The quantal release of neurotransmitter underlies information processing by the brain, but the basic mechanisms responsible for this mode of signaling remain poorly understood. What controls the tonic release of neurotransmitter, either by spontaneous vesicle fusion or by non-vesicular efflux across the plasma membrane? What determines the amount of neurotransmitter stored per synaptic vesicle, a poorly understood determinant of quantal size? What is the molecular basis for the corelease of two classical transmitters by one neuron, and for synaptic vesicle pools?
We previously identified three distinct protein families that transport classical neurotransmitters into secretory vesicles, but their intracellular location has made them very difficult to study. We have now developed a variety of biochemical and biophysical methods including fluorescence measurements, live cell imaging and electrophysiology that enable us to characterize their function. We have also begun to identify mechanisms that control transport activity, with important implications for the non-vesicular release of transmitter as well as the regulation of synaptic strength.
Synaptic vesicles reside in functionally distinct pools, and we have begun to identify the molecules that distinguish between vesicle pools. We are now using these differences to understand their physiological role in synaptic transmission and development. To understand why many neurons release two classical transmitters, we use genetic manipulation in mice together with biochemistry and physiology.
The presynaptic protein alpha-synuclein has a causative role in Parkinson’s disease and seems involved in essentially all forms of the disorder. However, the function of synuclein at the nerve terminal remains unknown. We have found that it inhibits neurotransmitter release, and are now elucidating the mechanism responsible.
In addition to classical neurotransmitters, peptide hormones and neural peptides sort to a pathway capable of regulated exocytosis but the mechanism by which they form has remained a major question in eukaryotic cell biology. We have recently identified some of the first components of the cytosolic machinery that produce dense core vesicles, and are now exploring their function using a combination of biochemistry and live cell imaging.
For all of these studies, we are developing systems to explore their role in synaptic transmission using electrophysiology and in behavior using genetic manipulation in mice.