Elsevier

Acta Histochemica

Volume 120, Issue 1, January 2018, Pages 46-55
Acta Histochemica

Vitamin E can improve behavioral tests impairment, cell loss, and dendrite changes in rats’ medial prefrontal cortex induced by acceptable daily dose of aspartame

https://doi.org/10.1016/j.acthis.2017.11.004Get rights and content

Highlights

Abstract

Aspartame is an artificial sweetener used in about 6000 sugar-free products. Aspartame consumption could be associated with various neurological disorders. This study aimed to evaluate the effect of aspartame onmedial Prefrontal Cortex (mPFC) as well as neuroprotective effects of vitamin E. The rats were divided into seven groups, including distilled water, corn oil, vitamin E (100 mg/kg/day), and low (acceptable daily dose) and high doses of aspartame (40 and 200 mg/kg/day) respectively, with or without vitamin E consumption, for 8 weeks. Behavioral tests were recorded and the brain was prepared for stereological assessments. Novel objects test and eight-arm radial maze showed impairmentoflong- and short-termmemoriesin aspartame groups. Besides, mPFC volume, infralimbic volume, neurons number, glial cells number, dendrites length per neuron,and number of spines per dendrite length were decreased by 7–61% in the rats treated with aspartame. However, neurons’ number, glial cells number, and rats’ performance in eight-arm radial mazes were improved by concomitant consumption of vitamin E and aspartame. Yet, the mPFC volume and infralimbic cortex were protected only in the rats receiving the low dose of aspartame + vitamin E. On the other hand, dendrites length, spines number,and novel object recognition were not protected by treatment with vitamin E + aspartame. The acceptable daily dose or higher doses of aspartame could induce memory impairments and cortical cells loss in mPFC. However, vitamin E could ameliorate some of these changes.

Introduction

Aspartame is an artificial sweetener,which is around 200 times sweeter than sugar. Therefore, it is used in about 6000 sugar-free products, including carbonated soft drinks, hot chocolate, chewing gums, candies, deserts, tabletop sweeteners, vitamins, and cough drops as a substitution for sugar (Adaramoye and Akanni, 2016, Sahar and Omar, 2009). Aspartame is absorbed from the intestine and is quickly metabolized to its fundamental constituents by the liver in rodents, primates, and humans, which may generatepoisonous or adverse effects in animal model systems (Finamor et al., 2014). Aspartame consumption was reported to be associated with various symptoms in the centralnervous system, such as seizures, memory deficits, cholinergic symptoms, headaches, personality disorders, visual problems, dizziness, and ontogenesis (Sahar and Omar, 2009, Christian et al., 2004). Sahar and Omar (2009) also indicated that aspartame could affect the frontal cortex. The hippocampal region and prefrontal cortex are the fundamental parts of the brain,which are involved in learning and memory activities. The effects of aspartame on these structures are mainly focused on the hippocampal region; however, the prefrontal cortex hasreceived less attention. In addition, the majority of academic theses have evaluated biochemical and electrophysiological activities of these regions, and structural changes of prefrontal cortex have not received adequate attention (Simintzi et al., 2007a, Simintzi et al., 2007b).Therefore, the first aim of the present study is toevaluate the possible toxic effects of long-term aspartame consumption (8 weeks) on the medial Prefrontal Cortex (mPFC),which takes part in memory and learning. Rats’ mPFC is mainly subdivided into three cytoarchitectonic subareas, namely Anterior Cingulate Cortex (ACC), Infralimbic Cortex (ILC), and Prelimbic Cortex (PLC) (Dalton et al., 2016, Rafati et al., 2017).This study also aims to find a protective agent to be used in case of exposure to aspartame. Vitamin E is a recognized neuroprotectant and has been used as a therapeutic agent in neurodegenerative diseases.Vitamin E can be found naturally in some foods and is available as a nutritional supplement. Therefore, it may fulfill aputative protective function in the present study (Yin et al., 2015, Sakr et al., 2015).The acceptable daily intake (ADI) for aspartame is 40 mg/kg body weight (Ashok and Sheeladevi, 2014). Hence, the low and high doses of aspartame in this study were considered to be 40 mg/kg/day and 200 mg/kg/day, respectively. Considering the fact that individuals’ exact in take throughout the day and in diverse dietary habits are not known, the high dose was selected as 5 times higher than the ADI. Dosage of vitamin E was also selected according to previous studies, which reported the neuroprotective effects of this agent (Yin et al., 2015, Sakr et al., 2015). Overall, the present survey was conducted on a rat model of aspartame consumption to find answers to the following questions:

Do the rats’ visual learning and memory change after exposure tolow and high doses of aspartame? Is the rats’ spatial learning and memory affected differently following exposure to low and high doses of aspartame? Do the rats’ motor skills change after aspartame consumption? Does the volume of the mPFC (anterior cingulated, prelimbic, and infralimbic cortices) change after treatment with aspartame? Can the number of neurons and glial cells in the mPFC change after exposure to aspartame? Are the dendrites length and spines (mushroom, thin, and stubby subtypes) modified after exposure to aspartame? Can vitamin E prevent alteration in behavioral tests? Can vitamin E prevent changes in the mPFC structure in the animals treated with aspartame? To assess the structural changes of mPFC, the tissue was assessed using stereological methods.

Section snippets

Animals

This study was performed on 70 male Sprague-Dawley rats weighing 250–280 g and attwo months of age. They were obtained from the University’s Center of Comparative and Experimental Medicine. All animal were handled according to the Animal Care and Ethics Committee of the University (Agreement License No. 95–7663).

Experimental design

The animals were randomly categorized into seven groups each containing 10 rats. The rats in groups I to VII received daily oral gavages of distilled water, corn oil, vitamin E (100 

Novel object recognition analysis

According to Fig. 2A–C the whole exploration time in the training, short- and long-term memory exams were discovered to be increased in aspartame + vitamin E (low and high dose) compared to aspartame (low and high dose) group suggesting an improved memory function in aspartame- plus vitamin E treated animals. Results showed in Fig. 2D and Epropose that vitamin E treatment in high dose of aspartame animals either in short- or long-term memory exam could protect memory function from the negative

Discussion

The present study confirmed the adverse consequences of aspartame consumption on some brain functions and histological changes in the mPFC in rats. Thus, more attention should be paid to the usage of artificial sweeteners. Based on the results,even the acceptable daily dose of aspartame could induce memory changes and cortical cell loss. Besides, the novel-object recognition test and eight-arm radial maze permitted assessment of the visual and spatial memory performances.

The first part of our

Conclusions

Consumption of the acceptable daily dose or higher doses of aspartame for eight weeks could induce memory changes, cortical cells loss (neurons and glia), and change in dendritic morphology in the mPFC of male rats. Yet, vitamin E could ameliorate some of these changes.

Disclosure

Authors report no conflict of interest.

Acknowledgements

This article was a part of the thesis written by Mahboubeh Jahangir, M.Sc. student of Anatomy and financially supported by grant No. 95-7663 from Shiraz University of Medical Sciences, Shiraz, Iran. The work was performed at Histomorphometry and Stereology Research Center, Shiraz University of Medical Sciences, Shiraz, Iran. Hereby, the authors would like to thank Ms. A. Keivanshekouh at the Research Improvement Center of Shiraz University of Medical Sciences for improving the use of English in

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