Connections between the trigeminal mesencephalic nucleus and the superior colliculus in the rat.

Retrograde tracing methods are employed here to demonstrate that neurons in the trigeminal mesencephalic nucleus (5me) project to the superior colliculus (SC) in the rat. These neurons, mainly of small size, are situated bilaterally in the caudal part of the nucleus. Anterograde tracing studies demonstrated the existence of SC projections to neurons in 5me. The SC fibers contact 'en passant' small as well as large cell bodies of 5me neurons. These pathways suggested a role of the 5me neurons in oculomotor control and associated oro-facial functions.