Researchers at the University of California, Davis have developed a rapid, noninvasive tool to track neurons and biomolecules activated in the brain by psychedelic drugs. The protein-based tool, which is called Ca2+-The activated Split-TurboID, or CaST, is described in research published in Methods of Nature.
There is growing interest in the value of psychedelic-inspired compounds as treatments for brain disorders such as depression, PTSD, and substance use disorder. Psychedelic compounds such as LSD, DMT, and psilocybin promote the growth and strengthening of neurons and their connections in the brain’s prefrontal cortex. The new tool could help scientists uncover the benefits of psychedelic treatments for patients with brain disorders.
“It’s important to think about the cellular mechanisms that these psychedelics act on,” said Christina Kim, an assistant professor of neurology at the UC Davis Center for Neuroscience and School of Medicine and affiliated with the UC Davis Institute for Psychedelics and Neurotherapeutics. “What are they? Once we know that, we can design different variants that act on the same mechanism but with fewer side effects.”
This research provides scientists with a new technique that could be used to trace step-by-step the molecular signaling processes that are responsible for the beneficial neuroplastic effects of these compounds. Moreover, CaST accomplishes the task of cell labeling in a rapid time frame, 10 to 30 minutes instead of the hours that other labeling methods typically take.
“We engineered these proteins in the lab so that they can be packaged into DNA and then introduced into harmless adeno-associated viruses,” Kim said. “Once we introduce the CaST tool and these proteins into neurons, they incubate inside the cells and begin to express themselves.”
The research was conducted in collaboration with David Olson, founding director of the Institute for Psychedelics and Neurotherapeutics and professor in the departments of Chemistry, Biochemistry and Molecular Medicine.
A snapshot of the brain
The CaST tool takes advantage of changes in intracellular calcium concentrations, a nearly universal marker for tracking a neuron’s activity. When neurons show high activity, they have high levels of calcium. CaST uses this signal to label the cell with a small biomolecule called biotin.
In the study, Kim and his colleagues administered the psychedelic psilocybin to mice. They then used CaST along with biotin to identify neurons with increased calcium in the prefrontal cortex. The prefrontal cortex is an area affected by many brain disorders and also an area where psychedelics promote neuronal growth and strengthening.
The researchers also monitored head-twitch responses in the mice. Head-twitch responses are the main behavioral correlate of psychedelic-induced hallucinations.
“The nice thing about CaST is that it can be used in a freely behaving animal,” Kim said, noting that other cell-labeling technologies require stabilizing a mouse’s head to achieve imaging. “Biotin is also an excellent labeling substrate because there are many preexisting commercial tools that can report whether biotin is present or not just by a simple staining and imaging method.”
The proof-of-concept experiment provided what Kim called “a camera snapshot” of the areas of the prefrontal cortex activated by psilocybin.
Next steps
Kim and his colleagues are now working on methods that would enable whole-brain cellular labeling using the CaST tool. They are also exploring ways to enrich the signature of individual proteins produced by neurons affected by psychedelics.
“We can send those samples to the UC Davis Proteomics Center and they can give us an objective picture of all the proteins we identified,” Kim said. “We want to examine their entire content in terms of what proteins they express, what genes they express, and try to see what’s different in the psilocybin-treated animals compared to control animals or animal models of disease.”
The goal is to identify how psychedelics benefit the cellular profiles of those with brain disorders, elucidating the step-by-step cellular process of their therapeutic effects.
Kim expressed interest in conducting future experiments in collaboration with the Olson lab that use the CaST tool to compare psychedelic-induced neural activity to activity induced by nonhallucinogenic neurotherapeutics.
“CaST will be an important tool to study the mechanisms of action of these neurotherapeutic drugs,” Kim said.
Other UC Davis authors involved in the study include senior authors Run Zhang and Maribel Anguiano, and Isak K. Aarrestad, Sophia Lin, Joshua Chandra and Sruti S. Vadde.
The work was supported by grants from the Brain and Behavior Research Foundation, the Kinship Foundation, the Arnold and Mabel Beckman Foundation, the NIH, the NSF, and the Boone Family Foundation.