Brain alcohol dehydrogenase.

Significant alcohol dehydrogenase activity has been demonstrated in the soluble fraction of rat brain and is very similar to the liver enzyme in kinetic properties and responses to inhibitors. A cerebral mechanism that oxidizes ethanol may play a significant role in local adjustments during exposure to ethanol and in the pathogenesis of the neural disorders associated with chronic alcohol ingestion or withdrawal.

Induction of brain D(--)-beta-hydroxybytrate dehydrogenase activity by fasting.

D(m)-beta-hydroxybutyrate dehydrogenase activity is very low in normal adult rat brain; but during fasting it increases severalfold in parallel with the ketosis. The increase may represent part of a mechanism by which the brain adapts to changing patterns of substrate supply during starvation.

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

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

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

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

Reexamination of glucose-6-phosphatase activity in the brain in vivo: no evidence for a futile cycle.

Glucose-6-phosphatase activity in the rat brain in vivo was estimated by measuring the differential loss of tritium and carbon-14 from the glucose pool labeled by a mixture of [2-3H]glucose and [U-14C]glucose. The results provide no evidence of significant dephosphorylation of glucose-6-phosphate and do not support the hypothesis of a futile cycle involving glucose-6-phosphatase activity in the brain.

Functional plasticity in the immature striate cortex of the monkey shown by the [14C]deoxyglucose method.

Autoradiographic representation of the local rates of cerebral glucose utilization and local cerebral functional activity by means of the [14C]deoxyglucose technique reveals the existence of the ocular dominance columns in the striate cortex of the monkey in the first day of life. In contrast to the stability of these columns in more mature brain, monocular deprivation for 3 months from the first day of life results in their complete disappearance and a reversion of the autoradiographic pattern to that seen in animals with normal binocular vision. These results are consistent with a reorganization of the representation of the visual fields of the two eyes in the striate cortex and provide additional evidence of the plasticity of the striate cortex of the monkey in early life.

Metabolic mapping of the brain during rewarding self-stimulation.

Local rates of cerebral glucose utilization were measured in rats by the quantitative 2-deoxy-D-[14C]glucose autoradiographic method during electrical stimulation of the ventral tegmental area. Rats trained in intracranial self-stimulation showed a pattern of changes in forebrain metabolic activity distinctly different from the pattern seen in rats stimulated by the experimenter. These findings provide information about the distribution of local cerebral activity specific to reinforced instrumental behavior.

Mapping of functional neural pathways by autoradiographic survey of local metabolic rate with (14C)deoxyglucose.

An enzymatic preparation from human brain converts tryptamine to tryptoline (9H-1,2,3,4-tetrahydropyrido(3,4-b)indole) in the presence of 5-methyltetrahydrofolic acid. Similarly, N-methyltryptamine and 5-hydroxytryptamine yield 1-methyltryptoline and 5-hydroxytryptoline, respectively. Neither in vitro nor in vivo formation of these compounds by human tissues has been described.

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

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

Cerebral glucography with positron tomography. Use in normal subjects and in patients with schizophrenia.

Local cerebral uptake of deoxyglucose labeled with fluorine 18 was measured by positron-emission tomography in eight patients with schizophrenia who were not receiving medication and in six age-matched normal volunteers. Subjects sat in an acoustically treated, darkened room with eyes closed after injection of 3 to 5 mCi of deoxyglucose 18F. After uptake, seven to eight horizontal brain scans parallel to the canthomeatal line were done. Scans were treated digitally, with a 2.3-cm strip peeled off each slice and ratios to whole-slice activity computed. Patients with schizophrenia showed lower ratios in the frontal cortex, indicating relatively lower glucose use than normal control subjects; this was consistent with previously reported studies of regional cerebral blood flow. Patients also showed diminished ratios for a 2.3-cm square that was positioned over central gray-matter areas on the left but not on the right side. These findings are preliminary; issues of control of mental activity, brain structure identification, and biologic and anatomic heterogeneity of schizophrenia remain to be explored.

The neuromuscular pathology of the Eosinophilia-Myalgia syndrome.

The Eosinophilia-Myalgia Syndrome (EMS) is a recently reorganized disorder in patients ingesting pharmacologic doses of L-tryptophan. We studied the lesions of skeletal muscle, peripheral nerve and skin in 12 cases of EMS. Perimyositis was severe in four, moderate in two, mild in three and absent in three cases. The lesions contained many eosinophils, T-helper cells, mast cells and activated macrophages. Type 2 myofiber atrophy was present in five cases and in one, this was the only pathologic finding. Severe epineurial inflammation was seen in the three sural nerve biopsies. Indirect evidence for peripheral neurologic involvement in three other cases consisted of inflammation surrounding intramuscular nerve twigs (two cases) and neurogenic atrophy (one case). Phlebitis accompanied the connective tissue inflammation in five cases and endarteritis in one. Fasciitis was present in three of four skin biopsies and dermal fibrosis in one.

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

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

Influence of gamma-hydroxybutyrate on the relationship between local cerebral glucose utilization and local cerebral blood flow in the rat brain.

The relationship between local cerebral glucose utilization (LCGU) and local CBF (LCBF) was examined during the action of gamma-hydroxybutyrate (GHB) (900 mg/kg i.v.) in conscious rats. GHB induced discrepant effects on blood flow and metabolism. LCGU was markedly depressed in all structures examined, whereas LCBF was differently affected in that no related changes were observed. Global glucose utilization was markedly depressed (-51%), whereas global blood flow was not significantly altered. The marked dissociation between the changes in global glucose utilization and global blood flow induced by GHB is reflected only to a minor degree in the local values inasmuch as the correlation between LCGU and LCBF was only slightly weakened and its heterogeneity was increased.

Model of kinetic behavior of deoxyglucose in heterogeneous tissues in brain: a reinterpretation of the significance of parameters fitted to homogeneous tissue models.

Effects of tissue heterogeneity on regional CMRglc (rCMRglc) calculated by use of the deoxyglucose (DG) method at 45 min following the pulse of DG were evaluated in simulation studies. A theoretical model was developed to describe the kinetics of DG uptake and metabolism in heterogeneous brain tissues. Rate constants were fitted to simulation data for mixed tissue and rCMRglc computed on the basis of this tissue heterogeneity model. The results were compared with those obtained by use of the original model of the DG method for homogeneous tissue, both without (3K model) and with (4K model) a term to describe an apparent loss of deoxyglucose-6-phosphate (DG-6-P). As a direct consequence of tissue heterogeneity, the effective rate constant for phosphorylation of DG, k3*, declined with time. To compensate for the time-changing k3*, estimates of the dephosphorylation rate constant, k4*, were artifactually high when the 4K model was used, even though no dephosphorylation of DG-6-P actually occurred. The present study demonstrates that the finding of a significant k4*, at least within 45 min following a pulse of DG, may not represent dephosphorylation at all, but rather the consequence of measuring radioactivity in a heterogeneous tissue and applying a model designed for a homogeneous tissue. Furthermore, the high estimates of k4* resulted in significant overestimation of rCMRglc. When rCMRglc was computed with the conventional single-scan or autoradiographic method at 45 min after a pulse of DG, the 3K and tissue heterogeneity models yielded values that were within 5% of the true weighted average value for the heterogeneous tissue as a whole. We conclude that the effects of tissue heterogeneity alone can give the appearance of product loss, even when none occurs, and that the use of the 4K model with the assumption of product loss in the 45-min experimental period recommended for the DG method may lead to overestimation of the rates of glucose utilization.

Metabolites of 2-deoxy-[14C]glucose in plasma and brain: influence on rate of glucose utilization determined with deoxyglucose method in rat brain.

The [14C]deoxyglucose ([14C]DG) method depends upon quantitative trapping of metabolites in brain at the site of phosphorylation, and in the usual procedure it is assumed that all the label in plasma is in free DG. Our previous finding of labeled nonacidic derivatives of DG in plasma raised the possibility that some metabolites of DG might not be fully retained in body tissues and therefore cause overestimation of the integrated specific activity of the precursor pool determined from assay of label in plasma and/or underestimation of the true size of the metabolite fraction in brain. In the present study, metabolism of DG in rat tissues by secondary pathways was examined and found to be more extensive than previously recognized. When 14C-labeled compounds in ethanol extracts of either plasma or brain were separated by anion exchange HPLC, eight fractions were obtained. 14C-labeled metabolites in plasma were detected after a 35-min lag and gradually increased in amount with time after an intravenous pulse. In brain, deoxyglucose-6-phosphate was further metabolized, mainly to deoxyglucose-1-phosphate and deoxyglucose-1,6-phosphate. These are acid-labile compounds and accounted for approximately 20% of the 14C in the metabolite pool in brain. The rate constants for net loss of 14C from the metabolite pool between 45 and 180 min after a pulse were similar (0.4-0.5%/min) in vivo and in intact postmortem brain. The rate constant for loss of deoxyglucose-6-phosphate (DG-6-P) in vivo (approximately 0.7%/min) was, however, about twice that for postmortem brain, suggesting that a significant fraction of the DG-6-P lost in vivo is due to its further metabolism by energy-dependent reactions. 14C-labeled metabolites of [14C]DG in plasma and brain do not interfere with determination of local rates of glucose utilization in brain in normal, conscious rats by the autoradiographic method if the prescribed procedures and a 45-min experimental period are used.

Direct chemical measurement of the lambda of the lumped constant of the [14C]deoxyglucose method in rat brain: effects of arterial plasma glucose level on the distribution spaces of [14C]deoxyglucose and glucose and on lambda.

The lumped constant in the operational equation of the 2-[14C]deoxyglucose (DG) method contains the factor lambda that represents the ratio of the steady-state tissue distribution spaces for [14C]DG and glucose. The lumped constant has been shown to vary with arterial plasma glucose concentration. Predictions based mainly on theoretical grounds have suggested that disproportionate changes in the distribution spaces for [14C]DG and glucose and in the value of lambda are responsible for these variations in the lumped constant. The influence of arterial plasma glucose concentration on the distribution spaces for DG and glucose and on lambda were, therefore, determined in the present studies by direct chemical measurements. The brain was maintained in steady states of delivery and metabolism of DG and glucose by programmed intravenous infusions of both hexoses designed to produce and maintain constant arterial concentrations. Hexose concentrations were assayed in acid extracts of arterial plasma and freeze-blown brain. Graded hyperglycemia up to 28 mM produced progressive decreases in the distribution spaces of both hexoses from their normoglycemic values (e.g., approximately -20% for glucose and -50% for DG at 28 mM). In contrast, graded hypoglycemia progressively reduced the distribution space for glucose and increased the space for [14C]DG. The values for lambda were comparatively stable in normoglycemic and hyperglycemic conditions but rose sharply (e.g., as much as 9-10-fold at 2 mM) in severe hypoglycemia.

Comparative effects of acute and chronic administration of amphetamine on local cerebral glucose utilization in the conscious rat.

The 2-deoxyglucose method was employed in rats following either acute or chronic administration of d-amphetamine. The drug was given either by a single intravenous and/or repeated daily intraperitoneal injections or by osmotic pumps implanted subcutaneously. Each mode of administration resulted in a specific constellation of metabolic effects. Acute doses of d-amphetamine, 5 mg/kg, stimulated glucose utilization in a number of cerebral structures, particularly the components of the extrapyramidal motor system. No effects were observed in components of the mesolimbic dopaminergic system. Repeated daily doses of 5 mg/kg for 2 weeks had no effects unless the dosage was progressively increased to toxic levels of 15 mg/kg over a 3-week period. Dosage sustained by osmotic pumps (12-15 mg/kg/day for 1 week or 6-7 mg/kg/day for 2 weeks), however, resulted in a selected increase in glucose utilization in the nucleus accumbens, an important component of the mesolimbic system. This finding may be of significance to the mechanism of amphetamine psychosis, which is sometimes regarded as a model of schizophrenia and is considered to be evidence in support of the dopamine hypothesis of the disease.

Local cerebral glucose utilization in normal female rats: variations during the estrous cycle and comparison with males.

The quantitative 2-[14C]deoxyglucose autoradiographic method was used to study the fluctuations of energy metabolism in discrete brain regions of female rats during the estrous cycle. A consistent though statistically nonsignificant cyclic variation in average glucose utilization of the brain as a whole was observed. Highest levels of glucose utilization occurred during proestrus and metestrus, whereas lower rates were found during estrus and diestrus. Statistically significant fluctuations were found specifically in the hypothalamus and in some limbic structures. Rates of glucose utilization in the female rat brain were compared with rates in normal male rats. Statistically significant differences between males and females at any stage of the estrous cycle were confined mainly to hypothalamic areas known to be involved in the control of sexual behavior. Glucose utilization in males and females was not significantly different in most other cerebral structures.

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.

Local cerebral blood flow during hibernation, a model of natural tolerance to "cerebral ischemia".

The breakdown of cellular homeostasis and progressive neuronal destruction in cerebral ischemia appears to be mediated by a complex network of causes that are intricately interrelated. We have investigated a physiological state existing normally in nature in which mammals appear to tolerate the ordinarily detrimental effects of ischemia with reduced oxygen availability and to resist activation of self-destructive processes, i.e., mammalian hibernation. Ground squirrels (Spermophilus tridecemlineatus) were chronically implanted with arterial and venous catheters and telemetry devices for electroencephalography, electrocardiography, and monitoring of body temperature. The animals were placed in an environmental chamber at an ambient temperature of 5 degrees C. Entrance into hibernation was characterized by a drop in heart rate followed by a gradual decline in body temperature and an isoelectric electroencephalogram. Cold-adapted active animals that were not hibernating served as controls. Cerebral blood flow (CBF) was measured in both groups with the autoradiographic [14C]iodoantipyrine method. Mean (+/- SD) mass-weighted CBF in the brain was 62 +/- 18 ml 100 g(-1) min (-1) (n = 4) in the control group but was reduced to ischemic levels, 7 +/- 4 ml 100 g(-1) min (-1) (n = 4), in the hibernating animals (p < 0.001) [corrected]. No neuropathological changes were found in similarly hibernating animals aroused from hibernation. Hibernation appears to be actively regulated, and hormonal factors may be involved. The identification and characterization of such factors and of the mechanisms used by hibernating species to increase ischemic tolerance and to blunt the destructive effects of ischemia may enable us to prevent or minimize the loss of homeostatic control during and after cerebral ischemia in other species.