PET imaging in the photosensitive baboon: case-controlled study.
OBJECTIVE
The baboon (Papio hamadryas spp) offers a natural primate animal model of photosensitive generalized epilepsy. This study compared changes in cerebral blood flow (CBF) during intermittent light stimulation (ILS) between photosensitive and asymptomatic baboons.


METHODS
Six photosensitive, epileptic (PS) and four nonphotosensitive, asymptomatic (CTL) baboons, matched for age, gender, and weight, were selected based on previous scalp EEG evaluation. Continuous intravenous ketamine (5-13 mg/kg) was used for sedation. Subjects underwent five sequential blood-flow PET studies within 60 min with 20 mCi (15)O-labeled water. Images were acquired in 3D mode (CTI/Siemens HR+ scanner, 63 contiguous slices, 2.4-mm thickness). Three resting scans were alternated with two activation scans during ILS. ILS was performed at 25 Hz for 60 s before to 60 s after the start of an activation scan. PET images were coregistered with MRI (3T Siemens Trio, T(1)-weighted 3D Turboflash sequence; TE/TR/TI, 3.04/2,100/785 ms; flip angle, 13 degrees). PET scans were reviewed and corrected for motion artifact. Resting scans were contrasted with activation scans and averaged independently for both groups. Quantitative CBF analyses were performed for the occipital and motor cortices.


RESULTS
The CTL baboons showed greatest ILS-induced activation in the left middle frontal and inferior temporal gyri, left brainstem structures and right postcentral gyrus, bilateral occipital lobes, and in the posterior cingulate gyrus and cerebellum. In contrast, the PS animals showed strongest ILS activation in the right anterior cingulate and medial orbital gyri, amygdala, globus pallidum, and left inferior and superior temporal gyri. A striking finding was the absence of occipital and variable motor cortex activation in the PS animals. Deactivations were noted in the right orbitofrontal and anterior cingulate cortices in the CTL baboons and in the posterior cingulate gyrus, brainstem and cerebellum of the PS animals.


CONCLUSIONS
The patterns of ILS-induced CBF changes differed between CTL and PS groups. These differences of activations and inhibitions suggest involvement of specific cortical-subcortical or networks in photosensitivity.
Szabó
C Akos
CA
South Texas Comprehensive Epilepsy Center, University of Texas Health Science Center at San Antonio, Texas 78284-7883, USA. Charles.Szabo@uhs-sa.com
Narayana
Shalini
S
Kochunov
Peter V
PV
Franklin
Crystal
C
Knape
Koyle
K
Davis
M Duff
MD
Fox
Peter T
PT
Leland
M Michelle
MM
Williams
Jeff T
JT
D000818:Animals; D016022:Case-Control Studies; D002540:Cerebral Cortex / Q000098:blood supply* / Q000000981:diagnostic imaging*; D004195:Disease Models, Animal; D004569:Electroencephalography / Q000706:statistics & numerical data; D020195:Epilepsy, Reflex / Q000175:diagnosis / Q000000981:diagnostic imaging* / Q000235:genetics*; D005260:Female; D005625:Frontal Lobe / Q000098:blood supply / Q000000981:diagnostic imaging; D007839:Functional Laterality; D021621:Imaging, Three-Dimensional; D008279:Magnetic Resonance Imaging / Q000379:methods; D009044:Motor Cortex / Q000098:blood supply / Q000000981:diagnostic imaging; D009778:Occipital Lobe / Q000098:blood supply / Q000000981:diagnostic imaging; D010104:Oxygen Radioisotopes; D010215:Papio; D010775:Photic Stimulation; D049268:Positron-Emission Tomography; D012039:Regional Blood Flow / Q000502:physiology; D013702:Temporal Lobe / Q000098:blood supply / Q000000981:diagnostic imaging; D014867:Water
D010104:Oxygen Radioisotopes; D014867:Water