Effect of undernutrition on DNA and RNA synthesis in subcellular fractions from different regions of the developing rat brain

Soyabean fortification and enrichment of regular and quality protein maize tortillas affects brain development and maze performance of rats

The brain development and performance of rats fed throughout two generations with an indigenous maize tortilla-based diet was studied. The experiment compared casein control with five different diets produced from: regular fresh masa; regular, enriched dry masa flour containing thiamin, riboflavin, niacin, folic acid, Fe and Zn (REDMF); dry masa flour fortified with 60 g/kg defatted soyabean meal and enriched (FEDMF); enriched quality protein maize (QPM) flour (EQPM); QPM flour fortified with 30 g/kg defatted soyabean meal and enriched (FEQPM). In both generations, brain and cerebellum weights and myelin concentration were significantly higher (P < 0.05) in rats fed the FEDMF and FEQPM diets. There was no significant difference (P > 0.05) in brain DNA in first-generation rats; however, second-generation rats fed FEDMF, EQPM and FEQPM tortillas had higher cerebral DNA, neuron size and brain activity as estimated by the RNA:DNA ratio. Short-term and long-term memory performance in the Morris maze improved (P < 0.05) among rats fed the FEDMF, FEQPM and EQPM diets. Second-generation rats fed the FEDMF and FEQPM diets had a superior (P < 0.05) working memory and learning performance. The utilisation of regular or QPM tortillas enriched with selected micronutrients and fortified with soyabean is highly recommended to assure adequate brain development. The high lysine-tryptophan QPM made it possible to save half of the soyabean flour without sacrificing the nutritional value of soyabean-fortified tortillas.

Circadian oscillations of DNA synthesis in rat brain

The possibility that the synthesis of brain DNA undergoes a circadian fluctuation was examined in male adult Wistar rats, kept under natural lighting conditions or born and raised under artificial lighting conditions. Groups of rats were taken every 4 h during the 24 h, injected subcutaneously with [methyl-3H]thymidine and killed 4 h later. By cosinor analysis, the DNA specific activity of cerebral hemispheres and brainstem was found to show a significant 24 h rhythm with the peak at the beginning of the dark period (waking period). By contrast, in kidney, the peak of the circadian rhythm of DNA specific activity occurred during the light period (sleep period), in agreement with literature data. On the other hand, in 4-week-old rats, born and raised in artificial lighting conditions, brain DNA specific activity followed a 12 h rhythm, in agreement with the lack of a significant diurnal oscillation of the sleep--waking structure. It is concluded that brain DNA synthesis undergoes a circadian fluctuation in association with the circadian rhythm of waking.

Postnatal ontogeny of uridine kinase in the cerebellum, hypothalamus, and cerebral cortex of the rat

Postnatal developmental patterns of uridine kinase were determined in crude subcellular fractions of the rat cerebellum, hypothalamus and cerebral cortex at ages 3 through 60 days. The highest specific activity and predominant distribution of enzyme was in the 105,000 g supernatant of the 3 brain regions. Enzyme activity in hypothalamus and cerebral cortex was maximum at 3 days and decreased with age; in cerebellum it increased through 13 days and decreased thereafter. Thus, the pattern of activity in hypothalamus and cerebral cortex paralleled changes in DNA and RNA synthesis through age 60 days; in cerebellum, it more closely approximated changes in DNA synthesis during early development. Changes in Km with aging suggest that the brain regions contain more than one form of enzyme. The highest particulate activity was in the microsomal fraction of the cerebellum and hypothalamus at all ages and in the cortex at 35 and 60 days. Relative specific activity for microsomal fractions of the brain regions at 60 days indicate a concentration of the enzyme which may be relevant in the maintenance of RNA activity in adult brain.

RNA synthesis in neuronal and glial cell nuclei from rat cerebral hemispheres during early postnatal development

RNA synthesis in rat cerebral hemispheres at 1, 5, and 10 days of age and the relative contribution brought by neuronal and glial nuclei to RNA synthesis was investigated. The experiments were carried out both in vivo (by i.p. injection of [3H]uridine) and in vitro (either by incubation of tissue slices with [3H]uridine or by determination of RNA polymerase activities). The labeling of RNA decreases from 1 to 10 days of age both in vivo and in vitro; the decrease is of the same extent in neuronal and glial nuclei. RNA polymerase activity Mg2+-dependent does not change significantly from 1 to 10 days of age either in total, in neuronal, or in glial nuclei, whereas the Mn2+-dependent activity increases significantly over the same developmental period studied. The significance of RNA polymerase assay as an index of in vivo RNA synthesis is discussed.

Effect of undernutrition on some enzymes involved in the salvage pathway of purine nucleotides in different regions of developing rat brain

The effect of undernutrition on the activity of two key enzymes of purine salvage pathway, namely hypoxanthine-guanine phosphoribosyltransferase (HGPRTase) and adenine phosphoribosyltransferase (APRTase), in cerebral hemispheres, cerebellum and brain stem of rats at different days of postnatal development was studied. The activity of HGPRTase and of APRTase is significantly lower in all brain regions of undernourished animals at 5 days after birth; between 10 and 15 days of age there is a recovery of the enzymatic activity which is particularly evident in the cerebellum. Successively both enzymatic activities decrease reaching at 30 days of age values quite similar to those of controls. These results indicate that undernutrition during fetal and postnatal development, impairs and delays the activity of the enzymes of purine salvage pathway.