Most behavioural studies using microdialysis sampling require tethering of the animal to the microdialysis system so that the animal is freely moving but not freely roaming.  In this paper, we describe an on-animal separation-based sensor that combines microdialysis sampling with microchip electrophoresis.  The goal is to develop a miniaturized device that can be placed on-animal and is capable of continuously monitoring drug and neurotransmitter concentrations in the brains of freely roaming sheep. Such as device, combined with video recording, will make it possible to directly correlate in vivo concentrations with animal behaviour.  Microchip electrophoresis is employed for the analysis since it makes it possible to separate and detect several analytes simultaneously with good temporal resolution. Analytes are detected using electrochemical detection. This detection mode is particularly well suited for such portable analysis systems since the electrode and the potentiostat are easily miniaturized. The current on-animal system is about the size of a lunch box and is run by a laptop battery.  The instrument is remotely controlled using telemetry. The system was first demonstrated by monitoring the generation of nitric oxide from subcutaneous infusions of nitroglycerin in freely roaming sheep. Recent progress on the development of an on-animal sensor for the continuous monitoring of biogenic amines in brain microdialysis samples will be presented.

The authors gratefully acknowledge the support of the NIH National Institute of Neurological Disorders and Stroke (NS042929 and SBIR NINDS 64644).