Immunohistochemical study for histamine in the retina of mammal

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Histamine is widely distributed in various organ. The retina of mammal contains histamine, too. However, there is little knowledge of the role of histamine in the retina of mammal. To understand the role of histamine in the retina of mammal, we first examined the localization of histamine in the retina of rats by light and electron microscopy using immunohistochemistry. As the results, the histamine-like immunoreactivity was observed in the processes of rod cells, rod spherules and a part of the free surface of endothelial cells of retinal vessels. Other cells in the retina had no histamine-like immunoreactivity. In the rod spherules, the histamine-like immunoreactivity was granular. These immunoreactive granules seemed to be synaptic vesicles. However, synaptic vesicles around the synaptic ribbon of the rod spherules had no histamine-like immunoreactivity. the control groups were the antiserum added to with the excess pure histamine, nonimmune rabbit serum and PBS, all of which were substituted for the antiserum. The control groups had no immunoreactivity. This result shows that only rod cells contain histamine-like material in the cell body. Secondary, we examined the localization of histidine-decarboxylase by light microscopy using immunohistochemistry to investigate the production of histamine in the rod cells. The immunoreactivity for histidine-decarboxylase was observed in the outer half of outer plexiform layer. This result shows that the visual cells contain histidine-decarboxylase-like material, and suggests that the rod cells can make histamine. Our present study suggests that histamine is produced in rod cells and acts as the neurotransmitter or the neuromodulator in the rod cells of rats. With respect to histamine on the, free surface of the blood vessels, histamine may regulate the permeability and the relaxation of retinal blood vessels.