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R. D. Glickman, R. G. Yusupov, N. Akimov, L. J. Frishman, D. W. Marshak; Histamine Reduces Sensitivity of ON Ganglion Cells in the Primate Retina. Invest. Ophthalmol. Vis. Sci. 2008;49(13):5787.
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In primates, histaminergic retinopetal axons arise from perikarya in the hypothalamus and terminate in the inner plexiform layer. Previously, we have shown that exogenous histamine reduces the amplitude of light responses of many types of retinal ganglion cells (RGC). Here we report a quantitative description of histamine’s effect on the sensitivity of ON-type RGCs in baboon retina.
Baboon eyes (n = 8) were obtained from the Southwest Foundation for Biomedical Research, San Antonio, TX. After hemisection and removal of the vitreous, the eyecups were transported to the laboratory in oxygenated Ames medium in the dark. Under dim red light, pieces of eyecup were placed in a superfusion chamber, and a recording array (NeuroNexus) with 4 tetrodes was advanced into the ganglion cell layer. The retina was dark-adapted for 30 min. Light responses were elicited with an LED photostimulator (560 nm) producing 5 ms flashes in the scotopic range (0.002 - 2.3 Rh*/rod), from darkness at a rate of 2 flashes/sec. After characterizing the light response of isolated RGCs, histamine (HA, 1 to 5 µM) was applied in the perfusion bath, and the effects on the cells’ response properties were observed.
The current result set is based on 113 RGCs with ON-type light responses. A Naka-Rushton model was fit to the initial portion of the intensity-response functions, and the slope of a tangent to the initial segment was used as a metric of the sensitivity of the cells before and after histamine treatment. In 82 cells, HA decreased the sensitivity to a mean of 32.9% of the pre-HA level, while in 14 cells, HA increased the sensitivity by a mean of 60% over the pre-HA level. HA affected the sensitivity by less than 20% in the remaining 17 cells. The cells whose sensitivity was increased by histamine (avg. pre-HA slope=678.1±612.3) were compared with the cells whose sensitivity was decreased (avg. pre-HA slope=1244.2±1558.3); however, the difference in the slope parameter was not significant.
The majority of ON-type RGCs responded to the application of histamine with a reduction in sensitivity. M-cells are known to be more sensitive than P-cells; however, the groups of HA sensitivity-increasing cells and HA sensitivity-decreasing cells both contained high and low sensitivity cells. Because the slope parameter of these groups did not differ significantly, we conclude that HA can affect the sensitivity of M-type and P-type cells similarly.
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