An untraditional look at essential oils and the nervous system: beyond olfaction.
Ask a random person walking down the street whether scents or odours can have an impact on behaviour and the answer will undoubtedly be yes. If the person had an interest in science they might even give you a concise explanation of the process. “When odour molecules are inhaled they pass up the nostrils until they arrive at a postage-stamp sized region known as the olfactory epithelium,” she might say. “Here the odor molecules are picked up my chemoreceptors, initiating action potentials, sending messages to the brain. Once recognized by the limbic system, this information is received, interpreted and possibly initiates a response,” she might conclude. (1)
This concept is not a new one. Aromachology, the scientific study of the effects of fragrances and scents on the mind and behavior, has received significant attention from such bodies as the Sense of Smell Institute. (2) Aromatherapy—the therapeutic use of essential oils—is often mistakenly reduced to or equated with the concept of “smell things feel better”. Yet despite this common misconception, the therapeutic use of essential oils on the nervous system is ever growing.
In the United States, natural health clinics and health resorts are increasingly incorporating the use of these steam distilled plant products as part of their offerings. In England, the National Health Service (NHS) not only allows users access to this form of treatment, General Practitioners have been known to refer patients to clinical aromatherapists—practitioners who are clinically trained in the use of essential oils. Thus, aromatherapy is no longer considered merely a potentially pleasing treatment for those with chronic conditions; an awareness of the use of these concentrated oils as powerful healing agents that can be applied to the body in a variety of ways is reflected in the NHS’s incorporation of aromatherapy as part of their primary care improvement plan. (3) In France, the use of essential oils is regarded even more rigorously as a medical discipline. The origin of the modern field of aromatherapy, France represents one of the few countries where combinations of essential oils are used as part of standard, rather than alternative, practice. (4) Physicians who specialize in the art of phytotherapy (plant-based medicine) regularly prescribe specific concentrations of oils internally for patients, particularly in anti-infectious and nervous system disorders. They rely heavily on their knowledge of the various chemical constituents that make up each essential oil associated with each plant (i.e. alpha-eudesmol, linalool, and thujone) and a series of tests performed at specialized high technology labs designed to test essential oils for purity, French doctors who use essential oils treat these items with the same. (5)
As an aromatherapist myself—albeit an American trained one— I am forced to ask, how are we to understand the effect of essential oils on the nervous system? In what ways do essential oils impact the nervous system in ways unrelated to olfaction? For example, how does the absorption of volatile essential oil constituents into the skin during massage effect the nervous system? What happens when essential that are ingested orally (either in capsule form or directed on the tongue) under the instruction of a French physician? In short, how can we formulate and restructure our knowledge of aromatherapy as a potential treatment for nervous system disorders?
Before jumping in to how essential oils and their constituents work on a molecular level, it is useful to review the general characteristics of essential oils. Essential oils consist primarily of chemicals composed of branched five carbon chains. These chains can be arranged seemingly in a myriad of ways to form larger and more complex molecular structures, through the three-dimensional arrangement and orientation of side chains. Hundreds of different constituents may be present in any given oil. These constituents work synergistically and contribute to the potential uses of an oil.
How do essential oils enter the body? These volatile oils readily diffuse through protective skin layers because of their small size and lipophilic (fat-loving) nature. They may also penetrate hair follicles on the surface of the skin. Once essential oils penetrate the dermis they may bind with a number of lipids in the blood such as albumin or globulin lipoproteins. Essential oils may also enter the bloodstream via absorption through the respiratory system. Absorption by this means is more likely to occur with smaller and lighter essential oils constituents which adhere to the lipophilic surface of the lungs. Once they are in the bloodstream, essential oils tend to accumulate in the tissues and on lipids in the body, rather than in components of blood which are hydrophilic in nature. Although they share many of the same building blocks, the precise arrangement of different constituent groups facilitates their interaction with enzymes and cellular receptor proteins. Because they are small and lipophilic, essential oils will also easily diffuse across cell membranes which are composed of a phospholipids bilayer. (5) (6)
But what are the exact mechanisms by which essential oils effect the body? Different chemical constituents react differently, but the chemicals constituents within oils that have pharmacodynamic effects on the nervous system fall into three main categories of action: those that interfere with enzyme function, those that interfere with ion channel function, and those that change the nature of receptor interactions.(6)
Lavender (lavandula angustifolia) essential oil is one of the most commonly used essential oils. It plays as significant role in the essential oil pharmacopoeia as Tylenol does in the field of standard pharmaceutical drugs. Lauded for its sedative, topical anaesthetic, and antidepressant characteristics, it is an example to use starting point to consider these questions. Although the oil contains a variety of chemical constituents such as linalyl acetate (40%), linalool (31.5%) and Z-beta-ocimene (6.7%), linalool probably plays a key role in the oil’s effect on the central nervous system. (5) (6) (7)
Constituents with enzyme function may inhibit acetylcholinesterase—an enzyme that breaksdown the neurotransmitter acetylcholine at the synaptic cleft in order for nerve impulses to be sent through the synaptic gap. (6) Linalool slows and inhibits the release of acetylcholine, reducing the length of time that the channels are open in the neuromuscular junction. (8) In other words linalool reduces the efficacy of the nerve impulse in acetycholine release action. This response may contribute to its sedative and calming effects. But linalool’s nervine effects are not limited to its inhibition of acetylcholinesterase. An article in the Journal of Neural Transmission demonstrates that linalool suppresses calcium ion channels, resulting in the suppression of voltage-gated channels. (9) In short, linalool prevents some calcium from entering or leaving the neuron. Since calcium is required for the transmission of action potentials across the synapse, linalool action here would also contribute to the oils sedative effects.
Lavender’s antinociceptive (pain relieving ability) has been connected to the fact that its constituents act as anatagonist to N-Methyl--aspartate (NMDA) receptors.(10) NMDA receptors play a role in opening ion channels to nonselective cations. (11) Thus they play a key role in the flow of both sodium and potassium ions. By preventing ions to flow freely into the cell the development the ideal charge distribution across the membrane cannot be maintained. Thus the neuron will not be able to consistently transmit action potentials to the post-synaptic cells. (12) When we consider that lavender essential oil has over three mechanisms by which it may contribute induce sedative feelings and antidepressive feelings, recognize the possible uses of essential oils as an effective pharmacological tool.
The previous smattering examples of nervine effects produced by essential oils, demonstrate the flexibility in the modes of action available to essential oils. We can now envision how essential oils that have penetrated the skin will interact with the body’s nervous system. Although I have primarily emphasized the nervine activity of linalool, it has served to highlight how the therapeutic use of essential oils for nervine function is inherently complex. When one considers that lavender essential oil is composed of over six essential oils present in proportions of over 1% in the oil and more than three further constituents in quantities of less than 1% we can begin to imagine how these oils may impact the body. (5)
Essential oils which enter the bloodstream can work in a number of different ways. They are not limited by the input information of sensory neurons. Indeed, essential oils are multi-faceted; they interact easily with the body’s different sites and help to trigger different processes. Our body’s own transmitter and receptor molecules both inside and on the surface of our cells appear to speak the same language of communication of receipt and transmission. The ability of essential oils to generate multiple effects is, in my opinion, an advantage. If we recognize that the nervous system is a multiple pattern generator/recognition system, then we should approach potential treatments in the same light. Essentials oils, with their synergistic and complex multidimensional nature, offer greater potential for effective treatment underscored by a wider range of administrative flexibility.
(1) http://serendip.brynmawr.edu/bb/neuro/neuro99/web2/Smith.html; Biology 202 home page, on the Serendip web site
(2) http://www.senseofsmell.org/; Sense of Smell Institute webpage.
(3) http://www.nhsdirectory.org/default.aspx; National Health Service website.
(4) http://www.bioexcel.com/sciarticles.htm ; Bioexcel website homepage.
(5) Price, Shirley and Len Price. Aromatherapy for Healthcare Professionals. 2nd Edition. London: Churchstone Living 1999
(6) Bowles, Joy. The Chemistry of Aromatherapeutic Oils. 3rd edition. Crows Nest: Allen and Unwin.
(7) Schnaubelt, Kurt. Medical Aromatherapy: Healing with Essential Oils. Berkeley: Frog Limited 1998
(8)http://www.sciencedirect.com/science?_ob=ArticleURL&_udi=B6T0N-49560RN-2&_user=10&_coverDate=06%2F30%2F2003&_rdoc=1&_fmt=&_orig=search&_sort=d&view=c&_acct=C000050221&_version=1&_urlVersion=0&_userid=10&md5=842cff1e080ef4d3c76a44b21c7b547d; Review article excerpt on Science Direct. “Salvia for dementia therapy: review of pharmacological activity and pilot tolerability clinical trial”
(9) Narusuye, K., F. Kawai, et al. (2005). "Linalool suppresses voltage-gated currents in sensory neurons and cerebellar Purkinje cells." Journal of Neural Transmission 112(2): 193-203.
(10) Peana, A., M. Graziella De Montis, et al (2004) “Effects of (-)-linalool in the acute hyperalgesia induced by carrageenan, -glutamate and prostaglandin E2”. European Journal of Pharmacology. 497(3):279-284
(11) http://en.wikipedia.org/wiki/NMDA_Receptor_Antagonist; Wikipedia entry “NMDA Receptor Antagonist”.
(12) http://en.wikipedia.org/wiki/NMDA_Receptor; Wikipedia entry “NMDA Receptor”.