Effects of gamma ray irradiation on energy metabolism in the rat brain: a 31P nuclear magnetic resonance spectroscopy study.

OBJECT: Gamma Knife surgery (GKS) is performed to treat patients with functional neurological diseases, but the neurophysiological mechanisms of GKS's biological effects with subnecrotic doses remain largely undefined. The purpose of the present study was to investigate the effects of gamma irradiation on energy metabolism in the rat brain by using 31P nuclear magnetic resonance spectroscopy (31P-NMRS). METHODS: The whole brains of Wistar rats were irradiated with a subnecrotic (60-Gy) dose of radiation. One week after the irradiation, brain slices (400 microm thick) were incubated in standard artificial cerebrospinal fluid to undergo 31P-NMRS investigation. Changes in high-energy phosphate, phosphocreatine (PCr), and gamma-ATP, as well as inorganic phosphate levels before, during, and after ischemic stress for 64 minutes were measured. Histological findings were also evaluated using light and electron microscopy. The decrease in the PCr level was significantly slower during ischemia and recovery after reperfusion was significantly faster and greater in the gamma-irradiated rats than in the control animals. The gamma-ATP level after ischemia was also higher in the gamma-irradiated rats than in the controls. Neither neuronal damage nor astrocytosis was observed in the irradiated cerebral cortices. CONCLUSIONS: Gamma irradiation with a subnecrotic dose may have neuroprotective effects that maintain a more stable cellular phosphorylation potential after ischemic stress. Such effects of GKS on energy metabolism coupled with neurotransmission (glutamate-glutamine cycling between neurons and astrocytes) may play a role in the treatment of neurological disease.