In a study published on October 12, 2022, researchers from Stanford University confirmed that they successfully transplanted human neurons into the brains of newborn rats. Scientists hope to use this advancement to study human neurological conditions or to test new psychiatric drugs. 

For the transplant, scientists created clumps of human brain cells called “organoids,” which grew into new neurons and rewired themselves into a newly formed nervous system. They developed the organoids from human skin cell samples, which they could convert into neurons through a series of chemical reactions in the rat brain. Although researchers have performed a similar neuron transplant on adult rats in the past, the still-developing brains of younger rats allowed the human neurons to integrate into the body more efficiently. Each of the newborn rat transplant candidates also had dysfunctional immune systems to prevent the rejection of the foreign cells. The leading neuroscientist of the study Dr. Sergiu Pasca and his colleagues, ran experiments on the rats to analyze the effects of the transplanted organoids on their behavior. 

To analyze how the cells could impact the rats, researchers used optogenetics, a technology involving the alteration of cells to respond to light. Scientists repeatedly gave water to the rats while a blue light was shone. The optogenetics technique proved successful when after two weeks, the rats expected to be given water whenever they saw the same light. 

One major goal of the study was to find methods for revealing how different gene-related conditions can affect the brain. Therefore, in a particular experiment, researchers implanted an organoid made of cells from a patient with Timothy’s syndrome, a life-threatening genetic condition that affects the heart. The Timothy’s syndrome organoid was implanted on one side of the rat’s brain, and a typical organoid was placed on the other. Both organoids grew and developed connections, but the Timothy’s syndrome cells developed twice as many receptors. 

Some critics are concerned with the ethics of this study and experimentation blurring lines between animals and humans. However, Dr. Pasca and his team believe their research will help scientists study patterns in neurological conditions like autism, epilepsy, and schizophrenia and test the safety and effectiveness of psychological medications. 

Works Cited: 

New York Times: https://www.nytimes.com/2022/10/12/science/human-brain-cells-organoids-rats.html?searchResultPosition=10

New Scientist: https://www.newscientist.com/article/2342138-human-neurons-transplanted-into-a-rats-brain-influence-its-behaviour/#:~:text=Human%20neurons%20transplanted%20into%20a%20rat’s%20brain%20influence%20its%20behaviour,-Researchers%20propose%20that&text=Human%20neurons%20have%20been%20transplanted,to%20test%20new%20psychiatric%20drugs.

Cleveland Clinic: https://my.clevelandclinic.org/health/diseases/22698-timothy-syndrome#:~:text=Timothy%20syndrome%20is%20a%20rare,can%20lead%20to%20cardiac%20arrest.

The Swaddle: https://theswaddle.com/human-neurons-were-transplanted-into-rats-to-study-brain-disorders-is-it-ethical/

By: Lily Schwedhelm, Junior Editor in-Chief, SNHS Member