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Received Aug 14, 2017; Accepted Jan 4, 2018
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1. Introduction
Neurodegeneration in individuals with Alzheimer’s disease (AD), Parkinson’s disease (PD), and other neurodegenerative disorders is multifactorial, of which a complex set of toxic reactions, including inflammation, glutaminergic neurotoxicity, increased iron levels, accumulation of reactive oxygen and/or nitrogen species (ROS/RNS), depletion of endogenous antioxidant, reduced expression of neurotropic factors, and increased expression of apoptosis-related proteins, lead to neuronal cell death and damage [1]. Learning and memory are generated by an experience-dependent and long-lasting modification of the central nervous system (CNS), which involve the activation of diverse neurotransmitters, such as dopamine and serotonin, and the receptor-linked enzymes that are responsible for the activation of intercellular second messengers [2]. Particularly, cholinergic neurons in the brain of patients with AD are vulnerable, and cholinergic function plays an important role in the learning and memory process. Cholinergic neurons in the CNS are degenerated in patients with AD, which is correlated with senile dementia severity and degree of degeneration [3].
In this study, because the regulation of the cholinergic system is a key process in memory function, scopolamine (SCO), an experimental tool that induces cognitive dysfunction, was utilized, which is a tropane alkaloid exhibiting muscarinic antagonistic effects. The administration of SCO induces central cholinergic blockade and produces a reversible and well-described impairment in maintaining attention, processing information, and acquiring new knowledge in rodents and humans [4]. In in vivo animal models, SCO induced deficits in learning and memory as assessed by contextual and cued fear conditioning, inhibitory avoidance, and spatial learning tasks [4, 5]. Recently, studies showed that memory impairment in an SCO-treated animal model is associated with the altered status of brain oxidative stress and subsequent degenerative changes within the forebrain cholinergic system [6].
Biologically active phytochemicals in plants or plant products and herbal ingredients that can be used to develop practical natural medicines have been a topic of interest [7]. Traditional oriental herbs contain a wide variety of biologically active compounds, which is being used for the treatment of various types of chronic and acute diseases for thousands of...