Mysterious magno.

Abstract

Fish have three otolithic endorgans that may be involved in auditory processing: saccule, lagena, and utricle. One or more of those endorgans may serve a vestibular (tilt) function. In general, vestibular inputs are distributed more ventrally than auditory inputs in the medulla of teleost fishes, but there are zones of overlap with the more dorsal auditory sites. The octaval nucleus magnocellularis (Magno) receives overlapping input from all three endorgans, but Magno is not part of the ascending auditory circuit in the oyster toadfish, Opsanus tau, and the sensory role of this nucleus is unknown. Extracellular recordings were conducted in Magno and neurobiotin was injected at successful recording sites to confirm location and label local cell types. Sinusoidal particle motion stimuli (50–303 Hz) were presented at multiple stimulus levels to assess relative sensitivity. The data indicate that some cells in Magno respond to auditory frequencies at biologically relevant levels. While these results are suggestive, many attempts to record auditory responses in the divisions of Magno were negative, indicating that only a subset of cells is auditory.