Radiation treatment is a crucial tool for treating brain tumors, but it has the unfortunate side effect of promoting cognitive decline. One of the pathways that this is believed to occur is through decreased neurogenesis in the dentate gyrus of the hippocampus.
Manda et al recently investigated the support for this hypothesis using a mouse model of irradiation. Mice in the irradiation group had about 50 +/- 5 immature cells in the dentate gyrus as opposed to about 200 +/- 30 in the control group, a statistically significant decrease. The irradiation group also had about 5 +/- 1 proliferating cells in the dentate gyrus as opposed to about 17 +/- 2 in the control group, another statistically significantly decrease.
The researchers also proposed a treatment for the damage due to irradiation: pretreatement with melatonin. Melatonin is good as crossing the blood-brain barrier because it is naturally found in the brain, and it is proficient at scavenging free-radicals and reducing thus reducing oxidative stress.
Compared to the non-melatonin irradiattion treatment groups (noted above), the melatonin groups had on average 35% more immature cells and 25% more proliferating cells. Also, the melatonin had no statistically significant effect in non-irradiation treatment groups, suggesting that the reason for this difference was due to free-radical scavenging and reduced oxidative stress.
If it is true that decreased neurogenesis is responsible for the cognitive behavioral decline following brain irradiation, then that provides additional evidence for the importance of neurogenesis to cognitive function. This study also has obvious possible implications to the treatment of brain tumors in neurology.
Manda K, Ueno M, Anzai K. 2009 Cranial irradiation-induced inhibition of neurogenesis in hippocampal dentate gyrus of adult mice: attenuation by melatonin pretreatment. Journal of Pineal Research 48: 71-78. doi: 10.1111/j.1600-079X.2008.00632.x.