Olfactory bulb function

A high concentration of DOPs is found in the olfactory bulb, the neocortex, caudate putamen, and in the spinal cord, but they are also present in the gastrointestinal tract and other peripheral tissues. The functional roles of DOP are less clearly established than for MOP they may have a role in analgesia, gastrointestinal motility, mood and behaviour as well as in cardiovascular regulation [2]. 

Kumar A., Dudley C. and Moss R. (1999). Functional dichotomy within the vomeronasal system distinct zones of neuronal activity in the accessory olfactory bulb correlate with sex-specific behaviors. J Neurosci 19, 1-6. 

Astic, L. and Saucier, D. (1981) Ontogenesis of the functional activity of rat olfactory bulb autoradiographic study with the 2-deoxyglucose method. Brain Res. 254, 243-256. 

An important insight from many studies (28) is that the response patterns—the molecular images—at various levels in the central olfactory pathway are set up by the differential responses of the ORCs in the peripheral receptor epithelium. These studies also suggest that functional modules, which may correspond to recognizable structural units such as individual glomeruli with their associated cells, in the olfactory bulb or lobe participate in the analysis of olfactory information conveyed to them... 

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. 

The fly antennal lobe contains at least 43 glomeruli which are likely to be the functional homologs of glomeruli in the vertebrate olfactory bulb (Laissue et al.,... 

Johnson B. A., Ho S. L., Xu Z., Yihan J. S., Yip S., Hingco E.E. and Leon M. (2002) Functional mapping of the rat olfactory bulb using diverse odorants reveals modular responses to functional groups and hydrocarbon structural features. J. Comp. Neurol. 449(2), 180-194. 

Flavors and fragrances are sensory stimuli. Of the two, flavors are more complex because they act on the olfactory bulb via their volatile components and on the taste buds which are stimulated by both volatile and non-volatile components. The overall response to a flavor is a synthesis of the effects of both types of components. The response to fragrances, on the other hand, results only from the action of volatile components. Because flavors and fragrances function via a common mechanism, many volatile materials are used for both purposes. This is nicely illustrated by the perfumers vocabulary for fragrance materials. A collection of some 160 words published by a famous perfumer, Ernest Shiftan (1) included 75 words usually associated with flavors such as almond, bacon, coconut, honey, lime, raspberry, spicy and vanilla. 

When a molecule binds with its receptor site the olfactory cells become stimulated and send an impulse along the olfactory nerve. The olfactory nerve is the first cranial nerve. Cranial nerves that carry impulses into the brain are called sensory, while those that carry impulses away are called motor. Sensory information from the olfactory receptors of the nose is carried as a sensory impulse in the olfactory nerve to an area of the brain called the olfactory bulb. It is the olfactory regions of the brain that interpret this sensory information and distinguish different smells. Structures associated with the sense of smell are located in an area of the fore-brain (at the front) called the rhinencephalon. The rhinencephalon is not fully understood and its function is not restricted to olfaction or smelling. The olfactory tract then connects with another area called the neocortex that allows us to be aware of and to recognise odours or smells... 

Olfactory signals that leave the olfactory bulbs travel by several routes to the higher centers of the brain where the phenomenon of odor develops eventually. Remarkably, the architecture of the olfactory parts of the brain is consistent across all mammahan species research on other animals throws considerable fight on the function in humans. The entire process is well reviewed by Wilson and Stevenson (4) and by Delano and Sobel (10). 

Other models include the olfactory bulbectomy model (Song and Leonard, 2005). Lesions of the olfactory bulb cause behavioral changes, inteipreted to result from disturbed function of the limbic system. These behaviors are reversed by chronic antidepressant administration. 

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