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Ye Long, Andrea Bordt, Weiley Liu, Stephen Lee, Elizabeth Davis, David W Marshak; Wide-field stratified amacrine cells in primate retina contain CART. Invest. Ophthalmol. Vis. Sci. 2015;56(7 ):3232. doi: https://doi.org/.
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© ARVO (1962-2015); The Authors (2016-present)
The goal of this study was to localize the neuropeptide Cocaine- Amphetamine- Regulatory Transcript (CART) in macaque and baboon retinas.
For electron microscopy, retinas were labeled with antibody to CART using an immunoperoxidase method. For light microscopy, frozen sections or flat mount preparations were labeled with antibodies against CART and either GABA, Tyrosine Hydroxylase (TH), Glycine Transporter (GlyT) 1 or Protein Kinase C (PKC). In situ hybridization for Papio anubis CART prepropeptide mRNA was performed manually on paraffin sections using RNAscope® 2.0 HD.
CART mRNA probe bound to perikarya in the in the INL and GCL. CART antibody labeled a subset of amacrine cells in the INL and, less frequently, in the GCL. The labeling patterns in primate retina were identical using two antisera raised against different portions of the CART molecule, and the labeling was completely blocked when the antiserum was preincubated with synthetic peptide. CART-positive dendrites were found throughout the IPL but were most common in stratum 5 close to the GCL. The CART-positive amacrine cells resembled the wide-field stratified types described using the Golgi method, and based on their soma sizes and spatial distribution there appeared to be 2 subtypes. They were GABA-positive and GlyT1-negative. The CART-positive amacrine cells received synapses from bipolar cell axons and made synapses onto the axons in a reciprocal configuration, and based on the light microscopic results with anti-PKC, these are likely rod bipolar cells. They also received synapses from amacrine cells on their primary dendrites, and based on the light microscopic results with anti-TH, these are likely to be dopaminergic.
The pattern of labeling was different from that in rodents, where CART is found in dopaminergic amacrine cells and ON-OFF direction-selective ganglion cells. The CART-positive cells in primates resembled A17 and serotonin-accumulating amacrine cells of other mammals, and they would be expected to play a major role in rod vision. They cells would be expected to depolarize in response to light stimuli in the scotopic range, and the rod bipolar cells are likely to be the primary targets of the CART they release. Based on work on rat hippocampal cells, one possible effect of CART is to block L-type voltage-gate Ca++ channels, which are known to be present on the axon terminals of primate rod bipolar cells.
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