Beschreibung:
<jats:p><jats:bold>Abstract—</jats:bold> Although biochemical and electron microscopic evidence has shown that RNA molecules may be found within axons, the origin of this RNA is not known. In order to determine if the RNA found in axons is synthesized in the nerve cell body and axonally transported, we have studied the effect of the RNA inhibitor cordycepin (3′‐deoxyadenosine) on the retinal synthesis and axonal migration of radioactive RNA. Ten μg of cordycepin was injected into the right eye of 11 fish and 3 h later [<jats:sup>3</jats:sup>H]uridine was injected into the same eye. Twelve control fish were injected with [<jats:sup>3</jats:sup>H]uridine only and all fish were sacrificed 6 days later. Results of RNA extraction of retina and tecta showed that cordycepin decreased retinal RNA synthesis by approx 24%, while inhibiting the amount of [<jats:sup>3</jats:sup>H]RNA appearing in the contralateral tectum by 74%. Since the transport of RNA precursors was depressed by only 50%, (significantly different from the effect on RNA, <jats:italic>P</jats:italic> < 0.01) it seems unlikely that the action of cordycepin in decreasing tectal [<jats:sup>3</jats:sup>H]RNA levels was due solely to a decrease in the availability of labeled precursors for tectal RNA synthesis.</jats:p><jats:p>For the purpose of blocking tectal RNA synthesis, 200 μg of cordycepin was injected intracranially several days after the intraocular injection of [<jats:sup>3</jats:sup>H]uridine. This route of cordycepin administration failed to significantly block the appearance of [<jats:sup>3</jats:sup>H]RNA in the tectum, suggesting that at least some of the [<jats:sup>3</jats:sup>H]RNA in the tectum was synthesized before arrival in the tectum itself.</jats:p><jats:p>To be sure that cordycepin itself was not being transported, we injected cordycepin into the right eye of fish and 5 days later, injected fish intracranially with [<jats:sup>3</jats:sup>H]uridine. Autoradiograms were prepared and grains were counted over the fiber layers of left (experimental) and right (control) tecta. No significant difference was observed in the number of grains of left vs right tecta indicating that cordycepin itself is not axonally transported.</jats:p><jats:p>These experiments support earlier findings from our laboratory which suggest that RNA may be axonally transported in goldfish optic fibers.</jats:p>