Demonstration of low flow push-pull perfusion

Methods to follow in vivo chemical composition provide information regarding the processes of intercellular communication. There is a need for methods that provide chemical information from small volumes of the central nervous system (CNS) without sacrificing neurochemical recovery. One method that offers potential for providing such information is push-pull perfusion. In this study a low flow push-pull perfusion system is introduced that provides high (70-80%) in vitro recoveries. A concentric probe design is used with a 27-gauge stainless steel outer cannula for saline infusion and an inner fused silica capillary for fluid withdrawal. Flow rates of 10-50 nl/min were reliably generated and were well matched in vitro. Sampling was performed in the striatum of an anesthetized rat generating a 0.5 microl sample every 12 min. Capillary electrophoresis was used to determine glutamate levels in each sample; the basal level was found to be 1.97+/-0.70 microM. The method described was also demonstrated to deliver L-trans-pyrrolidine-2,4-dicarboxylic acid through the perfusion solution while sampling. Post-sampling histological analysis demonstrates little tissue disturbance to the sampled region. These data provide evidence that low flow push-pull method is a viable alternative for studying neurochemical signaling in the CNS.