bluuebunny/crossref_metadata_2025_split huggingface dataset:
FUNCTIONAL PROPERTIES OF NEURONAL AND GLIAL ISOENZYMES OF BRAIN ENOLASE
Authors: Marangos P. J. , Parma A. M. , Goodwin F. K. 
Published: October 2006

Abstract—Two of the major brain enolase (EC 4.2.1.11) isoenzymes exist as cell specific forms. The neuron specific enolase (NSE) is localized in neurons and the non‐neuronal enolase (NNE) in glial cells. A third enolase containing one subunit from each of the above species is also present in brain and has been designated hybrid enolase. The stabilities of the brain enolases towards incubation with chloride and bromide salts is markedly different. NNE is rapidly inactivated upon incubation in 0.5 M‐KCI or KBr while NSE is minimally effected and the hybrid has an intermediate stability. The inactivation is temperature dependent and reversible by salt removal. Magnesium exerts a stabilizing effect on each enzyme form. The mechanism of the reversible salt inactivation involves dissociation of the enolase subunits with reassociation occurring during reactivation.The brain enolases also display marked stability differences during incubation in 3 M‐urea. with the neuronal form again being more stable. The urea inactivation was highly reversible for NNE but only marginally so for NSE. The neuronal enolase is also by far the most stable of the brain enolases at 50°C.
PSYCHOLOGICAL STRESS REDUCES CYCLIC 3′,5′‐ADENOSINE MONOPHOSPHATE LEVELS IN THE CEREBRAL CORTEX OF CONSCIOUS RATS, AS DETERMINED BY A NEW CRYOGENIC METHOD OF RAPID TISSUE FIXATION1
Authors: Skinner James E. , Welch K. M. A. , Reed Jane C. , Nell Janet H. 
Published: October 2006

Abstract— Cryoplates were implanted on the surface of the cortex in 32 chronic rat preparations. These devices were used both to freeze and to extract small samples of tissue. Coolant was circulated through each device by small flexible polyethylene tubes. Two series of experiments were performed. In the first, the animals were unrestrained and showed no behavioral signs of stress during the freeze fixation. The temperature responses of the cryoplates were very rapid (−632°C/s), and samples more than 1 mm thick were frozen and extracted within a few hundred ms following the onset of cooling. Each sample was analyzed for 3′.5′‐adenosine monophosphate (cyclic AMP) and protein content. The results from the cryoplate group (25.6 ± 15.6pmol cyclic AMP/mg protein) were compared to those obtained from two other groups in which freeze fixation was produced by immersion in liquid nitrogen (13.6 ± 4.6pmol/mg protein) or decapitation into liquid nitrogen (18.6 + 7.6pmol/mg protein). In the second series of experiments, three types of stress (limb restraint, non‐adaptation to the experimental situation, and moderate cutaneous electric shock) were induced separately in order to determine the influence of each on cortical levels of cyclic AMP. Control animals were highly adapted to the experimental situation, freely moving and not shocked. The samples from each of the stressed groups showed a statistically significant (P≤. 0.01) reduction in cyclic AMP in comparison with the level in the controls (control: 29.3 pmol/mg protein; restrained: 14.2pmol/mg protein; unadapted: 9.6pmol/mg protein; shocked: 7.1 pmol/mg protein). Thus, psychological and physical stress reduced cyclic AMP content in parietal cortex.Results from the second series of experiments suggest that the significantly higher mean and larger standard deviation of the cryoplate group in the first series are due to less psychological and physical stress being evoked by our method; different types of stress appear to account for the two different lower levels found in the immersion and decapitation groups. We believe that our method of cryogenic tissue fixation offers an improved approach to study of the neurochemical correlates of behavioral and neuroelectric events in the conscious animal.
EFFECT OF TRANSIENT ISCHEMIA ON MONOAMINE LEVELS IN THE CEREBRAL CORTEX OF GERBILS1,2
Authors: Gaudet Robert , Welch K. M. A. , Chabi Eva , Wang Tseng‐Pu 
Published: October 2006

Abstract— Cortical monoamine changes during ischemic episodes of varied duration and their sequence of changes following cerebral reperfusion were studied in the gerbil. Forty‐one percent of 280 animals exhibited signs of cerebral hemispheric ischemia (stroke) after unilateral common carotid artery occlusion. Norepinephrine (NE) levels decreased after 60 min in the occluded hemisphere of stroked animals but dopamine (DA) levels were unaltered. S‐Hydroxytryptamine (5‐HT) levels became bilaterally reduced in both stroked and non‐stroked animals as soon as S min after occlusion.Upon reperfusion after periods of 30 or 60 min of occlusion there was a bilateral rebound increase of cortical NE and DA levels to well above control values in stroked and non‐stroked animals. 5‐HT levels remained reduced in both groups.Results suggest disorder of monoamine metabolism in ischemic brain which persists during the early reperfusion period, perhaps contributing to deficits in neurological function.Monoamine changes in contralateral non‐ischemic hemispheres both during the occlusion and reperfusion periods are thought further evidence of diaschisis.
ENDOGENOUS LEVELS OF NEUROTRANSMITTER CANDIDATES IN PHOTORECEPTOR CELLS OF THE TURTLE RETINA
Authors: Sarthy P. Vijay , Lam Dominic M. K. 
Published: October 2006

Abstract—The neurotransmitter used by vertebrate photoreceptors has not been identified, although aspartic acid, glutamic acid and acetylcholine have all been suggested as possible candidates. In the present study, we have measured the endogenous levels of these substances in isolated photoreceptors of the turtle retina. Fractions containing over 80% of identified photoreceptors were obtained by enzymatic dissociation of the retina followed by velocity sedimentation at unit gravity. The endogenous levels of free amino acids in these fractions were measured by amino acid analysis and the ACh content was measured by a radiochemical assay. In addition, identified photoreceptors were drawn into a micropipet individually under visual observation and their ACh content was determined. Our results show that while the concentrations of free aspartic acid and glutamic acid in isolated photoreceptors are similar to those found in the retina, the concentration of ACh in cone photoreceptors (0.1–0.2 mM) is 2‐ to 3‐fold higher than that in the turtle retina. This result combined with the findings of others suggests that turtle cone photoreceptors may be cholinergic
METABOLISM OF ARACHIDONOYL PHOSPHOGLYCERIDES IN MOUSE BRAIN SUBCELLULAR FRACTIONS
Authors: Sun Grace Y. , Su Kwei L. 
Published: October 2006

Abstract— Mouse brain subcellular fractions were prepared at 1, 12, and 24 h and 3 and 8 days after intracerebral injections of [1‐14C]arachidonate. Initially, radioactivity was mainly distributed in the microsomal and synaptosomal fractions, but the proportion of radioactivity in the myelin increased from 5 to 16% within 8 days. Radioactivity of the microsomal lipids started to decline at 1 h after injection, and the decay was represented by two pools with half‐lives of 19 h and 10 days, respectively. Radioactivity in the synaptosomal and myelin fractions did not reach a maximum until 24 h after injections. The half‐life for turnover of synaptosomal lipids was 9 days.The decline of radioactivity measured in the microsomal fraction was due mainly to diacyl‐GPC and diacyl‐GPI, since radioactivity of other phosphoglycerides (diacyl‐GPS, diacyl‐GPE and alkenyl‐acyl‐GPE) continued to increase for 12‐24 h. In this fraction, half‐lives of 10‐14 h were obtained for the fast turnover pools of diacyl‐GPC and diacyl‐GPI, and slow turnover pools with half‐lives of 7 days for diacyl‐GPI and 10‐14 days for other phosphoglycerides were also present. Among the synaptosomal phosphoglycerides, radioactivity of diacyl‐GPI declined in a biphasic mode, thus exhibiting half‐lives of 5 h and 5 days. Incorporation of labelled arachidonate into diacyl‐GPE and diacyl‐GPS in the synaptosomal fractions was observed for a period of 24 h. The half‐lives for these phosphoglycerides ranged from 8 to 12 days. Results of the study have demonstrated the presence of small pools of arachidonoyl‐GPI in synaptosomal and microsomal fractions which were metabolically more active than other arachidonoyl containing phosphoglycerides.
TRANSPORT OF SUGARS INTO MICROVESSELS ISOLATED FROM RAT BRAIN: A MODEL FOR THE BLOOD‐BRAIN BARRIER1
Authors: Kolber Alan R. , Bagnell C. Robert , Krigman Martin R. , Hayward Jean , Morell Pierre 
Published: October 2006

Abstract— Microvessels (primarily capillaries) were isolated from the brains of rats 25‐35 days of age. This preparation was characterized by light, transmission, and scanning electron microscopy. Transmission electron microscopy revealed that the endothelial cell membranes were intact and were impermeable to horseradish peroxidase. However, scanning electron microscopy revealed that damage to the membrane occurred during isolation. The isolated microvessel preparations were metabolically competent as demonstrated by their ability to metabolize [14C]glucose.Aliquots of microvessel preparation were incubated with radioactive non‐metabolizable analogs of D‐glucose at various concentrations. The kinetics of accumulation of radioactivity in the capillaries were analyzed according to a model for carrier‐mediated diffusion and affinity constants for 3‐O‐methyl‐ D‐glucose and 2‐deoxyglucose were calculated (about 18 mM at 20°C in each case). These affinity constants are somewhat greater than that expected from whole animal experiments reported by other laboratories. This discrepancy is probably accounted for by the presence of a passive diffusion component. However, despite this complication, the primary mechanism for entry of D‐glucose analogues at physiological concentrations is compatible with carrier‐mediated transport since: the uptake of sugar analogs was shown to be saturable, to exhibit competition for uptake between structurally similar molecules, and to be non‐concentrative. In contrast, the uptake of glycerol, mannitol, and L‐glucose by isolated microvessels obeyed the kinetics of simple passive diffusion and was not saturable.Our results are compatible with the concept that the capillary is the anatomic locus of the blood‐brain barrier and that this structure contains the carrier‐mediated transport system for monosaccharide penetration into brain.
KINETICS OF BLOOD‐BRAIN BARRIER TRANSPORT OF PYRUVATE, LACTATE AND GLUCOSE IN SUCKLING, WEANLING AND ADULT RATS
Authors: Cremer Jill E. , Cunningham Vincent J. , Pardridge William M. , Braun Leon D. , Oldendorf William H. 
Published: October 2006

Abstract— The kinetics of the uptake from blood to brain of pyruvate, lactate and glucose have been determined in rats of different ages. The carotid artery single injection technique was used in animals anaesthetized with pentobarbital. The rates of influx for each substrate were determined over a range of concentrations for the different age‐groups. Data were analysed in terms of the Michaelis‐Menten equation with a component to allow for non‐saturable diffusion. Values are given for Km, Vmax and Kd. In suckling rats (15‐21 days) the Vmax values for both pyruvate and lactate were 2.0 μmol g−1 min−1. In 28‐day‐old rats the Vmax values had fallen to one‐half and in adults they were less than one‐tenth. Km, values were higher in the younger animals. The rate of glucose transport in suckling rats was half that of 28‐day‐old and adults although there was no difference with age in the Km values.The results are discussed in relation to the net flux of these substrates in and out of brain during different stages of post‐natal development.
EFFECTS OF GABA ANALOGUES OF RESTRICTED CONFORMATION ON GABA TRANSPORT IN ASTROCYTES AND BRAIN CORTEX SLICES AND ON GABA RECEPTOR BINDING
Authors: Schousboe A. , Thorbek P. , Hertz L. , Krogsgaard‐Larsen P. 
Published: October 2006

Abstract—The effects of a variety of acyclic or heterocyclic GABA analogues on GABA receptor binding and on high affinity transport of GABA in cultured astrocytes and mini‐slices of brain cortex were studied. The receptor and transport sites were found to be stereospecific and they exhibited opposite stereoselectivity for (R)‐ and (S)‐trans‐4‐amino‐4‐methylcrotonic acid and (R)‐ and (S)‐β‐proline. The most potent inhibitors of GABA binding were (RS)‐4, 5‐dihydromuscimol, muscimol, GABA, isoguvacine and isonipecotic acid with IC50values of, respectively, 0.009, 0.006, 0.033, 0.037 and 0.33 μM. Under the present experimental conditions the following compounds inhibited preferentially the glial transport system: (3RS, 4SR)‐4‐hydroxynipecotic acid, guvacine, (RS)‐N‐methylnipecotic acid, (RS)‐β‐proline and β‐alanine (IC50 values 10, 25, 70, 320 and 1000 μM, respectively vs. 200, 100, 300, 1200 and >5000 for neuronal transport). On the other hand, (R)‐trans‐4‐amino‐4‐methylcrotonic acid, (3RS, 4SR, 5SR)‐4‐hydroxy‐5‐methymipecotic acid and (RS)‐3‐hydroxy‐5‐aminovaleric acid preferentially inhibited neuronal transport as studied in mini‐slices of brain cortex (IC50 values 160, 300 and 430 μM, respectively vs. 500, > 5000 and 1400 μM for glial transport).
The Characterization of [3H] Adenosine Uptake into Rat Cerebral Cortical Synaptosomes
Authors: Bender A. S. , Wu P. H. , Phillis J. W. 
Published: October 2006

Abstract: Uptake of adenosine, a putative inhibitory transmitter or modulator, was investigated in rat cerebral cortical synaptosomes. The accumulation of [3H]adenosine into synaptosomes, using an adenosine concentration of 10 μ.m, was linear for 30 min at 37°C. The uptake appeared to be mediated by kinetically saturable processes with apparent Km's of 1 μam (“high‐affinity A”) and 5 μm (“high‐affinity B”), both of which were partially sensitive to the presence of external sodium and calcium ions. Both uptake processes were partially inhibited by 2,4‐dinitrophenol, implying the presence of active uptake and diffusional components. A study of the metabolites of adenosine taken up by the two uptake systems indicates that the major metabolites were adenosine and nucleotides. However, adenosine incorporated by the high‐affinity A uptake system is more likely to form deaminated metabolites, such as hypoxanthine and inosine, indicating a possible functional difference between the two uptake processes. A detailed comparison of the inhibitory properties of certain adenosine analogues and other pharmacological agents has revealed differences between the two adenosine uptake systems. Since the glial contamination in synaptosomal preparations is well established, one of the uptake systems we observed in the present study might be of glial origin. This notion is supported by the findings that the Km values and kinetic properties of papaverine action in the synaptosomal high‐affinity A uptake system are similar to those of astrocytes reported in the literature. In conclusion, the uptake processes of synaptosomal preparations show that accumulation of adenosine into neuronal (and possibly glial) elements may play a major role in regulating the extracellular adenosine concentration. Uptake inhibitors, such as diazepam, may exert, at least in part, their pharmacological actions by interfering with the regulation of extracellular adenosine concentrations.
Multiple α2‐Noradrenergic Receptor Sites in Rat Brain: Selective Regulation of High‐Affinity [3H] Clonidine Binding by Guanine Nucleotides and Divalent Cations
Authors: Rouot Bruno M. , U'Prichard David C. , Snyder Solomon H. 
Published: October 2006

Abstract:Both kinetic and equilibrium experiments indicate the presence of distinct high‐ and low‐affinity [3H]clonidine binding associated with α2‐ noradrenergic receptors in rat cerebral cortex membranes. Guanine nucleotides selectively decrease the numbers of high‐affinity [3H]clonidine binding sites, with no influence on the low‐affinity sites. The influence of nucleotides is exerted by GTP, its nonmetabolized analogue, guanyl‐5′‐yl imidodiphosphate, and GDP–but not by GMP, ADP, ATP, and AMP. In contrast, divalent cations increase high‐affinity [3H]clonidine binding‐an effect not evident at low‐affinity sites. Manganese is the most potent of the divalent cations, while magnesium and calcium are less active. Divalent cations and guanine nucleotides appear to elicit interactive rather than simply additive influences upon α2‐receptors. The inhibitory influence of sodium upon α2‐receptor binding of [3H]clonidine is exerted to the same extent upon both high‐ and low‐affinity [3H]clonidine binding.
Interactions of Divalent Cations and Guanine Nucleotides at α2‐Noradrenergic Receptor Binding Sites in Bovine Brain Mechanisms
Authors: U'Prichard David C. , Snyder Solomon H. 
Published: October 2006

Abstract:Guanine nucleotides selectively decrease binding of the agonist ligands [3H]clonidine and [3H]epinephrine to α2‐noradrenergic receptors in calf cortex membranes. In the presence of 1.0 mM‐calcium,‐magnesium, ormanganese, inhibition by GTP of [3H]clonidine binding is reversed, so that low concentrations of GTP increase [3H]clonidine binding, whereas high GTP concentrations cause a secondary decrease. In the presence of divalent cations, low concentrations of guanyl‐5′‐yl imidodiphosphate [Gpp(NH)p], unlike GTP, do not increase binding. Differences between effects of GTP and Gpp(NH)p in the presence of divalent cations are also observed with [3H]epinephrine binding to rat and calf cortex α2‐receptors. In reversing the inhibition of α2‐agonist binding by GTP, manganese, with an ED50 of 21 μM, is much more potent and effective than magnesium or calcium. Manganese by itself increases [3H]clonidine binding by 20% an effect which is irreversible, while the interactive effects of manganese and GTP are reversible. Divalent cations also antagonize the sodium‐induced inhibition of α2‐agonist binding in calf cortex membranes, and manganese has similar ED50 values in antagonizing both sodium and GTP.
The Lipid Composition of Rat CNS Axolemma‐enriched Fractions
Authors: DeVries George H. , Zmachinski Catherine J. 
Published: October 2006

Abstract:The lipid composition is reported for rat CNS axolemma‐enriched membrane fractions isolated from rat CNS white matter via a purified preparation of myelinated axons. The more dense axolemma‐enriched fraction is 51.5% lipid, comprised of 21.3% cholesterol, 11.3% galactolipid (cerebrosides and sulfatides in a molar ratio of 1.3:1.0), 24.2% ethanolamine glycerophospholipid (41.0% in the plasmalogen form), 27.8% choline glycerophospholipid (14.7% in the plasmalogen form), 5.3% serine glycerophospholipid, 2.8% inositol glycerophospholipid, and 2.0% sphingomyelin. The less dense axolemma‐enriched fraction has a lipid composition that is intermediate between that of the more dense axolemma‐enriched fraction and the concomitantly isolated myelin; this myelin has a lipid composition consistent with that previously reported for myelin isolated by an alternative procedure. A concomitantly isolated and operationally defined myelin‐free axon fraction has a lipid composition distinct from that which we have previously reported for a rat CNS myelin‐free axon preparation. The more dense axolemma‐enriched fraction contains 11.94 μg ganglioside NeuNAc per mg dry weight in contrast to the myelin fraction, which contains 0.88 μg ganglioside NeuNAc per mg dry weight, This axolemma‐enriched fraction contains all the major brain‐type gangliosides, while myelin contains mostly ganglioside GMI. The lipid composition of these fractions is compared with that of other neuronal and axolemmal preparations. The origin and function of the axolemmal glycolipid are discussed.
Multiple Molecular Forms of Acetylcholinesterase in Rat Vagus Nerve, Smooth Muscle, and Heart
Authors: Skau K. A. , Brimijoin S. 
Published: October 2006

Abstract:Extracts of rat tissues were subjected to ultracentrifugation on linear density gradients of sucrose (5–20%) and fractions of these gradients were analyzed for acetylcholinesterase (AChE) activity. Most of the AChE activity in extracts of vagus nerve was found to sediment at 10S. However, 16S AChE, previously thought to be confined to somatic motor nerves and skeletal muscle, was observed to accumulate rapidly at a nerve ligation. A search for this rapidly sedimenting form of AChE was carried out in tissues receiving vagal innervation. Significant amounts of 16S AChE were detected in the heart, especially in the right atrium, and in several regions of the gut. It was concluded that 16S AChE is distributed more widely than has previously been recognized.
Endogenous Substrates Utilized by Rat Brain in Severe Insulin‐Induced Hypoglycemia
Authors: Agardh Carl‐David , Chapman Astrid G. , Nilsson Bengt , Siesjö Bo K. 
Published: October 2006

Abstract: Several previous studies have demonstrated that severe hypoglycemia is accompanied by consumption of endogenous brain substrates (glycolytic and citric acid cycle metabolites and free amino acids) and some have shown a loss of structural components as well, notably phospholipids. In the present study, on paralysed and artificially ventilated rats, we measured cerebral oxygen and glucose consumption during 30 min of hypoglycemic coma (defined as hypoglycemia of sufficient severity to cause cessation of spontaneous EEG activity) and calculated the non‐glucose oxygen consumption. In an attempt to estimate the missing substrate we measured tissue concentrations of phospholipids and RNA.After 5 min of hypoglycemic coma, tissue phospholipid content decreased by about 8% with no further change during the subsequent 55 min. A similar reduction remained after 90 min of recovery, induced by glucose administration following 30 min of coma. Since no preferential loss of polyenoic fatty acids or of ethanolamine phosphoglycerides occurred, it is concluded that loss of phospholipids was due to phospholipase activity rather than to peroxidative degradation. The free fatty acid concentration increased sixfold after 5 min of coma and remained elevated during the course of hypoglycemia. A 9% reduction in tissue RNA content was observed after 30 min of hypoglycemia.Calculations indicated that available endogenous carbohydrate and amino acid substrates were essentially consumed after 5 min of coma, and that other non‐glucose substrates must have accounted for approximately 50μmol·g−1 of oxygen (8.3 μmol·g−1 in terms of glucose equivalents) within the 5–30 min period. The 10% reduction in phospholipid‐bound fatty acids was more than sufficient (in four‐ to fivefold excess) to account for this oxygen consumption. However, since no further degradation occurred in the 5–30 min period, there is no simple, direct, quantitative relationship between oxygen consumption and cortical fatty acid oxidation during this interval. The possibility thus remains that unmeasured exogenous or endogenous substrates were utilized.