Neurotensin-like and somatostatin-like immunoreactivity within amacrine cells of the retina

Neurotensin-like and somatostatin-like immunoreactivity was demonstrated in the pigeon retina, using both immunohistochemical and radioimmunoassay techniques.Immunohistochemical studies utilized both the indirect immunofluorescence and immunoperoxidase procedures with two well-characterized antisera to neurotensin and three well-characterized antisera to somatostatin. Specific immunoreactivity of each antiserum was established by absorption with either 10 μM synthetic neurotensin, somatostatin or leu⁵-enkephalin. Specific immunohistochemical staining for neurotensin and for somatostatin was observed within separate populations of multistratified amacrine cells. Neurotensin-like and somatostatin-like immunoreactivity were observed within somata located in the inner nuclear layer and within varicose processes ramifying in laminae 1, 3 and 4 of the inner plexiform layer. Immunoreactive somata and processes were observed throughout the retina and their density appeared to be greatest within central retinal regions. The somata-containing neurotensin-like and somatostatin-like immunoreactivity measured about 7 μm in diameter. The cell to cell spacing of neurotensin-like immunoreactive somata was approximately 30 μm and the cell to cell spacing of somatostatin-like immunoreactive somata was approximately 27 μm in central retinal regions. Within more peripheral retinal regions, immunoreactive cells were spaced farther apart.Radioimmunoassays utilizing well-characterized antisera to neurotensin and somatostatin demonstrate specific neurotensin-like and somatostatin-like immunoreactivity in acetic acid extracts of the retina. The concentration of immunoreactive neurotensin is 59 ± 7 fmoles per whole retina (mean ± S.E.M.) or 15.4 ± 2 fmoles per mg protein. The concentration of immunoreactive somatostatin is 2209 ± 440 fmoles per whole retina or 527 ± 76 fmoles per mg protein.These results demonstrate the existence of two additional neuropeptides within selected populations of retinal amacrine cells. The localization of several different neuropeptides within the retina suggests that neuropeptides play a specific role in retinal function.