Olfaction vomeronasal organ

Interaction between chemical senses 5.8.1 Olfaction-vomeronasal organ interaction... 

Graves B.M. and Duvall D. (1985). Mouth — gaping and head — shaking by Prairie Rattlesnakes are associated with vomeronasal organ olfaction. Copeia, 496-497. 

Moran D.T., Monti-Bloch L., Stensaas, L. and Berliner, D. (1994). Structure and function of the human vomeronasal organ. In Handbook of Olfaction and Gustation (Doty R., eds.). M. Dekker, New York Basel, pp. 793-820. 

Wysocki C.J. and Wysocki L. (1995). Surgical removal of the vomeronasal organ and its verification. In Experimental Cell Biology of Taste and Olfaction (Spielman A. and Brand J., eds.). CRC Press, Boca Raton, pp. 49-58. 

Although the vomeronasal system is specialized to detect stimuli in a liquid environment, it probably is not functional in utero, at least in mice. Fluorescent microspheres were not taken up by the vomeronasal organ as the access canal is not open yet in utero. In rats, by contrast, the canal is open before birth and the microspheres can be taken up. The olfactory epithelium of the main olfactory system plays a greater role prenatally, as evidenced by the uptake of radiolabeled 2-deoxyglucose (Coppola and Coltrane 1994). Fetal mice respond to amyl acetate and isovaleric acid delivered into the nasal cavity through a tiny cannula (Coppola, 2001). In both rats and mice, the main olfactory system, and not the vomeronasal system, appears to mediate prenatal olfaction (Coppola, 2001). 

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. 

The vapor pressure criterion pertains especially to animals that possess sensory apparatus that humans lack. Many mammals have a morphologically distinct chemo-sensory organ called the vomeronasal organ (VNO) (Meredith, 1998), which is vestigial in human beings. The VNO appears to respond to nonvolatile chemical stimuli that arrive as airborne particles. The VNO may also have the capacity to detect volatile stimuli, and the remaining guidelines help differentiate its inputs from olfaction. 

Experimental work has revealed a complex relationship between the vomeronasal and olfactory systems. Although the vomeronasal system mediates most of the classical primer effects, olfaction appears to regulate, in part, the expression of at least one. Normally, the reproductive systems of rats do not respond to shortened daylengths however, removal of the olfactory and accessory olfactory bulbs or intranasal zinc sulfate treatment, but not removal of the vomeronasal organ, induces photoperiodism in rats (Nelson et al., 1985). Furthermore, many behavioral responses to chemical cues are affected by lesion of the vomeronasal system (see Table 1). Hence, the vomeronasal system and olfaction modulate both primer and signaller effects, and may interact depending upon past experience. This latter contention has been pursued in our laboratories in studies of animals lacking the sensory afferents of the vomeronasal system. 

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