Veronica Egger: The rodent olfactory bulb granule cell dendrite - an alliance of independent mini-neurons?

University of Regensburg

 

Abstract

The vertebrate olfactory bulb processes olfactory stimuli within a two-stage network, with the stage first located in the glomerular input layer and the second in the external plexiform layer below. These subnetworks are bridged via the principal mitral and tufted cells; both strongly draw on dendrodendritic interactions, with the axonless inhibitory granule cells being the main players in the second stage. Granule cells are directing their sole output towards the long lateral dendrites of mitral and tufted cells via reciprocal dendrodendritic synapses, that are located within large spines.

In spite or because of their apparently reduced anatomy, granule cells are capable of various modes of dendritic signalling. To dissect the reciprocal interactions, we are using two-photon Ca²⁺ imaging and uncaging of glutamate in acute slices of juvenile rat olfactory bulbs in conjunction with whole cell recordings and compartmental modeling. Our observations indicate that single inputs to the granule cell spine are capable of eliciting a purely local sodium spike, which then engenders release of GABA. Thus the reciprocal spine functions as a mini-neuron that can provide recurrent inhibition independently of its ‘mother neuron’. Next, I will discuss how local spine spikes interact with global action potentials, resulting in sublinear summation of Ca²⁺. Finally, multi-site holographic stimulation now allows us to investigate interactions between spines during dendritic integration.

Organized by

Susanne Schreiber / Margret Franke