Autoradiography of nucleoside uptake into the retina
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A selective uptake mechanism for some nucleosides and related substances was found in retinae of light adapted rabbits and fish. After the intravitreal injection in vivo of [(3)H]adenosine, [(3)H]inosine, [(3)H]guanosine and certain related compounds, the distribution of radioactivity was studied by autoradiography. Retinae were also incubated in [(3)H]adenosine and [(3)H]inosine and then were similarly processed. In rabbits, the accumulation of radioactivity from [(3)H]adenosine and [(3)H]guanosine was predominantly into glial cells, but also into neurons. [(3)H]Inosine labelled glia almost exclusively. However, the adenosine analog, [(3)H]methylphenylethyl-adenosine, resulted in well-defined neuronal labelling in this species. In fish, a few photoreceptor cell bodies exhibited strong radioactivity with the nucleosides, presumably representing incorporation into nucleic acids of replicating cells. Labelling was also seen in horizontal cells, amacrine cells and ganglion cells after the injection of either [(3)H]adenosine, [(3)H]guanosine or [(3)H]inosine. To some extent, the selective accumulation of radioactivity is likely to be due to cell replication, but in most neurons, other factors must be responsible. Judging from what is known about the actions of adenosine in central nervous tissue, signal transmission in the retina could be such a factor.