Distribution of corticotropin-releasing factor mRNA and immunoreactivity in the central auditory system of the rat.

Hybridization histochemical and immunohistochemical methods were used to characterize the distribution of corticotropin-releasing factor (CRF) messenger RNA (mRNA) and peptide, respectively, in the central auditory system of the rat. Cell bodies expressing CRF mRNA and/or immunoreactivity (IR) were detected at each level of the system, including sparse or equivocal localizations in the dorsal cochlear nucleus, the medial nucleus of the trapezoid body, and the lateral superior olive. More prominent groups of cells expressing CRF mRNA and CRF-IR were found in the nuclei of the lateral lemniscus, the shell of the inferior colliculus, the medial division of the medial geniculate body and in primary auditory cortices. The latter showed the greatest density of CRF-expressing interneurons, distributed primarily in layers II, III and V, of any neocortical area. Results obtained using the two staining methods were in good agreement, except in the cochlear and superior olivary nuclei, where cells displaying CRF-IR were apparent in far greater abundance than those expressing CRF mRNA. CRF-IR fibers and terminals were detected in regions generally consistent with the cellular localizations described above. These results provide evidence for a surprisingly widespread expression of CRF in the auditory system of the rat. This includes generally low levels of expression in components of the primary auditory path (cochlear nucleus, trapezoid body, superior olive, lemniscal nuclei). CRF appears to be more prominently expressed in so-called non-primary components of the auditory system, including aspects of the medial geniculate body that constitute an interface between the auditory system and stress-related limbic system circuitry.