DESCENDING TELENCEPHALIC INFORMATION REACHES LONGITUDINAL TORUS AND CEREBELLUM VIA THE DORSAL PREGLOMERULAR NUCLEUS IN THE TELEOST FISH, PANTODON BUCHHOLZI - A CASE OF NEURAL PREAPTATION

The weakly electric mormyrids are known to have an ascending neuronal pathway that reaches the diencephalon and carries information concerne d with electrolocation. The recipient diencephalic center, the dorsal preglomerular nucleus, receives a massive telencephalic input and proj ects to the corpus and valvula cerebelli. This circuitry has been inte rpreted as a uniquely derived (autapomorphic) feature for mormyrids. I n the present study, we demonstrate with the fluorescent systems resce nt neuronal tracer DiI that the closely related, but non-electrorecept ive, teleost Pantodon buchholzi possesses a dorsal preglomerular nucle us with similar telencephalo-cerebellar circuitry. The projection to t he cerebellum only reaches the corpus, however, not the valvula cerebe lli. Further, the dorsal preglomerular nucleus of Pantodon displays a descending pathway via the torus longitudinalis. Two phylogenetic inte rpretations for the presence of telencephalo-cerebellar pathways in bo th mormyrids and Pantodon are possible: if such a pathway existed as a preaptation in the common ancestor of mormyrids and Pantodon, it must be an exaption for electroreception in mormyrids, since this sensory modality evolved anew in this teleost group; alternatively, the pathwa y evolved in parallel homoplasy, once in Pantodon, as part of a descen ding premotor pathway, and independently in mormyrids, where the syste m gains access to ascending electrosensory information.