Extracellular Fluid Collection and Analysis of Drosophila melanogaster Brain Tissue with μ-Low-Flow Push-Pull...

The development of methods to generate quantitative chemical content information from precise tissue locations is needed to understand fundamental cellular and tissue physiology. This work describes a method to perfuse the extracellular fluid of fly brains in vivo using μ-low-flow push-pull perfusion (μLFPP) for quantitative chemical content determinations. Miniaturization of push-pull perfusion probe designs allowed the development of methods for probe tip placement into and sampling from the fruit fly's brain. Perfusate analysis identified and quantified arginine, octopamine, histidine, taurine, glycine, glutamate, and aspartate. The perfusate data did not exhibit any statistical differences based on sex. The perfusate analysis was compared to hemolymph samples to confirm probe placement in fly brain tissues. The appearance of probe placement into the brain space was confirmed with the following observations. Hemolymph and perfusate samples were found to contain analytes unique to each sample type. Quantitated levels of perfusate were not a simple dilution of hemolymph content. Further, the discovery of perfusates with composition similar to both hemolymph and brain perfusate when damage was intentionally inflicted supports the observation that perfusates are distinct from hemolymph. The analysis of perfusate collected for greater than an hour of sampling exhibits the possibility of monitoring applications. Altogether, this work demonstrates the viability of performing μ-low-flow push-pull perfusion for in vivo studies of fly brain tissues to identify and quantitate neurotransmitter content.