It’s really difficult to convince a mature brain to grow new neurons.
This difficulty is one of the reasons that prognoses for brain injuries or degenerative brain diseases are so scary; outside the hippocampus or olfactory bulb, once a neuron is gone, its place in the connectome is empty.
Introducing individual stem cells or neurons in solution doesn’t work: the specific adhesive and signaling connections between neurons are so important that when disrupted by a or stroke, the network can’t recover healthy function faster than its constituent cells die off.
In light of restrictions like these, scientists wondered whether they might not get better results by introducing intact networks of neurons into damaged brains, rather than individual neurons in isolation.
“If the scaffolds were too dense, the stem cell-derived neurons were unable to integrate into the scaffold, whereas if they are too sparse then the network organization tends to be poor,” explains Prabhas Moghe, Ph.D., co-senior author of the paper.
The researchers found that the scaffolded, interconnected neurons survived much better than individual neurons when injected into the mouse brains, on the order of a 40-fold improvement.
The scaffolded neurons exhibited electrical activity and better outgrowth in the mouse brains, and once they were ensconced the transplanted neurons began to express proteins important to the formation of synapses – a solid indication that the transplanted cells could integrate themselves into the host brain tissue.