The origins of the centrifugal fibers to the olfactory bulb in the goldfish, Carassius auratus: an experimental study using the fluorescent dye primuline as a retrograde tracer.

The origin of the centrifugal fibers to the olfactory bulb in the goldfish was examined by injecting a fluorescent dye, primuline, into the olfactory bulb by means of hydraulic pressure. Three to five days after the primuline injection, which was confined to the unilateral olfactory bulb, a large number of primuline-labeled perikarya appeared in two telencephalic areas on the ipsilateral side: the area ventralis telencephali pars dorsalis (Vd) and the ventral part of the area dorsalis telencephali pars lateralis (Dlv). No labeled cells were observed in the other olfactory bulb or in the contralateral telencephalic hemisphere or more posterior part of the brain. A combination of the primuline injection and the transection of either the medial or lateral olfactory tract showed that the main course of the centrifugal fibers was through the medial olfactory tract. These results may support Sheldon's opinion that the so-called tractus olfactorius ascendens, which corresponds to the medial part of the medial olfactory tract, is a centrifugal bundle originating from the cells in the nucleus medianus. The areas of the telencephalic hemisphere into which the olfactory bulbar fibers projected were also examined and compared with the originating areas of the centrifugal fibers. There was a considerable overlap between these two areas. This suggests a reciprocal connection between the olfactory bulb and the telencephalon.