EVALUATION OF NOOTROPIC ACTIVITY OF METHANOL STEM EXTRACT OF PARQUETINA NIGRESCENS AFZEL IN MICE

ABSTRACT

Parquetina nigrescens is a plant with numerous ethnomedicinal uses in African traditional medicine practice. In the South Western part of Nigeria, the stems and roots are roasted, powdered then mixed with pap taken as memory enhancer and for its antiaging effect. This study therefore, aimed to investigate the nootropic activity of the methanol stem extract of P. nigrescens. Phytochemical screening was carried out on the methanol extract and the median lethal dose (LD50) determined using the Organisation for Economic Cooperation and Development in Europe (OECD) 425 limit test. The effect of the extract on cognition was evaluated at doses of 250, 500 and 1000 mg/kg using the elevated plus maze, Barnes maze and novel object recognition test models while the antiamnesic potential was investigated against scopolamine and diazepam induced amnesia. The effect of the extract on exploratory behaviour was also studied using the open field test and hole-board test. The behavioural cognitive enhancing effect of the extract on sub-chronically scopolamine induced cognitive deficit in mice was evaluated in an elevated plus maze and novel object recognition test thereafter, the brain tissue was assayed for malondialdehyde, superoxide dismutase, reduced glutathione and acetylcholinesterase. The results of the phytochemical screening of the extract revealed the presence of carbohydrates, tannins, saponins, phenolics, unsaturated sterols but absence of alkaloids, cardiac glycosides and triterpenes. The LD50 was estimated to be ≥ 5000 mg/kg. Piracetam a standard nootropic agent and the extract decreased transfer latencies at all doses on day 1 and day 2 in the elevated plus maze. In the Barnes maze, the escape latency and escape errors were decreased significantly (p < 0.05, p < 0.01) respectively by the extract at 1000 mg/kg and 250 and 1000 mg/kg respectively. The time spent in target quadrant was significantly (p < 0.01) increased at doses of 250 and 500 mg/kg. Piracetam decreased escape latency, escape errors and increased time spent in target quadrant. Discrimination index in the novel object recognition test was significantly (p < 0.01) increased by piracetam and the extract at all doses tested. Piracetam and the extract at all doses significantly (p < 0.05) decreased the transfer latencies increased by diazepam (0.7 mg/kg) on day 1 and non-significantly on day 2 but failed to reverse the scopolamine (1 mg/kg) induced increase in transfer latencies except for piracetam. The extract did not increase number of square cross and rearing, while number of central square cross was significantly (p < 0.01) increased at all doses tested in the open field test. Piracetam increased the number of square, central square cross and rearing. There was significant (p < 0.01) increase in the number of head dip in the hole-board test by the extract which was not observed with piracetam. In the sub-chronic study, piracetam and the extract decreased the transfer latencies on day 1 and 2 in an elevated plus maze and increase discrimination index in the novel object recognition test. The level of malondialdehyde was significantly (p < 0.01) reduced. Piracetam and the extract at all doses tested significantly (p < 0.01) increased superoxide dismutase level. The level of reduced glutathione was non-significantly increased by the extract and piracetam. The activity of the enzyme acetylcholinesterase was not decreased by the extract and piracetam. The methanol stem extract of P. nigrescens possesses nootropic-like activity and antiamnesic effect which may possibly be mediated via inhibition of the GABAergic pathway and this study provides some scientific justification for the ethnomedicinal use of the plant as a memory enhancer.

CHAPTER ONE

1.0 INTRODUCTION

Nootropic is sometimes called cognitive, memory, intelligence enhancer or motivational and stress management agent capable of preserving the neurones and directly affecting the level of neurotransmitters (Babija et al., 2016). It is regarded to be any substance, drug or supplement with the ability of improving cognitive function, particularly executive functions, memory, creativity or motivation in healthy individuals (Lanni et al., 2008; Frati et al., 2015). The term nootropic is coined from the Greek words nous (mind) and trepein (to turn) (Giurgea, 1972; Gazzaniga and Michael, 2006). Nootropic is a class of psychotropic agents with selective facilitatory effect on integrative functions of the central nervous system especially on the intellectual performance, learning and memory (Chintawar et al., 2002).

The cognitive enhancing effect of nootropics has led many individuals to consider them as reliable supplements in the renovation of memory in order to improve their intellectual abilities. These drugs are purportedly used primarily to treat cognitive or motor function difficulties attributable to disorders such as Alzheimer’s disease (AD), Parkinson’s disease (PD), Huntington’s disease (HD), Attention Deficit Hyperactivity Disorder (ADHD). Among students, they are used to increase productivity despite lack of safety data about their long term usage (Babija et al., 2016).

Nootropics are used to reduce neurotoxins and alleviate cognitive deficits in the damaged brain. They work by increasing the supply of neurochemicals and oxygen to the brain or stimulate nerve growth. These drugs are able to protect the brain from disruptive conditions and enhance the efficacy of neuronal function. Dietary supplements, such as vitamins, Omega-3, iron, amino acids and other nutrients also have nootropic potential by frequently replenishing neurotransmitters and glucose in the brain (Malik et al., 2007; Joshi, 2013).

“Smart drugs” have also been seen as having nootropic potentials most especially from the mass media, since they are associated with increased intelligence, motivation and mental energy. However, unlike smart drugs which can often cause side effects with long-term use, nootropics are regarded to be safe, neuroprotective and pose a very low risk of side effects when they are used appropriately. Their action is not a matter of short term central stimulation such as psychostimulants but rather of a long term metabolic facilitation, manifesting itself especially when the nerve cell metabolism is disturbed by hypoxia, trauma, intoxication and so forth (Bruno and Nicolaus, 1982; Doru, 2011).

A number of medicinal plants have been used in traditional medicine practice as brain tonic or nootropic. One of such plants with long history of ethnomedicinal usage in India traditional medicine is Bacopa monniera which is used in the treatment of poor cognition and lack of concentration (Russo and Borrelli, 2005).

The traditional system of medicine is replete with medicinal plants claimed to promote learning, memory and intelligence. Several medicinal plants have been used for decades in different cultures to improve memory and ameliorate aging examples of which include: Lycium barbarum L (China), Corydalis spp (Denmark), Melissa officinalis (Iran) among many others (Yu et al., 2005; Adsersen et al., 2006). Plants like Glychyrryza glabra, Bacopa monniera, Azadiracta indica, Vitis vimifera, Albyzzia lebbeck, Ocimum sanctum, Phyllanthus amarus, Tinospora cordifolia and so forth have been investigated for their effect on cognition (Joshi and Parle, 2006a; Ladde et al., 2011). In Nigeria, one of such medicinal plants which is claimed to have memory enhancing and antiaging effect and used among the Yorubas of the South Western Nigeria is Parquetina nigrescens (Elufioye et al., 2012).

1.1 Statement of the Research Problem

Cognitive impairment is on the increase due to aging of the population most often accompanied with many neurodegenerative diseases like dementia, Alzheimer’s disease, Parkinson‟s disease and so forth. These neurodegenerative diseases impact negatively on the cognitive functions of individuals thus making it a relevant issue from the scientific and public health perspectives (Ferreira et al., 2006; Devi et al., 2011).

According to the World Health Organization (WHO), 5% of men and 6% of women 60 years and above suffer from dementia of Alzheimer‟s disease (AD) worldwide (Alzheimer‟s Facts and Figures, 2016). In Africa, dementia and the likes are usually considered as normal part of ageing (Rhiannon et al., 2012). It is one of the costliest chronic disease conditions with considerable financial, social and emotional burdens associated in caring for patients with the disease condition (Akhondzadeh and Noorozian, 2002).

There are few drugs known to improve cognitive functions. The most commonly used ones are not only stimulants like amphetamine, methylphenidate, caffeine and so forth but also have addictive potential of becoming a major public health problem (Fond et al, 2015). Most of the currently used drugs (donepezil, rivastigmine, galantamine e.t.c) in restoring normal cognitive function in patients with cognitive impairment only provide symptomatic relief and do not halt the progression of the disease. The side effects associated with their use have also made them of limited benefit (Deepika et al., 2010).

1.2 Justifications

Memory is important for human survival and personal identity. Diseases affecting cognitive functions will result to inability to recognise and respond appropriately to threats in the natural and social environment; perform basic motor skills and ultimately affect reasoning and decision making (Glannon, 2006).

Cognitive enhancers are in demand, whether in healthy populations or for those with cognitive deficit and current pharmacological enhancers offer only slightly modest benefits (Leslie et al., 2015). Enhancing memory with nootropics will benefit individuals and promotes effective processing of information in decision making thus creating a more informed population (Glannon, 2006).

Several drugs such as lecithin, 4-Aminopyridine, piracetam all of which stimulate the release of acetylcholine have been investigated and have shown unimpressive improvement in the treatment of cognitive disorders. The use of acetylcholinesterase inhibitors such as donepezil, rivastigmine and galantamine has been shown to improve cognition only in patients with mild to moderately severe cognitive deficit. Side effects such as agitation, confusion, anorexia, weight loss and so forth have made them of limited benefit (Shetty and Woodhouse, 1999).

The traditional system of medicine has used herbs, nutraceuticals for controlling age related neurodegenerative disorders (Joshi and Parle, 2006a). More than 70% of people in developing countries of Africa use medicinal plants for their health care needs because, the modern health care delivery is beyond the reach of people most especially those living in rural areas, making them to greatly rely on readily available medicinal plants in their neighbourhoods (Birhan et al., 2011).

Parquetina nigrescens is a common medicinal plant used as memory enhancer among the Yoruba people of South Western Nigeria (Elufioye et al., 2012). However there is no data in the literature on its nootropic activity.

1.3 Aim and Objectives

1.3.1 Aim

To evaluate the nootropic activity of the methanol stem extract of P. nigrescens.

1.3.2 Objectives

i. To determine the phytochemical constituents of the methanol stem extract of P. nigrescens.

ii. To estimate the oral median lethal dose (LD50) of the methanol stem extract of P. nigrescens.

iii. To investigate the learning and memory enhancing effect of methanol stem extract of P. nigrescens.

iv. To assess the effect of methanol stem extract of P. nigrescens on exploratory behaviour.

v. To investigate the acute anti-amnesic effect of the methanol stem extract of P. nigrescens.

vi. To investigate the effect of the methanol stem extract of P. nigrescens on some biochemical markers of cognition.

1.4 Research Hypothesis

Methanol stem extract of Parquetina nigrescens possesses nootropic activity and improved biochemical cognitive markers.