Bergamot essential oil (BEO), Citrus aurantium subsp. bergamia (Risso) Wright & Arn. (Rutaceae), is used widely in aromatherapy to reduce stress and anxiety despite limited scientific evidence. A previous study showed that BEO significantly increased gamma-aminobutyric acid levels in rat hippocampus, suggesting potential anxiolytic properties. The aim of this study was to investigate the effect of BEO (1.0%, 2.5% and 5.0% w/w) administered to rats on both anxiety-related behaviours (the elevated plus-maze (EPM) and hole-board tests) and stress-induced levels of plasma corticosterone in comparison with the effects of diazepam. Inhalation of BEO (1% and 2.5%) and injection of diazepam (1 mg/kg, i.p.) significantly increased the percentage of open arm entries on the EPM. The percentage time spent in the open arms was also significantly enhanced following administration of either BEO (2.5% and 5%) or diazepam. Total arm entries were significantly increased with the highest dose (5%), suggesting an increase in locomotor activity. In the hole-board test, 2.5% BEO and diazepam significantly increased the number of head dips. 2.5% BEO and diazepam attenuated the corticosterone response to acute stress caused by exposure to the EPM. In conclusion, both BEO and diazepam exhibited anxiolytic-like behaviours and attenuated HPA axis activity by reducing the corticosterone response to stress.

Vetiver essential oil (VEO) has been used in aromatherapy for relaxation. This study aimed to investigate the effects of VEO on an anxiety-related behavioural model (the elevated plus-maze, EPM) and immediate-early gene c-fos in amygdala, known to be involved in anxiety. Male Wistar rats were administered diazepam (1 mg/kg i.p.) for 30 min or inhalated with VEO (1%, 2.5% or 5% w/w) for 7 min prior to exposure to the EPM. Then, the effects of 2.5% VEO, the anxiolytic dose, on c-fos expression in amygdala were investigated. The rats given either 2.5% VEO or diazepam exhibited an anxiolytic-like profile in the EPM. VEO and diazepam significantly increased c-fos expression in the lateral division of the central amygdaloid nucleus (CeL). Therefore, the anxiolytic properties of VEO might be associated with altering neuronal activation in CeL. However, future studies are needed to investigate the precise mechanism of action of VEO.

Salivary cortisol has been increasingly used as a stress biomarker since saliva sampling induces less additional stress than blood sampling. Enzyme-linked immunosorbent assay (ELISA) has been commonly used to measure salivary cortisol in stress related research. Recently, electrochemiluminescence (ECL), a routine immunoassay analyser, has been suggested to measure salivary cortisol. Therefore, the aims of this study are: (1) to compare salivary cortisol level measured by ELISA and ECL and (2) to determine the relationship between salivary cortisol and serum cortisol measured by ECL. Both salivary and serum samples were collected from 83 volunteers for cortisol measurement by ECL analysis. The salivary cortisol value was 3% of that of the serum cortisol. For ECL, the positive correlation between salivary and serum cortisol levels was significant (r = 0.84; p < 0.001). The measurement by two different methods did not show any significant difference (p = 0.5497). The correlation of salivary cortisol values measured by both techniques was significant (r = 0.81; p < 0.001). The result suggests that ECL seems to be more practical and cheaper for salivary cortisol measurement.

No abstract

Abstract:Objectives: The aim of this study was to investigate the effect of linalool in chronically stressed rats on their behaviour as related to depressive disorders and BDNF (brain-derived neurotropic factor) protein in the hippocampus. Methods: Either Tween 80 or linalool (50, 160, 500 mg/kg) was intraperitoneally administered to rats, daily, for two weeks. Some rats were housed in home cages but the others were induced with chronic restrained stress (15 min daily). At the end of the treatment, the rats were assessed for depressive-like behaviour using the forced swimming test. At the end of the behaviour test, the animals were immediately decapitated and the hippocampus of each animal was removed for the measurement of the BDNF protein by ELISA. Result: The immobility time was significantly increased (p < 0.05) but time of climbing was significantly decreased (p < 0.05). The restrained rats treated with linalool, 500 mg/kg, displayed immobility times less than those of their controls (p < 0.05) while these rats showed significantly more climbing than in the control rats (p < 0.05). Linalool showed no effect on the BDNF protein in the hippocampus. Conclusions: linalool decreases behaviour related to depressive disorders but it has no effect on the BDNF protein in chronic restrained stress.