Nerve growth factor (NGF) receptor expression in chicken cranial development

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Abstract
In order to map the expression of receptors for nerve growth factor (NGF) during brain and cranial ganglia development, iodinated NGF (125IβNGF) was used as a probe in an autoradiographical analysis performed between embryonic day 3 (E3) and posthatching day 3 (P3) of chicken development. Heavy autoradiographic labelling was observed at the classical NGF target sites, the proximal cranial sensory ganglia and the sympathetic superior cervical ganglion, throughout development and after hatching. In contrast, only weak Labelling could be detected during a restricted time span in the vestibulocochlear (E4–E8) and the distal cranial sensory ganglia (E4–E10), the neurons of which originate from the otic and epibranchial placodes. Specific 125b̃3NGF binding was also observed in various brain regions during early brain development. NGF receptor expression there followed a characteristic pattern. The neuroepithelial layer displayed very low levels of specific 125Ib̃NGF binding, while strong 125Ib̃NGF labelling was found in the mantle layer. Brainstem somatomotor nuclei, visceromotor columns, brain-stem alar plate, cerebellar anlage, tectum, and basal forebrain (epithalamus, striatum) were found to be transiently labelled by 125Ib̃NGF in early development (E4–E12). Non-nervous tissues such as parts of the otic vesicle epithelium and skeletal muscle anlagen of the head were also labelled. These results, showing specific binding of 125Ib̃NGF to cranial cells of different origin (neural tube, neural crest, placode, and possibly mesoderm) strengthen the concept that NGF may have diverse functions in growth and differentiation of various tissues and cell types.