Review articlePlants and the central nervous system
Introduction
Mind-altering drugs, especially plants, have always fascinated human beings. Surrounded by mystic superstitions, magic thoughts and religious rituals, they have always occupied man's attention. Among the plants used by humans, those able to alter the conscience and the sensorium have drawn special consideration. In fact, due to their astonishing effects, the psychodysleptic drugs (according to the Delay and Deniker, 1961, nomenclature), also called hallucinogenic drugs, have occupied much of the researchers' time, directed most of their thoughts and efforts towards attempts to understand their mechanism of action, and, hence, to understand human behavior, thoughts, humor, sensations, etc.
However, the challenge of trying to unravel the mechanisms of action on mood, humor, cognition, sensorium, etc., led to an inconvenience: to ignore, or to face as low priority, the fact that plants could also have beneficial properties to treat mental disease and some psychic ailments. Furthermore, as most of the plants were first used by the so-called primitive cultures, their occasional use by the White occidental culture was relegated to a second plan, being considered as sorcerer's therapeutics. In this respect, it is pertinent to quote a sentence from the first description in 1651 of a Mexican hallucinogenic plant (ololiuqui): “A thousand visions and satanic hallucinations appeared to them” (Hofmann, 1982).
A perverse result of such posture was a neglect of and probably more, a disdain, for all kinds of therapeutics based on plants.
Thus, until recently, very little attention was given by the scientific community to the benefits, as accepted by folk medicine, of the therapeutic usefulness of plants endowed with psycholeptic and psychoanaleptic (Delay and Deniker, 1961) properties.
Fortunately, this bad tide has recently turned due to several reasons, among them the wrong belief that plants, by originating directly from nature, must be less toxic than synthetic drugs. Another important aspect for this turning point was the realization by the pharmaceutical industry that plants, after all, could be a good business as more and more people were prone to look for this unconventional form of therapy. For example, Eisenberg et al. (1993) found that among American citizens, between 20% and 28% used alternative treatments for central nervous system (CNS) symptoms such as insomnia, headache, anxiety and depression; 3% of those patients had used herbal medicines.
If one wants to go down to the bottom of the problem, it is worth mentioning the fascinating study by Dossaji et al. (1989). They describe the unusual feeding behavior in wild chimpanzees consuming leaves of plants of the Aspilia, Lippia, Hibiscus and Rubia genera; these are plants used by humans for medicinal purposes. Female chimpanzees used to swallow Aspilia leaves more often than males (Dossaji et al., 1989).
In the same line of reasoning, the words of Schultes (1990) also apply here:
People whom we have to consider members of less-advanced societies have consistently looked to the Plant Kingdom … for the betterment of life.
Should we as chemists, pharmacologists and botanists—with so many and varied means at our disposal—not take a lesson from them?
This review article deals with plants possessing psychoanaleptic, psycholeptic or psychodysleptic effects on the CNS. However, because of the huge amount of plants belonging to these categories, we decided to select a few plants and to focus our attention on them, mostly concerning their clinical use. Furthermore, plants that had been thoroughly studied in the past and were the object of many published articles, as in the cases of, for example, Papaver somniferum L., Coffea arabica L., Cannabis sativa L., Theobroma cacao L., Erythroxylum coca Lam., Thea spp., Rauwolfia serpentina Benth. et Kurz., Hypericum perforatum L., Panax ginseng C.A. Mey., Piper methysticum, Ginkgo biloba L., to mention just a few ones, will not be approached.
In order to attain this goal, we have searched articles published since 1995 in Planta Medica (George Thieme Verlag), Phytotherapy Research (Wiley), Fitoterapia (Elsevier), Journal of Ethnopharmacology (Elsevier) and Phytomedicine (Gustav Fischer), and scattered studies in other journals and books.
For further discussion on the therapeutic use of medicinal herbs, see Craig (1997), Wong et al. (1998), Nwosu (1999), Briskin (2000), Elvin-Lewis (2001) and Phillipson (2001).
Section snippets
Psychoanaleptic (stimulant) plants with emphasis on anorectic or weight-reducing properties
Nature provides human beings with a myriad of plants possessing CNS stimulant properties. For example, in a recent book on medicinal plants from Brazil (Mors et al., 2000), 103 species are listed as having excitatory, analeptic, anti-exhaustion and aphrodisiac effects.
Many of the plants endowed with CNS stimulant effects, as a rule, synthesize substances containing the phenylethylamine or xanthine moieties, which are able to enhance catecholaminergic effects and/or to act on adenosine
Plants with psychodysleptic properties
Hallucinogens, psychotomimetics, psychometamorphics, entactogens psychotogens, psychedelics, psychodysleptics, etc., are all synonymous with the word phantastica used by L. Lewin in 1924. A brief description of the effects of these drugs follows:
- –
on cognition: interference with memory, attention, reasoning and orientation, all important cognitive functions;
- –
on sensorium: illusion, delusion, depersonalization, lack of contact with reality and sensorial alterations such as loss of sensitivity to
Analgesic plants
A recent global review article (Almeida et al., 2001) on plants endowed with analgesic activity disclosed 202 active species involving 79 families; the search encompassed the years 1965–1999, yielding a total of 263 scientific papers, 129 of them published in the 1990s. Interestingly enough, P. somniferum is not present in the list. From January 2000 to September 2002, 66 more studies on analgesic plants were published in Phytomedicine, Fitoterapia, Planta Medica, Journal of Ethnopharmacology
Conclusion
- 1.
Plants have been used by human beings since immemorial times to cure diseases and to promote relief from ailments. There were times when they were the most important sources of medicines for people. However, beginning in the late 1940s, this old form of therapeutics began to lose its importance, being more and more replaced by synthetic remedies. The lessons from millennia were forgotten and were considered “unscientific.”
- 2.
On the other hand, such ancient use of plants was a lead for scientists
References (180)
- et al.
The psychopharmacology of hallucinogens
Neuropsychopharmacology
(1996) - et al.
Plants with central analgesic activity
Phytomedicine
(2001) - et al.
Effect of valepotriates on the behavior of rats in the elevated plus-maze during diazepam withdrawal
Eur. J. Pharmacol.
(1994) - et al.
The use of benzodiazepines in anxiety and other disorders
Eur. Neuropsychopharmacol.
(1999) - et al.
Report on the NIH workshop on pharmacologic treatment of obesity
Am. J. Clin. Nutr.
(1994) - et al.
Ginseng pharmacology
Biochem. Pharmacol.
(1999) Medicinal use of ginseng and related plants in the Soviet Union: recent trends in the soviet literature
J. Ethnopharmacol.
(1982)- et al.
Association of road-traffic accidents with benzodiazepine use
Lancet
(1998) - et al.
Identification and quantitation of 1,2,3,4,-tetrahydro-β-carboline, 2-methyl-1,2,3,4,-tetrahydro-β-carboline, and 6-methoxy-1,2,3,4,-tetrahydro-β-carboline as in vivo constituents of rat brain and adrenal gland
Biochem. Pharmacol.
(1981) - et al.
Pharmacy and herbal medicine in the US
Soc. Sci. Med.
(1999)
Potential use of medicinal plants in the treatment of alcoholism
Fitoterapia
Recent findings of green tea extract AR25 (Exolise) and its activity for the treatment of obesity
Phytomedicine
Phytochemicals: guardians of our health
J. Am. Diet Assoc.
Eleutherococcus senticosus (Rupr. & Maxim.) Maxim. (Araliaceae) as an adaptogen: a closer look
J. Ethnopharmacol.
Some ethnopharmacological notes on African hallucinogens
J. Ethnopharmacol.
Differential interactions of dimethyltryptamine (DMT) with 5-HT1A and 5-HT2 receptors
Biochem. Pharmacol.
The scientific, quasi-scientific and popular literature on the use of St. John's wort in the treatment of depression
J. Affect. Disord.
Anti-anxiety studies on extracts of Passiflora incarnata Linneaus
J. Ethnopharmacol.
Adaptogenic and cardioprotective action of ashwagandha in rats and frogs
J. Ethnopharmacol.
Should we be concerned about herbal remedies
J. Ethnopharmacol.
Pharmacological activity of guaraná (Paullinia cupana Mart.) in laboratory animals
J. Ethnopharmacol.
Panax ginseng pharmacology: a nitric oxide link?
Biochem. Pharmacol.
(+) Amphetamine-stimulus generalization to an herbal ephedrine product
Pharmacol. Biochem. Behav.
Effects and aftereffects of ibogaine on morphine self-administration in rats
Eur. J. Pharmacol.
Effects of ibogaine on acute signs of morphine withdrawal in rats: independence from tremor
Neuropharmacology
Investigation of hallucinogenic and related β-carbolines
Drug Alcohol. Depend.
Kava pyrones exert effects on neuronal transmission and transmembraneous cation currents similar to established mood stabilizers—a review
Prog. Neuropsychopharmacol. Biol. Psychiatry
Schisandra chinensis (Turcz.) Baill
Fitoterapia
Sundry episodes in the history of coca and cocaine
J. Ethnopharmacol.
Antinociception induced by civamide, an orally active capsaicin analogue
Pain
Aqueous extract of valerian root (Valeriana officinalis L.) improves sleep quality in man
Pharmacol. Biochem. Behav.
Double blind study of a valerian preparation
Pharmacol. Biochem. Behav.
Daime—a ritual herbal potion
J. Ethnopharmacol.
Dependence studies of new compounds in the rhesus monkey, rat and mouse
NIDA Res. Monogr.
β-Carbolines, psychoactive compounds in the mammalian body. Part I
Med. Biol.
β-Carbolines, psychoactive compounds in the mammalian body. Part II
Med. Biol.
Khat: pharmacological and medical aspects and its social use in Yemen
Phytother. Res.
Characterization of the discriminative stimulus properties induced by 5-HT1 and 5-HT2 agonists in rats
Pharmacol. Toxicol.
Pharmacological and clinical studies of ephedrine and other thermogenic agonists
Obes. Res.
Benzodiazepine-like compounds and GABA in flower heads of Matricaria chamomilla
Phytother. Res.
St John's wort (Hypericum perforatum L.): a review of its chemistry, pharmacology and clinical properties
J. Pharm. Pharmacol.
Kava-kava and anxiety: growing knowledge about the efficacy and safety
Life Sci.
Use of nonprescription weight loss products: results from a multistate survey
JAMA
Kava safety questioned due to case reports of liver toxicity
HerbalGram
Hypericum perforatum
Fitoterapia
An herbal supplement containing Ma Huang–Guarana for weight loss: a randomized, double-blind trial
Int. J. Obes.
Obesity, fat intake, and chronic disease
Psychopharmacology
New substances of plant origin which increase nonspecific resistance
Annu. Rev. Pharmacol.
Medicinal plants and phytomedicines. Linking plant biochemistry and physiology to human health
Plant Physiol.
Naturally occurring antinociceptive substances from plants
Phytother. Res.
Cited by (293)
The impact of traditional kava (Piper methysticum) use on cognition: Implications for driver fitness
2022, Journal of EthnopharmacologyAnti-inflammatory activity of ayahuasca: therapeutical implications in neurological and psychiatric diseases
2021, Behavioural Brain ResearchNeuropharmacological potentials of β-carboline alkaloids for neuropsychiatric disorders
2021, European Journal of Pharmacology