SYSTEMIC NITRIC-OXIDE SYNTHASE INHIBITION DOES NOT AFFECT BRAIN OXYGENATION DURING CORTICAL SPREADING DEPRESSION IN RATS - A NONINVASIVE NEAR-INFRARED SPECTROSCOPY AND LASER-DOPPLER FLOWMETRY STUDY

Cortical spreading depression (CSD) has been implicated in the migrain e aura and in stroke. This study demonstrates near-infrared spectrosco py (NIRS) for the first time as capable of noninvasive on-line detecti on of CSD in the pentobarbital-anesthetized rat. CSD was accompanied b y a brief and rapid increase of regional CBF (by laser-Doppler flowmet ry) to 200-400% baseline. NIRS demonstrates that this hyperperfusion i s associated with concentration increases of oxyhemoglobin, while deox yhemoglobin decreases. Simultaneously, oxygen partial pressure, measur ed on the brain surface with a solid-state polarographic probe, was sh own to be raised by at least 14 mm HE during CSD. Oxygen-dependent pho sphorescence life-time quenching measurements confirmed this finding. NIRS data on cytochrome aa(3), however, showed a CSD-related shift tow ard a more reduced state, despite raised blood oxygenation. This may s uggest either limited O-2 transport from the blood to mitochondria or decreased oxygen utilization during CSD as supposed by theories about compartmentalization of energy metabolism favoring glycolytic rather t han aerobic energy supply during CSD. However, the data on cytochrome aa(3) warrant caution and rue discussed critically. Nitric oxide synth ase inhibition by systemic application of N'-nitro-L-arginine had no s ignificant effect on the perfusion response or the tissue Po-2 during CSD. During most CSD episodes, a brief decrease in MABP by 4-8 mm Hg w as noted that might be caused by functional decortication during CSD.