Projection of the corpus mamillare to the dorsal thalamus in a percomorph teleost, tilapia (Oreochromis niloticus)

The corpus mamillare in tilapia is a prominent nucleus in the inferior lobe and has been shown to receive gustatory afferents from the inferior lobe and lateral torus, and to project to the telencephalon, nucleus ventromedialis thalami, optic tectum, and nucleus posterior periventricularis. The present study also revealed that the corpus mamillare receives afferents from the corpus glomerulosum pars anterior and nucleus lateralis valvulae, and projects to the nucleus dorsomedialis thalami in additional to fiber connections of the corpus mamillare in the above-mentioned. Because the corpus glomerulosum pars anterior is known to be a visual relay nucleus, the present study suggests that the percomorph corpus mamillare may also receive visual input besides gustatory information. Projection of the corpus mamillare to the nucleus dorsomedialis thalami was confirmed by reciprocal tracer injections. Tracer injections into the corpus mamillare densely labeled terminals in the ipsilateral nucleus dorsomedialis thalami. In contrast, injections into the nucleus dorsomedialis thalami labeled neurons in the ipsilateral corpus mamillare. Therefore, we suggest that the nucleus dorsomedialis thalami is a main projection target of the corpus mamillare in percomorph teleosts.