Ultrastructural studies on membrane, cytoskeletal, mucous, and protective compartments in olfaction

Abstract

There is a great variety in the morphological appearance of olfactory structures across the metazoan animal kingdom. Despite this variety the receptive structures themselves have a strikingly similar architecture, namely some type of elongated cellular extension that is spanned by a membrane and surrounded by mucus. These cellular extensions can either be modified primary or secondary cilia, or microvilli. There are more similarities between membranes of these extensions than between the cytoskeletal elements immediately underneath the membranes. One might infer that the cytoskeletal elements of the cellular extensions merely serve as a scaffold for the membranes, whereas the similarity in membrane ultrastructure provides morphological evidence supporting the concept that these membranes are responsible for the initial olfactory transduction process. The transduced message is transported to the brain, where it is decoded to initiate the cascade of events resulting in the organisms' appropriate behavioral response to the initial odorous stimulus. The varying appearance of olfactory structures across the animal kingdom is probably produced by evolutionary pressure to adapt the olfactory system to the animal's environment. This review deals with the ultrastructural aspects of these facets of olfaction.

Mechanisms of Regulation of Olfactory Transduction and Adaptation in the Olfactory Cilium

“…In this way, most likely, the dendritic knob is the main site of endocytosis and exocytosis of GPCRs. Menco and colleagues [80], [81] had observed particles in the membranes of olfactory cilia, and plenty of endocytotic vesicles in the dendritic knob surrounding the olfactory cilia [82]. Additionally, proteomic analysis of the olfactory cilium has identified the presence of Rab proteins [83], [84].…”

Olfactory Cilia: Linking Sensory Cilia Function and Human Disease

“…Because there are numerous cilia (10-30) per cell and because of the large distance they project from the dendritic knob, there is substantial overlap of cilia from different OSNs (Menco 1997). This intertwined mat of cilia increases the sensory surface of the OE by over 40 times thus increasing our ability to detect odorants (Menco 1992).…”

Pheromone Sensing in Mammals: A Review of the Vomeronasal System

“…Here, long cilia embedded in nasal mucus provide an extensive surface area for interaction with odorants. The process of neurotransduction occurs within these cilia [134]. The ciliary membrane contains receptor proteins and elements of the olfactory transduction machinery, allowing these cellular compartments to act as chemosensory units, initiating signal detection.…”