Afferent and Efferent Connections of Nucleus praeeminentialis in the Channel Catfish: A Reevaluation

Nucleus praeeminentialis (nPr) is an isthmic nucleus that has been described in the brains of electrosensory teleost fishes and a single non-electrosensory species. The nucleus receives axon collaterals of ascending medullary sensory lemniscal neurons. Axons of nPr neurons project in turn back down onto those same populations of medullary projection neurons via a descending parallel fiber system (the molecular layer or cerebellar crest). Thus nPr forms a link in a sensory feedback loop that modulates the activity of neurons that relay information from medulla to midbrain. The purpose of this study is to investigate the nature of the afferent and efferent connections of the nPr with the specific aim of investigating other sources of input into this modulatory circuit. Transport of neuronal tracers (horseradish peroxidase, DiI and dextran amines) revealed that nPr has extensive interconnections with nuclei in the basal metencephalon, cerebellum, octavolateralis column and basal medulla. A previously described source of afference, the torus semicircularis in the mesencephalon, was not indicated by our studies. Our studies suggest that in addition to regulating the sensitivity and resolution of electrosensory and mechanosensory lateral line systems, the nPr may play a role in the resolution of signal ambiguities posed by auditory or vestibular stimulation of the saccular endorgan of the inner ear.