AMPA receptor subunit-specific antibodies were used to determine if the distribution of excitatory amino acid receptors in the owl's auditory brainstem and midbrain nuclei reflected specializations for temporal processing. Each auditory nucleus displays characteristic levels of immunostaining for the AMPA receptor subunits GluR1-4, with high levels of the subtypes which exhibit rapid desensitization (GluR4 and 2/3). In the auditory brainstem, levels of GluR2/3 and GluR4 were very high in the cochlear nucleus magnocellularis and the nucleus laminaris. The different cell types of the cochlear nucleus angularis and the superior olive were characterized by heterogeneous GluR2/3 and 4 immunostaining. GluR1 levels were very low or undetectable. In the lemniscal nuclei, most neurons contained low levels of GluR1, and dense GluR2/3 and GluR4 immunoreactivity, with high levels of GluR4 in the dendrites. Levels of GluR4 were higher in the anterior portion of the ventral nucleus of the lateral lemniscus. The divisions of the inferior colliculus could be distinguished on the basis of GluR1-4 immunoreactivity, with high levels of GluR4 and moderate levels of GluR1 in the external nucleus. No major differences were observed between the pathways for encoding time and sound level cues.