Vomeronasal organ specificity

Takami S., Getchell, M. and Chen, Y. (1993). Neurone-specific compounds in the receptor cells of the adult human vomeronasal organ. Neuroreport 4, 375-378. 

Pheromones in urine will suffer degradation, hydrolysis, oxidation, and ultraviolet radiation effects. For example, the (Z)-7-12-acetyl derivative in elephant urine will gradually hydrolyze (Rasmussen, 1988). In this case, the lipoprotein carriers of the elephant acetate may also determine the life time of the signal besides serving to filter and select odorants, confer specificity, and play a critical role in the transport and transfer of an active ligand to the vomeronasal organ (Rasmussen and Schulte, 1998). 

Vertebrates possess three primary chemosensory systems gustation ( taste ), trigeminal, and olfaction ( smell ) but only one of these, the olfactory system, mediates responses to pheromones. Chemicals that stimulate the olfactory system are known as odorants and comprise one type of biological cue (any entity that stimulates a sensory system). Bouquets of odorants that can be discriminated as specific entities are termed odors. The olfactory system contains olfactory receptor neurons (ORNs) that comprise cranial nerve I and project directly to the forebrain. ORNs are now known to express only one to a few olfactory receptor proteins ( receptors ), which means that the chemoreceptive range of each neuron can be very narrow. The olfactory system also has several subcomponents including the vomeronasal organ, which is described below. 

Both primitive and advanced forms have been examined for vomeronasal excitation. The turtle VN nerve was the subject of EOG recordings elicited by small organic molecules and by specific signal compounds (Tucker, 1963 Hatanaka, 1987). The simple arrangement of the chelonian accessory area (Fig. 2.8) allows air or liquid delivery hence the preferred odourant vehicle varies with habitat across the aquatic or terrestrial turtles, and the land tortoises (Chap. 1 and Halpem, 1992). 

It has long been suspected that HG secretions may play a role in the vomeronasal sense in squamates (esp. snakes) and caecilian lissamphibians. In both cases, the HG is the only possible source of orbital fluids in the NLD, which leads from the orbit directly into the VNO. The specific role of the HG secretions in VNO function remains unknown for both taxa, but it has been suggested in each case that they may act as a solvent for VNO-sensitive odor particles, possibly as an analog to the secretions of the Bowman s glands of the nasal olfectory organ. 

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