Some primary olfactory axons project to the contralateral olfactory bulb in Xenopus laevis

Cobaltous lysine and horseradish peroxidase (HRP) were used to trace primary olfactory axons to their terminations. The tracers were taken up in the olfactory mucosa and transported to the olfactory bulb. The results suggest that either HRP or cobaltous-lysine methods are useful and simple tools for studying such connections. In addition to the ipsilateral projection, we report here for the first time a projection to the medial part of the contralateral olfactory bulb. The overlaps of ipsi- and contralateral inputs to the medial bulb provide further evidence that its functions in frogs may be different from the lateral part, because other connections differ as well.