D-serine is a co-agonist at NMDA receptors in the brain but the study of this amino\ud acid is restricted by current techniques. I have designed highly sensitive D-serine\ud biosensors that permit accurate real-time recordings of D-serine in the brain in a\ud selective manner. I demonstrate that these tools are ideal for investigating factors\ud involved in the regulation of this amino acid and the role that D-serine plays in\ud excitotoxic cell death mediated via NMDA receptors.\ud I have established that the extracellular basal concentrations of D-serine in the rat\ud brain are heterogeneous and vary even within brain structures. This suggests that Dserine\ud is an important regulatory constraint for NMDA receptor activation, as\ud receptor response can only be potentiated in regions with low D-serine content.\ud Additionally, I show that these microelectrode biosensors have the potential to be\ud used in vivo to detected extracellular D-serine levels.\ud In addition I have observed real-time activity dependent regulation (both loss and\ud release) of D-serine by ionotropic glutamate receptor agonists AMPA, NMDA and\ud kainate, PAR1-agonist TFFLLRNH2 and high frequency stimulation in vitro in a\ud number of brain areas. A decrease in D-serine concentration is potentially\ud neuroprotective as it suggests a reduction in NMDA receptor activation. However,\ud D-serine release can be observed in regions where the co-agonist site of the NMDA\ud receptor is likely to be already saturated implying an alternative function of D-serine\ud in the brain. These findings indicate multifaceted regulation of this amino acid that is\ud brain-region specific.\ud Finally, I have investigated the role of D-serine release during models of stroke\ud (hypoxia and ischemia) and found that D-serine levels are reduced in brain regions\ud deprived of oxygen. This is ultimately neuroprotective as it will reduce over -\ud excitation at the NMDA receptor during these insults. In the more profound model of\ud stroke, oxygen-glucose deprivation, D-serine is eventually released. This release\ud precedes anoxic depolarisation and could therefore contribute to its initiation via\ud enhanced activation of the NMDA receptor
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