The significance of odours
The EU-funded ODORPROCESSING (Genetic analysis of olfactory processing and function) project has investigated the functional properties of neural circuits underlying olfactory sensory processing. Smells are recognised by odorant receptors (ORs) that in turn activate sensory neurons with resulting activity in the olfactory bulb and then higher olfactory centres in the brain. Different odours are linked to appropriate behavioural responses. OR gene choice during transcriptional regulation was investigated using transgenic mice. The results showed that OR loci are slow to be activated and that later spatial restriction is accomplished by repression. This suggests a kinetic model for initiation of OR gene choice and repression of unselected OR alleles. Researchers altered neural activation by odours using experimental mice in which 95 % of all sensory neurons express the same receptor. Analysis of data from these transgenic mice indicates that the recognition of patterns of neural activity is critical for odour detection. Researchers tested this model using two-photon in vivo imaging approaches to define patterns of glomerular activity and its transformation into cortical odour representations. They used transgenic mice to characterise odour-initiated neural activity in defined neural cell types. Analysis suggests that inhibition at multiple steps along the olfactory pathway plays a key function in the processing of odour-initiated neural activity. Overall, the data shows that glomerular activity can be transformed by olfactory bulb neural circuits. Moreover, highly degraded sensory input can produce meaningful odour information indicating an important link between olfactory processing and behaviour. Application of these high-tech tools in live animals has enabled investigation of the functional organisation of neural circuits and their role in olfactory-driven behaviours.
Keywords
Smell, olfactory sensory processing, odorant receptors, kinetic model, olfactory-driven behaviour