NEUROKININ-1 RECEPTOR EXPRESSION IN THE RAT RETINA

Tachykinin (TK) peptides influence neuronal activity in the inner reti na of mammals. The aim of this investigation was to determine the cell ular localization of the neurokinin 1 receptor (NK1), whose preferred ligand is the TK peptide substance P (SP), in the rat retina. These st udies used a polyclonal antiserum directed to the C-terminus of rat NK 1. The majority of NK1-immunoreactive (IR) cells were located in the p roximal inner nuclear layer (INL), and very rarely they were found in the distal INL. Some small and large NK1-IR somata were present in the ganglion cell layer. NK1-IR processes were densely distributed across the inner plexiform layer (IPL) with a maximum density over lamina 2 of the IPL. Immunoreactive processes also crossed the INL and ramified in the outer plexiform layer where they formed a sparse meshwork. NK1 -IR processes were rarely observed in the optic nerve fiber layer. Dou ble-label immunofluorescence studies with different histochemical mark ers for bipolar cells indicated that NK1 immunoreactivity was not pres ent in bipolar cells. Together, these observations indicate that NK1 i mmunoreactivity is predominantly expressed by amacrine, displaced amac rine, interplexiform, and some ganglion cells. Double-label immunofluo rescence experiments were also performed to characterize NK1-containin g amacrine cells. Sixty-one percent of the gamma-aminobutyric acid (GA BA)-IR cells, 71% of the large tyrosine hydroxylase (TH)-IR cells, and 100% of the small TH-IR cells contained NK1 immunoreactivity. In addi tion, most (91%) of the NK1-IR cells had GABA immunoreactivity. In con trast, vasoactive intestinal polypeptide-, TK-, choline acetyltransfer ase-, and parvalbumin-IR amacrine cells did not express NK1 immunoreac tivity. Overall, the present findings suggest that SP acts directly up on several cell populations, including GABA-containing amacrine cells and ganglion cells, to influence visual information processing in the inner retina. (C) 1997 Wiley-Liss, Inc.