ABSTRACT
In this study, evaluation of the protective effect of aqueous and ethanol fruit extracts of Phoenix dactylifera L. on mercury-induced neurotoxicity in Wistar rats, phytochemical screening of P. dactylifera fruit extracts (aqueous and ethanol) revealed the presence of flavonoids, saponins, tannins and alkaloids. The protective effect of the extracts were assessed on mercury-induced cerebral, cerebellar and hippocampal neurotoxicity in Wistar rats. Evaluation of the protective effect of P. dactylifera fruit extracts involved the following investigations: brain morphological studies; histometry of pyramidal cells of cerebral cortex- layer V and CA1 and CA3 hippocampal regions, and Purkinje cells of the cerebellar cortex; routine histological and histochemical studies of cerebral and cerebellar cortices, and hippocampus (CA1 and CA3 regions); neurobehavioural studies employing elevated plus maze (EPM) to assess anxiety-related behavior, transfer latency (TL) on EPM open arm and Morris water maze (MWM) to evaluate learning and memory, forelimb grip strength (FGS) test to assess muscular strength in the forelimbs and beam walking test (BWT) to monitor motor coordination and balance of Wistar rats; neurochemical analysis to assess the concentration of neuro-trace elements (copper, Cu; iron, Fe; manganese, Mn and zinc, Zn) in brain-tissue homogenate and biochemical analysis to assess lipid peroxide levels and antioxidant enzyme activity (malondialdehyde, MDA; superoxide dismutase, SOD; catalase, CAT and glutathione peroxidase, GPx) in blood serum and brain-tissue homogenate, and acetylcholinesterase (AchE) activity for endogenous enzyme in brain-tissue homogenate of Wistar rats. Seventy-two (72) Wistar rats (male and female) were divided into two experimental categories: 1 (twenty-four (24) rats, consisting of three groups; I – III served as the common groups) and 2 (forty-eight (48) rats, subdivided into treatment categories: A and B of twenty-four (24) rats each, consisting of three groups; IV – VI). Thus, each category consisted of six groups (I – VI) of eight rats each. Group I served as control and was administered distilled water (0.5 ml) while, groups II – VI were treatment groups. Neurotoxicity was induced in rats by the administration of mercury – mercuric chloride (HgCl2). Group II was administered HgCl2 (5 mg/kg); group III was administered vitamin C (100 mg/kg) as reference drug; groups IV, V and VI were administered fruit extract of P. dactylifera (250 mg/kg, 500 mg/kg and 1,000 mg/kg,
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respectively) followed, concomitantly, by HgCl2 (5 mg/kg) for a period of two weeks. Rats in category A were administered aqueous fruit extract of P. dactylifera (AFPD), while category B were administered ethanol fruit extract of P. dactylifera (EFPD); all administrations were via oral route. Results revealed that, exposure to HgCl2 resulted in neurotoxicity in rats, which was evident from morphologic, histometric, histologic and histochemical alterations in brain; HgCl2 induced anxiety-related responses, short- and long-term memory impairments and motor deficits in neurobehavioural assessment and, altered the levels of neurochemical and biochemical constituent in rats. However, administration of AFPD and EFPD revealed the potentials of the extracts as neuroprotective agent in the following ways: brain morphologic features and histometric characteristic of brain regions (cerebral and cerebellar cortices and hippocampus) were preserved relative to the control; histologic and histochemical alterations in cerebral and cerebellar cortices and hippocampal regions (CA1 and CA3) were ameliorated relative to the control; anxiety-related responses, short- and long-term memory impairments, and motor coordination and balance deficits in neurobehavioural assessment were ameliorated relative to the control; Alterations in the concentration levels of neuro-trace elements (Fe, Mn, Cu and Zn), MDA and endogenous antioxidants (SOD, CAT, GPx), and endogenous enzyme (AchE) activity levels were moderately ameliorated relative to the control. The neuroprotective property of extracts, relative to the reference (vitamin C), is rather similar, and is attributed to antioxidant properties of constituent phytochemicals, such as flavonoids. Neuroprotective activity was dose dependent; 500 and 1,000 mg/kg doses possessing maximal activity for both extracts – with EFPD more efficacious. In conclusion, findings suggest that, AFPD and EFPD are potentially efficacious in ameliorating mercury-induced alterations in the brain (cerebral and cerebellar cortices and hippocampus) of Wistar rats and could be potential candidates for application in the management and treatment of reactive oxygen species-induced neurodegenerative diseases.
TABLE OF CONTENTS
Title Page….……………………………………………………………..……………….i
Declaration……….………………………………..……………………………………ii
Certification……………………………………………………………….………..……iii
Dedication………..…………..………………………………………………….………iv
Acknowledgements…………..………………………………………………….………v
Abstract…………..……………………………………………………………………vii
Table of contents….………………………………………………………….…………ix
List of figures….……………………………………………………….………………..xvi
List of tables…………………………………………………………………………..xviii
List of plates……………………………………………………………………………xix
List of appendices……………………………………………………………………..xxvi
List of abbreviations…………………………………………………………….……xxvii
CHAPTER ONE
1.0 Introduction…………………………………….………………..…………………….1
1.1 Background Information………………………………………………………..…….1
1.2 Mercury……………………………………………………………………..…….……3
1.3 Phoenix dactylifera L. (Date Palm)…………………………………………….………5
1.4 Statement of the Research Problem……………………………….………………….7
1.5 Significance of the Study……………………………………………………………….8
1.6 Study Hypothesis………………………………………………………………………..8
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1.7 Aim and Objectives of the Study………………………………….…………………..9
1.7.1 Aim…………………………………………………………………………………….9
1.7.2 Objective………………………………………………………………………………9
CHAPTER TWO
2.0 Literature Review………………………………………………..….…….…………11
2.1 Mercury……………………………………………………………………..………..11
2.1.1 Definition……………………………………………………………………………13
2.1.2 Chemistry…………………………………………………………………………….14
2.1.3 History………………………………………………………………………………..15
2.1.4 Toxicity…………………………………………………………….………………..17
2.1.4.1 Sources of Mercury Exposure……………………………………….…………….19
2.1.4.2 Mercury Poisoning……….…………………………………………..……………21
2.1.4.2.1 Systemic Disruptions……………………………………………………………..21
2.1.4.2.2 Immunological Reactions…………………………………………..……………24
2.1.4.2.3 Neurological……………………………………………………………..………26
2.2 Plant……………………………………………………………………………………30
2.2.1 Medicinal Plants……………………………………………………………………..30
2.2.1.1 Neuroprotective Plants…………………………………………….………………31
2.2.2 Phoenix dactylifera (Date Palm)………………………………….…………………33
2.2.2.1 Taxonomy………………………………………………………………………….34
2.2.2.2 Botanical Description……………………………………………………….………35
2.2.2.3 Varieties of Date Palm……………………………………………………….…….35
2.2.2.4 Nutritional Composition……………………………………………………….…..35
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2.2.2.5 Phytochemistry……………………………………………………………………..36
2.2.2.6 Medicinal Applications of Phoenix dactylifera…………………………….……..37
2.3 Brain……………………………..………………………………………….…………44
2.3.1 Embryology……………………………………………………….…………………45
2.3.1.1 Origin of the Nervous System……………………………………………..………45
2.3.1.1.1 Development of the Brain……………………………………..…………………46
2.3.2 Gross Anatomy……………………………………………………..………………..51
2.3.2.1 Cerebrum…………………………………………………………………….…….52
2.3.2.1.1 Hippocampus…………………………………………………………………….53
2.3.2.2 Midbrain………………………………………………………..………………….55
2.3.2.3 Pons……………………………………………………………….……………….56
2.3.2.4 Medulla…………………………………………………………………………….56
2.3.2.5 Cerebellum………………………………………………………………..……….56
2.3.3 Brain Histology……………………………………………….……………………..57
2.3.3.1 Cerebrum………………………………………………………..…………………57
2.3.3.1.1 Neurone Types in the Cerebral Cortex…………………………………….……57
2.3.3.1.2 Layers of the Neocortex…………………………………………………………..59
2.3.3.2 Hippocampus…………………………………………………………..…………..60
2.3.3.2 Cerebellum……………………………………..………………….………….……61
2.3.4 Histometry……………………………………………………………………………62
2.3.5 Neurobehavioural Testing…………………………………………………………….63
2.3.5.1 Learning and Memory……………………………………………..……….………63
2.3.5.2 Anxiety-Like Behaviour………………………………………….………….……..64
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2.3.5.3 Beam Walking………………………………………………………..…………….65
2.3.5.4 Forelimb grip strength test…………………………………………….…………..66
2.4 Vitamin C……………………………………………………………………………..66
2.4.1 Definition……………………………………………………………………………67
2.4.2 Chemistry……………………………………………………………………………68
2.4.3 Biosynthesis…………………………………………………………………..……..69
2.4.4 Metabolism………………………………………………………………..…………70
2.4.4.1 Redox Metabolism of Ascorbic Acid………………………….…………………..70
2.4.4.2 Ascorbic Acid Availability and Transport…………………….…………………..71
2.4.5 The Roles of Ascorbic Acid in Biological Pathways…………………..…………….72
2.4.6 Vitamin C and Mercuric Intoxication…………………………………..……………75
CHAPTER THREE
3.0 Materials and Methods……………………………………………………………….77
3.1 Materials…………………………………………………………..…………………..77
3.1.1 Plant Material……………………………………………….……………………….77
3.1.2 Experimental Animals………………………………………………………………..77
3.1.3 Drugs……………………………………………………………………….………..77
3.1.4 Neurobehavioural Set-up………………………………………………….…………78
3.1.5 Animal Feed…………………………………………………………………………..78
3.1.6 Other Materials……………………………………………………..………………..78
3.2 Methods…………………………………………………………………………………79
3.2.1 Plant Extract Preparation………………………………………………….…………..79
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3.2.2 Phoenix dactylifera Phytochemical Screening…………………………..….………..80
3.2.3 Dose Preparation of Fruit Extract of Phoenix dactylifera ……………….………….80
3.2.4 Dose Preparation of Mercury………………………………………………….…….80
3.2.5 Dose Preparation of Vitamin C (Standard Drug)……………………………..……..81
3.2.6 Experimental design………………………………………………………………….81
3.2.7 Experimental Procedure……………………………………………………………..85
3.2.7.1 Neurobehavioural/ Cognitive Studies……………………………………..………85
3.2.7.2 Sensory-motor Activity, Motor Coordination and Balance Studies………..……..87
3.2.7.3 Morphological Studies……………………………………………………………..89
3.2.7.4 Histological and Histochemical Studies……………………………………………90
3.2.7.5 Neurochemical and Biochemical Studies………………….………………………90
3.3 Data Analysis…………………………………………………………………..………92
CHAPTER FOUR
4.0 Results……………………………………………………………..…………………..93
4.1 Phytochemical Analysis……………………………………..…….…………………93
4.2 Physical Observation……………………………………….………………………..93
4.3 Morphological Studies……………………………………………..…………………96
4.3.1 Morphometry…………………………………………………………………………96
4.3.2 Histometric Studies…………………………………………………………………..99
4.3.2.1 Cerebral and Cerebellar Cortices Histometric Characteristics……………………..99
4.3.1.2 CA1 and CA3 Hippocampal Regions Histometric Characteristics………..……..103
4.4 Histological and Histochemical Studies…………………………..………….…….108
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4.4.1 Histological and Histochemical Features of the Cerebral Cortex…………………..108
4.4.1.1 Histological and Histochemical Features of the Cerebral Cortex of Control (Untreated) Wistar Rat………………………………………………….………..108
4.4.1.2 Histological and Histochemical Features of the Cerebral Cortex of Treated
Wistar Rats…………………………………………………………..……………..113
4.4.2 Histological and Histochemical Features of the Cerebellar Cortex……….……….128
4.4.2.1 Histological and Histochemical Features of the Cerebellar Cortex of Control (Untreated) Wistar Rat……………………………………………………………128
4.4.2.2 Histological and Histochemical Features of the Cerebellar Cortex of Treated
Wistar Rats………………………………………………………………………….128
4.4.3 Histological and Histochemical Features of the Hippocampus…………………….143
4.4.3.1 Histological and Histochemical Features of the Hippocampus of Control (Untreated) Wistar Rat………………………………………….………………..158
4.4.3.2 Histological and Histochemical Features of the Hippocampus of Treated
Wistar Rats………………………………………………………………………..158
4.5 Neurobehavioural Studies…………………………………………..…….………..165
4.5.1 EPM Studies……………………………………..…………………………………165
4.5.2 TL on EPM open arm…………………………………………………..…………..186
4.5.3 MWM Studies………………………………………..…………………………….186
4.5.4 FGS Studies…………………………………………………………………………190
4.5.5 BWT Studies………………………………………………………………………..195
4.6 Neurochemical/ Biochemical Studies……………………………..…………..……200
4.6.1 Neurochemistry of Neuro-trace Elements……………………….………………….200
4.6.2 Biochemistry of Lipid Peroxide Levels and Antioxidant Enzyme Activity….…….202
4.6.3 Biochemistry Endogenous Enzyme Activity………………………………………..215
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CHAPTER FIVE
5.0 Discussion……………………………………………………………………………218
5.1 Phytochemical studies………………………………………..………..………….…218
5.2 Physical Observation…………………………………………..………..…………..218
5.3 Morphological Studies…………….………………………..…………..…….……..219
5.4 Histological and Histochemical Studies……………………………………….……221
5.5 Neurobehavioural Studies……………………………………………….…….…….229
5.6 Neurochemical/ Biochemical Studies…………………………………..…….……..236
CHAPTER SIX
6.0 Summary, Conclusion and Recommendation…………………………………….247
6.1 Summary……………………………………………………………………………..247
6.2 Conclusion………………………………………………………………..…………..249
6.3 Recommendation…………………………………………………………………….250
REFERENCES…………………………………………………………….…..………..251
APPENDICES……………………………………………………………….…………..292
CHAPTER ONE
1.1 Background Information
Mercury is a widespread environmental and industrial pollutant that exerts toxic effect on a variety of vital organs; it induces severe alterations in the tissues (Lund et al., 1993; Mahboob et al., 2001; Sener et al., 2007; Wadaan, 2009; Xu et al., 2012), causes numerous neurological abnormalities (Auger et al., 2005; Kingman et al., 2005) and produces peripheral neuropathy (Boyd et al., 2000; Chuu et al., 2007) in experimental animals and human beings.
The central nervous system (CNS) is one of the most vulnerable organs affected by mercury toxicity. Within the CNS, two of the most often affected areas are the cerebral cortex (Eto et al., 2001; Ferraro et al., 2009) and the cerebellum (Fonfria et al., 2005; Korogi et al., 2011).
Nature is, and will still serve as, the man’s primary source for the cure of his ailments. However, the potential of higher plants as sources for new drugs is still largely unexplored (Oke, 2002). About 80% of people in the developing countries rely on phytomedicine for primary healthcare for man and livestock (Harvey, 1999). In traditional practices of medicine, numerous plants have been used to treat cognitive disorders, including neurodegenerative diseases such as Alzheimer’s disease (AD) and other memory related disorders (Kumar and Khanum, 2012).
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Phoenix dactylifera (date palm) fruits, an important component of diet in the arid and semiarid regions of the world (Biglari et al., 2008) are a good source of energy, vitamins, and a group of elements like phosphorus, iron, potassium, and a significant amount of calcium (Abdel-Hafez et al., 1980; Usama et al., 2009). Dates contain vitamins and are widely used in traditional medicine for the treatment of various disorders e.g. memory disturbances, fever, inflammation, paralysis, loss of consciousness, nervous disorders (Nadkarni, 1976). It is also used in the treatment for sore throat, to relieve fever, cystitis, gonorrhea, edema, liver and abdominal troubles and to counteract alcohol intoxication (Barh and Mazumdar, 2008; Al-daihan and Bhat, 2012).
Several pharmacological studies have been conducted on Phoenix dactylifera and it has been demonstrated to have antiulcer activity; anticancer activity; anti-diarrhoeal activity; hepatoprotective activity; antimutagenic activity; antiinflammatory activity; in vitro antiviral activity; effect on reproductive system; antihyperlipidemic activity; nephroprotective activity and antioxidant activity (Vyawahare et al., 2009; Agbon et al., 2013).
Several researchers have also documented the antioxidant property of Phoenix dactylifera (Mohamed and Al-Okbi, 2004; Allaith and Abdul, 2005; Al-Qarawi et al., 2008). Of late, more attention has been paid to the role of natural antioxidants mainly phenolic compounds, which may have more antioxidant activity than vitamins C, E, acarotene (Vinson et al., 1998; Haslam, 2006).
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1.2 Mercury
Mercury is a heavy metal contaminant with potential for global mobilization following its give off from anthropogenic activities or natural processes (Gochfeld, 2003). In nature, elemental mercury (Hg0) can be biotransformed and converted to methylmercury (MeHg), which is the most toxic form of mercury in the environment (Malm, 1998; Eisler, 2004; Clarkson and Magos, 2006). The studies about MeHg toxicity became ubiquitous and diversified since the outbreak of environmental catastrophes such as those in Minamata (1950s) and Niigata (1960s). In such episodes, as a consequence of MeHg exposure, the exposed individuals exhibit severe forms of neurological disease which include a collection of cognitive, sensory, and motor disturbance (Takeuchi et al., 1979; Eto, 2000).
The studies on MeHg toxicity have tried to evaluate its impact on several ecosystems around the world, including places in Japan, Irak, Canada, Africa, including Brazilian Amazon, and India (Malm, 1998; Harada et al., 2001; Agarwal et al., 2007) as well as to understand its toxicological effect on biological systems. MeHg was firstly recognized as a potent neurotoxicant for the adult nervous system in studies performed on exposed workers of a chemical factory in England (Hunter et al., 1940; Hunter and Russell, 1954). Later, its importance as a neurotoxicant for the nervous system during development was recognized in the Minamata’s outbreak (Takeuchi et al., 1979; Eto, 2000). Since then, several studies of exposed human populations as well as experiments with laboratory animals demonstrated that exposure to toxic levels of MeHg during pre- and post-natal life causes neurological abnormalities, cognitive impairment, and behavioural disturbance (Steuerwald et al., 2000; Cordier et al., 2002).
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Mercury exists in three predominant forms: elemental (Hg0), organic (such as, methylmercury –MeHg), and inorganic (mercuric chloride – HgCl2) mercury (Clarkson and Magos, 2006). Each form has its own effects, routes of absorption and tissue specificity. Organic mercury is the most deadly of the mercury compounds, probably due to its ability to penetrate cells (Abdel-Salam et al., 2010).
Mercury poisoning can result from inhalation, ingestion or absorption through the skin and may be highly toxic and corrosive once absorbed into blood stream (Wadaan, 2009). The major sources of mercury load in humans are food contamination, drug and vaccine preservatives, dental amalgams, or occupational exposure (Clarkson, 2002). Both acute and chronic exposure to mercury is also known to cause a variety of neurological or psychiatric disorders (Choi et al., 1988; Meyer-Baron et al., 2002; Clarkson et al., 2003; Mutter et al., 2005).
The central nervous system (CNS) (developing and adult) is one of the most vulnerable organs affected by mercury toxicity. Within the CNS, two of the most often affected areas are the cerebral cortex (Eto et al., 2001; Ferraro et al., 2009) and the cerebellum (Fonfria et al., 2005; Korogi et al., 2011). In the adult brain, MeHg poisoning damages the so-called primary areas of the cerebral cortex, affecting the visual, auditory, somatic sensory, and motor cortex, as well as the hippocampus and the granule layer of the cerebellum, causing a remarkable loss of neurones in these brain regions.
On the other hand, in the developing brain there is a widespread neuronal loss throughout the CNS, what has been interpreted as due to the high MeHg sensitivity of the immature CNS (Steuerwald et al., 2000). The neural disease due to MeHg neurotoxicity includes
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such symptoms as visual field constriction, somatic sensory disturbance, hearing disturbance, cerebellar ataxia, dysarthria, and mnemic deficits (Lakowicz and Anderson, 1980; Carta et al., 2003; Silveira et al., 2003).
The mechanisms underlying mercury-induced toxicity remain largely unknown. However, several studies have shown toxic effects of organic MeHg on the CNS as it can easily cross the blood–brain barrier and accumulate in the brain at high concentrations (Clarkson and Magos, 2006; Farina et al., 2011). MeHg has been reported to interact with a wide range of cellular targets and affect multiple cellular functions. These toxic effects include, but are not limited to, the inhibition of neuronal ion channels (Pekel et al., 1993; Sirois et al., 1996; Peng et al., 2002), disruption of presynaptic transmitter release and postsynaptic receptor function (Castoldi et al., 2001; Yuan and Atchison, 2003; Yuan and Atchison, 2005), damage to neuronal cytoskeleton components and DNA structures (Castoldi et al., 2000; Eto et al., 2001; Juarez et al., 2005) and alteration of Na+/K+ ATPase and mitochondrial function (Atchison and Hare, 1994; Insug et al., 1997; Aschner et al., 2000; Limke and Atchison, 2002).
1.3 Phoenix dactylifera L. (Date Palm)
Medicinal herbs are indispensible part of traditional medicine practiced all over the world due to easy access, low cost, least risk and low side effect profile (Sujith et al., 2012). The cultural use of medicinal plants is wide spread in Africa (Ashafa and Olunu, 2011). The World Health Organization (WHO) estimates that up to 80% of the world’s population relies on traditional medicinal system for some aspect of primary health care (Farnsworth et al., 1985).
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Phoenix dactylifera L. (date palm) a diploid with 2n = 36, is a member of the monocot family Arecaceae classified as a dioecious tall evergreen tree (Zohary and Hopf, 1993). The date palm is known to be one of the oldest cultivated trees in the world (Dowson, 1982; Abdulla, 2008). Date palm has been an important crop in arid and semiarid regions of the world. It has always played an important part in the economic and social lives of the people of these regions. The fruit of the date palm is well known as a staple food. It is composed of a fleshy pericarp and seed. Date palms have been cultivated in the Middle East over at least 6000 years ago (Copley et al., 2001).
Date palm is believed to have been introduced into Nigeria in the early 8th century by Arab traders from North Africa. Date fruits are a highly valued delicacy among many communities in Nigeria, especially during ceremonies and festivals. The national consumption of dates in 2009 is estimated at 8,958 metric tons which placed the country among the world top 10 consumers of date (Sani et. al., 2010).
Phoenix dactylifera Linn. is known in Arabic as Nakl; fruit as Balah and Tamr; in English as Date palm, in French as Dattier and in Hausa (Nigeria) as Dabino. P. dactylifera L is well known in northern Nigeria (with almost desert-like climate; the states in this axis are Jigawa, Borno, Kebbi, Yobe, Sokoto, Katsina and Zamfara) (Okere et. al., 2010).
The various parts of this plant are widely used in folk medicine for the treatment of various ailments. In fact, Muslims believe that “He who eats seven dates every morning will not be affected by poison or magic on the day he eats them” (Miller et al., 2003). Dates are widely used in traditional medicine for the treatment of various disorders e.g. memory disturbances, fever, inflammation, paralysis, loss of consciousness, nervous disorders
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(Nadkarni, 1976), and as a detersive and astringent in intestinal troubles. It is also used in the treatment for sore throat, colds, bronchial asthma, to relieve fever, cystitis, gonorrhea, edema, liver and abdominal troubles and to counteract alcohol intoxication (Barh and Mazumdar, 2008). Dates are a good source of energy, vitamins, and a group of elements like phosphorus, iron, potassium, and a significant amount of calcium (Abdel-Hafez et al., 1980). Dates contain at least six vitamins including a small amount of vitamin C, and vitamins B1 (thiamine), B2 (riboflavin), nicotinic acid (niacin) and vitamin A (Al-Shahib and Marshall, 1993).
Recent studies indicate that the aqueous extracts of dates have potent antioxidant activity (Mansouri et al., 2005); several researchers have also documented the antioxidant property of P. dactylifera (Mohamed and Al-Okbi, 2004; Allaith and Abdul, 2005; Al-Qarawi et al., 2008). The antioxidant activity is attributed to the wide range of phenolic compounds in dates including p-coumaric, ferulic, sinapic acids, flavonoids and procyanidins (Gu et al., 2003).
1.4 Statement of the Research Problem
Mercury is present in various environmental media and food, and has caused a variety of documented, significant adverse impacts on human health and wildlife throughout the world (Xu et al., 2012).
Despite massive efforts in search of new drugs that counteract mercurial toxicity, there are no effective treatments available that completely abolish its toxic effects. The use of chelating agents assists the body’s ability to eliminate mercury from the tissues (Carvalho et al., 2007). However, these drugs appear to be of limited use, because of their adverse
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side effects (Tchounwou et al., 2003) and limited ability to cross the blood-brain barrier (Aposhian et al., 1995; Martins et al., 2009).
Some studies have focused their efforts on the protective effects of natural compounds in various neuropathological conditions (Martins et al., 2009). However, the neuroprotective potential of higher plants as sources for new drugs is still largely unexplored.
There is paucity of literature on the potential beneficial effects of fruit extracts of P. dactylifera against the neurotoxicity induced by mercury in Wistar rats.
1.5 Significance of the Study
1. The present study is of importance in the identification and evaluation of available natural agents as alternatives to currently used antioxidant drugs, which are frequently not free from adverse effects.
2. Results of this study could lead to the identification of safe and more effective agent that is affordable and readily available which is key to combating the problem of brain related disorders especially in developing countries.
3. Knowledge gained from this study could provoke the minds of indigenous researchers unto directing their research focus into the field of neuroscience, ethnopharmacology and medicinal plants.
1.8 Study Hypothesis
Aqueous and ethanol fruit extracts of Phoenix dactylifera has protective effect on mercury-induced neurotoxicity in Wistar rats.
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1.9 Aim and Objectives of the Study
1.7.1 Aim
The aim was to evaluate of the protective effect of aqueous and ethanol fruit extracts of Phoenix dactylifera L on mercury-induced neurotoxicity in Wistar rats.
1.7.2 Objectives
The objectives were to:
1. Morphologically, histologically and histochemically investigate the protective effect of aqueous and ethanol fruit extracts of Phoenix dactylifera L on mercury-induced cerebral, cerebellar and hippocampal neurotoxicity in Wistar rats.
2. Investigate the cognitive effects of aqueous and ethanol fruit extracts of P. dactylifera on mercury-induced hippocampal toxicity in Wistar rats using Elevated Plus Maze test and Morris Water Maze test for spatial memory and learning.
3. Investigate the effect of aqueous and ethanol fruit extracts of P. dactylifera on mercury-induced cerebellar and cerebral toxicity in Wistar rats using Beam Walking test for motor coordination and balance and Forelimb Grip Strength test for sensory-motor activity.
4. Neurochemically investigate the protective effect of aqueous and ethanol fruit extracts of P. dactylifera on mercury-induced neurotoxicity in Wistar rats using biochemical analysis for metal (copper, Cu; iron, Fe; manganese, Mn and zinc, Zn) estimation, lipid peroxide levels and antioxidant enzyme activity (malondialdehyde – MDA, superoxide dismutase – SOD, catalase – CAT and glutathione peroxidase – GPx), and endogenous enzyme (acetylcholinesterase –AchE) activities.
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5. Evaluate the neuroprotective effect of aqueous and ethanol fruit extracts of P. dactylifera on mercury-induced neurotoxicity in Wistar rats using an established antioxidant, vitamin C, as a standard.
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