Brain organoids transplanted into rats respond to visual stimuli

A team of scientists has shown that laboratory-grown human brain organoids transplanted into rat brains respond to visual stimuli such as flashing lights.

Details of the study have been published this Thursday in the journal Cell Stem Cell.

After several decades of research, it has been shown that it is possible to transplant human neurons into rodent brains and, more recently, that human brain organoids can be integrated into developing rodent brains.

However, whether organoid grafts can be functionally integrated into the visual system of injured adult brains has yet to be studied.

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To study it, the team transplanted tissue from a brain organoid (its structure is similar to that of the brain) into the injured brains of rats.

So, “we were able to observe individual neurons within this structure to better understand the integration of the transplanted organoids.”details lead author H. Isaac Chen of the University of Pennsylvania.

The researchers cultured neurons generated from human stem cells in the laboratory for about 80 days before grafting them into the brains of adult rats that had suffered damage to the visual cortex.

At three months, the grafted organoids had integrated into the host brain: they became vascularized, grew, sent out neural projections, and formed synapses with host neurons.

The team used fluorescently labeled viruses that hop across synapses, from neuron to neuron, to look at the physical connections between the organoid and the brain cells of the host rat, as well as “we were able to trace the neural connections from the animal’s retina”Chen explains.

They then exposed the animals to flashing lights and alternating black and white bars, and used electrode probes to measure the activity of individual neurons within the organoid when the animals were faced with these visual stimuli.

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“We saw that a good number of organoid neurons responded to specific orientations of light, which proves that these organoid neurons are capable of not only integrating with the visual system, but also of adopting very specific functions of the visual cortex.”emphasizes the researcher.

“We did not expect to see this degree of functional integration so soon”says Chen, because “There have been other studies on single cell transplantation showing that even 9 or 10 months after transplanting human neurons into a rodent, they are still not fully mature”.

But “neural tissues have the potential to reconstruct injured brain areas”concludes the researcher.

and although “We haven’t figured it all out”Chen points out, “This is a very solid first step. Now we want to understand how organoids might be used in other areas of the cortex, not just the visual, and we want to understand the rules that guide how organoid neurons integrate into the brain so we can better control that process and make it happen more quickly.”.

(With information from EFE)