Synaptic transmission and glutamate transporters
In the central nervous system, the extracellular concentration of the neurotransmitter, L- glutamate, is critical both because of its role in synaptic transmission and its excitotoxicity. The actions of synaptically released glutamate are terminated by diffusion out of the synaptic cleft and by glutamate transporters expressed on neurons and astrocytes. Excitatory amino acid transporters, EAATs, are membrane proteins that use the electrochemical gradient of Na+, H+, and K+ ions to drive the concentrative uptake of glutamate. In addition, EAATs permit the opening of an anion channel uncoupled from amino acid uptake. Together these conductances allow the real time monitoring of glutamate transporters.
My research focuses on glutamate transporters and their function during synaptic transmission. Experiments in the lab incorporate a multidisciplinary approach of electrophysiological, imaging methods, and molecular biological approaches to study the activity of synapses and glutamate transporters.
One model system that we use to study the actions of glia and neuronal uptake are slices from cerebellum. The cerebellum is responsible for coordinated skilled movements and the control of muscle tone. The functional output of the cerebellum is through Purkinje cells. Each Purkinje cell receives excitatory input from thousands of parallel fibers and a single climbing fiber. These excitatory synapses are isolated from one another by Bergmann glia membranes that express a high density of glutamate transporters. In addition, glutamate released into the synaptic cleft is cleared via transporters found on the postsynaptic Purkinje cells. By recording and imaging Purkinje cells and Bergmann glia (see below), we study how transporters can influence the strength of synaptic signals and regulate the signal transduction pathways underlying cerebellar long-lasting plasticity. We are also using computer models and heterologous expression systems to study the biophysical properties of these molecules. By combining these methods, we aim to better understand glutamate transporters and their physiological roles in normal and pathological states.
Cerebellar Purkinje cell (above) and Bergmann glia (below) filled through a patch
pipette with Alexa 594 and imaged with a multiphoton microscope.
(Click
images for high resolution
graphic.)
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