This review discusses the expression and cellular localization of the neuro
peptide somatostatin (SRIF) and one of the SRIF subtype (sst) receptors, ss
t, in the mammalian retina. SRIF immunoreactivity is predominantly localize
d to a sparse population of amacrine and displaced amacrine cells in the ga
nglion cell layer in several mammalian retinas including the rat, rabbit, c
at, and primate. These cells, characterized by multiple processes, form a s
parse network in the inner plexiform layer (IPL) in all retinal regions. Ve
ry few processes are also in the outer plexiform layer. In contrast to the
predominant distribution of SRIF processes to the IPL, there is a widesprea
d distribution of sst(2A) immunoreactivity to both the inner and outer reti
na in all mammalian retinas studied to date. In rabbit retina, sst(2A) immu
noreactivity is predominant in rod bipolar cells and in sparse wide-field a
macrine cells. In the rat retina, sst(2A) immunoreactivity is localized to
several neuronal cell types-cone photoreceptors, horizontal cells, rod and
cone bipolar cells, and amacrine cells. Reverse-transcriptase-polymerase ch
ain reaction analysis found that set, mRNA is expressed in the rat retina,
while sst(2A) mRNA is not detected. Finally, in the primate retina sst(2) i
mmunoreactivity is predominant in cone photoreceptors, with additional immu
nostained cell bodies and processes in the inner retina. These findings ind
icate that SRIF may modulate several neuronal cell types in the retina, and
that it has a broad influence on both scotopic and photopic visual pathway
s. (C) 2000 Wiley-Liss. Inc.