Current medical practices for patients suffering from brain cancer involve the irradiation of the brain. This technique is used to slow the progression of the cancerous proliferation and increase the survivability of patients. However, according to a recent study published in the journal Proceedings of the National Academy of Sciences, patients who undergo this irradiation therapy are more susceptible to cognitive function deterioration.
The research team from the University of California, Irvine, from the United States, consisting of professor Vipar Parihar and professor Charles Limoli, investigated the effects of cranial irradiation on laboratory mice. The results of their investigation show that the radiation exposure is responsible for neurodegenerative changes in the architecture of the brain. These changes are similar to the neurodegenerative changes that occur in patients suffering from diseases such as Alzheimer’s or Huntington’s.
Cranial irradiation therapy is currently the leading therapy scheme used for all forms of adult and pediatric brain cancer. This is due to its ability to stop or at least limit the further growth of the tumors. Although it increases the survivability rates and lifespan of patients, cranial irradiation also accounts for reducing the life quality, through irreversible cognitive damage. The exposure of the CNS (central nervous system) to radiation causes memory problems, attention disorders, learning impairments and other cognitive damage.
To better understand the implications of radiation exposure, the research team used laboratory mice. These mice were exposed to two levels of radiation, 1 Gy and 10 Gy respectively. These doses of radiation are both much lower than the maximum levels of radiation that the central nervous system can suffer before it gets damaged. After 10 and 30 days, the research team killed the mice and used their brains for further investigation. Specifically, they investigated the hippocampus, which is the structure of the brain involved in memorizing and learning.
The researchers revealed that there were dose-dependent reductions caused to the dendrites of the neurons. These reductions involved the area and the length of the dendrites, and the branching between neurons. All of these reductions were found after the 30 day mark. Furthermore, the number and the density of the bulbous extensions and the dendritic spines, decreased. Dendritic spines are an important part of the connections formed inside the central nervous system, being associated with memory storage. The correlation between the number of dendritic spines and the density of the synapses is responsible for the cognitive abilities of each individual.
Huntington’s, Alzheimer’s, and other neurodegenerative diseases are characterized by the reduction of the dendritic complexity. Furthermore, the abnormalities of the dendritic spines can be associated with other diseases, such as AIDS-related dementia, temporal lobe epilepsy, Rett’s, Down’s, and Fragil-X syndromes.
The two researchers conclude that the reduction of the dendritic spine density and the persistence of the neurodegenerative damage caused by irradiation for more than 30 days is consistent with the fact that the damage caused is irreversible.