African traditional medicine, which is diverse because of the vast range of habitats, languages and cultural groups, has a long history of use, and in some countries up to 90% of the population relies on plants as the only source of medicines. Countries north of the Sahara have a similar ethnopharmacology because of an influence from Islamic cultures over many centuries. Sub-Saharan cultures are more diverse but do share some common features, such as the consideration of spiritual influences and beings in the disease and healing process. In sub-Saharan Africa, the influence of European culture came quite late and was diversifled because of the different colonial powers and the climate being generally not very amenable to growing some of the traditional European plants. Therefore, the endemic medical systems were arguably more preserved than in many parts of South America, where European domination occurred two or three centuries earlier. However, in the more remote parts of the continent, especially where there was also considerable biodiversity, extensive knowledge about the medicinal uses of the local plants remained, and consequently, several drugs have been included in European medicine over the years.
Jaborandi leaves are obtained from various species of Pilocarpus (Rutaceae), found in South America, but members of this genus are also found in the West Indies and Central America, although to a lesser extent. The leaves from species of Pilocarpus, including Pilocarpus microphyllus Stapf, have been used traditionally in South America to induce sweating and urination, considered to eliminate toxins from the body. The leaves contain a number of imidazole alkaloids including pilocarpine, which has structural similarities to acetylcholine and is a muscarinic receptor agonist.
Chewing the leaves of Jaborandi therefore produces cholinergic effects such as contraction of the pupils and excessive salivation. It is for this action that salts of pilocarpine have been used as topical treatments to reduce the raised intra-ocular pressure that occurs in glaucoma. Since modulation of the cholinergic system is considered to be involved in learning and memory processes, muscarinic receptor modulators could be used clinically to achieve cognitive improvements. Pilocarpine has been shown to enhance cognitive performance in rodents, although studies to investigate cognitive effects in humans are lacking, probably due to its poor pharmacokinetic profile as it poorly penetrates the blood-brain barrier, in addition to having undesirable side-effects, such as nausea and vomiting, sweating and bradycardia. Although, it has been suggested that co-administration of a compound that blocks peripheral muscarinic receptors with pilocarpine, or with other muscarinic receptor agonists, may reduce the potential for adverse effects. It should also be noted that CNS symptoms may be induced or exacerbated with the use of pilocarpine eye drops in patients with Alzheimer’s disease.
Ptychopetalum olacoides Benth.
Ptychopetalum olacoides Benth. (Olacaceae) originates from the Amazon and the roots have been used as a traditional remedy for a variety of ailments of the CNS and stress, particularly age-related conditions. The roots are known commonly as ‘mara-puama’, ‘muirapuama’ or ‘miranta’ and are now internationally available in general health-food stores. An ethanol extract of the roots of this plant improved memory retrieval when administered to both young and ageing rodents. The mechanisms of action to explain these effects and the active compounds are unknown. Some studies show root extracts of P. olacoides to have antioxidant, acetylcholinesterase inhibitory and neuroprotective activities, effects that could explain the experimental and reputed effects on memory function. More studies are necessary to investigate further the underlying modes of action that the compounds from the roots of this plant have on the CNS and any clinical relevance this remedy may have in cognitive disorders.