Neuroimaging in Baboons

Abstract

The use of animal models is crucial because many important scientific questions require experimental designs precluded in humans by ethical considerations. These designs include experimental brain lesions, investigational treatments, untreated controls for disease, and invasive physiological monitoring. Important brain functions differ between primates and rodents (Berger et al., 1991), so some investigations of human-relevant physiology require nonhuman primate subjects. Additionally, development of new research techniques in nonhuman primates allows estimation of the data required to judge safety for later human applications, such as dosing and toxicology for a new computed tomography (CT) contrast agent. Baboons (Papio spp.) have been employed for neuroimaging studies for many years. A primary motivation for their use is their relatively large brain (approximately 185 mL as opposed to 55–110 mL for various macaque species). This advantage is especially salient, given theoretical and practical limitations on image resolution for important imaging methods. An additional advantage of baboons is their relative hardiness in the laboratory setting. The primary limitations of baboons for research, compared with macaques, involve larger bodies, less docile behavior, and lesser ability to learn. The larger size translates to higher space requirements for laboratory housing, and to increased strength, hence danger to humans if agitated. The other two limitations lead to difficulty in training baboons for awake studies. Some important neuroimaging studies can be performed in sedated animals. However, other experimental designs require interaction with the animal during the scan, and some physiological measurements are affected by sedation with any class of anesthetic (Grome and McCulloch, 1981; Mies et al., 1981; McCulloch, 1984; Nehls et al., 1990; Ueki et al., 1992; Engber