Regional cerebral glucose utilization measured with the 2--[ 14C] deoxyglucose technique: its use in mapping functional activity in the nervous system

The results of studies with the [ 14C] deoxyglucose technique unequivocally establish that functional activity in specific components of the central nervous system is, as in other tissues, closely coupled to the local rate of energy metabolism. Stimulation of functional activity increases the local rate of glucose utilization; reduced functional activity depresses it. These changes are so profound that they can be visualized directly in autoradiographic representations of local tissue concentrations of [ 14C] deoxyglucose-6-phosphate. Indeed, the existence of such evoked metabolic responses to experimentally induced alterations in local functional activity, together with the ability to visualize them by the [ 14C] deoxyglucose method, has become the basis of a potent technique for the mapping of functional pathways in the central nervous system (Kennedy et al., 1975, 1976; Plum et al., 1976).

Influence of dopaminergic systems on the lateral habenular nucleus of the rat

The alterations in glucose utilization in the lateral habenular nucleus following the systemic administration of a putative dopaminergic agonist and antagonist have been examined in 48 rats by means of the autoradiographic 2-deoxyglucose technique. The administration of apomorphine (0.15--5 mg/kg) resulted in significant dose-dependent reductions (by 25 +/- 5% following 0.5 mg/kg) in glucose utilization in the lateral habenula. Haloperidol administration (0.01--10 mg/kg) was associated with increased (by 46 +/- 17% with 0.1 mg/kg) glucose utilization in the lateral habenula. The effects of apomorphine upon metabolic activity in the lateral habenula can be prevented by the prior administration of haloperidol (0.1 mg/kg). These observations provide evidence that metabolic activity in the lateral habenula, a nucleus occupying a strategic position between the forebrain and the mesencephalon, may be regulated by the activity in dopaminergic systems.

A computer-assisted image-processing system for the analysis of autoradiographs of cerebral metabolic activity

A computerized image-processing system has been developed for quantitative analyses of the autoradiographs obtained with the [14C]deoxyglucose method. By means of this system, these cerebral metabolic images can be digitized and the resultant data can be manipulated for image construction, enhancement, enlargement, and microdensitometric analysis. It is also possible to generate quantitative color-coded metabolic maps that display the distribution of the actual rates of local glucose utilization throughout the entire central nervous system with a resolution conservatively estimated to be equivalent to that of a full-width-half-maximum of approximately 100 micron.

Effects of ageing on local rates of cerebral glucose utilization in the rat

The effects of ageing on local rates of glucose utilization in 47 brain structures in resting conscious rats have been examined. Three age groups have been studied: young adult (4 to 6 months), middle-aged (14 to 16 months), and aged (26 to 36 months). The results show that ageing per se is associated with decreases in rates of glucose utilization in specific brain regions. The decreases were not progressive with age, probably because of the influence of a survival effect. Age-related pathological changes are known to occur in some of the brain structures in which decreases in rates of glucose utilization were found. Selective decreases were also found in the caudate-putamen, the parietal cortex and in structures associated with vision and audition. In these latter structures the changes may reflect reductions in local functional activity, perhaps due to decreased sensory input from the primary sensory organs.

Computerized densitometry and color coding of [14C] deoxyglucose autoradiographs

A computerized image processing system has been developed for quantitative analyses of autoradiographs obtained with the [14C]deoxyglucose method. The system is composed of standard, commercially available components and includes a scanning microdensitometer, computer, image memory and display system, and monochrome and color monitors. The associated computer programs are written in PASCAL. Autoradiographs are automatically scanned, and the optical density of each spot is digitized at a maximum resolution of 65,536 readings per 6.4 x 6.4 mm area and stored in memory. Images can be reconstructed from the data in memory, displayed on the monitors, and utilized for microdensitometric analyses or manipulated for image enhancement, enlargement, or weighted averaging of selected regions. The digitized data can also be utilized to solve the operational equation of the [14C]deoxyglucose method, and color-coded images of autoradiographs can be reconstructed so that each color represents a narrow range of the rate of glucose utilization. By means of this system, it is possible to generate quantitative metabolic maps that display the distribution of actual rates of local glucose utilization throughout the entire central nervous system in regions as small as 100 micrometers or less.

Local cerebral energy metabolism: its relationship to local functional activity and blood flow

The results of studies with the (14C)deoxyglucose technique unequivocally establish that local energy metabolism in cerebral tissues is, as in other tissues, closely coupled to local functional activity. Stimulation of local functional activity increases the local rate of glucose utilization; reduced functional activity depresses it. Local cerebral blood flow is normally distributed among the cerebral structures in almost exact proportion to their rates of glucose utilization and changes together with local glucose consumption in response to altered local functional activity. These results demonstrate that the level of functional activity in the structural and functional components of the central nervous syetem regulates the local rate of energy metabolism, and local blood flow is adjusted to the local metabolic demand.

Effect of platelet lysate on growth and sulfated glycosaminoglycan synthesis in articular chondrocyte cultures

Human platelet lysate (PL) has a strong growth promoting action on rabbit articular chondrocytes in monolayer culture. The responsible factor is heat stable (56 degrees C, 30 minutes) and above 10,000 MW. PL (80 microgram protein/ml) reduces cell protein content and sulfated glycosaminoglycan synthesis. Synthesis of DNA is stimulated within the first 12 hours of culture but the decline in radiosulfate incorporation lags. PL acts to a slight extent on chondrocytes in serum-free media, but its effect is potentiated by "platelet-poor human serum" or fetal bovine serum. PL is one of several agents having such effects on chondrocytes cultured in serum-containing media. Stimulation of growth in this cell type thus reduces nonreplicative biosynthetic activity nonspecifically. In the epiphyseal growth plate and in pathologic alterations of permeability of the matrix of articular cartilage, platelet-derived factors, together with somatomedin or other cofactors in serum, may be the principal mediator of growth of chondrocytes in vivo.

Retina-dependent activation by apomorphine of metabolic activity in the superficial layer of the superior colliculus

Studies of the effect of the dopamine agonist apomorphine on local cerebral glucose utilization by means of the carbon-14-labeled deoxyglucose method demonstrate a dose-dependent metabolic activation in the superficial layer of the superior colliculus in the rat. Apomorphine stimulated glucose utilization in a number of other cerebral structures, but only the effect in the superficial layer of the superior colliculus depended on an intact retinal input. This effect was present with the animal in the light or in the dark, but was abolished by enucleation, which left the effects in other cerebral structures unimpaired. Activation of the superificial layer of the superior colliculus appears, therefore, to be secondary to an action of apomorphine on dopaminergic systems within the retina.

Metabolic mapping of neural pathways involved in gastrosecretory response to insulin hypoglycaemia in the rat

1. The central nervous structures involved in the gastrosecretory effect of insulin hypoglycaemia were investigated in twenty urethane-anaesthetized rats, previously provided with a chronic gastric fistula, by means of the 2-deoxy-D-[(14)C]glucose autoradiographic technique.2. Gastric secretion increased in animals in which plasma glucose concentration was reduced to a range of 84-133 mg/100 ml. (mean +/- S.E. of mean, 94 +/- 3) as compared to a range of 125-215 mg/100 ml. (mean +/- S.E. of mean, 162 +/- 8) in animals with normal gastric secretion.3. In fourteen of nineteen structures examined the rate of glucose utilization remained constant over the range of plasma glucose concentrations of 84-215 mg/100 ml. These structures included the ventromedial nucleus of the hypothalamus, the mamillary nuclei, the medial geniculate nuclei, globus pallidus, zona incerta, nucleus ambiguus, supraoptic nucleus, paraventricular nucleus, medial nucleus of the solitary tract, dorsal tegmental nucleus, red nucleus, inferior olivary nucleus, hippocampus and amygdaloid complex.4. A significant inverse correlation between plasma glucose concentration and the rate of glucose consumption was found in the lateral nucleus of the solitary tract, dorsal nucleus of the vagus, perifornical area where fibres of the medial forebrain bundle course, the superior olivary nucleus and the interstitial nucleus of the stria terminalis.5. Except for the superior olivary nucleus and the interstitial nucleus of the stria terminalis, all the structures affected by low plasma glucose concentration have previously been shown to participate in the gastrosecretory response to blockade of glucose utilization by pharmacological doses of 2-deoxy-D-glucose, indicating that these same nuclei are also activated by hypoglycaemia.

The effect of serum on monolayer cell culture of mammalian articular chondrocytes

Large variations were found in the ability of six species of sera to support growth of rabbit, human and dog articular chondrocytes in monolayer culture. In most instances the DNA content of the cell pellets increased directly as the serum concentration rose from 10 to 30%. Indications of inhibitory as well as growth-promoting actions were found in some sera. Stimulation of rabbit chondrocyte proliferation by increasing concentrations of serum was accompanied by a reduction of radiosulfate incorporation and cell protein content. There was no consistent relation between the response of chondrocytes from a given species and its homologous serum. However, the growth of human chondrocytes was greatly potentiated by human serum provided that interference with initial attachment of the cells to the culture flask by homologous serum was overcome by priming with fetal calf serum.

Mapping of local cerebral functional activity by measurement of local cerebral glucose utilization with [14C]deoxyglucose

A method has been developed to measure the rates of glucose utilization in the individual structural and functional components of the central nervous system. It can be applied to conscious as well as anaesthetized animals. The method is based on the use of [14C]deoxyglucose as a tracer for glucose consumption. [14C]Deoxyglucose-6-phosphate accumulates in the tissue in a mathematically definable relationship to the rate of the tissue's glucose utilization. The [14C]deoxyglucose-6-phosphate concentrations in the various tissues of the nervous system are measured by a quantitative autoradiographic technique. The autoradiographs themselves are pictorial representations of the relative rates of glucose consumption in these tissues. Application of this method to rats and monkeys in various states of altered function demonstrates a clear and close relationship between the local levels of functional activity and energy metabolism. The method appears to be useful for mapping functional neural pathways on the basis of evoked metabolic responses (Plum, Gjedde and Samson, 1976).

Specific distribution of metabolic alterations in cerebral cortex following apomorphine administration

The topographic distribution of dopaminergic receptors in the cerebral cortex closely parallels that of the dopaminergic innervation. In the rat, dopaminergic axons which originate in the mesencephalon are confined to a few discrete regions of the neocortex--anterior cingulate cortex, entorhinal cortex, frontal cortex (particularly anteromedial and supragenual areas) and the transitional zone between the neocortex and the pyriform cortex. Moreover, biochemical examinations of processes generally considered to be indicative of dopaminergic neuro-transmission--neuronal uptake of labelled dopamine or dopamine-activation of adenylate cyclase activity--have confirmed a highly restricted locus of action of dopaminergic systems in the cerebral cortex. We describe here data obtained using the 2-deoxyglucose technique in conjunction with conventional neuropharmacological techniques, suggesting that the influence of dopaminergic systems on cortical function extends beyond the known confines of the mesocortical dopaminergic system.

Tomographic measurement of local cerebral glucose metabolic rate in humans with (F-18)2-fluoro-2-deoxy-D-glucose: validation of method

Tracer techniques and quantitative autoradiographic and tissue counting models for measurement of metabolic rates were combined with positron computed tomography (PCT) and (F-18)2-fluoro-2-deoxy-D-glucose (FDG) for the measurement of local cerebral metabolic rate for glucose (LCMRGlc) in humans. A three-compartment model, which incorporates hydrolysis of FDG-6-PO4 to FDG, was developed for the measure of kinetic constants and calculation of LCMRGlc. Our model is an extension of that developed by Sokoloff et al. Although small, hydrolysis of FDG-6-PO4 was found to be significant. A PCT system, the ECAT, was used to determine the rate constants, lumped constant, and stability of the model in human beings. The data indicate that cerebral FDG-6-PO4 in humans increases for about 90 minutes, plateaus, and then slowly decreases. After 10 minutes, cerebral blood FDG activity levels were found to be a minor fraction of tissue activity. Precursor pool turnover rate, distribution volumes, and red blood cell-plasma concentration ratios were determined. Reproducibility (precision) of LCMRGlc measurements (approximate 2 cm2 regions) was +/- 5.5% over a 5-hour period. The replacement of arterial blood sampling with venous sampling was validated.

Metabolic mapping of functional activity in the hypothalamo-neurohypophysial system of the rat

Physiological stimulation of the hypothalamo-neurohypophysial system by salt loading of rats resulted in a dramatically increased glucose utilization in the posterior pituitary but not in the paraventricular or supraoptic nuclei. The good correlation between glucose utilization and neural activity in the posterior pituitary (that is, nerve terminals) contrasted with the lack of correlation in the paraventricular and supraoptic nuclei (that is, the sites of the cell bodies of the same neurons). This difference in the metabolic response to functional activity between the two regions of these neurons can be explained by the differences in surface-to-volume ratios of these regions.

A Proposed Model of Boundary Lubrication by Synovial Fluid: Structuring of Boundary Water

On the basis of data obtained from in-vitro friction tests using both cartilage and widely differing artificial surfaces, a general model for boundary lubrication of joint cartilage by synovial fluid is presented. It postulates that one portion of the synovial lubricating glycoprotein (LGP) is adsorbed to the surface. Reduction in surface shear is accomplished by formation of hydration shells about the polar portions of the adsorbed LGP creating a thin layer of viscous structured water at the surface. Mutual electrostatic repulsion between charged polysaccharide moieties aids in separation of the adsorbed surface layers. The hydration shell also serves as a check valve to control the movement of water out of and into the cartilage matrix during motion.

Osmotic opening of the blood-brain barrier and local cerebral glucose utilization

The effects of osmotic opening of the blood-brain barrier (BBB) on local cerebral glucose utilization (LCGU) were studied in rats with the carbon 14-deoxyglucose method. The BBB was opened to Evans blue dye by unilateral carotid artery perfusion with hypertonic mannitol solution. (14C)-Deoxyglucose was injected 15 minutes or two to three hours later. Osmotic opening of the BBB resulted in focal areas of intense LCGU in affected areas of the perfused hemisphere. In the contralateral hemisphere, glucose utilization was diminished, especially in cerebral cortical areas. The effects were reversible. LCGU was normal in both hemispheres when permeability to Evans blue returned to normal two to three hours after carotid artery perfusion. In 3 of 5 experiments the administration of high doses of intravenous diazepam immediately following carotid artery perfusion with mannitol prevented an increase in LCGU in the perfused hemisphere but did not prevent lowering of LCGU in the contralateral hemisphere. Increased LCGU following osmotic opening of the BBB was not accompanied by a rise in local cerebral blood flow as measured by the iodoantipyrine method. Blood flow was, in fact, significantly decreased.

Cerebral glucose utilization: local changes during and after recovery from spreading cortical depression

Cerebral glucose utilization is markedly increased in most areas of the cerebral cortex and reduced in many subcortical structures during spreading cortical depression. During recovery, cortical glucose utilization is still elevated, but the increased metabolic activity is distributed in columns running perpendicularly through the cortex.

The [18F]fluorodeoxyglucose method for the measurement of local cerebral glucose utilization in man

A method has been developed to measure local glucose consumption in the various structures of the brain in man with three-dimensional resolution. [18F]-2-deoxy-2-fluoro-D-glucose is used as a tracer for the exchange of glucose between plasma and brain and its phosphorylation by hexokinase in the tissue. A mathematical model and derived operational equation are used which enable local cerebral glucose consumption to be calculated in terms of the following measurable variables. An intravenous bolus of [18F]-2-deoxy-2-fluoro-D-glucose is given and the arterial specific activity monitored for a predetermined period of from 30 to 120 minutes. Starting at 30 minutes, the activity in a series of sections through the brain is determined with three-dimensional resolution by an emission tomographic scanner. The method was used to measure local cerebral glucose consumption in two normal volunteers. The values in gray matter structures range from 5.79 mg/100 g per minute in the cerebellar cortex to 10.27 in the visual cortex, whereas, in white matter structures, the values range from 3.64 mg/100 g per minute in the corpus callosum to 4.22 in the occipital lobe. Average values for gray matter, white matter, and whole brain metabolic rates, calculated as a weighted average based on the approximate volume of each structure, are 8.05, 3.80, and 5.90 mg/100 g per minute, respectively. The value of 5.9 mg/100 g per minute compares favorably with values previously reported.

Local cerebral glucose utilization in the normal conscious macaque monkey

The [14C]deoxyglucose method for quantitative determination of local cerebral glucose utilization was extended to the macaque monkey. The necessary constants required by its operational equation were evaluated. The lumped constant, measured in 7 normal conscious monkeys, was found to equal 0.344 (SEM, +/- 0.036). The rate constants were also estimated and found to be very similar to those obtained previously in the rat. With these essential constants evaluated, the method was applied to normal conscious monkeys. Local cerebral glucose utilization was found to vary marked throughout the brain but to fall within two distributions, a higher one in gray matter and lower one in white matter. In general, the values fell in a range to be expected from previous measurements of average energy metabolism in the brain as a whole. The values were considerably lower than those observed previously in the conscious rat. Marked heterogeneity of rates of glucose utilization were observed in a number of anatomical structures. In some cases the patterns of heterogeneity were consistent with known histological cytoarchitecture; in others the heterogeneity did not conform with known cytoarchitectural features but corresponded to patterns previously demonstrated by electrophysiological techniques. Many of the regions of the cerebral cortex showed columnar patterns of distribution of higher and lower rates of glucose utilization. These may be a metabolic reflection of the columnar organization of function within the cerebral cortex.