Local cerebral glucose consumption in the artificially ventilated rat: influence of nitrous oxide analgesia and of phenobarbital anesthesia

Differential effects of gaseous versus injectable anesthetics on changes in regional cerebral blood flow and metabolism induced by l-DOPA in a rat model of Parkinson's disease

Preclinical imaging of brain activity requires the use of anesthesia. In this study, we have compared the effects of two widely used anesthetics, inhaled isoflurane and ketamine/xylazine cocktail, on cerebral blood flow and metabolism in a rat model of Parkinson's disease and l-DOPA-induced dyskinesia. Specific tracers were used to estimate regional cerebral blood flow (rCBF - [¹⁴C]-iodoantipyrine) and regional cerebral metabolic rate (rCMR - [¹⁴C]-2-deoxyglucose) with a highly sensitive autoradiographic method. The two types of anesthetics had quite distinct effects on l-DOPA-induced changes in rCBF and rCMR. Isoflurane did not affect either the absolute rCBF values or the increases in rCBF in the basal ganglia after l-DOPA administration. On the contrary, rats anesthetized with ketamine/xylazine showed lower absolute rCBF values, and the rCBF increases induced by l-DOPA were masked. We developed a novel improved model to calculate rCMR, and found lower metabolic activities in rats anesthetized with isoflurane compared to animals anesthetized with ketamine/xylazine. Both anesthetics prevented changes in rCMR upon l-DOPA administration. Pharmacological challenges in isoflurane-anesthetized rats indicated that drugs mimicking the actions of ketamine/xylazine on adrenergic or glutamate receptors reproduced distinct effects of the injectable anesthetics on rCBF and rCMR. Our results highlight the importance of anesthesia in studies of cerebral flow and metabolism, and provide novel insights into mechanisms mediating abnormal neurovascular responses to l-DOPA in Parkinson's disease.

Asymmetric regional cerebral blood flow in sedated baboons measured by positron emission tomography (PET)

The analysis of structural brain asymmetry has been a focal point in anthropological theories of human brain evolution and the development of lateralized behaviors. While physiological brain asymmetries have been documented for humans and animals presenting with pathological conditions or under certain activation tasks, published studies on baseline asymmetries in healthy individuals have produced conflicting results. We tested for the presence of cerebral blood flow asymmetries in 7 healthy, sedated baboons using positron emission tomography, a method of in vivo autoradiography. Five of the 7 baboons exhibited hemispheric asymmetries in which left-sided flow was significantly greater than right-sided flow. Furthermore, the degree of asymmetry in 8 of 24 brain regions was found to be significantly correlated with age; older individuals exhibited a higher degree of asymmetry than younger individuals. Cerebral blood flow itself was uncorrelated with age, and differences between males and females were not significant.

GLUT1-deficiency: barbiturates potentiate haploinsufficiency in vitro

Barbiturates are known to inhibit glucose transport mediated by the facilitative sugar transporter GLUTI. We have studied such inhibition in children with GLUT1-deficiency. Zero-trans influx of 14C-labeled 3-O-methyl glucose (3OMG) into erythrocytes of patients (n = 3) was 35% of controls (n = 6). Preincubation with 10 mM phenobarbital or pentobarbital reduced patients' 30MG influx to 17%. In patients and controls, preincubation with barbiturates significantly decreased Vmax in a dose-dependent manner (for pentobarbital, IC50 = 0.84 mM, patient 2). The apparent Km in individuals remained largely unchanged. Three-OMG influx without preincubation resulted in a stronger inhibition at lower barbiturate concentrations. The patients' data are discussed in the light of individual missense mutations (patient 1: R126L and K256V; patient 2: T310I; patient 3: S66F) in the GLUTI gene. In conclusion, in controls and patients with GLUT1-deficiency barbiturates interact with GLUT1, lowering its intrinsic activity. The use of barbiturates in this condition for anesthesia or as anticonvulsants could therefore potentially aggravate the existing glucose transport defect and may put these patients at increased risk.

Barbiturates inhibit hexose transport in cultured mammalian cells and human erythrocytes and interact directly with purified GLUT-1

Barbiturates reduce cerebral blood flow, metabolism, and Glc transfer across the blood-brain barrier. The effect of barbiturates on hexose transport in cultured mammalian cell lines and human erythrocytes was studied. Pentobarbital inhibits [3H]-2-dGlc uptake in 3T3-C2 murine fibroblasts by approximately 95% and approximately 50% at 10 and 0.5 mM, respectively. Uptake of [3H]-2-dGlc is linear with time in the presence or absence of pentobarbital, and the percent inhibition is constant. This suggests that hexose transport, not phosphorylation, is inhibited by barbiturates. Inhibition by pentobarbital of hexose transport in 3T3-C2 cells is rapid (< 1 min), is not readily reversible, is not altered by the presence of albumin [1% (w/v)], and is independent of temperature (4-37 degrees C) and the level of cell surface GLUT-1. The IC50's for inhibition of hexose transport in 3T3-C2 cells by pentobarbital, thiobutabarbital, and barbital are 0.8, 1.0, and 4 mM, respectively. This is consistent with both the Meyer-Overton rule and the pharmacology of barbiturates. Neither halothane (< or = 10 mM) nor ethanol [< or = 0.4% (v/v)] significantly inhibits hexose transport. Inhibition by pentobarbital (0.5 mM) of [3H]-2-dGlc uptake by 3T3-C2 cells decreases the apparent Vmax (approximately 50%) but does not alter the apparent Km (approximately 0.5 mM). Inhibition of hexose transport by barbiturates, but not ethanol [< or = 0.4% (v/v)], is also observed in human erythrocytes and four other cultured mammalian cell lines. Pentobarbital quenches (Qmax approximately 75%) the intrinsic fluorescence of purified and reconstituted GLUT-1 (Kd approximately 3 mM). Quenching is independent of Glc occupancy, is unchanged by mild proteolytic inactivation, and does not appear to directly involve perturbations of the lipid bilayer. We propose that barbiturates can interact directly with GLUT-1 and inhibit the intrinsic activity of the carrier. Glc crosses the blood-brain barrier primarily via the GLUT-1 of the endothelial cells of cerebral capillaries. Partial inhibition of this process by barbiturates may be of significance to cerebral protection.

Anaerobic glycolysis preceding white-matter destruction in experimental neonatal hydrocephalus

The metabolic changes in neonatal hydrocephalus that lead to permanent brain injury are not clearly defined, nor is the extent to which these changes can be prevented by a cerebrospinal fluid shunt. To clarify these processes, cerebral glucose utilization was examined using [14C]2-deoxyglucose autoradiography in 1-month-old kittens, kaolin-induced hydrocephalic littermates, and hydrocephalic kittens in which a ventriculoperitoneal shunt had been inserted 10 days after kaolin injection. The hydrocephalic kittens showed thinning of the cerebral mantle and an anterior-to-posterior gradient of enlargement of the ventricular system, with a ventricle:brain ratio of 24% for the frontal and 35% for the occipital horns compared with control (< 0.5%) and shunted (< 5%) animals. White matter in hydrocephalic animals was edematous. Myelination was delayed in the periventricular region and in the cores of the cerebral gyri. Glucose utilization in hydrocephalic and shunted animals was unchanged from control animals in all gray-matter regions examined. However, in hydrocephalic animals, the frontal white matter exhibited a significant increase in glucose utilization (25 mumol.100 gm-1.min-1) in the cores of gyri compared with normal surrounding white-matter values (14.8 mumol.100 gm-1.min-1). Very low values (mean 4 mumol.100 gm-1.min-1) were found in areas corresponding to severe white-matter edema, and these areas were surrounded by a halo of increased activity (24 mumol.100 gm-1.min-1). In contrast, cytochrome oxidase activity in white matter was homogeneous. Shunting resulted in restoration of the cerebral mantle thickness, a return to normal levels of glucose utilization in the white matter, and an improvement in myelination. It is suggested that the areas of increased glucose utilization seen in the white matter represent anaerobic glycolysis which, if untreated, progresses to infarction. The pattern of this increased glucose utilization matches that of expected myelination and, during this period of high energy demand, white matter may be susceptible to the hypoperfusion associated with hydrocephalus.

Functional integration of cortical grafts placed in brain infarcts of rats

Five to 6 days after a right middle cerebral artery occlusion, a cell suspension of fetal neocortex was grafted into the infarcted area of adult spontaneously hypertensive rats. Three to 17 months later, functional integration of the grafts into the afferent somatosensory pathway was tested using the 2-[14C]deoxyglucose method for estimation of glucose utilization. Grafted rats (n = 8) and control rats (n = 5) with no arterial occlusion were stimulated in the left vibrissal region resulting in an increased glucose utilization in the left trigeminal sensory nucleus and the right ventroposterior nucleus of the thalamus, whereas the same regions in a group (n = 5) of nonstimulated grafted rats were not activated. Glucose uptake in the right somatosensory cortex of control rats was 96 +/- 5 (mean +/- SEM) mumol/100 gm/min. Neocortical grafts consumed less glucose than cortex in control rats but the vibrissae-stimulated group displayed a 110% higher value than the nonstimulated grafted group (32 +/- 5 vs 15 +/- 2, p < 0.05). We conclude that graft glucose metabolism is increased following stimulation of the host somatosensory pathway, which demonstrates that transplanted neurons can be functionally integrated with neural circuitries of the host after an ischemic insult.

Effect of alpha-chloralose, halothane, pentobarbital and nitrous oxide anesthesia on metabolic coupling in somatosensory cortex of rat

The effect of various anesthetics on the functional-metabolic coupling of cerebral cortex was studied in rats submitted to unilateral somatosensory stimulation. The regional cerebral metabolic rate of glucose (CMRglc) was measured autoradiographically using the 2-deoxyglucose method, and somatosensory activation was carried out by electrical stimulation of the left forepaw. In animals treated with 70% nitrous oxide, 0.5% halothane/70% nitrous oxide or 40 mg/kg pentobarbital, CMRglc of somatosensory cortex did not change despite generation of primary evoked cortical potentials. Anesthesia with 80 mg/kg alpha-chloralose, in contrast, led to a focal increase of CMRglc in the primary somatosensory cortex from 52.1 +/- 18.3 to 73.1 +/- 18.9 mumol/100 g/min (means +/- s.d.). Metabolic activation was strictly confined to the forelimb (FL) area of somatosensory cortex, and it exhibited a laminar pattern with maximal activation in layers I, II and IV. The preservation of functional-metabolic coupling under a surgical dose of chloralose renders this anesthetic particularly suited for the investigation of coupling processes under conditions where the experimental requirements preclude the use of unanaesthetized animals.

Rapid feasibility studies of tracers for positron emission tomography: high-resolution PET in small animals with kinetic analysis

The development of methods for production of a radiotracer for use in human studies with positron emission tomography (PET) is often a time-consuming process of optimizing radiolabelling yields and handling procedures. Sometimes the radiotracer is not the original drug, but rather a derivative with unknown in vivo pharmacological properties. We have developed a fast and simple method of testing putative new PET tracers in vivo in small animals. The procedure has been validated in rats with different PET tracers with known kinetic and pharmacological properties ([2-18F]2-fluoro-2-deoxy-D-glucose, [N-methyl-11C]Ro 15-1788, and [15O]butanol). The tracer concentration in arterial blood was continuously measured to obtain the brain input function. Following image reconstruction of the scans, time-activity curves of selected regions of interest were generated. Estimations of CMRglc (1.0 +/- 0.2 mumol g-1 min-1), CBF (1.4 +/- 0.4 ml g-1 min-1) and transport rate constants for [N-methyl-11C]Ro 15-1788 (K1 = 0.44 +/- 0.01 ml g-1 min-1 and k2 = 0.099 +/- 0.005 min-1) as well as calculated first pass extraction (0.32 +/- 0.1) are in reasonable agreement with literature values. Small animal studies require minimal amounts of radioactivity and can be performed without sterility and toxicology tests. They may serve as a preliminary basis for radiation safety calculations because whole body scans can be performed even with a head scanner.(ABSTRACT TRUNCATED AT 250 WORDS)

Influence of nitrous oxide administration and discontinuation thereof on blood flow in cerebral cortex, cerebellum and brain stem in the rat

The effect of nitrous oxide on blood flow in the cerebral cortex, the cerebellum and the brain stem was evaluated in a rat model. Catheters were surgically implanted in advance to avoid influence from other anaesthetics. The animals were housed in a plastic tube where they were allowed to breathe spontaneously. Blood flow was determined with a microsphere technique. Animals were exposed to nitrous oxide, 75-80%, for 45 min and blood flow was measured after 15 and 45 min exposure and was compared to values obtained during room air breathing. In one animal group, nitrous oxide was administered for 45 min and blood flows were measured after 5 and 30 min withdrawal of the gas. Results showed that all animals had significant hyperventilation. In three groups CO2 had to be added to inspiratory gases to normalize arterial blood gases. This was interpreted as caused by stressful experimental conditions, not blunted by the nitrous oxide. Cortical blood flow values in the control situation were also higher than obtained in other animal studies. Despite this, nitrous oxide showed a significant vasodilation in the cerebral cortex and the brain stem at 15 min exposure. At discontinuation of nitrous oxide administration, blood flow values had decreased at 5 min.

Central action of psychomotor stimulants on glucose utilization in extrapyramidal motor areas of the rat brain

Psychomotor stimulants increase regional cerebral metabolic rates for glucose (rCMRglc). To determine if effects in motor areas reflect limb movements, we measured rCMRglc in gallamine-paralyzed rats given cocaine, methylenedioxymethamphetamine, amphetamine, or phencyclidine. Results resembled findings in partially immobilized rats. One difference was lack of cocaine-induced stimulation in the caudate-putamen despite an increase in partially immobilized rats. Therefore, stimulant-induced rCMRglc stimulation in most motor areas is a primary CNS effect.

Effects of MK-801 upon local cerebral glucose utilisation in conscious rats and in rats anaesthetised with halothane

The effects of MK-801 (0.5 mg/kg i.v.), a non-competitive N-methyl-D-aspartate (NMDA) antagonist, upon local cerebral glucose utilisation were examined in conscious, lightly restrained rats and in rats anaesthetised with halothane in nitrous oxide by means of the quantitative autoradiographic [14C]-2-deoxyglucose technique. In the conscious rats, MK-801 produced a heterogenous pattern of altered cerebral glucose utilisation with significant increases being observed in 12 of the 28 regions of gray matter examined and significant decreases in 6 of the 28 regions. Pronounced increases in glucose use were observed after MK-801 in the olfactory areas and in a number of brain areas in the limbic system (e.g., hippocampus molecular layer, dentate gyrus, subicular complex, posterior cingulate cortex, and mammillary body). In the cerebral cortices, large reductions in glucose use were observed after administration of MK-801, whereas in the extrapyramidal and sensory-motor areas, glucose use remained unchanged after MK-801 administration in conscious rats. In the halothane-anaesthetised rats, the pattern of altered glucose use after MK-801 differed qualitatively and quantitatively from that observed in conscious rats. In anaesthetised rats, significant reductions in glucose use were noted after MK-801 in 10 of the 28 regions examined, with no area displaying significantly increased glucose use after administration of the drug. In halothane-anaesthetised rats, MK-801 failed to change the rates of glucose use in the olfactory areas, the hippocampus molecular layer, and the dentate gyrus.(ABSTRACT TRUNCATED AT 250 WORDS)

Regional cerebral blood flow in acute hypertension induced by adrenaline, noradrenaline and phenylephrine in the conscious rat

Hypertension was induced in conscious rats by intravenous infusion of phenylephrine (3, 6 or 12 micrograms kg-1 min-1), noradrenaline (3 micrograms min-1) or adrenaline (3 micrograms kg-1 min-1). Local cerebral blood flow was measured autoradiographically in 24 defined brain structures using [14C]iodoantipyrine as the diffusible tracer. The mean arterial pressure induced by adrenaline, noradrenaline and the two higher doses of phenylephrine was 158-168 mmHg with no significant differences between the groups. Only adrenaline significantly increased local cerebral blood flow in nine of the 24 structures studied. The smaller capacity for autoregulation after adrenaline compared with other drugs might be related to a beta-adrenoreceptor-stimulating effect.

Modifications of the permeability of the blood-brain barrier and local cerebral metabolism in pentobarbital- and ketamine-anaesthetized rats

The state of deep surgical anaesthesia, induced by intraperitoneal injection of pentobarbital sodium (54 mg/kg) or ketamine hydrochloride (150 mg/kg) in the rat, was accompanied by a significant reduction in the permeability of the blood-brain barrier evaluated by calculating a unidirectional blood-to-brain constant (Ki) for the circulating tracer [14C]alpha-aminoisobutyric acid. Pentobarbital-induced anaesthesia was also characterized by a widespread and marked depression of local cerebral glucose utilization; on the contrary, when rats were anaesthetized with ketamine, cerebral glucose utilization increased in the striatum and hippocampus and decreased in the cerebellum and brain-stem. It is suggested, as a hypothesis, that two different mechanisms, depending on the kind of the anaesthetic drug used, may be involved in the changes in the permeability of the blood-brain barrier, observed in anaesthetized animals: (a) a neurogenic component; (b) a direct interaction of the anaesthetic with elements of the microvasculature.

Preischemic hyperglycemia enhances postischemic depression of cerebral metabolic rate

The objective of the present study was to explore metabolic correlates to the appearance of postischemic seizures and the enhancement of brain damage observed in subjects that are made hyperglycemic prior to the induction of ischemia. To that end, transient forebrain ischemia of 10-min duration was induced in normo- and hyperglycemic rats, with subsequent measurements of local CMRglc (LCMRglc) after 3, 6, 12, and 18 h of recirculation. We posed the questions of whether postischemic depression of LCMRglc is exaggerated by preischemic hyperglycemia and whether there are signs of localized increases in LCMRglc in hyperglycemic rats, reflecting subclinical seizure activity. The results confirmed the presence of a long-lasting postischemic depression of LCMRglc in normoglycemic rats. This depression was partially but not tightly related to the degree of reduction of local CBF during ischemia. The depression was most pronounced in neocortical areas and in the hippocampus, but notably it was less pronounced in the densely ischemic caudoputamen. Little or no reduction of LCMRglc was observed in moderately or mildly ischemic structures such as the hypothalamus, red nucleus, and cerebellum. Preischemic hyperglycemia markedly accentuated the postischemic depression of LCMRglc. For example, although the subjects quickly regained wakefulness and motility, they had LCMRglc values in neocortical areas that remained below 50% of control. Corresponding but quantitatively less pronounced reductions in LCMRglc were observed in other areas. Notably, preischemic hyperglycemia reduced postischemic LCMRglc also in areas that showed only moderate to mild reductions in CBF during the ischemia. The results thus demonstrate that preischemic hyperglycemia has pronounced metabolic effects in the postischemic recovery period. The data provide no indication that postischemic seizures, which develop after a recovery period of approximately 24 h, are preceded by the appearance of hypermetabolic "seizure" foci.

Simultaneous, quantitative measurement of local blood flow and glucose utilization in tissue samples in normal and injured feline brain

Cerebral blood flow (CBF) and local cerebral glucose utilization (LCGU) were measured using radioactive microspheres and [14C]2-deoxyglucose, respectively, in 26 brain regions in control animals (n = 8) and in animals (n = 4) sustaining low-level experimental brain injury. Examination of the initial (resting) CBF measurement in the uninjured cats revealed two subgroups with significantly (p less than 0.01) different CBF levels. In uninjured cats with normal CBF levels (33.4 +/- 1.8 ml/100 g/min) there was a close linear relationship between CBF and LCGU (n = 0.71, p less than 0.01). In contrast, the remainder of the uninjured cats exhibited abnormally high levels of CBF (72.6 +/- 9.9 ml/100 g/min) and the absence of a close relationship between CBF and LCGU (r = 0.27). One hour following low-level (2.0 atm) fluid percussion brain injury, CBF was increased and LCGU was decreased, though not significantly. The relationship between CBF and LCGU remained intact (r = 0.66, p less than 0.01) in most brain regions. However, the relationship between CBF and LCGU in the hippocampus differed significantly from the relationship between the two parameters in the rest of the brain. Thus, the use of the radioactive microsphere method for CBF measurements allows multiple measurements of CBF and permits the assessment of the status of the cerebral vasculature prior to experimental manipulations such as traumatic brain injury. In view of our current findings of an abnormal relationship between CBF and LCGU in cats with high resting CBF levels, this is an important advantage. In addition, the combination of the microsphere and 2-DG techniques within the same tissue samples allows for the investigation of the effects of traumatic injury on the important relationship between CBF and LCGU.

Local spinal cord glucose utilization in conscious and halothane-anaesthetized rats

The authors used the 2-[14C]deoxyglucose method to study local spinal and cerebral glucose utilization simultaneously during 1.2 per cent halothane anaesthesia in adult Sprague-Dawley rats. In conscious animals (n = 5) the rate of glucose utilization in lumbar spinal gray matter was about 50 per cent lower than that of cerebral cortex. Halothane anaesthesia (n = 6) reduced spinal cord and cerebral metabolic rate. Spinal glucose utilization was reduced 12-35 per cent, but this was less than the 45-70 per cent decrease halothane produced in 8 of 16 cerebral structures examined and was independent of the hypotension produced. These results indicate that halothane is a spinal metabolic depressant but that its effects on this tissue are substantially less than those it has on many cerebral structures.

Local cerebral glucose consumption during ethanol withdrawal in the rat: effects of single and multiple episodes and previous convulsive seizures

Local cerebral glucose consumption (l-CMRgl) was studied using [14C]2-deoxyglucose autoradiography in minimally restrained rats during acute (12 or 18 h postwithdrawal (p.w.] and late (14 days p.w.) ethanol withdrawal, as well after 10 previous, weekly withdrawal episodes as after a similar period of isocalorical feeding. A period of two days of intoxication was established by gastric intubation. Spontaneous incomplete convulsive seizures were observed during the 8th to 10th withdrawal episode. Audiogenic seizures occurred following stimulation during the 6th and 10th withdrawal episode. Animals with previous spontaneous or audiogenic seizure were distributed randomly and evenly among the groups. l-CMRgl values were adjusted to a temperature of 38 degrees C. During acute withdrawal, l-CMRgl was significantly reduced by 18-32% in cortical and most limbic regions, but unchanged in cerebellum and subcortical structures as compared with the neutral state (late withdrawal and control groups). l-CMRgl was relatively more lowered in the amygdala in animals with previous spontaneous withdrawal seizures and in structures belonging to the auditory system in animals with previous audiogenic seizures. l-CMRgl did not differ among neutral groups. The lowered l-CMRgl in cortical and limbic regions during withdrawal contrasts to the results of previous studies. This difference may be attributed to the minimal restraint of animals in this study. The pattern of l-CMRgl in acute and late withdrawal animals with previous spontaneous withdrawal seizures is consistent with a mechanism comparable to electrical amygdala kindling contributing to seizure genesis.

The effects of nitrous oxide on the central endogenous pro-opiomelanocortin system in the rat

The hypothesis that nitrous oxide stimulates the central pro-opiomelanocortin system in vivo was explored in this study. A concentration-dependent stimulation of central pro-opiomelanocortin neuropeptides was demonstrated after exposures to variable concentrations of nitrous oxide with oxygen. Rats exposed to 60% and 80% nitrous oxide with oxygen demonstrated an elevation of beta-endorphin concentration along the neuraxis involved with analgesia; no similar effect was observed in alpha-MSH concentration, neither duration of exposure nor acclimation to the enclosed environment altered this stimulation. The discontinuation of nitrous oxide exposure resulted in the diminution of beta-endorphin concentration to pre-exposure levels in 15-30 min. With an ACTH1-39 antisera, a semiquantitative increase in opiocortin immunoreactivity after exposures to nitrous oxide was demonstrated. In conclusion, the increase in beta-endorphin concentration and immunoreactive ACTH1-39 staining in the cells of origin, areas of fiber projection and terminal fields suggest that nitrous oxide stimulates the central pro-opiomelanocortin system in vivo in the rat.

Double-label autoradiographic deoxyglucose method for sequential measurement of regional cerebral glucose utilization

A new double-label autoradiographic glucose analog method for the sequential measurement of altered regional cerebral metabolic rates for glucose in the same animal is presented. This method is based on the sequential injection of two boluses of glucose tracer labeled with two different isotopes (short-lived 18F and long-lived 3H, respectively). An operational equation is derived which allows the determination of glucose utilization for the time period before the injection of the second tracer; this equation corrects for accumulation and loss of the first tracer from the metabolic pool occurring after the injection of the second tracer. An error analysis of this operational equation is performed. The double-label deoxyglucose method is validated in the primary somatosensory ("barrel") cortex of the anesthetized rat. Two different rows of whiskers were stimulated sequentially in each rat; the two periods of stimulation were each preceded by an injection of glucose tracer. After decapitation, dried brain slices were first exposed, in direct contact, to standard X-ray film and then to uncoated, "tritium-sensitive" film. Results show that the double-label deoxyglucose method proposed in this paper allows the quantification and complete separation of glucose utilization patterns elicited by two different stimulations sequentially applied in the same animal. The double-label deoxyglucose is of potential usefulness in sensory physiology since it makes possible the separate mapping of regional cerebral glucose utilization patterns elicited by two sequentially applied sensory stimulations in the same animal. The method allows the quantification of a step-like change in regional cerebral glucose utilization in the same animal. It could be used to study the cerebral metabolic effects induced by neuropharmacological agents or surgical interventions applied during the experiment. Using each animal as its own control eliminates intersubject variability. Thus experimental cost and effort can be saved, and the reliability of the results obtained can be increased.

Vertical and horizontal visual whole-field motion differently affect the metabolic activity of the rat medial terminal nucleus

The metabolic activity of the medial terminal nucleus (MTN) of the Accessory Optic System was studied by means of the [14C]2-deoxyglucose (2-DG) method in Long-Evans rats exposed to moving and stationary visual stimuli. In particular we explored the rate of local cerebral glucose utilization (LCGU) and the spatial distribution of 2-DG uptake within MTN related to visual stimuli capable of triggering optokinetic nystagmus. It was found that increases in MTN metabolism accompanied the retinal slip signals evoked by whole-field visual patterns moving in the vertical as well as in the horizontal direction. At the same level of luminous flux neither the same but stationary pattern, nor constant, diffuse illumination were able to elicit comparable changes in MTN metabolic rates. The effects of vertical and horizontal motions differed, however, from each other. In binocular testing LCGU rates resulted significantly higher after vertically moving patterns and upon the same stimulus condition the spatial distribution of 2-DG matched very closely the spatial distribution of the retinal afferents and the cellular density within MTN, in sharp contrast with the diffuse spreading out of the label across the nucleus following horizontal motion. In monocular testings only the vertically moving patterns were able to increase LCGU rates significantly and then in contralateral MTN alone. However, comparison between the levels of glucose consumption measured in binocular and in monocular vision also showed the involvement of the uncrossed retinal path in relaying the retinal slip signals to MTN. No difference in LCGU and in spatial distribution of the label were finally observed in relation to the upward or to the downward direction of the moving pattern.

Failure of glucose and branched-chain amino acids to normalize brain glucose use in portacaval shunted rats

Several abnormalities in brain and plasma amino acid concentrations caused by portacaval shunting in rats return toward normal after 4 days of intravenous infusion with either glucose or glucose with branched-chain amino acids. To assess the effect of such treatment on brain energy metabolism, regional brain glucose use was measured using [14C]glucose and autoradiography, 5 weeks after portacaval shunting. In one experiment intravenous glucose or glucose with branched-chain amino acids was given for 4 days. In a separate experiment the treatment was given orally for 2 weeks, and in addition to glucose use, brain monoamines and amino acids were measured. No other food was provided; the rats had free access to water. Normally fed shunted rats and sham-operated rats served as controls. Both types of oral treatment lowered the high concentrations of tyrosine, phenylalanine, and glutamine in plasma and brain. Glucose without amino acids normalized brain tryptophan. Levels of brain norepinephrine, 5-hydroxytryptamine (serotonin), and 5-hydroxyindoleacetic acid were significantly raised after shunting. Treatment had no effect on norepinephrine but the glucose diet brought the indoles into the normal range. In contrast, neither intravenous nor oral treatment affected brain glucose use, which remained depressed by 25-30% in all brain areas examined.

Forebrain ischemia in the rat. Relation between duration of ischemia, use of adjunctive ganglionic blockade and long-term recovery

The relation between duration of ischemia, use of adjunctive ganglionic blockade and long-term recovery was studied in a rat model giving reversible subtotal forebrain ischemia. Ischemia was induced by bilateral carotid artery clamping and controlled hemorrhage to a mean arterial pressure of 50 mm Hg in animals artificially ventilated under 70% N2O. After variable lengths of time, the clamps were removed and the drawn blood was reinfused. In some animals, the ganglion blocker Arfonad was given (group A+) on induction of ischemia to facilitate hypotension. There was a strict dose-response relationship between duration of ischemia and mortality. Mortality was higher among animals not given Arfonad (group A-; 37% after 10 min of ischemia and 100% after 13 min) than in group A+ (about 20% after 12-13 min of ischemia, 50% after 15 min and 80% after 19 min). In group A+ more than half of the animals died later than 24 h after ischemia. All of them were hyperexcitable and 12% died during witnessed epileptic fits. Group A- animals regularly died within the first 24 h, with no indication of central nervous system involvement. Less blood had to be drawn to attain hypotension (mean arterial pressure 50 mm Hg) in group A+ (1.5 +/- 0.3 ml/100 g b.w.) than in group A- (2.5 +/- 0.2 ml/100 g b.w.). Group A+ also had less "washout" acidosis 5 min after reinfusion of the shed blood than group A- (15 min of ischemia: pH 7.24 +/- 0.07 v 6.96 +/- 0.06).(ABSTRACT TRUNCATED AT 250 WORDS)

Alterations in perfused capillary morphometry in awake vs anesthetized brain

This study quantitatively compared various indices of perfused capillary morphometry in pentobarbital-anesthetized and awake rat brains. We hypothesized that barbiturate anesthesia would reduce intraregional differences in percent perfused capillary volume and surface area. A high-molecular-weight FITC-labeled Dextran was injected intravenously into awake or barbiturate-anesthetized (50 mg/kg i.p.) rats. After 20 s, the animal was decapitated and the head frozen in liquid N2. Nine brain regions were isolated and mounted in a microtome cryostat. Sections, 2 microns thick, were photographed with a fluorescent microscope to detect the perfused capillaries. The sections were stained for alkaline phosphatase to visualize the total capillary network. Standard morphometric techniques were employed to determine the total and perfused volume (Vv), surface area (Sv) per mm3 and diameter (D) from the photographs. There were no significant differences in any index of total capillary morphometry among the regions in the anesthetized brain. Approximately half of the average total capillary bed was perfused and there were no significant differences in percent perfused Vv or Sv between awake and anesthetized brains. There were significant differences among the various brain regions in the perfused capillary bed of the awake rat. The percent perfused capillary Vv and Sv in the awake rat was significantly greater in the thalamus and anterior cortex than in other brain regions. In awake rats, the percent perfused capillary Vv ranged from 67.9 +/- 4.7% (mean +/- S.E.M.) in the thalamus to 26.1 +/- 4.3% in the posterior cortex. Thus, while the average percent perfused indices of capillary morphometry were not altered by anesthesia, regional differences in these indices among the examined regions were abolished with anesthesia.

Pentoxifylline: cerebral blood flow and glucose utilization in conscious spontaneously hypertensive rats

Pentoxifylline, 0.30 mg/kg/min, significantly reduced cerebral blood flow by 10-44% in 19 of 23 regions studied in conscious spontaneously hypertensive rats. Bilateral ligation of the common carotid arteries reduced cerebral blood flow to 24-46% of resting values in 20 structures; a further reduction to 10-27% of resting values was seen after pentoxifylline in 10 cortical or subcortical structures. Thus, in conscious hypertensive rats, there is no evidence that pentoxifylline redistributes blood flow from normal to low flow brain regions. Pentoxifylline did not reduce the metabolic rate of glucose.

Ascending reticular activating system in the rat: a 2-deoxyglucose study

The autoradiographic [14C]2-deoxyglucose (2-DG) method was used to map ascending pathways which are influenced by arousing electrical stimulation of the midbrain reticular formation (RET) in alert rats. The major finding was that RET stimulation produces selective patterns of metabolic activation and suppression in discrete brain regions. The regions activated were limited to specific intralaminar, medial and anterior thalamic nuclei, and to the entire auditory system. Conversely, a large suppression of 2-DG uptake was observed in most of the cerebral cortex, limbic and extrapyramidal structures, whereas at the same time some brain regions were left unaffected. Striking similarities were found between the functional pathways affected differentially by RET stimulation and well-defined cholinergic pathways which originate in the midbrain tegmentum. Structures which showed metabolic activation are part of the dorsal cholinergic pathway, whereas the regions suppressed are part of the ventral cholinergic pathway and its higher-order projections. The results support the conclusion that cholinergic pathways represent the thalamic and extrathalamic divisions of the reticular activating system. Our observations provide the first anatomical demonstration that RET stimulation has widespread and differential effects on cerebral metabolism. They also support the concept that arousing electrocortical desynchronization involves reticular activation of thalamocortical neurons, which in turn have widespread suppressive influences on cortical metabolism.

Deoxyglucose uptake and choline acetyltransferase activity in cerebral cortex following lesions of the nucleus basalis magnocellularis

The uptake of [3H]2-deoxyglucose (2-DG) into various brain regions of rats with unilateral or bilateral lesions of the nucleus basalis magnocellularis (nBM) was measured. The activity of choline acetyltransferase (ChAT) in these brain regions was also determined. Lesions of the nBM caused a significant decrease in cortical ChAT activity but had no effect on 2-DG accumulation. Pentobarbital treatment reduced 2-DG accumulation in all brain areas examined and these reductions were not influenced by the nBM lesions. The results indicate that a decrease in the cholinergic innervation of the cortex does not influence cortical glucose utilization. It appears unlikely, therefore, that the reported decrease in cortical glucose utilization in Alzheimer's disease is related to degeneration of the nBM-cortical cholinergic projection.

Regional brain glucose metabolism in chemically-induced seizures in the rat

Measurement of regional brain glucose metabolism may give information concerning the mechanism of neuronal cell death developing after prolonged periods of epileptic activity. Regional brain glucose utilization was measured in paralyzed ventilated rats during seizures induced by L-allylglycine, kainic acid and bicuculline using the [14C]deoxyglucose method. Regional brain glucose concentration was measured in another series of rats, after similar periods of seizure activity, to permit a more accurate calculation of the lumped constant. In L-allylglycine-induced seizures regional brain glucose concentration did not vary from control values, so no correction of the lumped constant was necessary. Regional brain glucose utilization increased throughout the brain, the largest increase being in the hippocampus (control 36 +/- 6 mumol 100 g-1 min-1; seizure 120 +/- 12 mumol 100 g-1 min-1). In kainic acid-induced seizures, brain glucose concentration fell in the hippocampus, involving some correction of the lumped constant. Increases in glucose utilization were limited primarily to the hippocampus, with some involvement of the inferior colliculus. The ventral hippocampus showed the largest increase in glucose utilization (control 34 +/- 5 mumol 100 g-1 min-1; seizure 167 +/- 10 mumol 100 g-1 min-1). In bicuculline-induced seizures, in starved rats, brain glucose concentration fell in all regions investigated and no increase in regional glucose utilization was recorded. In L-allylglycine and kainic acid-induced seizures, the hippocampus, a region vulnerable to neuronal damage, shows the largest increase in glucose utilization. Studies involving bicuculline need further investigation, due to severe perturbation of brain and plasma glucose concentration.

Regional cerebral blood flow in conscious stroke-prone spontaneously hypertensive rats

Regional cerebral blood flow (rCBF) was measured autoradiographically with [14C]iodoantipyrine as a diffusible tracer in two strains of conscious normotensive rats (Wistar Kyoto and local Wistar) and in two groups of spontaneously hypertensive stroke-prone rats (SHRSP) with a mean arterial pressure (MAP) below or above 200 mm Hg. In spite of the large differences in arterial pressure, rCBF did not differ significantly between the hypertensive and the normotensive groups in any of the 14 specified brain structures measured. However, rCBF increased asymmetrically within part of the caudate-putamen in two of nine SHRSP with a MAP above 200 mm Hg, indicating a regional drop in the elevated cerebrovascular resistance.

Local cytochrome oxidase activity in the cerebral cortex of the rat, histochemically detected with the DAB-method: a micro-densitometric and electron microscope study

For demonstration of the local cytochrome oxidase activity, coronal sections through the frontal cortex of four Sprague-Dawley rats were incubated with DAB medium after Seligman et al. (1968). The pattern of distribution of the DAB reaction product (DAB-RP) was measured at a wavelength of 460 nm. Cryostat sections were scanned with a microdensitometer. The cytochrome reaction product was accumulated in the laminae I and IV. A comparative morphometric study of mitochondrial profiles in ultra-thin sections through equivalent cortical regions showed an approximately similar distribution in percentage of areal density of the mitochondria labeled by DAB-RP. On average 30% of the mitochondrial profiles were labeled with DAB-RP which was localized in the intracristate spaces and the outer mitochondrial compartment. The marked mitochondria mainly occurred in dendrites. Furthermore, the mean and median value of the size distribution of marked mitochondrial profiles was shifted to greater values when compared with non-marked ones.

Local blood flow and glucose consumption in the rat brain during sustained bicuculline-induced seizures

The present study addresses the problem of whether brain structures which have been shown to develop neuronal cell damage in recurrent or prolonged epileptic seizures have higher metabolic rates and/or less pronounced increases in blood flow rates than others during sustained seizures. To that end, local cerebral blood flow (CBF) and glucose utilization (CMRgl) were measured autoradiographically in ventilated rats, in which seizures of 20, 60, or 120 min duration were induced by i.v. bicuculline. After 20 and 60 min of seizure activity, local CBF increased 2- to 4-fold in most of the 21 structures analysed. However, there was a marked heterogeneity with CBF values varying between 150% (caudoputamen) and 500% (globus pallidus) of control. After 120 min, CBF in several structures, notably cortical and limbic regions, fell in spite of unchanged blood pressure and continued seizure activity. Changes in local CMRgl were equally heterogenous, and correlated poorly with blood flow rates. Some structures (the cerebral cortices and 3 limbic areas) showed a sustained 2-4 fold increase in CMRgl. In these, metabolic rate and blood flow were initially matched but CBF subsequently fell to yield a pattern of relative hypoperfusion. Other structures showed no, or only moderate, increases in CMRgl. In spite of this, CBF increased markedly to yield a pattern of relative hyperemia. It is concluded that bicuculline-induced seizures represent a condition in which structures, observed to be prone to develop cell damage, show grossly enhanced metabolic rate and develop relative underperfusion. Furthermore, the results suggest that structures with a large increase of the metabolic rate during seizures, develop a striking mismatch between local metabolic rate and blood flow.

Cerebral circulatory responses to hypercapnia and hypoxia in the recovery period following complete and incomplete cerebral ischemia in the rat

In this study we examined the reactions of cerebral vessels to hypercapnia and hypoxia during the recovery period following cerebral ischemia. We used ventilated, lightly anesthetized rats and induced complete ischemia by CSF compression, incomplete ischemia by bilateral carotid occlusion combined with hypotension. After 15 min of ischemia and 60 min of recirculation the animals were rendered hypercapnic or hypoxic for 2-3 min and local CBF was then measured autoradiographically with 14C-iodoantipyrine. Following complete ischemia vascular CO2 responsiveness was abolished or attenuated in most structures analysed. However, there was a considerable interstructural heterogeneity. For example, in the cerebellum and the red nucleus flow rates were observed which approached values obtained in hypercapnic control animals, whereas CO2 responsiveness was abolished in several cortical areas and hippocampus. The response to CO2 following incomplete ("forebrain") ischemia varied considerably. In the cerebral cortices areas with low flow rates were often mixed with hyperemic zones, and in most structures that had very low flow rates during ischemia, CO2 responsiveness was lost or grossly attenuated. Structures that had suffered moderate or only mild ischemia had better retained or completely preserved CO2 response. The cerebrovascular reaction to hypoxia was found to be attenuated in most, but not abolished in any of the structures examined. In general, the vascular response to hypoxia was better preserved than that to hypercapnia. Reactivity was similar following complete and incomplete ischemia. As observed during hypercapnia, there were pronounced interstructural variations with considerable increases in flow rates e.g. in the substantia nigra and the cerebellum.

Lactate uptake and release in the presence of glucose by sympathetic ganglia of chicken embryos and by neuronal and nonneuronal cultures prepared from these ganglia

Uptake and output of lactate were measured in lumbar sympathetic chains excised from embryos of white leghorn chickens, 14-15 days old. The chains, typically containing 30-40 micrograms of protein, were incubated in Eagle's minimum essential medium containing bicarbonate buffer, 6-17 mM glucose, various concentrations of lactate, and either [U-14C]lactate, [1-14C]glucose, or [6-14C]glucose. The average rate of uptake of labeled lactate was measured with incubations of 5-6 h, starting with various external lactate concentrations. From these data the instantaneous relation between lactate uptake rate and concentration was deduced with a simple computerized model. The instantaneous uptake rate increased with the concentration according to a relation that fit the Michaelis-Menten equation, with Vmax = 360 mumol/g protein/h and Km = 4.8 mM. Substantial fractions of the lactate carbon were recovered from tissue constituents and in several nonvolatile products in the medium, as well as in CO2. Glucose uptake averaged about 108 mumol/g protein/h and did not vary greatly with external lactate concentration, although the metabolic partitioning of glucose carbon was considerably affected. Regardless of initial concentration, the lactate concentration in the medium tended to change towards approximately 0.6 mM, showing that uptake equaled output at this level, with rates at about 40 mumol/g protein/h. With the steady-state concentration of 0.6 mM lactate, about 20% of the glucose carbon was shunted out into the medium before it was reabsorbed and metabolized into various products. Lactate uptakes by neuronal and nonneuronal cultures prepared from the ganglia did not differ consistently from one another or from uptake by undissociated ganglia. The neuronal cultures tended to oxidize a greater fraction of the consumed lactate to CO2 and to convert a smaller fraction of the lactate to products in the medium than did the nonneuronal cultures. Computer modeling, using known parameters for blood-brain transport of lactate in the adult rat and data on uptake by the ganglia, suggests that lactate may supply substantial fuel to the brain, even in the presence of abundant glucose, when the lactate concentration in the blood is raised to levels commonly observed in exercising humans, such as 10-20 mM. This is in agreement with the findings of several investigators in hypoglycemic humans and in animals with intermediate blood lactate concentrations.

The effects of apomorphine upon local cerebral glucose utilization in conscious rats and in rats anesthetized with chloral hydrate

The effects of the dopaminergic agonist apomorphine (1 mg . kg-1 i.v.) upon local cerebral glucose utilization in 43 anatomically discrete regions of the CNS were examined in conscious, lightly restrained rats and in rats anesthetized with chloral hydrate by means of the quantitative autoradiographic [14C]2-deoxyglucose technique. In animals anesthetized with chloral hydrate, glucose utilization was reduced throughout all regions of the CNS from the levels observed in conscious animals, although the magnitude of the reductions in glucose use displayed considerable regional heterogeneity. With chloral hydrate anesthesia, the proportionately most marked reductions in glucose use (by 40-60% from conscious levels) were noted in primary auditory nuclei, thalmaic relay nuclei, and neocortex, and the least pronounced reductions in glucose use (by 15-25% from conscious levels) were observed in limbic areas, some motor relay nuclei, and white matter. In conscious, lightly restrained rats, the administration of apomorphine (1 mg . kg-1) effected significant increased in glucose utilization in 15 regions of the CNS (e.g., subthalamic nucleus, ventral thalamic nucleus, rostral neocortex, substantia nigra, pars reticulata), and significant reductions in glucose utilization in two regions of the CNS (lateral habenular nucleus and anterior cingulate cortex). In rats anesthetized with chloral hydrate, the effects of apomorphine upon local glucose utilization were less widespread and less marked than in conscious animals. In only two of the regions (the globus pallidus and septal nucleus), which displayed increased glucose use following apomorphine in conscious rats, were significant increases in local glucose utilization observed with this agent in chloral hydrate-anesthetized rats. In the pars compacta of the substantia nigra, in which apomorphine increased glucose utilization in conscious animals, significant reductions in glucose utilization were observed following apomorphine in rats anesthetized with chloral hydrate. The profound effects of chloral hydrate anesthesia upon local cerebral glucose use, and the modification by this anesthetic regime of the local metabolic responses to apomorphine, emphasize the difficulties which exists in the extrapolation of data from anesthetized animals to the conditions which prevail in the conscious animal.

Effect of nitrous oxide on local cerebral glucose utilization in rats

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.

No effect of hyperketonemia on local cerebral glucose utilization in conscious rats

Local cerebral glucose utilization was measured by the [14C]2-deoxy-D-glucose method in conscious control and hyperketonemic rats. Hyperketonemia was induced by 3 days of starvation or by infusion of 3-hydroxybutyrate in fed rats. These treatments produced combined blood ketone body concentrations (acetoacetate + 3-hydroxybutyrate) of from 1.2 to 2.4 mM. Neither treatment significantly affected glucose utilization in any of the 15 brain regions studied. These observations indicate that hyperketonemia in resting, conscious rats does not interfere with brain uptake and phosphorylation of glucose.

Functional activity of substantia nigra grafts reinnervating the striatum: neurotransmitter metabolism and [14C]2-deoxy-D-glucose autoradiography

Dopaminergic innervation of the caudate nucleus in adult rats can be partially restored by the grafting of embryonic substantia nigra into the overlying parietal cortex with concomitant compensation of certain behavioral abnormalities. In this study the function of such grafts was investigated neurochemically by quantification of transmitter metabolism and glucose utilization in the reinnervated target. Rats with unilateral 6-hydroxydopamine lesions of the nigrostriatal bundle received a single graft to the dorsal caudate-putamen and were screened for rotational behavior following 5 mg/kg methamphetamine. The grafts restored dopamine concentrations in the caudate-putamen from initially less than 0.5% to an average of 13.6% of normal in rats with behavioral compensation. The ratio of 3,4-dihydroxyphenylacetic acid to dopamine, which is a measure of the rate of transmitter turnover, were equivalent in transplanted and normal control rats. Moreover, measurements of DOPA accumulation for a 30-min period after DOPA decarboxylase inhibition indicated similar fractional dopamine turnover rates in normal and transplant-reinnervated tissues. Correlations between rotational behavior and dopamine concentrations showed that reinnervation to only 3% of normal was sufficient to counterbalance the motor asymmetry. Measurements of glucose utilization by [14C]deoxyglucose autoradiography indicated equivalent metabolic rates for the grafted tissue and the intact substantia nigra. 6-Hydroxydopamine denervation of the caudate-putamen had no significant effect on neuronal metabolism in that region, nor did subsequent reinnervation from a graft. Grafts, however, were associated with a 16% reduction of glucose uptake in the ipsilateral globus pallidus, indicating a significant transsynaptic influence of the nigral transplants on neuronal metabolism in the host brain. Overall the results indicate that behaviorally functional neuronal grafts spontaneously metabolize dopamine and utilize glucose at rates characteristic of the intact nigrostriatal system. This provides further evidence that ectopic intracortical nigral transplants can reinstate dopaminergic neurotransmission in regions of the host brain initially denervated by the 6-hydroxydopamine lesion.

Local cerebral glucose metabolism in newborn dogs: effects of hypoxia and halothane anesthesia

Local cerebral glucose utilization (LCGU) was measured in 36 neuroanatomical structures of normal awake, halothane-anesthetized, and hypoxic newborn puppies by the autoradiographic 2-[14C]deoxyglucose method. In normal animals, LCGU was highest in the vestibular nucleus and in other gray matter nuclei of the brainstem and declined in a caudal-to-rostral progression through the neuraxis (i.e., LCGU of cerebellum greater than thalamus approximately equal to caudate-putamen greater than cerebral cortex). Lowest rates of glucose metabolism were detected in white matter structures. Halothane anesthesia (1.5% inspired) caused few changes in local glucose metabolism, the most notable being decreased LCGU among structures of the auditory system (cochlear nucleus, lateral lemniscus, inferior colliculus) and increased LCGU in the interpeduncular nucleus. Acute systemic hypoxia (arterial oxygen tension of approximately 12 mm Hg) produced markedly heterogeneous effects on local glucose metabolism: LCGU was increased in some gray matter structures, decreased in the thalamus, and substantially increased in the subcortical white matter and corpus callosum. In puppies whose brains were frozen in situ after 55 minutes of hypoxia, the concentration of lactate was increased ten- to elevenfold in cortical gray and subcortical white matter, but the concentrations of glucose, adenosine triphosphate, and phosphocreatine declined to a greater extent in the white matter. The results suggest that during hypoxia the high rate of glycolysis in white matter exceeded substrate supply so that glucose availability became the limiting factor for local energy production. Such a mechanism may contribute to the white matter injury that often develops following hypoxic-ischemic insults in the perinatal period.

A radioisotopic method for the simultaneous quantitation of regional cerebral blood flow and glucose utilization in small dissected samples: validation studies and values in the nitrous oxide-anesthetized rat

A method is described for the simultaneous determination of the rates of regional cerebral blood flow (rCBF) and regional cerebral glucose utilization (rCMRgl) in 6-7 mg brain samples dissected from multiple areas of interest. The method utilizes [131I]iodoantipyrine ([131I]IAP) to measure rCBF by indicator fractionation, and [14C]2-deoxyglucose to measure rCMRgl. [131I]IAP was synthesized with specific activity exceeding 350 Ci/mmol and radiochemical purity greater than 99.5% by the radioiodination of antipyrine with Na131I. A triple-counting strategy was developed to quantitate 14C activity of the dissected brain samples in the presence of 131I. The factors contributing to the propagated error of the double-label separation strategy were defined and optimal assay parameters were determined. The separation strategy was validated by measuring rCBF simultaneously with both [131I]IAP (x) and [14C]IAP (y) in a series of rats. The equation of the regression line was y = 1.025 x -0.065 (correlation coefficient 0.985), denoting excellent agreement. In another series of 5 normocapnic rats anesthetized with nitrous oxide, rCBF and rCMRgl were measured simultaneously. In individual animals, the rates of rCBF within 14-16 brain areas were closely coupled to their respective rates of glucose metabolism. For the group data, the linear regression equation relating rCBF (y) to rCMRgl (x) was y = 1.76 x + 0.13 (correlation coefficient 0.93, P less than 0.001). These studies provide direct evidence, based upon data obtained in the same brain, of a close coupling of regional metabolic rate and blood flow.

Local cerebral glucose utilization during development and aging of the Fischer-344 rat

Local cerebral glucose utilization was measured in brain regions of awake Fischer-344 rats. Measurements were taken in 15 regions of 1-month-old rats, and 19 regions of 3-, 12-, 24-, and 34-month-old rats. Between 1 and 3 months, glucose utilization tended to increase in all brain regions; statistically significant increases occurred in seven regions. Between the ages of 3 and 12 months, glucose utilization decreased significantly in 12 regions. The greatest reductions (25% or more) occurred in the striatum, inferior colliculus, and pons, but the hypothalamus and thalamus, nucleus accumbens, and septum showed no statistically significant change. Cerebral glucose utilization did not change between 12 and 24 months or between 24 and 34 months of age. The results demonstrate a rise in cerebral glucose utilization with development from 1 to 3 months, a decline between 3 and 12 months, and a constancy in the second and third years that does not reflect reported senescence-associated neurochemical and morphological cerebral changes.

Effects of methamphetamine on blood flow in the caudate-putamen after lesions of the nigrostriatal dopaminergic bundle in the rat

Methamphetamine was given to rats with unilateral 6-hydroxydopamine lesions of the nigrostriatal dopaminergic bundle. In these animals local cerebral blood flow, measured autoradiographically with [14C]iodoantipyrine as the diffusible tracer, was more than twice as high in the denervated caudate-putamen as compared to control. Measurements of local glucose consumption with the [14C]deoxyglucose technique showed no corresponding change in local metabolic rate. In fact, glucose consumption was lower in the caudate-putamen on the lesion side. The results show that the amphetamine-induced increase in cerebral blood flow does not require an inact nigrostriatal dopaminergic system. Furthermore, dopamine released by amphetamine seems to constrict the vessels and reduce the blood flow in the caudate-putamen.

Local cerebral blood flow in the brain during bicuculline-induced seizures and the modulating influence of inhibition of prostaglandin synthesis

The purpose of this study was to measure changes in local cerebral blood flow (1-CBF) during generalized seizures, and to study whether or not formation of prostaglandins or related substances contributes to the increased flow rates. Seizures were induced in ventilated rats maintained on 70% N2O and 30% O2 by the i.v. injection of the GABA receptor blocker bicuculline (1.2 mg . kg-1). Formation of prostaglandins was inhibited by the administration of the fatty acid cyclo-oxygenase inhibitor indomethacin (10 mg . kg-1). Local CBF in 21 defined brain structures was measured autoradiographically with 14C-iodoantipyrine as the diffusible tracer. After 20 min of continuous seizure activity 1-CBF increased 1.5--5-fold, the smallest increases (less than 200% of control) being observed in frontal and auditory cortex and in the caudoputamen, and the largest (greater than 400% of control) in substantia nigra, thalamus, visual cortex, lateral geniculate and hypothalamus. In general, the largest increases in 1-CBF occurred in sensory and limbic systems (and hypothalamus) while motor systems showed a pronounced variability. In the majority of structures examined indomethacin failed to modify the CBF response during seizures. Although this result suggests that seizures, in contrast to hypercapnia, lead to an increased CBF by other mechanisms than those related to prostaglandin formation, some structures (nucleus ruber, cerebellum, and superior colliculus) showed a clearly reduced 1-CBF in indomethacin-treated animals.

Effects of immobilization stress on regional cerebral blood flow in the conscious rat

Immobilization stress of conscious, normotensive, freely breathing 10-month-old Wistar-Kyoto rats produced an overall decline in regional cerebral blood flow (rCBF), as measured with [14C]iodoantipyrine, except at the frontal lobe. In 14 brain regions, rCBF fell by an average of 14.3% after 5 min of immobilization and by 11.9% after 15 min. Immobilization stress also stimulated hyperventilation and thereby reduced PaCO2. The slope relating rCBF to PaCO2 averaged 1.5 ml 100 g-1 min-1 mm Hg-1 in 9 significantly affected regions. The findings suggest that rCBF declines during immobilization stress because of cerebrovascular constriction caused by a reduction in PaCO2. Comparison of the average slope with published values in indicates furthermore that were PaCO2 to remain unchanged during immobilization, rCBF would increase by at most 20%.

Influence of nitrous oxide on local cerebral blood flow in awake, minimally restrained rats

In order to evaluate the effect of 70-80% N2O on local cerebral blood flow (1-CBF) in the rat brain, we developed a procedure for measuring CBF by an autoradiographic [14C]iodoantipyrine technique in awake, minimally restrained animals. Results on 1-CBF, as measured in 22 different structures, showed little variability between animals. In the majority of structures analyzed, 70-80% N2O failed to alter 1-CBF. These included all cerebral cortical and most subcortical structures. However, nitrous oxide reduced CBF in the inferior colliculus and the superior olive, in two of the limbic structures analyzed, and in the hypothalamus. In no structure, except the striatum (p less than 0.05), was a significant increase in 1-CBF obtained in N2O-breathing animals. However, the results suggest that CBF may have been increased in the auditory cortex. Immobilization was found to reduce 1-CBF in the cerebellum, inferior colliculus, superior olive, hippocampus, and septal nuclei. The results also suggest that the procedure somewhat increased CBF in frontal and parietal cortex. When the results obtained in awake, air-breathing animals were compared with those obtained in immobilized animals ventilated on N2O, there was no significant increase in any of the structures analyzed, although there were suggested increases in all cortical areas except the visual cortex. However, the data showed that ventilation with 70-80% N2O significantly decreased CBF in several structures (inferior colliculus, superior olive, hippocampus, amygdala, septal nuclei, and hypothalamus). In some of these, the effects of 70-80% N2O and of immobilization were obviously additive.

Local cerebral glucose consumption during insulin-induced hypoglycemia, and in the recovery period following glucose administration

Using the 14C-deoxyglucose technique, we estimated local glucose consumption in the rat brain (1-CMRgl) in hypoglycemia of sufficient severity to cause cessation of spontaneous EEG activity, and in the recovery period following a 30 min period of such hypoglycemia. After 5 and 30 min of hypoglycemia. 1-CMRgl was markedly reduced in many cerebral structures (cerebral cortices, caudateputamen, thalamus, and hippocampus) but unchanged or only moderately reduced in other structures (cerebellar cortex, hypothalamus, and pontine grey). The results indicate that differences in 1-CMRgl were caused by regional differences in the true or apparent kinetic constants for glucose transport, or that the consequences of a hypoglycemic derangement of cellular metabolism interfered with glucose transport in some regions. Local CMRgl was markedly heterogenous in the recovery period, induced by glucose administration in animals with a prior (30 min) period of hypoglycemia. In general, a reduced posthypoglycemic glucose consumption was correlated to low 1-CMRgl values during hypoglycemia. However, the hippocampus provided an exception since its CMRgl returned to control values. A correlation with previous measurement of local cerebral blood flow (1-CBF) demonstrates that regions having a pronounced reduction in 1-CMRgl during hypoglycemia developed a mismatch between blood flow and metabolic rate in the recovery period, the flow showing a disproportional reduction.

Local cerebral blood flow in the rat during severe hypoglycemia, and in the recovery period following glucose injection

In order to assess the influence of severe hypoglycemia on local cerebral blood flow (1-CBF) artificially ventilated rats, maintained on 70% N2O, were injected with insulin to provide either an EEG pattern of slow-wave polyspikes, or cessation of spontaneous EEG activity for 5, 15 or 30 min ("coma"). In other animals, glucose was injected at the end of a 30 min period of "coma" and 1-CBF was measured after recovery periods of 5, 30, 90, or 180 min. Local CBF was measured autoradiographically with 14C-iodoantipyrine as the diffusible tracer. In the slow-wave polyspike period 1-CBF was increased in most of the structures studied, and reached values that were 1.4 to 3.2 times greater than control. In many structures, cessation of EEG activity was accompanied by a further increase in 1-CBF, with some structures (thalamus, hypothalamus, pontine gray, and cerebellar cortex) showing flow rates of 400--500% of control. The increase in 1-CBF was unrelated to arterial hypertension, hypercapnia, or hypoxia. 5 min after glucose injection the hyperemia persisted in only some of the structures studied; in others, the 1-CBF were close to, or below, control values. During the subsequent recovery period 1-CBF was markedly reduced with some structures (cerebral cortical areas, hippocampus, and caudate-putamen) showing flow rates of only 20--35% of control. In others, notably pontine gray and cerebellar cortex, secondary hypoperfusion was never observed. The hypoperfusion was unrelated to arterial hypertension, hypocapnia, or increase in intracranial pressure. It is concluded that, like hypoxia and ischemia, substrate deficiency due to hypoglycemia is accompanied by vasodilatation in the brain. Furthermore, like long-lasting ischemia, severe hypoglycemia is followed by a delayed hypoperfusion syndrome that, by restricting oxygen supply, may well contribute to the final cell damage incurred.