scholarly journals The Deoxyglucose Method in the Ferret Brain. II. Glucose Utilization Images and Normal Values

1989 ◽  
Vol 9 (1) ◽  
pp. 43-52 ◽  
Author(s):  
C. Redies ◽  
M. Diksic ◽  
Y. L. Yamamoto
Keyword(s):  
Rate Constants ◽  
Glucose Utilization ◽  
Normal Values ◽  
Brain Size ◽  
Experimental Period ◽  
Brain Structures ◽  
Rate Limiting Step ◽  
Rate Limiting ◽  
The Brain ◽  
Deoxyglucose Method

To measure cerebral glucose utilization with the autoradiographic deoxyglucose method, the tracer transfer rate constants and lumped constants must be known. 2-Deoxyglucose (2-DG) and fluorodeoxyglucose (FDG) constants were determined in 18 gray and white matter brain structures of the anesthetized ferret. The ferret is a domestic carnivore particularly suitable for deoxyglucose studies because of its small brain size and low body weight. The average gray matter rate constants for tracer transfer across the blood-brain barrier are similar for 2-DG and FDG in the ferret brain ( K*1 = 0.21 ml/g/min and k*2 = 0.39 min−1). The rate constant for the rate-limiting step of tracer phosphorylation, k*3, is 1.6 times higher for FDG than for 2-DG (0.21 vs. 0.13 min−1). Loss of metabolized tracer is about 1–1.5%/min throughout the ferret brain for both tracers as estimated for a 180 min experimental period. Taking into account this loss, the lumped constant is 0.92 for FDG and 0.68 for 2-DG. Glucose utilization values in the brain of the anesthesized ferret range from 33 μmol/100 g/min in the corpus callosum to 104 μmol/100 g/min in the caudate nucleus. Representative glucose utilization images of coronal sections of the ferret brain are shown. Brain structures are identified on the same slices counterstained with thionin.

scholarly journals The Deoxyglucose Method in the Ferret Brain. I. Methodological Considerations

1989 ◽  
Vol 9 (1) ◽  
pp. 35-42 ◽  
Author(s):  
C. Redies ◽  
M. Diksic
Keyword(s):  
Glucose Utilization ◽  
Order Kinetic ◽  
Tracer Injection ◽  
Rate Limiting Step ◽  
Constant Determination ◽  
Lumped Constant ◽  
Methodological Considerations ◽  
Rate Limiting ◽  
The Brain ◽  
Deoxyglucose Method

In the brain of the anesthetized ferret, the 2-deoxyglucose (2-DG) transfer rate constants required to determine cerebral glucose utilization by the deoxyglucose method were calculated from regional gray matter time-radioactivity curves measured for 180 min after tracer injection. Results suggest that loss of metabolized tracer from brain occurs at a rate of about 1%/min for the first 180 min after injection if the rate constant of the rate-limiting step for loss of metabolized tracer ( k*4) represents a first-order kinetic process. A simulation experiment shows that, whether k*4 is assumed to be 0 or 0.01 min−1, has a negligible influence on glucose utilization rates obtained in conventional 45 min autoradiographic experiments provided that the entire analysis, including lumped constant determination, is carried out in a consistent way. The 2-DG lumped constant for k*4 = 0 is 0.54, and 0.68 for k*4 = 0.01 min−1.

scholarly journals Brain Glucose Levels in Portacaval-Shunted Rats with Chronic, Moderate Hyperammonemia: Implications for Determination of Local Cerebral Glucose Utilization

1994 ◽  
Vol 14 (1) ◽  
pp. 113-124 ◽  
Author(s):  
Nancy F. Cruz ◽  
Gerald A. Dienel
Keyword(s):  
Glucose Utilization ◽  
Normal Values ◽  
Brain Structures ◽  
Glucose Content ◽  
Brain Glucose ◽  
Glucose Levels ◽  
Lumped Constant ◽  
Dg Method ◽  
The Brain

Rates of glucose utilization (lCMRglc) in many structures of the brain of fed, portacaval-shunted rats, when assayed with the [14C]deoxyglucose (DG) method in our laboratory, were previously found to be unchanged (30 of 36 structures) or depressed (6 structures) during the first 4 weeks after shunting, but to rise progressively to higher than normal values in 25 of 36 structures from 4–12 weeks. In contrast, lCMRglc, when assayed with the [14C]glucose method in another laboratory, was depressed in most structures of brains of 4–8-week shunted rats that had relatively high brain ammonia levels. There was a possibility that the increases in lCMRglc obtained with the [14C]DG method may have been artifactual, due, in part, to a change in brain glucose content which could alter the value of the lumped constant of the DG method. Brain glucose levels of shunted rats were, therefore, assayed by both direct chemical measurement in freeze-blown samples and by determination of steady-state brain:plasma distribution ratios for [14C]methylglucose; the methylglucose distribution ratio varies as a function of plasma and tissue glucose contents. Within a week after shunting, ammonia levels in blood and brain rose to 0.25–0.30 m M and 0.35–0.70 μmol/g, respectively, and mean plasma glucose levels fell from 9–10 m M to 7.4–8.5 m M, and then remained nearly constant. Brains of fedshunted rats had normal glycogen levels and stable but moderately reduced glucose contents between 1 and 12 weeks (i.e., 1.9–2.2 μmol/g). [14C]Methylglucose distribution ratios were essentially the same as those in controls in 22 brain structures at 2 and 8 weeks after shunting. Because brain glucose levels remained stable from 1 to 12 weeks after shunting, there is no evidence to support the hypothesis that the value of the lumped constant would have changed and caused an artifactual rise in lCMRglc.

scholarly journals Effects of Insulin on Local Cerebral Glucose Utilization in the Rat

1987 ◽  
Vol 7 (3) ◽  
pp. 309-314 ◽  
Author(s):  
Giovanni Lucignani ◽  
Hiroki Namba ◽  
Astrid Nehlig ◽  
Linda J. Porrino ◽  
Charles Kennedy ◽  
...  
Keyword(s):  
Steady State ◽  
Glucose Utilization ◽  
Average Rate ◽  
Experimental Period ◽  
Ventromedial Nucleus ◽  
Local Cerebral Glucose Utilization ◽  
Cerebral Glucose Utilization ◽  
Hypothalamic Nuclei ◽  
The Brain ◽  
Deoxyglucose Method

The effects of hyperinsulinemia on local cerebral glucose utilization were studied by the quantitative autoradiographic 2-[14C]deoxyglucose method in normal conscious rats under steady-state normoglycemic conditions. Hyperinsulinemia and a steady state of normoglycemia were achieved and maintained during the experimental period by a continuous intravenous (i.v.) infusion of insulin given simultaneously with a programmed i.v. infusion of D-glucose. Hyperinsulinemia under normoglycemic conditions did not change the average rate of glucose utilization in the brain as a whole, but significant increases in local glucose utilization were found selectively in the ventromedial, dorsomedial, and anterior hypothalamic nuclei. The results suggest that a known anatomical pathway linking the dorsomedial and anterior nuclei with the ventromedial nucleus of the hypothalamus may be physiologically activated in response to hyperinsulinemia.

scholarly journals Effect of Nitrous Oxide on Local Cerebral Glucose Utilization in Rats

1982 ◽  
Vol 2 (4) ◽  
pp. 481-486 ◽  
Author(s):  
Martin Ingvar ◽  
B. K. Siesjö
Keyword(s):  
Nitrous Oxide ◽  
Glucose Utilization ◽  
Red Nucleus ◽  
Brain Structures ◽  
Subcortical Structures ◽  
Local Cerebral Glucose Utilization ◽  
Cerebral Glucose Utilization ◽  
Spontaneously Breathing ◽  
The Brain ◽  
Deoxyglucose Method

The influence of 70–80% N2O on local local cerebral glucose utilization (CMRg1) in the rat brain was studied with the [14C]deoxyglucose method in minimally restrained, spontaneously breathing animals 75 min following discontinuation of halothane anaesthesia. Nitrous oxide was found to have only small effects on local CMRg1 in the majority of the 25 structures analyzed. When corrections were made for a small difference in body temperature between nitrous oxide–breathing animals and those breathing air, nitrous oxide was found to significantly increase local CMRg1 in some subcortical structures by 15–25% (red nucleus, thalamus, geniculate bodies, and superior colliculus), and to decrease local CMRg1 in nucleus accumbens and sensorimotor cortex by comparable amounts. Thus, although nitrous oxide does not alter overall glucose utilization in the brain, it differentially affects CMRg1 in some brain structures.

scholarly journals Beyond the Active Site: Mechanistic Investigations of the Role of the Secondary Coordination Sphere and Beyond on Multi-Electron Electrocatalytic Reactions and Their Relations Between Kinetics and Thermodynamics

2020 ◽  
Author(s):  
Vincent Wang
Keyword(s):  
Thermodynamic Parameters ◽  
Coordination Sphere ◽  
Active Site ◽  
Rate Constants ◽  
Reduction Reaction ◽  
Rate Limiting Step ◽  
Limiting Step ◽  
Secondary Coordination Sphere ◽  
Catalytic Rate ◽  
Rate Limiting

<p>The development of an electrocatalyst with a rapid turnover frequency, low overpotential and long-term stability is highly desired for fuel-forming reactions, such as water splitting and CO<sub>2</sub> reduction. The findings of the scaling relationships between the catalytic rate and thermodynamic parameters over a wide range of electrocatalysts in homogeneous and heterogeneous systems provide useful guidelines and predictions for designing better catalysts for those redox reactions. However, such relationships also suggest that a catalyst with a high catalytic rate is typically associated with a high overpotential for a given reaction. Inspired by enzymes, the introduction of additional interactions through the secondary coordination sphere beyond the active site, such as hydrogen-bonding or electrostatic interactions, have been shown to offer a promising avenue to disrupt these unfavorable relationships. Herein, we further investigate the influence of these cooperative interactions on the faster chemical steps, in addition to the rate-limiting step widely examined before, for molecular electrocatalysts with the structural and electronic modifications designed to facilitate the dioxygen reduction reaction, CO<sub>2</sub> reduction reaction and hydrogen evolving reaction. Based on the electrocatalytic kinetic analysis, the rate constants for faster chemical steps and their correlation with the corresponding thermodynamic parameters are evaluated. The results suggest that the effects of the secondary coordination sphere and beyond on these fuel-forming reactions are not necessarily beneficial for promoting all chemical steps and no apparent relation between rate constants and thermodynamic parameters are found in some cases studied here, which may implicate the design of electrocatalysts in the future. Finally, these analyses demonstrate that the characteristic features for voltammograms and foot-of-the-wave-analysis plots are associated with the specific kinetic phenomenon among these multi-electron electrocatalytic reactions, which provides a useful framework to probe the insights of chemical and electronic modifications on the catalytic steps quantitatively (i.e. kinetic rate constants) and to optimize some of critical steps beyond the rate-limiting step.</p>

scholarly journals The evolution of complex brains and behaviors in African cichlid fishes

2010 ◽  
Vol 56 (1) ◽  
pp. 144-156 ◽  
Author(s):  
Caroly A. Shumway
Keyword(s):  
Visual Acuity ◽  
Social Organization ◽  
Habitat Complexity ◽  
Brain Size ◽  
Brain Structures ◽  
Cichlid Fishes ◽  
African Cichlid ◽  
Monogamous Species ◽  
And Behavior ◽  
The Brain

Abstract In this review, I explore the effects of both social organization and the physical environment, specifically habitat complexity, on the brains and behavior of highly visual African cichlid fishes, drawing on examples from primates and birds where appropriate. In closely related fishes from the monophyletic Ectodinii clade of Lake Tanganyika, both forces influence cichlid brains and behavior. Considering social influences first, visual acuity differs with respect to social organization (monogamy versus polygyny). Both the telencephalon and amygdalar homologue, area Dm, are larger in monogamous species. Monogamous species are found to have more vasotocin-immunoreactive cells in the preoptic area of the brain. Habitat complexity also influences brain and behavior in these fishes. Total brain size, telencephalic and cerebellar size are positively correlated with habitat complexity. Visual acuity and spatial memory are enhanced in cichlids living in more complex environments. However habitat complexity and social forces affect cichlid brains differently. Taken together, our field data and plasticity data suggest that some of the species-specific neural effects of habitat complexity could be the consequence of the corresponding social correlates. Environmental forces, however, exert a broader effect on brain structures than social ones do, suggesting allometric expansion of the brain structures in concert with brain size and/or co-evolution of these structures.

scholarly journals Control analysis applied to single enzymes: can an isolated enzyme have a unique rate-limiting step?

1993 ◽  
Vol 294 (1) ◽  
pp. 87-94 ◽  
Author(s):  
G C Brown ◽  
C E Cooper
Keyword(s):  
Rate Constants ◽  
General Assumption ◽  
Control Analysis ◽  
Rate Limiting Step ◽  
Limiting Step ◽  
Steady State Rate ◽  
Carbamate Kinase ◽  
State Rate ◽  
Rate Limiting ◽  
Control Coefficients

Control analysis is used to analyse and quantify the concept of a rate-limiting step within an enzyme. The extent to which each rate constant within the enzyme limits the steady-state rate of the enzyme and the levels of enzyme intermediate species are quantified as flux and concentration control coefficients. These coefficients are additive and obey summation theorems. The control coefficients of triose phosphate isomerase, carbamate kinase and lactate dehydrogenase are calculated from literature values of the rate constants. It is shown that, contrary to previous assumption, these enzymes do not have a unique rate-limiting step, but rather flux control is shared by several rate constants and varies with substrate, product and effector concentrations, and with the direction of the reaction. Thus the general assumption that an enzyme will have a unique rate-limiting step is unjustified.

Reactions of 1-substituted 2,4,6-trinitrobenzenes with nucleophiles

1979 ◽  
Vol 44 (5) ◽  
pp. 1453-1459 ◽  
Author(s):  
Jaromír Kaválek ◽  
Ahmad Ashfaq ◽  
Vojeslav Štěrba
Keyword(s):  
Methyl Ether ◽  
Rate Constants ◽  
Equilibrium Constants ◽  
Nucleophilic Aromatic Substitution ◽  
Aromatic Substitution ◽  
Phenyl Ester ◽  
Methyl Derivative ◽  
Rate Limiting Step ◽  
Limiting Step ◽  
Rate Limiting

Rate constants have been determined of nucleophilic aromatic substitution of 2,4,6-trinitrophenyl methyl ether (Ia), 2,4,6-trinitrophenyl ethanoate (Ic), 2,4,6-trinitrochlorobenzene (Ib), 2,4,6-trinitrodiphenyl ether (Id), 2,4,6-trinitro-4'-bromodiphenyl ether (Ie), 2,3',4,6-tetranitrodiphenyl ether (If) and 2,4,4',6-tetranitrodiphenyl ether (Ig) with methoxide, ethanoate and methyl cyanoethanoate (II) anions in methanol. For the compounds Ia,b rate and equilibrium constants of addition of the anion II(-) at positions 3 and 5 have been measured, too. In reactions of the compounds Ia to Ig with ethanoate anion the first (rate-limiting) step produces the phenyl ester Ic which reacts with a further ethanoate anion to give 2,4,6-trinitrophenol (Ih) and ethanoic anhydride. In reactions of the bromo derivative Ie and, to a still larger extent, compound Id the methyl derivative Ia is formed besides the compound Ih.

Local cerebral glucose utilization in fetal and neonatal sheep

1984 ◽  
Vol 246 (4) ◽  
pp. R608-R618 ◽  
Author(s):  
R. M. Abrams ◽  
M. Ito ◽  
J. E. Frisinger ◽  
C. S. Patlak ◽  
K. D. Pettigrew ◽  
...  
Keyword(s):  
Energy Metabolism ◽  
Glucose Utilization ◽  
Average Rate ◽  
Sensory Stimulation ◽  
Mammalian Brain ◽  
Local Cerebral Glucose Utilization ◽  
Cerebral Energy Metabolism ◽  
Cerebral Glucose Utilization ◽  
The Brain ◽  
Deoxyglucose Method

The newborn mammalian brain of several species has been shown to have a lower average rate of energy metabolism and a narrower range of rates in its various components than is found in maturity. In a further study of cerebral energy metabolism during development, we have employed the [14C]deoxyglucose method for measuring local cerebral glucose utilization in fetal and neonatal sheep. After establishing the lumped constant to be 0.40 and finding the rate constants for the kinetic behavior of deoxyglucose in plasma and brain to be close to those in other species, we measured the rates of glucose utilization in 44 regions of the brain. The rates were low and homogeneous in midgestation, except for those of brain stem nuclei of the auditory and vestibular systems and those of the hippocampus which were relatively high. In the last 7 wk, local rates rose approximately threefold. After birth there was a further average increase of 50% above full-term levels. The study shows that cerebral energy metabolism rises in most structures during prenatal maturation, a time when sensory stimulation is at a relatively low level and behavioral responses are minimal.

scholarly journals Erratum

1989 ◽  
Vol 9 (2) ◽  
pp. 247-248
Keyword(s):  
Blood Flow ◽  
Glucose Utilization ◽  
Normal Values ◽  
Montreal Neurological Institute ◽  
Cereb Blood Flow ◽  
Mcgill University ◽  
Deoxyglucose Method

The Deoxyglucose Method in the Ferret Brain. II. Glucose Utilization Images and Normal Values C. Redies, M. Diksic, and Y. L. Yamamoto Cone Laboratory, Montreal Neurological Institute, and Department of Neurology and Neurosurgery, McGill University, Montreal, Quebec, Canada (Article appeared in J Cereb Blood Flow 9:43–52 (1989)) The captions for Tables 1 and 2 that appeared on pages 44 and 45 were inadvertently switched. They appear correctly below. [Table: see text] [Table: see text]

Sign in / Sign up

Export Citation Format

Share Document