GABAERGIC TERMINALS IN NUCLEUS MAGNOCELLULARIS AND LAMINARIS ORIGINATE FROM THE SUPERIOR OLIVARY NUCLEUS

The auditory brainstem nuclei, angularis (NA), magnocellularis (NM), a nd laminaris (NL) of the chicken, Gallus, contain terminals that stain for antibodies against the inhibitory neurotransmitter, gamma-aminobu tyric acid (GABA). Some of these terminals originate from cells surrou nding nucleus magnocellularis. Results from this study indicate that t he majority of the GABAergic terminals found in NA, NM and NL originat e from the superior olivary nucleus (SON). Injections of cholera toxin and horseradish peroxidase show that superior olivary nucleus (SON) n eurons, which respond to pure tones, project bilaterally to NA, NM and NL. NA and NL are reciprocally connected with the SON. More NA cells project to the SON than NL cells. While SON neurons project to NM, NM neurons do not project axons back to the SON. The configuration of SON terminals in NA, NM and NL matches the pattern of GABA-immunoreactive puncta seen in these three nuclei: they surround individual NM cells, congregate in the dendritic neuropil of NL, and blanket the NA. The d ata indicate that NA, NM and NL may be affected by two different inhib itory cell types: local interneurons and SON neurons. Patterns of conn ectivity described in this report suggest that the activity of NA cell s could influence NM and NL cell physiology. Specifically, increases i n NA cell activity could augment the effects of GABAergic SON neurons on NM and NL. Hence, binaural perception in the chicken may be more de pendent upon changes in intensity cues than previously believed. (C) 1 994 Wiley-Liss, Inc.