Neural organoids have been heralded as having\u00a0huge potential\u00a0for\u00a0advancing\u00a0our\u00a0knowledge\u00a0of the brain in several\u00a0fields. These include\u00a0exploring\u00a0the responses of\u00a0brain\u00a0tissue to drugs, investigating\u00a0the effect of specific genetic mutations on\u00a0neural electrical\u00a0activity\u00a0and characterising\u00a0how neural systems develop.\u00a0<\/p>\n
In the past, viability of these systems has been limited by their scalability,\u00a0reproducibility\u00a0and longevity.\u00a0<\/p>\n
New research from King’s College London has\u00a0succeeded\u00a0in scaling\u00a0up the organoid approach; providing a new system where the effects of drugs, genetic mutations, and development can be tested at higher throughput and over much longer periods of time.\u00a0<\/p>\n
“Functional genomic and pharmacological studies of neurodevelopment often depend on reliable measures of neuronal function, not just cell identity. Our approach makes it possible to follow neural network activity over time and\u00a0will allow us and others to\u00a0directly compare the effects of drugs or gene variants across many parallel cultures.”\u00a0–\u00a0Professor Deepak Srivastava, Professor of Molecular Neuroscience,\u00a0King’s College London.\u00a0<\/p>\n
Current challenges in organoid research\u00a0<\/p>\n
Lab grown neural networks\u00a0can be 2D or 3D and both have advantages and disadvantages.\u00a0Traditional 3D neural organoids are highly variable, being made up of many\u00a0different types\u00a0of cells\u00a0that make each organoid slightly different. While\u00a0variety in neuron types is viewed as a sign of a healthy organoid, this can present challenges for reproducibility,\u00a0which is particularly important\u00a0when testing drugs\u00a0or trying to understand the function of a specific gene.\u00a0<\/p>\n
Additionally,\u00a0it is hard to record electrical activity from\u00a03D organoids as their structure means researchers can\u00a0usually\u00a0only record from the surface\u00a0of the organoid, or only from\u00a0one\u00a0neuron\u00a0at a time if they want to go deeper into the tissue.\u00a0<\/p>\n
Other groups have been growing neurons in the lab in 2D, allowing researchers to record electrical activity from many neurons\u00a0over time. However, these 2D networks lack the diversity of neuron types and support cells seen in 3D organoids and\u00a0real brains.\u00a0<\/p>\n
The best of both worlds: Making 3D organoids 2D\u00a0to reduce variability\u00a0<\/p>\n
Dr Adam\u00a0Pavlinek, Professor\u00a0Anthony Vernon,\u00a0Professor Deepak Srivastava, and colleagues wanted to keep the diversity of neurons found in 3D organoids, but have the benefits\u00a0of\u00a02D approaches, namely the ability to record\u00a0changes in activity\u00a0over\u00a0time and to test drugs and other manipulations at scale.\u00a0<\/p>\n
To do this, the researchers\u00a0first\u00a0grew\u00a0organoids in the lab and\u00a0then broke\u00a0them\u00a0down\u00a0into\u00a0individual\u00a0cells\u00a0in a process called dissociation. This gave the researchers many\u00a0different types\u00a0of developing neurons that they could grow on a 2D plate.\u00a0They then mixed cells from different organoids together to make the cell\u00a0mixture less variable.\u00a0This resulted in multiple neural networks next to each other on one plate, all coming from similar origins.\u00a0Pooling cells from many organoids reduced variability by averaging over the variation between the original organoids.\u00a0<\/p>\n
To ensure they could record the electrical activity of the neurons, researchers let the disassociated neurons grow on a plate with electrodes on it, called a microelectrode array.\u00a0<\/p>\n
Recording over many days\u00a0<\/p>\n
On the microelectrode array, the researchers could watch the neurons develop\u00a0networks\u00a0over many days and record their electrical activity throughout. In two dimensions, researchers could\u00a0monitor\u00a0the neurons developing for much longer than with 3D organoids. They saw neurons\u00a0transitioning\u00a0from asynchronous electrical activity, commonly seen in developing brains, to synchronised firing as the cells matured and the connections between them formed.\u00a0<\/p>\n
Separating sources of variation\u00a0<\/p>\n
The\u00a0approach taken\u00a0also meant the\u00a0researchers\u00a0could separate the effects of technical versus biological variability. They could have many versions of the same cell types from the same neural organoids plated alongside each other and see if the neurons developed similar connections and if they responded similarly to drugs.\u00a0<\/p>\n
“The\u00a0neurons\u00a0in organoids have a remarkable ability of self-assembling into networks, we think the balance of\u00a0neuron\u00a0cell types\u00a0in these networks may affect their\u00a0electrical activity\u00a0and\u00a0may\u00a0underlie the differences we see\u00a0between networks.”\u00a0–\u00a0Dr Adam\u00a0Pavlinek, first author.<\/p>\n
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