Development of neuropeptide Y-immunoreactive neurons in the rat retina

Neuropeptide Y-like immunoreactivity (NPY-LI) was examined in the rat retina by radioimmunoassay and immunocytochemistry during prenatal and postnatal development. NPY-LI appears late in gestation (embryonic day [E18]), at which time it is present in small quantities (0.038 +/- 0.005 pm/mg protein) and the NPY-LI is confined to cells in the ganglion cell layer. The concentration of NPY-LI rises steadily over pre- and postnatal development; and on postnatal day 6 (P6), immunoreactive cells first appear in the inner nuclear layer. At eye opening (P13), there is a large increase in NPY-LI (0.207 +/- 0.035 pm/mg protein), and immunoreactive cells can be seen in the innermost row of the inner nuclear layer (INL) as well as in the ganglion cell layer (GCL). As the retina matures, the levels of NPY-LI fall to adult levels (0.080 +/- 0.019 pm/mg protein) and the peptide is confined to two subpopulations of cells, one in the INL and one in the GCL. The transient increase in NPY-LI at eye opening suggests that it may have a role at this time in modulating developing retinal circuitry. This pattern is very different from that of somatostatin-like immunoreactivity which appears earlier in development in high quantities and decreases prior to synaptogenesis and eye opening.