Cholinergic neurons of the chicken ciliary ganglion contain somatostatin

Somatostatin immunoreactivity was studied in the avian ciliary ganglion by immunocytochemistry and radioimmunoassay. Immunoreactivity was localized to small diameter cell bodies of neurons from embryos, newly-hatched and adult preparations. Immunostaining of ganglia with a mixture of antisera to substance P and monoclonal antibody to somatostatin indicated that a number of somatostatin-immunoreactive neurons were surrounded by substance P-immunoreactive boutons, which characteristically terminate on choroidal neurons. Staining with a mixture of antisera to choline acetyltransferase and antibody to somatostatin showed that the somatostatin-immunoreactive neurons were less intensely-stained for choline acetyltransferase than were the neurons lacking somatostatin immunoreactivity. Bundles of nerve fibers showing somatostatin and choline acetyltransferase immunoreactivity were found in the choroid layers of the eye. Radioimmunoassay indicated the presence of somatostatin immunoreactivity in both chick and quail ganglia; the somatostatin immunoreactivity eluted from high pressure liquid chromatography in the same positions as authentic somatostatin 14 and 28. These results show that somatostatin is contained in cholinergic choroidal neurons in the chick and quail ciliary ganglion.