Changes in magnetization transfer MRI correlate with spreading depression-induced astroglial reactivity and increased protein expression in mice.
OBJECTIVE
Gliosis refers to a range of glial cell transformations that vary according to specific brain pathologic states. Disease, however, is not a prerequisite for gliosis because glial reactivity may also be seen in regions of increased physiologic activity. Our study tests the hypothesis that high-field-strength magnetization transfer MRI is a sensitive technique for detecting transient glial reactivity after experimental spreading depression, a relatively benign perturbation unaccompanied by cell injury.


METHODS
Unilateral neocortical spreading depression was elicited in mouse cerebral hemispheres and confirmed by transcranial blood flow and extracellular potential measurements. After 3 days, mice were imaged at 4 T using magnetization transfer techniques. Astroglial reactivity was determined immunohistochemically, and protein expression in control and experimental hemispheres was compared using proteomic techniques.


RESULTS
Sixteen ([mean +/- SD] +/- 3) spreading depressions (n = 10) were recorded in experimental hemispheres. Spreading depression was never observed in control hemispheres. At 3 days, an 8% decrease (p < 0.05, n = 4) in magnetization transfer signal intensity was measured in experimental hemispheres, which was associated with a 37% increase (p < 0.001, n = 4) in the intensity of glial fibrillary acidic protein staining. Proteomic analysis performed 3 days after the induction of spreading depression showed upregulation of at least 56 proteins, including extracellular and intracellular elements.


CONCLUSIONS
Magnetization transfer at 4.0-T MRI is a sensitive method for detecting glial reactivity and changes in protein expression not associated with cell injury. These results suggest magnetization transfer MRI techniques may have potential for detecting glial reactivity in physiologic processes such as learning and in early disease states.
Lascola
Christopher D
CD
Department of Radiology, Duke University Medical Center, Box 3808, Durham, NC 27710, USA.
Song
Allen W
AW
Haystead
Timothy A
TA
Warner
David S
DS
Verleysen
Katleen
K
Freed
Tiffany A
TA
Provenzale
James M
JM
D000818:Animals; D002540:Cerebral Cortex / Q000378:metabolism* / Q000503:physiopathology*; D013181:Cortical Spreading Depression / Q000502:physiology*; D005911:Gliosis / Q000175:diagnosis* / Q000378:metabolism / Q000503:physiopathology; D007150:Immunohistochemistry; D008279:Magnetic Resonance Imaging / Q000379:methods*; D008297:Male; D051379:Mice; D008810:Mice, Inbred C57BL; D011506:Proteins / Q000378:metabolism*
D011506:Proteins