THE LABELLING OF THE GANGLIOSIDIC FRACTION FROM BRAINS OF RATS EXPOSED TO DIFFERENT LEVELS OF STIMULATION AFTER INJECTION OF [6-3H]-GLUCOSAMINE

6-³H] Glucosamine was injected into rats and then they were submitted for 1 h to light (about 1100 lux) and sound, while their controls were kept in darkness. Two series of experiments were done: in one, the animals received the injection intracerebrally; in the other, the injection was intraperitoneal. In both series the ratios of specific radioactivities (c.p.m./μmol of NANA) in mitochondria1 gangliosidic fractions to those in synaptosomal gangliosidic fractions were higher for rats exposed to illumination and sound ?+ 74 per cent, P < 0·01 and + 49 per cent, P < 0·001 (in respectively, experiments with intracerebral and intraperitoneal injections) than for animals kept in dark. For animals iqjected intraperitoneally the specific radioactivity of the mitochondria1 gangliosidic fraction from rats exposed to light was higher (+ 11 per cent, P < 0.05) than that obtained from animals kept in dark. For synaptosomes the specific radioactivity of the gangliosidic fraction obtained from animals exposed to light was lower (?15 per cent, P < 0.01) than that obtained from animals kept in dark. In animals kept under the experimental conditions already described for more than 1 h the differences tended to disappear. No differences were observed between the two groups of rats in the amounts of radioactivity found in the brain.