Chick auditory terminals contain dynorphin-like immunoreactivity

Dynorphin-like immunoreactivity (DYN-I) was studied in the auditory brain stem of chick hatchlings using an antiserum to dynorphin-B. DYN-I was found in a few small cells in the nucleus laminaris (NL) and in the superior olive (SO). Dendrites in NL also appeared immunostained. DYN-I, however, was especially prominent in the cochlear nucleus magnocellularis (NM). A few DYN-I somata could be found within NM particularly in medial regions of this nucleus. Most DYN-I, however, was localized to calyceal-type structures, reminiscent of primary auditory nerve terminals, surrounding nerve cell bodies in NM. To determine whether DYN-I is contained within auditory end-bulbs of Held, the basilar papilla (avian cochlea) was removed unilaterally. After 5 days survival, there were very few DYN-I terminals in NM on the operated side of the brain compared with the unoperated side. This novel finding suggests that primary auditory nerve terminals in NM may contain the opioid peptide, dynorphin.