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First published online July 20, 2006
Journal of Experimental Biology 209, 2902-2910 (2006)
Published by The Company of Biologists 2006
doi: 10.1242/jeb.02348

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Functional imaging of dolphin brain metabolism and blood flow

Sam Ridgway^1,2,*, Dorian Houser³, James Finneran¹, Don Carder¹, Mandy Keogh¹, William Van Bonn¹, Cynthia Smith¹, Miriam Scadeng², David Dubowitz², Robert Mattrey² and Carl Hoh²

¹ SPAWAR Systems Center San Diego, Division 235, 53560 Hull Street, San Diego, CA 92152-5001, USA
² School of Medicine, University of California, San Diego, CA 92093, USA
³ BIOMIMETICA, 7951 Shantung Drive, Santee, CA 92071, USA

View larger version (131K): [in a new window]   Fig. 1. A trained dolphin slides out of the water onto a padded transport mat. (A) Dolphin swims around its bay enclosure. (B) The dolphin is signaled to station in front of the trainer. (C) The dolphin slides out onto the padded transport mat. (D) The padded sides of the transport mat are brought together so that the dolphin is secure in the mat with the lateral walls up and fastened.

View larger version (26K): [in a new window]   Fig. 2. Unihemispheric slow waves appearing on the left brain hemisphere EEG 1 h after a dose of 0.55 mg kg-1 of diazepam. ECG, electrocardiogram.

View larger version (168K): [in a new window]   Fig. 3. (A) Ultrasound of the vetrum of the dolphin's neck showing the common brachiocephalic vein (outlined by arrows) where the ligand was injected (in the past this vein was sometimes called innominate). (B) Illustration from a dissection showing the anatomy of the area.

View larger version (127K): [in a new window]   Fig. 4. MRI scan of dolphin WEN with a 0.5 T AIRIS II open scanner. The animal rests on a thin rubber pad. The forward half of the body rests on the scanner while the rear body rests on a special table constructed for dolphin scans. Attendants stabilize the animal and keep it wet while the trainer is stationed in front of the dolphin. A standard human back coil is placed around the dolphin's head immediately behind the blowhole to cover the area of the brain.

View larger version (95K): [in a new window]   Fig. 5. (A) Time-of-flight magnetic resonance image (MRI) from dolphin WEN demonstrating anterior blood flow through arteries of the brain outlined by the box. (B) Fused MRI and SPECT images from co-registered scans made in the same dolphin. The colored region corresponds to a reduction in blood flow; the color bar indicates the relative degree of blood flow reduction with red indicating maximum reductions in blood flow. The yellow arrow indicates the central venous sinus. The red arrows indicate the homolog cerebral artery on the right side of the brain that does not show blood flow reduction. Registration, image analysis and fusion were performed with ANALYZE.

View larger version (95K): [in a new window]   Fig. 6. Four planes from a control FDG PET scan of dolphin WEN registered to a 0.5 T scan of the same animal. No diazepam was given before the ligand injection. (A) left sagittal section (B) right sagittal section showing the vertex of the skull (V) and the planes of the axial section (Ax) and coronal section (Cx). (C) The coronal section showing the left nasal cavity (Ln), the right nasal cavity (Rn), and the planes of the axial section (Ax), left sagittal section (Lx), and the right sagittal section (Rx). (D) Axial section. The color bar indicates relative degree of glucose metabolism with red indicating maximum.

View larger version (86K): [in a new window]   Fig. 7. A subtraction of a diazepam scan from a non-diazepam scan of dolphin WEN registered to twelve 3.0 T MRI sections of dolphin MAY. From left to right: coronal (A-C), axial (E-G), left sagittal (I-K) and right sagittal (M-O). Lines on scan sections (D,H,L,P) at the bottom of each column indicate the plane of sections from the three scans in the same column above. The color indicates the relative degree of metabolic reduction in the diazepam scan with red indicating maximum reductions in glucose consumption. In this series there is an overall reduction in metabolism in the right brain hemisphere; however, there are some areas of lower metabolism in the left hemisphere, especially in frontal areas.

View larger version (115K): [in a new window]   Fig. 8. Comparison of four sections each of two different scans of dolphin OLY. The left column (A-D) shows a scan without diazepam while the center column shows sections from a scan with diazepam (E-H). Overall, metabolism is lower in the left hemisphere. The color bar indicates the relative degree of glucose metabolism in sections A-H with red indicating maximum. The right hand column shows oblique axial scans (as indicated in the upper right, section I) of dolphin MAY's MRI, to which have been registered the difference volumes between the two scans. In sections J-L, the colored regions correspond to a reduction in metabolism in the diazepam scan; the color indicates the relative degree of metabolic reduction with red indicating maximum reductions in glucose consumption.