Abstracts

Rationale: Located in the inner mitochondrial membrane, flavoproteins are oxidized to produce changes in endogenous fluorescence signals during metabolic activity. This autofluorescence has been applied to monitor aerobic energy metabolism and indirectly monitors neuronal activity by exploiting the close coupling between neuronal activity and mitochondrial metabolism. The relationship between optical maps of metabolism, blood flow, hemoglobin oxygenation and light scatter during epileptic events is not clearly understood and critical to an understanding of epileptic neurovascular coupling and non-invasive imaging of epilepsy. Methods: We induced acute focal ictal discharges in the rat neocortex by injection of 4-aminopyridine (4-AP, 15mM, 0.5 μl). Interictal spikes were induced with iontophoresis of bicuculline methiodide (BMI) in rat neocortex. The local field potential was recorded to identify the ictal and interictal discharges. For flavoprotein autofluorescence imaging, a 420-490nm excitation filter, a 510nm dichroic mirror, and a 510nm long-pass emission filter were used to measure the mitochondrial metabolism. Hemodynamic signals and light scatting were performed by intrinsic optical imaging at 570nm, 610nm and 800nm. Maps were thresholded at 50% of the maximum amplitude of the signal for comparison. Results: Both BMI interictal spikes and 4-AP spontaneous ictal events induced a strong change in autofluorescence. The maximum amplitude of fluorescence changes were 8.4±2.6 % (n=3 rats) and 2.1±0.5% (n=2 rats) for ictal discharges and interictal spikes, respectively. Metabolic maps had less vascular artifact than hemodynamic maps but were less focal than light scatter maps. Conclusions: The findings suggest that flavoprotein autofluorescence imaging might provide a powerful tool to map neuronal activity and mitochondrial metabolism in neocortical epilepsy.