Abstract
Purpose: :
Very recently, the authors found more than six times higher levels of neurokinin (NK) A–like immunoreactivities in the human retina when compared with substance P (SP). The present study aimed to find out how much of these immunoreactivities can be attributed to NKA and NKB and then the exact distribution pattern of both NKA and NKB was evaluated in the human retina and compared with that of SP.
Methods: :
NKA–like immunoreactivities were characterized in the human retina by reversed phase HPLC followed by radioimmunoassay using the K12 antibody which recognizes both NKA and NKB. Furthermore, the retinae of a 22– and 70–years old donor were processed for double–immunofluorescence NKA/SP and NKB/SP.
Results: :
NKA contributes to approximately two thirds and NKB to approximately one third of the immunoreactivities measured with the K12 antibody. NKA was found to be localized in sparse amacrine cells in the proximal inner nuclear layer and in displaced amacrine cells in the ganglion cell layer with processes ramifying in stratum 3 of the inner plexiform layer but also in sparse ganglion cells whereas staining for NKB was only observed in ganglion cells and in the nerve fiber layer. Double–immunofluorescence revealed cellular colocalization of NKA with SP and also of NKB with SP.
Conclusions: :
The levels of NKA and NKB are more than three and two times higher than those of SP, respectively. Since the prefered receptor of NKA, the NK2 receptor, is thought to be absent in the retina and since at least in the rat retina the NK1 receptor is much more prominently expressed in the inner retina than its prefered ligand SP, NKA may act on the NK1 receptor. This would indicate similar functional roles and because of the much higher levels, NKA may functionally be the much more important peptide than SP. The localization of NKB exclusively in ganglion cells is atypical and unique for neuropeptides and this peptide may be involved in the transfer of visual informations into the central nervous system.
Keywords: neuropeptides • retina • pharmacology