Distinctive neuronal organization of the olfactory bulb of the laboratory shrew

The organization of the main olfactory bulb of an insectivore, the laboratory shrew (Suncus murinus), was studied morphologically. We found particular small spherical regions, nidi, at the border between the glomerular and external plexiform layer (EPL), which were intensely GAD positive, 30-60 microm in diameter, and where no olfactory nerves were seen. Around the nidus small calbindin D28k-positive GABAergic neurons, perinidal cells, were clustered. Furthermore, a distinctive type of newly discovered neurons, which we named tasseled cells, located at the middle of the EPL extended dendrites to the nidus, where their small tuft-like complicated branches made synapses with perinidal cells. The present study showed that the basic components of the olfactory bulb are not necessarily constant in all mammals.