Distribution of CNTF receptor α protein in the central nervous system of the chick embryo

Ciliary neurotrophic factor (CNTF) promotes the survival and differentiation of various neuronal and glial cell populations in the nervous system of vertebrates. In mammals, the ligand‐binding α‐subunit of the CNTF receptor (CNTFRα) is expressed in a variety of neuronal populations, including all CNTF‐responsive cells. Previous studies suggested that functional differences in the CNTF/CNTF receptor system between chicks and mammals exist. The purpose of the present study was to examine the temporal and spatial expression pattern of the chick CNTFRα protein during CNS development. Receptor expression was detectable by immunoblotting in all CNS areas tested but showed area‐specific developmental regulation. Interestingly, two variants of CNTFRα, 69 and 65 kD, were identified by immunoblotting with a shift from the higher to the lower molecular mass species occurring during development. Immunoreactivity for CNTFRα protein was preferentially observed in neuropil and white matter structures of the developing CNS while neuronal somata generally appeared unlabeled. For example, expression was observed in the olfactory system, in the telencephalon, in parts of the somatosensory system, in components of the tectofugal pathway, in the cerebellum, and in auditory brainstem nuclei. Fiber tracts that exhibit CNTFRα immunoreactivity were the lateral forebrain bundle, occipitomesencephalic tract, quintofrontal tract, and vestibular nerve. Our study identifies potential new targets of a chick CNTF‐related molecule and reveals significant regional differences of CNTFRα protein expression between chick and mammals. These results suggest that the CNTF receptor performs distinct developmental functions in different animals. J. Comp. Neurol. 461:111–122, 2003. © 2003 Wiley‐Liss, Inc.