bluuebunny/crossref_metadata_2025_split huggingface dataset:
CYCLIC NUCLEOTIDE PHOSPHODIESTERASE IN RAT NEOSTRIATUM: PROPERTIES OF THE ENZYME IN CRUDE HOMOGENATES
Authors: Minneman K. P. 
Published: October 2006

Abstract—Homogenates of rat neostriatum hydrolysed cGMP faster than cAMP at both high (100μM) and low (1 μM) substrate concentrations, although the hydrolysis of both nucleotides exhibited similar kinetic properties. Kinetic analysis of the effect of substrate concentration on the rate of cAMP and cGMP hydrolysis gave results characteristic of a negatively cooperative enzyme species, with two apparent Km's for each nucleotide. The ratio between the Vmax, of the high Km, form and the Vmax of the low Km form was similar in various subcellular fractions of neostriatal tissue, in a preparation of synaptic membranes from whole brain, and in homogenates of other brain regions, including both neural‐rich and glial‐rich tissues. In homogenates of neostriatum cAMP could almost completely block cGMP hydrolysis and vice versa. The kinetics of this inhibition were competitive at low (1 μM) substrate concentrations, and non‐competitive at high (100 μM) substrate concentrations. Various phosphodiesterase inhibitors failed to preferentially inhibit the hydrolysis of either nucleotide at high or low nucleotide concentrations.Preliminary studies of the effect of a Ca2+ dependent endogenous activator preparation on the hydrolysis of cyclic nucleotides in homogenates of rat neostriatum showed a specific activation of cGMP hydrolysis at low nucleotide concentrations. The rate of cGMP hydrolysis at 1 μM substrate concentration was doubled in the presence of the activator preparation and 100μM‐CaCl2, while cGMP hydrolysis at 100 μM or cAMP hydrolysis at both 1 μM and 100μ.M remained unaffected.These observations raise the possibility that cAMP and cGMP may be hydrolysed by the same enzyme in rat neostriatum and that an endogenous activating factor may determine the relative affinities of the enzyme for the two nucleotides.
CYCLIC NUCLEOTIDE PHOSPHODIESTERASE IN RAT NEOSTRIATUM: MULTIPLE ISOELECTRIC FORMS WITH SIMILAR KINETIC PROPERTIES
Authors: Minneman K. P. 
Published: October 2006

Abstract—Separation of multiple forms of cyclic nucleotide phosphodiesterase from the soluble supernatant fraction of rat neostriatum by isolectric focusing yielded five separate peaks of cyclic nucleotide hydrolysing activity. Each separated enzyme form displayed a complex kinetic pattern for the hydrolysis of both cyclic AMP and cyclic GMP, and there were two apparent Km's for each nucleotide. At 1 μM substrate concentration, four enzyme forms exhibited higher activity with cyclic AMP than with cyclic GMP, while one form yielded higher activity with cyclic GMP than with cyclic AMP. Cyclic AMP and cyclic GMP were both capable of almost complete inhibition of the hydrolysis of the other nucleotide in all the peaks separated by isoelectric focusing; the IC50's for this interaction correlated well with the relative rates of hydrolysis of each nucleotide in each peak. The ratio of activity at 1 μM substrate concentration for the five enzyme forms separated by isoelectric focusing was 10:10:5:15:1 for cyclic AMP hydrolysis; and 6:6:4:8:2 for cyclic GMP hydrolysis; and the isoelectric points of the five peaks were 4.3, 4.45, 4.7, 4.85, and 5.5, respectively. Known phosphodiesterase inhibitors did not preferentially inhibit any of the separated forms of activity for either cyclic AMP or cyclic GMP hydrolysis, at either high (100 μM) or low (1 μM) substrate concentrations. Preliminary examination of the subcellular distribution of the different forms of enzyme activity indicated a different degree of attachment of the various forms to particulate tissue components. Isoelectric focusing of the soluble supernatant of rat cerebellum gave rise to a slightly different pattern of isoelectric forms from the neostriatum, indicating a different cellular distribution of the isoelectric forms of PDE in rat brain.Polyacrylamide disc gel electrophoresis of the soluble supernatant of rat neostriatum also generated a characteristic pattern of five separate peaks of cyclic nucleotide phosphodiesterase activity, each of which hydrolysed both cyclic AMP and cyclic GMP. Polyacrylamide gel electrophoresis of single enzyme forms previously separated by isoelectric focusing gave single peaks, with a marked correspondence between the enzyme forms produced by isoelectric focusing and those produced by gel electrophoresis, suggesting that both protein separation procedures were isolating the same enzyme forms.The results indicate the existence of multiple isoelectric forms of cyclic nucleotide phosphodiesterase in the soluble supernatant fraction of rat neostriatum, all of which exhibit similar properties. In this tissue a single kinetic form of this enzyme appears to exist displaying complex kinetic behaviour indicative of negative cooperativity and hydrolysing both cyclic AMP and cyclic GMP, with varying affinities.
THE EFFECTS OF ASPHYXIA ON 5‐HYDROXYTRYPTAMINE METABOLISM IN THE IMMATURE RAT BRAIN
Authors: Tricklebank M. D. , Pickard F. J. , Dobbing J. 
Published: October 2006

Abstract—Fire‐day‐old rats subjected to prolonged asphyxia at 37°C show a slower rate of synthesis of 5‐HT as measured by the accumulation of the amine after inhibition of monoamine oxidase. During recovery from asphyxia 5‐HT synthesis is markedly stimulated when measured over a 50 or 90 min period. No change in 5‐HT synthesis was observed in 5‐day‐old rats during recovery from cold exposure or immobilization. The results indicate that the persistent increase in synthesis that follows resuscitation may be related to asphyxia per se rather than to the stress component of the treatment.
5‐HYDROXY‐l‐TRYPTOPHAN DECARBOXYLASE ACTIVITY: MICROASSAY AND DISTRIBUTION IN DISCRETE RAT BRAIN NUCLEI
Authors: Saavedra J. M. 
Published: October 2006

Abstract— 5‐Hydroxy‐l‐tryptophan decarboxylase (EC 4.1.1.28) activity was measured in discrete regions of the rat brain by means of a sensitive micromethod lhat allows the quantitation of enzyme activity in μg amounts of brain tissue.A good correlation was obtained between serotonin levels and 5‐hydroxy‐l‐tryptophan decarboxylase activity in all the brain regions examined. Wide differences in enzyme activity were found in the different brain nuclei, with a 20‐fold difference in activity between the most active region (the nucleus raphe dorsalis) and the least active regions (the corpus callosum and the optic tract).
SIMULTANEOUS ISOLATION OF PURIFIED MICROSOMAL and MYELIN FRACTIONS FROM RAT SPINAL CORD
Authors: Toews A. D. , Horrocks L. A. , King J. S. 
Published: October 2006

Abstract— The fraction that sediments between 2 × 105g‐min and 6 × 106g‐min from dilute dispersions of rat brain in 0.32 m‐sucrose is a microsomal fraction with very little contamination by myelin. A crude microsomal fraction prepared in the same way from rat spinal cord contains more myelin than microsomes. Centrifugation of the crude microsomal fraction in 0.85 m‐sucrose gave a floating fraction, an infranatant fraction (purified microsomes) and a small pellet. The purified microsomes contained very little myelin as judged by electron microscopy and polyacrylamide gel electrophoresis. The lipid composition resembled that of spinal cord myelin except that the purified microsomes contained relatively less cholesterol and ethanolamine plasmalogens. The content of galactolipids was much greater in spinal cord microsomes than in brain microsomes. The spinal cord CDP‐ethanol‐amine:diglyceride ethanolaminephosphotransferase activity (EC 2.7.8.1) was concentrated in the purified microsomes.A spinal cord myelin fraction isolated from the 2 × 105g‐min pellet was quite pure as judged by electron microscopy, enzyme activities and polyacrylamide gel electrophoresis. No NADPH‐cyto‐chrome c reductase activity (EC 1.6.2.3) could be detected in the purified myelin. The ethanolaminephosphotransferase specific activity was about 5% of that found in the purified microsomal fraction. The protein content was 25% by weight for spinal cord myelin and 31% for brain myelin. Of the total spinal cord 2′,3′‐cyclic nucleotide‐3′‐phosphohydrolase activity, 16% was lost from the crude myelin during purification, 21% was recovered in the purified myelin, and 11% was found in the floating fraction from the crude microsomes. The purified myelin and microsomal fractions from spinal cord were relatively pure. Additional myelin was recovered in the floating fraction from the crude microsomes.
THE EFFECT OF GRADUAL CHANGES IN TEMPERATURE ON THE RELEASE OF HORMONES FROM NERVE ENDINGS ISOLATED FROM BOVINE NEURAL LOBES1
Authors: Baker Ruth V. , Hope D. B. 
Published: October 2006

Abstract— Homogenates of bovine neural lobe tissue were fractionated by differential centrifugation at 20°C or at 4°C and the distribution of activities of vasopressin and oxytocin among the fractions was compared. The ratio of total hormone to protein (mg) in the homogenate was similar at the two temperatures. At 20°C a much smaller proportion of the total hormone was recovered in the soluble fraction (100,000 gav supernatant), than at 4°C with a corresponding increase in recovery in the nerve‐ending fraction (800–3000 g sediment).Nerve endings isolated at 4°C did not, when incubated, release hormone in response to changes in temperature. Nerve endings isolated at 20°C released hormone when the temperature was reduced below 15°C. Gradual reduction in temperature led to hormone release unaccompanied by lactate dehydrogenase release. Incubation of nerve endings for 10 min at 10°C increased the release of vasopressin and of neurophysin without any increase in lactate dehydrogenase. These results demonstrate that release of vasopressin by cold stimulation occurs by way of exocytosis.
CHOLINE AND ACETYLCHOLINE IN RATS: EFFECT OF DIETARY CHOLINE
Authors: Haubrich D. R. , Wang Pauline F. L. , Chippendale T. , Proctor Elizabeth 
Published: October 2006

Abstract– The concentration of free choline in peripheral tissues (duodenum, heart, kidney, liver, stomach and plasma) of rats was found to be related to the amount of free choline in the diet. Under steady‐state conditions, the concentration of free choline in plasma varied from a minimum of approx 6 nmol/ml (in rats fed a choline‐deficient diet) to a maximum value not exceeding 21 nmol/ml. The concentration of plasma choline was elevated above 21 nmol/ml for a short time after parenteral administration of choline chloride or one of its precursors (CDP choline or phosphorylcholine), but was not affected by stress, endocrine manipulations, drug treatments or the time of day when rats were killed.The metabolism of intravenously administered [methyl‐3H] choline was accelerated in peripheral tissues (except plasma) of choline‐deficient rats, indicating that free choline is not preserved during choline deficiency by a reduction in its rate of turnover. Furthermore, the decrease in concentration of plasma choline that occurred in rats fed a choline‐deficient diet was prevented by addition of deanol (dimethylaminoethanol) to the diet. These results indicate that free choline in peripheral tissues of rats is derived from both free choline in the diet, and from precursors of choline present within the diet.In contrast to the effects in peripheral tissues, the concentration of free choline in brain was not reduced by dietary deprivation of free choline; however, the increase in free choline that occurred when rats were decapitated was reduced in brains by deficiency of choline, suggesting a decrease in the concentration of esterified forms of cerebral choline.The concentration of acetylcholine was not reduced in the brain, duodenum, heart, kidney or stomach of 21‐week old rats raised from birth on a choline‐deficient diet, in the duodenum of rats given a choline‐deficient diet for 1, 5 or 11 days, or in brains of rats deprived of free choline for 1 or 11 days. However, the rate of in vivo synthesis of ACh from [methyl‐3H]choline was accelerated in cholinergic tissues that were depleted of free choline (i.e. duodenum, heart and stomach).
THE TOXIC EFFECT OF SODIUM GLUTAMATE ON RAT RETINA: CHANGES IN PUTATIVE TRANSMITTERS AND THEIR CORRESPONDING ENZYMES
Authors: Karlsen R. Lund , Fonnum F. 
Published: October 2006

Abstract– Subcutaneous administration of high doses of sodium glutamate to rats during their first week after birth produced an almost total loss of choline acetyltransferase, a 90% reduction in glutamate decarboxylase and 70% reductions in acetylcholinesterase and DOPA decarboxylase activities in the adult retina. In addition there was a 70% decrease in GABA and 35‐55% decrease in aspartate, glutamate, glycine, alanine and glutamine. No reduction in taurine was observed. The results support the view that the enzymes are mainly localized in the interneurons of retina and that taurine is present in the photoreceptor cells.Glutamate treatment was also followed by a small reduction in choline acetyltransferase and glutamate decarboxylase of the superior colliculus and in choline acetyltransferase of hippocampus, whereas no changes could be detected in the lateral geniculate body of the adult rat. Unilateral enucleation performed on 1‐day‐old animals did not alter choline acetyltransferase, acetylcholinesterase, glutamate decarboxylase and DOPA decarboxylase activities in the superior colliculus and in the lateral geniculate body of the adult rat.
CYCLIC NUCLEOTIDES IN MURINE BRAIN: THE TEMPORAL RELATIONSHIP OF CHANGES INDUCED IN ADENOSINE 3′,5′‐MONOPHOSPHATE AND GUANOSINE 3′,5′‐MONOPHOSPHATE FOLLOWING MAXIMAL ELECTROSHOCK OR DECAPITATION
Authors: Lust W. D. , Goldberg N. D. , Passonneau J. V. 
Published: October 2006

Abstract–Adenosine 3′,5′‐cyclic monophosphate (cyclic AMP) levels increase about 5‐fold in the cerebral cortex and 2‐fold in the cerebellum following electroconvulsive shock (ECS). The peak levels of cyclic AMP occur at 45 s after ECS in the cerebral cortex, and at 15 s in the cerebellum. In the cerebral cortex, ECS produces twice the cyclic AMP accumulation as does decapitation in a comparable time period; however, the relative effect of a number of neurotropic agents on the cyclic AMP accumulation is essentially the same, whether stimulated by decapitation or by ECS. In the cerebellum, the levels of guanosine 3′,5′‐cyclic monophosphate (cyclic GMP) also increase following ECS. The cyclic GMP levels are greatest at 60 s after ECS during the postictal depression. An association between elevated cerebellar cyclic GMP and depression seems unlikely, since CNS depressants either lowered or had no effect on cyclic GMP levels. From these results, cyclic nucleotide profiles following treatments such as ECS or decapitation may be useful in elucidating the molecular events involved in seizures, brain injury and ischemia.
CYCLOHEXIMIDE ALTERS AXONAL TRANSPORT AND SUBCELLULAR DISTRIBUTION OF DOPAMINE‐β‐HYDROXYLASE ACTIVITY
Authors: Brimijoin S. 
Published: October 2006

Abstract—Administration of cycloheximide, 10 mg/kg s.c. led within 4 h to an approx 30% reduction of dopamine‐β‐hydroxylase (DBH) activity in the abdominal portion of rat sciatic nerves. At least two more hours elapsed before DBH activity in the distal part of these nerves began to fall. This pattern suggests reduced synthesis or delivery of DBH into axons but continued transport of previously delivered enzyme. Coinciding with the time at which DBH activity began to fall in distal segments of sciatic nerve, there was a marked reduction in the accumulation of DBH activity above a ligature in this region. Between 4 and 8 h after administration of cylcoheximide, 10 mg/kg, accumulation above a ligature was 70% less than in untreated nerves (P < 0.001), a reduction significantly greater (P < 0.05) than the accompanying 28% loss of baseline DBH activity. At the same time, the clearance of DBH activity from nerve regions distal to a ligature was greatly reduced. This pattern is consistent with the depletion of a minor but rapidly transported compartment of DBH. Six hours after administration of cylcoheximide, 10 mg/kg, the apparent subcellular distribution of DBH in distal regions of sciatic nerve was altered by a significant 36% loss in sedimentable DBH activity, with non‐significant changes in othcr fractions. This suggests that rapidly transported DBH, depleted from the nerve by cycloheximide‐induced inhibition of protein synthesis, is more highly associated with intraneuronal particles than is slowly transported or stationary DBH.
THE UPTAKE OF BIOGENIC MONOAMINES BY THE ISOLATED AURICLE OF THE SNAIL (HELIX POMATIA)
Authors: Hiripi L. , Neuhoff V. , Osborne N. N. 
Published: October 2006

Abstract—The uptake of [3H]5HT, [3H]dopamine, [3H]noradrenaline and [3H]octopamine into the auricle of Helix pomatia was studied.When tissues were incubated at 25°C in media containing radioactive amines, tissue:medium ratios of about 49:1, 14:1 and 5:1 for 5‐HT, dopamine, noradrenaline, and octopamine respectively were obtained after a 20–30 min incubation time. Tissues incubated at 25°C in media containing radioactive amines for 20–30 mins showed that almost all (96%) the radioactivity was present as unchanged [3H]5‐HT, [3H]dopamine, [3H]octopamine or [3H]noradrenaline.The high tissue:medium ratios for 5‐HT and dopamine, but not for noradrenaline and octopamine, showed saturation kinetics which were dependent upon temperature and sodium ions. From the Lineweaver–Burk plots, two uptake mechanisms for 5‐HT at 25°C were resolved; the high affinity uptake process having a Km1 value of 6.0 ± 10−8m and a Vm1 value of 0.115 nmol/g/min while the lower affinity process had a Km2 value of 1.04 ± 10−6m and a Vm2 value of 0.66nmol/g/min. At 0°C a single uptake mechanism for 5‐HT occurred which gave a Km value of 5.02 ± 10−8m and a Vm value of 0.0165 nmol/g/min. In the case of dopamine, the Lineweaver–Burk plot at 25°C showed a single uptake process with values for Km and Vm of 1.55 ± 10−7m and 0.086 nmol/g/min respectively. This process did not function at 0°C.The effect of various agents and ions upon the accumulation processes for all amines was also studied, and the data indicate that the same neurons probably accumulate more than one amine type.It is concluded that 5‐HT and dopamine uptake in the auricle is a mechanism for inactivating these substances at 25°C and that an uptake mechanism for 5‐HT also functions at 0°C. The results are discussed from the point of view of 5‐HT's being the cardioexcitatory substance in the snail heart.
DARK REARING and VISUAL STIMULATION IN THE RAT: EFFECT ON BRAIN ENZYMES
Authors: Sinha A. K. , Rose S. P. R. 
Published: October 2006

Abstract— Enzyme activities in motor and visual cortex and cerebellum of rats reared for 50 days in the dark (D) were compared to levels in normally reared (N) and in dark‐reared littermates exposed to 3 h of visual stimulation (L). Amongst 6 acid hydrolases, two, acid phosphatase and galactosaminadase, showed no effect of dark rearing. In three of the others, glucuronidase, glucosaminidase and galactosidase, activity tended to be lower in D than L. In glucosaminidase, N was similar to D and L above both, while in (total) glucosidase, galactosidase and glucuronidase, N was higher than D and L approached N. There were fewer changes in cerebellum than in cortex.Visual cortex acetylcholinesterase was 29% higher in L than in D, and 41% higher in L than in N, but there were no significant differences in AChE or BChE in motor cortex or cerebellum. Choline acetyltransferase was higher by 30% in L and D in visual cortex, and 22% in motor cortex. There were no differences in the cerebellum. There were no differences in the levels of activity of glutamate decarboxylase or Na+, K+, Mg2+ ‐ATPase in any region or condition.The significance of both the apparently transient and more permanent effects of dark rearing and light exposure on the enzymes studied, and discrepancies with other reports of enzyme changes in dark rearing are discussed.
THE ROLE OF LIPIDS IN THE OBSERVED LACK OF PHOSPHATIDYLCHOLINE EXCHANGE IN MYELIN
Authors: Brammer M. J. , Sheltawy A. 
Published: October 2006

Abstract— When exchange between liposomal phosphatidylcholine and that in a whole myelin fraction from guinea‐pig brain was studied, very little exchange was observed. In order to investigate the reason for this phenomenon, myelin lipids in the Ca2+ form were prepared and subjected to sonication under the same conditions usually used to study phosphatidylcholine exchange. Despite the high cholesterol content in these extracts, this treatment produced liposomes of a size (12 nm Stoke's radius) similar to that of pure phosphatidylcholine liposomes. In this form, myelin total lipids were capable of undergoing exchange, and this was only demonstrable in the fraction containing phosphatidylcholine and that containing phosphatidylinositol. Since the level of acidic phospholipids in these total lipid extracts is potentially capable of producing 40% inhibition of phosphatidylcholine exchange (Hellingset al, 1974; Brammer & Sheltawy, 1975), control experiments were carried out to ensure that the observed phosphatidylcholine exchange in the myelin lipid extract was not due to the loss of phosphoinositides. This was found to be the case, and it was concluded therefore that total myelin lipids, in the Ca2+ form, are capable of phosphatidylcholine exchange and that the observed lack of it in the whole myelin is due either to the effect of myelin proteins or the compact structure of the myelin membrane.Calculations based on the difference between the rate of phosphatidylcholine exchange in the myelin liposomes and in the sonicated phosphatidylcholine liposomes indicated that the phosphatidylcholine is asymmetrically distributed in the myelin liposomes. Almost all the phosphatidylcholine seems to be present in the outer half of the bilayer.
THE ACTION OF TRIETHYLTIN ON THE RESPIRATION OF RAT BRAIN CORTEX SLICES
Authors: Lock E. A. 
Published: October 2006

Abstract—Glucose oxidation by rat brain cortex slices is inhibited by low concentrations of triethyltin and this sensitive inhibition is shown to be chloride‐dependent. Pyruvate oxidation is only inhibited at high concentrations of triethyltin whether chloride is present or not. In contrast, the stimulation of both glucose and pyruvate oxidation observed with low concentrations of triethyltin prior to inhibition is chloride‐dependent. The results are discussed in relation to the chloride‐hydroxide exchange reaction known to be mediated across the inner mitochondrial membrane by triethyltin and other organo‐metals.