Accessory olfactory system

The vertebrates produce, send and detect information which is conveyed by one or more molecular types. Chemical information of biological value (semiochemicals) which partly or wholly activates the accessory olfactory system (AOS) is transferred during intra- and inter-species communication. The compounds involved convey messages of social importance originating from the need to co-ordinate gamete release. It seems quite likely that gradual improvements by selection of semiochemical molecules and their receptors eventually enhanced the reproductive benefits both for the sender and for the receiver (Sorensen, 1996). The dual olfactory systems interpret chemical input to allow the discrimination of odour... 

Beauchamp G.K., Martin I., Wysocki C.J. and Wellington J.L. (1983). The accessory olfactory system role in maintenance of chemoinvestigatory behavior. In Chemical Signals in Vertebrates 3 (Miiller-Schwarze D. and Silverstein R., eds.). Plenum, New York, pp. 73-86. 

Cohen-Tannoudji J., Lavenet C., Locatelli A., Teillet Y. and Signoret J.R (1989). Non involvement of the accessory olfactory system in the LH reponse of anestrous ewes to male odor. J Reprod Fertil 86, 135-144. 

Coppola D.M. and Millar L.C. (1994). Stimulus access to the accessory olfactory system in the prenatal and perinatal rat. Neuroscience 60, 463-468. 

Dudley C.A. and Moss R.L. (1994). Lesions of the accessory olfactory bulb decrease lordotic responsiveness and reduce mating-induced c-fos expression in the accessory olfactory system. Brain Res 642, 29-37. 

Halpem M., Shapiro L. and Jia C. (1998). Heterogeneity in the accessory olfactory system. Chem Senses 23, 477-481. 

Lau Y. and Cherry J. (2000). Distribution of PDE4A and G(o)-alpha immunoreactivity in the accessory olfactory system of the mouse. Neurorep 11, 27-32. 

Levy F., Locatelli A., Piketty V., Tillet Y. and Poindron P. (1995). Involvement of the main but not the accessory olfactory system in maternal behavior of primiparous and multiparous ewes. Physiol Behav 57, 97-104. 

Mendoza A. (1993). Morphological studies on the rodent main and accessory olfactory systems the regio olfactoria and vomeronasal organ. Anat Anz 175, 425-446. 

Meredith M. (1991a). Sensory processing in the main and accessory olfactory systems comparisons and contrasts. J Ster Biochem Molec Biol 39(4b), 601-614. 

Mori K., von Campenhausen H. and Yoshihara Y. (2000). Zonal organization of the mammalian main and accessory olfactory systems. Phil Trans Roy Soc B 355, 1801-1812. 

O Connell R.J. and Meredith (1984). Effects of volatile and non-volatile chemical signals on male sex behaviors mediated by the main and accessory olfactory systems. Behav Neurosci 98, 1083-1093. 

Schwarting G.A., Drinkwater D. and Crandall J.E. (1994). A unique neuronal glycolipid defines rostrocaudal compartmentalization in the accessory olfactory system of rats. Brain Res 78, 191-200. 

Sipos M.L., Wysocki C.J., Nyby J.G., Wysocki L., et al. (1995) An ephemeral pheromone of female house mice perception via the main and accessory olfactory systems. Physiol Behav 58, 529-534. 

Wong M., Chen Y. and Moss R. (1993). Excitatory and inhibitory synaptic processing in the accessory olfactory system of the female rat. Neurosci 56, 355-365. 

Restrepo, D., Arellano, J., Oliva, A. M., Schaefer, M. L. and Lin, W. (2004) Emerging views on the distinct but related roles of the main and accessory olfactory systems in responsiveness to chemosensory signals in mice. Horm. Behav. 46, 247-256. 

Lloyd-Thomas, A. and Keveme, E.B. (1982) Role of the brain and accessory olfactory system in the block to pregnancy in mice. Neuroscience 7, 907-913. 

Abstract In this chapter, we review recent data about the involvement of both the main and the accessory olfactory system in mate recognition and the control of sexual behavior in mice. Whereas the main olfactory system seems to play a central role in mate recognition in both male and female mice, clear sex differences emerge with regard to which olfactory system plays a more important role in the control of sexual behavior. Indeed, the main but not the accessory olfactory system seems to be more important in regulating sexual behavior in male mice, whereas in female mice, the accessory olfactory system seems to play a critical role in the control of mating. 

By contrast, the accessory olfactory system is thought to be involved in the detection of odors that influence a variety of reproductive and aggressive behaviors (Keverne 1999). Sensory neurons are located in the vomeronasal organ (VNO) and detect pheromones which gain access to the VNO by a pumping mechanism (Meredith and O Connell, 1979). VNO neurons send projections to the accessory olfactory bulb (AOB). Mitral cells of the AOB project in turn to the medial nucleus of the amygdala olfactory information is then dispatched to several hypothalamic regions such as the bed nucleus of the stria terminalis, the medial preoptic area and the ventromedial hypothalamus (Scalia and Winans 1975). 

Main vs Accessory Olfactory System in Mate Recognition and Sexual Behavior... 

Functional Interaction of Main and Accessory Olfactory Systems... 

As with many macrosmatic mammals, rodents have two separate chemosensory systems, the main olfactory system (MOS) and accessory olfactory system (AOS), which respond to social odors. Importantly, these sensory systems differ not only in their peripheral morphology and central projections, but also in the types of chemosignals that they process (Meredith 1991). Sensory neurons of the MOS, which are located in the main olfactory epithelium and project to the main olfactory bulbs, process volatile chemicals and can detect odors at a distance. In contrast, sensory neurons of the AOS, which are located in the vomeronasal organs (VNO) and project to the accessory olfactory bulbs, primarily process large, non-volatile chemicals and require contact for stimulation (Meredith 1991). 

The vomeronasal system, also known as the accessory olfactory system, consists of chemoreceptors, organized into the VNO, the vomeronasal nerve, its terminal, the accessory olfactory bulb, and more central pathways. First described by Jacobson in 1811, the VNO has been studied intensely. We now know how stimuli reach it and what behaviors it mediates. The VNO occurs in amphibians, reptiles, and mammals. Among mammals, it is best developed in marsupials and monotremes. In birds it only appears during embryogenesis. The VNO and its function are best known for squamate reptiles, particularly snakes, and rodents and ungulates among the mammals. 

From the accessory bulb, projections lead to the medial nuclei and posteri-omedial portion of the cortical nuclei of the amygdala. The amygdala in turn is connected to higher centers via the stria terminalis, and hypothalamic structures. Thus, the accessory olfactory system represents a neural pathway separate from the main olfactory system. Both project into absolutely different parts of the amygdaloids (Powers and Winans, 1975 Powers etal, 1979). 

Male mice learn about female cues. In the presence of females, a male emits ultrasonic vocalizations. These vocalizations become less frequent after extirpation of the VNO. The more experience a male has had with females, the smaller the deficit he suffers. The learning is mediated by interaction between the main olfactory system and the accessory olfactory system after vomeronasal deprivation, olfactory cues maintain the behavior (Wysocki etal., 1986). 

The terrestrial salamander Plethodonjordani applies courtship pheromone to the female hy ruhhing or slapping his mental gland directly on the female s nares. This way the pheromone can stimulate the vomeronasal organ and accessory olfactory system. Experimental application of mental gland extracts to the nares of females accelerated the time until active courtship started (Houck etal., 1998). 

Nerve transection experiments have shown that normal estrus cyclicity and behavioral estrus in mice relies on sensory input through the main olfactory bulbs and does not require the accessory olfactory system (Rajendren and Dominic, 1986). 

Estradiol subsequently builds up in the blood and first (within 2 to 12 hours) reduces the levels of follicle-stimulating hormone (FSH) and the amplitude of LH pulses, then (within 12 to 48 hours) causes preovulatory surges of LH and FSH. The former promotes ovulation and development of a corpus luteum (reviewed in Martin et ah, 1986). Two compounds have been indicated in the effect of the odor of ram s fleece on LH secretion in anestrous ewes. These are 1,2-hexadecanediol and 1,2-octadecanediol. In Merino sheep at least, maximum stimulation of ovulation requires full exposure to a ram, such as fenceline contact in pastures. Olfactory cues from the ram s wool, presented in a facemask for the ewe, are ineffective by themselves visual and tactile stimuli are also important. The Merino breed does not rely as much on olfactory cues as other breeds of sheep (Pearce and Oldham, 1988). The effect is not necessarily species specific hair extract from male goats stimulates LH release in ewes. For this effect, the accessory olfactory system is not necessary (Signoret etah, 1989). 

Reynolds, J. and Keverne, E. B. (1979). The accessory olfactory system and its role in the pheromonally mediated suppression of oestrus in grouped mice. Journal of Reproduction andPertility 57,31-35. 

Olfactory communication is very common among animals, and since the discovery of an accessory olfactory system in humans, possible human olfactory communication has gained considerable scientific interest. Several studies [242] indicate that humans indeed seem to use olfactory communication and are even able to produce and perceive certain pheromones recent studies have found that pheromones may play... 

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