title: Functional imaging of dolphin brain metabolism and blood flow.
abstract: This report documents the first use of magnetic resonance images (MRIs) of living dolphins to register functional brain scans, allowing for the exploration of potential mechanisms of unihemispheric sleep. Diazepam has been shown to induce unihemispheric slow waves (USW), therefore we used functional imaging of dolphins with and without diazepam to observe hemispheric differences in brain metabolism and blood flow. MRIs were used to register functional brain scans with single photon emission computed tomography (SPECT) and positron emission tomography (PET) in trained dolphins. Scans using SPECT revealed unihemispheric blood flow reduction following diazepam doses greater than 0.55 mg kg(-1) for these 180-200 kg animals. Scans using PET revealed hemispheric differences in brain glucose consumption when scans with and without diazepam were compared. The findings suggest that unihemispheric reduction in blood flow and glucose metabolism in the hemisphere showing USW are important features of unihemispheric sleep. Functional scans may also help to elucidate the degree of hemispheric laterality of sensory and motor systems as well as in neurotransmitter or molecular mechanisms of unihemispheric sleep in delphinoid cetaceans. The findings also demonstrate the potential value of functional scans to explore other aspects of dolphin brain physiology as well as pathology.
authors.affiliation: SPAWAR Systems Center San Diego, Division 235, 53560 Hull Street, San Diego, CA 92152-5001, USA. sridgway@UCSD.edu
authors.forename: Sam
authors.initials: S
authors.lastname: Ridgway
authors.forename: Dorian
authors.initials: D
authors.lastname: Houser
authors.forename: James
authors.initials: J
authors.lastname: Finneran
authors.forename: Don
authors.initials: D
authors.lastname: Carder
authors.forename: Mandy
authors.initials: M
authors.lastname: Keogh
authors.forename: William
authors.initials: W
authors.lastname: Van Bonn
authors.forename: Cynthia
authors.initials: C
authors.lastname: Smith
authors.forename: Miriam
authors.initials: M
authors.lastname: Scadeng
authors.forename: David
authors.initials: D
authors.lastname: Dubowitz
authors.forename: Robert
authors.initials: R
authors.lastname: Mattrey
authors.forename: Carl
authors.initials: C
authors.lastname: Hoh
mesh_terms: D000818:Animals; D050681:Bottle-Nosed Dolphin / Q000033:anatomy & histology / Q000378:metabolism*; D001921:Brain / Q000098:blood supply* / Q000378:metabolism*; D008279:Magnetic Resonance Imaging / Q000662:veterinary; D008297:Male; D049268:Positron-Emission Tomography / Q000662:veterinary