CNTFRalpha and CNTF expressions in the auditory brainstem: light and electron microscopy study

CNTF receptor alpha (CNTFRalpha) is involved in the development, the maintenance and the regeneration of a variety of brain structures. However, its in vivo distribution has not been determined in the auditory system. CNTFRalpha expression was studied in developing and adult rat brainstem auditory nuclei using immunohistochemistry. At birth, the CNTFRalpha immunolabeling was clearly present in somata of the external nucleus of the inferior colliculus but was diffuse throughout brainstem auditory nuclei. The labeling was present in most brainstem auditory nuclei by post-natal day (PND) 6. The intensity of the staining subsequently increased to its highest level at PND21 and decreased to an adult-like appearance by the fourth post-natal week. In adult, CNTFRalpha labeling occurred in most neurons of the cochlear nucleus (CN), the lateral superior olive (LSO), the medial superior olive (MSO), and the medial nucleus of the trapezoid body (MNTB). CNTFRalpha labeling first appeared in the central nucleus of the inferior colliculus (IC) by the end of the fourth week. There was a general increase in the expression of CNTFRalpha that begins prior to the onset of hearing and reaches its highest level after this important developmental stage. Ultrastructural analysis in the adult ventral CN revealed the presence of CNTFR in post-synaptic sites. The presence of CNTF has been investigated in the adult using both Western blot and immunohistochemistry. Western blot showed the presence of CNTF in both peripheral and central auditory structures. The CNTF label was generally localized to the somatic compartment, in axons and as puncta surrounding neuronal cell bodies and dendrites. Differential CNTF labeling was observed between the different auditory nuclei. CNTF staining is present in neurons of the CN, the MNTB and the LSO, while it is restricted to axons and puncta surrounding neuronal somata in the IC. The clear presence of CNTFRalpha at post-synaptic terminals and that of its ligand the CNTF in axons and puncta surrounding neuronal cell bodies suggest an anterograde mode of action for CNTF in the central auditory system.