Abstracts

Epileptic events elicit an increase in neuronal metabolism and an increase in cerebral blood flow (CBF), bringing oxygenated hemoglobin to the activated neurons. Whether CBF and oxygenation are adequate to meet metabolic demand in the focus and surround is unknown., We induced acute focal seizures in the rat neocortex by injection of 4-aminopyridine (4-AP, 15mM, 0.5 [mu]l). The local field potential was recorded to identify the ictal discharge. The partial pressure of tissue oxygen (pO2) and CBF were measured with two Clark-style polarographic oxygen microelectrodes and two probes of laser Doppler flowmetry located in the focus and surround. Optical spectroscopic imaging was used to measure deoxyhemoglobin (Hbr), oxyhemoglobin (HbO2) and total hemoglobin (Hbt)., The duration of ictal discharge ranged from 50 to 200 sec (n=15 rats). CBF in the focus increased 150.0[plusmn] 13.7 % (p[lt]0.05, n=4 rats) but decreased in the surround by 90.9[plusmn] 2.5% (p[lt]0.03, n=4 rats). Tissue pO2 decreased by 64.3[plusmn]7.8 % (p[lt] 0.05, n=5 rats) in the focus during the ictal discharge and then increased at the termination of ictal event. In the surround tissue pO2 increased by 120.5 [plusmn] 5.1 % (p[lt] 0.05, n=5 rats). The optical spectroscopic analysis showed the spatial extent of the perfusion and oxymetric responses., These results demonstrated a prolonged epileptic dip in both tissue and hemoglobin oxygenation during ictal events in spite of a dramatic increase in CBF in the region of focus. In the surround, pO2 increased in spite of a decrease in CBF, consistent with a decrease in neuronal activity and metabolism., (Supported by NIH NS043799-04 and NS049482-01].)