Post-traumatic stress disorder (PTSD) is an anxiety disorder often triggered by exposure to stressful, distressing, or frightening events, or the sudden and unexpected death of a loved one.
The person with the disorder tends to relive the traumatic experience through flashbacks and nightmares. The severe anxiety caused by PTSD may last months or even years, and it can have a significant impact on the person’s life.
Chronic stress is thought to play a role in activating and exacerbating inflammation in the peripheral immune system. Research has suggested that peripherally circulating immune cells may be able to cross the blood-brain barrier and cause inflammation in the central nervous system, which may contribute to mental health disorders, including PTSD. However, the link between fear memory and the immune system is not entirely understood.
Furthermore, treatment for PTSD is currently limited to two FDA-approved medications and psychotherapy practices, including cognitive and exposure therapies.
Cassandra Moshfegh, a research assistant in Paul Marvar’s laboratory at the George Washington University, and colleagues sought to investigate the effect of orange essential plant oil on PTSD symptoms. Previous studies have shown that orange essential oil may have a depressant-like effect on the central nervous system.
The team presented the research at the American Physiological Society’s annual meeting during the Experimental Biology 2017 conference, held in Chicago, IL.
Essential oils are naturally produced by plants and can be used for therapeutic purposes. The aromatic compounds of orange essential oil are usually extracted from the peel of the orange. Essential oils can be inhaled, applied to the skin, or ingested in foods or beverages.
Orange essential oil significantly reduced fear-associated behavior
Orange essential oil was tested in mice to determine the impact of the compound on fear memory and immune cell activation. The researchers used Pavlovian Fear Conditioning – a behavioral mouse model – “to study the formation, storage, and expression of fear memories as a model for PTSD.”
Pavlovian Fear Conditioning pairs a tone with a negative stimulus, such as a shock to the foot, which provokes fear as a response in the mice. The mice form an associative memory between the tone and the stimulus. When presented with the tone alone, the mice exhibit a fear response and typically freeze. This response diminishes slowly as time goes on.
Moshfegh and team divided the mice into three groups. The first group of 12 mice was exposed to the audio tone alone, 12 mice received water and fear conditioning, and the remaining 12 mice were exposed to orange essential oil by inhalation 40 minutes prior to and after the fear conditioning.
The researchers found that the mice exposed to orange essential oil were significantly less likely to exhibit freezing behavior and stopped freezing altogether earlier than the mice that received water and fear conditioning. Moreover, the mice exposed to orange essential oil experienced a significant decrease in the immune cells linked to the “biochemical pathways” associated with PTSD.
The mechanism behind the differences in behavior between the two groups could be explained by the variations found in gene expression in their brains.