylcholine output or to decrease postsynaptic acetylcholine receptor activation-may mediate the negative effects on memory of muscarinic antagonists.

A comparative study of neuroprotective effect of angiotensin converting enzyme inhibitors against scopolamine-induced memory impairments in rats

The comparative study of neuroprotective effect of angiotensin converting enzyme inhibitors against scopolamine-induced neuroinflammation in albino Wistar rats was studied. Male albino rats were administered with scopolamine to induce memory impairment. The standard nootropic agent, piracetam (200 mg/kg b.w., [i.p.]), perindopril (0.1 mg/kg b.w., [i.p.]), enalapril (0.1 mg/kg b.w., [i.p.]), and ramipril (0.1 mg/kg b.w., [i.p.]) were administered in different group of animals for 5 days. On 5^th day, scopolamine (1 mg/kg b.w., i.p.) was administered after 60 min of the last dose of test drug. Memory function was evaluated in Morris water maze (MWM) test and pole climbing test (PCT). Biochemical estimations like glutathione (GSH), malondialdehyde (MDA), and acetylcholinesterase activity in the brain were estimated after completion of behavior study. All three test groups shows improvement in learning and memory in comparison to control group. Perindopril treated group showed a more effective significant decrease in escape latency time and transfer latency time compared to enalapril and ramipril treated group on day 4 in MWM test and PCT, respectively. Perindopril shows a significant reduction in MDA level and acetylcholinesterase activity and a significant rise in GSH level compared to enalapril and ramipril. The finding of this study indicates that Perindopril is more effective in memory retention compared to enalapril and ramipril.

Streptozotocin Intracerebroventricular-Induced Neurotoxicity and Brain Insulin Resistance: a Therapeutic Intervention for Treatment of Sporadic Alzheimer's Disease (sAD)-Like Pathology

Alzheimer's disease (AD) is a neurodegenerative disorder that is remarkably characterized by pathological hallmarks which include amyloid plaques, neurofibrillary tangles, neuronal loss, and progressive cognitive loss. Several well-known genetic mutations which are being used for the development of a transgenic model of AD lead to an early onset familial AD (fAD)-like condition. However, these settings are only reasons for a small percentage of the total AD cases. The large majorities of AD cases are considered as a sporadic in origin and are less influenced by a single mutation of a gene. The etiology of sporadic Alzheimer's disease (sAD) remains unclear, but numerous risk factors have been identified that increase the chance of developing AD. Among these risk factors are insulin desensitization/resistance state, oxidative stress, neuroinflammation, synapse dysfunction, tau hyperphosphorylation, and deposition of Aβ in the brain. Subsequently, these risk factors lead to development of sAD. However, the underlying molecular mechanism is not so clear. Streptozotocin (STZ) produces similar characteristic pathology of sAD such as altered glucose metabolism, insulin signaling, synaptic dysfunction, protein kinases such as protein kinase B/C, glycogen synthase-3β (GSK-3β) activation, tau hyperphosphorylation, Aβ deposition, and neuronal apoptosis. Further, STZ also leads to inhibition of Akt/PKB, insulin receptor (IR) signaling molecule, and insulin resistance in brain. These alterations mediated by STZ can be used to explore the underlying molecular and pathophysiological mechanism of AD (especially sAD) and their therapeutic intervention for drug development against AD pathology.

Interactions between levetiracetam and cardiovascular drugs against electroconvulsions in mice

BACKGROUND

Hypertension and heart failure belong to common comorbid conditions with epilepsy so drug interactions between antiepileptics and cardiovascular drugs are possible in clinical practice. The aim of this study was to evaluate the effects of angiotensin AT1 receptor antagonists (losartan potassium and candesartan cilexetil), angiotensin-converting enzyme (ACE) inhibitors (captopril and perindopril arginine) and diuretics (hydrochlorothiazide and ethacrynic acid) on the anticonvulsant activity of levetiracetam (LEV) in mice.

METHODS

The protective action of LEV was examined in the maximal electroshock seizure threshold test. Drugs were administered intraperitoneally (ip). Additionally, combinations of cardiovascular drugs with LEV were tested for adverse effects in the passive avoidance task and the chimney test.

RESULTS

Losartan potassium (50mg/kg), candesartan cilexetil (8mg/kg), captopril (50mg/kg), hydrochlorothiazide (100mg/kg) and ethacrynic acid (100mg/kg) did not affect the anticonvulsant activity of LEV. Perindopril arginine (10mg/kg) raised the convulsive threshold for LEV administered at doses of 100, 300 and 500mg/kg. This interaction could be pharmacodynamic in nature because the brain concentration of LEV remained unchanged by perindopril. The adverse effects of the combined treatment with LEV and cardiovascular drugs were not observed in the passive avoidance task or the chimney test.

CONCLUSIONS

Although experimental data can be hardly extrapolated to clinical practice, it is suggested that perindopril arginine may positively influence the anticonvulsant action of LEV in epileptic patients. The use of losartan potassium, candesartan cilexetil, captopril, hydrochlorothiazide or ethacrynic acid in patients treated with LEV seems neutral regarding its anticonvulsant activity.

Long-term administration of scopolamine interferes with nerve cell proliferation, differentiation and migration in adult mouse hippocampal dentate gyrus, but it does not induce cell death

Long-term administration of scopolamine, a muscarinic receptor antagonist, can inhibit the survival of newly generated cells, but its effect on the proliferation, differentiation and migration of nerve cells in the adult mouse hippocampal dentate gyrus remain poorly understood. In this study, we used immunohistochemistry and western blot methods to weekly detect the biological behaviors of nerve cells in the hippocampal dentate gyrus of adult mice that received intraperitoneal administration of scopolamine for 4 weeks. Expression of neuronal nuclear antigen (NeuN; a neuronal marker) and Fluoro-Jade B (a marker for the localization of neuronal degeneration) was also detected. After scopolamine treatment, mouse hippocampal neurons did not die, and Ki-67 (a marker for proliferating cells)-immunoreactive cells were reduced in number and reached the lowest level at 4 weeks. Doublecortin (DCX; a marker for newly generated neurons)-immunoreactive cells were gradually shortened in length and reduced in number with time. After scopolamine treatment for 4 weeks, nearly all of the 5-bromo-2'-deoxyuridine (BrdU)-labeled newly generated cells were located in the subgranular zone of the dentate gyrus, but they did not migrate into the granule cell layer. Few mature BrdU/NeuN double-labeled cells were seen in the subgranular zone of the dentate gyrus. These findings suggest that long-term administration of scopolamine interferes with the proliferation, differentiation and migration of nerve cells in the adult mouse hippocampal dentate gyrus, but it does not induce cell death.

Effect of homeopathic Lycopodium clavatum on memory functions and cerebral blood flow in memory-impaired rats

BACKGROUND

Lycopodium clavatum (Lyc) is a widely used homeopathic medicine for the liver, urinary and digestive disorders. Recently, acetyl cholinesterase (AchE) inhibitory activity has been found in Lyc alkaloid extract, which could be beneficial in dementia disorder. However, the effect of Lyc has not yet been explored in animal model of memory impairment and on cerebral blood flow.

AIM

The present study was planned to explore the effect of Lyc on learning and memory function and cerebral blood flow (CBF) in intracerebroventricularly (ICV) administered streptozotocin (STZ) induced memory impairment in rats.

MATERIALS AND METHODS

Memory deficit was induced by ICV administration of STZ (3 mg/kg) in rats on 1st and 3rd day. Male SD rats were treated with Lyc Mother Tincture (MT) 30, 200 and 1000 for 17 days. Learning and memory was evaluated by Morris water maze test on 14th, 15th and 16th day. CBF was measured by Laser Doppler flow meter on 17th day.

RESULTS

STZ (ICV) treated rats showed impairment in learning and memory along with reduced CBF. Lyc MT and 200 showed improvement in learning and memory. There was increased CBF in STZ (ICV) treated rats at all the potencies of Lyc studied.

CONCLUSION

The above study suggests that Lyc may be used as a drug of choice in condition of memory impairment due to its beneficial effect on CBF.

Improvement in spatial memory dysfunction by telmisartan through reduction of brain angiotensin II and oxidative stress in experimental uremic mice

AIMS

We previously reported that chronic uremia induces spatial working memory dysfunction in mice, and that it is attributed to cerebral oxidative stress. The source of oxidative stress was considered to be uremic toxins, but this remains unclear. In the present study, we examined whether the brain renin-angiotensin system was activated in the CKD mouse model, and whether it contributed to cognitive impairment.

MAIN METHODS

CKD was induced in 8-week-old male mice by 5/6 nephrectomy. Mice were divided into four groups: control mice administered tap water (Cont-V), control mice treated with 0.5mg/kg/day telmisartan, an angiotensin II (AII) receptor blocker, for 8 weeks (Cont-T), CKD mice administered tap water (CKD-V), and CKD mice treated with 0.5 mg/kg/day telmisartan for 8 weeks (CKD-T). After the treatment period, a radial arm water maze (RAWM) test was performed, and angiotensin II (AII) concentrations and markers of oxidative stress were measured in the brains of mice.

KEY FINDINGS

Errors in the RAWM test were more frequent in the CKD-V group than in the Cont-V group. In addition, errors in the CKD-T group were comparable to control mice. Tissue brain AII concentrations were greater in the CKD-V group compared with the other groups. Oxidative DNA damage and lipid peroxidation in the brain were also greater in the CKD-V group compared with the other groups.

SIGNIFICANCE

Our results suggest that brain AII levels were exaggerated in CKD mice, and that this contributes to cognitive impairment through oxidative stress.

Treadmill exercise ameliorates short-term memory disturbance in scopolamine-induced amnesia rats

Purpose

Scopolamine is a nonselective muscarinic cholinergic receptor antagonist, which induces impairment of learning ability and memory function. Exercise is known to ameliorate brain disturbance induced by brain injuries. In the present study, we investigated the effect of treadmill exercise on short-term memory in relation to acetylcholinesterase (AChE) expression in the hippocampus, using a scopolamine-induced amnesia model in mice.

Methods

To induce amnesia, 1 mg/kg scopolamine hydrobromide was administered intraperitoneally once per day for 14 days. A step-down avoidance test for short-term memory was conducted. AChE histochemistry, immunohistochemistry for collagen IV, and doublecortin were performed.

Results

Short-term memory deteriorated in the mice with scopolamine-induced amnesia, concomitant with enhanced AChE expression and suppression of angiogenesis in the hippocampus. Critically, treadmill exercise ameliorated short-term memory impairment, suppressed AChE expression, and enhanced angiogenesis in the mice with scopolamine-induced amnesia.

Conclusions

Overexpression of AChE is implicated in both brain and renal disease. The findings of our study indicate that treadmill exercise may be of therapeutic value in neurodegenerative and renal diseases by suppressing the effects of AChE expression.

Ameliorative effect of Noni fruit extract on streptozotocin-induced memory impairment in mice

This study evaluated the effects of a standardized ethyl acetate extract of Morinda citrifolia L. (Noni) fruit on impairment of memory, brain energy metabolism, and cholinergic function in intracerebral streptozotocin (STZ)-treated mice. STZ (0.5 mg/kg) was administered twice at an interval of 48 h. Noni (50 and 100 mg/kg, postoperatively) was administered for 21 days following STZ administration. Memory function was evaluated using Morris Water Maze and passive avoidance tests, and brain levels of cholinergic function, oxidative stress, energy metabolism, and brain-derived neurotrophic factor (BDNF) were estimated. STZ caused memory impairment in Morris Water Maze and passive avoidance tests along with reduced brain levels of ATP, BDNF, and acetylcholine and increased acetylcholinesterase activity and oxidative stress. Treatment with Noni extract (100 mg/kg) prevented the STZ-induced memory impairment in both behavioral tests along with reduced oxidative stress and acetylcholinesterase activity, and increased brain levels of BDNF, acetylcholine, and ATP level. The study shows the beneficial effects of Noni fruit against STZ-induced memory impairment, which may be attributed to improved brain energy metabolism, cholinergic neurotransmission, BDNF, and antioxidative action.

Catalpol Induces Neuroprotection and Prevents Memory Dysfunction through the Cholinergic System and BDNF

To investigate the role and mechanism of catalpol on neuroprotective effects and memory enhancing effects simultaneously, neuroprotective effects of catalpol were assessed by neurological deficits score, TTC staining, and cerebral blood flow detecting. Morris water maze was employed to investigate its effects on learning and memory and then clarify its possible mechanisms relating the central cholinergic system and BDNF. Edaravone and oxiracetam were used for positive control drugs based on its different action. Results showed that catalpol and edaravone significantly facilitated neurological function recovery, reduced infarction volume, and increased cerebral blood flow in stroke mice. Catalpol and oxiracetam decreased the escape latency significantly and increased the numbers of crossing platform obviously. The levels of ACh, ChAT, and BDNF in catalpol group were increased in a dose-dependent manner, and AChE declined with a U-shaped dose-response curve. Moreover, the levels of muscarinic AChR subtypes M₁ and M₂ in hippocampus were considerably raised by catalpol. These results demonstrated that catalpol may be useful for neuroprotection and memory enhancement, and the mechanism may be related to the central cholinergic system.

Inhibition of central angiotensin II enhances memory function and reduces oxidative stress status in rat hippocampus

While it is now well established that the independent brain renin-angiotensin system (RAS) has some important central functions besides the vascular ones, the relevance of its main bioactive peptide angiotensin II (Ang II) on the memory processes, as well as on oxidative stress status is not completely understood. The purpose of the present work was to evaluate the effects of central Ang II administration, as well as the effects of Ang II inhibition with either AT1 and AT 2 receptor specific blockers (losartan and PD-123177, respectively) or an angiotensin-converting enzyme (ACE) inhibitor (captopril). These effects were studied on the short-term memory (assessed through Y-maze) or long-term memory (as determined in passive avoidance) and on the oxidative stress status of the hippocampus. Our results demonstrate memory deficits induced by the administration of Ang II, as showed by the significant decrease of the spontaneous alternation in Y-maze (p=0.015) and latency-time in passive avoidance task (p=0.001) when compared to saline. On the other side, the administration of all the aforementioned Ang II blockers significantly improved the spontaneous alternation in Y-maze task, while losartan also increased the latency time as compared to saline in step-through passive avoidance (p=0.042). Also, increased oxidative stress status was induced in the hippocampus by the administration of Ang II, as demonstrated by increased levels of lipid peroxidation markers (malondialdehyde-MDA concentration) (p<0.0001) and a decrease in both antioxidant enzymes determined: superoxide dismutase-SOD (p<0.0001) and glutathione peroxidase-GPX (p=0.01), as compared to saline. Additionally, the administration of captopril resulted in an increase of both antioxidant enzymes and decreased levels of lipid peroxidation (p=0.001), while PD-123177 significantly decreased MDA concentration (p>0.0001) vs. saline. Moreover, significant correlations were found between all of the memory related behavioral parameters and the main oxidative stress markers from the hippocampus, which is known for its implication in the processes of memory and also where RAS components are well expressed. This could be relevant for the complex interactions between Ang II, behavioral processes and neuronal oxidative stress, and could generate important therapeutic approaches.

Effect of angiotensin II on spatial memory, cerebral blood flow, cholinergic neurotransmission, and brain derived neurotrophic factor in rats

RATIONAL

Studies have shown the involvement of angiotensin II (Ang II) in neurobehavioral aspects, but the exact role of Ang II in memory is still ambiguous.

OBJECTIVE

This study explored the effect of central Ang II on spatial memory along with cholinergic neurotransmission, brain energy metabolism, cerebral blood flow (CBF), and brain-derived neurotrophic factor (BDNF) in rats.

METHODS

Spatial memory was evaluated by Morris water maze (MWM) after Ang II (ICV) administration in male Sprague-Dawley rats. CBF was measured by laser Doppler flowmetry. Oxidative stress adenosine triphosphate (ATP), BDNF, acetylcholinesterase (AChE), and acetylcholine (ACh) were estimated in the cortex and hippocampus at 1, 24, and 48 h after Ang II administration. The effect of AT1 and AT2 receptor blocker (candesartan and PD123,319, respectively), AChE inhibitor (donepezil), and antioxidant melatonin was studied on memory, CBF, and biochemical parameters.

RESULTS

Ang II caused spatial memory impairment by affecting acquisition, consolidation, and recall in the MWM test along with a significant reduction in CBF. Ang II significantly reduced ACh level and caused oxidative stress in the rat brain 1 h post-injection. No significant change was observed in BDNF, AChE, and ATP level. Candesartan and donepezil prevented Ang II-induced memory impairment, reduction in CBF and ACh level. However, PD123,319 and melatonin failed to prevent Ang II-induced memory impairment but improved CBF partially.

CONCLUSION

This study suggests that Ang II, via the AT1 receptor, affects spatial memory formation, CBF, and ACh level while AT2 receptor has no significant role.

Combretum mucronatum and Capparis thonningii prevent scopolamine-induced memory deficit in mice

CONTEXT

Roots of Combretum mucronatum Schumach. & Thonn. (Combretaceae) and Capparis thonningii Schum. (Capparaceae) are used in southwest Nigeria in the treatment of inflammatory disorders and mental illness.

OBJECTIVE

This study evaluated the antidementic effect of the methanol root extracts of C. mucronatum and C. thonningii on scopolamine (3 mg/kg, i.p.) induced memory impairment in mice.

MATERIALS AND METHODS

The effect of C. mucronatum and C. thonningii (50-200 mg/kg) administered orally for 3 days on memory impairments induced in mice by scopolamine was assessed in the passive avoidance and Morris water maze test and compared with that of tacrine (5 mg/kg, i.p.). The activities of acetylcholinesterase (AchE) and antioxidant enzymes were estimated in the brain after the completion of behavioral studies.

RESULTS

C. mucronatum and C. thonningii root extracts (50-200 mg/kg) reversed scopolamine-induced memory deficit with significant (p < 0.05) increase in transfer latency in passive avoidance test. Similarly, the extracts (200 mg/kg) ameliorated memory deficit as a result of significant (p < 0.001) decrease in escape latency and path length in Morris water maze test. The increased AChE activity induced by scopolamine was significantly (p < 0.05) inhibited by C. mucronatum and C. thonningii (100 and 200 mg/kg) treatment which was similar to the effect of tacrine. Both extracts significantly (p < 0.05) attenuated scopolamine-induced increase in oxidative stress parameters as well as restoration of glutathione activity.

DISCUSSION AND CONCLUSION

C. mucronatum and C. thonningii extracts possess significant anticholinesterase, antioxidant and antidementic properties, which may be useful in the management of Alzheimer's disease.

Renin-Angiotensin system and sympathetic neurotransmitter release in the central nervous system of hypertension

Many Studies suggest that changes in sympathetic nerve activity in the central nervous system might have a crucial role in blood pressure control. The present paper discusses evidence in support of the concept that the brain renin-angiotensin system (RAS) might be linked to sympathetic nerve activity in hypertension. The amount of neurotransmitter release from sympathetic nerve endings can be regulated by presynaptic receptors located on nerve terminals. It has been proposed that alterations in sympathetic nervous activity in the central nervous system of hypertension might be partially due to abnormalities in presynaptic modulation of neurotransmitter release. Recent evidence indicates that all components of the RAS have been identified in the brain. It has been proposed that the brain RAS may actively participate in the modulation of neurotransmitter release and influence the central sympathetic outflow to the periphery. This paper summarizes the results of studies to evaluate the possible relationship between the brain RAS and sympathetic neurotransmitter release in the central nervous system of hypertension.

Chronic inhibition of central Angiotensin-converting enzyme ameliorates colchicine-induced memory impairment in mice

Preclinical and clinical studies indicated involvement of the central renin-angiotensin system (RAS) in memory functions. However, the role of central angiotensin-converting enzyme (ACE) in memory function is still unclear. The present study investigated the involvement of central ACE in colchicine-induced memory impairment in the context of cholinergic function and oxidative stress. Memory impairment was induced by intracerebral colchicine administration in mice. The ACE inhibitor, perindopril (0.05 and 0.1 mg/kg/day), was administered orally for 14 days. Memory function was evaluated by the Morris water maze (MWM) test from the 14^th day on after colchicine injection. Donepezil was used as a standard. Parameters of oxidative stress and cholinergic function, ACE activity in serum and the brain were estimated after the completion of behavioral studies. Colchicine caused memory impairment as revealed by no significant change in latency to reach a hidden platform in the MWM test. Furthermore, there was a significant increase in MDA, ROS, and nitrite levels with a reduction in GSH level and acetylcholinesterase (AChE) activity in the brain of colchicine-treated mice. Colchicine significantly increased brain ACE activity without affecting serum ACE. Donepezil prevented colchicine-induced memory impairment in mice. The antidementic effect of perindopril may be attributed to reduced oxidative stress and improvement in cholinergic function. Moreover, the elevated brain ACE activity was also inhibited by perindopril. The study showed that central ACE plays an important role in colchicine-induced memory deficit, corroborating a number of studies that show that treatment with ACE inhibitors could be neuroprotective.