Scientists from Johns Hopkins University claim to have grown a series of "mini-brains" from human skin cells, which they say could soon replace the use of animals in drug tests. Containing several different types of neurons and displaying some of the same connectivity seen in real human brains, these tiny bundles of cells can easily be produced in large numbers, and could be put into widespread production as early as this year.

The use of animals to study the effects of neurological drugs is controversial for a number of reasons, of which ethical concerns are just one. On top of this is the fact that human brains differ from those of other species in many ways, meaning that results obtained in animal models are often not reproducible in people.

Presenting their new method at the recent annual meeting of the American Association for the Advancement of Science (AAAS), researchers explained how they grew the miniature brains by genetically reprogramming skin cells to create induced pluripotent stem cells (iPSCs), which were then stimulated to develop into brain cells. iPSCs are "blank slate" cells that can be created by altering the expression of certain genes responsible for maintaining the specific characteristics of specialized cells.

Each mini-brain takes two months to develop and measures about 350 micrometers across, making them just about visible to the human eye. While human brains contain several hundred different types of neurons, the tiny structures feature just four of these. In addition, they contain astrocytes, which play a key role in supporting neurons, as well as oligodendrocytes, which make up the fatty protective sheaths that insulate neurons and facilitate the transmission of information.

Using an electrode array, the researchers were able to monitor the electrical activity of these structures when exposed to different types of drugs, indicating that they do indeed function just like real brains and may therefore provide a reliable model for the study of neurological compounds. Crucially, because these brains are derived from human cells, the results of these studies may provide a more dependable indication of the effects of these drugs on humans than current animal models do, although the small number of cell types is a limitation.

Furthermore, according to lead researcher Thomas Hartung, it is possible to create specific mini-brains using the cells of people suffering from certain conditions such as autism or dementia, in order to study how drugs affect these particular traits.

With a patent for these mini-brains currently being filed, Hartung told attendees at the AAAS meeting that he believes “the future of brain research will include less reliance on animals, more reliance on human, cell-based models.”