Susan Voglmaier, MD, PhD

Vesicle Trafficking and Neurotransmitter Release

Brain processes underlying behavior, cognition, and emotion involve communication between neurons by the regulated release of neurotransmitter from synaptic vesicles.  Synaptic vesicles reside in several functional pools in the presynaptic terminal that are defined by their location and probability of fusion upon stimulation.  The high frequency of transmitter release observed at many synapses requires mechanisms to recycle synaptic vesicle membrane, proteins, and transmitter locally at the nerve terminal.  Variation in the kinetics of vesicle recycling or mobilization from vesicle pools may shape the amount and pattern of neurotransmitter output, and hence contribute to information processing and some forms of synaptic plasticity.  We are using a variety of complementary approaches—including biochemistry, live cell imaging, and mouse genetics—to understand how trafficking of synaptic vesicle components regulates synaptic transmission.

We use and develop optical tools to image the dynamics of synaptic vesicle components.  Fusions of vesicular neurotransmitter transporters with a pH-sensitive GFP provide optical probes for imaging activity of neurotransmitter systems in individual neurons, circuits, and networks.  My lab has developed optical reporters of calcium dynamics and synaptic vesicle recycling based on the vesicular glutamate and GABA transporters (VGLUT1-, VGLUT2-, and VGAT-pHluorins), which are involved both in synaptic vesicle filling and trafficking.  The long-term goal of this line of research is to target differences in the regulation of transporter trafficking to normalize the balance of excitation and inhibition--in the case of VGLUT and VGAT--and the balance of cortical and subcortical circuit input--in the case of VGLUT1 and VGLUT2--in schizophrenia, autism, epilepsy, and other neuropsychiatric diseases.

Multiple mechanisms have been proposed to mediate the recycling of synaptic vesicles, but most models assume that the protein components of the vesicles recycle together.  However, specific sorting signals and protein interactions of the vesicular neurotransmitter transporters direct recycling of this protein to different pathways with kinetic and mechanistic differences. We are investigating the molecular mechanisms and regulation of individual synaptic vesicle protein recycling, which could result in activity-dependent alterations of synaptic vesicle (and plasma membrane) protein composition influencing transmitter release.  These mechanisms may contribute to the different physiological properties observed at different types of synapses.

Using live cell imaging, we demonstrated that VGLUT1, VGLUT2, and VGAT rely to differing extents on a novel pathway of synaptic vesicle protein recycling that uses the endocytic adaptor protein AP-3. The AP-3 pathway sorts vesicle proteins to pools with different probabilities of release, and may change the protein composition and release properties of individual synaptic vesicles. We are investigating the role of signaling molecules upstream of vesicle release. The mechanisms of action of atypical and experimental antipsychotics targeting presynaptic 5HT2A and mGluR2/3 receptors presumably converge at a final common pathway of decreased glutamate release from VGLUT2+ thalamocortical terminals. Working forward from presynaptic receptor activation and backwards from synaptic vesicle exocytosis, my lab is exploring presynaptic signaling networks upstream of glutamate release to identify novel therapeutic targets to normalize brain circuits in neuropsychiatric disease.

The specific expression of VGLUTs and VGAT makes it possible to identify the neurotransmitter phenotype of individual synaptic vesicles and boutons.  We have developed BAC transgenic mice expressing VGLUT1 and VGLUT2-pHluorin, which selectively label cortical and subcortical pathways, offering a unique opportunity to visualize activity in two discrete glutamatergic pathways into the prefrontal cortex. We hypothesize that selective modulation of synaptic vesicle recycling or other aspects of presynaptic function between VGLUT1 and 2 synapses could normalize the balance of thalamic and cortical input to cortical circuitry in neuropsychiatric disorders such as schizophrenia, bipolar disorder, hyperactivity, anxiety, and panic disorder.  VGLUT2, which may recycle by mechanisms associated with immature synapses, is highly expressed early in development, but is later replaced by VGLUT1 in cortex and hippocampus. This developmental remodeling of presynaptic circuit elements, along with synaptic pruning, may expose previously silent wiring defects during later stages of brain development in schizophrenia.  
We are interested in studying the effect of drugs, treatments, or genes on neurotransmitter release in specific brain regions and circuits that may be relevant to neuropsychiatric disease.  Our long term goal is to use these tools to gain insight into the pathophysiology of neuropsychiatric diseases and aid the development of novel therapeutics that alter synaptic transmission and behavior by altering neurotransmitter release.

Current Projects

• Molecular Mechanisms of Synaptic Vesicle Recycling
• Regulation of Glutamate Release as a Therapeutic Strategy in Schizophrenia
• Imaging Circuits, E/I and Cortical/Subcortical Balance
• Normalizing Presynaptic Dysfunction Resulting from Decreased Neuroligin Expression

Lab Members

Haiyan Li, PhD
Postdoctoral Fellow
[email protected]

Reno Reyes, PhD
Postdoctoral Fellow
[email protected]

Jody Williams
Administrative Staff
[email protected]

Lab Website

Academic community service and committee membership:

Psychiatry: Director, Research Residency Training Program; Diversity Committee-Co-chair Research Task Force; Residency Selection