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

Background: In 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 method: We 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 (18)F-fluorodeoxyglucose (FDG) PET and CT.

Results: The new device did not substantially affect (18)F-FDG PET images. Repositioning of the rat's head across sessions and experimenters was at a level of submillimeter accuracy.

Comparison with existing method: The errors of radioactivity concentration of (18)F-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.

Conclusions: The developed fixation device is useful for longitudinal behavioral and brain imaging studies in rats.