Organization and connections of the dorsal descending nucleus and other presumed acoustic areas in the brainstem of the teleost fish, Astronotus ocellatus.
This study provides new information on brainstem areas, assumed to be auditory based on observations in other species, in the oscar, Astronotus ocellatus. The primary goal of the study was to explore the morphology of the dorsal descending octaval nucleus, which contains a population of neurons that receives acoustic afferents from the inner ear. Using cytoarchitectonic and connectional criteria, we revised the previously defined dorsal boundary of the descending octaval nucleus, such that the most dorsomedial neurons in this nucleus are positioned ventral to the cerebellar crest and medial to nucleus medialis. At some levels, these dorsomedial cells are continuous with another part of the dorsal descending nucleus that underlies nucleus medialis. The terminal fields of the saccule and lagena are located within this latter, more ventral part of the dorsal descending nucleus. However, the dorsomedial cells that are proximate to the cerebellar crest have long ventral dendrites that extend into these terminal fields, and therefore likely receive saccular and lagenar input. In contrast to a previous report, saccular afferents terminate more medially within the dorsal descending nucleus than do lagenar inputs. Injections of horseradish peroxidase in nucleus centralis of the torus semicircularis revealed that many descending nucleus neurons that lie within the saccular and lagenar terminal fields, including the dorsomedial neurons proximate to the cerebellar crest, project to this acoustic midbrain area. These injections also revealed a secondary octaval population like that described in otophysan fishes.
O'Marra
S K
SK
Neuroscience Program, Oberlin College, OH 44074, USA.
McCormick
C A
CA
D000344:Afferent Pathways / Q000033:anatomy & histology; D000818:Animals; D001306:Auditory Pathways / Q000033:anatomy & histology*; D001933:Brain Stem / Q000033:anatomy & histology*; D010471:Perches / Q000033:anatomy & histology*; D000159:Vestibulocochlear Nerve / Q000033:anatomy & histology