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Psilocybin, a psychedelic compound found in “magic mushrooms,” has shown promise in the treatment of mental health conditions. However, the substances is also known to induce acute anxiety. New research published in iScience sheds light on the biological underpinnings of this anxiety, suggesting it stems from different brain processes than those driving the psychedelic effects.
“While many scientific studies are currently looking into how psychedelics in general, and psilocybin in particular, may be used clinically to reduce depression and anxiety in the long term, only a handful of studies and researchers are looking into the mechanisms of how these same psychedelics sometimes cause anxiety during their use. Particularly high anxiety can be attributed to what is often referred to as ‘bad trips,’ but anxiety is also sometimes present in generally positive psychedelic experiences,” explained study author Evan Elliott, an associate professor of molecular neuroscience at Bar Ilan University.
Using a controlled experimental setup involving male C57BL/6J mice, the researchers administered varying doses of psilocybin and observed the resulting behavioral changes and neuronal activities. C57BL/6J mice are a strain of inbred laboratory mice known for their robust health and consistent genetic background. They are often used in research due to their well-characterized physiology and behavior, which provide a reliable and standardized model for investigating the neurological and behavioral effects of psychoactive substances.
In behavioral tests designed to assess anxiety-like behaviors—such as the marble burying test, the open field test, the dark-light box, and the elevated plus maze—the mice exhibited increased anxiety symptoms following administration of psilocybin.
Notably, the results showed a dose-dependent increase in anxiety; higher doses of psilocybin led to more pronounced anxiety behaviors. For instance, in the open field test, mice treated with higher doses spent significantly less time in the center of the arena, indicative of increased anxiety levels. Similarly, in the elevated plus maze, which assesses anxiety based on the preference of mice for open versus closed spaces, those receiving higher psilocybin doses spent less time in the open arms.
Neuronal activation was assessed by measuring the expression of c-Fos, a protein often used as a marker of neuronal activity, in brain areas associated with stress and anxiety such as the basolateral amygdala and the dentate gyrus of the hippocampus. The researchers found that psilocybin significantly increased c-Fos expression in these areas, confirming that psilocybin activates neurons in key regions involved in anxiety processing.
To investigate whether the 5-HT2A receptor, which psilocybin is known to activate, was also responsible for the anxiety effects, mice were pre-treated with ketanserin, a 5-HT2A receptor antagonist. Interestingly, while ketanserin reduced the psychedelic effects of psilocybin, such as the head twitch response (a commonly used behavioral proxy for psychedelic effects in mice), it did not mitigate the anxiety-related behaviors. This suggests that psilocybin’s anxiety-inducing effects might be mediated through different pathways or receptors, independent of the 5-HT2A receptor.
The researchers also explored changes at the molecular level, specifically analyzing protein phosphorylation patterns in the amygdala, a brain region crucial for emotional processing. The phosphoprotein analysis revealed that psilocybin altered the phosphorylation state of many proteins involved in synaptic function. Some of these changes were reversed by ketanserin, indicating their mediation by the 5-HT2A receptor.
However, a significant number of phosphoprotein changes remained unaffected by ketanserin, pointing to alternative pathways through which psilocybin induces anxiety. This part of the study highlighted the complexity of psilocybin’s action in the brain, involving multiple signaling pathways and molecular mechanisms.
“The average person should understand that increased anxiety, as some level, is an expected part of the psychedelic experience,” Elliott told PsyPost. “The anxiety may be induced by different processes in the brain than the psychedelic response, and therefore future studies may find how the anxiety response can be either inhibited or better utilized in the therapeutic context.”
The study adds a crucial piece to the puzzle of how psilocybin affects the brain, suggesting that its anxiety-inducing effects are mediated through mechanisms distinct from those producing its psychedelic effects. But several unanswered questions remain. The exact types of neurons affected by psilocybin and whether these specific changes correlate with behavioral outcomes remain unclear. Moreover, the analysis was broad and did not focus on amygdala subregions, which might yield more detailed insights.
Future research will aim to determine whether the anxiety induced by psilocybin is an essential part of its therapeutic effects or if it can be mitigated or bypassed. Understanding these mechanisms could refine the use of psilocybin, potentially enhancing its effectiveness as a treatment for psychological disorders.
Elliott highlighted two key questions that he and his research team plan to address in the future: “1.) Can psychedelic-induced short-term anxiety be prevented? 2.) Is psychedelic-induced anxiety a part of the therapeutic process or is it dispensable in the therapeutic process?”
The study, “Psilocybin induces acute anxiety and changes in amygdalar phosphopeptides independently from the 5-HT2A receptor,” was authored by Ram Harari, Ipsita Chatterjee, Dmitriy Getselter, and Evan Elliott.
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