Metabolic and functional consequences of inhibiting adenosine deaminase during renal ischemia in rats.

The concentrations of renal ATP have been measured by 31P-nuclear magnetic resonance (NMR) before, during, and after bilateral renal artery occlusion. Using in vivo NMR, the initial postischemic recovery of ATP increased with the magnitude of the residual nucleotide pool at the end of ischemia. ATP levels after 120 min of reflow correlated with functional recovery at 24 h. In the present study the effect of blocking the degradation of ATP during ischemia upon the postischemic restoration of ATP was investigated. Inhibition of adenosine deaminase by 80% with the tight-binding inhibitor 2'-deoxycoformycin led to a 20% increase in the residual adenine nucleotide pool. This increased the ATP initial recovery after 45 min of ischemia from 52% (in controls) to 62% (in the treated animals), as compared to the basal levels. The inhibition also caused an accelerated postischemic restoration of cellular ATP so that at 120 min it was 83% in treated rats vs. 63% in untreated animals. There was a corresponding improvement in the functional recovery from the insult (increase of 33% in inulin clearance 24 h after the injury). Inhibition of adenosine deaminase during ischemia results in a injury similar to that seen after a shorter period of insult.

Cerebral lactate turnover after electroshock: in vivo measurements by 1H/13C magnetic resonance spectroscopy.

We reported earlier that brain activation by 10 s of cortical electroshock caused prolonged elevation of brain lactate without significant change in intracellular pH, brain high-energy phosphorylated metabolites, or blood gases. The metabolic state of the elevated lactate has been investigated in further experiments using combined, in vivo 1H-observed 13C-edited nuclear magnetic resonance spectroscopy (NMRS), homonuclear J-edited 1H-NMRS, and high-resolution 1H-NMRS of perchloric acid extracts to monitor concentrations and 13C-isotopic fractions of brain and blood lactate and glucose. We now report that electroshock-elevated lactate pool in rabbit brain approaches equilibrium with blood glucose within 1 h. There was nearly complete turnover of the raised lactate pool in brain; any pool of metabolically inactive lactate could not have been > 5% of the total. In the same experiments, blood lactate underwent < 50% turnover in 1 h. The new 1H-spectroscopic methods used for these experiments are readily adaptable for the study of human brain and may be useful in characterizing the metabolic state of elevated lactate pools associated with epilepsy, stroke, trauma, tumors, and other pathological conditions.

Brain creatine kinase with aging in F-344 rats: analysis by saturation transfer magnetic resonance spectroscopy.

We measured in vivo forward flux of the creatine kinase reaction in rat forebrain in young (Y: 6 month, n = 13), mid-aged (M: 12 month, n = 7) and aged (O: 27 month, n = 10) animals using 31P magnetic resonance saturation transfer. Forward flux was reduced in the aged rats (Y: 0.42 +/- 0.08; M: 0.41 +/- 0.10; O: 0.31 +/- 0.03 s(-1) +/- SD; p = 0.008 O vs. Y). In vitro studies in a subset of the same rats showed a parallel decline in CK activity (Y: 2.16 +/- 0.40; M: 2.17 +/- 0.25; O: 1.56 +/- 0.06 IU +/- S.D.; p = 0.002 O vs. Y). The in vivo spectroscopic and in vitro biochemical measures were significantly correlated. Reduced creatine kinase activity could account for the observed decreased forward flux in aging brain. Intracellular pH, phosphocreatine/inorganic phosphate ratio, and phospocreatine/gamma-adenosine triphosphate ratio did not differ between groups. Forward flux may represent a better measure of brain energy function than relative phosphocreatine or adenosine triphosphate levels observable in vivo.

A novel metallo-beta-lactamase, Mbl1b, produced by the environmental bacterium Caulobacter crescentus.

Caulobacter crescentus 101123 possesses a gene (Mbl1b) encoding a metallo-beta-lactamase with 32% amino acid identity to the L1 metallo-beta-lactamase from Stenotrophomonas maltophilia. The gene was cloned into an expression vector and the enzyme, Mbl1b, was expressed in Escherichia coli. Mbl1b was purified. Catalytic properties for several antibiotics were determined. The enzyme exhibits Michaelis-Menten kinetics for imipenem, meropenem and nitrocefin but substrate inhibition kinetics with cefoxitin, cefaloridine, penicillin G and ampicillin. A homology model predicts Mbl1b has the same structural fold as other metallo-beta-lactamases with a detailed structure very similar to L1 but whereas L1 is a homotetramer, Mbl1b is monomeric. The main differences between Mbl1 and L1 are in the N-terminal region.

Cerebrovascular changes in the basal ganglia with HIV dementia.

BACKGROUND: HIV dementia is a form of subcortical dementia. Clinical, radiologic, pathologic, and biochemical studies suggest a major contribution of basal ganglia dysfunction to the pathogenesis of this disorder. Many investigators have proposed a contribution of a disrupted blood-brain barrier (BBB) to the pathogenesis of HIV dementia. OBJECTIVE: To identify microvascular abnormalities in vivo in basal ganglia or white matter of persons with HIV dementia. METHODS: Time course of MRI postcontrast enhancement was determined in basal ganglia and white matter of HIV-infected persons without dementia (Memorial Sloan Kettering [MSK] score of 0; n = 4); HIV-infected persons with mild dementia (MSK score of 0.5; n = 2); and HIV-infected persons with moderate-to-severe dementia (MSK > or = 1.0; n = 6). RESULTS: Increased basal ganglia enhancement was observed in individuals with moderate-to-severe dementia relative to nondemented individuals, both immediately and 30 minutes after contrast administration. Decline of basal ganglia enhancement was slower in the moderately to severely demented patients and, when normalized to intravascular enhancement of sagittal sinus, suggested leakage of contrast agent, consistent with increased permeability of BBB. A significant correlation between the postcontrast fractional enhancement at 30 minutes (FE30) and the MSK score was noted. White matter showed no significant differences in postcontrast enhancement among the three groups. CONCLUSION: Increased early enhancement in basal ganglia of the HIV dementia group is consistent with increased regional cerebral blood volume (rCBV). Increased late enhancement is strongly suggestive of BBB disruption. Similar abnormalities were absent in the white matter adjacent to the caudate nucleus.

Women at risk for AD show increased parietal activation during a fluency task.

BACKGROUND: Imaging studies have shown disparities in resting metabolism and in functional activation between cognitively normal individuals at high and low risk for AD. A recent study has shown increased parietal activation in high-risk subjects during a paired associates recall task, which the authors postulated might overlap activation typically observed in verbal fluency. OBJECTIVE: To determine whether parietal activation is altered in a letter fluency task in cognitively normal individuals at high risk for AD. METHODS: fMRI was used to compare cortical activation between two groups of cognitively normal women differing in their risk for developing AD. A letter fluency task was used, which activates left frontal and parietal regions. The risk groups differed in family history of AD and APOE allele status but were matched in age, education, and measures of cognitive performance. Average age of the study participants was 53 years. RESULTS: The regional patterns of brain activation were similar between groups and similar to patterns observed by other investigators. However, the high-risk group showed significantly increased activation in the left parietal region despite identical letter fluency performance between risk groups. CONCLUSIONS: Cognitively normal individuals at high risk for AD show increased brain activation in the left parietal region with letter fluency, a region adjacent to that observed by others using a recall task. This convergence of results indicates disruption of functional circuits involving the left parietal lobe in asymptomatic individuals at increased risk for AD.

Altered brain activation in cognitively intact individuals at high risk for Alzheimer's disease.

OBJECTIVE: To determine whether brain function is altered in cognitively normal individuals at high risk for AD several years before the typical age at onset for this illness. BACKGROUND: Neuropathologic alterations in AD precede cognitive impairment by several years. It is unknown whether functional alterations in neural circuitry accompany these neuropathologic changes, and if so, whether they may be detectable before onset of symptoms. METHODS: We used functional MRI to compare cortical activation between two groups of cognitively normal women differing only in their risk for developing AD. Visual naming and letter fluency tasks were used to activate brain areas subserving object and face recognition, previously described sites of hypometabolism and neuropathologic alteration in AD. The risk groups differed in family history of AD and apolipoprotein E allele status, but were matched in age, education, and measures of cognitive performance. Average age of the study participants was 52 years. RESULTS: The regional patterns of brain activation were similar between groups. However, the high risk group showed areas of significantly reduced activation in the mid- and posterior inferotemporal regions bilaterally during both tasks despite identical naming and letter fluency performance. CONCLUSIONS: Cognitively normal individuals at high risk for AD demonstrate decreased brain activation in key areas engaged during naming and fluency tasks. Decreased activation in the high risk group may be a consequence of the presence of subclinical neuropathology in the inferotemporal region or in the inputs to that region. If so, these findings provide evidence of a window of opportunity for disease-modifying treatment before the onset of symptomatic AD.

Neural substrates of facial emotion processing using fMRI.

We identified human brain regions involved in the perception of sad, frightened, happy, angry, and neutral facial expressions using functional magnetic resonance imaging (fMRI). Twenty-one healthy right-handed adult volunteers (11 men, 10 women; aged 18-45; mean age 21.6 years) participated in four separate runs, one for each of the four emotions. Participants viewed blocks of emotionally expressive faces alternating with blocks of neutral faces and scrambled images. In comparison with scrambled images, neutral faces activated the fusiform gyri, the right lateral occipital gyrus, the right superior temporal sulcus, the inferior frontal gyri, and the amygdala/entorhinal cortex. In comparisons of emotional and neutral faces, we found that (1) emotional faces elicit increased activation in a subset of cortical regions involved in neutral face processing and in areas not activated by neutral faces; (2) differences in activation as a function of emotion category were most evident in the frontal lobes; (3) men showed a differential neural response depending upon the emotion expressed but women did not.

Cortical activation in confrontation naming.

Functional magnetic resonance imaging was used to detect cortical activation in the right and left perisylvian cortex of seven young adult right-handed volunteers in response to a letter fluency task and to a visual naming task using standardized line drawings. Both letter fluency and visual naming activated left dorsolateral prefrontal cortex (Brodmann's areas 6, 9, 44 and 45). Only visual naming activated area 37 (a cortical region with strong connections to visual association areas), visual association area 19, and areas 39 and 21 previously shown to activate with auditory semantic tasks. This study supports a role for area 37 as participant in a visual lexicosemantic processing network which may otherwise overlap the auditorysemantic network.

13C-NMR measurements of muscle glycogen during low-intensity exercise.

Glycogen metabolism in exercising gastrocnemius muscles was examined by natural abundance 13C nuclear magnetic resonance (NMR) spectroscopy. Five-minute 13C-NMR measurement of muscle glycogen had a reproducibility of +/- 6.5% (+/- 4.8 mM). Experiments were performed on healthy fed male and female subjects. Two protocols were followed. 1) Subjects performed plantar flexion from rest at 15, 20, or 25% of maximum voluntary contraction for up to 9 h. 2) Subjects predepleted gastrocnemius glycogen with heavy exercise and then either performed low-intensity exercise as before or rested. Gastrocnemius glycogen was measured by NMR at rest and after each hour of exercise. In some sessions, both the exercised leg and the nonexercised leg were monitored with 13C-NMR. In protocol 1, blood velocity in the femoral artery was similarly assessed with ultrasonography. During low-intensity exercise from rest (protocol 1) muscle glycogen fell to a new steady-state value after several hours and then remained constant despite continued exercise. Mean blood velocity increased ninefold within 2 min of onset of exercise and remained constant thereafter. After predepletion (protocol 2), muscle glycogen was repleted both during low-intensity exercise and at rest. After 1 h the amount of glycogen repletion was greater when coupled with light exercise [48.5 +/- 2.8 mM after 1 h of exercise, 39.7 +/- 1.1 mM after 1 h of rest (P less than 0.05)]. During subsequent light exercise, glycogen reached a steady-state value similar to that obtained in protocol 1, while in resting, recovery glycogen levels continued to increase (+2.7 mM/h) over a 7-h period.(ABSTRACT TRUNCATED AT 250 WORDS)

Human muscle glycogen resynthesis after exercise: insulin-dependent and -independent phases.

To study the effects of glycogen depletion and insulin concentration on glycogen synthesis, gastrocnemius glycogen was measured with 13C-nuclear magnetic resonance at 4.7 T after exercise. Subjects performed single-leg toe raises to deplete gastrocnemius glycogen to 75, 50, or 25% of resting concentration (protocol I). Insulin dependence of glycogen synthesis was assessed after depletion to 25% with (protocol II) and without (protocol III) infusion of somatostatin to inhibit insulin secretion. After depletion to 75 and 50%, glycogen resynthesis rates were similar (2.4 +/- 0.7 and 2.8 +/- 0.6 mM/h, respectively). When glycogen was depleted to 25% (< 30 mM), the resynthesis rate was significantly higher (P < 0.02) at 33 +/- 7 mM/h, and it declined to 3.5 +/- 0.9 mM/h at > 35 mM glycogen. At < 35 mM glycogen, synthesis was not affected by low insulin (24 +/- 4 mM/h, protocol vs. 19 +/- 3 mM/h, protocol III), whereas at > 35 mM glycogen, synthesis ceased without insulin (-0.07 +/- 0.19 mM/h, protocol II). After depletion to 25% (protocol III), plasma lactate transiently increased (0.81 mM at rest, 1.82 mM 0 h after exercise, and 0.76 mM 2 h after exercise), whereas other plasma constituents did not significantly change. We conclude that after depletion to < 30 mM initial glycogen resynthesis is insulin independent and glycogen dependent, which suggests local control.

Heterogeneity at the beta-lactamase structural gene ampC amongst Citrobacter spp. assessed by polymerase chain reaction analysis: potential for typing at a molecular level.

Considerable biochemical diversity and polynucleotide sequence variation have been reported amongst strains of Citrobacter spp. However, sequence heterogeneity has not been investigated at gene loci of clinical relevance. In this study, sequence heterogeneity in the beta-lactamase structural gene, ampC, amongst 91 clinical isolates of Citrobacter spp. that showed resistance to various third-generation cephalosporins was investigated. Variation was examined by high-stringency polymerase chain reactions (PCR) with primers homologous to the known ampC sequences of C. freundii strains OS60 and I113, and C. diversus NF85. If an isolate contained an ampC gene homologous to one of these three characterised ampC genes, a single PCR band of a predictable size was generated with the appropriate primer set; 50 (60%) of isolates gave a PCR product of the expected size with the OS60 primer set and nine (10%) gave a product with the I113 primer set. All these 59 isolates were identified as C. freundii by API-20E strips. Six isolates (7%) gave a product with the C. diversus NF85 primer set but only four of these were identified as C. diversus in API-20E tests; the other two isolates were identified as C. freundii. Of the 91 isolates, 28 (31%), were identified as either C. freundii or C. diversus, but gave no PCR product with any primer set tested. Five of these showed no homology to any of the reference strain ampC PCR products in hybridisation tests. Nevertheless, all showed beta-lactamase activity. Overall, this method allowed the identification of novel ampC gene loci, which may serve as a basis for the identification of Citrobacter spp. rapidly at a molecular level.

Functional MRI of apomorphine activation of the basal ganglia in awake rhesus monkeys.

Functional magnetic resonance imaging (fMRI) was used to analyze blood oxygen level-dependent (BOLD) responses in the nigrostriatal system (caudate nucleus, putamen and substantia nigra) of awake rhesus monkeys to systemic apomorphine administration. The study (1) measured BOLD responses as an index of neuronal activity in the three structures following injections of the mixed D1/D2 agonist, and (2) assessed the effects of isoflurane anesthesia on the fMRI responses. Compared to control saline injections, 0.1 mg/kg apomorphine significantly activated the caudate nucleus (P < or = 0.005), putamen (P < or = 0.001) and substantia nigra (P < or = 0.005). The responses were consistent with activation of GABAergic neurons in these three structures seen in other animal models. Isoflurane gas measurably blunted the response to apomorphine, so that a significant apomorphine activation was only seen in the substantia nigra of anesthetized animals. Even there, the mean MR signal change was reduced from 9.8% in awake monkeys to 2.3% in anesthetized animals. The data support the hypothesis that fMRI can be used to study the effects of drugs that alter basal ganglia activity in awake rhesus monkeys.

Age-associated changes in rhesus CNS composition identified by MRI.

Multispectral automated segmentation of MR images of the brains of 10 young (5-8 years), 10 middle-aged (12-17 years), and 11 old (21-27 years) female rhesus monkeys revealed age-associated changes in brain volume and composition. Total brain parenchymal volume (expressed as fraction of intracranial volume-%ICV) decreased at a linear rate of 0.3+/-0.04% ICV/year. Up to age approximately 15 years, this loss was almost entirely due to gray matter loss, with a compensatory increase in cerebrospinal fluid (CSF), and possibly some white matter. Brain tissue composition, expressed as the gray matter/white matter volume ratio confirmed that gray matter loss exceeded white matter loss, but the rate of decline in the gray/white ratio began to slow after approximately 15 years. Comparison of these age-associated changes in rhesus brain with those in humans suggest that the brain aging in rhesus is a good model of human brain aging, but occurs approximately 3-fold faster.

Differences in functional magnetic resonance imaging activation by category in a visual confrontation naming task.

OBJECTIVE: Cortical processing involved in seemingly similar tasks may differ in important ways. The authors mapped cortical regions engaged in a commonly performed picture naming task, seeking differences by semantic category. Functional magnetic resonance imaging was used during presentation of standardized line drawings in 18 healthy right-handed female participants, comparing living versus nonliving entities. During visual naming, across categories there was strong activation of left frontal (BA45/47), bilateral temporo-occipital junction (BA19), and inferior temporal regions (BA36/37). Activation of right inferior temporal cortex (BA19 and BA37) was greater during naming of living versus nonliving category items. No category differences in activation strength in the left temporal lobe were observed. The authors conclude that visual semantic operations may involve visual association cortex in the right temporal lobe in women.

Principal component analysis of the dynamic response measured by fMRI: a generalized linear systems framework.

Principal component analysis (PCA) is one of several structure-seeking multivariate statistical techniques, exploratory as well as inferential, that have been proposed recently for the characterization and detection of activation in both PET and fMRI time series data. In particular, PCA is data driven and does not assume that the neural or hemodynamic response reaches some steady state, nor does it involve correlation with any pre-defined or exogenous experimental design template. In this paper, we present a generalized linear systems framework for PCA based on the singular value decomposition (SVD) model for representation of spatio-temporal fMRI data sets. Statistical inference procedures for PCA, including point and interval estimation will be introduced without the constraint of explicit hypotheses about specific task-dependent effects. The principal eigenvectors capture both the spatial and temporal aspects of fMRI data in a progressive fashion; they are inherently matched to unique and uncorrelated features and are ranked in order of the amount of variance explained. PCA also acts as a variation reduction technique, relegating most of the random noise to the trailing components while collecting systematic structure into the leading ones. Features summarizing variability may not directly be those that are the most useful. Further analysis is facilitated through linear subspace methods involving PC rotation and strategies of projection pursuit utilizing a reduced, lower-dimensional natural basis representation that retains most of the information. These properties will be illustrated in the setting of dynamic time-series response data from fMRI experiments involving pharmacological stimulation of the dopaminergic nigro-striatal system in primates.

Mapping drug-induced changes in cerebral R2* by Multiple Gradient Recalled Echo functional MRI.

A multiple Gradient Recalled Echo MRI sequence was used to map spatial and temporal changes in the rate of MR signal decay (R2*) in response to L-3,4-dihydroxyphenylalanine (levodopa) in the striatal dopaminergic system of a rhesus monkey unilaterally lesioned with 4-phenyl-1,2,3,6-tetrahydropyridine hydrochloride (MPTP). R2* decreased significantly in the right (dopamine depleted) putamen and caudate following levodopa. More focal areas of smaller R2* decline were also observed in these structures in the left hemisphere. The observed spatial and temporal patterns of R2* change support the view that the method is monitoring changes in neural activity.

Hepatic perfusion index: a multicentre trial.

The reproducibility and accuracy of the hepatic perfusion index (HPI) was examined by consideration of in vitro and in vivo factors. A phantom was used to simulate liver blood flow and data acquired on nine gamma cameras. Dynamic hepatic scintigraphy was undertaken on 28 patients at two centres and values obtained for the HPI. Results from the phantom study showed good agreement between the nine cameras and also with the HPI values predicted from the measured phantom flow rates. The results of the patient study indicated a high degree of conformity between observers (r = 0.95, S.E = 0.03) but poorer correlation between the HPI values from the two centres (r = 0.67, S.E. = 0.09). These results imply that centres wishing to use HPI clinically should establish their own range of normality.

Intra- and inter-subject variability of high field fMRI digit maps in somatosensory area 3b of new world monkeys.

This study evaluates the intra- and inter-subject variability of digit maps in area 3b of anesthetized squirrel monkeys. Maps were collected using high field blood oxygenation level dependent (BOLD) functional magnetic resonance imaging (fMRI). BOLD responses to individual digit stimulations were mapped and their response properties (location, area of activation, % signal change, time to peak response) were compared within and across imaging sessions separated by up to 20 months. During single digit stimulation using a block design, the spatiotemporal response of the BOLD signal for individual runs within and across sessions and animals was well conserved, with a time to peak BOLD response of 20+/-4 s. The variability in the center of BOLD activation in area 3b was 0.41+/-0.24 mm (mean+/-SD) across individual 5-7 min runs within a scanning session and 0.55+/-0.15 mm across sessions. The average signal change across all animals, runs and sessions was 0.62+/-0.38%, and varied 32% within and 40% across sessions. In a comparison of the stability and reproducibility of the area of single digit activation obtained using three approaches, use of a fixed statistical threshold (P<10(-5)) yielded an average area of 4.8+/-3.5 mm(2) (mean+/-SD), adaptive statistical thresholding 1.32+/-1.259 mm(2) (mean+/-SD), and combined fixed statistical and adaptive BOLD signal amplitude 4.4+/-2.5 mm(2) (mean+/-SD) across image runs and sessions. The somatotopic organization was stable within animals across sessions, while across animals, there was some variation in overall activation pattern and inter-digit distances. These results confirm that BOLD activation maps of single digits in area 3b as characterized by activation center, signal amplitudes, and temporal profile are very stable. The activation sizes determined by various criteria are the most variable measure in this preparation, but adaptive statistical thresholding appears to yield the most stable and reproducible maps. This study serves as a baseline assessment of the limits imposed on the detection of plastic changes by experimental variations of the digit BOLD fMRI activation maps in normal animals, and as an indicator of the likely performance limits in human studies.

Selective potentiation of the metabotropic glutamate receptor subtype 2 blocks phencyclidine-induced hyperlocomotion and brain activation.

Previous preclinical and clinical studies have demonstrated the efficacy of group II metabotropic glutamate receptor (mGluR) agonists as potential antipsychotics. Recent studies utilizing mGluR2-, mGluR3-, and double knockout mice support that the antipsychotic effects of those compounds are mediated by mGluR2. Indeed, biphenyl indanone-A (BINA), an allosteric potentiator of mGluR2, is effective in experimental models of psychosis, blocking phencyclidine (PCP)-induced hyperlocomotion and prepulse inhibition deficits in mice. In this study, we administered the NMDA receptor antagonist PCP (5.6 mg/kg i.p.) to rats, an established animal model predictive of schizophrenia. Here, we show that BINA (32 mg/kg i.p.) attenuated PCP-induced locomotor activity in rats. Using behaviorally relevant doses of BINA and PCP, we performed pharmacological magnetic resonance imaging (phMRI) to assess the specific brain regions that underlie the psychotomimetic effects of PCP, and examined how BINA modulated the PCP-induced functional changes in vivo. In anesthetized rats, acute administration of PCP produced robust, sustained blood oxygenation level-dependent (BOLD) activation in specific cortical, limbic, thalamic, and striatal regions. Pretreatment with BINA suppressed the amplitude of the BOLD response to PCP in the prefrontal cortex, caudaute-putamen, nucleus accumbens, and mediodorsal thalamus. Our results show key brain structures underlying PCP-induced behaviors in a preclinical model of schizophrenia, and, importantly, its reversal by potentiation of mGluR2 by BINA, revealing specific brain regions functionally involved in its pharmacological action. Finally, our findings bolster the growing body of evidence that mGluR2 is a viable target for the treatment of schizophrenia.