Oregon Health & Science University
Glutamate is the primary neurotransmitter governing excitatory synaptic transmission in the central nervous system. Because glutamate is not enzymatically degraded, after release from vesicles into the synaptic cleft or from other sources, it must be removed from the extracellular space. This task is accomplished by Na+-dependent high-affinity glutamate transporters. Glutamate uptake by transporters prevents excitotoxicity and maintains the precision of synaptic transmission. In this thesis, I explored the role of transporters in controlling glutamate concentrations in and around synapses. In Chapter 1, we designed experiments to estimate the ambient concentration of glutamate in the extracellular space of rodent hippocampal brain slice. The value was ~25 nM, which is lower than the sensitivity of most glutamate receptors. Transporter function was necessary to maintain this low concentration of extracellular glutamate. We examined this finding in more detail in Chapter 2, exploring the distribution of ambient glutamate in the hippocampal neuropil. Extracellular glutamate is low throughout the neuropil indicating that transporters are not positioned to preferentially protect synaptic structures from ambient glutamate exposure. Instead, transporters prevent tonic activation of both synaptic and extrasynaptic receptors by maintaining low concentrations of ambient glutamate, likely due to the high density of transporters throughout the synapse-rich neuropil. These roles are integral in maintaining precise synaptic transmission.
Neuroscience Graduate Program
School of Medicine
Herman, Melissa A., "Control of extracellular glutamate by transporters in the CNS" (2009). Scholar Archive. 507.