Understanding the relationship between behavior and underlying brain function constitutes one of the most complex intellectual challenges today. Functional neuroimaging represents an essential technology toward meeting this challenge. The large number of animal models of human brain disorders that have been established in rats and mice makes these species ideal candidates for brain mapping. A central dilemma, however, in conventional neuroimaging techniques is that immobilization of the subject, necessary to avoid movement artifact, extinguishes all but the simplest behaviors. The result is that brain function of such core animal behaviors as aggression, mating, feeding, and fear, remains poorly understood. To address the problem of immobilization, we have recently developed a miniature, self-contained, fully implantable infusion pump that in freely-moving animals allows intravenous bolus administration of imaging radiotracers by remote activation. Now with proof of principle demonstrated and a working model of the pump in use, a number of critical milestones remain necessary for widespread application and use of this technology in the scientific community. We now propose a novel microbolus infusion pump (MIP) that will allow greater flexibility of this tool in a broad range of experimental environments. For applications in small table-top experimental paradigms, we propose to power the MIP by a transcutaneous radiofrequency power link to an external resonating inductive coil driven by a novel Class E transmitter. This will allow the MIP to be powered and triggered remotely, and will make the device independent of finite battery power. For use of the MIP in open cage paradigms, we propose the use of a battery, rechargeable in the animal's homecage using the radiofrequency power link that enables the MIP to also operate independently when the animal is roaming free. A frequency-gated, optical controller in this design will allow transcutaneous triggering of the MIP from several meters distance, insensitive to ambient light. To miniaturize the MIP for use in mice, we propose to design a miniature, pressurized liquid reservoir and drug ejection chamber, and to develop and validate a miniature electrothermal valve. Application of the MIP to brain mapping in freely moving rats, as well as mice will be tested in a small table-top experimental paradigm (Conditioned Fear Response), as well as in an open cage study (Morris Water Maze). Cerebral blood flow related tracer distribution will be assessed using [14C]-iodoantipyrine injections followed by autoradiography. Research is conducted by an interdisciplinary team to develop a tool that can be applied not only to the brain mapping of basic neuronal circuits underlying normal and abnormal behavior, but also to behavioral pharmacology and in-vivo physiologic studies in small animal models. ? ?
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