David Ruhl

David Ruhl
Ph.D. Candidate


Edwin R. Chapman

Research Description:

I am pursuing two primary projects in the Chapman lab. The first aims to determine the molecular basis of spontaneous ("miniature") synaptic transmission. These miniature synaptic events are both useful indices of synaptic strength and have been shown to play a homeostatic function of tonically suppressing local dendritic translation. There are multiple Ca-2+ sensing molecules implicated in this single-vesicle exocytosis (ex, synaptotagmin I, doc2α, doc2β, Ca-2+-sensitive GPCR) but a coherent model of the pathway(s) regulating miniature transmission (and whether/how they differ from the pathways regulating evoked transmission) is lacking. I am using patch clamping and optical methods to measure spontaneous release in primary hippocampal cultures of mice lacking one or a combination of these proteins, and am using pharmacological manipulations to dissect the pathways involved.

The second project concerns the basis of network oscillations in vitro. Coherent oscillatory activity - qualitatively similar to that observed in vivo - can be modeled in a culture preparation, and elimination of the asynchronous phase of neurotransmitter release abolishes these oscillations. In vitro modeling of such "persistent reverberation" is essential because the overwhelming complexity of in vivo neural circuits makes the dissection of variables underlying network behavior difficult. I've shown that knock-out of doc2α (which our lab identified as the putative Ca-2+ sensor for asynchronous release) abolishes persistent reverberation, consistent with an essential role for asynchronous transmission. Most existent models of reverberatory activity, however, have singled out NMDA currents or the overall network connectivity as the key factors. I am varying these parameters independently to develop a quantitative model of their relative importance. NMDAR function is varied pharmacologically, connectivity is varied by culturing networks of various densities on glial microislands, and we are currently developing a method (with initial success) to systematically vary the kinetics of exocytosis. This will help clairify they synaptic basis of coherent neuronal oscillations.