Using Positron Emission Tomography Imaging of the Parrot Brain to Study Response to Clinical Pain
To advance veterinary analgesia therapy, we developed methodology for positron emission tomography (PET) imaging of Hispaniolan parrots (Amazona ventralis).
Four adult Hispaniolan parrots (265–315 g, age 15+ years) were scanned under isoflurane anesthesia with 2-deoxy-2-[18F]-fluoro-D-glucose (FDG); 1 mCi was administered intravenously (IV) while birds were in the University of Wisconsin (UW) microPET P4 (Concorde Microsystems, Knoxville, TN, USA).1 To aid compartmental model analysis, studies were first performed with transmission scans followed by emission scans begun at FDG injection. In these kinetics studies, two parrots were positioned to obtain cardiac images for determination of blood pool–time activity curves, and two parrots were positioned to observe the time course in the brain. All four parrots were imaged in control and arthritic conditions in the subsequent pain response study. Four hours prior to FDG injection, the right tarsal joint was injected with either 0.1 ml saline (control) or 3 mg sodium urate microcrystals in saline (experimental arthritis). Birds were kept alone in quiet darkened cages for 30 minutes following FDG injection, then anesthetized and positioned for scanning. PET scans were obtained during the period 45–95 minutes following FDG injection.
Analysis was performed using SPM and Spamalize.2 Magnetic resonance imaging (MRI) scans, acquired at the UW Veterinary School, were inspected for gross differences between subjects, and one image was selected as a template. Lacking a parrot brain atlas, the template MRI was manually rotated to correspond to the orientation in a chick brain atlas.3 Control and stimulus PET images were manually registered by rigid body rotations and translation to the MRI template to within 1 mm. A brain mask drawn on the MRI template was applied to all 8 PET images, which were then further aligned automatically by rigid body rotations and translations and smoothed with a 4-mm kernel. A whole-brain voxel-wise t-test was performed comparing the images of the four birds in the stimulus vs. the control state. Based on the resulting statistical parametric map, regions of interest were drawn, normalized to whole brain image intensity, and compared between stimulus and control conditions.
Preliminary analysis suggests increased glucose metabolism under the arthritis condition occurs in the portion of the avian brain called the ectostriatum. Anatomic identification of regions needs to be refined with further studies. The method using FDG shows promise for PET imaging of parrot brain function, and further work is planned to study where in the parrot brain kappa opioid receptor occupancy is affected during the same pain model of arthritis.
Funding was provided by the University of Wisconsin School of Veterinary Medicine Companion Animal Fund.
1. Tai, C., A. Chatziioannou, S. Siegel, J. Young, D. Newport, R.N. Noble, R.E. Nutt, and S.R. Cherry. 2001. Performance evaluation of the microPET P4: a PET system dedicated to animal imaging. Phys. Med. Biol. 46:1845–1862.
2. Oakes, T.R. Spamalize. http://tezpur.keck.waisman.wisc.edu/∼oakes/spam/spamframes.htm. (VIN editor: This link was not accessible as of 1-27-21.)
3. Kuenzel W.J., and M. Masson. 1988. A stereotaxic atlas of the brain of the chick (Gallus domesticus). Johns Hopkins University Press, Baltimore, MD.