Olfactory Development

The Development of the Olfactory System

In rats, the sense of smell is probably the most important source of information about its environment.  Many mammals, including rodents, are “macrosmatic” and the olfactory bulb, the accessory olfactory bulb, the anterior olfactory nucleus, and the primary olfactory cortex are major structures in the telencephalon.  The olfactory bulb is intriguing for two reasons.  First, granule cells in the olfactory bulb are mainly generated after birth and continue forming during the adult period.  Second, the germinal source of these granule cells is a ROSTRAL MIGRATORY STREAM (first described in Altman, 1969) that extends from the subventricular/subependymal zone of the anterior horn of the lateral ventricle along the ventricular extension into the olfactory bulb.  In newborn and immature rats, the rostral migratory stream is large.  With age, the stream thins as the brain lengthens, but it is still easily recognizable in adult rats.  This stream is also believed to be the source of the adult-generated small glioform neurons that disperse throughout the neocortex.  For that reason, it is the subject of intensive study today.  The common attribution of the discovery of the rostral migratory stream to other sources reflects lack of respect for the history of neuroscience.