The so-called dendritic thorns run through a mouse brain like bright, yellow lightning. They sit on the dendrites, the fine branches of nerve cells through which information is received, and form the contact points with other cells. You can see a “hotspot” in which a particularly large number of these thorns are close together.
Researchers led by Ryo Egashira from Kyushu University in Japan discovered this previously unknown structure when they examined the cerebral cortex of mice. This consists of six layers and forms highly complex neural networks. The team focused on nerve cells in the fifth layer, which bundle many signals and transmit information between areas. Using high-resolution microscopy, the researchers were able to visualize the distribution of dendritic spines along entire nerve cells for the first time.
The finding calls into question the common “adolescent synaptic pruning” hypothesis, according to which the brain primarily breaks down synaptic connections in youth. Developmental analyzes showed that such neuronal hotspots are still missing in the early stages of life in mice: in young animals, the spines are relatively evenly distributed. Only during adolescence do they condense and form synapse densities. These results suggest that connections not only disappear during this phase, but also re-emerge at certain points. If this structure is disrupted, it could play a crucial role in at least some forms of schizophrenia, says Egashira.
To test this assumption, the team examined mice with mutations in genes linked to schizophrenia. While the density of dendritic spines in these animals was still normal in the first weeks of life, the new formation was significantly disturbed during adolescence. This meant that the synaptic hotspot could not form properly. However, the study is based on mice, and it is not clear whether similar processes occur in the brains of primates or humans.