Radiation should be avoided, but there are some scenarios where the body must be exposed to radiation, such as in chemotherapy and radiotherapy. A study appearing in Scientific Reports explores how the brain responds to radiation therapy and why patients who have gone through radiation therapy often experience cognitive difficulties afterwards.
The study explains that a healthy brain (not exposed to radiation) and the immune system work together to restructure the connections between neurons. When the brain is exposed to radiation, this process runs amok and overcompensates for the restructuring of the connections (synapses) between the neurons. As the restructuring becomes overactive, the ends of the nerve cells (neurons) which function to form synapses (connections) with their neighboring neurons are destroyed.
The immune system cell responsible for the overcorrection and premature destruction of these connecting nodes are microglia, specialized cells which find and destroy infections and repair tissue damage. Microglia are constantly working to connect and restructure the connections between neurons. They destroy the nodal connection between neurons when a protein signal is sent out that instructs the microglia to destroy the synapse connection at the end of the neuron when the connection is not needed anymore.
To study the microglia in depth, the research team observed mice that they had exposed to the same levels of radiation which humans receive during cranial radiotherapy. The microglia cells were sent into action and began removing the nodal connections from neurons, specifically the younger nodes of the synapses. Scientists believe that these younger nodes play an integral role in the formation of new memories, and the damage to these synaptic connections explain the changes in cognitive function after cranial radiotherapy that affects many patients. The study also found a correlation between the gender of the mice and the degree of damage that was suffered: male mice had more damage.
To counter these effects, research is being conducted to find ways to prevent this damage to nerve cells from happening. Blocking the receptor which the microglia use to remove the synaptic node from neurons has been tested in mice successfully, and the loss of critical synapses was reduced. Other possible methods to mitigate the loss of the synapses include reducing the local immune response in the brain to stop the microglia from overreacting.
Hinkle, Joshua J., et al. “Cranial Irradiation Mediated Spine Loss Is Sex-Specific and Complement Receptor-3 Dependent in Male Mice.” Scientific Reports, vol. 9, no. 18899, 11 Dec. 2019, https://www.nature.com/articles/s41598-019-55366-6.