Local and global cerebral blood flow and glucose utilization in the alpha-galactosidase A knockout mouse model of Fabry disease

Fabry disease is an X-linked lysosomal disorder characterized by deficient alpha-galactosidase A activity and intracellular accumulations of glycosphingolipids, mainly globotriaosylceramide (Gb3). Clinically, patients occasionally present CNS dysfunction. To examine the pathophysiology underlying brain dysfunction, we examined glucose utilization (CMR(glc)) and cerebral blood flow (CBF) globally and locally in 18 brain structures in the alpha-galactosidase A gene knockout mouse. Global CMR(glc) was statistically significantly reduced by 22% in Fabry mice (p < 0.01). All 18 structures showed decreases in local CMR(glc) ranging from 14% to 33%. The decreases in all structures of the diencephalon, caudate-putamen, brain stem, and cerebellar cortex were statistically significant (p < 0.05). Global cerebral blood flow (CBF) and local CBF measured in the same 18 structures were lower in Fabry mice than in control mice, but none statistically significantly. Histological examination of brain revealed no cerebral infarcts but abundant Gb3 deposits in the walls of the cerebral vessels with neuronal deposits localized to the medulla oblongata. These results indicate an impairment in cerebral energy metabolism in the Fabry mice, but one not necessarily due to circulatory insufficiency.

Some highlights in the emergence of modern concepts of osteoarthritis

The present-day concept that osteoarthritis may be amenable to biological modification rather than a hopeless expression of old age or injury has historical roots in the period of 1935 through the early 1970s. One root was the structural and chemical delineation of the connective tissues: discovery of the proteoglycans and multiple molecular species of collagen. Another was the recognition of the ability of mature articular chondrocytes to replicate themselves rather than being terminally differentiated. A third was the elucidation of the engineering physiology of the joint: the role of matrix hydrophilia to the material properties of articular cartilage and biolubrication. Each root has direct relevance to ongoing therapeutic approaches to degenerative joint disease. The early epidemiological studies of Kellgren and Lawrence evolved into new techniques for testing their validity in clinical practice. Along the way there was a rich 2-way interaction between scientists and clinicians in arriving at these ideas.

Correlation between local glucose transporter densities and local 3-O-methylglucose transport in rat brain

The present study addresses the question whether local glucose transport kinetics are correlated with local glucose transporter densities in the brain. In 47 brain structures the local rate constants for 3-O-[(14)C]methylglucose (3-O-MG) transport, K(1) and k(2,) were quantified, and local glucose Glut1 and Glut3 transporter densities were determined by immuno-autoradiographic methods. Statistically significant correlations were found between the rate constants for glucose transport and the transporter densities. The correlations were tighter for Glut1 than for Glut3. Inasmuch as 3-O-MG is transported by the same transporter as glucose, these results indicate that the local densities of glucose transporters determine local glucose transport rates in the brain.

Brain glucose utilization in mice with a targeted mutation in the thyroid hormone alpha or beta receptor gene

Brain glucose utilization is markedly depressed in adult rats made cretinous after birth. To ascertain which subtype of thyroid hormone (TH) receptors, TRalpha1 or TRbeta, is involved in the regulation of glucose utilization during brain development, we used the 2-[(14)C]deoxyglucose method in mice with a mutation in either their TRalpha or TRbeta gene. A C insertion produced a frameshift mutation in their carboxyl terminus. These mutants lacked TH binding and transactivation activities and exhibited potent dominant negative activity. Glucose utilization in the homozygous TRbetaPV mutant mice and their wild-type siblings was almost identical in 19 brain regions, whereas it was markedly reduced in all brain regions of the heterozygous TRalpha1PV mice. These suggest that the alpha1 receptor mediates the TH effects in brain. Inasmuch as local cerebral glucose utilization is closely related to local synaptic activity, we also examined which thyroid hormone receptor is involved in the expression of synaptotagmin-related gene 1 (Srg1), a TH-positively regulated gene involved in the formation and function of synapses [Thompson, C. C. (1996) J. Neurosci. 16, 7832-7840]. Northern analysis showed that Srg1 expression was markedly reduced in the cerebellum of TRalpha(PV/+) mice but not TRbeta(PV/PV) mice. These results show that the same receptor, TRalpha1, is involved in the regulation by TH of both glucose utilization and Srg1 expression.

A computationally efficient algorithm for determining regional cerebral blood flow in heterogeneous tissues by positron emission tomography

Inclusion of brain tissues with different rates of blood flow and metabolism within a voxel or region of interest is an unavoidable problem with positron emission tomography due to its limited spatial resolution. Because regional cerebral blood flow (rCBF) is higher in gray matter than in white matter, the partial volume effect leads to underestimation of rCBF in gray matter when rCBF in the region as a whole is determined. Furthermore, weighted-average rCBF itself is underestimated if the kinetic model used in the analysis fails to account for the tissue heterogeneity. We have derived a computationally efficient method for estimating both gray matter and weighted-average rCBF in heterogeneous tissues and validated the method in simulation studies. The method is based on a model that represents a heterogeneous tissue as a weighted mixture of two homogeneous tissues. A linear least squares algorithm is used to estimate the model parameters.

Effects of anesthesia on functional activation of cerebral blood flow and metabolism

Functional brain mapping based on changes in local cerebral blood flow (lCBF) or glucose utilization (lCMR(glc)) induced by functional activation is generally carried out in animals under anesthesia, usually alpha-chloralose because of its lesser effects on cardiovascular, respiratory, and reflex functions. Results of studies on the role of nitric oxide (NO) in the mechanism of functional activation of lCBF have differed in unanesthetized and anesthetized animals. NO synthase inhibition markedly attenuates or eliminates the lCBF responses in anesthetized animals but not in unanesthetized animals. The present study examines in conscious rats and rats anesthetized with alpha-chloralose the effects of vibrissal stimulation on lCMR(glc) and lCBF in the whisker-to-barrel cortex pathway and on the effects of NO synthase inhibition with N(G)-nitro-L-arginine methyl ester (L-NAME) on the magnitude of the responses. Anesthesia markedly reduced the lCBF and lCMR(glc) responses in the ventral posteromedial thalamic nucleus and barrel cortex but not in the spinal and principal trigeminal nuclei. L-NAME did not alter the lCBF responses in any of the structures of the pathway in the unanesthetized rats and also not in the trigeminal nuclei of the anesthetized rats. In the thalamus and sensory cortex of the anesthetized rats, where the lCBF responses to stimulation had already been drastically diminished by the anesthesia, L-NAME treatment resulted in loss of statistically significant activation of lCBF by vibrissal stimulation. These results indicate that NO does not mediate functional activation of lCBF under physiological conditions.

Stimulation of matrix formation in rabbit chondrocyte cultures by ascorbate. 1. Effect of ascorbate analogs and beta-aminopropionitrile

The most consistent effects of 0.2 mM L-ascorbate on monolayer cultures of rabbit articular chondrocytes were a diversion of incorporated radiosulfate into a pericellular matrix and enhancement of cell proliferation. Only with certain batches of fetal bovine serum (FBS) was there a cell-for-cell increase of proteoglycan synthesis. These actions increased as the cell inoculum rose from 0.5 to 2 x 10(5) cells/T25 flask. Maximal effects of ascorbate and D-isoascorbate were found over a range of 0.05-0.2 mM. L-Dehydroascorbic acid was less effective than either, and no stimulatory action was exerted by L-cysteine, glutathione, dithiothreitol, methylene blue, or phenazine methosulfate. Ascorbate increased the hypro:pro ratio of newly synthesized proteins. beta-Aminopropionitrile (1 mM) reduced the proportion of [3H]hydroxyproline and [35S]O4-proteoglycans in the ascorbate-supplemented matrix 31 and 7%, respectively. In corresponding electronmicrographs, the number of pericellular filaments was reduced. We conclude: (a) Ascorbate has a general anabolic effect on chondrocytes in culture and enhances matrix assembly through mechanisms other than its redox function; (b) deposition of proteoglycans in the matrix is not simply the result of mechanical entrapment by allysine- or hydroxyallysine-derived cross-linking of collagen; and (c) contradictory reports on the subject result from variations in the serum employed, inoculum density, and concentration of ascorbate.

Regional differences in mechanisms of cerebral circulatory response to neuronal activation

Vibrissal stimulation raises cerebral blood flow (CBF) in the ipsilateral spinal and principal sensory trigeminal nuclei and contralateral ventroposteromedial (VPM) thalamic nucleus and barrel cortex. To investigate possible roles of adenosine and nitric oxide (NO) in these increases, local CBF was determined during unilateral vibrissal stimulation in unanesthetized rats after adenosine receptor blockade with caffeine or NO synthase inhibition with N(G)-nitro-L-arginine methyl ester (L-NAME) or 7-nitroindazole (7-NI). Caffeine lowered baseline CBF in all structures but reduced the percent increase during stimulation only in the two trigeminal nuclei. L-NAME and 7-NI lowered baseline CBF but reduced the percent increase during stimulation only in the higher stations of this sensory pathway, i.e., L-NAME in the VPM nucleus and 7-NI in both the VPM nucleus and barrel cortex. Combinations of caffeine with 7-NI or L-NAME did not have additive effects, and none alone or in combination completely eliminated functional activation of CBF. These results suggest that caffeine-sensitive and NO-dependent mechanisms are involved but with different regional distributions, and neither fully accounts for the functional activation of CBF.

Effects of the Na(+)/H(+) exchanger monensin on intracellular pH in astroglia

Stimulation of astroglial glucose utilization by the Na(+)/H(+) exchanger monensin is only partially blocked by ouabain. The present studies show that monensin also raises intracellular pH in astroglia. Because increased pH stimulates phosphofructokinase activity, the ouabain-insensitive portion of the stimulation of cerebral glucose utilization (CMR(glc)) appears to be due to stimulation of glycolysis by intracellular alkalinization.

Selection of an adaptive test statistic for use with multiple comparison analyses of neuroimaging data

Statistical analysis of neuroimages is commonly approached with intergroup comparisons made by repeated application of univariate or multivariate tests performed on the set of the regions of interest sampled in the acquired images. The use of such large numbers of tests requires application of techniques for correction for multiple comparisons. Standard multiple comparison adjustments (such as the Bonferroni) may be overly conservative when data are correlated and/or not normally distributed. Resampling-based step-down procedures that successfully account for unknown correlation structures in the data have recently been introduced. We combined resampling step-down procedures with the Minimum Variance Adaptive method, which allows selection of an optimal test statistic from a predefined class of statistics for the data under analysis. As shown in simulation studies and analysis of autoradiographic data, the combined technique exhibits a significant increase in statistical power, even for small sample sizes (n = 8, 9, 10).

Negligible glucose-6-phosphatase activity in cultured astroglia

2-Deoxy[14C]glucose-6-phosphate (2-[14C]DG-6-P) dephosphorylation and glucose-6-phosphatase (G-6-Pase) activity were examined in cultured rat astrocytes under conditions similar to those generally used in assays of glucose utilization. Astrocytes were loaded with 2-[14C]DG-6-P by preincubation for 15 min in medium containing 2 mM glucose and 50 microM 2-deoxy[14C]glucose (2-[14C]DG). The medium was then replaced with identical medium including 2 mM glucose but lacking 2-[14C]DG, and incubation was resumed for 5 min to diminish residual free 2-[14C]DG levels in the cells by either efflux or phosphorylation. The medium was again replaced with fresh 2-[14C]DG-free medium, and the incubation was continued for 5, 15, or 30 min. Intracellular and extracellular 14C contents were measured at each time point, and the distribution of 14C between 2-[14C]DG and 2-[14C]DG-6-P was characterized by paper chromatography. The results showed little if any hydrolysis of 2-[14C]DG-6-P or export of free 2-[14C]DG from cells to medium; there were slightly increasing losses of 2-[14C]DG and 2-[14C]DG-6-P into the medium with increasing incubation time, but they were in the same proportions found in the cells, suggesting they were derived from nonadherent or broken cells. Experiments carried out with medium lacking glucose during the assay for 2-deoxyglucose-6-phosphatase activity yielded similar results. Evidence for G-6-Pase activity was also sought by following the selective detritiation of glucose from the 2-C position when astrocytes were incubated with [2-3H]glucose and [U-14C]glucose in the medium. No change in the 3H/14C ratio was found in incubations for as long as 15 min. These results indicate negligible G-6-Pase activity in cultured astrocytes.

Cerebral blood flow responses to somatosensory stimulation are unaffected by scopolamine in unanesthetized rat

Studies with positron-emission tomography have indicated that muscarinic acetylcholine receptors may be involved in the mechanism of enhancement of cerebral blood flow (CBF) by neuronal functional activation. We examined the effects of muscarinic receptor blockade by scopolamine on the local CBF responses to vibrissal stimulation in the whisker-to-barrel cortex sensory pathway in unanesthetized rats. Local CBF was measured by the quantitative autoradiographic [(14)C]iodoantipyrine method. Scopolamine (0.4 or 0.8 mg/kg) was injected i.v. 30 min before measurement of local CBF; control rats received equivalent volumes of physiological saline. Vibrissae on the left side of the face were stroked continuously throughout the 1-min period of measurement of CBF. Local CBF was determined bilaterally in four structures of the pathway, i.e., spinal and principal sensory trigeminal nuclei, ventral posteromedial thalamic nucleus, and barrel field of the sensory cortex, as well as in four representative structures unrelated to the pathway. The higher dose of scopolamine raised baseline CBF in the two trigeminal nuclei, but neither dose diminished the percentage of increases in local CBF because of vibrissal stimulation in any of the stations of the pathway. These results do not support involvement of muscarinic receptors in the mechanism of enhancement of local CBF by functional neuronal activation, at least not in the whisker-barrel cortex sensory pathway in the unanesthetized rat.

Cerebral oxygen/glucose ratio is low during sensory stimulation and rises above normal during recovery: excess glucose consumption during stimulation is not accounted for by lactate efflux from or accumulation in brain tissue

Functional activation stimulates CMRglc more than CMRO2 and raises lactate levels in brain. This has been interpreted as evidence that brain work is supported mainly by energy derived from anaerobic glycolysis. To determine if lactate production accounts for the "excess" glucose consumption, cerebral arteriovenous differences were measured in conscious rats before, during, and 15 minutes after sensory stimulation; the brains were rapidly frozen in situ immediately after completion of blood sampling and assayed for metabolite levels. The molar O2/glucose uptake ratio fell from 6.1+/-1.1 (mean+/-SD) before stimulation to 5.0+/-1.1 during activation (P<0.01); lactate efflux from brain to blood was detectable at rest but not during stimulation. By 15 minutes after activation, O2 and lactate arteriovenous differences normalized, whereas that for glucose fell, causing the O2/glucose ratio to rise above preactivation levels to 7.7+/-2.6 (P<0.01). Brain glucose levels remained stable through all stages of activity. Brain lactate levels nearly doubled during stimulation but normalized within 15 minutes of recovery. Brain glycogen content fell during activation and declined further during recovery. These results indicate that brain glucose metabolism is not in a steady state during and shortly after activation. Furthermore, efflux from and increased content of lactate in the brain tissue accounted for less than 54% of the "excess" glucose used during stimulation, indicating that a shift to anaerobic glycolysis does not fully explain the disproportionately greater increases in CMRglc above that of CMRO2 in functionally activated brain. These results also suggest that the apparent dissociation between glucose utilization and O2 consumption during functional activation reflects only a temporal displacement; during activation, glycolysis increases more than oxidative metabolism, leading to accumulation of products in intermediary metabolic pools that are subsequently consumed and oxidized during recovery.

Effects of diazepam and ketamine administered individually or in combination on regional rates of glucose utilization in rat brain

The effects of diazepam, which acts at GABAA receptors to enhance the effects of GABA, and ketamine, a non-competitive N-methyl-D-aspartate receptor antagonist, on local rates of cerebral glucose utilization (ICMRglc) were examined in unrestrained rats. Four groups were studied: vehicle-injected controls; and ketamine-treated, diazepam-treated and combined ketamine- and diazepam-treated animals. Ketamine alone produced a heterogeneous pattern of changes in ICMRglc (e.g. significant increases in the corpus callosum, olfactory tubercle and the entire Papez circuit, in addition to other limbic areas, and significant decreases in lateral habenula and some components of the auditory system). Diazepam alone statistically significantly decreased ICMRglc in the brain as a whole and in most areas of the cerebral cortex, thalamus and limbic system. The most remarkable effects of the two drugs administered together on ICMRglc occurred in the limbic system where the dramatic increases observed with ketamine alone were prevented by treatment with diazepam.

Histomorphometry of the aging human patella: histologic criteria and controls

OBJECTIVE

A histomorphometric analysis of patellae from necropsies on persons between the third and tenth decades of life was carried out to trace the natural history of osteoarthritis.

DESIGN

Minutiae of the histological changes in the surface and basilar portions of the articular cartilage were developed as criteria for the quantitation. A total of 99 patellas were harvested in the stated age range. The present study reports the results of ten grossly and radiologically normal specimens from subjects 23-32 years old served as controls.

RESULTS

None of the control patellae were entirely histologically normal. Abnormality of the cartilage surface did not consistently proceed remodeling at the attachment to the subchondral plate.

CONCLUSIONS

This observation throws into question the concept that osteoarthritis has a single histogenesis or always arises in articular cartilage.

Energetics of functional activation in neural tissues

Glucose utilization (ICMRglc) increases linearly with spike frequency in neuropil but not perikarya of functionally activated neural tissues. Electrical stimulation, increased extracellular [K+] ([K+]o), or opening of Na+ channels with veratridine stimulates ICMRglc in neural tissues; these increases are blocked by ouabain, an inhibitor of Na+,K+-ATPase. Stimulating Na+,K+-ATPase activity to restore ionic gradients degraded by enhanced spike activity appears to trigger these increases in ICMRglc. Cultured neurons behave similarly. Astrocytic processes that envelop synapses in neuropil probably contribute to the increased ICMRglc. ICMRglc in cultured astroglia is unaffected by elevated [K+]o but is stimulated by increased intracellular [Na+] ([Na+]i), and this stimulation is blocked by ouabain or tetrodotoxin. L-Glutamate also stimulates ICMRglc in astroglia. This effect is unaffected by inhibitors of NMDA or non-NMDA receptors, blocked by ouabain, and absent in Na+-free medium; it appears to be mediated by increased [Na+]i due to combined uptake of Na+ with glutamate via Na+/glutamate co-transporters.

The effects of pharmacological doses of 2-deoxyglucose on cerebral blood flow in healthy volunteers

The effects of glucose deprivation on cerebral blood flow (CBF) have been extensively investigated during insulin-induced hypoglycemia in laboratory animals. Pharmacological doses of glucose analog, 2-deoxyglucose (2DG), is an alternative glucoprivic agent that in contrast to insulin, directly inhibits glycolysis and glucose utilization. Both glucoprivic conditions markedly increase CBF in laboratory animals. How 2DG affects CBF in humans is still undetermined. In the present study we have employed H215O positron emission tomography (PET) to examine the effects of pharmacological doses of 2DG (40 mg/kg) on regional and global cerebral blood flow in 10 brain areas in 13 healthy volunteers. 2DG administration significantly raised regional CBF (rCBF) in the cingulate gyrus, sensorimotor cortex, superior temporal cortex, occipital cortex, basal ganglia, limbic system and hypothalamus. 2DG produced a trend towards elevated CBF in whole brain and frontal cortex, while no changes were observed in the corpus callosum and thalamus. In addition, 2DG significantly decreased body temperature and mean arterial pressure (MAP). Maximal percent changes in hypothalamic rCBF were significantly correlated with maximal changes in body temperature but not with MAP. These results indicate that cerebral glucoprivation produced by pharmacological doses of 2DG is accompanied by widespread activation of cortical and subcortical blood flow and that the blood flow changes in the hypothalamus may be related to 2DG-induced hypothermia.

Estimation of component and parameter distributions in spectral analysis

A method is presented for estimating the distributions of the components and parameters determined with spectral analysis when it is applied to a single data set. The method uses bootstrap resampling to simulate the effect of noise on the computed spectrum and to correct for possible bias in the estimates. A number of bootstrap procedures are reviewed, and one is selected for application to the kinetic analysis of positron emission tomography dynamic studies. The technique is shown to require minimal assumptions about noise in the measurements, and its small sample properties are established through Monte-Carlo simulations. The advantages and limitations of spectral analysis with bootstrap resampling for deriving inferences for tracer kinetic modeling are illustrated through sample analyses of time-activity curves for [18F]fluorodeoxyglucose and [15O]-labeled water.

Blockade of cerebral blood flow response to insulin-induced hypoglycemia by caffeine and glibenclamide in conscious rats

The possibility that adenosine and ATP-sensitive potassium channels (KATP) might be involved in the mechanisms of the increases in cerebral blood flow (CBF) that occur in insulin-induced hypoglycemia was examined. Cerebral blood flow was measured by the [14C]iodoantipyrine method in conscious rats during insulin-induced, moderate hypoglycemia (2 to 3 mmol/L glucose in arterial plasma) after intravenous injections of 10 to 20 mg/kg of caffeine, an adenosine receptor antagonist, or intracisternal infusion of 1 to 2 mumol/L glibenclamide, a KATP channel inhibitor. Cerebral blood flow was also measured in corresponding normoglycemic and drug-free control groups. Cerebral blood flow was 51% higher in untreated hypoglycemic than in untreated normoglycemic rats (P < 0.01). Caffeine had a small, statistically insignificant effect on CBF in normoglycemic rats, but reduced the CBF response to hypoglycemia in a dose-dependent manner, i.e., 27% increase with 10 mg/kg and complete elimination with 20 mg/kg. Chemical determinations by HPLC in extracts of freeze-blown brains showed significant increases in the levels of adenosine and its degradation products, inosine and hypoxanthine, during hypoglycemia (P < 0.05). Intracisternal glibenclamide had little effect on CBF in normoglycemia, but, like caffeine, produced dose-dependent reductions in the magnitude of the increases in CBF during hypoglycemia, i.e., +66% with glibenclamide-free artificial CSF administration, +25% with 1 mumol/L glibenclamide, and almost complete blockade (+5%) with 2 mumol/L glibenclamide. These results suggest that adenosine and KATP channels may play a role in the increases in CBF during hypoglycemia.

Determination of local brain glucose level with [14C]methylglucose: effects of glucose supply and demand

Methylglucose can be used to assay brain glucose levels because the equilibrium brain-to-plasma distribution ratio for methylglucose (Ce*/Cp*) is quantitatively related to brain (Ce) and plasma (Cp) glucose contents. The relationship between Ce and Ce*/Cp* predicted by Michaelis-Menten kinetics has been experimentally confirmed when glucose utilization rate (CMRGlc) is maintained at normal, resting levels and Cp is varied in conscious rats. Theoretically, however, Ce and Ce*/Cp* should change when CMRGlc is altered and Cp is held constant; their relationship in such conditions was, therefore, examined experimentally. Drugs were applied topically to brains of conscious rats with fixed levels of Cp to produce focal alterations in CMRGlc, and Ce and Ce*/Cp* were measured. Plots of Ce as a function of Ce*/Cp* for each Cp produced straight lines; their slopes decreased as Cp increased. The results confirm that a single theoretical framework describes the relationship between Ce and Ce*/Cp* as either glucose supply or demand is altered over a wide range; they also validate the use of methylglucose to estimate local Ce under abnormal conditions.

Effects of elevated plasma epinephrine on glucose utilization and blood flow in conscious rat brain

Acute glucoprivation increases cerebral blood flow (CBF), which is often attributed to the associated rise in plasma epinephrine levels. This study examined directly the effects of comparable increases in plasma epinephrine levels achieved by continuous intravenous infusions of epinephrine in normoglycemic, unanesthetized rats on local and overall CBF and cerebral glucose utilization (1CMRglc). CBF was determined by the autoradiographic [14C]iodoantipyrine method in six unanesthetized rats in which epinephrine dissolved in 1% ascorbic acid-1 mM EDTA was infused at a rate of 1 microg/min and in five normal controls infused with the vehicle alone. 1CMRglc was determined by the autoradiographic [14C]deoxyglucose method in six conscious rats infused similarly with the epinephrine solution and in six normal controls treated with the vehicle alone. The epinephrine infusions raised arterial plasma epinephrine levels 10- to 20-fold and increased arterial blood pressure and plasma glucose levels. Local CBF, however, was significantly changed (P < 0.05, Student's t-test) in only 2 of 25 structures examined, and the changes were decreases not increases. 1CMRglc was not changed significantly in any of 42 brain structures examined, and average blood flow and glucose utilization in the brain as a whole were unaffected. These results show that high circulating levels of epinephrine similar to those accompanying glucoprivation alter neither local nor overall CBF and glucose utilization and cannot explain the increases in CBF associated with glucoprivation.

Positive correlations between cerebral protein synthesis rates and deep sleep in Macaca mulatta

Local rates of cerebral protein synthesis (ICPSleu) were determined with the autoradiographic L-[1-14C]leucine method in seven awake and seven asleep, adult rhesus monkeys conditioned to sleep in a restraining chair in a darkened, ventilated chamber while EEG, EOG, and EMG were monitored. Prior to the period of measurement all animals slept for 1-4 h. Controls were awakened after at least one period of rapid-eye-movement (REM) sleep. Experimental animals were allowed to remain asleep, and they exhibited non-REM sleep for 71-99% of the experimental period. Statistically significant differences in ICPSleu between control and experimental animals were found in four of the 57 regions of brain examined, but these effects may have occurred by chance. In the sleeping animals, however, correlations between ICPSleu and percent time in deep sleep were positive in all regions and were statistically significant (P < or = 0.05) in 35 of the regions. When time in deep sleep was weighted for the integrated specific activity of leucine in grey matter, positive correlations were statistically significant (P < or = 0.05) in 18 regions in the experimental animals. These results suggest that rates of protein synthesis are increased in many regions of the brain during deep sleep compared with light sleep.

Examination of potential mechanisms in the enhancement of cerebral blood flow by hypoglycemia and pharmacological doses of deoxyglucose

Cerebral blood flow (CBF) rises when the glucose supply to the brain is limited by hypoglycemia or glucose metabolism is inhibited by pharmacological doses of 2-deoxyglucose (DG). The present studies in unanesthetized rats with insulin-induced hypoglycemia show that the increases in CBF, measured with the [14C]iodoantipyrine method, are relatively small until arterial plasma glucose levels fall to 2.5 to 3.0 mM, at which point CBF rises sharply. A direct effect of insulin on CBF was excluded; insulin administered under euglycemic conditions maintained by glucose injections had no effects on CBF. Insulin administration raised plasma lactate levels and decreased plasma K+ and HCO3- concentrations and arterial pH. These could not, however, be related to the increased CBF because insulin under euglycemic conditions had similar effects without affecting CBF; furthermore, the inhibition of brain glucose metabolism with pharmacological doses (200 mg/kg intravenously) of DG increased CBF, just like insulin hypoglycemia, without altering plasma lactate and K+ levels and arterial blood gas tensions and pH. Nitric oxide also does not appear to mediate the increases in CBF. Chronic blockade of nitric oxide synthase activity by twice daily i.p. injections of NG-nitro-L-arginine methyl ester for 4 days or acutely by a single i.v. injection raised arterial blood pressure and lowered CBF in normoglycemic, hypoglycemic, and DG-treated rats but did not significantly reduce the increases in CBF due to insulin-induced hypoglycemia (arterial plasma glucose levels, 2.5-3 mM) or pharmacological doses of deoxyglucose.

Visually guided reaching with the forelimb contralateral to a "blind" hemisphere in the monkey: contribution of the cerebellum

Metabolic activity was mapped in the cerebellar cortex and its major inputs and projection targets in monkeys performing visually guided reaching with the left forelimb. Normal monkeys and monkeys deprived of visual input to the right cerebral hemisphere by right optic tract section, combined in some cases with forebrain commissurotomy, were studied. We reported previously that visually guided reaching with the left forelimb activated the motor cortex of the right hemisphere equally in all these monkeys, indicating that reaching was controlled by the right hemisphere whether it was visually intact or "blind" [Savaki H.E. et al. (1993) J. Neurosci. 13, 2772-2789]. In the present study, metabolic activations were observed in the left cerebellar hemispheric extensions of vermian lobules V, VI and VIII, again regardless of whether the right hemisphere was visually intact or "blind". In intact monkeys, however, the activations were significantly smaller in the lateral than in the paravermal zone of these hemispheric extensions, whereas in tractotomized/commissurotomized monkeys the activations were equal in the two zones. The greater activations in the left lateral zone in tractotomized/commissurotomized monkeys may represent compensation in part for the visual deafferentation of the right cerebral hemisphere. Also observed were metabolic activation in the left dorsolateral pontine nucleus in tractotomized/commissurotomized monkeys and metabolic depression in the left dentate nucleus in visually intact monkeys. This pattern of results suggests the following conclusions. The activated loci in the left cerebellar cortex combine (i) visual information about the target relayed by seeing cerebral hemispheres, and (ii) sensorimotor information concerning intended and actual movements of the left forelimb relayed by the right cerebral hemisphere and the limb, respectively, and then (iii) send this integrated information back to the motor cortex of the right cerebral hemisphere, thus enabling it to guide the left forelimb to the target whether the hemisphere is visually intact or "blind".

Influence of glucose supply and demand on determination of brain glucose content with labeled methylglucose

The equilibrium brain/plasma distribution ratio for 3-0-methyl-D-glucose (methylglucose) varies with plasma and tissue glucose contents and can be used to determine local glucose levels in brain. This ratio was previously found to rise as brain glucose concentration fell in response to lowered plasma glucose content. The ratios, however, differed with the same tissue glucose levels in conscious and pentobarbital-sedated rats, suggesting that changes in metabolic demand might alter the quantitative relationship between the methylglucose distribution ratio and brain glucose concentration. To examine this possibility, metabolic rate was varied by focal drug application, and hexose concentrations measured in treated and surrounding tissue. When tissue glucose levels were reduced by raised metabolic demand, methylglucose distribution ratios also fell. When brain glucose levels rose due to reduced consumption, the methylglucose distribution ratio also rose. Thus, in contrast to the inverse relationship between brain/plasma methylglucose ratio and brain glucose concentration when brain glucose content is altered secondarily to changes in plasma glucose level, changes in brain glucose content induced by altered glucose utilization cause the brain glucose level and methylglucose distribution ratio to rise and fall in a direct relationship. Determination of brain glucose content from methylglucose distribution ratios must take into account rates of glucose delivery and consumption.

Effects of aging on regional rates of cerebral protein synthesis in the Sprague-Dawley rat: examination of the influence of recycling of amino acids derived from protein degradation into the precursor pool

The quantitative autoradiographic L-[1-14C]leucine method for determination of regional rats of cerebral protein synthesis (1CPSleu) requires knowledge of the degree of recycling of leucine derived from protein degradation into the precursor pool of protein synthesis. The influence of recycling can be evaluated by measuring lambda, the steady state ratio of the leucine specific activity in the precursor amino acid pool (t-RNA-bound leucine) to that in the arterial plasma. To define the changes in 1CPS(leu) during the process of normal aging in the rat we have evaluated lambda in middle-aged (14 months) and aged (24 months) rats and compared its values with those obtained previously in young adult rats (two months of age). The results show that the value of lambda is the same in all three age groups, and that there is no change with aging in the fraction of leucine in the precursor pool derived from protein degradation. Our previously reported regional rates of protein synthesis in young adult and aged rats were based on the assumption that there was no recycling of leucine derived from protein degradation into the precursor pool of protein synthesis [Ingvar M.C., Maeder P., Sokoloff L. and Smith C.B. (1985) Brain 108, 155-170]. These values have been recalculated in the present study in order to take into account the appropriate correction for recycling. The recalculated rates are higher than those reported previously, but the effects of aging in the brain as a whole and in some specific brain regions are confirmed. Decreased 1CPS(leu) was observed by middle-age, and in this cross-sectional study did not appear to decrease further. Of the 39 brain regions examined decreases were found throughout the brain with some proclivity for the brain stem. In comparison with young adults the weighted average rate of protein synthesis in the brain as a whole was found to be decreased by 16 and 11% in the middle-aged and aged groups, respectively.

Determination of local rates of 45Ca influx into rat brain by quantitative autoradiography: studies of aging

Calcium homeostasis in brain is altered in many conditions, but there is no method to assay quantitatively local calcium flux into brain in vivo. 45Ca uptake into gross-dissected brain regions was measured and compared with results obtained with a quantitative autoradiographic procedure developed to assay influx of 45Ca into brain. Regional calcium contents, brain-to-plasma distribution ratios for calcium and 45Ca, apparent plasma-to-brain transfer coefficients, and net uptake of 45Ca into gross-dissected regions varied by as much as 80%. Local rates of net uptake of 45Ca into 34 structures determined by autoradiography varied by 12- to 14-fold, and rates of movement of 45Ca down concentrations gradients varied by a factor of 7. Previous studies with gross-dissected brain regions suggested changes in calcium uptake into brain during aging, but the values of all the variables assayed in the present study were similar in young adult, middle-aged, and old male rats. A quantitative autoradiographic procedure to assay levels of 45Ca in brain provides the anatomical resolution required to investigate local calcium flux in a variety of physiological and pathological conditions.

Lack of effects of inhibition of nitric oxide synthesis on local glucose utilization in the rat brain

The effects of chronic treatment with NG-nitro-L-arginine methyl ester, a potent inhibitor of nitric oxide synthase activity, on local cerebral glucose utilization were examined in conscious rats. Intraperitoneal injections of 50 mg/kg of the nitroarginine twice daily for 4 days have been found to result in almost complete inhibition of nitric oxide synthase activity in brain. Local cerebral glucose utilization was determined by means of the quantitative autoradiographic [14C]deoxyglucose method in an experimental group (n = 7) of rats that were treated with the nitroarginine according to this schedule and in a normal control group (n = 7) treated similarly with saline. The rats were conscious but partially restrained during the determinations of local cerebral glucose utilization. The nitroarginine treatment raised mean arterial blood pressure statistically significantly to 147 +/- 3 mm Hg (mean +/- SEM) from a level of 120 +/- 5 mm Hg in the saline controls (p < 0.001 by grouped t test), but there were no statistically significant effects on glucose utilization in any of 39 brain structures examined. It is concluded that nitric oxide normally exerts no significant influence on energy metabolism in the rat brain.

Selective metabolic activation by apomorphine in striosomes of denervated striatum in MPTP-induced hemiparkinsonian monkeys

Results of previous studies have suggested differences in the regulatory mechanisms in striatal striosomes and matrix following interruption of dopaminergic input to the striatum by MPTP in the monkey. In the present study we have investigated the possibility that stimulation of dopamine receptors by apomorphine modifies glucose metabolism differentially in the two striatal compartments of unilaterally MPTP-lesioned monkeys. Apomorphine treatment was found to result in higher rates of glucose utilization in the denervated striatum than in the intact hemisphere. Furthermore, the effect was more robust in the striosomes than in the matrix, thus providing evidence for differential functional and/or metabolic regulation in striatal striosomes and matrix in parkinsonian syndromes.

Role of sodium and potassium ions in regulation of glucose metabolism in cultured astroglia

Effects of increasing extracellular K+ or intracellular Na+ concentrations on glucose metabolism in cultures of rat astroglia and neurons were examined. Cells were incubated in bicarbonate buffer, pH 7.2, containing 2 mM glucose, tracer amounts of [14C]deoxyglucose ([14C]dGlc), and 5.4, 28, or 56 mM KCl for 10, 15, or 30 min, and then for 5 min in [14C]dGlc-free buffer to allow efflux of unmetabolized [14C]dGlc. Cells were then digested and assayed for labeled products, which were shown to consist of 96-98% [14C]deoxyglucose 6-phosphate. Increased K+ concentrations significantly raised [14C]deoxyglucose 6-phosphate accumulation in both neuronal and mixed neuronal-astroglial cultures at 15 and 30 min but did not raise it in astroglial cultures. Veratridine (75 microM), which opens voltage-dependent Na+ channels, significantly raised rates of [14C]dGlc phosphorylation in astroglial cultures (+20%), and these elevations were blocked by either 1 mM ouabain, a specific inhibitor of Na+,K(+)-ATPase (EC 3.6.1.37), or 10 microM tetrodotoxin, which blocks Na+ channels. The carboxylic sodium ionophore, monensin (10 microM), more than doubled [14C]dGlc phosphorylation; this effect was only partially blocked by ouabain and unaffected by tetrodotoxin. L-Glutamate (500 microM) also stimulated [14C]dGlc phosphorylation in astroglia--not through N-methyl-D-aspartate or non-N-methyl-D-aspartate receptor mechanisms but via a Na(+)-dependent glutamate-uptake system. These results indicate that increased uptake of Na+ can stimulate energy metabolism in astroglial cells.

Analysis of time courses of metabolic precursors and products in heterogeneous rat brain tissue: limitations of kinetic modeling for predictions of intracompartmental concentrations from total tissue activity

The efficacy of various kinetic models to predict time courses of total radioactivity and levels of precursor and metabolic products was evaluated in heterogeneous samples of freeze-blown brain of rats administered [14C]deoxyglucose ([14C]DG). Two kinetic models designed for homogeneous tissues, i.e., a no-product-loss, three-rate-constant (3K) model and a first-order-product-loss, four-rate-constant (4K) model, and a third kinetic model designed for heterogeneous tissues without product loss [Tissue Heterogeneity (TH) Model] were examined. In the 45-min interval following a pulse of [14C]DG, the fit of the TH Model to total tissue radioactivity was not statistically significantly better than that of the 3K Model, yet the TH Model described the time courses of [14C]DG and its metabolites more accurately. The TH- and 4K-Model-predicted time courses of [14C]DG and its metabolites were similar. Whole-brain glucose utilization (CMRglc) calculated with the TH or 3K Model, approximately 75 mumol 100 g-1 min-1, was similar to values previously determined by model-independent techniques, whereas CMRglc calculated with the 4K Model was 44% higher. In a separate group of rats administered a programmed infusion to attain a constant arterial concentration of [14C]DG that minimizes effects of tissue heterogeneity as well as any product loss, CMRglc calculated with all three models was 79 mumol 100 g-1 min-1 at 45 min after initiation of the infusion. Statistical comparisons of goodness of fit of total tissue radioactivity were, therefore, not indicative of which models best describe the tissue precursor and product pools or which models provide the most accurate rates of glucose utilization.

Preservation of autoregulatory cerebral vasodilator responses to hypotension after inhibition of nitric oxide synthesis

Effects of inhibition of nitric oxide (NO) synthesis on the cerebrovascular autoregulatory vasodilator response to hypotension were studied in conscious rats. Cerebral blood flow (CBF) was determined with [14C]iodoantipyrine in a saline-treated control group and in three groups following inhibition of NO synthase activity by twice daily intraperitoneal injections of 50 mg/kg of NG-nitro-L-arginine methyl ester (L-NAME) for four days. In the saline-control group (n = 8) and in the L-NAME-treated Group (a) (n = 8) CBF was determined while systemic mean arterial blood pressure (MABP) remained at its resting level (means +/- S.D., 128 +/- 6 and 151 +/- 11 mmHg, respectively). In the other groups CBF was determined after MABP was reduced by blood withdrawal to 118 +/- 9 and 88 +/- 8 mmHg in Groups (b) (n = 8) and (c) (n = 8), respectively. Despite the elevated MABP, global CBF was significantly lower in L-NAME-treated Group (a) than in the saline-controls (P < 0.005), indicating cerebral vasoconstriction resulting from inhibition of NO synthesis. Global CBF was not significantly reduced further in the two groups with hypotension. Local CBF in the hypotensive rats showed no significant reductions below values in L-NAME-treated control rats (Group (a)) in 31 of 32 brain structures; the only exception was in the auditory cortex of the severely hypotensive rats (Group (c)). The autoregulatory mechanism for cerebral vasodilatation to compensate for reduced arterial blood pressure is maintained following inhibition of NO synthesis.

Lipochondral degeneration of capsular tissue in osteoarthritic hips

Lipochondral degeneration (LCD) was found in the capsular tissue of 33 of 74 resected osteoarthritic hips studied retrospectively and in 14 of 35 studied prospectively, but never in a control group (n = 46). The process arose in the ligamentous structures that had undergone nodular chondroid metaplasia. The lesion was characterized by vacuolar distention of chondrocytes, eventual necrobiosis, and formation of acellular pools of lipid material. The latter was shown by oil red O staining and electron microscopy. Matrix alterations included glycosaminoglycan depletion, formation of elastin-related material, and degeneration of collagen fibers. There was no significant correlation (p = 0.05) between the occurrence of LCD and the severity of the osteoarthritis; neither was any association found with age, sex, calcium pyrophosphate dihydrate deposition, diabetes mellitus, or coronary artery disease.

Rates of glucose utilization in brain of active and hibernating ground squirrels

Rates of glucose utilization (CMRGlc) were determined in some cerebral structures of active warm- and cold-adapted ground squirrels and hibernating ground squirrels with [14C]deoxyglucose (DG) by direct chemical measurement of precursor and products in samples dissected from funnel-frozen brain. The rate of supply relative to demand of glucose and [14C]DG in brain of hibernating animals was similar to or greater than that of controls. [14C]DG cleared from the plasma in hibernators much more slowly than in active animals, and the level of unmetabolized [14C]DG in brain and the integrated specific activity of the precursor pool in plasma exceeded those of the active animals by 4- to 10-fold. At 45 min after an intravenous pulse of [14C]DG, the unmetabolized [14C]DG remaining in the brains of the hibernators accounted for approximately 96% of the total 14C compared with approximately 10-15% in the active animals. The value of lambda, a factor contained in the lumped constant of the operational equation of the [14C]DG method, was estimated for each animal and found to be relatively constant over the sixfold range of glucose levels in the brains of all animals. Calculated CMRGlc in squirrels in deep hibernation was only 1-2% of the values in active animals.

Effects of acute and delayed effects of prior chronic cocaine administration on regional rates of cerebral protein synthesis in rats

Single or repeated treatments with cocaine (15 mg/kg, i.p.) in rats modify rates of local cerebral protein synthesis (ICPSleu) measured with the [1-14C]leucine method. A single dose of cocaine to naive rats reduced ICPSleu by about 10% throughout the brain; the most statistically significant reduction was in the nucleus accumbens, shell portion (P = .0003). A comparable dose of cocaine administered acutely after 1 wk of daily cocaine injections had no effects on ICPSleu. Delayed effects of prior chronic cocaine treatment were studied in experiments in which one rat of each pair received injections with saline for 8 days and the other cocaine, and on the 15th day ICPSleu was measured. In these experiments delayed effects of the chronic cocaine treatment were observed; in the cocaine-treated rats ICPSleu was significantly increased in selective brain regions, i.e., prefrontal and primary olfactory cortex (P < .006). These results suggest that acute effects of a single dose of cocaine and residual effects of chronic cocaine treatment on ICPSleu are distinctly different and occur in different regions of the brain.

Labeling of metabolic pools by [6-14C]glucose during K(+)-induced stimulation of glucose utilization in rat brain

[6-14C]Glucose is the tracer sometimes recommended to assay cerebral glucose utilization (CMRglc) during transient or brief functional activations, but when used to study visual stimulation and seizures in other laboratories, it underestimated CMRglc. The metabolic fate of [6-14C]glucose during functional activation of cerebral metabolism is not known, and increased labeling of diffusible metabolites might explain underestimation of CMRglc and also reveal trafficking of metabolites. In the current studies cerebral cortex in conscious rats was unilaterally activated metabolically by KCl application, and CMRglc was determined in activated and contralateral control cortex with [6-14C]glucose or 2-[14C]deoxy-glucose ([14C]DG) over a 5- to 7-min interval. Local 14C concentrations were determined by quantitative autoradiography. Labeled precursor and products were measured bilaterally in paired cortical samples from funnel-frozen brains. Left-right differences in 14C contents were small with [6-14C]glucose but strikingly obvious in [14C]DG autoradiographs. CMRglc determined with [6-14C]glucose was slightly increased in activated cortex but 40-80% below values obtained with [14C]DG. [14C]Lactate was a major metabolite of [6-14C]glucose in activated but not control cortex and increased proportionately with unlabeled lactate. These results demonstrate significant loss of labeled products of [6-14C]glucose from metabolically activated brain tissue and indicate that [14C]DG is the preferred tracer even during brief functional activations of brain.

Role of the cerebellar fastigial nucleus in the physiological regulation of cerebral blood flow

Local cerebral blood flow (ICBF) was measured with [14C]iodoantipyrine in conscious, unrestrained rats during electrical stimulation of the fastigial nucleus (FN). Electrode position in the FN was determined by blood pressure (MABP) responses to stimulation under anesthesia. In nine rats in which MABP responses had been variable under anesthesia, bipolar stimulation (50 Hz, 0.5 ms, 1 s on/1 s off) with currents of 30-100 microA after recovery from anesthesia produced stereotypic behavior but little effect on MABP and ICBF. In seven other conscious rats currents could be raised to 75-200 microA without inducing seizures, resulting in sustained MABP elevations during the ICBF measurement and significantly increased ICBF in the sensory-motor (+45%), parietal (+31%), and frontal cortices (+56%) and the caudate-putamen (+27%) above control values (n = 9). Glucose utilization, measured with [14C]deoxyglucose, in rats similarly stimulated was significantly increased in six structures, including some of the above, indicating increases in ICBF due to metabolic activation. Unilateral or bilateral electrolytic lesions of the FN, placed 6-7 days before ICBF measurement, had negligible effects on resting ICBF and on autoregulation in conscious rats. These results fail to support a specific role for the FN in physiological regulation of cerebral blood flow in unanesthetized rats.

Increases in local cerebral blood flow associated with somatosensory activation are not mediated by NO

Effects of inhibition of nitric oxide (NO) synthase by NG-nitro-L-arginine methyl ester (L-NAME) on the increases in local cerebral blood flow (LCBF) produced in the whisker-to-barrel sensory pathway by vibrissal stimulation were studied in conscious rats with the autoradiographic iodo[14C]antipyrine method. Unilateral whisker stroking increased LCBF in the ipsilateral trigeminal spinal and principal sensory nuclei, contralateral ventral posteromedial thalamic nucleus, and contralateral somatosensory barrel cortex. Intravenous L-NAME (30 mg/kg) lowered baseline LCBF without altering the percent increases due to stimulation. Intracisternal infusions of L-NAME in doses about 10 times the molar content of free arginine in brain inhibited brain NO synthesis activity by 88%, but the percent augmentations of LCBF by stimulation remained unchanged. Chronic treatment with L-NAME (50 mg/kg ip twice daily for 4 days) inhibited NO synthase activity in brain by 84% but also failed to reduce the percent increases in LCBF due to stimulation. These results indicate that NO does not mediate the increases in LCBF associated with functional activation.