New Method Developed in Kim Lab Tracks How Psychedelics Affect Neurons in Minutes

UC Davis researchers have developed a rapid, noninvasive tool to track the neurons and biomolecules activated in the brain by psychedelic drugs. The protein-based tool, which is called Ca^2+-activated Split-TurboID, or CaST, is described in research published in Nature Methods.

There has been mounting interest in the value of psychedelic-inspired compounds as treatments for brain disorders including depression, post-traumatic stress disorder, and substance use disorder, among others. Psychedelic compounds — like LSD, DMT and psilocybin — promote the growth and strengthening of neurons and their connections in the brain’s prefrontal cortex. Those afflicted with brain disorders showcase signs of neural atrophy in this region.

“It’s important to think about the cellular mechanisms that these psychedelics act upon,” said Christina Kim, an assistant professor of neurology, a core faculty member at the UC Davis Center for Neuroscience and an affiliate of the Institute for Psychedelics and Neurotherapeutics. “What are they? Once we know that, we can design different variants that target the same mechanism but with fewer side effects.”

This research provides scientists with a new technique that could be used to track step-by-step the molecular signaling processes that lead to these compounds’ beneficial neuroplastic effects. 

What’s more, CaST accomplishes the task of cellular tagging in rapid time, taking 10 to 30 minutes rather than the hours typical of other tagging methods.    

“We designed these proteins in the lab that can be packaged into DNA and then put into harmless adeno-associated viruses,” Kim said. “Once we deliver the CaST tool and these proteins into neurons, then they incubate inside the cells and start expressing.”

The research was conducted in collaboration with David Olson, the founding director of the UC Davis Institute for Psychedelics and Neurotherapeutics and a professor of chemistry, and biochemistry and molecular medicine  

 

A camera snapshot of the brain

The CaST tool takes advantage of changes in intracellular calcium concentrations, a nearly universal marker to track activity in a neuron. When neurons exhibit high activity, they exhibit high calcium levels. CaST uses this cue to tag the cell with a small biomolecule called biotin, which experimenters deliver to the mouse.

In the study, Kim and her colleagues dosed mouse models with the psychedelic psilocybin. They then used the CaST tool in tandem with biotin to identify neurons with increased calcium in the prefrontal cortex. The prefrontal cortex is an area affected by many brain disorders. It’s also an area where psychedelics promote neuronal growth and strengthening.

The researchers conducted the experiment while also monitoring the mouse models’ head-twitch responses. Head-twitch responses are the primary behavioral correlate for hallucinations caused by psychedelics.

“What’s nice about CaST is that it can be used in a freely behaving animal,” said Kim, noting that other cellular tagging technologies require stabilizing a mouse’s head to accomplish imaging. “Biotin is also a great tagging substrate because there are many pre-existing commercial tools that can report whether biotin is present or not just by a simple staining and imaging method.” 

The proof-of-concept experiment gave what Kim called “a camera snapshot” of the areas in the prefrontal cortex activated by psilocybin.

Next steps

Kim and her colleagues are now working on methods to enable brain-wide cellular labeling with the CaST tool. Additionally, they’re 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 Core Facility and they can give us an unbiased picture of all the proteins we identified,” Kim said. “We want to examine their entire contents in terms of what proteins they express, what genes they express, and try to see what’s different in psilocybin-treated animals versus control animals or animal models of diseases.”  

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 Olson’s lab that use the CaST tool to compare the neuronal activity induced by psychedelics to the activity induced by non-hallucinogenic neurotherapeutics.

“CaST will be an important tool for studying the mechanisms of action of these neurotherapeutic drugs,” Kim said. 

Additional UC Davis authors on the study include David E. Olson, lead authors Run Zhang and Maribel Anguiano, and Isak K. Aarrestad, Sophia Lin, Joshua Chandra, and Sruti S. Vadde.