Cerebral energy metabolism in childhood

Studies of the dynamics of cerebral energy metabolism are mainly based on the analysis of changes in blood flow, the state of the BBB, and glucose and oxygen metabolism in humans and animals.

In newborns, compared with adults, the local cerebral blood flow (LMC) is low. In rats, blood flow rises in the forebrain in the first three months after birth, which roughly corresponds to the first decade of human life. The density of capillaries in rats in various parts of the brain increases mainly in the first month of life.

The supply of energy substrates from the blood to the brain is via the BBB. It is believed that the main functions of the BBB mature in the prenatal period. More recently, evidence has emerged indicating a number of subtle rearrangements in intracranial vascular resistance and changes in capillary size that occur during the development of humans and animals. The BBB ion permeability was studied in situ by measuring transendothelial electrical resistance in anesthetized rats from 17 days of gestation to 33 days after birth. The BBB in 17-20-day-old fetuses had a resistance of 310 Ohm cm 2 and intermediate properties between dense and perforated epithelium. Starting from the 21st day of pregnancy, the resistance increased to 1128 Ohm cm 2 , which indicated an increase in the density of the endothelium and low ion permeability. On the 28-33th day after birth, the resistance changed little and amounted to 1462 Ohm cm 2 . The BBB and glucose transport through it forms completely in rats by the 20th day of life. Thus, the maturation of the BBB is reflected in an increase in its electrical resistance, and the high electrical resistance corresponds to the selective BBB permeability for ions, which is necessary for the effective regulation of the ionic composition of the interstitial fluid .

The flow of glucose from the blood to the brain is associated with the development of a system of transport proteins, the main of which are GLUT 1 and GLUT 3 , which are located in the BBB, as well as in neurons and glia. Studies in rats showed that GLUT 1 with a molecular weight of 55 kDa is in endothelial cells, GLUT 1 with a molecular mass of 45 kDa is in the unvascularized brain, probably in glia; GLUT 3 is a major neuronal glucose transporter. The increase in glucose utilization by the brain during maturation is closely related to the pattern of expression of non-vascular GLUT 1 (45 kDa) and more specific GLUT 3 . It is suggested that cellular expression of the glucose transporter protein is an indicator of glucose utilization in the brain of developing rats.

In newborns, the intensity of glucose metabolism is low. Glucose metabolism is increased between the ages of 1 to 3 months, which roughly corresponds to the first decade of life of the forehead in the brain of rats century . Data on the characteristics of changes in glucose metabolism in various brain structures in humans during development are obtained. The highest rate of glucose metabolism (SMH) in newborns occurs in the sensorimotor cortex, thalamus, brain stem and cerebellar worm. During the first year of life, the SMG pattern changes in accordance with the maturation of phylogenetically younger structures. In the second and third month, the highest SMH is observed in the parietal, temporal, primary visual regions of the cortex, in the basal ganglia and cerebellar hemispheres. Glucose metabolism remains low in the dorsolateral portion of the visual cortex compared with the primary visual cortex. SMG is low in the frontal areas up to 2-4 months. By the end of the first year, the SMG pattern is qualitatively the same as that of an adult, but quantitative changes occur throughout the entire childhood period. In the interval from 4 to 9 years, the highest values ​​of SMG of the cortex and relatively young subcortical formations are observed, then already at the end of the second decade of life, SMG decreases by almost half .

In early childhood, in the central nervous system, ketone bodies are used as an energy substrate in addition to glucose, which leads to brain acidification . For this reason, the correlation between the intensity of cerebral blood flow and glucose metabolism at this age is less than in adult orgism .

As the brain develops and oxidative reactions intensify, the number of mitochondria per nerve cell doubles . When the brain matures, the content of the main components of the respiratory chain of mitochondria increases 2-3 times: cytochromes and the flavors of oproteins .

In the early stages of postnatal ontogenesis, the ability to maintain constant pH is limited showed that acute metabolic acidosis (or alkalosis), which was created in immature rats to test their ability to maintain pH in the brain, stabilized between 7.1 and 7.5 in the cortex after a week after birth. At this age, the rat brain was more resistant to metabolic acidosis than alkalosis.

The increase in cerebral blood flow and glucose metabolism occurs in parallel with an increase in the functional activity of the brain. It is assumed that the fast ascending part of the SMG curve is associated with overproduction of synapses and terminals, the plateau – with a period of increased energy requirements due to the active formation of synaptic contacts between neurons, the descent period – with selective reduction of synapses, during this period there is a noticeable decrease in brain plasticity .

local_offerevent_note September 5, 2019

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