Projection of sensory neurons with microvilli to the lateral olfactory tract indicates their participation in feeding behaviour in crucian carp

In the olfactory system of vertebrates, a large number of primary sensory n eurons terminate in glomeruli in the olfactory bulb, where they make synaps es with a significantly smaller number of secondary neurons. We applied sma ll amounts of a lipophilic neural tracer (Dil) in the glomerular regions of the lateral olfactory bulb in crucian carp, and investigated the centrifug al migration of this stain through the secondary neurons towards the brain and peripherally to the sensory neurons of the olfactory epithelium. In pre parations where only the secondary neurons of the lateral olfactory tract ( LOT) were stained, the majority (76%) of sensory neurons had cell bodies in the intermediate layer of the olfactory epithelium. Scanning electron micr oscopy revealed that most of the sensory neurons with cell bodies in the in termediate layers of the olfactory epithelium feature microvilli. Based on observations that the secondary neurons of the LOT mediate feeding behaviou r, we feel that there is strong evidence to indicate that the sensory neuro ns that exhibit microvilli are responsible for mediating the behavioural pa tterns related to feeding. These results are discussed in relation to physi ological experiments on the properties of the sensory neurons and to studie s of the innervation pattern of sensory neurons.