Developmental anatomy of the primary olfactory pathway in the opossum Monodelphis domestica.

It has been shown in previous studies that the marsupial central nervous system is born at a relatively immature state. Although olfaction is thought to play a role in guiding the locomotion of the newborn, the cellular substrates on which this notion is based have not been systemically investigated. This review article summarises the anatomical development of the primary olfactory pathway in the postnatal Monodelphis. The olfactory epithelium and bulb appear morphologically immature at birth although some of the olfactory neurons are shown to express olfactory marker protein. The olfactory tissues subsequently undergo a rapid sequence of developmental events during the first two postnatal weeks. The evidence shows that the marsupial and eutherian olfactory system share a similar temporal sequence of developmental processes although the former proceeds at a lag time of about 10-14 days compared to that a mice (using the date of birth as a common reference point). Much physiological and behavioral studies remain to be done before we can be certain about the time at which functional maturity is attained in this system.