Central projections of the octaval nerve in larval lamprey: an HRP study

HRP tracing techniques and silver staining methods were used to investigate the central projections of the octaval nerve of the larval sea lamprey (Petromyzon marinus). We compare our findings with those reported for the adult and for other anamniotes. The general pattern of afferent projections (to the ventral octavolateral area of the medulla oblongata and to the cerebellar plate) is similar to that in the adult, although we did not observe projections to the trigeminal, reticular or contralateral medullary areas. We describe the pattern of connections of the octaval afferents with the different octaval nuclei (i.e. subdivisions of the ventral octavolateral area), and report the presence of a small number of efferent vestibular neurons.