New research published in the journal Neuroscience provides evidence that nitrous oxide may be an effective treatment for symptoms associated with post-traumatic stress disorder. The study found that exposure to this gas, commonly known as laughing gas, reduced anxiety-like behaviors in rats that had been subjected to severe stress. Additionally, the researchers observed that this treatment stimulated the growth of new neurons in the hippocampus, a brain region essential for memory and emotional regulation.
Post-traumatic stress disorder is a serious mental health condition that can develop after an individual experiences a dangerous or shocking event. The prevalence of this disorder has increased in recent years following global crises such as the COVID-19 pandemic and various geopolitical conflicts. Individuals with this condition often suffer from flashbacks, severe anxiety, and a constant state of hyperarousal.
Current treatments for this disorder often involve psychotherapy and medications such as selective serotonin reuptake inhibitors. However, a significant number of patients do not respond adequately to these standard interventions. This gap in effective care has led scientists to investigate alternative therapeutic options that can provide rapid relief from symptoms.
One area of focus in this research is the hippocampus. This part of the brain plays a central role in how we process memories and handle stress. Previous studies indicate that chronic stress can physically alter the hippocampus, leading to a reduction in its volume. This shrinkage is often linked to a decrease in neurogenesis, which is the process by which the brain creates new neurons.
The authors of the new study sought to test whether nitrous oxide could reverse these negative changes. Nitrous oxide is an anesthetic gas often used in dental and medical procedures. Recent investigations have suggested that it possesses rapid antidepressant properties, potentially working by blocking specific receptors in the brain to boost neural plasticity.
“This study was motivated by the sharp rise in anxiety, depression, and PTSD observed during the COVID-19 pandemic, highlighting an urgent need to explore effective therapeutic options for stress-related disorders,” said study author Wassim Abou-Kheir, a professor at the American University of Beirut.
“Given this real-world mental health crisis, we sought to address the gap in understanding how treatments targeting neural plasticity might alleviate PTSD symptoms. Our laboratory’s primary focus is on neurogenesis, which provided a natural framework for this investigation. By integrating our expertise with the emerging need for PTSD therapies, we examined whether enhancing neurogenesis could have therapeutic potential. This approach was further supported by our previous findings demonstrating that nitrous oxide treatment increases hippocampal neurogenesis, which led us to investigate its effects in a PTSD context.”
To test their hypothesis, the researchers employed a group of twenty adult male Sprague Dawley rats. They utilized a well-established experimental protocol known as the Single Prolonged Stress model to induce symptoms mimicking post-traumatic stress disorder. This model is designed to disrupt the animal’s normal stress response system.
The stress protocol consisted of three consecutive stages. First, the rats were immobilized in a confined space for two hours. Immediately following this restraint, they were placed in a forced swim test for twenty minutes. Finally, the animals were exposed to an anesthetic gas called isoflurane until they lost consciousness.
After recovering from these stressors, the rats were housed individually. This social isolation was intended to replicate the withdrawal often seen in humans suffering from trauma. A separate control group of rats did not undergo these stress procedures and remained in standard housing conditions.
The researchers waited nine days after the stress induction to begin the treatment phase. They divided the stressed rats and the control rats into subgroups. Half of the animals in each group were exposed to a gas mixture containing 70 percent nitrous oxide and 30 percent oxygen.
The exposure sessions lasted for one hour. The researchers repeated this treatment on days 11, 14, and 16 following the initial stress event. The remaining rats in both the stress and control groups were exposed to regular atmospheric air during these same time periods.
To measure the effects of the treatment, the team used a behavioral test called the Elevated Plus Maze. This apparatus consists of two open, elevated arms and two enclosed, protected arms. Rats that are experiencing high levels of anxiety typically avoid the open arms and stay in the enclosed spaces.
The researchers also utilized a Y-maze test to assess spatial memory and exploratory behavior. This test relies on a rodent’s natural tendency to explore new environments. A reduction in exploratory behavior in this maze is often interpreted as a sign of cognitive or memory impairment.
Beyond behavioral observation, the study examined biological changes within the brain. The researchers injected the rats with a compound called BrdU. This substance incorporates itself into the DNA of dividing cells, allowing scientists to track and count newly born neurons.
Four weeks after the injections, the researchers examined the brain tissue. They specifically focused on the dentate gyrus region of the hippocampus. They counted the number of cells marked with BrdU to determine the rate of neurogenesis. They also used immunofluorescence staining to look for markers of inflammation in brain support cells called microglia and astrocytes.
The results of the behavioral tests showed a clear distinction between the groups. The rats exposed to the stress model initially exhibited significant anxiety-like behavior. In the Elevated Plus Maze, these animals made significantly fewer entries into the open arms compared to the control group.
However, the stressed rats that received nitrous oxide treatment displayed a marked recovery. Their behavior in the maze changed significantly, as they spent more time exploring the open arms. The data showed that their anxiety levels had returned to a range comparable to that of the unstressed control rats.
The results from the Y-maze were less definitive regarding long-term effects. Initially, the stressed rats showed reduced exploration of the novel arm, suggesting some memory impairment. By the end of the four-week period, however, these deficits appeared to resolve naturally in both treated and untreated groups.
The biological examination of the brain tissue provided evidence supporting the behavioral findings. The researchers found that the Single Prolonged Stress model caused a severe reduction in the number of new neurons in the hippocampus. The untreated stressed rats had lower counts of BrdU-positive cells compared to the controls.
“One surprising finding was the extent to which PTSD alone suppressed hippocampal neurogenesis,” Abou-Kheir told PsyPost. “At the time of this study, this level of impairment had not been well documented, making it a novel and unexpected result. This observation underscored the profound impact of traumatic stress on brain plasticity and further strengthened the rationale for targeting neurogenesis as a therapeutic strategy.”
This suppression of neurogenesis was effectively reversed in the group treated with nitrous oxide. The rats that inhaled the gas showed a robust increase in the number of new brain cells. The cell counts in the treated stress group were statistically similar to those found in the healthy control animals.
The study did not find significant changes in the support cells of the brain. The optical density of markers for microglia and astrocytes remained consistent across all groups. This suggests that the treatment did not cause overt structural changes to these specific cell types, at least detectable by the methods used.
These findings suggest that nitrous oxide may help the brain repair itself following trauma. The gas appears to counteract the suppressive effects of stress on the hippocampus by promoting the birth of new neurons. This restoration of neural plasticity correlates with the observed reduction in anxiety behaviors.
“The key takeaway for the average person is that our findings suggest nitrous oxide can stimulate the growth of new neurons in the hippocampus, a brain region essential for memory and emotional regulation,” Abou-Kheir explained. “In our study, this increase in neurogenesis was associated with a reduction in anxiety-like symptoms in a well-established animal model of PTSD.”
“Because nitrous oxide is already considered a safe and feasible treatment, our results indicate it may have the potential to help alleviate PTSD symptoms by enhancing the brain’s natural capacity for recovery. Therefore, our study suggests that nitrous oxide can help the brain heal itself during PTSD by promoting the growth of new brain cells in an area important for memory and emotional control.”
But there are some limitations to this study that should be considered. The research was conducted using a rodent model, which cannot fully capture the complexity of human psychological disorders. While the Single Prolonged Stress model is a standard tool in neuroscience, it is an approximation of the human experience of trauma.
Additionally, the study only utilized male rats. Sex differences are known to influence how the brain responds to stress and how it metabolizes treatments. It remains unclear whether female subjects would demonstrate the same physiological and behavioral responses to nitrous oxide exposure.
“While this study was conducted in an animal model, the observed reductions in anxiety-like behavior and the enhancement of hippocampal neurogenesis suggest a biologically significant effect,” Abou-Kheir said. “Importantly, the potential value of these findings lies in the feasibility and safety profile of nitrous oxide, highlighting its promise as a therapeutic option that could be translated into clinical settings with minimal risk.”
The authors propose that nitrous oxide could serve as a potential therapeutic intervention for patients who do not respond to traditional treatments. Because the gas is already widely used in medicine and has a known safety profile, it represents a feasible option for clinical translation.
Future research is needed to explore the long-term impacts of this treatment. The researchers intend to investigate whether age influences the efficacy of nitrous oxide.
“A key next step for this line of research is to investigate age-related sensitivity to PTSD,” Abou-Kheir explained. “Specifically, we aim to examine how exposure to the SPS model affects neurogenesis in younger versus older animals, and whether the efficacy of nitrous oxide treatment differs across age groups. Understanding these age-dependent effects will be critical for determining how broadly applicable neurogenesis-targeting therapies may be across the lifespan.”
The study, “Nitrous oxide promotes exploratory activity and stimulates neurogenesis in a male rat model of post-traumatic stress disorder,” was authored by Batoul Darwish, Jad El Masri, Lina Hourieh, Ziad Nahas, Wassim Abou-Kheir, and Farah Chamaa.
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