When talking about prevalent and debilitating mental health issues, most people do not immediately think of Post Traumatic Stress Disorder (PTSD), even though nearly 10% of the population will at some point in their lives be diagnosed with it. After a global event as widely traumatic as the COVID-19 pandemic, it is especially important now to understand the causes of and potential treatments for PTSD. PTSD is a psychiatric disorder that develops after a traumatic event and can manifest as anxiety, depression, and unwanted flashbacks to the trauma. A global pandemic lasting several years and resulting in over 5 million deaths could cause this on a massive scale. Even though the effects of PTSD can be life altering by making socialization, working, and even normal everyday life a challenge, much remains unknown about the underlying neurological and molecular causes of PTSD as well the physical and behavioral manifestations of it. Student researchers at UCSD are tackling the neurological roots of PTSD.
The Neurological Causes of PTSD
Romona Dong, a third year student researcher in the Spitzer Lab, is working to understand the mechanisms in the brain that cause PTSD symptoms by looking at neurotransmitter level switching in mice after a stimulated trauma, in this case an electric shock. Specifically, she focuses on brain plasticity, which is the ability of the brain and nervous system to rewire its activity and physical properties as a response to external stimuli. Dong looks at neurotransmitter changes, one of the ways that the brain changes, after a period of sustained fear. She hypothesizes that a period of sustained exposure to stress (electric shock) causes a switch in the neurotransmitters produced in the brain from glutamate to GABA, which then causes PTSD-like symptoms such as fear and anxiety. Though there has not been much prior research on possible connections between glutamate, GABA, and PTSD, Dong studies these neurotransmitters because glutamate has an excitatory effect on the neurons, and GABA has an inhibitory effect. The shift from glutamate to GABA presence implies a change in activity of the neurons and her research focuses on how the shift in neurotransmitters might relate to behavioral change.
To study these changes, Dong uses a mouse model to observe the levels of these two in the brain before and after a period of sustained fear, meant to stimulate the trauma that causes PTSD in humans. This experiment is conducted through three groups of mice: one control group, one given mild but unexpected electric shocks as stressful external stimuli in a chamber, and the third group injected with GABA. Dong also observed the behavior of all three groups of mice through a phenomenon known as “freezing time,” or the amount of time a mouse spends frozen in fear after a stressful event. She defines freezing time as the manifestation of PTSD symptoms in mice, which have been noted to display this behavior when they experience electric shock. She found that both traumatized and mice injected with GABA displayed higher freezing times than the control group mice, which had zero freezing time in the shock chamber. After analyzing the brains of the shocked mice through immunostaining, which highlights the levels of different neurotransmitters in the brain in different colors, Dong also found that the shocked mice had higher levels of GABA and lower levels of glutamate in their brain than the control mice. These findings support the hypothesis that PTSD symptoms, such as freezing time as a result of shock, are caused by higher levels of GABA being released and replacing glutamate in the brain after a traumatic event.
Dong’s experiments also study the effects of different medications on PTSD symptoms, including how the medication’s response changes with the amount of time between its administration and the original trauma. Dong experimented with injecting both the shocked and GABA injected mice with Fluoxetine, a medication commonly used to treat PTSD in humans. She found that while the medication lowered the freezing time in all the mice, it was much more effective when administered to the mice shortly after their shock, rather than several hours after. This suggests that PTSD can be treated more effectively if treatment begins as soon after the trauma as possible, which is a vital discovery to improving mental health care in PTSD.
Ramona’s mouse model can be applied to humans, since both animals display similar levels of brain plasticity and use similar neurotransmitters in their brain, including glutamate and GABA. Even though sustained fear reactions in mice cannot be directly equated to PTSD in humans without further research, this research on brain plasticity and neurotransmitter switching can be used to both better understand the neurological effects of trauma on the human brain and the underlying physical causes of PTSD, which can lead to better, more effective treatments. Dong’s mouse model research could be vital to improving the lives of millions of people around the world suffering from PTSD by giving more accurate solutions to an under-researched mental health issue.
Further Research on Treatments for PTSD and Alcoholic Relapse Behavior
While Romona’s research focuses on neurological changes, other UCSD labs look at the broader behavioral changes that occur in PTSD, such as alcholic tendencies and relapse behavior. One such lab is the Zorilla Lab, whose focus is to demystify the genetic mechanisms of the stress and reward circuits in our brain. Applications of their research target binge eating disorders, anxiety and depression disorders, and alcoholism and drug addiction. ​​Research shows that those who experience irregularities are likely to seek external stimulation through risk-taking and addiction. Eleanna Sakoulas, a fourth-year undergraduate at the Zorilla Lab, is researching how PTSD can cause such behavioral changes, specifically alcoholic relapses.
Using a rat model, Sakoulas studied the correlation between gene expression and relapse behavior after a long period of stress. The premise of the experiment was to find genes that are present in higher expressions which act as markers in determining the process of relapse behavior. Sakoulas used these marker results to test how drugs targeting the gene of interest can change the relapse response. Previous studies have shown that the level of expression of the proteins DeltaFosB and glucocorticoid receptors (GRα and GRβ) depends on the amount of stress the rat experienced. Therefore, Sakoulas hypothesized that these genes that code for DeltaFosB, GRα and GRβ) would be expressed in higher amounts after simulating an alcoholic relapse.
The general steps of the experiment were exposing the rat subjects to shock, drinking, extinction, renewed drinking, and then conducting brain tissue analysis. During the first “shock” stage, rats are placed into an operon chamber (a box used to store rats that are test subjects in behavioral research) and exposed to a light cue before being shocked. The stimuli are paired to create an association of stress with the light in the rats, simulating PTSD. Throughout the experiment, the rats are reintroduced to the light to observe their stress response. In the next “drinking” stage, the rats are placed back into the operon chamber and are rewarded with alcohol when they press a lever. During the “extinction” stage, Sakoulas leaves the levers in the chamber. However, when pressed, no alcohol will be released for the rats to consume. In the “renewed drinking” stage, the rats are rewarded with alcohol when they press the lever. Finally, the researchers analyze their brain samples using quantitative polymerase chain reaction (qPCR) to measure gene expression.
Sakoulas found that there was a strong correlation between the suppression of the FKBP51 gene and blood alcohol concentration which partially affirms her initial hypothesis that the proteins DeltaFosB, GRα and GRβ would be upregulated in PTSD. FKBP51 is an important regulator in stress responses since it modulates GRα and GRβ. Since FKBP51 is down-regulated, there will be more expression of the GRα and GRβ genes, as Eleanna hypothesized. This indicates that higher amounts of stress are correlated to more drinking behavior. Based on this, her next research focus is the effect of inhibiting FKBP51 on relapse behavior to demonstrate if a causal relationship exists between the two. Inhibition of FKBP51 will be achieved by injecting the rats with different amounts of the FKBP51 inhibiting drugs, Benztropine and SAFit2, during the “renewed drinking phase.” The results of her new project on Benztropine and SAFit2 can help determine if targeting the FKBP51 gene will help treat alcohol relapse in those who have PTSD.
Conclusion
After the pandemic began in March 2020, studies have shown high levels of PTSD symptoms in young adults. This is especially applicable for college students, who went through months of continual stress over distance learning, isolation from peers, and uncertainty about the future. In order to effectively address the effects the pandemic will have on the mental health of students, both neurological and behavioral studies of PTSD must be conducted. Romona’s work at the Spitzer lab helps this cause by looking at freezing times in traumatized mice to observe how PTSD affects the production of neurotransmitters in the brain. On the other hand, Sakoulas works in the Zorilla lab to research the changes in addictive behavior as a result of stress. Both of these studies will make strides in how society approaches and treats those who have endured stressful situations.