In recent decades, the cure rates for adult and childhood brain tumors have improved. Unfortunately, many survivors now live with life-long side effects from the treatment itself. Radiation therapy is particularly damaging to the brain and results in long-term cognitive deficits. The majority of both laboratory and clinical investigation has focused on the negative effects of radiation on memory. The hippocampus, a brain structure important in memory formation where postnatal neurogenesis occurs, has been the sole focus. While memory is of great importance, deficits in attention and executive function may be equally debilitating for patients. Other brain areas, including the frontal cortex, control these functions and radiation effects on these non-neurogenic brain areas have been ignored. Moving outside the hippocampus to areas of the brain where neurogenesis does not occur, exciting new preliminary data indicate that neurons in the pre- frontal cortex are also susceptible to radiation-induced dysfunction. This challenges commonly held notions regarding the molecular and cellular mechanisms that underlie radiation-induced cognitive dysfunction. Such findings have the potential to explain fundamental aspects of radiation-induced cognitive decline. To identify such mechanisms we will use unique resources including simultaneous imaging and electrophysiological recordings of synaptic activity with radiation as well as in vivo assessments of persistent alterations in synaptic plasticity and dendritic structure in transgenic animals. In this proposal we will examine the role of acute glutamate toxicity following radiation, explore how synaptic function changes in the frontal cortex and determine the mechanisms leading to long lasting synaptic dysfunction. We will conduct the following aims; (1) define the role of glutamate toxicity and oxidative stress in the prefrontal cortex following radiation, (2) establish an animal model of radiation-induced attention and executive deficits and correlate these with alterations in synaptic function, (3) identify the role of epigenetic mechanisms in long lasting changes in synaptic structure and function following radiation. Knowledge of the early and late mechanisms involved will allow for the development of more effective preventative treatments or even reversal of pre-existing radiation-induced deficits.
The proposed research is relevant to public health in that the discovery of neuronal mechanisms underlying cognitive decline following therapeutic brain radiation is expected to transform our understanding of the damaging effects of radiation and reveal novel avenues for treatment. Thus the proposed studies are relevant to the National Cancer Institute and it's mission to support research to improve cancer treatment and rehabilitation.