Substances that have an anti-aggressive effect can be not only synthesized in laboratories but also found in various natural remedies. One category of such remedies is essential oils. Although they have traditionally been widely used to improve a person’s psychological state, the question of their effect on the nervous system is still insufficiently studied, especially when addressing the topic of aggressive behavior. However, existing research conducted on animals and even on humans indicates a great potential for studying this direction.
First, let us look at a study on the effect of a substance called linalool, which is present in a vast number of essential oils (bitter orange, neroli, petitgrain, rose, lavender, citronella, lemon, geranium, and others), on mice. It demonstrated that inhalation of this substance significantly reduces the number and duration of attacks on unfamiliar conspecifics, and at certain concentrations, almost completely eliminates them. At the same time, as shown in other experiments, such an effect cannot be explained by a general decrease in the activity of the mice, as this does not occur during the inhalation of linalool.
Another study was conducted on fighting fish, or Siamese fighting fish, whose males are known for their extremely aggressive behavior toward conspecifics, which is why they must be kept strictly alone. In the experiment, either lavender essential oil or pure linalool was used, which were added in various concentrations to a container of water. The test subject was placed in this container and given two minutes to acclimate, after which a container with another individual was placed next to it to allow visual contact. As a result, while individuals in the control group (without drugs) attempted to actively attack both during and after acclimation, individuals under the influence of both lavender essential oil and pure linalool showed almost no such behavior—their desire to attack disappeared. Moreover, although the aggressiveness of the individuals was restored over time, it did not return to the pre-test level even three months after the trial with the essential oil. Accordingly, we can conclude a limited permanent anti-aggressive effect from lavender oil.
But is all this applicable to humans? There are strong reasons to believe so, as many experiments have been conducted on the anti-aggressive effect of essential oils on people with cognitive impairments. A meta-analysis of 15 studies with 693 participants showed that although further research is needed to determine effective dosages and side effects, overall, the use of essential oils in therapeutic procedures has a significant anti-aggressive effect.
Although the mechanism of such an effect of essential oils is not yet sufficiently studied, it is known that their molecules can enter the hippocampus, the limbic system, and the amygdala of the brain through the nasal cavity and olfactory cells. It is worth noting that linalool and other substances from essential oils work as 5-HT1A receptor agonists (activating them), and such an effect is known for its selective anti-aggressive effect (eliminating attacking aggression without affecting defensive behavior and other activity), which is achieved through the strengthening of the violence inhibition mechanism. In addition, upon entering the blood, for example, through the skin, essential oils can affect various physiological reactions. Finally, by exerting a certain influence on the function of cholinergic synapses, they can prevent neurodegenerative processes.
The primary activity of the “Voluntarist” project is the study of the nature of violent behavior, in which we have succeeded thanks to the violence inhibition mechanism theory. Violence is primarily a pathology, a malfunction of internal neurophysiological mechanisms, causing a person to stop experiencing sufficient repulsion and resistance to causing harm to other people. Additionally, a series of animal experiments demonstrates the possibility of treating such a disorder; some agents are capable of eliminating attacking aggression in intraspecific clashes without affecting defensive aggression and other forms of behavior, i.e., acting selectively. Some of these agents are of natural origin, primarily belonging to Asian medicine.
Given the accessibility of agents in this category, distributed as medicinal herbs or bioactive supplements, organizing experiments to test them is not an overly difficult task and proved manageable even for a small team associated with our project. For now, the experiments are ongoing, and the final protocol and conclusions are still far off; however, some intermediate results have already demonstrated success that cannot go unshared.
1. Experimental Setup
The experiment consists of combining the resident-intruder paradigm and social isolation in rats. The development of territoriality (for example, in their own cage) and the absence of social contacts provoke attacking aggression in them when encountering a conspecific, especially if the latter has a lower weight. First, a series of control experiments is conducted, after which the agents can be tested. Due to the small number of available subjects (5 residents and 5 intruders), they are used repeatedly; however, experiments are conducted no more often than once every 3 days, and every other time a control experiment is performed to measure the aggressiveness of the resident subjects to ensure its presence and that any subsequent decrease observed will be due to the application of the agent rather than external factors.
2. Kamishoyosan and Si Ni San
Several already tested agents demonstrated a significant influence on rat behavior, but the reduction in aggressiveness either did not occur, was insufficient, or was non-selective. However, among them, one agent proved extremely effective. This is Kamishoyosan (and in our case, the Chinese analog Jia Wei Xiao Yao Wan produced by Min Shan) — a popular agent in Asian medicine that is potentially, based on pharmacological data, capable of activating the violence inhibition mechanism.
Relying on the fact that a scientific publication on this agent demonstrated only a partial effect in the case of a single oral application at a dosage of 400 mg/kg, we decided to test dosages of 500 mg/kg and 1 g/kg. Furthermore, the second dosage was applied to an extremely aggressive subject that always actively attacked a conspecific introduced into its cage. However, the original study did not measure aggressiveness specifically in intraspecific clashes, and according to another study, a dosage of 200 mg/kg is the best for maximizing social activity in mice during contact with conspecifics, so we decided to test that as well.
As expected, the effect of Kamishoyosan was neither sedative nor stimulating; it proved to be specifically anti-aggressive. Aggressive attacks were eliminated in all three experiments, and even if they appeared occasionally, it was exclusively in non-intense forms. At the same time, while dosages of 500 mg/kg and 1 g/kg did not disrupt the social and non-social activity of the rats, the reduction in their aggressiveness occurred through an increase in inactivity. On the other hand, the 200 mg/kg dosage replaced aggressive behavior specifically with non-aggressive social activity.
However, the question of the specific mechanism of Kamishoyosan’s action remained open. It was necessary to determine which specific component and bioactive substance from this mixture of herbal extracts produces this effect, so we decided to test the agent Si Ni San, which contains only three components from Kamishoyosan and was expected to produce the same effect. A dosage of 500 mg/kg was tested, and the result was confirmed — a previously highly aggressive subject, which had performed active attacks on the intruder subject, including during the control experiment before the application of the agent, ceased the attacks. At the same time, its non-social activity was not significantly reduced, and its social non-aggressive activity actually increased, although inactivity also increased, but not at the expense of these forms of activity (only at the expense of attacks). This means that the effect was specifically anti-aggressive, not sedative.
Detailed study of materials on mixtures similar to Si Ni San suggests to us that the main bioactive substance in them, including Kamishoyosan, may be paeoniflorin from the extract of Paeonia lactiflora (white peony) — one of the components of these mixtures. Research indicates that this substance both activates serotonin 5-HT/1A receptors and affects the expression of TPH2 and SERT genes associated with the functioning of serotonin and the violence inhibitor. Also, in general, substances from this extract further influence the expression of the MAO-A gene, which is also extremely important in the matter of aggressive behavior. Based on all this, we obtain the most promising candidate for a component from the previously mentioned mixtures that activates the violence inhibition mechanism.
3. Inhalation Experiments
In addition to oral application, in the case of some agents, inhalation (breathing in a drug with bioactive substances) can also be used. Especially considering the overall possibility of creating an effective agent of this kind; for example, the recently approved inhalation drug Zavzpret (or Zavegepant) proved so effective in the therapy of chronic migraine that in some patients it works in as little as 15 minutes and for 48 hours after application.
To date, we have managed to test three such agents containing the substances d-limonene and linalool, which act as agonists of serotonin 5-HT/1A receptors. All of them are essential oils from different parts of the bitter orange (Citrus aurantium). We used fruit peel oil, which consists almost entirely of d-limonene; flower oil (neroli), which roughly contains 34% linalool and 10% d-limonene; and twig and leaf oil (petitgrain), containing up to 40% linalool.
Inhalation was carried out as follows — for 10 minutes, a mixture of essential oil, an equal amount of emulsifier (oil solvent), and water if necessary, was evaporated in an isolated chamber (60 L). Then, a rat was placed in the chamber and remained there for another 10 minutes while the evaporation of the mixture into the chamber continued. 2 ml of bitter orange peel oil, 4.5 ml of neroli oil, and 5 ml of petitgrain oil were used in a mixture with a volume of 10 ml (sufficient for 20 minutes of evaporation).
All agents had a significant anti-aggressive effect; attacks were either completely eliminated or reduced to extremely rare and non-intense manifestations. And, of course, the effect is selective. Meanwhile, the inhalation of vapors of other essential oils (clove, lemongrass, sage), which do not contain these substances, did not eliminate intense aggressive attacks. Obviously, the substances in them do not act on the neurophysiological mechanisms associated with the violence inhibitor.
Experiments are still ongoing, and most likely other agents affecting the violence inhibitor will be found. However, we have already been able to confirm the very concept of this mechanism and the possibility of such an effect by using various methods of delivering active substances into the body.
I am also attaching recordings of the process of conducting successful experiments to the material:
