A field-potential study of centripetal and centrifugal connections of the olfactory bulb in the carp, Cyprinus carpio (L).

The projection areas of mitral cell axons in the lateral (LOT) and medial (MOT) olfactory tracts and the pathways of two groups of centrifugal fibers (with fast and slow conduction velocities) to the olfactory bulb were studied in the carp using the field potential method. Mitral cell axons of the LOT and those of the MOT projected to the overlapping areas in the bilateral telencephalon and preoptic area (POA), the contralateral MOT, and the nucleus posterior tuberis (NPT) in the diencephalon. However, the precommissural, ventromedial part of the ipsilateral telencephalon received the projection only from mitral cell axons of the MOT, not from those of the LOT. No projection was detected in the contralateral LOT and the contralateral olfactory bulb. The distribution of the fast and slow centrifugal fibers and/or their cells of origin were similar to each other. They were distributed bilaterally in the telencephalon and POA, in the NPT, and contralateral LOT and MOT. These areas overlapped with the projection areas of the mitral cell axons considerably. The results support and extend those obtained from anatomical studies.