Sampling fluid from slice chambers by microsiphoning

We have developed a simple technique that continuously samples perfusion fluid from an in vitro slice chamber and permits simultaneous electrophysiological recordings from a slice. This procedure uses a microsiphon that diverts approximately 1.5% of the total effluent of artificial cerebrospinal fluid from an interface slice chamber into a collection tube at a lower level outside the chamber. The tip of the microsiphon may be moved anywhere within the chamber without disturbing the slice. For optimum sampling of the release of substances from one area of a slice, the tip is positioned immediately downstream from the location being studied. Concentrations of several amino acids were measured to identify significant spatial and temporal characteristics of the technique and to demonstrate that spontaneous and induced release of amino acids from slices can be measured with adequate sensitivity and time resolution.