Imaging White Matter Signals in Epilepsy Patients

Abstract

We studied 15 temporal lobe epilepsy patients who presented with either neocortical or mesial temporal lobe epilepsy. Resected tissue from these patients was studied with neuromolecular imaging (NMI) using miniature carbon-based BRODERICK PROBE® stearic and lauric acid sensors. In separate studies, a sensor was inserted into neocortex or hippocampus, specifically into individual layers of neocortical temporal gyrus as well as temporal stem and hippocampal pyramidal layer, dentate gyrus, alveus, and subiculum. The catecholamines, dopamine and norepinephrine, and the indoleamine, serotonin, as well as ascorbic acid, an enzyme catalyst in the dopamine metabolic pathway, were detected in separate electroactive signals by these sensors in real time. Results showed that gray matter and white matter were readily distinguished both by characteristic microvoltammetric waveforms and by concentration differences, that is, (1) electroactive species for catecholamine signals in white matter were diffusion waveforms whereas the indoleamine waveform was an adsorption waveform and (2) concentrations of neurotransmitters were significantly lower in white matter than in gray matter. White matter signals were detected and distinguished from gray matter signals in both neocortical and hippocampal neuroanatomic substrates. Results showed that an average of 80% of patient electroactive signals for white matter in the three white matter structures were positive both for waveforms and for concentration characteristics. Another 21.4% and 10% were partially positive for white matter in alveus and subiculum, respectively, that is, positive for concentration characteristics but not positive for both catecholamine and indoleamine waveforms. An average of 90% of patient electroactive signals for gray matter were positive both for waveforms and for concentrations. Thus, NMI with these specialized sensors provide a unique technology for detecting, monitoring, and measuring neurotransmitters and related neurochemicals in white matter vis-a-vis gray matter in temporal lobe epilepsy patients.