An indirect trigeminocerebellar pathway through the nucleus lateralis valvulae in a perciform teleost, Oreochromis niloticus

The trigeminocerebellar pathways were investigated in a perciform teleost, tilapia (Oreochromis niloticus), by tract-tracing methods. Iontophoretic injections of 1% biotinylated dextran amine were conducted on the nucleus lateralis valvulae, cerebellum and sensory trigeminal nucleus for 30 min each injection. Injections of the nucleus lateralis valvulae were made restrictedly into the rostromedial part of the nucleus. Then, labeled neurons were seen in the bilateral sensory trigeminal nucleus, and descending trigeminal nucleus, mostly in the contralateral side. Labeled terminals were mainly observed in the ipsilateral corpus cerebelli and valvula cerebelli. Injections into either the corpus or valvula cerebelli labeled numerous neurons in the ipsilateral nucleus lateralis valvulae and fewer in the contralateral nucleus, while no neurons were labeled in the sensory trigeminal nucleus and descending trigeminal nucleus. Injections into the sensory trigeminal nucleus labeled terminals in the bilateral rostromedial part of the nucleus lateralis valvulae, with preference for the contralateral side. No labeled terminals were seen in the corpus and valvula cerebelli. The present results revealed an indirect trigeminocerebellar pathway through the nucleus lateralis valvulae, while a direct trigeminocerebellar pathway was not identified in the tilapia.