摘要:

Abstract—Studies on the incorporation of [14C]NaHCO3into both orotic acid and RNA in tissue slices reveal the occurrence of the complete orotate pathway for thede novobiosynthesis of pyrimidines in the rat brain. A comparison of the rates of incorporation of bicarbonate into orotic acid and RNA in tissue slices of brain and liver indicate the brain to be one‐fourth to one‐half as active as the liver in thede novobiosynthesis of pyrimidines. The results of this study favor the proposal that the adult rat brain can meet its needs for pyrimidines throughde novosynthesis and is not dependent upon salvage activity and an extraneural supply of pyrimi

ISSN:0022-3042    

DOI:10.1111/j.1471-4159.1972.tb06207.x

出版商:Blackwell Publishing Ltd    

年代:1972

数据来源: WILEY

摘要:

Abstract—Potassium transport was assessed within synaptic terminals isolated from cerebral cortices of rats which experienced one or two maximal electroshock (ES) convulsions daily. No significant change in endogenous K content was present after 2 consecutive days of ES‐seizures. However, K decreased 22 % and 41 % after 4 and 6 days of convulsions respectively. After 6 days, synaptosomes from ES rats were able to accumulate K to the same extent as controls and were inhibited by ouabain to an equivalent extent (50%). When these synaptosomes from ES rats were preloaded with high concentrations of K, K leaked out at an increased rate. When diphenylhydantoin (DPH) was administered intraperitoneally from the second to the sixth day of ES‐convulsions, the decrease in endogenous K induced by chronic convulsions was corrected. In ion‐free media or with 50 mM Na, DPH had no effects on the enhanced efflux of K observedin vitroafter ES‐seizures. However, with high Na (50–100 mm) and low K (0.2–1 mm) DPH stimulated K uptake but did not affect the ouabain inhibition. Under conditions optimal for K uptake (50 mmNa and 10 mmK), DPH did not affect K accumulation but it preventedin vitroouabain inhibition. Our results indicate that repeated ES‐convulsions decreased K content within isolated nerve terminals by enhancing its passive leakage.In vivoDPH prevented the effects of ES‐seizures by stimulating the Na‐K pump and not by directly

ISSN:0022-3042    

DOI:10.1111/j.1471-4159.1972.tb06208.x

出版商:Blackwell Publishing Ltd    

年代:1972

数据来源: WILEY

摘要:

Abstract—Clearance of [14C]DOPA and [14C]dopamine from CSF was investigated in anaesthetized rhesus monkeys (M. Mulatta) subjected to ventriculocisternal perfusion. The efflux coefficients, kVE, at tracer concentrations (3–5m) in the perfusate were 0.0487 ml/min and 0.0325 ml/min for [14C]DOPA and [14C]dopamine, respectively. Carrier DOPA (10 mm) in the perfusate decreased the efflux of [14C]DOPAsignificantly, but carrier dopamine had no appreciable effect on the clearance of [14C]dopamine. These findings suggest that DOPA is cleared from CSF in part by a saturable mechanism which may be located in the choroid plexus, whereas dopamine leaves the ventricular system by passive diffusion. Radioactivity in the caudate nucleus immediately adjacent to the perfused ventricle averaged 15.5 % and 12.6% of the radioactivity in the perfusates with [14C]DOPA or [14C]dopamine, respectively. These distribution percentages were similar to those found for various extracellular indicators after ventriculocisternal perfusion and may indicate that the efflux of intraventricularly‐administered exogenous DOPA and dopamine occurs in part through extracellular cha

ISSN:0022-3042    

DOI:10.1111/j.1471-4159.1972.tb06209.x

出版商:Blackwell Publishing Ltd    

年代:1972

数据来源: WILEY

摘要:

Abstract—The enzyme cytidine 5′‐monophospho‐N‐acetylneuraminic acid synthetase was studied in different parts of the calf brain. Characterization of partial purified enzyme preparations from cortical grey matter andcorpus callosumby means of pH optima andKmvalues, showed the enzyme of grey and white brain areas to be identical. Unexpectedly the regional differences of the enzyme activities per g wet tissue and per mg protein were very slight. From the presence of the enzyme in pure white brain areas, which are known to be poor in neuronal perikarya, and the fact that the enzyme is localized in the cell nucleus, we concluded that cytidine 5′‐monophospho‐N‐acetylneuraminic acid is produced in glia cell nuclei and that it is very likely that biosynthesis of sialo‐glycoproteins and/or ganglio‐sides occurs within glia cells.The enzyme activity per μmol DNA‐P is somewhat higher in grey than in white regions, indicating a slightly higher activity per neuronal than per glial nucleus.The regional differences of lipid and protein‐bound sialic acid and RNA show a striking similarity and contrast to those of the enzyme. These differences are interpreted in terms of a differential content

ISSN:0022-3042    

DOI:10.1111/j.1471-4159.1972.tb06210.x

出版商:Blackwell Publishing Ltd    

年代:1972

数据来源: WILEY

摘要:

Abstract—At various times during a 2‐day study, the levels of adenine nucleotides and selected glycolytic intermediates were determined in brains of chicks fed a diet containingd‐galactose (40%, w/w). The levels of ATP and glucose 6‐phosphate had decreased by 9 h after initiation of the diet, whereas those of fructose 1,6‐diphosphate, 3‐phosphoglycerate,l‐α‐glycerophosphate, and lactate were not reduced until after 18 h had elasped. Although glucose 1‐phosphate was not appreciably affected, glucose and glycogen were depleted during the latter stages of the toxicity. The cerebral levels of 3′,5′‐cyclic AMP and citrate did not differ significantly between the two dietary groups at 48 h. The changes in the levels of cerebral glycolytic intermediates and high‐energy phosphates during ischemia indicated that the glycolytic rate was diminished in the chicks fed galactose and that high‐energy phosphate compounds were depleted sooner than in controls. After intraperitoneal injection of [14C]glucose, the specific radioactivity and levels of glucose in the plasma from chicks fed either diet were similar, whereas they were significantly reduced in the brains from galactosefed animals. We suggest that galactose interferes with the uptake of glucose into the brain and that this mechanism may be an important factor ind‐galactose‐in

ISSN:0022-3042    

DOI:10.1111/j.1471-4159.1972.tb06211.x

出版商:Blackwell Publishing Ltd    

年代:1972

数据来源: WILEY

摘要:

Abstract—[14C] orotic acid and [3H]l‐leucine were injected intraperitoneally into two groups of rats, aged 12 and 24 months, respectively. The apparent turnover of RNA and protein from several subcellular fractions was assessed by following the loss of label from these fractions with time. The curves for apparent turnover of all protein fractions from mitochondria were single exponential curves. Total mitochondrial protein from younger animals had a half‐life of 26.8 days. Two protein subfractions, protein insoluble in cold perchloric acid and chloroform‐methanol (residual protein) and protein soluble in chloroform‐methanol (C–M protein) had similar half‐lives: 26.3 and 26.1 days, respectively. For the older animals the half‐lives were 23.5 days for total protein, 17.4 for residual protein and 30.4 for C–M protein. The difference between the two protein subfractions from mitochondria of the older animals suggests an age‐associated deviation from the synchrony of synthesis and degration of proteins in this organelle.Further deviation from the unit concept of mitochondrial turnover was seen in the apparent turnover of mitochondrial RNA. Mitochondrial RNA had half‐lives of 10.0 and 11.6 days for older and younger animals, respectively, with no significant difference between the groups. No age‐associated difference was observed in the apparent turnover of sRNA. This fraction exhibited a double exponential turnover pattern; the first component in both cases had a half‐life of about 5–8 days and the second component 13–16 days. Ribosomal RNA and protein from both older and younger animals exhibited multiexponential kinetics but both components, RNA and protein, within each age group appeared to turn over synchronously. Average values for apparent turnover of total ribosomes (RNA and protein) were 18.2 days for the older animals and 7.4 days for the younger animals. The age‐associated difference

ISSN:0022-3042    

DOI:10.1111/j.1471-4159.1972.tb06212.x

出版商:Blackwell Publishing Ltd    

年代:1972

数据来源: WILEY

摘要:

Abstract—Fructose levels were determined in plasma and brain of 8‐ to 12‐day‐old mice at intervals after the injection of 30 mmol/kg intraperitoneally; controls received NaCl, 15 mmol/kg. In normal animals brain fructose increased very slowly despite a rapid rise in plasma levels (120 times the control value in 5 min). At 40 min the cerebral level was 1.54 ± 0.23 mmol/kg; the corresponding plasma level was 47.1 ± 4.8 mM. The data suggest that fructose can serve as a source of energy to the brain in times of critical need: during insulin hypoglycemia brain fructose increased to only 0.88 ± 0.05 mmol/kg during the same interval (40 min) despite plasma fructose values equal to those in control animals; also 30 s after cerebral ischemia (decapitation) brain fructose fell from a zero time value of 1.19 ± 0.09 mmol/kg (20 min after fructose injection) to 0.76 ± 0.06 mmol/kg (P= 0.005). Under both circumstances (hypoglycemia and ischemie anoxia) an apparent threshold concentration of fructose for utilization was observed—0.6–0.7 mmol/kg. The most likely explanation for this finding appears to be that this level of fructose was in the extracellular space of the brain. Hexokinase activity in brain homogenates of 8‐ to 12‐day‐old mice with fructose and ATP at concentrations foundin vivoand during ischemie anoxia did not appear to be rate‐limiting. We concluded that the major handicap to the use of fructose by the brain was the limited penetration of fructose fro

ISSN:0022-3042    

DOI:10.1111/j.1471-4159.1972.tb06213.x

出版商:Blackwell Publishing Ltd    

年代:1972

数据来源: WILEY

摘要:

Abstract—Axonal transport was studied in two efferent projections of thesubstantia nigra: (1) the nigro‐striatal system; and (2) the nigro‐thalamic system. [14C]leucine was injected stereotaxically into the leftsubstantia nigraof rats. At various intervals thereafter significant amounts of [14C]protein were found in the midbrain (which surrounded the injection site),hypothalamus, thalamusandcorpus striatumon the injected side of the brain. By determining the temporal characteristics of the distribution of [14C]protein, axonal transport from thesubstantia nigrato thethalamusandcorpus striatumcould be inferred. Fast (approximately 50 mm/day) and slow (approximately 1 mm/day) rates of flow were evident in both systems. Either electrolytic lesions of the medial forebrain bundle or intraventricular pretreatment with 6‐hydroxydopamine (200 μg) produced a substantial decrease in the amount of labelled protein reaching thecorpus striatumbut not in that reaching thethalamus.The decrease following electrolytic lesions correlated significantly with the decrease in the activity of striatal tyrosine hydroxylase, but after 6‐hydroxydopamine the decrease in axonal transport was consistently less than the loss of striatal tyrosine hydroxylase. This difference indicated that a portion (perhaps as much as 20 per cent) of the nigro‐striatal neurons are non‐catecholaminergic. Finally, we present data which suggest that in contrast to effects on peripheral neurons, 6‐hydroxydopamine destroys the cell bodies as well as nerve terminals of adrenergic neurons in the centra

ISSN:0022-3042    

DOI:10.1111/j.1471-4159.1972.tb06214.x

出版商:Blackwell Publishing Ltd    

年代:1972

数据来源: WILEY

摘要:

Abstract—The cerebro‐visceral connective ofAnodonta cygneahas been shown to provide a convenient system for experiments on fast axonal transport. The transport mechanism is directional, independent of the cell bodies, inhibited by cyanide, dinitrophenol and colchicine but is resistant to anoxia. Although the rate of transport increases with temperature above 15°C it is more or less temperature‐independent from 4 to 15°C, i.e. over the normal temperature range of this pond‐dwellin

ISSN:0022-3042    

DOI:10.1111/j.1471-4159.1972.tb06215.x

出版商:Blackwell Publishing Ltd    

年代:1972

数据来源: WILEY

摘要:

Abstract—Anin vitrosystem from the frog has been used to study fast axonal transport of glycoproteins. The migration of [3H]fucose‐, [3H]glucosamine‐ and [35S]sulphate‐labelled material was followed from the dorsal ganglia, along the sciatic nerve towards the gastrocnemius muscle.The distribution in different subcellular fractions, effect of cycloheximide and transport kinetics did not differ very much between fucose‐ and glucosamine‐incorporation into the nerve. Cycloheximide blocked the synthesis of TCA‐insoluble radioactivity, which was transported at a rate of 60–90 mm per day at 18°C, more effectively than the synthesis of stationary proteins in the ganglia. About 10 per cent of the TCA‐insoluble and transported radioactivity was extracted by chloroform‐methanol (2:1, v/v) and might be glycolipids and the rest glycoproteins. Results suggest that TCA‐soluble activity, which was recovered in the nerve, originated in part from labelled macromolecules consumed along the axons. The rapidly transported TCA‐insoluble radioactivity was 85 per cent particulate and mainly associated with structures sedimenting in the microsomal fraction.[35S]Sulphate‐labelled TCA‐insoluble material was resistant towards chloroform‐methanol (2:1, v/v) extraction and rapidly transported from the ganglia into the nerve. The synthesis was inhibited by cycloheximide. The material, probably proteoglycans, represented a quantitatively minor par

ISSN:0022-3042    

DOI:10.1111/j.1471-4159.1972.tb06216.x

出版商:Blackwell Publishing Ltd    

年代:1972

数据来源: WILEY