Effect of ciliary neuronotrophic factor on somatostatin expression in chick ciliary ganglion neurons

The normal development of somatostatin (SOM) expression in neurons of the chick ciliary ganglion and the effects of ciliary neuronotrophic factor (CNTF) on SOM induction in cultured ciliary ganglion neurons, were studied by immunocytochemical techniques. SOM immunoreactivity was first detectable in some neurons of the ganglion at embryonic day (E)8 and between E14 to hatch, 44-46% of the neuronal population contained the peptide. It was inferred that essentially all choroid neurons, which constitute 50% of the neuronal population, contain SOM. Culture studies indicated that CNTF supported both the SOM positive choroid neurons and the SOM negative ciliary neurons. Although CNTF was necessary for the survival and maturation of cultured ciliary ganglion neurons, it did not influence either the induction or maintenance of SOM expression in these neurons. CNTF may instead act as a permissive factor, allowing the induction of SOM in neurons of the ciliary ganglion by other, more specific, factors.