NEURONS OF THE OLFACTORY ORGAN PROJECTING TO THE CAUDAL TELENCEPHALONAND HYPOTHALAMUS - A CARBOCYANINE-DYE LABELING STUDY IN THE BROWN TROUT (TELEOSTEI)

The caudal extrabulbar projections and their neurons of origin in the trout were studied after carbocyanine-dye (DiI) labelling in either th e olfactory organ or the caudal telencephalon. DiI application to the caudal telencephalon labelled bipolar neurons in the olfactory epithel ium, where they were sparsely distributed throughout the olfactory lam ellae. Labelled fibres ran scattered in the olfactory nerve without fo rming bundles. DiI application to the olfactory organ labelled extrabu lbar projections to the ventral telencephalon, preoptic region and tub eral hypothalamus. These results confirm that primary sensory fibres r unning in the medial olfactory tract of trout have an olfactory origin .