Neuronal and Glial Cell Populations in the Piriform Cortex Distinguished by Using an Approximation of q-Space Imaging after Status Epilepticus
Shawnee Eidta,
Edward J. Kendalla,b and
André Obenausb,c
a Division of Biomedical Engineering, University of Saskatchewan, Saskatoon, Canada
b Department of Medical Imaging, University of Saskatchewan, Saskatoon, Canada
c The Radiobiology Program, Loma Linda University, CA
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FIG 1. Spatial and temporal evolution of injury after pilocarpine-induced seizures. ROIs—piriform cortex (PC) and amygdala (A)—are defined on the first control image. Increased signal intensity in the piriform cortex and amygdala returned to control levels by 7 days. Diffusion maps were generated from unweighted (b = 0 s/cm2) and weighted (b = 30,000 s/cm2) images. Note increased signal intensity in the piriform cortex (arrows); corresponding hypointensities are seen on ADC maps, particularly at 12 hours (arrows).
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FIG 2. Typical results from a pilocarpine-treated animal at 12 hours after seizure induction illustrate the incremental contrast changes associated with increasing diffusion weighting (b value) during the evolution of injury. Note the decrease in signal intensity with increased b-value weighting.
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FIG 3. Plot of ADC versus b value in the rat piriform cortex-amygdala complex after pilocarpine-induced seizures. An isochromatic population features contiguous ADC values that fall on a horizontal line. Dotted line on the control plot illustrates the two isochromats in control animals. The line for low b value (nonzero slope) likely represents a heterogeneous cellular population, whereas the zero-slope line is likely composed of a more homogeneous cellular population. After seizures, ADC decreases, and control isochromats realign (12 and 24 hours). At 7 days, an additional isochromat emerges; this may reflect the histologically evident gliosis in the piriform cortex.
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FIG 4. Extrapolation from our dataset to high b values yielded mean displacement and probability of zero-displacement plots.
A, Plot shows the transient decrease in mean proton displacement after seizure-induced injury. A moderate decrease is evident in the mean diffusion distance that returns to control levels by 7 days.
B, Similarly, the probability of a proton having zero displacement after seizure induction rapidly and markedly decreases at 12 hours. By 24 hours, this rebounds, indicating transient changes in the tissue matrix in the piriform cortex. By 7 days, the probability of zero displacement is reduced compared with that in control animals. Together, these extrapolation parameters support tissue remodeling that occurs as result of seizure-induced lesions.
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FIG 5. Cresyl violet (A and B) and silver impregnation (C and D) stains of the piriform cortex (magnification x10).
A, Sections in a control rat after imaging shows no loss of neurons. Note the density of darkly stained neuronal nuclei in layers II and III.
B, Seven days after the induction of seizures, marked neuronal loss and vacuolization of layers II and III are seen. Note the decreased neuronal density of layer II (arrows).
C, Section in a control animal confirms the lack of neuronal loss.
D, Few argyrophilically stained neurons (arrowheads) are visible deep in the piriform cortex 7 days after seizure induction, because most degeneration took place earlier. Note the loss of neurons in layer II (arrows) and vacuolization of layer III.
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FIG 6. GFAP-stained sections of the piriform cortex-amygdala complex.
A, Control section reveals a uniform and diffuse staining pattern.
B, At 12 hours, section shows increased staining properties, particularly at the intersection of layer I and II (arrows).
C, This staining pattern was exacerbated at 24 hours, with increased vacuolization in layers II–IV (arrows).
D, Seven days after seizures, GFAP staining is substantially increased in layers I, II and IV. However, layer III (region bounded by dotted lines) is virtually devoid of GFAP staining but stains with OX42, an immunologic stain for microglia (data not shown). G indicates gliosis.
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