The effects of undernutrition upon the energy reserve of the brain and upon other selected metabolic intermediates in brains and livers of infant rats

In vivo effect of chronic hypoxia on the neurochemical profile of the developing rat hippocampus

The cognitive deficits observed in children with cyanotic congenital heart disease suggest involvement of the developing hippocampus. Chronic postnatal hypoxia present during infancy in these children may play a role in these impairments. To understand the biochemical mechanisms of hippocampal injury in chronic hypoxia, a neurochemical profile consisting of 15 metabolite concentrations and 2 metabolite ratios in the hippocampus was evaluated in a rat model of chronic postnatal hypoxia using in vivo 1H NMR spectroscopy at 9.4 T. Chronic hypoxia was induced by continuously exposing rats (n = 23) to 10% O2 from postnatal day (P) 3 to P28. Fifteen metabolites were quantified from a volume of 9-11 microl centered on the left hippocampus on P14, P21, and P28 and were compared with normoxic controls (n = 14). The developmental trajectory of neurochemicals in chronic hypoxia was similar to that seen in normoxia. However, chronic hypoxia had an effect on the concentrations of the following neurochemicals: aspartate, creatine, phosphocreatine, GABA, glutamate, glutamine, glutathione, myoinositol, N-acetylaspartate (NAA), phosphorylethanolamine, and phosphocreatine/creatine (PCr/Cr) and glutamate/glutamine (Glu/Gln) ratios (P < 0.001 each, except glutamate, P = 0.04). The increased PCr/Cr ratio is consistent with decreased brain energy consumption. Given the well-established link between excitatory neurotransmission and brain energy metabolism, we postulate that elevated glutamate, Glu/Gln ratio, and GABA indicate suppressed excitatory neurotransmission in an energy-limited environment. Decreased NAA and phosphorylethanolamine suggest reduced neuronal integrity and phospholipid metabolism. The altered hippocampal neurochemistry during its development may underlie some of the cognitive deficits present in human infants at risk of chronic hypoxia.

The influence of growth retardation on perinatal hypoxic-ischemic brain damage

The effect of growth retardation on the extent of brain damage produced by hypoxia-ischemia was assessed in immature rats. Newborn rats were raised in litters of 6 or 14 pups from day 2 to 7. On postnatal day 7, those immature rats raised in litters of 14 weighed 18% less than animals raised in litters of 6 (P less than 0.001). They then were subjected to cerebral hypoxia-ischemia by unilateral common carotid artery ligation followed by 3 h of exposure to 8% oxygen-92% nitrogen at 37 degrees C. Upon return to their dams, all litters were culled to 6 pups. At 30 days of age, the animals underwent perfusion-fixation of their brains under pentobarbital anesthesia. Brain damage was assessed by measuring the length and width of each cerebral hemisphere. The extent of brain damage varied from no difference in the size of the two cerebral hemispheres to marked shrinkage of the hemisphere ipsilateral to the common carotid artery occlusion. The range of brain damage between the well-nourished and poorly nourished animals was comparable. Rank order of the extent of damage demonstrated significantly greater tissue injury in those animals well nourished prior to hypoxia-ischemia (Mann-Whitney U-test; P = 0.003). The results indicate that nutritional deprivation in the immature rat is associated with a decreased rather than increased susceptibility to brain damage arising from hypoxia-ischemia. The findings of the investigation have relevance to the human infant suffering from intrauterine growth retardation (IUGR).

Mechanisms of increased brain glucose and glycogen after hydrocortisone: possible clinical significance

We reported previously that chronic administration of hydrocortisone to normal developing mice increases the brain glucose content and cerebral energy reserve. The present report concerns possible mechanisms of this action. Increases in brain glucose (and glycogen) levels were not due to reduction of cerebral metabolic rate, and the effect of hydrocortisone in facilitating transport of hexose from blood to brain was not impressive. Chronic hydrocortisone treatment induced increases in the activities of brain glycerophosphate dehydrogenase and pyruvate carboxylase in vivo; there was no effect on eleven other enzymes of brain glucose and glycogen metabolism. In normal nursing mice, hydrocortisone produced consistent elevations in plasma beta-hydroxybutyrate (and glycerol) levels. Brain beta-hydroxybutyrate levels were also increased. Therefore, the brain glucose concentration may be elevated in these animals because of the availability of an increased supply of ketone bodies as alternative substrates for cerebral oxidative metabolism and biosynthesis. Ketonemia, elevated cerebral glucose and beta-hydroxybutyrate concentrations, and increased glycerophosphate dehydrogenase activity in brain suggest possible explanations for the beneficial action of adrenocorticotropic hormone and glucocorticoids in the treatment of infantile myoclonic epilepsy and other neurological disorders.