Postnatal development of NK1, NK2, and NK3 neurokinin receptors expressionin the rat retina

The biological effects of tachykinins are mediated by three distinct recept ors, the neurokinin 1 receptor (NK1-R), NK2-R, and NK3-R. There is no infor mation available concerning the development of these receptors in the retin a. In the present study, we investigated the localization of tachykinin rec eptors, using antisera directed against NK1-R, NK2-R, and NK3-R in the adul t and developing rat retinas. Numerous NK1-R immunoreactive (NK1-R IR) cell s were already observed in the proximal part of the neuroblastic layer in t he retina at postnatal day 5 (P5). The distribution and intensity of NK1-R IR cells and processes in the inner nuclear layer (INL) and inner plexiform layer (IPL) at P10 were similar to those of adult retina, Most NK1-R IR ce lls located in the proximal part of INL, which were morphologically amacrin e cells, In the contrast to the early expression of NK1-R LR cells, no NK3- R IR structures existed in the neuronal elements of the retina until P10. N K3-R IR processes were first detected in the outer plexiform layer (OPL) at PIG. At P15, NK3-R IR somata were slightly stained in the distal and middl e parts of the INL, and NK3-R IR processes were present in the OPL and the upper part of the LPL. During P15-P30, the number of NK3-R IR somata locate d in the INL remarkably increased. These NK3-R IR cells were morphologicall y bipolar and amacrine cells. This study provides differential cellular dis tribution of NK1-R LR cells and NK3-R IR cells in the INL of the rat retina . Our findings suggest that NK1-R and NK3-R are involved in different visua l circuits and retinal maturation, and NK3-R may play previously unknown im portant roles in the visual processes of the rat. (C) 1999 Elsevier Science B.V. All rights reserved.