Fig. 5

Neuronal circuitry in the olfactory bulb (OB). Schematic diagram of the connectivity between pre and postsynaptic cells in the OB. Within each glomerulus, olfactory sensory neurons (OSNs) expressing the same odorant receptor (OR) (indicated by drop shapes with the same color) form synapses with the postsynaptic cells, namely the mitral cells (MC) and tufted cells (TC), along with the periglomerular cells. The MC and TC extend their single apical dendrite within a single glomerulus whereas the lateral dendrites run along the external plexiform layer and form dendro-dendritic synapses with the granule cells, the major GABAergic inhibitory interneurons of the OB. The glomerulus defines, therefore, a functional unit, known also as olfactory column, where sensory information related to a give OR is processed. ONL = olfactory nerve layer, GL = glomerular layer, EPL = external plexiform layer, MC = mitral cell layer, IPL = internal plexiform layer, GCL = granule cell layer