Effects of gamma-ray irradiation on rat brain energy metabolism: a ³¹P-NMR study

Abstract

Local gamma-ray irradiation is applied clinically (Gamma Knife^®) to functional neurological diseases such as epilepsy and trigeminal neuralgia. However, the neurophysiological mechanisms of such effects are not clear yet. The effects of gamma-ray irradiation on energy metabolism of rat brain were evaluated using ³¹P-nuclear magnetic resonance (NMR). Whole brains of Wistar rats were irradiated with a sub-necrotic dose (60Gy) of gamma-ray (Gammacell^® 40 Exactor, Nordian). One week after the irradiation, the brain slices (400 μm) were subject to ³¹P-NMR study (AMX300wb^®, Bruker). The slices were perfused with standard artificial cerebrospinal fluid bubbled with 95% O₂ +5% CO₂ in a test tube. Levels of high-energy phosphates, phosphocreatine (PCr) and γ-ATP, were measured after the high-K⁺ stress (60 mM) for 16 min, repeated with an interval of one hour. PCr and γ-ATP levels after the second high K⁺ stress were significantly lower in the gamma-ray irradiated rats than in the control rats (p<0.05), whereas there were no differences after the first stress. These results suggested that development of energetic tolerance to high K⁺ stress was reduced in gamma-irradiated brain. Such effects on energy metabolism of brain may influence the glutamate/glutamine cycle between neurons and astrocytes, hence neurotransmission was impaired. These mechanisms may play a role in the clinical application of gamma-ray to functional neurological diseases. [J Physiol Sci. 2007;57 Suppl:S116]