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Pyrimidine metabolism during restorative brain growth after neonatal undernutrition in the rat
Insights
Undernourished rat pups showed reduced body and brain growth. However, key enzymes for DNA synthesis, thymidine kinase (TK) and thymidylate synthetase (TS), were elevated, indicating their importance in restorative brain growth.
Area of Science:
- Neuroscience
- Developmental Biology
- Biochemistry
Background:
- Early life undernutrition can impair brain development.
- Restorative growth periods are crucial for recovery from nutritional deficits.
Purpose of the Study:
- To investigate the impact of early life undernutrition on cerebellar growth and nucleic acid biosynthesis pathways in Wistar rat pups.
- To identify key enzymes involved in restorative brain growth following nutritional rehabilitation.
Main Methods:
- Wistar rat pups were subjected to differential undernutrition (lightest pups) or control conditions.
- Body weight, cerebellar weight, and cerebellar DNA content were measured.
- Enzyme activities of pyrimidine and nucleic acid biosynthesis pathways (TK, TS, UK, aspartate transcarbamylase) were assayed in cerebella.
Main Results:
- Undernourished light pups exhibited significantly reduced body weight, cerebellar weight, and cerebellar DNA compared to controls.
- Activities of thymidine kinase (TK) and thymidylate synthetase (TS) were significantly elevated in the cerebella of undernourished pups.
- No significant changes were observed in uridine kinase (UK) or aspartate transcarbamylase activities.
Conclusions:
- Elevated TK and TS activities suggest their critical role in facilitating DNA biosynthesis during restorative brain growth after undernutrition.
- The inter-conversion pathway for thymidylate synthesis is activated to support DNA replication during catch-up brain growth.
Abstract:
Three litters of 20 Wistar rat pups each were maintained until age 6 days at which time only the 4 lightest and 4 heaviest pups from each litter were left with the mother until age 13 days. Three control litters of eight pups each were also maintained for 13 days. At that time, the undernourished light pups showed body weight, cerebellar weight, and cerebellar DNA, respectively, of 79.2%, 86.6%, and 90.4% compared with a "combined control" group consisting of control pups plus undernourished heavy pups which were statistically indistinguishable with regard to these three measurements. After the week of "catch-up" or restorative body and brain growth, activities of enzymes from metabolic pathways leading to pyrimidine and nucleic acid biosynthesis were measured in cerebella from all three groups (control, undernourished heavy, and undernourished light). The salvage pathway enzyme thymidine kinase (TK) and the inter-conversion pathway enzyme thymidylate synthetase (TS) in the undernourished light group showed significant elevations of 32% and 11%, respectively, above activity in the combined control group. The salvage pathway enzyme uridine kinase (UK) and the de novo pathway enzyme aspartate transcarbamylase were not significantly different in cerebella from these two groups. The significant elevation in TK and TS in undernourished pups suggest that these enzymes are critical for restorative brain growth. The significant elevation of TS indicates that the inter-conversion pathway converting available uridylate, a ribonucleotide, to thymidylate, a deoxyribonucleotide, is activated in order to augment DNA biosynthesis.