Behavioral and electrophysiological studies of olfactory coding in fishes

To understand how olfactory stimuli are perceived in the brain, coding of olfactory information at the olfactory receptor neuron layer needs to be resolved; qualitative and quantitative properties of the olfactory code and its transfer into the olfactory bulb must be identified. The olfactory receptor neurons (ORNs) are involved into three successive steps of the coding mechanism: A) transduction mechanisms within the neurons, B) distribution of olfactory information across millions of olfactory receptor neurons that C), after convergence, evoke chemotopic patterns of glomerular activities in the olfactory bulb. After olfactory stimulation of brown bullhead catfish with amino acids č75%of spontaneously active olfactory receptor neurons are suppressed and only č25% are excited. The unexplained transduction mechanisms of suppression of spontaneous activity of the fish olfactory receptor neurons are currently investigated in our laboratory using patch clamp and other electrophysiological techniques. The primary scope of our study is to correlate the olfactory code for single amino acids with the ability of the catfish to discriminate olfactory stimuli. Quantification of physiological responses of several thousand of individual olfactory receptor cell to amino acid stimuli is currently under way using electrophysiological techniques. Descriptions of the olfactory receptor neuron responses to specific amino acids and their binary mixtures will be correlated with behavioral responses to the stimuli that are detected as different, equal or similar. Using binary mixtures the minimal differences in the olfactory code that are needed for olfactory discrimination will be identified.