A head-attachable device for injecting nanoliter volumes of drug solutionsinto brain sites of freely moving rats

We describe a head-mounted micropump-injection system designed for the infu sion of nanoliter volumes of drug solutions into discrete brain regions of the freely moving rats. Using a miniature step motor, the micropump-injecti on system can be readily constructed from commercially available supplies. In calibrating the micropump-injection system, we found that it will delive r a reliable volume of 50 nl per infusion over a 1-h period, with an infusi on given every 1 min. From in vivo testing, we also found that rats readily self-administered up to 100 infusions of D-amphetamine into the nucleus ac cumbens at regular intervals, suggesting that this system can deliver const ant volumes of infusions over time in freely moving rats. It (1) attaches e asily to an implanted guide, (2) is compact and durable, (3) weighs only 10 g, and (4) is well tolerated with no apparent discomfort to the animal. Th is system overcomes some of the weaknesses of currently used intracranial s elf-administration systems. Published by Elsevier Science B.V.