Effect of light on the labeling of optic tectum gangliosides after an intraocular injection of N-[3H]acetylmannosamine

Immediate early gene c-fos regulates the synthesis of phospholipids but not of gangliosides

Retinal ganglion cells isolated from chicks that in vivo were exposed to light have a higher phospholipid labeling capacity than those obtained from animals in the dark. Actinomycin D or a mixture of protein synthesis inhibitors or of antisense oligonucleotides to c-fos plus c-jun injected intraocularly 1 hr prior to the stimulation period, abolished the light-dark differences for phospholipids but not for gangliosides. Light stimulation induced the formation (and/or stabilization) of c-fos mRNA and of the protein c-Fos, indicating that immediate early gene induction, and consequently the synthesis of the protein(s) encoded, is essential to increase the synthesis of phospholipids but not of gangliosides. These results suggest a novel mechanism by which immediate early genes engram neural cells, modifying specifically the metabolism of cell constituents producing long-lasting changes in the cells.

Labeling of retina and optic tectum phospholipids in chickens exposed to light or dark

The labeling of retina ganglion cell and optic tectum phospholipids was determined in chickens given an intraocular injection of 32P and then either exposed to light or maintained in the dark. Significantly higher labeling was found in the optic tectum phospholipids of light-exposed compared with dark-maintained animals after 3-24 h of labeling. In the ganglion cells, the labeling of phospholipids increased in dark with respect to light at 15 and 30 min of labeling; from 60 min to 24 h, the labeling of phospholipids was significantly higher in light with respect to dark, even if the precursor pool showed a higher labeling in dark at all times studied. When labeling was allowed to proceed in the dark for 30 min and then half of the animals were exposed to light for 15 min, the labeling of ganglion cell phospholipids of light-exposed animals was significantly higher than those of animals kept in the dark. No individual phospholipid accounted for the differences observed in the labeling of the total phospholipid pool. These results are interpreted as an increase in the biosynthesis of phospholipids in the ganglion cell somas in light with respect to dark.

Optic nerve integrity is required for light to affect retina ganglion cell gangliosides

The labeling of retina ganglion cell and optic tectum gangliosides after an intraocular injection of N-[3H]acetylmannosamine ([3H]ManNAc) is higher in chickens exposed to light than in those maintained in darkness. In the present work we studied whether the signal for the higher labeling of ganglion cells in light originates in the photoreceptor layer or comes from the nerve terminal. For this purpose the labeling of ganglion cell gangliosides was determined in light and dark in chickens with one optic nerve severed. The results showed that the effect of light occurred only in the eye normally connected to the optic tectum. In the eye with its optic nerve severed, no difference was observed between the labeling of gangliosides in animals in light and dark, having both groups the labeling values of the normal eyes exposed to light. The results indicate that the information that decreases labeling in darkness or accelerates it in light originates in the nerve terminal.

Intraocular injection of tetrodotoxin in goldfish decreases fast axonal transport of [3H]glucosamine-labeled materials in optic axons

When physiological activity in goldfish visual system was abolished by repeated intraocular injection of tetrodotoxin (TTX), the fast axonal transport of radioactive amino acid-labeled protein in the optic axons was unaltered. However, the TTX treatment reduced the amount of [3H]glucosamine-labeled glycolipids that were axonally transported to the optic tectum, and may have decreased their rate of turnover in the tectum. A similar though smaller effect was observed for glucosamine-containing glycoproteins. These alterations in axonal transport may be the basis for at least some of the deleterious effects of TTX on axonal regeneration in this system.

Inhibition of the chicken retinal UDP-GaINAc:GM3, N-acetylgalactosaminyl-transferase by blood serum and by pineal gland extracts

The effects of the pineal gland extract and blood serum on the activity of the UDP-GalNAc:GM3, N-acetylgalactosaminyltransferase (GM3:GalNAc-T) from chicken retina were studied. Both preparations have inhibitory capability on the enzyme activity. Two types of inhibitory capabilities were found: one is heat labile and decomposes UDP-GalNAc and another is heat stable. When the pineal gland extracts were prepared from light-exposed chickens, the inhibitory capability increased with respect to the extracts from dark-maintained animals; vice versa, blood serum from dark-maintained animals had higher heat-labile and heat-stable capabilities than that from light-exposed chickens. In in vitro experiments, no difference was found in the inhibitory capability of blood serum extracts from pinealectomized animals compared to control animals. In vivo labeling experiments with pinealectomized animals in either light or dark showed similar differences in the labeling of the optic tectum gangliosides as the normal animals.

The effect of light exposure following an intraocular injection of [3H]N-acetylmannosamine on the labeling of gangliosides and glycoproteins of retina ganglion cells and optic tectum of singly caged chickens

Ten-day-old chickens that after a 2-day-period of adaptation to dark received an intraocular injection of [3H]N-acetylamannosamine ([3H]ManNAc) and were exposed, individually housed, to light, have more labeling in the gangliosides and glycoproteins of the ganglion cell layer of retina and in the contralateral optic tectum compared to their counterparts that remained in darkness. No differences were found in the labeling of the acid soluble fraction of the ganglion cell layer between the animals in dark and light at 0.5 and 5 h after the injection of [3H]ManNAc. No differences could be observed in the quality or storage of the gangliosides labeled in light with respect to those labeled in dark, but those labeled in light had a higher percent of labeling released by neuraminidase at 5 h after the intraocular injection of the labelled precursor. In animals exposed to intermittent light, the increased labeling with respect to dark was smaller than that found in animals exposed continuously to light.