Neuronal and Glial Cell Populations in the Piriform Cortex Distinguished by Using an Approximation of q-Space Imaging after Status Epilepticus

Abstract

BACKGROUND AND PURPOSE: Temporal lobe epilepsy produces an injury cascade that includes neuronal loss and gliosis. The pilocarpine model reliably reproduces the symptoms of temporal lobe epilepsy and the resulting neuronal glial changes can be accurately depicted on diffusion-weighted images. The judicious choice of diffusion-encoding gradients can isolate multiple apparently isochromatic diffusing populations, but the assignment of these populations to specific tissue characteristics has been difficult. We sought to distinguish neuronal tissue from glial cell-infiltrated tissue by using signatures from unique spin populations obtained from an approximation of q-space imaging.

METHODS: Ten male Sprague-Dawley rats received pilocarpine injections to induce seizures. All animals underwent diffusion-weighted imaging at 12 hours, 24 hours, and 7 days. At least two animals were selected for histologic analysis at each imaging time point.

RESULTS: The results indicated that seizure-induced neurologic dysfunction may have been reflected in the emergence of new spin populations. In the piriform cortex-amygdala region of interest, the mean free diffusion path increased from 12 to 20 μm within 12 hours of seizure onset and persisted for at least 7 days. These results were temporally correlated with histologic evidence of necrotic changes.

CONCLUSION: Our results suggest that even incomplete sampling of q space can provide useful physiologic information.