Giovanni Lucignani

Measurement of Local Cerebral Blood Flow with [14C]Iodoantipyrine in the Mouse

Local cerebral blood flow was measured in the mouse by means of the [14C]iodoantipyrine method. This method has been previously used in the monkey, dog, cat, and rat, but its application to small mammals such as the mouse requires special attention to potential sources of error. The small size of the mouse brain requires special attention to the rapid removal and freezing of the brain to minimize effects of postmortem diffusion of tracer in the tissue. Because of the relatively low diameter/length ratios of the catheters needed for arterial sampling in small animals, substantial errors can occur in the determination of the time course of the [14C]iodoantipyrine concentration in the arterial blood unless corrections for lag time and dead space washout in the catheter are properly applied. Local cerebral blood flow was measured in seven awake mice with appropriate care to minimize these sources of error. The values were found to vary from 48 ml/100 g/min in the corpus callosum to 198 ml/100 g/min in the inferior colliculus. The results demonstrate that the [14C]iodoantipyrine method can be used to measure local cerebral blood flow in the mouse and that the values in that species are, in general, somewhat higher than those in the rat.

Correlation of dose-dependent effects of acute amphetamine administration on behavior and local cerebral metabolism in rats

Rates of local cerebral glucose utilization were measured by means of the quantitative autoradiographic 2-[14C]deoxyglucose technique in conscious rats following the acute administration of D-amphetamine (0.2-5.0 mg/kg, i.v.). Changes in locomotor and stereotypic behavior in similarly treated rats were examined as well. Administration of low doses (0.2 and 0.5 mg/kg) of amphetamine resulted in increased locomotor activity, accompanied by elevations in glucose utilization limited mainly to the nucleus accumbens. A moderate dose of D-amphetamine (1.0 mg/kg) produced locomotion and stereotypic sniffing. Metabolic activity at this dose was increased in the nucleus accumbens, throughout neocortical areas, and in components of the extrapyramidal system. A high dose of amphetamine (5.0 mg/kg) produced stereotypic gnawing and licking and was associated with significant increases in glucose utilization in the extrapyramidal system, most prominently in the subthalamic nucleus. These data demonstrate that the acute administration of D-amphetamine produces effects on local cerebral glucose utilization and on behavior that differ with dose. The results also show a strong coupling between locomotion and the level of metabolic activity in the nucleus accumbens and demonstrate that the different forms of stereotypic behavior elicited by high and moderate doses of amphetamine are correlated with distinct patterns of distribution of local cerebral glucose utilization, indicating mediation by different neuronal circuits.

Regional cerebral metabolism of glucose in comatose and vegetative state patients

Regional cerebral metabolism of glucose (rCMRglu) was evaluated in patients who were in a coma and vegetative state to determine the level of brain function during these conditions. rCMRglu was measured in 17 discrete brain regions with (/-) [18F] -fluoro-2-deoxy-D-glucose (FDG) and positrn emission tomography (PET) in 15 patients with ;brain pathology subsequent to cardiorespiratory arrest (CA), head trauma (HT), or brain ischemia (BI) resulting from cerebrovascular accident or brain surgery. Five comatose patients (Coma group, n = 5), and 10 vegetative state patients (VS, patients awake but not aware) were studied. The VA patients were subdivided, according to the length of their VS condition, into a VS group (n = 6, < 3 months if CA or BI patients, or < 12 months if HT patients) and a persistent vegetative state group (PVS, n = 4, > 3 months if CA or BI patients of > 12 months if HT patients.) Ten normal age-matched subjects served as control. Global CMRglu was 6.72 +/- 0.93 (+/-SD) mg/100 g/min in control subjects. It was significantly (p < - 0.001) reduced to 3.70 +/- 61 in coma, to 3.45 +/- in VS, and to 2.33 +/- 0.34 mg/100 g/min in PVS patients. rCMRglu was significantly reduced (p < - 01001) from control values in all the 17 structures surveyed in every patient. In the Coma and VS groups, there was an overlapping of rCMRglu in the majority of the brain structures. (ABSTRACT TRUNCATED AT 250 WORDS)

Specificity and sensitivity of exercise-induced ST segment elevation for detection of residual viability : comparison with fluorodeoxyglucose and positron emission tomography

OBJECTIVES We evaluated the sensitivity and specificity of exercise-induced ST segment elevation for the detection of residual myocardial viability. BACKGROUND Assessment of residual viability after myocardial infarction is relevant for establishing indication for revascularization. We have previously shown that exercise-induced ST segment elevation is a marker of residual viability. METHODS We studied 34 patients with a previous Q wave myocardial infarction (anterior in 21, inferior in 13) of whom 18 (group A) had exercise-induced ST segment elevation in more than one lead (mean [+/- SD] 1.8 +/- 0.9 mm, range 1 to 4) and 16 (group B) did not. All patients underwent rest technetium-99m methoxyisobutyl isonitrile single-photon emission computed tomography (SPECT), fluorine-18 (F-18) fluorodeoxyglucose positron emission tomography and coronary angiography. The time elapsed between the infarction and the viability study was 72 +/- 108 days (range 15 to 400) in group A and 516 +/- 545 days (range 14 to 1,800) in group B. RESULTS The presence and site of previous infarction were confirmed by SPECT studies in all 34 patients. Uptake of F-18 fluorodeoxyglucose within the infarcted area was present in 18 of 18 patients in group A but in only 9 (56%) of 16 in group B (p < 0.01). In patients with an anterior infarction, the sensitivity, specificity and predictive accuracy of exercise-induced ST segment elevation for detection of residual viability were 82%, 100% and 86%, respectively (95% confidence intervals 46% to 83.5%, 59% to 100% and 55.6% to 87.1%, respectively). CONCLUSIONS Exercise-induced ST segment elevation in infarct-related leads has a high specificity and acceptable sensitivity for detection of residual viability within the infarcted area.

The lumped constant of the deoxyglucose method in hypoglycemia : effects of moderate hypoglycemia on local cerebral glucose utilization in the rat

The applicability of the [14C]deoxyglucose method for measuring local cerebral glucose utilization (lCMRglc) has been extended for use in hypoglycemia by determination of the values of the lumped constant to be used in rats with plasma glucose concentrations ranging from approximately 2 to 6 mM. Lumped constant values were higher in hypoglycemia and declined from a value of 1.2 at the lowest arterial plasma glucose level (1.9 mM) to about 0.48 in normoglycemia. The distribution of glucose, and therefore also of the lumped constant, was found to remain relatively uniform throughout the brain at the lowest plasma glucose levels studied. lCMRglc in moderate, insulin-induced hypoglycemia (mean arterial plasma glucose concentration ± SD of 2.4 ± 0.3 mM) was determined with the appropriate lumped constant corresponding to the animals plasma glucose concentration and compared with the results obtained in six normoglycemic rats. The weighted average rate of glucose utilization for the brain as a whole was significantly depressed by 14% in the hypoglycemic animals, i.e., 61 μmol/100 g/min in hypoglycemia compared to 71 μmol/100 g/min in the normoglycemic controls (p < 0.05). lCMRglc was lower in 47 of 49 structures examined but statistically significantly below the rate in normoglycemic rats in only six structures (p < 0.05) by multiple comparison statistics. Regions within the brainstem were most prominently affected. The greatest reductions, statistically significant or not, occurred in structures in which glucose utilization is normally high, suggesting that glucose delivery and transport to the tissue became rate-limiting first in those structures with the greatest metabolic demands for glucose.

Influence of Plasma Glucose Concentration on Lumped Constant of the Deoxyglucose Method: Effects of Hyperglycemia in the Rat

The lumped constant of the deoxyglucose method was determined by the steady-state, model-independent method in the brain of normal conscious rats with arterial plasma glucose concentrations varying from normoglycemia (i.e., 8 mM) to hyperglycemia (i.e., 31 mM). The lumped constant for brain was found to decrease very gradually with increasing arterial plasma glucose concentration from a value of ∼0.45 in the midnor-moglycemic range (i.e., 7–8 mM) to ∼0.38 at 28–31 mM. 3-O-[14C]Methylglucose was used to assess the distribution of glucose within the brain structures in hyperglycemia; the results indicated that the glucose concentration, and therefore also the values for the lumped constant, remain relatively uniform in hyperglycemia with arterial plasma glucose concentrations as high as 34 mM. The values for the lumped constant for rat brain determined in the present studies were combined with those previously determined in this laboratory for hypoglycemia and normoglycemia by the same method to provide a single source for the values for the lumped constant to be used over the full range of arterial plasma glucose concentrations. In several rats the lumped constant for cephalic extracerebral tissues was also evaluated in parallel with those for the brain. The lumped constant for the cephalic extracerebral tissues was found to be about twice that for brain and to be unaffected by changes in arterial plasma glucose levels.

Local Cerebral Glucose Utilization in Controlled Graded Levels of Hyperglycemia in the Conscious Rat

Local cerebral glucose utilization assayed by the [14C]deoxyglucose ([14C]DG) method and calculated by means of its operational equation with values for the rate constants and lumped constant determined in rats under physiological conditions remains relatively stable with variations in arterial plasma glucose concentration within the normoglycemic range. Large changes in arterial plasma glucose level may, however, significantly alter the values of these constants and lead to artifactual results. Values for the lumped constant have been measured and reported for a wide range of arterial plasma glucose concentrations ranging from hypoglycemia to hyperglycemia in the rat (Schuier et al., 1981; Suda et al., 1981; Pettigrew et al., 1983). In the present study we have redetermined the rate constants in rats with arterial plasma glucose levels clamped at ∼350, 450, and 550 mg/dl (i.e., 19, 25, and 31 mM) by a glucose clamp technique. The rate constants for the transport of DG from plasma to brain, K*1, and its phosphorylation in tissue, k*3, were found to decline with increasing plasma glucose levels, while the rate constant for its transport back from brain to plasma, k*2, remained relatively unchanged from its value in normoglycemia. These rate constants were used together with the previously determined values for the lumped constants to calculate local rates of cerebral glucose utilization in three groups of rats in which arterial plasma glucose levels were clamped at ∼350, 450, and 550 mg/dl (i.e., 19, 25, and 31 mM). Average glucose utilization in the brain as a whole was unchanged in hyperglycemia from the values calculated in normoglycemic rats with the standard normal set of constants. Changes in the rate of glucose utilization were found, however, in the hypothalamus, globus pallidus, and amygdala during hyperglycemia.

Invalidity of criticisms of the deoxyglucose method based on alleged glucose-6-phosphatase activity in brain.

Abstract: The observations made by Sacks et al. [Neurochem. Rea.8, 661–685 (1983)] on which they based their criticisms of the deoxyglucose method have been examined and found to have no relationship to the conclusions drawn by them. (1) The observations of Sacks et al. (1983) of constant concentrations of [14C]deoxyglucose and [14C]deoxyglucose‐6‐phosphate. predominantly in the form of product, reflects only the postmortem phosphorylation of the precursor during the dissection of the brain in their experiments. When the brains are removed by freeze‐blowing, the time courses of the [14C]deoxyglucose and [14C]deoxyglucose‐6‐phos‐phate concentrations in brain during the 45 min after the intravenous pulse are close to those predicted by the model of the deoxyglucose method. (2) Their observation of a reversal of the cerebral arteriovenous difference from positive to negative for [14C]deoxyglucose and not for [14C]glucose after an intravenous infusion of either tracer is, contrary to their conclusions, not a reflection of glucose‐6‐phosphatase activity in brain but the consequence of the different proportions of the rate constants for efflux and phosphorylation for these two hexoses in brain and is fully predicted by the model of the deoxyglucose method. (3) It is experimentally demonstrated that there is no significant arteriovenous difference for glucose‐6‐phosphate in brain, that infusion of [12P]glucose‐6‐phosphate results in no labeling of brain, and that the blood‐brain barrier is impermeable to glucose‐6‐phosphate. Glucose‐6‐phosphate cannot, therefore, cross the blood‐brain barrier, and the observation by Sacks and coworkers [J. Appl. Physiol.24, 817–827 (1968); Neuro‐chein. Res.8, 661–685 (1983)J of a positive cerebral arteriovenous difference for [14C]glucose‐6‐phosphate and a negative arteriovenous difference for [14C]glucose cannot possibly reflect glucose‐6‐phosphatase activity in brain as concluded by them. Each of the criticisms raised by Sacks et al. has been demonstrated to be devoid of validity.

Different patterns of local brain energy metabolism associated with high and low doses of methylphenidate relevance to its action in hyperactive children

Rates of local cerebral glucose utilization were measured by means of the quantitative autoradiographic [14C]deoxyglucose technique in conscious rats following the acute administration of methylphenidate hydrochloride (1.25-15.0 mg/kg). Significant dose-dependent alterations in metabolic activity were found in the components of the extrapyramidal system, including the substantia nigra, subthalamic nucleus, and the entopeduncular nucleus, as well as in the lateral habenula. Significant changes were also observed in the nucleus accumbens and olfactory tubercle, but occurred only following administration of low doses of methylphenidate. Comparison of the patterns of metabolic activity observed in this study with those obtained following the administration of other psychostimulant drugs suggests possible substrates for the therapeutic action of methylphenidate in the treatment of hyperactive children.

Effects of acute administration of caffeine on local cerebral glucose utilization in the rat

The quantitative 2-[14C]deoxyglucose autoradiographic method was used to study the effects of acute intravenous injections (15 min prior to study) of caffeine on brain energy metabolism. With doses of 0.1 mg/kg the effects of caffeine on cerebral glucose utilization were limited to the habenula, spinal trigeminal and paraventricular nuclei. After the 1.0 mg/kg dose significant increases were additionally seen in the caudate, ventral tegmental area and medial septum. After the injection of 10 mg/kg of caffeine, average glucose utilization of the brain as a whole was increased by 15%, and of 71 structures examined 31 structures were statistically significantly affected. Among these were all brainstem monoaminergic cell groupings, components of the extrapyramidal motor system, anterior cingulate, and medial prefrontal cortex. In the hypothalamus glucose utilization increased only in the paraventricular nucleus, arcuate nucleus, and median eminence. This study demonstrates that there is a correlation between the known stimulant effects of caffeine on behavior and widespread increases in glucose utilization throughout the brain.