Olfaction in Mammals

Stoddart D.M., ed. (1980). Olfaction in Mammals. Symposium of the Zoological Society of London, Academic Press, London, p. 368. 

Moulton D., Celebi G. and Fink R. (1970). Olfaction in Mammals — two aspects proliferation of cells in the olfactory epithelium and sensitivity to odors. In Taste and Smell in Vertebrates (Wolstenholme G. and Knight J., eds.). Ciba, London, pp. 227-250. 

In the same year as the NATO sponsored conference, a symposium entitled "Olfaction in Mammals" was held by the Zoological Society of London. Its objective, as with all other meetings, was to collect up-to-date information on progress in the field of chemical communication in vertebrates. 

While most of the volumes mentioned above were still oriented strongly towards insect research and Doty s book dealt with only one aspect of the behavioural function of olfaction in mammals, two books by D. M. Stoddart, namely, "Olfaction in Mammals" being the edited proceedings of the Symposium of the Zoological Society of London and "The Ecology of Vertebrate Olfaction," both published in 1980, focused exclusively on mammals. Taken together, the two books provide a comprehensive picture of all aspects of chemical communication in laboratory, domestic and wild mammals. 

There is a need for field experiments to complement general field observations and laboratory experiments on olfaction in mammals. Field experiments could include studying olfaction within the wider framework of ecological variation and adaptation. 

Stoddart, D. M., ed., 1980a, "Olfaction in Mammals," (Symp. Zool. Soc., Lond., 45) Academic Press, London and New York. 

Olfaction is of primary importance for social recognition in mammals, including mice. Thus mice use odors to distinguish sex, social or reproductive status of conspecifics (Brennan and Zufall 2006 Brown 1979). In addition, odors have been shown to facilitate the display of sexual behavior (e.g. Thompson and Edwards 1972) and to induce neuroendocrine responses (e.g. pregnancy block in female mice Brennan and Keverne 1997). 

Earlier, we encountered two examples of chemical communication. First, a small family of hydrocarbons secreted by the female brown algae gamete attracts a free-swimming male gamete. Fertilization follows. Second, bombykol, the sex attractant of the female silkworm moth, is a powerful lure for the male moth. What we need to do now is to expand on these examples. Let s begin with olfaction and taste in mammals. Later, we will move to the other end of the evolutionary scale and start with simple, unicellular organisms (the bacteria) and work our way back up. 

The relationship between central and peripheral oscillators is different in flies and mammals. In mammals, these oscillators form a hierarchy in which the central oscillator, which resides in the suprachiasmatic nucleus (SCN), functions as a master clock that is entrained by photic signals from the eye, and in turn drives subservient peripheral oscillators via humoral signals (Moore et al 1995, Yamazaki et al 2000, Kramer et al 2001, Cheng et al 2002). In contrast, both central and peripheral oscillators operate autonomously and are directly entrainable by light in Drosophila (Plautz et al 1997), thus obviating the need for a hierarchical system. Our results support the concept of independent oscillators in flies since central (sUN ) oscillators are not necessary for olfaction rhythms and local oscillators in antennae appear to be sufficient. 

Olfaction, like visual and taste perception, is an ancient process. Olfaction plays a role in sexual arousal. The olfactory system in mammals is remarkable with respect to the number of receptors engaged in monitoring odours. There are several thousand hepta-helical G-protein-coupled receptors in the olfactory epithelium and the nasal organ of a dog, and still about 1000 receptors in the corresponding human organs. It has been estimated that nearly 1% of all genes code for olfactory receptors alone. 

Mammalian Olfaction, Reproductive Processes and Behavior" (1976) which was edited by one of the wave of younger researchers, R. L. Doty, deals specifically with mammals, as the title shows. It contains up-to-date information on the role of smell in the reproductive behaviour and endocrinology of mammals, and in addition, accommodates chapters on the anatomy, physiology and development of the nasal chemosensory pathways and an important critique of the pheromone concept in mammalian chemical communication by J. R. Beauchamp, R. L. Doty, D. G. Moulton and R. A. Mugford. A review of reproductive endocrine influences on human nasal chemoreception emphasizes the pressing need for more intensive critical investigation of the behavioural role of olfaction in humans, a line of research which, in fact, Doty subsequently followed up. 

Bronson, F.H. Pheromonal Influences of Endocrine Regulation of Reproduction. Endocrine Responses to Primer Pheromones in Mammals. In W. Breipohl ed. Olfaction and Endocrine Regulation, p. 103-113. London IRI Press Limited. 1982. 

Rosenblatt l.S. (1983). Olfaction mediates developmental transition in the altricial newborn of selected species of mammals. Dev Psychobiol 16, 347-375. 

While the mammals predominate in their integration and representation of the sensory world, their noses still tell the brain directly about its chemical space. To explain the workings of accessory olfaction, we need to trace the path of a signal molecule from the moment it leaves its source until a response occurs in the recipient. The events which occur en route will determine the effectiveness of the intended communication. 

The other major class of extracellular LBPs of mammals is the lipocalins (Flower, 1996). These are approximately 20 kDa, P-sheet-rich proteins, performing functions such as the transport of retinol in plasma or milk, the capture of odorants in olfaction, invertebrate coloration, dispersal of pheromones, and solubilizing the lipids in tears (Flower, 1996). The retinol-binding protein (RBP) of human plasma is found in association with a larger protein, transthyretin, the complex being larger than the kidney threshold and thus not excreted, although the RBP itself may dissociate from the complex to interact with cell surface receptors in the delivery of retinol (Papiz et al., 1986 Sundaram et al., 1998). 

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