Central lateral line pathways in a vocalizing fish

Abstract

The organization of the central lateral line pathways in the midshipman fish, Porichthys notatus, was identified following biotin injections into physiologically identified sites in the lateral line-recipient nucleus ventrolateralis in the midbrain. Retrogradely filled neurons are located primarily in nucleus medialis, the principal termination site of lateral line nerve afferents in the medulla, whereas terminal fields are mainly identified in isthmal (nucleus praeeminentialis) and diencephalic (posterior thalamic) nuclei. Compared to other teleosts, nucleus medialis has a distinctive cytoarchitecture in that most of its somata are confined to a dense cell plate adjacent to the fourth ventricle. Injections into nucleus ventrolateralis reveal a caudal (MEDc) and a rostral (MEDr) division of nucleus medialis which are separated by a dorsomedial division of the descending octaval nucleus. MEDc is further divisible into a caudal spherical and a more extensive rostral Purkinje-like cell division. MEDr includes a caudal division of Purkinje-like cells and a rostral division of round and fusiform-shaped cells that form a lateral band under the cerebellar crest. In addition to labeling terminals in nucleus ventrolateralis, biotin injections into MEDc and MEDr further distinguish intrinsic connectivity within nucleus medialis, and also label somata and terminals within other octavolateralis nuclei in the medulla. Injections into both nucleus ventrolateralis and nucleus medialis identify sites which may be processing information from both the auditory and lateral line systems, including the eighth nerve-recipient descending octaval nucleus, the acoustic division of the midbrain, and nucleus praeeminentialis which receives auditory input from the midbrain in midshipman.