| dc.description.abstract | Undernutrition in suckling rat pups was induced by increasing the litter size. The control group contained 6 pups per mother, while the undernourished group contained 16-18 pups per mother until weaning (21 days of age). After weaning, the undernourished rats were either rehabilitated by providing food ad libitum along with controls or continued to be undernourished by allowing only one-third the amount of diet consumed by controls up to 8 weeks of age.
1. Undernutrition significantly curtailed the body and brain weights of rats. The reductions in body and brain weights were 48% and 16% at 3 weeks and 55% and 15% at 8 weeks, respectively. In rehabilitated rats, the body and brain weights were improved but were still markedly lower than controls, the reduction being 18% and 12%, respectively.
2. The cell number (as judged by DNA content) was significantly reduced in whole brain as well as in the cerebellum in the undernourished group. The cell number in cortex or brain stem was not significantly affected.
3. In 3-week-old underfed rats, the protein to dry matter (DM) ratio was not significantly altered either in the whole brain, cortex, brain stem, or cerebellum, indicating that cell size is unaltered with neonatal undernutrition.
4. The total lipid, phospholipid, and cholesterol contents were 20 to 30% reduced in undernourished brains, which were statistically significant. The reduction in galactolipids was the most pronounced, being 35%.
5. The concentrations of total as well as various lipid classes were significantly low in underfed rats, though the magnitude of the effect varied among them. The reductions in lipid concentrations in undernourished brains at 3 and 8 weeks of age, respectively, were: 22.9% and 24.7% for galactolipids, 11.3% for cholesterol, and 8.5% and 7.2% for phospholipids. These results indicate that undernutrition significantly affects the lipid composition of the brain.
6. Rehabilitation of the underfed rats from the 3rd week through the 8th week by feeding ad libitum improved the content as well as the concentration of all lipid classes, but still the values were significantly lower than the corresponding controls.
7. Among the individual phospholipids, the contents of phosphatidylcholine, phosphatidylethanolamine, phosphatidylserine, and plasmalogens were significantly affected, whereas sphingomyelin and phosphatidylinositol were not altered with undernutrition. However, while the concentrations (per g) of phosphatidylethanolamine and plasmalogens were most significantly reduced, phosphatidylcholine was moderately affected and others were not significantly affected.
8. Rehabilitation reversed the effect on the content of phosphatidylcholine and phosphatidylserine, while phosphatidylethanolamine and plasmalogens remained significantly lower than controls. Nevertheless, the concentrations of all but plasmalogens became comparable to controls on rehabilitation, suggesting that the nutritional stress on plasmalogens is more permanent.
9. Studies on the incorporation of 32Pi^{32}P_i32Pi into phospholipids by brain homogenates showed that maximal incorporation occurs in the presence of pyruvate plus malate and ATP in the incubation medium. Under these conditions, 85 to 88% of the radioactivity of the total phospholipids was accounted for by the acidic phospholipids (phosphatidic acid and inositol phosphatides).
10. Undernutrition did not affect the incorporation of 32Pi^{32}P_i32Pi into total phospholipids up to 14 days, but at 21 days, the incorporation was significantly high in undernourished rats.
11. Incorporation into polyphosphoinositides, sphingomyelin, phosphatidylcholine, phosphatidylserine, and phosphatidylethanolamine was significantly low in 14-day-old rats, whereas in 21-day-old undernourished rats, incorporation into all the phospholipids was significantly high, which may have relevance to the heightened emotionality reported in undernourished rats.
12. Incorporation of 32Pi^{32}P_i32Pi into phospholipids by homogenates was not enhanced by acetylcholine, suggesting that a certain amount of cellular integrity is necessary to evoke neurotransmitter response (phospholipid effect).
13. An in vitro system utilizing brain tissue suspensions obtained by passing the tissue through nylon meshes of defined pore size was developed. This method afforded highly reproducible phospholipid effects with various neurotransmitters.
14. Acetylcholine, norepinephrine, and serotonin enhanced the incorporation of 32Pi^{32}P_i32Pi into phospholipids by 203%, 516%, and 150%, respectively, with the coarsest cortical suspensions. The stimulation of 32Pi^{32}P_i32Pi incorporation into phospholipids by these neurotransmitters was greater with coarse suspensions and decreased progressively with finer suspensions. These results also suggest that sufficient cellular integrity is necessary for obtaining the phospholipid effect.
15. Studies on the relative distribution of radioactivity in various phospholipids showed that basal incorporation mainly occurred into phosphatidic acid and inositol phosphatides. With decreasing size of tissue suspension, the relative percentage of radioactivity decreased in inositol phosphatides, while it increased in phosphatidic acid. These results suggest that finer suspensions have relatively less post-synaptic structure, which is probably necessary for the synthesis of inositol phosphatides.
16. Stimulation of 32Pi^{32}P_i32Pi incorporation into phospholipids by acetylcholine, norepinephrine, and serotonin was found mainly in the phosphatidic acid fraction. While acetylcholine stimulated incorporation significantly only into phosphatidic acid, norepinephrine and serotonin evoked considerable stimulation in other phospholipids as well.
17. The concentrations of neurotransmitters required for maximum stimulation of 32Pi^{32}P_i32Pi into phospholipids were found to be 10^-5 M for acetylcholine and 10^-5 M for norepinephrine and serotonin.
18. In weanling rats, the stimulation of 32Pi^{32}P_i32Pi into phospholipids of various regions with acetylcholine was in the order: cerebral cortex > brain stem > cerebellum; with norepinephrine, the order was: cerebral cortex > cerebellum > brain stem; with serotonin, the order was: cerebellum > brain stem > cerebral cortex. These results indicate regional differences in neurotransmitter-evoked phospholipid effects.
19. Serotonin stimulation in cerebellum was 251% over control, whereas its stimulations in cortex and brain stem were only 129% and 135%, respectively. This profound phospholipid effect by serotonin in cerebellum suggests serotonergic synapses preponderate in cerebellum.
20. The stimulation of 32Pi^{32}P_i32Pi incorporation by all three neurotransmitters increased with age in cortex, brain stem, and cerebellum, but the magnitude of increase differed in each region, suggesting a progressive increase in synaptic density during brain development.
21. Postnatal undernutrition until weaning affected neurotransmitter-stimulated phospholipid metabolism in some regions. The phospholipid effect due to acetylcholine, norepinephrine, and serotonin was significantly low in the brain stem, but not in the cortex of 21-day-old undernourished rats. In the cerebellum, while the phospholipid effect with acetylcholine was higher, the effect with norepinephrine was lower, and that due to serotonin was not significantly changed. From these data, it may be concluded that cholinergic, adrenergic, and serotonergic synapses are relatively spared in the cortex but significantly affected in the brain stem. In the cerebellum of undernourished rats, the adrenergic and cholinergic, but not serotonergic systems, are altered.
22. The total and individual ganglioside contents were significantly low in undernourished rats. In 3- and 8-week-old underfed rats, the ganglioside contents per cent of control values were: GM1 - 55% and 75.5% for total gangliosides, GD1a - 63.5% and 67%, GD3b - 66.5% and 64%. All these reductions were statistically significant. Upon rehabilitation, while the contents of GD3b and GT became comparable to controls, total ganglioside, GM1, and GD1a contents remained significantly low.
23. Ganglioside concentrations were also significantly lower in undernourished rats. The total ganglioside concentrations expressed as µg MA/g in underfed rats were 86% and 88.5% of controls at 5 and 8 weeks of age, respectively. The concentrations of GD1a, GD3b, and GT1 were generally low in undernourished rats at both 3 and 8 weeks. These results suggest that undernutrition may reduce the number of synapses and might affect synaptic function.
24. Rehabilitation reversed the effects on total as well as individual gangliosides, indicating that the effect of undernutrition on gangliosides is not permanent.
25. • Rehabilitation reversed the effects on the total as well as individual gangliosides, indicating that the effect of undernutrition on gangliosides is not permanent.
26. • The fatty acid composition showed only marginal changes with undernutrition. There appeared to be higher amounts of ?-3 and lower amounts of ?-6 in rat brain gangliosides at 2 weeks of age in undernourished rats.
27. • Metabolism of gangliosides was studied in 21-day-old normal and undernourished rats through in vivo incorporation of [^14C]-glucosamine given intraperitoneally. The results showed that the total radioactivity in gangliosides per brain was significantly low, whereas the radioactivity per gram of tissue was not altered significantly in underfed rats.
28. • Pure myelin was isolated quantitatively from rat brains. The purity was ascertained by measuring the activity of the myelin marker enzyme, 2',3'-cyclic nucleotide 3'-phosphohydrolase. Myelin was quantitated by estimating protein and dry weight.
29. • The quantity of myelin (protein as well as dry weight) per gram or per brain was significantly lower in undernourished rats at both 3 and 8 weeks of age. Rehabilitation improved the quantity of myelin to some extent but was still significantly lower than controls. The reductions in the quantity of myelin (myelin protein/g) in undernourished rats were 16% at 3 weeks, 35% at 8 weeks, and 25.5% in rehabilitated animals. These results suggest that the quantity of isolated myelin is profoundly reduced in undernourished rats and that the deficit is irrecoverable.
30. • 2',3'-Cyclic nucleotide 3’-phosphohydrolase activity was measured in myelin isolated from control and undernourished rats to assess the quality of myelin. The specific activity of this enzyme was not altered significantly in undernourished rats either at 3 or 8 weeks of age, indicating that the quality of myelin may not be altered by undernutrition.
31. • To further assess the quality of myelin in undernourished rats, myelin protein composition was studied. Myelin proteins, separated by polyacrylamide gel electrophoresis and quantitated by colorimetric estimation, showed no discernible changes between control and undernourished rats. These results suggest that the composition of myelin is not altered by food deprivation.
32. • These studies were extended to find the effect of protein malnutrition on myelinogenesis. Protein malnutrition in suckling pups was induced from birth to 21 days of age by feeding the lactating dams a low-protein diet in the experimental group as against a 25% protein diet fed to control group mothers. After 5 weeks, malnourished pups were rehabilitated by feeding normal diet ad libitum along with controls up to 8 weeks.
33. • Protein malnutrition reduced the myelin content more drastically than did undernutrition. In 3-week-old protein-malnourished rats, there was a 27% reduction in myelin content per gram of brain, as compared to 16% in undernourished rats. The deficit in myelin quantity could not be recovered by rehabilitation. Thus, the results suggest that the quantity of myelin is irreversibly affected by protein malnutrition.
34. • The specific activity of 2',3'-cyclic nucleotide 3'-phosphohydrolase was significantly low in 3-week-old protein-malnourished rats, which, however, became comparable to controls on rehabilitation. These observations suggest that the quality of myelin is also changed with protein malnutrition, which may not be permanent.
35. • Myelin protein composition showed a selective and significant reduction in proteolipid protein in 3-week-old protein-malnourished rats, which was rectified on rehabilitation. These results corroborate the above finding that besides quantity, the quality of myelin is altered in protein-malnourished rats.
36. • The lipid composition of myelin isolated from the brains of 3-week-old protein-malnourished rats showed a significant reduction in cholesterol and plasmalogen contents (µmoles/mg myelin). These findings further support the contention that in protein malnutrition not only the quantity but also the quality of myelin is altered significantly.
37. • The specific activities of both ouabain-sensitive and ouabain-insensitive Na^+/K^+-ATPases continued to increase during development.
38. • On undernutrition, the specific activity of the ouabain-insensitive Na^+/K^+-ATPase was significantly higher at weaning, but on continued undernutrition up to 8 weeks, it became significantly lower. The ouabain-sensitive enzyme was not affected even after 8 weeks of undernutrition. From these results, it is suggested that whereas the ouabain-insensitive enzyme is affected by prolonged undernutrition, the ouabain-sensitive enzyme is not.
39. • The specific activity of the ouabain-insensitive Na^+/K^+-ATPase was significantly low in protein-malnourished rats even at 3 weeks, which on rehabilitation caught up with the controls. However, the ouabain-sensitive enzyme did not show any significant change in these rats as well. From these results, it is concluded that while the ouabain-insensitive Na^+/K^+-ATPase is significantly affected by protein malnutrition, the ouabain-sensitive enzyme is spared. | |
