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EFFECT OF ACTINOMYCIN‐D ON LABELLED MATERIAL IN THE RETINA AND OPTIC TECTUM OF GOLDFISH AFTER INTRAOCULAR INJECTION OF TRITIATED RNA PRECURSORS
Author(s) -
Ingoglia N. A.,
Grafstein Bernice,
McEwen B. S.
Publication year - 1974
Publication title -
journal of neurochemistry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.75
H-Index - 229
eISSN - 1471-4159
pISSN - 0022-3042
DOI - 10.1111/j.1471-4159.1974.tb04391.x
Subject(s) - rna , tectum , uridine , retina , guanosine , biochemistry , biology , chemistry , endocrinology , central nervous system , midbrain , neuroscience , gene
—After injection of [ 3 H]guanosine or [ 3 H]uridine into the eye of goldfish, labelled acid‐soluble radioactivity and RNA appeared in the contralateral optic tectum. When 0·1 μg actinomycin‐D was injected into the eye 4 h before the precursor, the labelled RNA in the retina by 18 h after the injection was only 23 per cent of normal, but the acid‐soluble radioactivity in the retina and the small amount of labelled acid‐soluble material conveyed to the tectum were not significantly affected; by 15–20 days after the injection the acid‐soluble radioactivity in the retina was reduced and the amount of labelled material conveyed to the tectum, including both RNA and acid‐soluble fractions, was less than normal. When the actinomycin was injected at various times before or after the precursor and measurements were made 6 days later, it was found that the amount of labelled RNA conveyed to the tectum was maximally decreased if the inhibitor was given simultaneously with or up to 4 h before the precursor, whereas the amount of RNA was normal if the incorporation of the precursor had been allowed to proceed for 12 h before the inhibitor was given. This result would be consistent with the view that much of the RNA conveyed to the tectum had been synthesized in the retina within 12 h of the injection of the precursor, and had then presumably been axonally transported in the optic nerve to the tectum. However, since the acid‐soluble material conveyed to the tectum was also reduced as a result of the actinomycin treatment, the results of these experiments with actinomycin do not unequivocally rule out the possibility that the RNA appearing in the tectum had been locally synthesized from the axonally transported acid‐soluble material. In the retina, both the labelled RNA and acid‐soluble fractions were reduced, to about 15 and 60 per cent of normal, respectively, without any relationship to the time between the injection of inhibitor and precursor. The discrepancy between the effects of the labelling of the retina and the labelling of material conveyed to the tectum could be correlated with the fact that the actinomycin caused severe damage to the retinal receptor cells, while leaving the ganglion cells relatively intact. The more pronounced effect of actinomycin on the receptor cells could in turn be correlated with the fact that these cells had a higher rate of RNA synthesis than the ganglion cells. This was demonstrated autoradiographically by the higher rate of incorporation of [ 3 H]uridine into the receptor cells. Intracranial injection of actinomycin did not affect significantly the amount of labelled RNA conveyed to the tectum, which would argue against the local synthesis of this RNA. It is not certain, however, that the actinomycin penetrated deeply enough into the tectum to be effective.