Journal of Neuroscience, Vol 10, 3045-3055, Copyright © 1990 by Society for Neuroscience
Localization of immunoreactive cholecystokinin precursor to amacrine cells and bipolar cells of the macaque monkey retina
DW Marshak, LB Aldrich, J Del Valle and T Yamada
Department of Neurobiology and Anatomy, University of Texas Medical School, Houston 77025.
We used antisera that recognized precursors of the neuropeptide
cholecystokinin extended at the carboxyl terminus in an immunocytochemical
study of the macaque retina. A subpopulation of bipolar cells with long,
obliquely oriented dendrites was labeled. Their axons terminated
exclusively in the fifth stratum of the inner plexiform layer, where they
contacted processes of amacrine and ganglion cells. Based on their
morphology, these cells appeared to be the type that contacts
short-wavelength cones selectively. Two types of amacrine cells were also
labeled, and processes from both types formed dense plexuses in the second
and fourth strata of the inner plexiform layer. The majority of their
synaptic connections were with other amacrine cells, but they had more
contacts with bipolar cell axons and retinal ganglion cell dendrites than
any other peptidergic cells in the macaque retina. We studied extracts of
macaque retina with gel- filtration chromatography and radioimmunoassays to
confirm our immunohistochemical results. We found cholecystokinin
octapeptide and other immunoreactive forms that were amidated at their
carboxyl termini and were therefore likely to be biologically active.
Unlike most other regions of the CNS, however, the retina had relatively
low concentrations of amidated forms, and forms with extended carboxyl
termini that are presumably their precursors were far more abundant. These
findings suggest that the rate of cholecystokinin synthesis in the retina
is quite high, as we would expect if the peptide were found in tonically
active neurons.