Effect of undernutrition on some enzymes of purine metabolism in different regions of developing rat brain

The effect of undernutrition on the activity of some enzymes involved in purine metabolism, ie, adenosine aminohydrolase, adenylate aminohydrolase, and inosine phosphorylase in cerebral hemispheres, cerebellum, and brain stem of rats at different days of postnatal development was studied. Adenosine aminohydrolase, adenylate aminohydrolase, and inosine phosphorylase were assayed by radiochemical methods which involve the measurement of the radioactive products formed, ie, inosine, IMP, and hypoxanthine, respectively. The results obtained indicate that undernutrition affects the activity of the enzymes which control the concentration of purine nucleotides to a different degree in the three brain regions examined.     

Effect of undernutrition on cell generation in the adult rat brain

Cell proliferation and cell death in the lateral ventricular subependymal layer were studied in acutely food-deprived and chronically undernourished 6-week-old rats. The length of the cell cycle was increased by 40–75%, while the DNA synthesis phase of the cycle was prolonged by 70–85%. The rate of cell acquisition was reduced to approximately half the control level, and the proportion of degenerating cells was significantly increased. The response to undernutrition of proliferating cells in the subependymal layer of adult rats differs from that in animals in the first two weeks of life, and resembles that seen in other tissues.     

Effect of liposomes containing cerebroside and cerebroside sulfate on cytoskeleton of cultured oligodendrocytes

Oligodendrocytes (OLs) and the myelin produced by them are enriched in two glycosphingolipids, galactosylceramide (GalC) and its sulfated form, cerebroside sulfate (CBS). We showed earlier that these two glycolipids in opposed liposomal membranes or in methanol solution can adhere to each other. Here we have examined the potential effect of an interaction between GalC/CBS in apposed membranes of oligodendrocytes (OLs) by incubating cultured OLs with GalC/CBS-containing liposomes and observing the effect on the membrane sheets produced by OLs and on the distribution of OL constituents using fluorescent antibodies and confocal microscopy. The GalC/CBS-containing liposomes caused redistribution or a decrease in the density of anti-GalC and anti-MBP staining but had no effect on the density or distribution of staining by anti-PI(4,5)P(2) that remained uniformly distributed in the membrane sheets. There was no apparent change in the area of the membrane sheets nor in the amount of MBP in OL membranes, as determined by slot blots. In addition, the GalC/CBS-containing liposomes caused depolymerization of microtubules and actin filaments suggesting that the interaction of GSL-containing liposomes with the extracellular surface of the OL caused transmission of a signal across the membrane. Because these two glycolipids can adhere to each other across apposed membranes, the liposomal glycolipids may be interacting with a GalC/CBS-enriched signaling domain in the OL plasma membrane.     

De novo biosynthesis of nucleotides and of nucleic acids in different regions of developing rat brain: Effect of undernutrition

The effect of undernutrition on the de novo biosynthesis of nucleic acids in cerebral hemispheres, cerebellum, and brain stem of rats at different days of postnatal development was studied. The experiments were carried out in vitro by measuring the incorporation of [¹⁴C]-formate into the adenine nucleotide of the acid-soluble fraction of RNA and DNA, as well as into the thymine of DNA. The results obtained indicate that undernutrition during fetal and postnatal development impairs the de novo synthesis of the purine nucleotides of RNA and DNA at 5 days of age and delays it thereafter in the various brain regions examined, particularly in the cerebellum.     

Changes in the amounts of chondroitin sulfate proteoglycans in rat brain after neonatal hypoxia-ischemia

Chondroitin sulfate proteoglycans have been shown to participate in the pathogenesis of neuronal damages in the injured adult central nervous system (CNS). Upregulated expression of chondroitin sulfate proteoglycans has been reported around the injured sites and depletion of these chondroitin sulfate proteoglycans brings about increased axonal regeneration in the injured adult CNS. To examine if chondroitin sulfate proteoglycans are also involved in the pathologic process of hypoxia-ischemia in the neonatal brain, expressions of three chondroitin sulfate proteoglycans, neurocan, phosphacan, and neuroglycan C, were examined in rat brains after neonatal hypoxia-ischemia. Hypoxic-ischemic rats were produced by ligating the right carotid artery of 7-day-old rats, followed by 8% oxygen exposure. Western blot analysis revealed that in contrast to injured adult CNS, the amount of neurocan was reduced 24 hr after hypoxia in the neonatal hypoxic-ischemic cerebral hemisphere. The amounts of phosphacan and neuroglycan C were also reduced significantly 24 hr after hypoxia at the right injured cortex compared to those at the left cortex. Surprisingly, the immunohistologic staining for phosphacan was conversely intensified both at 24 hr and 8 days after hypoxia at the infarcted area. In addition, the habenula and fascicules retroflexus in the right cerebral hemisphere degenerated and became intensely immunostained with the anti-phosphacan antibody shortly after hypoxia. Hypoxic-ischemic insult may unmask phosphacan epitopes at the injured sites, resulting in intensified immunostaining. Because intensified immunostaining for neurocan and neuroglycan C was not observed, unmasking seems to be specific to phosphacan among these three chondroitin sulfate proteoglycans.     

Effect of undernutrition on developing rat cerebellum: Some electrophysiological and neuromorphological correlates

Electrophysiological studies of Purkinje cells from the developing normal and undernourished rat cerebellar cortex were correlated with the neuromorphological studies. In undernourished animals the firing pattern of Purkinje cells was simpler as compared to complex electrical activity in normal animals. The firing frequency of Purkinje cells remained reduced in all the age-matched undernourished groups. The duration of a spike was also prolonged as compared to their normal age mates. Similarly the mean amplitude was also relatively smaller in the undernourished animals when compared with the normal litter mates. Undernourished animals exhibited typical increased stimulus thresholds, prolonged N-2 peak wave latencies, reduced number of functional components, amplitude and increased duration of mossy fiber response (MFR). The mossy fiber (MF) activity exhibited a sluggish rise in its amplitude, when stimulus intensity was increased in undernourished animals. A phenomenon of fatigue was observed with a significant reduction in the amplitude and frequency of Purkinje cell unit discharge on repeated MF stimulation in the undernourished animals. However, repeated MF stimulation provided a high frequency discharge in the normal as well as undernourished adult rats. Neuromorphological studies at light-microscopic level exhibited delayed cell migration from the external granular layer in the undernourished rats. At electron-microscopic level, intracellular morphology exhibited almost similar ultrastructural details except for a few minor alterations. A free ribosomal pool, immature development of E.R., increased incidence of lysosomes and electron-dense membrane stacks were observed in the Purkinje cells at 30 days in the undernourished animals. The results of the present study indicated that undernutrition affects the maturation of Purkinje cell regional neurocircuitry.     

2-Deoxyglucose uptake in the developing rat brain upon pre- and postnatal exposure to trichloroethylene

Trichloroethylene (TCE) is a widespread contaminant of drinking water sources. The effects of TCE on 2-deoxyglucose uptake by brain tissue were examined in pups from rat dams exposed to TCE in their drinking water. The pups were exposed throughout gestation and lactation. Deoxyglucose uptake in the cerebellum, hippocampus and whole brain of the pups during the first 21 days of life was measured using a modification of the 2-deoxy-D-glucose (2-DG) technique. We determined that TCE at a nominal concentration of 312 mg/l significantly depressed 2-DG uptake in the whole brains and cerebella of 7- to 21-day old pups. 2-DG uptake was also lower in the hippocampus of exposed pups at 7, 11 and 16 days, but returned to control levels by 21 days. No overt toxicity, such as lower body or brain weight, was observed at this exposure level. This decrease in 2-DG uptake reflects a decrease in glucose uptake and/or metabolism in the brains of animals exposed to TCE.     

Neurovascular coupling in the developing neonatal brain at rest

The neonatal brain is an extremely dynamic organization undergoing essential development in terms of connectivity and function. Several functional imaging investigations of the developing brain have found neurovascular coupling (NVC) patterns that contrast with those observed in adults. These discrepancies are partly due to that NVC is still developing in the neonatal brain. To characterize the vascular response to spontaneous neuronal activations, a multiscale multimodal noninvasive approach combining simultaneous electrical, hemodynamic, and metabolic recordings has been developed for preterm infants. Our results demonstrate that the immature vascular network does not adopt a unique strategy to respond to spontaneous cortical activations. NVC takes on different forms in the same preterm infant during the same recording session in response to very similar types of neural activation. This includes (a) positive stereotyped hemodynamic responses (increases in HbO, decreases in HbR together with increases in rCBF and rCMRO2), (b) negative hemodynamic responses (increases in HbR, decreases in HbO together with decreases in rCBF and rCMRO2), and (c) Increases and decreases in both HbO‐HbR and rCMRO2 together with no changes in rCBF. Age‐related NVC maturation is demonstrated in preterm infants, which can contribute to a better understanding/prevention of cerebral hemodynamic risks in these infants.     

Expression of NG2 and platelet-derived growth facto receptor alpha in the developing neonatal rat brain

Platelet-derived growth factor receptor alpha(PDGFRα) is a marker of oligodendrocyte precursor cells in the central nervous system. NG2 is also considered a marker of oligodendrocyte precursor cells. However, whether there are differences in the distribution and morphology of oligodendrocyte precursor cells labeled by NG2 or PDGFRα in the developing neonatal rat brain remains unclear. In this study, by immunohistochemical staining, NG2 positive(NG2~+) cells were ubiquitous in the molecular layer, external pyramidal layer, internal pyramidal layer, and polymorphic layer of the cerebral cortex, and corpus callosum, external capsule, piriform cortex, and medial septal nucleus. NG2~+ cells were stellate or fusiform in shape with long processes that were progressively decreased and shortened over the course of brain development. The distribution and morphology of PDGFRα positive(PDGFRα~+) cells were coincident with NG2~+ cells. The colocalization of NG2 and PDGFRα in the cell bodies and processes of some cells was confirmed by double immunofluorescence labeling. Moreover, cells double-labeled for NG2 and PDGFRα were predominantly in the early postnatal stage of development. The numbers of NG2~+/PDGFRα~+ cells and PDGFRα~+ cells decreased, but the number of NG2~+ cells increased from postnatal days 3 to 14 in the developing brain. In addition, amoeboid microglial cells of the corpus callosum, newborn brain macrophages in the normal developing brain, did not express NG2 or PDGFRα, but NG2 expression was detected in amoeboid microglia after hypoxia. The present results suggest that NG2 and PDGFRα are specific markers of oligodendrocyte precursor cells at different stages during early development. Additionally, the NG2 protein is involved in inflammatory and pathological processes of amoeboid microglial cells.     

Catecholamines in rat brain following postnatal undernutrition and nutritional rehabilitation

Norepinephrine and dopamine were examined in 19 discrete brain areas from the telencephalon, diencephalon, and mesencephalon of nutritionally rehabilitated adult rats following postnatal undernutrition from birth through 21 days of age. Following rehabilitation, catecholamine levels were not significantly different from control values in any of the areas examined. Catecholamine concentrations in young, undernourished rats are generally elevated (either from stress or from nutritional insufficiency). Data presented here show that whichever case is true, the early effect of undernourishment is transient and that normal values are restored by nutritional rehabilitation.     

Effect of neonatal hypothyroidism on the serotonin system of the rat brain

The effects of neonatal thyroidectomy and thyroid hormone replacement therapy on the development of serotonin-contaning neurons in discrete rat brain nuclei were studied. Newborn male rats were rendered hypothyroid by the injection of 125 μCi¹³¹I, and, after 45 days, were compared with normal littermate controls and¹³¹I-injected animal subsequently maintainde by dialy T₄ injections. The serotonin (5-HT) and 5-hydroxyindoleacetic acid (5-HIAA) contents of discrete brain nuclei remove by punches of frozen brain slices were measured by HPLC with electrochemical detection. 5-HT and 5-HIAA contents were significantly increased in many nuclei of the hypothyroid rat brain. By blocking the biosynthesis ot 5-HT with p-chlorophynelalanine we found that the activity of tryptophan hydroxylase is an important step in the stimulatory effect of hypothyroidism on the 5HT and 5-HIAA contents. Futhermore, we demonstrated after blockage of monomine oxidase activity with pargyline, a less pronounced decline of 5-HIAA in neonatal hypothyroid animals, thus causing a relative accumulation of this metabolite. These results demonstrate theat there are important modifications of the 5-HT system in the brain of neonatal hypothyroid rats. This may have an important role in the development of hypothyroid-induced impairments of central nervous system function.     

DSIP-like immunoreactivity in the developing rat brain

Delta sleep-inducing peptide (DSIP) is a naturally occurring nonapeptide that has been reported to affect sleep. The concentration of DSIP-like material was measured by a highly specific radioimmunoassay in brain tissue from developing rats. DSIP-like immunoreactivity was present in fetal brain at increased levels shortly before birth. In one experiment, a significant elevation in the concentration of the peptide occurred at postnatal day 20, but in a second, similar, study the increase occurred later. No marked differences in the levels of DSIP-like immunoreactivity were found in the brains of rats injected 2 months earlier with DSIP or among 10 parts of brains obtained at postnatal day 20. Regardless of the function of DSIP, it is available to the rat throughout early development.     

Effects of undernutrition on the serotonin neuron system in the developing brain: an immunohistochemical study

The effects of undernutrition during the first 3 weeks of postnatal life on the serotonin neuron system were investigated using a peroxidase-antiperoxidase immunohistochemical method. Undernourishment was induced by increasing the litter size from 6 to 18 mice during the first 3 weeks of postnatal life. At 15 days of age a morphological change (large swelling of serotonin-immunoreactive axons) was noted in various parts of the brain of the undernourished mice with no remarkable changes in dendrites and cell bodies. Quantitative immunohistochemical analysis at 60 days of age showed a significant decrease in serotonin-immunoreactive cell bodies in the nucleus linearis intermedius, the nucleus raphe obscurus, the total raphe system and the subpyramidal region. These results suggest that undernutrition during early postnatal life affected the serotonin neuron system with regional differences.     

Dynamics of microglia in the developing rat brain

Entrance of mesodermal precursors into the developing CNS is the most well-accepted origin of microglia. However, the contribution of proliferation and death of recruited microglial precursors to the final microglial cell population remains to be elucidated. To investigate microglial proliferation and apoptosis during development, we combined proliferating cell nuclear antigen (PCNA) immunohistochemistry, in situ detection of nuclear DNA fragmentation (TUNEL), and caspase-3 immunohistochemistry with tomato lectin histochemistry, a selective microglial marker. The study was carried out in Wistar rats from embryonic day (E) 16 to postnatal day (P) 18 in cerebral cortex, subcortical white matter, and hippocampus. Proliferating microglial cells were found at all ages in the three brain regions and represented a significant fraction of the total microglial cell population. The percentage of microglia expressing PCNA progressively increased from the embryonic period (25-51% at E16) to a maximum at P9, when the great majority of microglia expressed PCNA (92-99%) in all the brain regions analyzed. In spite of the remarkable proliferation and expansion of the microglial population with time, the density of microglia remained quite constant in most brain regions because of the considerable growth of the brain during late prenatal and early postnatal periods. In contrast, apoptosis of microglia was detected only at certain times and was restricted to some ameboid cells in white matter and primitive ramified cells in gray matter, representing a small fraction of the microglial population. Therefore, our results point to proliferation of microglial precursors in the developing brain as a physiological mechanism contributing to the acquisition of the adult microglial cell population. In contrast, microglial apoptosis occurs only locally at certain developmental stages and thus seems less crucial for the establishment of the final density of microglia.     

Metabolism of fucoglycoproteins in the developing rat brain

The amount of fucose bound to macromolecules in the particulate fraction of rat brain increased only slightly (from 7.7 to 9.9 μmoles/g protein) between the ages of 5 and 26 days. However, the incorporation of intraperitoneally injected [³H]fucose into the particulate fraction of brain decreased rapidly with age from the first to the twenty-sixth day after birth. A similar decrease in incorporation with age was also observed after intracerebral injection of the [³H]fucose andin vitro with slices of brain cortex.