The final talk of this day was by Jonathan Sweedler telling us about single cell neurobiology. His techniques mainly concerned various forms of chromatography. Single cell chromatography showed that serotonin is catabolized very quickly. Standard HPLC (high pressure liquid chromatography) was used to look at D-Aspartate and its role in neurons. They found that 80% of aspartate in certain sensory neurons is in the D-Form. This technique can even be used to analyze somata and processes of single neurons. He then went on to talk about his studies on the nitric oxide (NO) cycle. NO concentration in single cells can be measured by NO precursors and catabolites, using HPLC or electrophoresis. Single cell mass spectrometry is used primarily to study neuropeptides. This is being used in the Neuroproteomics Center on cell-to-cell signaling. A really neat MassSpac story was that they detected a prohormone neuropeptide (APGWa) which is not cleaved as predicted but the last two peptides stay fused and get bonded together by sulfate bridges. Interestingly, this dimer cannot be synthesized in vitro until now, presumably because in the neurons chaperones help folding the peptides in a way currently impossible in vitro. Mass spectrometry imaging can be used to identify the localization of neuropeptides in single neurons.