CATIONIC COMPOSITION OF RAT CEREBRAL CORTEX SLICES. COMPARATIVE STUDY DURING DEVELOPMENT

Abstract—

• 1 Slices of cerebral cortex isolated from 20-day-old rats, when incubated in an appropriate oxygenated saline, show only a slight increase in weight (± 0.4 per cent of initial fresh wt.). At 30 days, under the same conditions, this increase in weight is 12.4 per cent. This is similar to the value observed in adult animals (13.6 per cent).
• 2 Modifications of the cationic content of slices in the case of 20-day-old animals are very slight while in 30-day-old animals they are greater and similar to those observed with adults.
• 3 The inulin space of 20- and 30-day-old rats are the same. The swelling exhibited by the slices isolated from 30-day-old animals may reasonably be attributed to a cellular uptake of extracellular fluid. This is accompanied by an increase of the Naf concentration and by a decrease of the K⁺ concentration. The values observed are similar to those observed with adult rats.
• 4 Comparing our results with previous histological and histochemical data, it may be suggested that the modifications of cationic content, as well as the swelling of slices isolated from 30-day-old rats or adult animals, are solely attributable to changes affecting glial cells and more specifically the astrocytes.

     

EFFECT OF THYROID HORMONE ON THE BIOCHEMICAL MATURATION OF RAT BRAIN: CONVERSION OF GLUCOSE-CARBON INTO AMINO ACIDS

• 1 The rapid and extensive conversion of glucose-carbon into amino acids is an index of the final coordination of the mechanisms underlying energy metabolism in the adult brain. This phenomenon develops in the rat during a short period extending from 10 to about 19 days after birth. The underlying factors have been analysed.

• 2 The development of the pattern of distribution of glucose-carbon characteristic of the adult brain was markedly influenced by the thyroid state of the animals. The age-curve for the conversion of glucose-carbon into brain amino acids was displaced to the left after treatment with thyroid hormone (T₃) in infancy thus indicating an accelerated maturation. Conversely, neonatal thyroidectomy resulted in a significant retardation in the conversion of glucose-carbon into amino acids.

• 3 The specific radioactivity of glutamate increased five-fold in the brain of normal rats from the 10th to the 19th day of age. The values (as a percentage of those for littermate controls) were 220 in the case of the 10 day-old thyroid treated rats and about 30 for the 19 day-old thyroid deficient animals. At the age of 10 days neither treatment affected the concentration of glutamate which was also only slightly less than the control values in the brain of 19 day-old thyroid deficient animals (–17 per cent).

• 4 Specific pool(s) of glutamate associated with the formation of GABA can be demonstrated in the brain of 19 day-old rats after administration of [U-¹⁴C]glucose as a result of anoxia post mortem. These pools did not develop in the brain of 10 day-old animals. Neonatal thyroidectomy retarded the development of these glutamate pools.

• 5 Evidence is summarized which indicates that the development of the rapid conversion of glucose-carbon into amino acids reflects the enlargement, during maturation, of the metabolic compartments which are associated with neuronal processes.

     

DEVELOPMENTAL CHANGES IN Na+, K+ AND ATP AND IN THE LEVELS AND TRANSPORT OF AMINO ACIDS IN INCUBATED SLICES OF RAT BRAIN

Abstract—

• 1 Upon incubation, slices of brain tissue took up fluid; the degree of swelling increased with increasing age. No sweiling occurred in slices from foetal brain. Since this swelling was associated with increases in the inulin space, the percentage of inulin space in slices at the end of incubation increased during brain development.
• 2 Most of the capacity for ion transport seemed to be absent from foetal brain. In vivo and in slices, Na⁺ was very high and K⁺ was very low in comparison to levels at other ages. There was a rapid change around birth, but no significant change at later ages. Upon incubation, Na⁺ levels increased in other slices, but not in slices of foetal brain.
• 3 Upon incubation of the slices, ATP levels were restored to levels close to those in the living brain; there were no significant alterations in available energy during development to explain changes in amino acid transport.
• 4 The composition of the free pool of cerebral amino acids in vivo changed with development, with some compounds (glutamic acid and related compounds) increasing, others (mostly‘essential’amino acids) decreasing, with age. These changes were not linear with time, and the level of a compound might exhibit several peaks during development.
• 5 The uptake (influx) of taurine, glutamate and glycine into brain slices increased rapidly during the foetal and early neonatal periods, reached a maximum between 2 and 3 weeks of postnatal age and then declined to adult levels. The levels of steady-state uptake with glycine also exhibited a maximal peak at 2-3 weeks of postnatal age. Steady-state uptake of taurine and glutamate reached adult levels by about 3 weeks of age.
• 6 The pattern of inhibition of amino acid transport by two specific amino acid analogues changed during development for some amino acids (GABA, glycine and glutamate), indicating an alteration in substrate specificity.
• 7 The results demonstrate complex changes in cerebral amino acid transport during development, with several maxima or minima and with changes in specificity for at least some compounds.

     

DEVELOPMENTAL PROFILES OF GANGLIOSIDES IN HUMAN AND RAT BRAIN

Abstract— The developmental profiles of individual gangliosides of human brain were compared with those of rat brain. Interest was focused mainly on the pre- and early postnatal development. Human frontal lobe cortex covering the period from 10 foetal weeks to adult age and the cerebrum of rat from birth to 21 days were analysed. Lipid-NANA and lipid-P were followed; in the rat, also protein and brain weight. A limited number of samples of human cerebral white matter and cerebellar cortex were also studied. The following major results were obtained:

• 1 The ganglioside concentration increased approximately three-fold within a short period: in rat cerebrum, from birth to the 17th day; in human cerebral cortex, from the 15th foetal week to the age of about 6 months. The largest increase in the rat brain occurred by the 11th to the 13th day; in human brain by term. The relative increase of gangliosides during this period was more rapid than that of phospholipids.
• 2 A hitherto unknown distinct early period of ganglioside and phospholipid formation in rat occurred by the second to fourth day.
• 3 The changes in brain ganglioside pattern, characteristic of the developmental stages of the rat, were found to be equally pronounced in the human brain.
• 4 Regional developmental differences in the ganglioside pattern were demonstrated in human brain. A characteristic white matter pattern, rich in monosialogangliosides, had developed by the age of 1 year. The increase in ganglioside concentration and the formation of the definitive ganglioside pattern of cerebellar cortex occurred later than in cerebral cortex. This cerebellar pattern was characterized by a very large trisialoganglioside fraction.
• 5 The two periods of rapid ganglioside metabolism in rat brain preceded the two periods of rapid protein biosynthesis.

     

VERÄNDERUNGEN DER AMINOSÄUREKONZENTRATIONEN IM RATTENHIRN BEI VERRINGERUNG DER K+-ZUFUHR IN VIVO

Abstract—

• 1 Resonium A, a cation exchange resin, administered orally caused no decrease of the potassium content in the CNS of the rat, but it provoked a potassium depletion in the liver tissue. However a slight increase could be detected in the ‘cortex’ and ‘striatum’.
• 2 A rise of the concentration of the free amino acids was found in ‘cortex’, ‘striatum’, ‘thalamus’ and cerebellum. Glutamic acid showed an increase of 70–80 per cent. GABA and glycine showed a remarkable increase of 280–330 per cent.
• 3 Restitution of K⁺ by feeding a potassium-rich diet brought the amino acid concentrations in the ‘cortex’ and cerebellum within a normal range. In ‘striatum’ and ‘thalamus’ an overshoot could be observed.
• 4 The experimental procedure for the estimation of free amino acids in brain tissue is discussed.

     

Mapping of mitochondrial metabolic competence by cytochrome oxidase and succinic dehydrogenase cytochemistry.

To map the mitochondrial capacity to provide adenosine triphosphate (ATP), the activities of cytochrome oxidase (COX) and succinic dehydrogenase (SDH) were respectively evidenced by diaminobenzidine (DAB) and copper ferrocyanide cytochemical techniques in the cerebellar cortex of adult rats. Sampling of the positive mitochondria was carried out by the disector procedure. The ratio (R) overall area of the precipitates due to COX activity within the single mitochondrion/area of the same organelle was automatically calculated to estimate enzyme activity vs mitochondrial size. The number of SDH-positive mitochondria/microm(3) of tissue (numeric density, Nv) was morphometrically calculated. Cytochemistry of key enzymes of the respiratory chain enables measurement of the actual capacity of individual mitochondria to provide ATP. This quantitative estimation allows morphofunctional mapping of the mitochondrial metabolic competence in discrete tissue and/or cellular compartments. (J Histochem Cytochem 49:1191-1192, 2001)     

PROTEIN SYNTHESIS BY HIGHLY AGGREGATED AND PURIFIED POLYSOMES FROM YOUNG AND ADULT RAT BRAIN

The state of aggregation and the activity of polyribosomes as well as the activity of the pH 5 enzyme fraction were studied at two stages of postnatal brain development, 9 and 50 days after birth. When the polyribosomes were prepared at 0°C in the presence of 5 mm -Mg²⁺, more than 85 per cent of the polyribosome material exhibited a sedimentation coefficient higher than 110 S. High Mg²⁺ concentrations are, therefore, unnecessary to obtain highly aggregated brain polyribosomes. The basal amino acid incorporating activity of both 9- and 50-day-old rat brain preparations is at least equal to that of rat liver. When prepared by the same procedure as above, 9-day-old rat brain polyribosomes seem to be more active (20 per cent) than those of adult brain. However, this difference in activity depends on the presence of a non-ribosomal inactive contaminant which is always present in higher amounts in adult brain preparations. When purified from this contaminant, the preparations do not differ in activity. High Mg²⁺ concentrations are also not necessary for optimal protein synthetic activity and, in fact, are inhibitory. When assayed with both types of highly aggregated polyribosomes, the pH 5 enzyme fraction from adult brain is clearly less active than that of 9-day-old rats. These results suggest that the loss of brain protein synthesis during development does not depend on the stability of the messenger RNA-ribosome complex but only on the soluble pH 5 enzyme fraction.     

Aggregation of parasitoids and density-independence of parasitism in field populations of the wasp Aphytis melinus and its host, the red scale Aonidiella aurantii

ABSTRACT.

• 1 Repeated counts were made of the number of adult Aphytis melinus (DeBach) wasps per fruit on Valencia oranges in an orchard over two successive periods. Resulting rates of parasitism per fruit were measured at the end of each period.
• 2 For both periods, corresponding to high and low mean numbers of adult parasites, there was a significant positive regresssion of adult wasps per fruit on the number of available hosts per fruit. However, there was a high level of variability about the regression, and the overall aggregative response appears to be weak.
• 3 For both periods, rates of parasitism per fruit were independent of host density per fruit and they showed a high level of variability at all densities. Similar patterns were found in another, commercial, orchard over a wide range of mean host densities.
• 4 There was no evidence for aggregation of parasites or density dependence of parasitism at a patch size corresponding to the whole tree.
• 5 Suggestions based on some host-parasitoid models, that aggregations of parasite attack in areas of high host density are necessary for effective biological control, are rejected. However, the model of Hassell (1982), incorporating aggregation of parasites and limitations on the effectiveness of the parasite, seems to fit the data quite well.

     

ONTOGENETIC DEVELOPMENT OF A PHOSPHODIESTERASE ACTIVATOR AND THE MULTIPLE FORMS OF CYCLIC AMP PHOSPHODIESTERASE OF RAT BRAIN

Abstract— The activity of cyclic AMP phosphodiesterase of rat cerebral homogenates increased several-fold between 1 and 60 days of age. Enzyme activity in the cerebellum, on the other hand, did not increase during this period. A kinetic analysis of the phosphodiesterase activity revealed evidence for multiple forms of the enzyme and indicated that the postnatal increase in phosphodiesterase activity of rat cerebrum was due almost exclusively to the high K_m enzyme. In cerebellum, the ratio of the high and low K_m enzyme remained fairly constant during ontogenetic development. Physical separation of the phosphodiesterases contained in 100,000 g soluble supernatant fractions of sonicated brain homogenates by polyacrylamide disc gel electrophoresis confirmed the presence of multiple enzyme forms. In adult rats we found six distinct peaks of phosphodiesterase activity (designated I to VI according to the order in which they were eluted from the column) in cerebellum and 4 forms of the enzyme (Peaks I through IV) in cerebrum. Brains of newborn rats had a different pattern and ratio of phosphodiesterase activities. For example, Peak I phosphodiesterase was undetectable in cerebrum or cerebellum of newborn rats. Moreover, in the cerebellum of newborn rats Peak II was the dominant peak whereas in the cerebellum of adult rats Peak III was the largest peak. A comparison of the multiple forms of phosphodiesterase from the cerebrum of newborn and adult animals suggested that the postnatal increase in phosphodiesterase activity previously seen in crude homogenates was due largely to an increase in a high K, Peak II phosphodiesterase. The ratios of activities of the other peaks and their sensitivities to an activator of phosphodiesterase were similar in newborn and adult rats. An endogenous heat-stable activator of phosphodiesterase was found in cerebrum, cerebellum and brain stem. In newborn rats, the cerebellum contained several-fold less activity of this activator than did cerebrum or brain stem. However, the activity of this activator increased with age in the cerebellum and would appear to have decreased postnatally in cerebrum and brain stem. These results suggest that some multiple forms of phosphodiesterase can develop independently and that changes in activities of these phosphodiesterases may occur by increases in the quantity of enzyme or by changes in the quantity of an endogenous activator of phosphodiesterase.     

PURIFICATION AND PROPERTIES OF CHOLINE ACETYLTRANSFERASE FROM OX BRAIN STRIATE NUCLEI

Abstract—

• 1 Choline acetyltransferase was purified from ox brain striate nuclei by an extraction step at pH 5, cation-exchange chromatography, fractional precipitation with ammonium sulphate, and chromatography on Sephadex G-200. The enzyme was obtained free of deacylases and cholinesterases, at specific activities of 01-0-3 μmol acetylcholine formed per min per mg protein.
• 2 The enzyme was found to be a stable and relatively basic protein, with a molecular weight of 65,000.
• 3 In the catalysed reactions, , k₁, was about four times k₂, and the equilibrium constant was approximately 40. For the forward reaction, the Michaelis constant for each substrate was independent of the concentration of the other (choline = 0-75 mM; acetyl-CoA = 10 μM), whereas in the back reaction one substrate increased the affinity for the other (acetylcholine = 0-75-5 MM; CoA = 25-150 μM).
• 4 CoA inhibited acetylcholine synthesis by competing with acetyl-CoA (K₁, = 16 μM). Acetylcholine slightly inhibited the forward reaction (e.g. 45 per cent in 200 mM) without competing with choline or acetyl-CoA. These data indicate an ordered reaction mechanism; acetyl-CoA probably always binds before choline.

     

ACETYLCHOLINE,CHOLINE AND CHOLINE ACETYLTRANSFERASE ACTIVITY IN THE DEVELOPING BRAIN OF NORMAL AND HYPOTHYROID RATS1

Abstract— Acetylcholine, choline and choline acetyltransferase activity were measured in the whole brains of normal and hypothyroid rats during development. At 1 day postpartum, brain acetylcholine was 73 per cent of adult levels. Propylthiouracil-induced hypothyroidism up to age 20 days did not alter brain acetylcholine concentrations, but at 30 days resulted in significantly decreased levels. At day 1, brain choline was 20 per cent higher than adult levels and decreased between days 8 and 10. In hypothyroid rats this phenomenon did not occur until days 15–20. At day 1 postnatally, choline acetyltransferase activity was only 7 per cent of adult levels, then between days 5 and 20 rose to 77 per cent of adult levels. Beginning at day 8, hypothyroidism resulted in significantly decreased enzyme levels. This effect could be reversed at day 17 by concurrent tri-iodothyronine substitution therapy. In hypothyroid rats, maximum brain choline acetyltransferase activity was 30 per cent less than normal adult levels.     

ISOLATION AND ELECTROPHORETIC IDENTIFICATION OF HISTONES OF RAT BRAIN AND LIVER

Abstract—

• 1 Relatively pure brain nuclei were prepared on a discontinuous sucrose gradient which gave yields of between 40 and 60 per cent.
• 2 An extraction procedure has been developed for the isolation of total histones from brain and liver nuclei. This procedure is also applicable to the isolation of histones directly from whole brain and liver.
• 3 The electrophoretic pattern of histones prepared from brain and liver by the above procedure was similar to that of calf thymus histones.

     

THE ACTIVATION OF THIAMINE DIPHOSPHATASE BY ATP IN RAT BRAIN

• 1 Thiamine diphosphatase (TDPase) of brain was activated by a low concentration of ATP.
• 2 In thiamine-deficient rats TDPase activity in the brain increased significantly relative to that in pair-fed animals, while in liver it decreased by the same amount as in the pair-fed controls.
• 3 Liver TDPase was localized almost entirely in the soluble fraction, but in the brain it was bound to insoluble protein. On treatment with Triton X-100 brain TDPase activity increased.
• 4 The ATP content of the brain of deficient rats, but not the ADP or AMP content, was significantly higher than in the control group. The level of inorganic phosphate in the brain and spinal cord of deficient animals was elevated markedly, while that of P-creatine was unchanged.
• 5 The possible roles of brain TDPase in relation to nerve conduction and the blood-brain barrier are discussed.

     

DNA and DNA-polymerase activity in chicken brain regions during ontogeny

Abstract—

• 1 The DNA content of cerebral hemispheres, optic lobes, cerebellum and remainder was determined in chicken brains from the 11th day of embryonic life to 6 weeks after hatch. Each region showed a characteristic pattern of variation during development. The cerebellum showed the most rapid and the optic lobes the least rapid rate of DNA increase during the period studied. The concentration of DNA within these regions decreased continuously with age except for that of the cerebellum which passed through a maximum just before hatching.
• 2 The nature of the DNA-polymerase activity in soluble extracts from these brain regions seemed to be similar to the properties reported for this enzyme activity in other vertebrate tissues. Glycerol was stimulatory and denatured DNA was preferred to native DNA as primer. The requirements for magnesium ions and DNA were absolute. The requirement for deoxynucleoside triphosphates indicated this to be a replicative rather than a terminal addition enzyme. At nearly every age the level of enzyme activity was highest in extracts from the embryonic cerebellum.
• 3 The particulate fraction from brain homogenates decreased the DNA-polymerase activity observed in soluble brain extracts. Data are presented which indicate that this inhibition was the result of dephosphorylation of the deoxynucleoside triphosphate substrates by an ATPase in the brain particulate fraction whose activity increases during ontogeny.

     

SUBCELLULAR DISTRIBUTION OF 5-HYDROXYTRYPTAMINE IN RAT BRAIN DURING DEVELOPMENT: EFFECT OF DRUGS AND FASTING

Abstract— Distribution of brain 5-HT content between the high-speed supernatant and particulate fractions under normal and experimental conditions was studied in postnatal and adult rats. In adult and 35-day-old rats the 5-HT content of the supernatant fraction was about 25% of that of the total homogenate and significantly higher than that in 1, 7 and 21-day-old rats. In 1-day-old rats fasting caused an increase of 100% in the turnover, 50% in the content and no alteration in the subcellular distribution of brain 5-HT, which suggests that under normal conditions 5-HT stores may be filled near to capacity. After 5-hydroxytryptophan administration, the 5-HT content of the adult rat brain increased 3-fold and that of the supernatant fraction to 35% of 5-HT content of the total homogenate. In postnatal rats, the brain 5-HT content rose to an adult level and the supernatant 5-HT percentage to a markedly higher than adult level, probably because of the known higher than adult 5-hydroxytryptophan decarboxylase activity of brain capillaries. Administration of tranylcypromine to adult rats caused a 2.6-fold increase of brain 5-HT content and a slight increase of the supernatant 5-HT percentage. At various times after the administration of the MAO inhibitors (tranylcypromine or pargyline) and fasting to the 1-day-old rats, brain 5-HT content increased 4, 5 and 7-fold, respectively, and the supernatant 5-HT rose consistently and, as in the adult, to about 30% of the 5-HT content of the total homogenate. After pargyline following reserpine pretreatment, the 5-HT content of the adult and 1-day-old rat brain increased to 2–3 times the control level and that of the supernatant fraction to about 40% of the 5-HT content of the total homogenate. The adult values for 5-HT in the particulate fraction of the 1-day-old rats after the drug treatments are in sharp contradiction to the low endogenous 5-HT content and known lack of nerve terminals and synaptic vesicles in their brains, and suggest that after MAO inhibition brain 5-HT neurons may bind the amine by some other mechanism than the Mg²⁺-ATP-dependent, reserpine-sensitive granular storage.     

LIFE HISTORY AND SEED DISPERSAL OF THE SHORT-LIVED CHAPARRAL SHRUB DENDROMECON RIGIDA (PAPAVERACEAE)

The natural history of the short-lived, fire-following shrub Dendromecon rigida Benth. was studied with emphasis on reproductive output and the consequences of seed dispersal, by intensive study of one population and comparisons with several others.

1. In 16 populations throughout California, mean seed weight ranged from 10 to 16 mg, and was not correlated with rainfall, elevation or latitude. Seed number per fruit ranged from 3 to 11. Adult populations ranged in size up to several million, but each was probably even-aged, established after recent disturbance. Seed-dispersing ants were found at all localities.
2. Reproduction began one year after establishment. Precocious reproduction did not increase mortality; rather, longer-lived plants were more fecund at all ages.
3. The percentage of the population reproducing and fruit number in the most fecund plants were directly related to rainfall in the preceding six months, regardless of plant age. Reproduction also differed according to topographic position.
4. Mean life expectancy of one-year-old plants was about six years, and only 5% survived to age 10 years. Intraspecific density effects were not apparent. Seed longevity probably exceeds adult longevity by a factor of five or ten.
5. The fruits are explosive and secondary dispersal is by gravity and ants. The ants are attracted to a caruncle which represents 14% of the propagule's caloric content. In the intensive study area ants removed more seeds from more sites than did vertebrate seed predators. Pogonomyrmex subnitidus developed large nests on open sites on ridges, and thus provided uphill (even interdrainage) dispersal; it discarded seeds on the soil surface, free to roll but open to predation. Camponotus species had fewer foragers but many small nests in well-covered sites, and discarded the seeds in underground refuse galleries. Dispersal thus affects exposure to predation, the microsite of germination, conspecific aggregation, and position in the mosaic patterns of topography and fire.

     

Formation of mitochondria in Boderia (Protozoa: Foraminiferida)

Summary Approximately 25 per cent of the mitochondria in one day old, rapidly growing, schizonts of Boderia vary considerably in their morphology from the consistently spherical organelles present in adult animals. Mitochondrial biogenesis by division is indicated and illustrated. The internal reorganisation of the mitochondrion which occurs prior to fission has not been reported previously for this organelle.     

RATES OF CEREBRAL GLUCOSE UTILIZATION IN RATS ANAESTHETIZED WITH PHENOBARBITONE

Abstract—

• 1 Intraperitoneal injection of phenobarbitone (250 mg/kg body wt.) into rats caused increased brain concentrations of glucose (100 per cent), glucose 6-phosphate (16 per cent) and ATP (12 per cent) and decreased concentrations of lactate (33 per cent) and ADP (15 per cent). A 31 per cent decrease in glutamate content was not statistically significant. No significant change occurred in the cerebral contents of glycogen or creatine phosphate.
• 1 The rates of increase in the brain of specific activities, in the first few minutes after systemic injection of [U-¹⁴C]glucose, of glucose, lactate, glutamate and glycogen were all halved by phenobarbitone. Calculated flux rates of ¹⁴C from glucose into metabolic intermediates and from lactate to glutamate were also decreased by 27–47 per cent; the effects on rate constants showed inconsistencies. The rate constants for conversion of glucose to lactate and to glutamate were decreased by 60–70 per cent, but that from lactate to glutamate was virtually unchanged. The rate constant for the flux from glucose to glycogen was reduced by 39 per cent, but the accumulation of glucose meant that the actual flux into glycogen increased by 20 per cent.
• 1 The results are interpreted in terms of an effect of the barbiturate not only on glucose transport, but also at an enzymic stage in glycolysis, possibly hexokinase or phosphofructokinase.

     

Cerebroside galactosidase: a method for determination and a comparison with other lysosomal enzymes in developing rat brain

• 1 A method is described for assaying brain for cerebroside galactosidase activity. The enzyme was liberated by sonication and addition of sodium taurocholate, then by digestion with pancreatic enzymes. It was further purified by precipitation at pH 3. The enzyme was then incubated with an emulsion of galactose-labelled cerebroside in taurocholate and oleate at pH 4·5, and the liberated galactose was determined by scintillation counting.
• 2 The content of cerebroside galactosidase in rat brain at various ages has been determined. The enzyme was present before cerebroside appears in noticeable amounts (4 days) and the amount rose considerably during the period of active cerebroside deposition and myelination. The amount then remained at a high concentration even in the adult.
• 3 Comparison with other lysosomal brain enzymes was made in the age study. Nitrophenyl galactoside hydrolase also increased during myelination but levelled off earlier; its activity paralleled the amount of ganglioside. Nitrophenyl glucoside hydrolase started at a lower level and decreased with age. Sulphatase activity rose during myelination, then decreased somewhat after 15 days. Ceramidase followed a pattern similar to that of nitrophenyl galactoside hydrolase; it is suggested that both of these enzymes reflect ganglioside metabolism.
• 4 The relative amounts of brain enzymes in different states were determined as a function of age in the case of cerebrosidase, nitrophenyl galactoside hydrolase and sulphatase. The proportion found in the high speed supernatant fraction was low but increased after myelination. The proportion that could be ‘solubilized’ by sonication decreased after myelination but the values differed greatly for the three enzymes. This treatment solubilized one-seventh of the cerebrosidase, half the nitrophenyl galactosidase and three-quarters of the sulphatase.

     

ROLE OF FETAL AND INFANT GROWTH IN PROGRAMMING METABOLISM IN LATER LIFE

Fetal growth and development is dependent upon the nutritional, hormonal and metabolic environment provided by the mother. Any disturbance in this environment can modify early fetal development with possible long-term outcomes as demonstrated by extensive work on ‘programming’. Growth restriction resulting from a deficit in tissue/organ cell number (as measured by tissue DNA content) is irrecoverable. However, when the cell size (or cell protein content) is reduced, the effects on growth may not be permanent. Recent epidemiological studies using archival records of anthropometric measurements related to early growth in humans have shown strong statistical associations between these indices of early development and diseases in later life. It has been hypothesised that the processes explaining these associations involve adaptive changes in fetal organ development in response to maternal and fetal malnutrition. These adaptations may permanently alter adult metabolism in a way which is beneficial to survival under continued conditions of malnutrition but detrimental when nutrition is abundant. This hypothesis is being tested in a rat model which involves studying the growth and metabolism in the offspring of rat dams fed a low-protein diet during pregnancy and/or lactation. Using this rat model, it has been demonstrated that there is:

• (i) Permanent growth retardation in offspring nursed by dams fed a low-protein diet.
• (ii) Permanent and selective changes in organ growth. Essential organs like the brain and lungs are relatively protected from reduction in growth at the expense of visceral organs such as the liver, pancreas, muscle and spleen.
• (iii) Programming of liver metabolism as reflected by permanent changes in activities of key hepatic enzymes of glycolysis and gluconeogenesis (glucokinase and phosphoenolpyruvate carboxykinase) in a direction which would potentially bias the liver towards a ‘starved’ setting. We have speculated that these changes could be a result of altered periportal and perivenous regions of the liver which may also affect other aspects of hepatic function.
• (iv) Deterioration in glucose tolerance with age.
• (v) An increase in the life span of offspring exposed to maternal protein restriction only during the lactation period, and a decrease in life span when exposed to maternal protein restriction only during gestation.

These studies show that hepatic metabolism and even longevity can be programmed by events during early life.