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Different sensory neurons and different neural pathways in the brain appear to be involved in the sensing of general odors and pheromones. This is critical because pheromones regulate behavior in many animals.

Evidence suggests that odorants are important for forming attachments by domestic chicks but there is little evidence that nestlings remember odorants presented soon after they are hatched. A new study investigates whether early exposure to nonaversive odorants alters a chick's responses to natural odours, such as food, feathers and faeces of adult chicken. The study concludes that chicks learn about their olfactory environment during the latter part of incubation and in the early posthatching period.

Tamias minimus, or least chipmunks may mark a patch of seeds, a type of behavior which is unusual in rodents, and is more often found in otters, wolves, foxes and coyotes. Unprofitable patches tend to be marked, and this means that the chipmunk may be signalling that the patch is depleted. This could benefit chipmunks other than the market. Marking may help jog the memory of the marker and help it to seek food more efficiently. Slightly depleted patches may be marked if the seeds are not of a type preferred by the chipmunk.

Rats' ability to discriminate between familiar conspecifics was investigated in a series of three experiments using a go/no-go discrimination procedure. Results of the first experiment revealed that rats are able to recognize conspecifics as individuals. The second experiment showed that rats had more difficulty in acquiring a reversed discrimination than a novel discrimination. Results of the last experiment indicated that rats can recognize individuals using only their olfactory signatures.

The role of olfaction on the homing ability of precocial or semi-precocial chicks of underground-nesting seabirds were analyzed in Hydrobates pelagicus or the British storm-petrel. Homing experiments with the British storm-petrel chicks indicated the absence of parent-offspring recognition after the end of brooding. However, British storm-petrel chicks exhibited olfactory homing abilities and are capable of nest recognition which were crucial for survival.

A project wherein 7 dogs carried out 617 trials, each trial including the differentiation of up to 700 people's 6 different body smells, helped illustrate that well trained and well selected dogs with an aptitude for scent differentiation efficiently performed this task in criminal investigations. Decline in scent differentiation performance, in some dogs, was attributed mainly to disruptions in their work schedule.

Vertebrates identify volatile odorants and attracting or repelling chemicals with the aid of olfaction. Chemosensory neurons in Caenorhabditis elegans, a soil nematode, are responsible for this detection, as laser ablation methods reveal. The neurons are minutely sensitive to volatile odorants, indicating the presence of complex sensory functions. Gene (odr) mutation antagonizes subset volatile odorants' chemotaxes, thereby affecting signal transduction.

The mechanism for olfactory discrimination in the channel catfish was investigated. A previous study has shown that the channel catfish olfactory epithelium possess a family of transmembrane olfactory receptors expressed in a selective manner by individual olfactory neurons. A topographic map developed via in situ hybridization methods showed the positions of olfactory neurons expressing different complements of olfactory receptors. The results showed that functionally distinct olfactory neurons are randomly distributed in the olfactory epithelium.

A study of the genes encoding the olfactory receptors in the channel catfish is presented. The study protocol involved the isolation of olfactory receptor cDNA. The results revealed a family of genes which encode seven transmembrane receptors that show considerable homology with rat olfactory receptors. Expression of these genes is restricted to olfactory sensory neurons, and each receptor is expressed only in a a small population of neurons.

The circuitry and synaptic mechanisms of the retina and olfactory bulb are discussed, with emphasis on recent advances and studies which shed light on the workings of other regions of the nervous system. Most of the recent findings are derived from studies of microelectrode recordings from single neurons, which have been useful in elucidating receptive field organization of retinal ganglion cells and odorant responses of mitral cells in the olfactory bulb. Future research will focus on the spatial and temporal resolution of cell population activity.

The mammalian olfactory system employs as much as 1,000 G protein-coupled receptors for the identification of odorants. Previous studies, however, have failed to devote adequate attention to the vomeronasal organ in the nasal septum, an olfactory organ with an independent group of receptor proteins. A third distinct class of mammalian olfactory receptors have been cloned. Results show the basic components for expressing olfactory pathways.

Memory traces include any molecular, biophysical or cellular change induced by learning that subsequently alter the processing and response of the nervous system while formation of normal olfactory memory requires the expression of the wild-type amnesiac gene in the dorsal paired medial neurons. Classical conditioning that includes olfactory learning leads to learned avoidance behaviour of the conditioned stimulus.

The sense of smell in human beings is one of the most important senses as it helps humans to distinguish between various odors. Various experiments are conducted to understand this unique gift that human's possess, and the year 2004's Nobel Prize in Physiology or Medicine awarded to Linda Buck and Richard Axel is a tribute to the efforts of all scientists involved in these researches.

The vomeronasal system is responsible for the detection of pheromones in mammals. These pheromones, which trigger off stereotyped behavioral responses that are unique to a species, are activated by genetically programmed neural pathways. Using gene targeting methods, it is shown that these pathways are made possible by the neural organization of vomeronasal system afferents. Results also indicate that the sensory neurons in the accessory olfactory bulb play a vital role in pheromone activation.