Short communicationsDevelopment of a removable head fixation device for longitudinal behavioral and imaging studies in rats

•We developed a novel head fixation device for behavioral and imaging studies.•It has an only small influence on the PET image in terms of attenuation of photons.•The heads of rats can be repositioned on a PET/CT bed at sub-millimeter accuracy.•The head attachment is removable from the rat's head.•The device is useful for combined behavioral and imaging studies.

BackgroundIn some behavioral neuroscience studies, an attachment is surgically fixed onto the head of an awake animal to allow the animal to perform learning tasks repeatedly in the same position in a task-training system. A recently developed task-training system enables operant conditioning of head-fixed rats within only a few days, and this system has been rigorously applied to record learning-associated neural activity using electrophysiological techniques. However, the head attachment of this device is made of metal and thus is not suitable for simultaneous brain imaging studies with X-ray computed tomography (CT), magnetic resonance imaging (MRI) or positron emission tomography (PET).New methodWe developed a novel head fixation device with a removable attachment to position the rat head precisely in both imaging and training devices across different sessions. The device consisted of a removable attachment, a clamp and a stage, all of which were made of PET/MRI compatible acrylic resin. We tested the usefulness of the device with 18F-fluorodeoxyglucose (FDG) PET and CT.ResultsThe new device did not substantially affect 18F-FDG PET images. Repositioning of the rat's head across sessions and experimenters was at a level of submillimeter accuracy.Comparison with existing methodThe errors of radioactivity concentration of 18F-FDG in the PET image were lower with the present attachment than with the conventional metal attachment. Repositioning accuracy was considerably improved compared with a visual inspection method.ConclusionsThe developed fixation device is useful for longitudinal behavioral and brain imaging studies in rats.