Filopodia and Circuit Construction

The Smith laboratory has shown that the thin protrusions, called filopodia, seen on developing neural arbors are extremely dynamic, extending and retracting from growing branches of both axons and dendrites on timescales of just a few seconds. The Smith lab has also shown that filopodial dynamics are intimately and bidirectionally linked to synaptogeneisis processes and synaptic function. The zebrafish in vivo time-lapse movie at left illustrates the dynamics of a dendritic arbor growth (red marks a single dendritic arbor) and synaptogenesis (green shows synaptic puncta). Filopodial dynamics are now being studied with the goal of developing new strategies for the repair of damaged or degenerating nervous systems.

Array Tomography

Immunofluorescence microscopy is one cell biology's most useful and profoundly important tools, but present immunofluorescence methods remain severely limited, especially as applied to imaging dense and complex molecular architectures such as the brain's. The Smith lab is developing new immunofluorescence methods that provides a breakthrough capabilities to resolve single synapses, arbors and networks within intact brain tissues. Here, dendrites and synapses are visualized in mouse cerebral cortex.

Astrocytic Calcium Waves

The Smith lab discovered in the late 1980s that neuro-transmitters could induce propagating Ca waves in astrocytes and networks of astrocytes. These Ca waves subsequently have been implicated in regulating neural networks, brain blood flow, and the generation of new neurons during development and later life. The study of astrocytic Ca waves is now helping develop new strategies for the repair of damaged and degenerating brains

Presynaptic Ca Signaling

Neurotransmitter release is triggered by voltage-dependent Ca channel opening, via an increase in intracellular Ca ion concen-tration. The Smith lab has pioneered techniques for measuring and imaging presynaptic Ca signals, of which one is illustrated here. These studies are helping us to develop new approaches to the diagnosis and treatment of mental and neurological diseases

Growth Cone Cytomechanics

The Smith lab pioneered the use of high-resolution video imaging techniques to study the cytoskeletal dynamics of neuronal growth cones. Here, DIC time-lapse microscopy was used to image the retrograde flow of filamentous actin in an Aplysia growth cone and identify the importance of actin-myosin interaction in growth cone dynamics

DNA Microarray Technology

Microarrays have revolutionized the study of the molecular genetic bases of tissues in health and disease. As part of a collaboration with the Stanford laboratory of Patrick O. Brown, the Smith lab designed, constructed and operated the first reader for fluorecent cDNA microarrays. In the early years, this was the reader that read all Stanford microarrays, and it was the prototype for many subsequent custom and commercial microarray fluorescence readers. Stephen Smith was also a Co-inventor of the Axon Genepix, the most successful reader for spotted microarrays.

Synaptic Vesicle Function

The Smith lab pioneered the use of fluores-cent dyes to study neurotransmitter release mechanisms at CNS synapses. This image sequence demonstrated sensitivity adequate to detect the release of a single synaptic vesicle, and opened new avenues to the quantitaive analysis of synaptic function

Cell-Cell Adhesion Dynamics

Work in collaboration with the laboratory of Prof. W. James Nelson in the Department of Molecular and Cellular Physiology pioneered the understanding of the dynamics of cadherins and related proteins at sites of new cell-cell contacts in epithelial-derived cell lines.

Calcium Dynamics

Many important events of cellular signaling occur on scales too small for measurement by known techniques, and require modeling and computational simulation. The simulation results shown here suggests that voltage-dependent calcium channel opening quickly depletes calcium ions from the synaptic cleft and therefore that limited synaptic cleft volume may impact presynaptic function very strongly.

Neuronal Pacemaker Oscillation

Neurons generate rhythmic oscillations that result from interplay of voltage-dependent ion channels and intracellular calcium concentration dynamics. Some of the most powerful lessons have been learned from invertebrate neurons such as the R15 burster of Aplysia, illustrated here by a recording from an early collaboartion with Stuart Thompson.

Biomicrophotonics

The Smith lab has collaborated for many years with the Stanford laboratory Prof. James Harris (Electrical Engineering) on projects aimed at developing novel microphotinic sensors of biological function. One current project aims to develop wireless implantable imaging systems to monitor function stably over long periods of time in freely behaving rodents.