An apparatus and behavioral training protocol to conduct positron emission tomography (PET) neuroimaging in conscious rhesus monkeys

Nonhuman primates offer a unique resource in neuroimaging research, providing the opportunity to manipulate appropriate biological and behavioral variables under well-controlled experimental conditions in an animal model that is closely related to humans, both functionally and neuroanatomically. The present report describes the development and standardization of PET neuroimaging protocols in conscious rhesus monkeys and their application to characterize the acute effects of cocaine on cerebral blood flow. Specific attention was devoted to the development of an effective and comfortable head restraint device to be used in the imaging of conscious monkeys. The restraint device was designed to attach to a standard primate chair to facilitate frequent immobilization. Subjects received extensive behavioral training prior to neuroimaging in order to ensure their comfort and minimize potential stress associated with the imaging protocols. Functional changes in cerebral blood flow were characterized in three subjects with the positron-emitting tracer 15O water following acute i.v. administration of cocaine. Regions of interest were defined on MRI scans with a high degree of accuracy. Cocaine caused pronounced increases in cerebral blood flow at 5 min postinjection that diminished markedly within 25 min. The results document the feasibility to conduct PET neuroimaging studies of cerebral blood flow in conscious nonhuman primates. Extension of the methodology to include brain activation during behavioral studies could contribute significantly to the growing discipline of behavioral neuroscience.