From the periphery to the brain: Wiring the olfactory system

Abstract

The olfactory system represents a perfect model to study the interactions between the central and peripheral nervous systems in order to establish a neural circuit during early embryonic development. In addition, another important feature of this system is the capability to integrate new cells generated in two neurogenic zones: the olfactory epithelium in the periphery and the wall of the lateral ventricles in the CNS, both during development and adulthood. In all these processes the combination and sequence of specific molecular signals plays a critical role in the wiring of the olfactory axons, as well as the precise location of the incoming cell populations to the olfactory bulb. The purpose of this review is to summarize recent insights into the cellular and molecular events that dictate cell settling position and axonal trajectories from their origin in the olfactory placode to the formation of synapses in the olfactory bulb to ensure rapid and reliable transmission of olfactory information from the nose to the brain.

Postnatal characterization of cells in the accessory olfactory bulb of wild type and reeler mice

“…Molecular and functional characteristics of these structures have been described (Lopez-Mascaraque and De Castro, 2002 ; for reviews Blanchart and Lopez-Mascaraque, 2011 ) but additional information, particularly regarding the AOB development, is still necessary to define the complete form and function of this system. On other hand, it is widely known that layered structures in the brain use Reelin (Reln) as a key molecule for proper neuronal positioning (Honda et al, 2011 ) and it appears to be relevant during the MOB layering (Wyss et al, 1980 ; Martin-Lopez et al, 2011 ).…”

Unraveling Cajal's view of the olfactory system

“…Furthermore, OSNs expressing the same receptor converge upon a stereotypical pair of glomeruli (Mombaerts et al, 1996 ). Nonetheless, the mechanisms by which a set of OSNs, expressing certain odorant receptor, innervates a discrete amount of glomeruli are not well-known; although it seems to be dependent on environmental cues, as well as on intrinsic OSN/odorant receptor factors (reviewed in Mombaerts, 2006 ; Blanchart and López-Mascaraque, 2011 ).…”

“…Besides, this layer contains an extremely interesting population restricted exclusively to the olfactory system regions, the olfactory ensheathing cells (Valverde and López-Mascaraque, 1991 ). During development, olfactory ensheathing cells coexist with astrocytes as part of the migratory mass (Doucette, 1990 ; De Carlos et al, 1996 ; Blanchart and López-Mascaraque, 2011 ; Blanchart et al, 2011 ). Olfactory ensheathing cells maintain certain progenitor characteristics (Schwarting et al, 2007 ) and are responsible, among other things, for the permissibility within the OB to OSNs axons growth during development and adulthood, thus being a key component of the ability of the OE to continually regenerate.…”

The olfactory system in Alzheimer’s disease: Pathology, pathophysiology and pathway for therapy

“…It is the only site of the central nervous system (CNS) where continuously replaced primary olfactory epithelial cells grow their axons into the CNS and form new functional synapses with the mitral cell processes in the olfactory bulb (OB) [3]. In addition, environmental factors such as toxins or pathogens can easily reach the CNS through the olfactory pathway.…”