The overall purpose of our research is to gain insight into the function and interrelationships of key molecules involved in chemosensory, which is olfactory, vomeronasal, and gustatory signaling based on their ultrastructural localization. The main olfactory organ (MO) with its sensory neurons that have long tapering cilia, and the vomeronasal (VNO) and gustatory organs with their sensory receptor cells that have many microvilli play distinct, but overlapping roles in the process of olfaction and taste respectively. It is thought that the MO particularly recognizes general odors while the VNO specifically recognizes conspecies and prey. The olfactory cilia, in particular their long distal parts, and VNO and gustatory microvilli provide a large area of interface between the external chemical environment and the sensory cells. Chemosensory signaling begins when odor or taste molecules interact with specific odor or taste receptors that are presumably located on these cilia and microvilli of MO, VNO, or taste receptor cells. The stimulus-receptor interaction eventually leads to an electrical signal in the receptor cells initiating the organism's appropriate response. Some indication of the location and topography of chemosensory signal processing has been gained through biochemical and physiological studies and through light microscopy. However, for detailed analyses of the sites of chemosensory signal transduction ultrastructural and ultrastructural cytochemical studies are necessary. Using a variety of probes, especially poly- and monoclonal antibodies combined with colloidal gold labeling and high-resolution imaging, we study the localization of the various components of the chemosensory signal-transduction apparatuses at a subcellular level. Such studies confirmed the supposition that some molecules of olfactory signaling, notably those involved in signal onset, including odor receptors and the current generating cyclic nucleotide gated channels are present in olfactory receptor cell cilia, especially their long and thin distal segments, though some molecules involved in the restoration of the signal apparatus, have a less confined distribution. Several molecules of VNO and taste transduction have been located on the appropriate microvilli of the receptor cells in these sensory systems.

Scanning electron micrograph of a dendritic ending of an olfactory receptor cell neuron in a 20-day old rat embryo. The olfactory cilia give the knob-shaped ending the appearance of a sea anemone. These cilia radiate all around the knob. Upon further development, the cilia become narrower and much longer, about 50x as long, enhancing chances of capturing odor molecules that enter the nose from the ambient environment. The parallel-aligned cilia above the knob are respiratory, non-sensory, cilia, as this image was taken at the border between the olfactory and nasal respiratory epithelium. Adapted from Figure 4, Chem. Senses 22: 295 (1997). Scale bar: 1 µm.

Links:

• Bert Menco's profile on Community of Science

• National Institute on Deafness and other Communication Disorders

• NSF: Environmental and Structural Systems Cluster (includes Sensory Systems)

• Sense of Smell Institute