Developmental expression of nenrokinin-1 and neurokinin-3 receptors in therat retina

Tachykinin (TK) peptides act on retinal neurons through neurokinin (NK) rec eptors. We examined the expression of neurokinin-1 (NK1; the substance P re ceptor), NK3 [the neurokinin B (NKB) receptor], and TK peptides in developi ng rat retinas. NK1 immunolabeling was found in newborn retinas in rare ama crine cells and in putative ganglion cells. At postnatal day 2 (PND 2), NK1 immunostaining was reduced greatly among ganglion cells, and it appeared i n many amacrine cells and in fibers in the inner plexiform layer (IPL), wit h the highest density in laminae 1, 3, and 5. A similar pattern was found a t PND 7. At PND 12, interplexiform NK1-immunoreactive (-IR) cells were dete cted, and NIK1-IR fibers in the IPL were concentrated in lamina 2, similar to what was seen in adults. NK3 was expressed mainly by OFF-cone bipolar ce lls, and the developmental pattern of NK3 was compared with that of cone bi polar cells that were labeled with antibodies to recoverin. Immature recove rin-IR cone bipolar cells were seen at PND 2. NK3 immunolabeling was detect ed first in the outer plexiform layer and in sparse bipolar cell somata at PND 10, when recoverin-IR cone bipolar cells are nearly mature. By PND 15, both the NK3 immunostaining pattern and the recoverin immunostaining patter n were similar to the patterns seen in adults. TK immunoreactivity was pres ent at PND 0 in amacrine cells and displaced amacrine cells. By PND 10, the morphologic maturation of TK-IR cells was complete. These findings indicat e that, in early postnatal retinas, substance P may act on NK1 receptors, w hereas NKB/NK3 interactions are unlikely, suggesting that there are differe nt levels of importance for different TK peptides in the developing retina. (C) 2000 Wiley-Liss, Inc.