Modification of brain waves and sleep parameters by Citrus reticulata Blanco. cv. Sai-Nam-Phueng essential oil

Abstract

Background: Citrus essential oil (EO) has been used for mood elevation and sedative hypnotic purposes. However, scientific proofs of its central nervous system (CNS) action remained largely unexplored. This study investigated chemotypes, electrical brain waves and sleep-wake effects of the essential oil from Citrus reticulata in rat model.

Methods: Chemical contents of citrus EO were analyzed using gas chromatography-mass spectrometry (GC-MS). Male Wistar rats implanted with electrodes on the frontal and parietal skulls were used for electroencephalographic (EEG) recording while inhaling the citrus EO (200 μl on cotton wool). Diazepam (10 mg/kg, p.o.) was used as a standard anxiolytic drug. EEG frequency analyses were performed by using Fast Fourier transform. All data were statistical analyzed using One-way ANOVA followed by Tukey's test.

Results: GC-MS analysis revealed d-limonene (95.7%) as a major constituent of citrus EO. The EEG results showed that overall EEG patterns of citrus EO effects were relatively similar to that of diazepam. However, significant differences between treatments were seen from sleep-wake analyses. Diazepam significantly increased episode numbers of awake and non-rapid eye movement (REM) sleep and reduced averaged episode duration. On the other hand, the citrus EO significantly decreased REM sleep latency and increased total time and episode numbers of REM sleep.

Conclusion: These findings demonstrated unique CNS effects of C. reticulata EO with EEG fingerprints and sleep-wake profiles. The data might be useful for citrus essential oil sub-classification and clinical application.

Keywords: Citrus reticulata; EEG; Essential oil; GC/MS; REM sleep; Sai-Nam-Phueng.

Graphical abstract

Fig. 1

Chemical composition of essential oil from C. reticulata Blanco. cv. Sai-Nam-Phueng peel (A). GC–MS chromatogram of C. reticulata cv. Sai-Nam-Pueung peel oil extracted by supercritical carbon dioxide method. (B) Essential oil from the peel of C. reticulata Blanco. cv. Sai-Nam-Pueung was analyzed by GC–MS. The major compositions were monoterpenes. d-Limonene was the main component of the essential oil.

Fig. 2

Effects of diazepam and citrus EO on frontal EEG powers of 6 discrete frequency ranges (n = 7–9). (A) Averaged percent baseline powers are expressed as means ± S.E.M. of spectral powers. (B) Powers of discrete frequency bands were divided for separately statistical analysis. ∗, ∗∗∗p < 0.05, 0.001, respectively, compared with control levels and ^#p < 0.05 compared with diazepam levels (one-way ANOVA followed by Tukey's post hoc test).

Fig. 3

Effects of diazepam and citrus EO on parietal EEG powers of 6 discrete frequency ranges (n = 7–9). (A) Averaged percent baseline powers are expressed as means ± S.E.M. of spectral powers. (B) Powers of discrete frequency bands were divided for separately statistical analysis. ∗p < 0.05, compared with control levels (one-way ANOVA followed by Tukey's post hoc test).

Fig. 4

Oscillations in the time domain of EEG powers in the frontal and parietal cortices. Percent baseline powers of 3 frequency ranges (0.8–7.0, 7.8–15.6 and 35.9–100 Hz) were analyzed every 1 min following administration with diazepam and citrus EO (n = 7–9).

Fig. 5

Raw EEG signals and spectrograms in the frontal and parietal cortices following oral administration of diazepam and inhalation of the citrus EO in comparison to that of control treatment (distilled water). Representative EEG tracings of each group were selected during awake (A), non-REM (B) and REM (C) sleep periods. Data were also converted into spectrograms to present electrical activity in frequency and time domains.

Fig. 6

Identification of awake (A), non-REM (B) and REM (C) periods. Multiple brain states were identified by using EEG spectral powers and spectrograms. Sleep-wake effects of administration with diazepam and citrus EO were determined in terms of sleep latency (D), number of episode (E), total time spent (F) and averaged episode duration (G) (n = 7–9). ∗, ∗∗p < 0.05, 0.01, 0.001, respectively, compared with control levels (one-way ANOVA followed by Tukey's post hoc test).