Afferent connections of the corpus cerebelli in holocentrid teleosts

The holocentrid corpus cerebelli (CC) is composed of the dorsal (CCd) and ventral (CCv) lobes. In the present study, afferent connections of the CCd and CCv in holocentrid teleosts (Sargocentron rubrum and S. diadema) were examined by means of tract-tracing methods. Tracer injections into either lobe of the CC labeled neurons in the ipsilateral area pretectalis pars anterior et posterior, nucleus paracommissuralis (NPC), nucleus accessorius opticus and nucleus tegmentocerebellaris. Labeled neurons were also present in the bilateral nucleus lateralis valvulae (NLV), nucleus raphes, nucleus reticularis lateralis and inferior reticular formation, and in the contralateral inferior olive. Injections into the CCd labeled only a few neurons in the area pretectalis pars anterior et posterior, nucleus accessorius opticus and nucleus tegmentocerebellaris, whereas many labeled cells were seen in these nuclei after CCv injections. Injections into the CCv also revealed afferent connections that were not observed after CCd injections. The CCv injections labeled additional neurons in the ipsilateral torus longitudinalis and nucleus subeminentialis and in the bilateral nucleus subvalvularis and nucleus of the commissure of Wallenberg. These differences in afferent connections suggest functional differences between the CCd and CCv. After injections into the CCd, labeled neurons in the NPC were restricted to a medial portion of the nucleus. On the other hand, after injections into the CCv, labeled neurons were found throughout the NPC. Labeled neurons in the NLV were mainly located in its rostral portion following CCd injections, whereas labeled neurons were mainly distributed in the medial portion following CCv injections. These observations suggest topographical organizations of the NPC-CC and NLV-CC projections.