The goals for my laboratory are to uncover mechanisms of synapse regulation in the mammalian brain and to understand how perturbations of synaptic transmission contribute to neurological diseases. Our studies utilize technology we developed to examine the biophysical, structural, and functional properties of individual synapses and dendritic spines. This is accomplished using novel microscopes that allow us to stimulate individual postsynaptic terminals directly while monitoring evoked electrical and biochemical signals. In addition, we design experiments in which effects of signaling pathways in individual cells are isolated and in which pre- and postsynaptic effects of perturbations are clearly separate. Our research has revealed a rich set of regulatory mechanisms and cellular specializations that allow each synapse to independently control the biochemical and electrical consequences of its stimulation. By applying the same quantitative and rigorous analysis of synaptic transmission to the study of rodent models of human disease, we have uncovered synaptic perturbations that likely contribute to the pathogenesis of tuberous sclerosis complex, an autism spectrum disorder, and Alzheimer's disease, a common late-onset form of dementia.
In all our studies, we use optical approaches to visually identify the active synapse and monitor activity in the postsynaptic terminal. This allows us to understand how the morphological and biophysical characteristics of the synapse affect its function. In addition, we use fluorescence-based reporters of cellular functions to study activity-dependent changes of the synapse that might not be revealed by the analysis of electrical signaling alone. With these approaches we are able to monitor the activity of signaling cascades in real time at individual synapses and thus preserve and understand the time and spatial dependence of pathway activation. Our analyses always include electrophysiological studies to reveal the role of the signaling pathway in regulating synapse function.
In the mammalian brain, most synapses communicate via the release of the neurotransmitter glutamate. Glutamatergic synapses are typically made onto the heads of dendritic spines, small (<1 femtoliter) cellular compartments that are separated from the rest of the cell by a thin neck. Many forms of synaptic plasticity are triggered by the transient activation of signaling pathways within the spine. The small size of spines, along with the heterogeneous and dynamic nature of synapses, poses great challenges to understanding the electrical and biochemical signaling pathways that underlie synaptic plasticity. To overcome these obstacles, we designed and built microscopes that combine two-photon laser-scanning microscopy (2PLSM) and two-photon laser photoactivation (2PLP). We use these microscopes to monitor and manipulate signaling cascades in individual dendritic spines in real time, while delivering controlled stimuli to the postsynaptic terminal. Because of the properties of two-photon excitation, we are able to use brief (~500 microsecond) laser pulses to release glutamate within brain slices and deliver stimuli that mimic the spatiotemporal profile of endogenously released glutamate.
My laboratory will continue its research into the mechanisms of synaptic plasticity in the mammalian brain. As motivated by the biology, we will continue to develop novel imaging and electrophysiological approaches for the analysis of synapse function. Our approach of studying signaling systems in situ—i.e., at the synapse—combined with rigorous electrophysiological and biophysical analysis will reveal the mechanisms of plasticity that control the synapse in the normal state and that are perturbed in human diseases.