LTBK-06. Memantine increases dendritic arborization and integration of immature neurons after cranial irradiation

Cranial irradiation (IR) is a cornerstone in the treatment of high-grade pediatric brain tumors. While lifesaving, it is associated with severe sequalae in 50-90 % of the survivors, as they often show disabling cognitive dysfunction, declined IQ, impaired processing speed, anxiety and posttraumatic stress symptoms, resulting in poorer academic accomplishments and social isolation. Memantine (Mem) is a non-competitive NMDA receptor antagonist and a potent enhancer of neural plasticity. It is used in the clinical setting in the treatment of Alzheimer’s disease and dementias and has been shown to enhance cognition in post-IR cancer survivors. Nevertheless, while an improvement in synaptic plasticity has been documented in association to hippocampal neurogenesis, the exact mechanisms underlying Mem’s actions are yet poorly understood. The goal of this project is to further dissect the actions of Mem and identify factors that contribute to hippocampal neurogenesis. To this end, 20-day-old C57BL6/J mice were subjected to a single dose of 7 Gy whole brain irradiation and then supplied with Mem in the drinking water to obtain a steady-state plasma concentration of the drug. Animals were then sacrificed at different time points and the brains harvested for immunohistochemical staining, bulk-RNA sequencing and electrophysiological studies. Sholl analysis of the morphological data of the new-born neurons of Mem treated animals showed a statistically significant increase in coverage area (500µm2 vs. 250µm2, p= <0,0001) and number of dendrites (15 vs. 5, p= <0,0001) compared to non-treated individuals. Preliminary analysis of the electrophysiological responses revealed no changes in the gamma oscillations in Mem treated irradiated mice. The attained results will shed light on the mechanisms of action and take steps towards establishing Mem as a neoadjuvant therapy for children undergoing IR. Ultimately, we aim to ameliorate IR-associated neurocognitive impairment and improve the quality of life of pediatric cancer survivors.