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Anne M. Andrews, chemistry professor at Pennsylvania State University and symposium co-organizer, also studies serotonin, but she studies it in genetically engineered knockout mice that don't express the gene for the serotonin transporter. Her ultimate interest is in how serotonin is involved in psychiatric and degenerative disorders. Serotonin has been implicated in a number of psychiatric disorders, such as depression and anxiety, and in diseases associated with aging, such as Parkinson's and Alzheimer's. -------------------------------------------------------------------------------- "There is a great need for increased development of analytical methods for measuring brain chemistry in temporally resolved ways." -------------------------------------------------------------------------------- Sweedler Amatore PHOTOS BY CELIA HENRY Andrews Shippy ANDREWS USES a variety of techniques depending on the information she's looking for. Microdialysis allows her to measure basal levels of synaptic serotonin in the brain. However, microdialysis is slow, so she can't use it to distinguish between release and reuptake of serotonin as separate processes. For faster measurements, she also uses carbon fiber microelectrodes. She uses the carbon electrodes in an ex vivo preparation known as synaptosomes, which are liposomes prepared from the animal's brain tissue. "For 40 years, biochemists and neuroscientists have been using this preparation to study uptake and receptor binding," Andrews told C&EN. Traditionally, synaptosomes are used with radioactively tagged neurotransmitters. However, when Andrews and her colleagues weren't able to see any differences in the rate of serotonin uptake between wild-type mice and mice that had one copy of their serotonin transporter gene inactivated (known as heterozygotes), they concluded that the traditional method was not sensitive enough. "We'd already shown that the protein expression was decreased by 50%. In addition, those animals had a behavioral phenotype," she said. "We began to suspect that the classic radiometric assay was not sufficiently sensitive to detect modest changes." When they started using electrochemical detection methods, Andrews thought the measurements should be done in synaptosomes so that they could be compared with the traditional radiometric method. Another reason for choosing synaptosomes is that, unlike dopamine, serotonin is not restricted to certain parts of the brain. "When we use chronoamperometry in synaptosomes, the signal that we're generating comes from serotonin that we've injected," Andrews told C&EN. "We know what the source of our electrochemical signal is under those conditions." With chronoamperometry, Andrews is getting 60 measurements per minute. At first, the serotonin uptake rates seemed slow, but then Andrews realized that they should bubble oxygen through the synaptosome solution, which caused a 100-fold increase in uptake. "We think the fact that we couldn't detect changes in heterozygote animals was a combination of the fact that the radiometric technique was insensitive and we weren't doing the experiment under biologically relevant conditions," Andrews told C&EN |
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