SUBSTANCE P-IMMUNOREACTIVE NEURONS IN THE HUMAN RETINA

Substance P (SP) is a neuropeptide that acts as a neurotransmitter or a neuromodulator in the retina. The aim of this study was to identify the type(s) and the distribution of the SP-immunoreactive (SP-IR) cell s in the human retina. We have used an antiserum to SP to immunostain neurons in postmortem human retinae. Immunostained retinae were proces sed with the avidin-biotin complex (ABC) to visualize the cells either whole mounted in glycerol or embedded in plastic. Some retinae were a lso sectioned at 20 mu m in order to obtain radial views of stained ce lls. SP-IR amacrine cells stain intensely and appear to be of a single type in the human retina. They are large-field cells with large cell bodies (16 mu m diameter) lying in normal or displaced positions on ei ther side of the inner plexiform layer (IPL). Their sturdy, spiny, and appendage-bearing dendrites stratify in stratum 3 (S3) of the IPL, wh ere many overlapping, fine dendrites intermingle to form a plexus of s tained processes. Either cell bodies or primary dendrites emit-an ''ax on-like'' process that, typically, divides into two long, fine process es, which run in opposite directions for hundreds of micrometers in S5 and S3 before disappearing as distinct entities in the stained plexus in S3. Long, fine dendrites also pass from the dendritic plexus to ru n in S5 and down to the nerve fiber layer to end as large varicosities at blood vessel walls. In addition, fine processes are emitted from t he dendritic plexus that runs in S1, and same pass up to the outer ple xiform layer (OPL) to run therein for short distances. The SP-IR amacr ine cell. has many similarities to the thorny, type 2 amacrine cells d escribed from Golgi studies. In addition to the SP-IR amacrine cells, a presumed ganglion cell type is faintly immunoreactive. Its 20-22 mu m cell body gives rise to a radiate, sparsely branched, wide-spreading dendritic tree running in S3. Its dendrites and cell body become enve loped by the more intensely SP-IR processes and boutons from the SP-IR amacrine cell type. The SP-IR ganglion cell type most resembles G21 f rom a Golgi study. (C) 1995 Wiley-Liss, Inc.