Neurodegenerative disease is a term applied to a variety of conditions which result from a chronic breakdown and deterioration of neurons, particularly, those of central nervous system (CNS) (Adewusi et al., 2010). Alzheimer's disease (AD), Parkison's disease, multiple sclerosis, amyotrophic lateral sclerosis and spongiform encephalopathy are some of the examples of neurodegenerative diseases (Chiba et al., 2007). AD is the most common of all neurodegenerative diseases (Citron, 2004; Tedeschi et al., 2008). These diseases are commonly found in elderly people. They are a major cause of morbidity, mortality and impose severe strains on the social welfare systems, and as a result are gaining increased recognition by the World Health Organisation (WHO) (Houghton and Howes, 2005).

Neurodegenerative diseases are characterized by a gradual onset of progressive symptoms including loss of memory and tremor, difficulty in learning or retaining information, inability to handle complex tasks, impaired spatial orientation and abilities, language deficits and behavioural changes (Adewusi et al., 2010). These symptoms have been recognized as a feature of increasing age for a long time and are acknowledged in many traditional medical systems. However, it is only recently that they have been recognized and received attention from mainstream medicine as distinctive diseases (Houghton and Howes, 2005).

The drugs currently available in the market for the treatment of various learning and memory disorders are associated with several side effects indicating need of substitute medication from alternative system of medicine (Pattewar et al., 2011). Plant materials have been a major source of natural therapeutic remedies and are used to treat various infectious diseases in many developing countries (Beverly and Sudarsanam, 2011; Dike et al., 2012). Medicinal plants have demonstrated their contribution to the treatment of diseases, such as HIV/AIDS, malaria, diabetes, sickle-cell anaemia, mental disorders (Elujoba et al., 2005) and microbial infections (Okigbo et al., 2005). According to the World Health Organization (WHO, 2001), 80% of the world population use medicinal plants in the treatment of diseases and in African countries, this rate is much higher. It has been estimated that up to 90% of the population in developing countries rely on the use of medicinal plants to help meet their primary health care needs (WHO, 2002). The use of traditional medicine is not restricted to the developing countries (Jimoh, 2006). According to Dike et al. (2012), a vast majority of prescription drugs used in the world contain compounds that are directly or indirectly, via semi-synthesis, derived from plants. A variety of plants has been reported to show AChE inhibitory activity and so may be relevant to the treatment of neurodegenerative disorders, such as AD (Mukherjee et al., 2007). Cyril–Olutayo et al. (2012) reported that in traditional practices of medicine, numerous plants have been used to treat cognitive disorders, including neurodegenerative diseases, such as AD and other memory related disorders. According to different cultural traditions, the use of complementary medicines such as plant extracts in dementia therapy varies (Cyril–Olutayo et al., 2012).

Celastrus paniculata Willd. seeds and oil have been used in Ayurvedic medicine for stimulating intellect and sharpening memory (Lekha et al., 2010). The roots of the Indian medicinal plant Clitoria ternatea L. have been reported to promote intellect (Taranalli and Cheeramkuzhy, 2003). Aqueous and ethanol extracts of several plants including Malvia parviflora L., Albizia adianthifolia  (Schumach.)  W.F.  Wight, Albizia suluensis Gerstner and Crinum moorei Hook. F. have been used in southern Africa to treat memory loss (Risa et al., 2004; Stafford et al., 2008). Ginkgo biloba L. has been used widely for the improvement of memory loss associated with abnormalities in blood circulation (Samuelsson, 2004). Galanthus species have been used traditionally in Bulgaria and Turkey for neurodegenerative conditions (Mukherjee et al., 2007).  Galanthamine is an Amaryllidaceae alkaloid first isolated in the 1950s from Galanthus nivalis L. (Shu, 1998). It also occurs in other genera of the Amaryllidaceae family, Narcissus and Lycoris species.

Nigeria as one of the most important countries in West Africa is richly blessed with great diversity of medicinal plants. However, some of these plants are becoming threatened and endangered (Sonibare and Abegunde, 2012). Hence, there is the need to document and research into various medicinal plants used in treating diseases in different parts of Nigeria. Ethnobotanical surveys of other diseases in the Southwestern part of Nigeria similar to the one presented in this work have been carried out by some researchers (Erinoso and Aworinde, 2012; Sonibare et al., 2009; Soladoye et al., 2010). The Yoruba traditional system of medicine also offers a number of safe treatments for CNS related disorders. Cyril–Olutayo et al. (2012) reported some of the plants used as memory enhancer and anti ageing in Ondo State, Nigeria. Elufioye et al. (2012) also reported some plants used for memory enhancement and antiaging in Sagamu, Nigeria. Some of these plants include Bryophyllum pinnatum (Lam) Kurz., Dioscorea mangenotiana Meige., Ficus exasperata Vahl., Jatropha curcas L., Carica papaya L., cola acuminata (P. Beav) Schott and End. These plant species can be used for the development of drugs for managing AD. This work was undertaken to document indigenous knowledge on the use of medicinal plants in the treatment of neurodegenerative disorders by the people of three local government areas (LGA) of Oyo state in South Western part of Nigeria with a view to promoting further studies on the biological activity of the plants.

Study area

The study area Oluyole LGA comprises 5 locations, namely Adebayo, Idi-Ayunre, CRIN (Cocoa Research Institute), Alaho and Ibusogboro. Ibadan South-East LGA comprises of Molete, Bode Market, Idi Arere, Challenge, Orita and Eyini. Akinyele LGA comprises Orogun, Ajibode, Ojoo, Idi-Ose, Moniya, Onidundu, Iroko and Ijaye. The three LGA are part of the 11 LGAs of Ibadan, Oyo State with latitude 7°22′N and longitude 3°55′E. The climate in the region is tropical with two distinct seasons:  dry and wet. The dry season is usually between November and February. Rainfall occurs almost throughout the year with an average annual rainfall of 250 cm. The indigenes encountered in this region are Yorubas and they are farmers by occupation, some of them are traders. The areas still

have many villages without access to modern health care and thereby wholly relying on traditionalists and TMPs for solutions to

their health challenges.

Data collection

The survey was carried out between June, 2012 and February, 2013. People that were interviewed, include Traditional Medicine Practitioners (TMPs), herb sellers, herbalists and the elderly who possess knowledge of medicinal plant use. Their ages ranged between 28 and 70. Village heads were consulted and LGA secretariats were visited to get information on where and how the TMPs could be met. The village heads gave the description of the residents or the herbalists and the elderly who had knowledge about the medicinal uses of plants. The LGA secretariats were visited and information about the TMPs were obtained. They usually meet fortnightly for their association meeting. Focused group discussion method was used here. The association of TMPs at Oluyole local government of Ibadan comprises both male and female, five members were in attendance on the day of the interview. During the interview, questions were thrown to the whole house and one person responded to the questions at different times. In another local government; four people were in attendance. Special markets designated for the sales of herbs were also visited and the herb sellers who were all women were interviewed. The interview was briefly interrupted by customers who came to buy herbs. Informed consent was obtained orally from all participants before the commencement of the interview.

The use of semi-structured questionnaire and oral interview were adopted to obtain the relevant ethno medicinal data. The questionnaire was administered to the respondents. Some of the questions they responded to include the name and the part of the medicinal plant used to treat neurodegenerative disorders, the preparation of the recipe, etc. (Appendix 1). Field note was taken during the survey and some of the herbalists showed us some of the plants around their house.  In most cases, the vernacular names of the plants were given; text books and research journals were consulted to verify the botanical names. Furthermore, the use-mentions   index  (UMi)   was  calculated   for  all   plants  (Andrade-

cetto, 2009). The UMi was taken as the number of use mentioned for a particular plant divided by the total number of informants interviewed.

Collection and authentication of plants

Plant samples were collected from the TMPs and herb sellers and were identified and authenticated at Forest Herbariun Ibadan (FHI) and voucher specimen were deposited at the Department of Pharmacognosy Herbariun, University of Ibadan (DPHUI).

Demographic data

The population of the respondents is made up of TMPs (32%), herbalists (18%), herb sellers (29%) and the elderly (21%) out of which 19 are males and 9 are females. Most of them were between ages 28 and 70 years. All the respondents were Nigerians from the Yoruba ethnic group with 18% practicing Christianity, 18% practicing traditional religion and the rest Islamic religion (Table 1).

Plant information and their families

Data from the survey revealed that neurodegenerative disorders are not only common among the aged, TMPs claimed that the disease is now rampant among the youths due to poor diet, taking of hard drugs, smoking and stress. Different symptoms of neurodegenerative disorders are known by  different  local  names,  such  as, ‘iyerira’, ‘aagana’, ‘olodeori’ and many TMPs encountered in the course of the survey claimed to have treated some of them with some herbs especially when discovered at the early stage. The plants mentioned include J. curcas L., Talinum triangulare (Jacq.) Willd., A. adianthifolia (Schumach.) W.F. Wight, and Bacopa floribunda (R.Br.) Wettst. Many of these plants are obtained from the forest, while some of them are collected from the garden around the house. For the free interviews, each of the respondents especially the herb sellers (4) mentioned three plants which should be prepared as concoction; leaves of B. floribunda, Spondias mombin L. and Digitaria horizontalis Willd. The other herb sellers (4) mentioned root of Rauvolfia vormitoria Afzel. and fruits of Piper guineense Schum. and Thonn. apart from the ones mentioned earlier. Herb sellers usually grow some of the herbs and they also work hand in hand with the herbalist to source for some other species in the forest. The other respondents, herbalists (5) and elderly (6) mentioned other plant species as shown in Table 1.

A total of 22 plant species (Table 2) belonging to 19 families were identified. Table 2 shows the list of identified plant species, families, local names and plant parts used. The most prominent among these plant families are the Fabaceae and the Musaceae with two species each. Other plant families, include Apocynaceae, Portulaceae, Srophuliaceae, Poaceae, Olacaceae, Zingiberaceae, Papilionaceae, Arecaceae, Piperaceae and Euphorbiaceae with one species each. In all, the most frequently mentioned species are B. floribunda (0.357), mentioned 10 times, S. mombin (0.214) mentioned 6 times, Aframomum melegueta (0.179) mentioned 5 times, D. horizontalis (0.143) mentioned 4 times, and R. vormitoria (0.107) mentioned 3 times by the respondents. The species distribution according to the ethnobotanical survey with UMi is given in Table 4. Different plant parts are used, but the predominant parts used are the leaves. Some of the herbs are prepared in combination with other herbs. During the interactions with the respondents, many of them claimed that a mixture of certain plants (B. floribunda, S. mombin and D. horizontalis) would be efficacious. Many of these plant species have some other ethnomedicinal uses like Musa sapientum is often used for ulcer, Allium cepa is used for hypertension, A. melegueta is used for cough and malaria, S. mombin is used for dysentery and as a purgative, J. curcas is used for pain relief and R. vormitoria is used for stomach disorder and tooth ache.

Sources of plant, mode of treatment

From the survey, 36% of the respondents employed plant and animal parts in their therapies, while 21% use herbs only (be it in fresh or dry forms). About 43% claimed that the treatment is accompanied with divination or incantation (Table 3). Many  of  the  respondents  claimed that the treatment has no side effects and when there is, it is usually mild like vomiting, headache, nausea and sleeping for long hours. It is generally observed that administration of plant decoctions rarely elicit noticeable side effects compared with orthodox drugs, because they are considered as nature cure (Morris, 2002).

Half of the respondents confirmed regular supply of their plant remedies from the forest, others (29%) usually sourced for plants either from the home gardens or markets. The TMPs especially and the herbalists usually source for plants in the forest and many of them grow herbs around their houses. The herb sellers usually grow some of the herbs and they also work hand in hand with the herbalist to source for some other species in the forest. Only very few (18%) claimed that the plants are not always available. This development supports the clamour for biodiversity preservation through cultivation and afforestation programmes (Ogbole et al., 2010). Knowledge of herbal treatment was mainly acquired either by ancestral means or by training or both, while the duration of treatment ranged from 2 to 3 weeks, 3-5 to 5-12 weeks as reported by 21, 29 and 14% of the respondents, respectively. 80% of the respondents claimed the use of verbal instructions in administering herbal recipes to their patients. This is believed to enhance the understanding of the dosage and methods of application of the remedies. In orthodox practice, written label instructions usually accompany prescriptions dispensed in the pharmacies or bought from the community pharmacies.

Method of preparation

Herbal remedies can either be prepared from dry plants from markets or freshly collected samples around homes or home gardens. However, respondents affirmed that both forms of plant materials are efficient in herbal preparation except in some cases where freshly collected samples are preferred. The main method of preparation is decoction (boiling in water). Others are infusion and concoction. Preference was shown for decoction. The time required for boiling varied and is dependent on plant parts or nature of plant. In all cases the preparation is to be taken orally.

Enumeration of recipes

The dried leaves of B. floribunda, S.mombin and D. horizontalis are boiled with water and made into a decoction. A cup ful is to be taken three times daily. The dried leaves of B. floribunda, S. mombin and D. horizontalis are grinded together and mixed with pap and should be taken regularly. The leaves of T. triangulare and A. adianthifolia are mixed with snail and ash and then burnt. The residue is then mixed with pap and should be taken regularly. The bark of Olax subscorpioidea Oliv. is cut into pieces and mixed with the leaves of Alium cepa; the mixture is put in a bottle and then water is added. The infusion is to be taken regularly. The fruit of M. sapientum, the leaves of Elaeis guineensis, fruit of A. melegueta and fish was cooked with rain water and eaten as soup. The leaves of B. floribunda, fruit of A. melegueta and the leaves of Abrus precatorius L. were sun dried and ground together or burnt together. The powder is then taken with pap regularly. The root bark of R. vormitoria is scrapped and dried. It is then ground into powder and taken with pap, a table spoonful of the powdered root for half a cup of pap. The fruit of J. curcas is dried and ground into powder and taken with pap. The leaves of Bombax buonopozense P. Beauv. are burnt with snail and taken. The leaves of Angraecum eichlerianus Bory is cooked as soup with fish and eaten. The leaves of Rinorea dentata (P. Beauv.) O Ktze. is cooked with snail and eaten. Dried leaves of B. floribunda and S. mombin are ground together and taken with pap or mixed with honey. The root of R. vormitoria, fruits of P. guineense and the leaves of A. cepa are ground together and taken with pap. The leaves of Angraecum eichlerianusis dried and ground into powder. The powder is poured into a hoe and the person licks the powder from the hoe with his mouth. The leaves of E. guineense, M. sapientum, A. melegueta and the feather of a cock is burnt together and taken with palm  oil  in  the morning.

Neurodegenerative disorders primarily affect the elderly population but from this survey, many of the respondents claimed that it is also common among the youths due to poor eating habit, taking of alcohol, stress and smoking. They have different local names for the different symptoms of neurodegenerative disorders e.g ‘iyerira, ‘aagana, ‘olodeori and they claimed to have treated some of them with some herbs, especially when discovered at the early stage. Numerous herbal extracts, containing several active constituents and often more than one plant species, have been used to treat neurodegenerative disorders. Amongst these are the Salvia species (Salvia officinalis L. and Salvia lavandulaefolia Vahl., Salvia miltiorrhiza Bung.) (Howes et al., 2003; Perry et al., 2000a, b), Cymbopogon schoenanthus (L.) Spreng. (Khadri et al., 2010), Terminalia chebula Retz. (Sancheti et al., 2009).

The findings from this survey revealed some plant families with the highest occurrence of species which include Fabaceae, Musaceae and Piperaceae with two species. Other plant families include Apocynaceae, Portulaceae, Srophuliaceae, Poaceae, Anarcadiaceae, Phyllantaceae,    Orchidaceae,    Olacaceae,     Liliaceae, Zingiberaceae, Papilinionaceae, Arecaceae, Bombaceae, and Euphorbiaceae with one species each. This suggests that these families can be explored scientifically for AD drug development.  Results also revealed that quite a number of plant parts especially the leaves, roots, fruits, seeds and very rarely the whole plants have been found efficient in the treatment of the disease. The most prominent plant species in the recipes according to the UMi were B. floribunda (Scrophuliaceae), S. mombin (Anarcadiaceae), D. horizontalis (Poaceae), A. melegueta (Zingiberaceae), R. vormitoria (Apocynaceae), M. sapientum, A. cepa (Liliaceae), E. guineense showing that they possess potential anticholinesterase and neuroproctective actions. Investigations on the plant parts used and the mode of preparation and administration indicated that irrespective of the plant part(s) or combinations used, water was the main medium for all the medicinal preparations. In addition to pure herbal preparations, in some cases the drug was administered along with honey, hot pap or palm oil. These supplement ingredients may be used to enhance the effect of the herbal preparations or are simply used to make the preparations palatable. Many scientific researchers have reported the anticholinesterase activity of some of the plants or other species of the families identified in this study. Some of these are B. buonopozense (Bombacaceae), J. curcas (Euphorbiaceae), S. mombin (Anarcadiaceae), B. monniera (Scrophuliaceae) and A. adianthifolia (Fabaceae) (Elufioye et al., 2010; Adewusi et al., 2010).

The survey revealed that majority of the plant species used for the treatment of neurodegenerative disorders are sourced from the wild. Regardless of how medicinally important the plants are, only very few cultivate them. The assessment reveals that little or no conservation strategies are in place to safeguard these plants. Awoyemi et al. (2012) reported that although, medicinal plants are necessary in deciding a programme of action for primary health care, most of the practitioners have not imbibed conservation techniques as most of these genetic resources are for now largely undocumented and the indigenous knowledge of their relevance are steadily being lost due to unsustained harvesting of plants from the wild. Sonibare and Abegunde (2012) reported that there are many cases of unsustainable harvesting of various medicinal plants in different communities in Africa and other continents of the world. In order to have a considerable long term effect on the environment, health care and economy, the use of important medicinal plants in a way and at a rate that does not threaten or endanger the plants must be ensured (Wong et al., 2001). It is therefore imperative to encourage cultivation and proper documentation of these plants, some of which have become endangered so as to conserve them and prevent them from going into extinction.

The result of this survey showed that majority (80%) of the herb sellers/ TMPs/herbalists claimed  no  occurrence of side effects following patients' use of herbal preparations. However, some of the traditional healers said that patients may have some nausea feeling like vomiting after taking the recipe; some of them may sleep for a very long time.

With this information on the local uses of these medicinal plants, subsequent isolation of the biologically active compounds from the plants can be carried out. The isolation, identification and purification of the bioactive compounds will certainly form the basis for future drug discovery and design from these indigenous medicinal plants. Conservation of the traditional knowledge and these medicinal plants is greatly advocated for. In this context, more detailed studies about the anticholinesterase activity of the medicinal plants identified in this survey are currently being carried out in our research laboratory, and the biological activity of the most promising plants will be further investigated, evaluated and elucidated. 

This study revealed twenty two medicinal plants used to treat memory related disorders in three LGAs in Ibadan, South Western part of Nigeria. The documentation is ethnopharmacologically relevant in view of the scarcity of information on plants used to treat neurodegenerative disorders in the area, where traditional healers claimed to have been managing and curing associated diseases with appreciable success. The results of this study therefore provide the basis for further studies on the phyto-constituents and compounds responsible for the treatment of neurodegenerative disorders. The study plays an important role in documenting and conserving traditional knowledge of plants for future use.

The authors would like to extend our gratitude to traditional healers and all other informants who showed their willingness to share their knowledge on the use of medicinal plants in treating neurodegenerative disorders.

Authors have none to declare.