Title:

Formation of discrete neuronal connectivity in the olfactory bulb

 

Speaker:

Takeshi Imai, Ph.D., Professor
Department of Developmental Neurophysiology, Graduate School of Medical Sciences, Kyushu University.
e-mail: t-imai<at>med.kyushu-u.ac.jp

 

Abstract:

In continuous neural maps, such as visual and auditory maps, spontaneous neuronal activity produced by the sensory organ plays an important role in establishing the precise topographic connectivity that occurs between pre- and post-synaptic neurons. In contrast, little has been known regarding the role of activity in establishing the discrete connectivity of the olfactory glomerular map. In the mouse olfactory bulb (OB), mitral cells initially extend multiple primary dendrites which connect to multiple glomeruli, but developmentally they prune all but one primary dendrite (during P3-6), producing a precise map. However, the mechanisms of this selective dendrite pruning have remained largely unknown. Here, we found that dendrite pruning is perturbed by the over-expression of Kir2.1 or NMDAR knockout in mitral cells, but not by sensory deprivation. To directly observe spontaneous activity in mitral cells, we performed in vivo two-photon calcium imaging in awake neonatal mice. We detected spontaneous activity in mitral cells, but not in axons of olfactory sensory neurons. Spontaneous activity was highly correlated among glomeruli at an early stage (P1-2); however, the pattern of the spontaneous activity became decorrelated and glomerulus-specific just prior to the pruning. Our results suggest that the decorrelating spontaneous network activity establishes the discrete connectivity in the OB.

In this seminar, I will also introduce tissue clearing methods, SeeDB and SeeDB2, developed in our laboratory and our ongoing work on synaptic mapping of neurons.

 

References:
Ke MT et al., (2016) Super-resolution mapping of neuronal circuitry with an index optimized clearing agent. Cell Rep 14, 2718-2732.
Ke MT, Fujimoto S, & Imai T. (2013) SeeDB: a simple and morphology-preserving optical clearing agent for neuronal circuit reconstruction. Nat Neurosci 16, 1154-1161.
SeeDB Resourses: https://sites.google.com/site/seedbresources/