Midbrain acoustic circuitry in a vocalizing fish

The mapping of auditory circuitry and its interface with vocal motor system s is essential to the investigation of the neural processing of acoustic si gnals and its relationship to sound production. Here we delineate the circu itry of a midbrain auditory center in a vocal fish, the plainfin midshipman . Biotin injections into physiologically identified auditory sites in nucle us centralis (NC) in the torus semicircularis show a medial column of retro gradely filled neurons in the medulla mainly in a dorsomedial division of a descending octaval nucleus (DO), dorsal and ventral divisions of a seconda ry octaval nucleus (SO), and the reticular formation (RF) near the lateral lemniscus. Biotin-filled neurons are also located at midbrain-pretectal lev els in a medial pretoral nucleus. Terminal fields are identified in the med ulla (ventral SO, RF), isthmus (nucleus praeeminentialis), midbrain (nucleu s of the lateral lemniscus, medial pretoral nucleus, contralateral NC, tect um), diencephalon (lateral preglomerular, central posterior, and anterior t uber nuclei), and teleneephalon (area ventralis). The medial column of tora l afferent neurons is adjacent to and overlapping the positions of DO and S O neurons shown previously to be linked to the vocal pacemaker circuitry of the medulla. Midshipman are considered "hearing generalists" because they lack the peripheral adaptations of "specialists" that enhance the detection of the pressure component of acoustic signals. Whereas the results indicat e a general pattern of acoustic circuitry similar to that of specialists, t hey also show central adaptations, namely, a vocal-acoustic interface in DO and SO related to this species' vocal abilities. J. Comp. Neurol. 419:505- 531, 2000. (C) 2000 Wiley-Liss, Inc.