Leopoldina news 4_2022 | Page 8

8 4 / 2022 // LEOPOLDINA / NEWS

“ Perspectives for research into diseases of the brain ”

Leopoldina member Hans Schöler and Jürgen Knoblich on the statement on brain organoids
A retinal organoid under the microscope : After staining with the assistance of antibodies , the light-sensitive molecules of the light-sensing cells of the retina can be seen in red and green . Small image : Brain organoids several millimetres in size in the Petri dish . Images : Yotam Menuchin Lasowski & Thomas Rauen ; MPI Münster ; IMBA
In October , the Leopoldina published the statement “ Brain Organoids – Model Systems of the Human Brain ”. It focuses on the perspectives and limits of research on tissue structures derived from stem cells as well as ethical and legal aspects .

The development and function of the human brain involves processes which do not occur in many animals . Therefore , the conventional approach of researching diseases and their cure in animal models has its limitations . Since it is usually neither possible nor ethically justifiable to conduct research on the living brain of a human , brain organoids are a promising alternative for carrying out research into brain disease outside of the human body .

Organoids are tissue cultures derived from stem cells grown three-dimensionally in a Petri dish and which mimic the cellular architecture and some functional aspects of an organ . Such organoids exist for different human organs . Brain organoids , like the human brain , consist of nerve and glial cells . However , a brain organoid does not represent the whole human brain , only structures that are typical for specific regions of the brain .
At present , human organoids can reach a diameter of five to ten millime- tres , which is at most the size of a pea . For comparison : The human brain with its approximately 86 billion neurons has an average volume of 1.23 litres . With up to 100 trillion neuronal contact areas , called synapses , it is also extremely complex .
Despite this , human organoids can still be used to gain important insights , which would not be possible with two-dimensional cell cultures . For example , the brain of the fruit fly Drosophila consists of only about 100,000 neurons . However , it supports a range of complex behaviours , including navigation and learning .
The statement therefore concludes that : Despite some limitations , brain organoids provide new insights into early brain development and the development