Urban Lab Research Activities

Overall goals
Currently, work in my lab focuses on understanding the physiological mechanisms underlying the functional and computational properties of brain neuronal networks, focusing on the olfactory system.  In particular, I am interested in describing the detailed anatomical and physiological properties of cells and synapses, and then constructing models that provide insight into how these physiological properties give rise to the functional circuits that transform and store information in the brain.  My goal is to use these models to get at the underlying computations that these physiological systems can be seen as implementing.

Here I outline the main lines of research currently going on in my lab, providing some detail about the issues that we seek to address and about the approaches we are taking. 

Outline of research

Lateral inhibition in the main olfactory system.  The working hypothesis of this work is that inhibitory interactions between nearby mitral cells can be seen as suppressing particular signals, allowing neurons to engage in a sort of local competition.  This competition results in some signals being suppressed or filtered, while others pass through to the cortex.  In particular, by combinations of paired whole cell recording and calcium imaging we have shown that the competitive inhibitory interactions between mitral cells are temporally specific (Kapoor and Urban, 2006) spatially/anatomically constrained (Egger and Urban, 2006) and activity-dependent (Arevian Kapoor and Urban submitted).

Neuronal synchronization and reliability.  Simultaneous firing, especially oscillatory firing, is a common feature of brain activity in many areas and across many species.  We are interested in uncovering biophysical and computational mechanisms of such synchronization in the olfactory system.  This work involves the combination of computational and physiological approaches to determine which aspects of neuronal dynamics, synaptic properties and anatomical connectivity are critical for the generation of synchronized activity (Galan et al., 2005).   We also have described a novel mechanism of synchronization in neurons whereby increased levels of aperiodic “noisy” inputs enhance the synchronized oscillatory firing of olfactory bulb mitral cells (Galan et al., 2006). 

Dendritic computation in the accessory olfactory system.  In the accessory olfactory system our work has focused on understanding how the accessory olfactory bulb neurons maintain high levels of both sensitivity and selectivity in their response properties.  Our working hypothesis is that the response of cells in the accessory olfactory bulb is influenced by local hotspots of activity in their dendritic trees.  These local hotspots of activity allow input to be integrated in a highly non-linear fashion and thus to respond with high fidelity to low concentration stimuli (Urban and Castro, 2005).  Further work is centered around the linkage between dendritic excitability and neurotransmitter release ion the accessory olfactory bulb (Castro and Urban in revision).    

Learning and neurogenesis in the olfactory system.  Finally, we are also pursuing questions related to the relationship between adult neurogenesis and olfactory learning.  Several subtypes of olfactory bulb interneurons are known to be replaced throughout life.  We are seeking to determine whether the rate or subtype specificity of neuronal replacement is altered by activity.  This work involves the use of viral vectors to label and alter the activity of small numbers of adult-born neurons.    

Development of novel technology for neuronal recording and labeling
We are also interested in developing and applying new approaches for physiological and anatomical analysis of neuronal circuits.  This includes the use of nanofabrication technologies to make very small (20-100 nm) solid conductor electrodes for neuronal recording, the use of bulk loaded calcium imaging techniques for recording population activity from groups of neurons in vitro and the development of new approaches to biolistic delivery of genetic and chemical markers to neuronal tissue in vitro and in vivo. 

References

Egger V, Urban NN (2006) Dynamic connectivity in the mitral cell-granule cell microcircuit. Seminars in Cell and Developmental Biology 17.
Galan RF, Ermentrout GB, Urban NN (2005) Efficient estimation of phase-resetting curves in real neurons and its significance for neural-network modeling. Phys Rev Lett 94: 158101.
Galan RF, Fourcaud-Trocme N, Ermentrout GB, Urban NN (2006) Correlation-induced synchronization of oscillations in olfactory bulb neurons. J Neurosci 26: 3646-3655.
Kapoor V, Urban NN (2006) Glomerulus-specific, long-latency activity in the olfactory bulb granule cell network. J Neurosci 26: 11709-11719.
Urban NN, Castro JB (2005) Tuft calcium spikes in accessory olfactory bulb mitral cells. J Neurosci 25: 5024-5028.