The central connections of the olfactory bulbs in cod, Gadus morhua L.

The central projections of the "classical" olfactory system of the cod, Gadus morhua were examined with horseradish peroxidase and cobalt tracing techniques. Label was applied to the olfactory bulb or selectively to central stumps of sectioned individual olfactory tract bundlets. The olfactory bulb projects bilaterally to restricted areas of the dorsolateral, ventromedial and basolateral telencephalon, anterior commissural and preoptic areas, habenular nuclei, dorsal thalamus and to the nucleus posterior tuberis in the diencephalon. An interbulbar connection courses in the medial olfactory tract (MOT). Contralateral projections were less pronounced than on the ipsilateral side. More specifically, the lateral olfactory tract (LOT) projects ipsilaterally to the telencephalon into the Dlv, Dc, Vs and Dp areas. The lateral bundlet of the medial olfactory tract (IMOT) terminates in the Dlv and Dc areas. The medial bundlet of the medial olfactory tract (mMOT) terminates in Vv and Vd. The fused lMOT and mMOT project to the caudal telencephalon in the Vs and Dp. Neurons projecting to the olfactory bulb were located bilaterally in the telencephalon. The majority of the bulbopetal fibers course via the lateral part of the MOT; a few neurons also project to the bulb through the other bundlets of the olfactory tract. The results are compared with previous studies on the olfactory projections of other teleost species and discussed with respect to the reported functional differentiation of the olfactory system in teleosts.