Electrochemical measurements of transmitters in flies, at cells, and from transmitter vesicles
Conference contribution, 2013
We have developed three electroanalytical methods to measure neurochemicals in ultrasmall biological environments. First, voltammetry in the fly brain has been used to understand the drug action. We have used this to study the action of methylphenidate on that of cocaine with an eventual goal of understanding and remediating cocaine addiction. Second, we have used small electrodes to measure neurotransmitter release from single cells, a method that has become commonplace after twenty years. Here, we have analyzed amperometric peaks corresponding to release at PC12 cells and found stable plateau currents during the decay of the peaks, indicating closing of the vesicle after incomplete release of the vesicular content. From careful analysis of these data, we have proposed a process for most exocytosis events where the vesicle partially opens to release transmitter and then closes directly again, leaving the possibility for both a stable pre and post spike foot to be observed with amperometry. Third, those experiments correlate well with those from the electrochemical cytometry method we developed to count electroactive molecules in individual synaptic vesicles in directly sampled populations from cells or brain tissue. With this method we can compare the total numbers of molecules to those released and only a fraction is in fact released both at cell models and in mammalian brains. Partial release is important in that it produces a new pharmaceutical paradigm and could be important in understanding learning and memory. It also makes it clear that the dynamics of vesicle opening, controlled largely by lipids, might be an important characteristic in neurotransmission.