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

Neuroprotection by Polyherbal Medicine Divya-Medha-Vati Against Scopolamine-Induced Cognitive Impairment Through Modulation of Oxidative Stress, Acetylcholine Activity, and Cell Signaling

Alzheimer disease is associated with cognitive impairments and neuronal damages. In this study, Scopolamine, a model drug used for the generation of Alzheimer-like symptoms induced cognitive dysfunction in C57BL/6 mice. It also elevated acetylcholine esterase (AcHE) activity, and reduced antioxidant (superoxide dismutase and catalase) activity in cortex tissue. Scop reduced neuronal density and increased pyknotic neurons in hippocampus tissue. In mouse neuroblastoma (Neuro2a) cells, Scop triggered a dose-dependent loss of cell viability and neurite outgrowth reduction. Scop-treated Neuro2a cells showed oxidative stress and reduction in mRNA expression for brain-derived neurotrophic factor (BDNF), nerve growth factor-1 (NGF-1), and Synapsin-1 (SYN-1) genes. Mice treated with Divya-Medha-Vati (DMV), an Ayurvedic polyherbal medicine showed protection against Scop-induced cognitive impairment (Morris Water Maze Escape Latency, and Elevated Plus Maze Transfer Latency). DMV protected against Scop-induced AcHE activity, and loss of antioxidant activities in the mice brain cortex while sustaining neuronal density in the hippocampus region. In the Neuro2a cells, DMV reduced Scop-induced loss of cell viability and neurite outgrowth loss. DMV protected the cells against induction of oxidative stress and promoted mRNA expression of BDNF, NGF-1, and SYN-1 genes. Phytochemical profiling of DMV showed the presence of Withanolide A, Withanolide B, Bacopaside II, Jujubogenin, Apigenin, Gallic acid, Caffeic acid, and Quercetin that are associated with antioxidant and neurostimulatory activities. In conclusion, the study showed that Divya-Medha-Vati was capable of promoting neuronal health and inhibiting Alzheimer-like cognitive dysfunction through enhanced antioxidant activities and modulation of neuronal activities.

The neurobiology and therapeutic potential of multi-targeting β-secretase, glycogen synthase kinase 3β and acetylcholinesterase in Alzheimer's disease

Alzheimer's Disease (AD) is the most common form of dementia, affecting almost 50 million of people around the world, characterized by a complex and age-related progressive pathology with projections to duplicate its incidence by the end of 2050. AD pathology has two major hallmarks, the amyloid beta (Aβ) peptides accumulation and tau hyperphosphorylation, alongside with several sub pathologies including neuroinflammation, oxidative stress, loss of neurogenesis and synaptic dysfunction. In recent years, extensive research pointed out several therapeutic targets which have shown promising effects on modifying the course of the disease in preclinical models of AD but with substantial failure when transposed to clinic trials, suggesting that modulating just an isolated feature of the pathology might not be sufficient to improve brain function and enhance cognition. In line with this, there is a growing consensus that an ideal disease modifying drug should address more than one feature of the pathology. Considering these evidence, β-secretase (BACE1), Glycogen synthase kinase 3β (GSK-3β) and acetylcholinesterase (AChE) has emerged as interesting therapeutic targets. BACE1 is the rate-limiting step in the Aβ production, GSK-3β is considered the main kinase responsible for Tau hyperphosphorylation, and AChE play an important role in modulating memory formation and learning. However, the effects underlying the modulation of these enzymes are not limited by its primarily functions, showing interesting effects in a wide range of impaired events secondary to AD pathology. In this sense, this review will summarize the involvement of BACE1, GSK-3β and AChE on synaptic function, neuroplasticity, neuroinflammation and oxidative stress. Additionally, we will present and discuss new perspectives on the modulation of these pathways on AD pathology and future directions on the development of drugs that concomitantly target these enzymes.

Antiamnesic effects of tofisopam against scopolamine-induced cognitive impairments in rats

In this study, we investigated the potential therapeutic effects of tofisopam, a 2,3-benzodiazepine derivative anxiolytic, on cognitive deficits in rats with scopolamine-induced amnesia. Cognitive performance of the rats was investigated by using the Morris water maze and passive avoidance tests. Changes in motor activity were assessed by using the activity cage and Rota-rod tests and then morphological changes in the hippocampus were assessed via immunohistochemical stainings. The results indicated that scopolamine impaired learning and memory parameters in rats. Worsened cognitive performance, neuronal loss, and decreased hippocampal synaptophysin, Ki-67, and glial fibrillary acidic protein density were observed. Tofisopam administration at a dose of 50 mg/kg for seven days improved the impaired cognitive performance, enhanced the attenuated synaptic transmission in the hippocampus, increased proliferation in subgranular zones, and improved the decrease in astrocytes in amnesic rats. These findings point out the anti-amnesic effects of tofisopam with concomitant improvements in the hippocampal synaptogenesis, neurogenesis, and glial plasticity, for the first time. Presented beneficial effects of tofisopam on cognitive dysfunctions may have a notable clinical value considering the fact that one of the most important side effects of 1,4-benzodiazepines, which are classical anxiolytic drugs, is amnesia. However, these preclinical results need to be confirmed with further clinical studies, first.

Intermittent fasting increases the expressions of SODs and catalase in granule and polymorphic cells and enhances neuroblast dendrite complexity and maturation in the adult gerbil dentate gyrus

Intermittent fasting (ImF) is known to reduce oxidative stress and affects adult neurogenesis in the hippocampal dentate gyrus. However, it is unknown how ImF affects endogenous antioxidants expressions, cell proliferation, and neuroblast differentiation and their dendrite remodeling over 3 months in the dentate gyrus of adult gerbils. The present study subjected 6‑month old male gerbils to a normal diet or alternate‑day ImF for 1, 2 and 3 months. Changes in body weight were not significantly different between gerbils fed a normal diet and on ImF. The present study also investigated the effects of ImF on antioxidant enzymes [superoxide dismutase (SOD)‑1, SOD2 and catalase] using immunohistochemistry, and endogenous cell proliferation, neuroblast differentiation and neuroblast dendrite complexity by using Ki67 (a cell proliferation marker) and doublecortin (neuroblast differentiation marker) immunohistochemistry in the dentate gyrus. SOD1, SOD2 and CAT immunoreactivities were shown in cells in the granule cell and polymorphic layers. SOD1, SOD2 and catalase immunoreactivity in the cells peaked at 2, 1 and 1 month, respectively, following ImF. Cell proliferation was ~250, 129 and 186% of the control, at 1, 2 and 3 months of ImF, respectively. Neuroblast differentiation was ~41, 32 and 12% of the control, at 1, 2 and 3 months of ImF, respectively, indicating that dendrites of neuroblasts were more arborized and developed at 3 months of ImF. Taken together, these results indicate that ImF for 3 months improves endogenous SOD1, SOD2 and catalase expressions and enhances cell proliferation, and neuroblast dendrites complexity and maturation in the adult gerbil dentate gyrus.

Changes in the Blood-Brain Barrier Function Are Associated With Hippocampal Neuron Death in a Kainic Acid Mouse Model of Epilepsy

The kainic acid (KA)-induced epilepsy experimental model is widely used to study the mechanisms underlying this disorder. Recently, the blood-brain barrier (BBB) has become an innovative alternative treatment target for epilepsy patients. KA causes neuronal injury and BBB damage in this experimental epilepsy model but the mechanisms underlying epilepsy-related neuronal injury, autophagy, and BBB damage remain unclear. Therefore, the present study investigated the relationships among neuronal injury, the expressions of autophagy-related proteins, and changes in BBB-related proteins during the acute phase of epilepsy to further understand the mechanisms and pharmacotherapy of epilepsy. NeuN immunohistochemistry and Fluoro-Jade B (FJ-B) staining in the hippocampal CA3 region revealed that neuronal death induced by intraventricular injections of 10 μg/kg KA was greater than that induced by 3 μg/kg KA. In addition, there were transient increases in the levels of microtubule-associated protein light chain 3-II (LC3I/II) and Beclin-1, which are autophagy-related proteins involved in neuronal death, in this region 24 h after the administration of 10 μg/kg KA. There were also morphological changes in BBB-related cells such as astrocytes, endothelial cells (ECs), and tight junctions (TJs). More specifically, there was a significant increase in the activation of astrocytes 72 h after the administration of 10 μg/kg KA as well as continuous increases in the expressions of platelet endothelial cell adhesion molecule-1 (PECAM-1) and BBB-related TJ proteins (Zonula occludens-1 and Claudin-5) until 72 h after KA treatment. These results suggest that the overexpression of autophagy-related proteins and astrocytes and transient increases in the expressions of BBB-related TJ proteins may be closely related to autophagic neuronal injury. These findings provide a basis for the identification of novel therapeutic targets for patients with epilepsy.

Melatonin Improves Cognitive Deficits via Restoration of Cholinergic Dysfunction in a Mouse Model of Scopolamine-Induced Amnesia

Melatonin is known to improve cognitive deficits, and its functions have been studied in various disease models, including Alzheimer's disease. In this study, we investigated effects of melatonin on cognition and the cholinergic system of the septum and hippocampus in a mouse model of scopolamine-induced amnesia. Scopolamine (1 mg/kg) and melatonin (10 mg/kg) were administered intraperitoneally to mice for 2 and 4 weeks. The Morris water maze and passive avoidance tests revealed that both treatments of scopolamine significantly impaired spatial learning and memory; however, 2- and 4-week melatonin treatments significantly improved spatial learning and memory. In addition, scopolamine treatments significantly decreased protein levels and immunoreactivities of choline acetyltransferase (ChAT), high-affinity choline transporter (CHT), vesicular acetylcholine transporter (VAChT), and muscarinic acetylcholine receptor M1 (M1R) in the septum and hippocampus. However, the treatments with melatonin resulted in increased ChAT-, CHT-, VAChT-, and M1R-immunoreactivities and their protein levels in the septum and hippocampus. Our results demonstrate that melatonin treatment is effective in improving the cognitive deficits via restoration of the cholinergic system in the septum and hippocampus of a mouse model of scopolamine-induced amnesia.

Vanillin improves scopolamine‑induced memory impairment through restoration of ID1 expression in the mouse hippocampus

4-Hydroxy-3-methoxybenzaldehyde (vanillin), contained in a number of species of plant, has been reported to display beneficial effects against brain injuries. In the present study, the impact of vanillin on scopolamine‑induced alterations in cognition and the expression of DNA binding protein inhibitor ID‑1 (ID1), one of the inhibitors of DNA binding/differentiation proteins that regulate gene transcription, in the mouse hippocampus. Mice were treated with 1 mg/kg scopolamine with or without 40 mg/kg vanillin once daily for 4 weeks. Scopolamine‑induced cognitive impairment was observed from 1 week and was deemed to be severe 4 weeks following the administration of scopolamine. However, treatment with vanillin in scopolamine‑treated mice markedly attenuated cognitive impairment 4 weeks following treatment with scopolamine. ID1‑immunoreactive cells were revealed in the hippocampus of vehicle‑treated mice, and were hardly detected 4 weeks following treatment with scopolamine. However, treatment with vanillin in scopolamine‑treated mice markedly restored ID1‑immunoreactive cells and expression 4 weeks subsequent to treatment. The results of the present study suggested that vanillin may be beneficial for cognitive impairment, by preventing the reduction of ID1 expression which may be associated with cognitive impairment.

Effects of Scopolamine and Melatonin Cotreatment on Cognition, Neuronal Damage, and Neurogenesis in the Mouse Dentate Gyrus

It has been demonstrated that melatonin plays important roles in memory improvement and promotes neurogenesis in experimental animals. We examined effects of melatonin on cognitive deficits, neuronal damage, cell proliferation, neuroblast differentiation and neuronal maturation in the mouse dentate gyrus after cotreatment of scopolamine (anticholinergic agent) and melatonin. Scopolamine (1 mg/kg) and melatonin (10 mg/kg) were intraperitoneally injected for 2 and/or 4 weeks to 8-week-old mice. Scopolamine treatment induced significant cognitive deficits 2 and 4 weeks after scopolamine treatment, however, cotreatment of scopolamine and melatonin significantly improved spatial learning and short-term memory impairments. Two and 4 weeks after scopolamine treatment, neurons were not damaged/dead in the dentate gyrus, in addition, no neuronal damage/death was shown after cotreatment of scopolamine and melatonin. Ki67 (a marker for cell proliferation)- and doublecortin (a marker for neuroblast differentiation)-positive cells were significantly decreased in the dentate gyrus 2 and 4 weeks after scopolamine treatment, however, cotreatment of scopolamine and melatonin significantly increased Ki67- and doublecortin-positive cells compared with scopolamine-treated group. However, double immunofluorescence for NeuN/BrdU, which indicates newly-generated mature neurons, did not show double-labeled cells (adult neurogenesis) in the dentate gyrus 2 and 4 weeks after cotreatment of scopolamine and melatonin. Our results suggest that melatonin treatment recovers scopolamine-induced spatial learning and short-term memory impairments and restores or increases scopolamine-induced decrease of cell proliferation and neuroblast differentiation, but does not lead to adult neurogenesis (maturation of neurons) in the mouse dentate gyrus following scopolamine treatment.

Effects of chronic scopolamine treatment on cognitive impairment and neurofilament expression in the mouse hippocampus

Neurofilaments (NFs) including neurofilament-200 kDa (NF-H), neurofilament-165 kDa (NF-M) and neurofilament-68 kDa (NF-L) are major protein constituents of the brain, and serve important roles in the regulation of axonal transport. NF alteration is a key feature in the pathogenesis of neurological disorders involving cognitive dysfunction. In the present study, cognitive impairments were investigated, via assessments using the Morris water maze and passive avoidance tests, in mice following chronic systemic treatment with 1 mg/kg scopolamine (SCO) for 4 weeks. SCO-induced cognitive impairments were significantly observed 1 week following the SCO treatment, and these cognitive deficits were maintained for 4 weeks. However, the NF immunoreactivities and levels were altered differently according to the hippocampal subregion following SCO treatment. NF-H immunoreactivity and levels were markedly altered in all hippocampal subregions, and were significantly increased 1 week following the SCO treatment; thereafter, the immunoreactivity and levels significantly decreased with time. NF-M immunoreactivity and levels gradually decreased in the hippocampus and were significantly decreased 4 weeks following SCO treatment. NF-L immunoreactivity and levels gradually decreased in the hippocampus, and were significantly decreased 2 and 4 weeks following SCO treatment. In conclusion, the results of the present study demonstrated that chronic systemic treatment with SCO induced cognitive impairment from 1 week following SCO treatment, and NF expression was diversely altered according to the hippocampal subregion from 1 week following SCO treatment. These results suggest that SCO-induced changes in NF expression may be associated with cognitive impairment.

Effects of long‑term scopolamine treatment on cognitive deficits and calcium binding proteins immunoreactivities in the mouse hippocampus

GABAergic projections terminate on numerous hippocampal interneurons containing calcium binding proteins (CBPs), including calbindin D-28k (CB), calretinin (CR) and parvalbumin (PV). Memory deficits and expression levels of CB, CR, and PV were examined in the hippocampal subregions following systemic scopolamine (Scop; 1 mg/kg) treatment for 4 weeks in mice. Scop treatment induced significant memory deficits from 1 week after Scop treatment. CB, CR and PV immunoreactivities distributions were in hippocampal subregions [CA1 and CA3 regions, and the dentate gyrus (DG)]. CB immunoreactivity (CB⁺) was gradually decreased in all subregions until 2 weeks after Scop treatment, and CB⁺ was decreased to the lowest level in all subregions at 3 and 4 weeks. CR⁺ in the CA1 region was gradually decreased until 2 weeks and hardly observed at 3 and 4 weeks; in the CA3 region, CR⁺ was not altered in all subregions at any time. In the DG, CR+ was gradually decreased until 2 weeks and lowest at 3 and 4 weeks. PV⁺ in the CA1 region was not altered at 1 week, and gradually decreased from 2 weeks. In the CA3 region, PV⁺ did not change in any subregions at any time. In the DG, PV⁺ was not altered at 1 week, decreased at 2 weeks, and lowest at 3 and 4 weeks. In brief, Scop significantly decreased CBPs expressions in the hippocampus ≥3 weeks after the treatment although memory deficits had developed at 1 week. Therefore, it is suggested that Scop (1 mg/kg) must be systemically treated for ≥3 weeks to investigate changes in expression levels of CBPs in the hippocampus.

Vanillin and 4-hydroxybenzyl alcohol attenuate cognitive impairment and the reduction of cell proliferation and neuroblast differentiation in the dentate gyrus in a mouse model of scopolamine-induced amnesia

4-Hydroxy-3-methoxybenzaldehyde (vanillin) and 4-hydroxybenzyl alcohol (4-HBA) are natural phenolic compounds, which present in many plants and have diverse biological properties. In this study, we examined effects of vanillin and 4-HBA on learning and memory function, cell proliferation, and neuroblast differentiation in the hippocampal dentate gyrus in a mouse model of scopolamine-induced amnesia. Scopolamine (SCO; 1 mg/kg/day, intraperitoneally), vanillin, and 4-HBA (40 mg/kg/day, orally) were administered for 28 days. Treatment with scopolamine alone impaired learning and memory function in the Morris water maze and passive avoidance tests, in addition, the treatment significantly reduced cell proliferation and neuroblast differentiation in the dentate gyrus, which were examined by immunohistochemistry for Ki-67 (a classic marker for cell proliferation) and doublecortin (a marker for neuroblasts). However, treatment with vanillin or 4-HBA significantly attenuated SCO-induced learning and memory impairment as well as the reduction of cell proliferation and neuroblast differentiation in the dentate gyrus. These results indicate that vanillin and 4-HBA may be helpful in improving cognitive function and in increasing endogenous neuronal proliferation in the brain.