Modification of sleep-waking and electroencephalogram induced by vetiver essential oil inhalation

INTRODUCTION

Essential oils (EOs) have been used for the mental improvement since ancient times. However, most of the initial researches have focused mainly on antimicrobial activity [1,2]. Therefore, various physiological effects of EOs have also been consistently confirmed [3,4]. There are many contemporary applications of EOs which are still controversial especially for mood enhancements. To validate these applications, scientific proof with objective assessments is needed. Most of the direct EO mechanisms in the central nervous system (CNS) have been obtained from animal studies. These included the effects of lavender oil inhalation on rat brain areas [5]. In addition, the effects of long-term lemon oil exposure on behavioral, hormonal, and neuronal parameters were demonstrated in rats [6]. In particular, the induction of dopamine release by green odor from rat striatal brain slices may suggest the underlying mechanisms of the EO that regulate reward, mood and attention [7]. Treatment with EO from Arachis hypogaea L. stem and leaf extract led to the increase in adenosine triphosphate levels in the brain of sleep-deprived rats [8]. This might explain central mechanism of sedative effects of the EO.

Recently, the application of EOs for therapeutic purposes has been progressively increasing. Significant improvement in sleep quality was confirmed in postpartum women [9]. Similar results in postpartum women were also seen for lavender fragrance EO [10]. Moreover, increased quality of sleep and reduced anxiety level were observed in patients with coronary artery disease who received lavender EO inhalation [11]. In nursing care for residents who suffered from dementia, anxiety and disturbed sleep patterns, beneficial effects of lavender EO were reported [12]. However, these findings were not well-accepted because aromatherapy has not been well evidence-based practice. Hence, further research with more scientific methodology is, in particular, needed in terms of efficacy confirmation of EO application.

Vetiveria zizanioides, an aromatic perennial grass, is widely grown in many tropical countries. Vetiver EO can be extracted using hydrodistillation of its roots. Vetiver EO exhibited an in vitro scavenging activity with β-vetivenene, β-vetivone, and α-vetivone as strong antioxidative constituents [13]. Until recently, vetiver EO was found to produce antioxidant activity against some oxidative stress effects [14].

However, effects of vetiver EO remained to be elucidated in terms of psychological and behavioral activities. The present study aimed to examine the effects of vetiver EO inhalation on sleep-waking and EEG patterns in rats. To mimic the realistic condition, extremely low amounts of vetiver EO were blown with controlled flow rate of ambient air for the inhalation. Following electrode implantation on the skull of rats, electroencephalography was used to record electrical brain wave of animals while receiving vetiver EO inhalation. For analysis, fast Fourier transform (FFT) was used to calculate EEG power to reflect the oscillatory rhythmicity of the brain as a function of frequency. In general, brain wave synchronization was expressed in power of either broad frequency spectrum or discrete frequency bands.

MATERIALS AND METHODS

RESULTS

DISCUSSION

Most of previous EO studies have confirmed the effects of EOs on the CNS by measuring behavioral, hormonal, cellular, and molecular parameters. These investigations used relatively indirect techniques that detected some physiological changes following EO administration. However, they revealed the potential of EOs in modifying CNS functions that regulate reward [18], mood [19-21], attention [22], and memory and learning [23]. In particular, there are only few studies that confirmed EO effects on the CNS by using electrical brain oscillations. Recently, the findings from our previous work clearly indicated the modification of electrical brain activity induced by orange (Citrus sp.) EO inhalation [24]. Increasing of slow wave oscillation (4-12 Hz) by orange EO suggested possible anxiolytic or sedative effects reported previously [24]. These data appeared to indicate that brain oscillations reflect spontaneous and direct activity of neural network circuits associated with behavioral status. Therefore, recording of EEG or electrocorticography might be the highly sensitive method to monitor effects of EOs on neural network activity.

In folklore medicine, V. zizanioides Linn or vetiver. has been used in the treatment of various illnesses including mental and emotional symptoms. In modern scientific studies, it was claimed to reduce oxidative stress according to its antioxidative [14,25] and scavenging [26] activities. The present study demonstrated the stimulating effects of vetiver EO inhalation with increased total awake period, gamma EEG power and decreased slow wave EEG power. Alterations of electrical brain wave by EOs have been reported in animal models. Previously, inhalation of citrus EO produced EEG patterns in both frontal and parietal cortices which might be associated with anxiolytic-like effect [24]. In addition, dose-dependent increase in the power of fast wave in the hippocampus and the cerebral cortex was also produced following intraperitoneal injection of bergamot EO [27]. Altogether, these findings collectively suggest that EOs are capable of modifying CNS functions. However, EOS are supposed to be applied through inhalation as the most common route for volatile substances. Therefore, it was an ideal purpose to examine the effects of inhaled vetiver EO on EEG pattern. As shown in the results, significant changes in EEG activity were seen following vetiver EO inhalation though the weight of the EO (in cotton wool) remained almost unchanged after the test. It means that the administration system ventilated extremely low amounts of the EO through recording chamber. This suggests that inhalation is probably the most effective route of EO administration. Previously, the inhalation has been consistently found to deliver EO to various organs including the brain and produce anxiolytic-like effect [28].

There are some advantages of EEG studies. With the use of FFT, it is possible to measure power in discrete frequency ranges of the EEG spectrum. Basically, slow frequency power increases during sleep, whereas fast frequency power is associated with wakefulness [29]. Mainly, overall brain wave activity can be overviewed in broad EEG power spectrum. Power alteration of some discrete frequency bands clearly reflects specific patterns of brain activity. In general, the decrease power in slow-wave activity and/or increase power in fast wave was positively correlated with increased alertness [30,31]. Moreover, EEG technique provides continuous data that reflect time course effect of EO treatment. In the present findings, refreshing action of vetiver EO was detected immediately after the inhalation started and persisted at least 1 h. This data would be beneficial for the odor management.

Most of previous reports of vetiver studies have focused on its anxiolytic or sedative effects proposed to be through GABAergic activities [32,33]. Moreover, it was also demonstrated to produce significant anticonvulsant activity in animal model [34]. In general, anticonvulsant drugs such as benzodiazepines and valproic acid are used against seizures both in patients and in animals by enhancing GABAergic synaptic transmission [35]. These findings might suggest sedative and hypnotic properties. However, the results from the present study indicated stimulating effect of vetiver EO. Apart from its anxiolytic or sedative property, the plant has also been tested for other CNS effects. In a study using mice model of amnesia induced by scopolamine, different extracts of vetiver significantly inhibited acetylcholinesterase activity and reversed the amnesia [36]. Consistently, the ethanolic extracts of this plant were found to enhance learning and memory possibly through cholinergic transmission in the brain [32]. Altogether, vetiver appeared to be capable of inducing learning process in the brain and exploratory behavior that would probably results in increasing alertness and fast frequency oscillation.

In terms of application, alertness is one of the basic factors that would enhance physical and mental performances. Previously, treatment with EO from Acori graminei rhizome resulted in improvement of cognitive performances and increased levels of neurotransmitters especially monoamines that would enhance wakefulness [23]. The use of vetiver EO for refreshing might be an alternative choice in addition to the consumption of tea or coffee. In terminal task, human subjects who inhaled the volatile compounds of vetiver EO showed faster reaction times and stimulation of sympathetic nerve activity [37]. Its volatile compounds may help subjects to maintain performance in a visual discrimination task. Ultimately, the stimulating effects of vetiver EO might be beneficial for learning and memory processes. In conclusion, the present findings provide information that vetiver EO may be used as a stimulant to improve alertness and task performance.