Glutamate-induced calcium loads: effects on energy metabolism and neuronal viability

1. Glutamate-induced increases in intracellular free Ca2+ concentration ([Ca2+]i) were recorded from cultured rat hippocampal neurons with single cell microfluorometry. The [Ca2+]i increase did not correlate with glutamate-induced cell death, consistent with the idea that Ca2+ accumulates in an intracellular store, and that loading this store might be toxic. 2. Glutamate-induced Ca2+ loads were buffered by a low-affinity, high-capacity process that was inhibited by the mitochondrial uncoupling agent FCCP and modulated by intracellular Na+. 3. Glutamate-induced Ca2+ loads also produced an intracellular acidification. The acidification was prevented by the metabolic inhibitor 2-deoxyglucose, mimicked by Ba2+, and inhibited by microinjection of ruthenium red. 4. These data are consistent with the hypothesis that mitochondria sequester glutamate-induced Ca2+ loads producing a metabolic acidosis; metabolic stress may contribute to glutamate-induced neuronal death.

Antiinflammatory drug effects on bone repair and remodeling in rabbits

Ketorolac and methylprednisolone effects on bone repair were studied. Demineralized bone matrix was used to graft the defects of rabbits' ulnae. Twenty-seven rabbits were divided into 4 groups: Group A (control group; no drug treatment), Group B (treated with ketorolac 2 mg/kg body weight daily), Group C (treated with ketorolac 4 mg/kg body weight daily), and Group D (treated with methylprednisolone 1 mg/kg body weight weekly). Drug treatment was continued for 6 weeks. The biomechanical results indicated methylprednisolone significantly deteriorated the mechanical properties of the grafted ulnae and the contralateral intact ulnae, although the effects were more pronounced in the grafted side. In Group B, there was minimum effect of ketorolac on the bone properties. In Group C, ketorolac significantly decreased the torsional stiffness and energy absorption of the grafted ulnae and also decreased the maximum torque in the intact and the grafted bones. It was concluded that the inhibitory effect of ketorolac on bone repair was dose dependent. In comparing the effects of ketorolac and methylprednisolone, the latter is more pronounced on torsional stiffness, but the effects on maximum torque and energy absorption were similar to ketorolac. The mechanism of the effects of ketorolac needs additional investigation.

Regional brain metabolic response to lorazepam in subjects at risk for alcoholism

The mechanisms underlying the blunted response to alcohol administration observed in subjects at risk for alcoholism are poorly understood and may involve GABA-benzodiazepine receptors. The purpose of this study was to investigate if subjects at risk for alcoholism had abnormalities in brain GABA-benzodiazepine receptor function. This study measured the effects of 30 micrograms/kg (i.v.) of lorazepam, on regional brain glucose metabolism using positron emission tomography and 2-deoxy-2[18F]fluoro-D-glucose in subjects with a positive family history for alcoholism (FP) (n = 12) and compared their response with that of subjects with a negative family history for alcoholism (FN) (n = 21). At baseline, FP subjects showed lower cerebellar metabolism than FN. Lorazepam decreased whole-brain glucose metabolism, and FP subjects showed a similar response to FN in cortical and subcortical regions, but FP showed a blunted response in cerebellum. Lorazepam-induced changes in cerebellar metabolism correlated with its motor effects. The decreased cerebellar baseline metabolism in FP as well as the blunted cerebellar response to lorazepam challenge may reflect disrupted activity of benzodiazepine-GABA receptors in cerebellum. These changes could account for the decreased sensitivity to the motor effects of alcohol and benzodiazepines in FP subjects.

Depression of thalamic metabolism by lorazepam is associated with sleepiness

Though it is well recognized that the pharmacological actions of benzodiazepines are mediated by facilitation of GABAergic neurotransmission, the consequences of these changes in regional brain function are not well understood. This study measured regional brain glucose metabolism using Positron Emission Tomography and 2-deoxy-2[18F]fluoro-D-glucose in normal controls (n = 21) investigated with and without lorazepam (30 micrograms/kg IV) and with flumazenil given after lorazepam (n = 9). Lorazepam markedly decreased metabolism in thalamus (23 +/- 8%) and occipital cortex (19 +/- 8%), and flumazenil partially reversed these changes. Changes in metabolic activity in thalamus were significantly correlated with lorazepam-induced sleepiness (r = .69, df 20, p < .0005) and there was a trend of an association between the reversal by flumazenil of lorazepam-induced change in thalamus and in sleepiness (r = .63, df 8, p = .07). Benzodiazepine-induced changes in thalamic activity may account for their sedative properties.

Serotonin 5-HT2 receptor availability in chronic cocaine abusers

Serotonin 5-HT2 receptor availability was evaluated in chronic cocaine abusers (n = 19) using positron emission tomography and F-18 N-methylspiperone and was compared to control subjects (n =19). 5-HT2 Receptor availability was measured in frontal, occipital, cingulate and orbitofrontal cortices using the ratio of the distribution volume in the region of interest to that in the cerebellum which is a function of Bmax/Kd. 5-HT2 Receptor availability was significantly higher in cingulate and orbitofrontal cortices than in other frontal regions or occipital cortex. The values were not different in normal subjects and cocaine abusers. These results did not show any changes in 5-HT2 receptor availability in cocaine abusers as compared to the control subjects.

Intracellular acidification is not a prerequisite for glutamate-triggered death of cultured hippocampal neurons

Glutamate decreased intracellular pH (pHi) in cultured rat hippocampal neurons. The protonophore, FCCP (1 microM), produced an acidification comparable to that produced by glutamate. Application of glutamate to FCCP-treated cells, returned pHi to resting levels. This alkaline shift resulted from a glutamate-induced membrane depolarization that removed the driving force across the plasmalemma for H+ entry via FCCP. The endogenous protonophore, arachidonic acid (10 microM), produced pHi changes similar to those elicited by FCCP. Because application of glutamate and FCCP in combination did not change pHi, this treatment was used to determine the role of glutamate-induced acidification in neurotoxicity. FCCP (1 microM, 5 min) did not affect neuronal viability, either alone or in combination with various concentrations of glutamate, as indicated by the release of lactate dehydrogenase into the bathing medium. Thus, acidification was not the cause of glutamate-induced cell death although, it may be symptomatic of neurotoxic processes.

Evaluation of age-related changes in serotonin 5-HT2 and dopamine D2 receptor availability in healthy human subjects

We assessed the relation between serotonin 5-HT2 receptor availability and aging and compared it with that for dopamine D2 receptors on 19 healthy male volunteers (age range, 21-49 years) using positron emission tomography (PET) and F-18 N-methylspiperone (NMS). 5-HT2 Receptor availability was obtained using the ratio of the distribution volume in the region of interest to that in the cerebellum (Bmax'/Kd' + 1). 5-HT2 Receptor measures were obtained in frontal and occipital cortices. D2 receptor availability in striatum was measured using the "ratio index". 5-HT2 Receptor availability decreased significantly with age. This effect was significantly more accentuated for 5-HT2 receptor availability in the frontal (r = 0.92, p < or = 0.0001) than in the occipital (r = 0.67, p < or = 0.0016) cortex (df = 1, p < 0.025). Dopamine D2 receptors were also found to decrease significantly with age (r = 0.63, p < or = 0.007). In a given subject, striatal D2 receptor availability significantly correlated with 5-HT2 receptor availability in the frontal (r = 0.51, p < or = 0.035) but not in the occipital cortex. These results document a decline in 5-HT2 and D2 receptor availability with age and showed an association between frontal 5-HT2 and striatal D2 receptors.

Age-related changes in brain: II. Positron emission tomography of frontal and temporal lobe glucose metabolism in normal subjects

While many neuropsychological studies have demonstrated age-related performance alterations in tests thought to reflect frontal and temporal lobe function, there is little direct observation and comparison of these hypothesized brain changes in vivo. The cerebral glucose metabolism of frontal, temporal, and cerebellar regions was examined in 40 young (mean = 27.5 +/- 4.9) and 31 elderly (mean = 67.6 +/- 8.8) normal males using PET-FDG. Univariate analysis showed age-related metabolic reductions in all frontal and temporal lobe regions. The reductions ranged from 13%-24% with the greatest changes in the frontal lobes. Multiple regression analyses showed a stronger age relationship with frontal lobe than with temporal lobe metabolism. The dorsal lateral frontal lobe was the region that appears to change most within the frontal lobes. Examination of the temporal lobe showed that age contributed equally to the metabolic variance of both the lateral temporal lobe and hippocampus. These results suggest that age-related metabolic changes exist in both frontal and temporal lobes and that the frontal lobe change is greater.

Haloperidol blocks the uptake of [18F]N-methylspiroperidol by extrastriatal dopamine receptors in schizophrenic patients

We had previously demonstrated extrastriatal uptake of [18F]N-methylspiroperidol (18F-NMS) in the human brain. This study evaluates the effect of haloperidol on 18F-NMS binding in extrastriatal brain regions. Six schizophrenic patients on haloperidol underwent two PET scans with 18F-NMS at 12 h and at 6 days after haloperidol withdrawal. There was a significant increase in 18F-NMS uptake in striatal, thalamic, and temporal regions but not in frontal, occipital, or cerebellar regions, following drug withdrawal. Haloperidol's ability to block the uptake of 18F-NMS is an indication of the specificity of the radioligand's binding in these regions and supports the postmortem data demonstrating the presence of dopamine D2 receptors in the thalamus and temporal cortex of the human brain.

Fungal virus capsids, cytoplasmic compartments for the replication of double-stranded RNA, formed as icosahedral shells of asymmetric Gag dimers

The primary functions of most virus capsids are to protect the viral genome in the extra-cellular milieu and deliver it to the host. In contrast, the capsids of fungal viruses, like the cores of all other known double stranded RNA viruses, are not involved in host recognition but do shield their genomes, and they also carry out transcription and replication. Nascent (+) strands are extruded from transcribing virions. The capsids of the yeast virus L-A are composed of Gag (capsid protein; 76 kDa), with a few molecules of Gag-Pol (170 kDa). Analysis of these 420 A diameter shells and those of the fungal P4 virus by cryo-electron microscopy and image reconstruction shows that they share the same novel icosahedral structure. Both capsids consist of 60 equivalent Gag dimers, whose two subunits occupy non-equivalent bonding environments. Stoichiometry data on other double-stranded RNA viruses indicate that the 120-subunit structure is widespread, implying that this molecular architecture has features that are particularly favorable to the design of a capsid that is also a biosynthetic compartment.

Glutamate-induced intracellular acidification of cultured hippocampal neurons demonstrates altered energy metabolism resulting from Ca2+ loads

1. Glutamate-evoked increases in intracellular free H+ concentration ([H+]i) were recorded from single rat hippocampal neurons grown in primary culture with carboxy SNARF-based dual emission microfluorimetry. The possibility that this acidification resulted from altered energy metabolism was investigated. 2. The response to 10 microM glutamate (delta pH = 0.41 +/- 0.14, mean +/- SD) was blocked by the N-methyl-D-aspartate (NMDA) receptor antagonist CGS19755 (10 microM) and required extracellular Ca2+. 3. Substituting the metabolic inhibitor 2-deoxyglucose for glucose in the extracellular buffer prevented glutamate-induced acidification. 4. Ba2+, which carries charge through Ca2+ channels, including the Ca2+ uniporter on the inner mitochondrial membrane, substituted for Ca2+ in mediating glutamate-induced cytoplasmic acidification. 5. Microinjection of ruthenium red, a compound that blocks mitochondrial Ca2+ sequestration, significantly inhibited glutamate-induced acidification. 6. The mitochondrial uncoupler, carbonyl cyanide-p-trifluoromethoxyphenyl-hydrazone (FCCP, 0.1 microM), mimicked and partially occluded the glutamate-induced [H+]i increase. 7. These findings indicate that glutamate-induced Ca2+ loads are sequestered by mitochondria, uncouple respiration, and produce metabolic acidosis. The glutamate-induced acidification is symptomatic of metabolic stress and may indicate that mitochondria play an important role in glutamate-induced neuronal death.

Effects of blood flow on [11C]raclopride binding in the brain: model simulations and kinetic analysis of PET data

To assess the stability of different measures of receptor occupancy from [11C]raclopride (a D2 antagonist) studies with positron emission tomography, we analyze data from five test/retest studies in normal volunteers in terms of individual model parameters from a three-compartment model, the distribution volume (DV) and the ratio of DVs from a receptor-containing region of interest to a non-receptor-containing region. Large variations were found in the individual model parameters, limiting their usefulness as an indicator of change in receptor systems. The DV ratio showed the smallest variation. Individual differences were reflected in the greater intersubject variation in DV than intrasubject variation. The potential effects of blood flow on these measurements were addressed both experimentally and by simulation studies using three models that explicitly incorporate blood flow into a compartmental model that also includes receptor-ligand binding. None of the models showed any variation in the DV with changes in blood flow as long as flow was held constant during the simulation. Experimentally, blood flow was significantly reduced by hyperventilation in a human subject. The DV was found to be reduced relative to baseline in the hyperventilation study, but the DV ratio remained unchanged. The effect of elevated and reduced flow was also tested in two baboon experiments in which PCO2 was varied. Some variability in the DV ratio was observed but was not correlated with changes in blood flow. This raises the possibility that other factors indirectly related to changes in blood flow (or PCO2) may cause changes in DV, and these effects need to be considered when evaluating experimental results.

Slow recovery of human brain MAO B after L-deprenyl (Selegeline) withdrawal

L-Deprenyl (Selegeline) is an enzyme-activated irreversible inhibitor of monoamine oxidase B (MAO B; EC 1.4.3.4). It is used to treat Parkinson's disease at a dose of 5 mg twice a day. Since enzyme inhibition is irreversible, the recovery of functional enzyme activity after withdrawal from L-deprenyl requires the synthesis of new enzyme. We have measured a 40 day half-time for brain MAO B synthesis in Parkinson's disease and in normal subjects after withdrawal from L-deprenyl. This is the first measurement of the synthesis rate of a specific protein in the living human brain. L-Deprenyl is currently used by 50,000 patients with Parkinson's disease in the United States and its use is expected to increase with reports that it may be beneficial in Alzheimer's disease. The slow turnover of brain MAO B suggests that the current clinical dose of L-deprenyl may be excessive and that the clinical efficacy of reduced dosing should be evaluated. Such an evaluation may have mechanistic importance as well as an impact on reducing the side effects and the costs arising from excessive drug use.

Intersubject variability of brain glucose metabolic measurements in young normal males

This study evaluates intersubject variability on regional glucose metabolic values in a group of 50 healthy right-handed males between 20 and 40 yr of age.

METHODS

Brain glucose metabolism was measured using PET and 2-deoxy-2[18F]fluoro-D-glucose under resting conditions and was separately assessed for subjects in their twenties (n = 34) and those in their thirties (n = 16).

RESULTS

Regional brain metabolic values showed significant intersubject variability with coefficients of variation (CV) that ranged between 11.1% to 15.2% (twenties) and 7.2% to 12.6% (thirties). Relative measures (regional/global) were less variable than absolute measures and the CV ranged between 4.1% to 8.3% (twenties) and 3.9% to 10% (thirties). Whereas global brain metabolic rate for subjects in their twenties was not significantly different from that of subjects in their thirties, the metabolic rate in left frontal regions was significantly lower in the older subjects.

CONCLUSION

The correlations between age and absolute and relative metabolism in the left frontal region were r = 0.438, p < 0.002 and r = 0.447, p < 0.001, respectively. This study shows significant intersubject variability for regional brain metabolic values in normal controls and documents age-related decreases in frontal metabolism that occur even in relatively young adults.

Effects of pollen from Typha angustata on the osteoinductive potential of demineralized bone matrix in rat calvarial defects

Typha angustata Bony et Chaub. is a traditional Chinese medicine, commonly used in China for a variety of clinical disorders, including atherosclerosis, cardiovascular diseases, uterus contraction, and wound healing. The effect of the pollen of Typha angustata on the bone inductive capacity of demineralized bone matrix is studied here. Demineralized bone matrix soaked with saline solution was implanted in 8-mm defects in rat calvaria. After surgery all rats received a 0.2-ml injection in the defect sites of Typha angustata extract, plasma, or saline 3 times weekly for 2 to 4 weeks. The repair of bone defects was evaluated by radiography and by histology at 2 and 4 weeks after surgery. Results indicated that the 3% Typha angustata extract and demineralized bone matrix combination produced substantially more bone than demineralized bone matrix alone, while plasma plus demineralized bone matrix induced the same amount of bone formation as Typha angustata extract plus demineralized bone matrix. The osteoinductive potential increased in a dose dependent manner, 3% Typha angustata extract plus demineralized bone matrix produced more bone than the 0.6% Typha angustata extract plus demineralized bone matrix at 2 and 4 weeks. This study demonstrates that an extract of the pollen of Typha angustata is capable of enhancing the osteoinductive potential of demineralized bone matrix.

Decreased dopamine transporters with age in health human subjects

The effects of aging on brain dopamine transporters was evaluated in 26 healthy male volunteers (age range, 21-63 years) using positron emission tomography and [11C]cocaine. The ratio of the distribution volume for [11C]cocaine in basal ganglia to that in cerebellum was used as a model parameter for dopamine transporter availability and showed a significant negative correlation with age (r = 0.65, p < 0.0005). This results document an age-related decline in dopamine transporters in healthy individuals.

Imaging endogenous dopamine competition with [11C]raclopride in the human brain

This study images dopamine release in response to a neurochemically specific challenge with the psychostimulant drug methylphenidate. Changes in synaptic dopamine induced by methylphenidate were evaluated with positron emission tomography and [11C]raclopride, a D2 receptor radioligand that is sensitive to endogenous dopamine. Methylphenidate significantly decreased striatal [11C]raclopride binding. The decrease was variable and was negatively correlated with age. Mood and anxiety at baseline, were also correlated with methylphenidate-induced DA changes. This strategy provides a tool to investigate the responsiveness of the dopamine system in the normal and diseased human brain and to investigate the neurochemical correlates of behavior.

Quantitative autoradiographic measurement of cocaine-induced regional myocardial metabolic changes in hypertensive rats

A rat model of hypertensive cardiomyopathy was studied to evaluate the acute effects of cocaine on the myocardium. Using autoradiographic microimaging techniques, myocardial perfusion (201Tl) and energy substrate utilization (glucose: [14C]2-fluoro-2-deoxy-D-glucose-[14C]2DG and fatty acid (15-[p-iodophenyl])-3-R,S-methyl pentadecanoic acid-[131I]BMIPP) were studied in Dahl strain salt-sensitive normotensive and hypertensive rats with and without intravenous cocaine. The right ventricle, septum, endocardium and epicardium of the left ventricle were analyzed. Increased perfusion (18%) was seen in the myocardium of the hypertensive rats as compared to the normotensive rats. There was higher [14C]2DG (254%) and lower fatty acid (13.2%) uptake in the hypertensive rats, indicative of a shift from aerobic to anaerobic substrate utilization. In cocaine-treated normotensive rats, a generalized decrease in myocardial perfusion (30%) and increased glucose metabolism (89%) was seen. In cocaine-treated hypertensive rats, the increased myocardial perfusion (16%) was heterogeneous and was more pronounced in septum and epicardium. The endocardium and epicardium in the hypertensive rats showed an overall increase (23%) in glucose utilization after cocaine which was not as dramatic as was seen in the normotensive heart and a slight increase in fatty acid utilization. These results are consistent with prior observations that under pressure overload the myocardium responds non-uniformly. It may well be that the hypertensive cardiomyopathic heart is unable to respond to the challenge of cocaine by further increasing glucose utilization. These data obtained in an animal model of hypertension seem to indicate that hypertension may increase the risk of cardiac complications related to cocaine.

Recovery of brain glucose metabolism in detoxified alcoholics

OBJECTIVE

To differentiate withdrawal-related abnormalities in brain glucose metabolism among alcoholics from abnormalities that may be irreversible or antedate alcohol use, the authors evaluated metabolic recovery during alcohol detoxification.

METHOD

Regional brain glucose metabolism was measured with positron emission tomography and 2-deoxy-2-[18F]fluoro-D-glucose in 10 male alcoholics at 8-15 days, 16-30 days, and 31-60 days after last use of alcohol. The alcoholics' metabolic values were compared with those of 10 age-matched male healthy volunteers.

RESULTS

Brain metabolism increased significantly during detoxification. There were significant differences in global and regional measures between the first and last time points but not between the second and third points, suggesting that recovery occurred predominantly within 16-30 days. Regional increases in metabolism were greater in the frontal regions. Whereas during the first evaluation the alcoholics showed significantly lower metabolism in various brain regions than the comparison group, at the end of detoxification the alcoholics showed significantly lower absolute and relative metabolic values in the basal ganglia and lower relative metabolic values in the parietal cortex. Among the alcoholics, but not the comparison group, metabolism in the frontal, parietal, and left temporal cortexes was negatively correlated with years of alcohol use and with age.

CONCLUSIONS

This study shows significant increases in brain metabolism during alcohol withdrawal and documents persistent low metabolic levels in the basal ganglia of detoxified alcoholics.

Methylphenidate decreases regional cerebral blood flow in normal human subjects

To assess the effects of methylphenidate (MP) on cerebral blood flow (CBF), 5 healthy males were studied using 15O-water and positron emission tomography before and after MP (0.5 mg/kg iv). MP significantly decreased whole brain CBF at 5-10 minutes (25 +/- 11%) and at 30 minutes (20 +/- 10%) after its administration. Decrements in CBF were homogeneous throughout the brain (regional decrements 23-30%) and probably reflect the vasoactive properties of MP. The vasoactive properties of MP should be considered when prescribing this drug chronically and/or when giving it to subjects with cerebrovascular compromise.

Spatial and temporal distribution of cocaine and effects of pharmacological interventions: wholebody autoradiographic microimaging studies

Whole body timed distribution of pharmacological doses of 14C-cocaine was studied in rats using quantitative autoradiographic microimaging. Rapid, intense uptake was seen in the brain, spinal cord, adrenals and nuchal brown fat pad. Clearance of cocaine was fastest from the cerebellum. Cortex activity reached soft tissue activity within 20 min. Uptake in the heart and adrenals was very intense following the same time course as in the brain. Kidney activity increased gradually at the same time as in the liver, probably representing specific binding as well as an excretory pathway of cocaine. Desipramine decreased uptake in the heart and adrenals and a piperazine derivative (GBR 12909) caused decreased uptake in the brain, heart and adrenals. Scopolamine, pentobarbital and cold cocaine caused decreased uptake in all organs and increased uptake (excretion) in the liver. Thus, cocaine appears to bind in the brain to the dopamine transporter and to a lesser extent to transporters for norepinephrine and serotonin. In the heart cocaine binds to norepinephrine, serotonin and dopamine. The targeting of cocaine to specific organs and the time sequence correspond to the pharmacological effects of cocaine.

Positron emission tomography study of human prostatic adenocarcinoma using carbon-11 putrescine

To evaluate [1-11C]putrescine ([11C]PUT) as a potential tracer for imaging and characterization of human prostatic adenocarcinoma, positron emission tomography (PET) was performed in eight patients and three normal controls. In addition, four of the patients and the three normal controls also had a prostate scan with 2-deoxy-2-[18F]fluoro-D-glucose (18FDG). Three of the patients had undergone resection of the prostate tumor and all of the patients except for one had bone metastasis. Carbon-11 rapidly accumulated in prostate, bone and rectum after injection of [11C]PUT. Maximal uptake was achieved 5 min after injection with minimal washout during the 50 min study period. The uptake of carbon-11 in the prostate of normal controls was significantly higher than that in the patients. However, three of the four patients scanned for metastatic bone lesions showed higher uptake in bone metastasis than in normal bone. Quantitation of 18FDG uptake in the prostate was hindered by the high accumulation of activity in the urinary bladder. [11C]PUT does not appear to be a useful tracer for assessing proliferation of human prostate adenocarcinoma. Its utility in the imaging of other cancers with high polyamine concentration remains to be investigated.

Monoamine oxidase B (MAO B) inhibitor therapy in Parkinson's disease: the degree and reversibility of human brain MAO B inhibition by Ro 19 6327

The possibility of slowing the progression of Parkinson's disease (PD) with inhibitors of monoamine oxidase B (MAO B) has stimulated the development of new MAO B inhibitor drugs. Ro 19 6327 is a highly selective inhibitor of MAO B currently under clinical investigation. We used positron emission tomography (PET) and the MAO B tracer [11C]L-deprenyl to determine the degree and reversibility of human brain MAO B inhibition by Ro 19 6327 in six early Parkinson's disease patients who were treated with different doses of Ro 19 6327 (25 mg [n = 3], 50 mg [n = 2], and 100 mg [n = 1]; 0.34 to 1.4 mg/kg) every 12 hours for 1 week. Each patient had three PET scans to assess baseline MAO B activity, degree of trough inhibition, and reversibility. A control group of four elderly normal subjects was scanned twice to assess reproducibility of repeated measures. Four of the patients showed reduction of MAO B concentration to 1% to 7% of baseline on doses of 0.43 mg/kg or greater, and the remaining two at 0.34 mg/kg showed significant but incomplete inhibition (10% to 21% of baseline in the global region and in the thalamus, basal ganglia, and mesencephalon). Thus, 0.4 mg/kg or greater of Ro 19 6327 given every 12 hours is the minimum dose necessary to provide > 90% inhibition of brain MAO B in patients with early PD. Brain MAO B activity returned to baseline values by 36 hours after drug discontinuation.

Demineralized bone matrix in the stabilization of porous-coated implants in bone defects in rabbits

Three types of grafts were investigated in rabbits to measure fixation strength of bony ingrowth into porous-coated titanium alloy implants. Autogeneic iliac crest bone (ABG), allogeneic demineralized bone matrix (DBM), and DBM augmented with fibrin glue (DBM + FG) grafts were compared with a press-fit implant control group. Initially, the ABG group required eight weeks and the DBM and DBM + FG groups 12 weeks to achieve fixation strength similar to that of the press-fit group at four weeks. Strength increased with time and at 16 weeks reached 83 kg in the ABG group, 71 kg in the DBM group, and 79 kg in the DBM + FG group, compared with 86 kg for the press-fit group. The ratio of the DBM and the DBM + FG group push-out forces to the ABG push-out force improved from 40% at four weeks to more than 80% at 16 weeks. Histologic analysis of bone ingrowth showed that at 12 weeks, bony ingrowth accounted for 21%, 22%, 16%, and 32% of the porous area in the ABG, DBM, DBM + FG, and press-fit groups, respectively. After eight weeks, there was no statistical difference between DBM, DBM + FG, and ABG grafts in either strength or bony ingrowth. The results demonstrate that over long periods, DBM grafts provide fixation stability comparable with that of autogeneic bone graft.

Decreased dopamine D2 receptor availability is associated with reduced frontal metabolism in cocaine abusers

Decreased dopaminergic function has been postulated to underlie cocaine addiction. To examine the possibility that dysfunction of brain regions subserved by the dopamine system could promote cocaine self-administration, positron emission tomography and a dual-tracer approach was used to examine dopamine D2 receptor availability and regional brain glucose metabolism in cocaine abusers. When compared to normal controls, cocaine abusers showed significant decreases in dopamine D2 receptor availability which persisted 3-4 months after detoxification. Decreases in dopamine D2 receptor availability were associated with decreased metabolism in several regions of the frontal lobes, most markedly orbito-frontal cortex and cingulate gyri. Dopamine dysregulation of these brain areas which are involved in the channeling of drive and affect could lead to loss of control resulting in compulsive drug-taking behavior.

Reproducibility of repeated measures of carbon-11-raclopride binding in the human brain

Carbon-11-raclopride has been successfully utilized with PET to assess changes in endogenous dopamine concentration after pharmacological intervention in the living baboon brain. For similar studies to be done in humans, measurements of 11C-raclopride with no intervention need to be reproducible. In order to test the reproducibility (test-retest) of 11C-raclopride binding in the human brain, we performed repeated studies on two different days. Studies were done in five normal controls with no pharmacological intervention. Time-activity (%dose/cc) curves for 11C-raclopride in the basal ganglia (BG) and cerebellum (CBL) were highly reproducible with an average difference in peak uptake for repeated studies in the same individual of 4%. The BG to CBL ratio for the average activity concentration between 30 and 60 min showed differences that ranged from -7% to 8% between the repeated studies. Graphical analysis to obtain the distribution volume revealed intrasubject values that ranged from -9% to 7% for the ratio of the distribution volume in BG to that in CBL. These studies demonstrate that in order to use 11C-raclopride to measure an individual's change in relative dopamine concentration secondary to pharmacological or behavioral intervention, a change in striatal 11C-raclopride binding in excess of 10% is required.

Decreased cerebral response to inhibitory neurotransmission in alcoholics

OBJECTIVE

Changes in gamma-aminobutyric acid (GABA)-benzodiazepine receptor function have been implicated in alcohol tolerance, withdrawal, and dependence. The purpose of this study was to investigate whether recently detoxified alcoholic subjects had abnormalities in brain GABA-benzodiazepine receptor function.

METHOD

The effect of 30 micrograms/kg of lorazepam on regional brain glucose metabolism was studied in 12 normal subjects and 10 alcoholic subjects with the use of positron emission tomography and [18F]fluorodeoxyglucose.

RESULTS

Lorazepam decreased whole brain glucose metabolism in both the normal subjects (13% change) and the alcoholic subjects (10% change), and the response was correlated with the concentration of lorazepam in plasma. Whereas the normal and alcoholic subjects showed similar responses to lorazepam in occipital and cerebellar metabolism, the alcoholic subjects showed significantly less of a response than the comparison subjects in the thalamus, basal ganglia, and orbitofrontal cortex. The rate of response in the orbitofrontal cortex was significantly correlated with cerebellar metabolism at baseline.

CONCLUSIONS

The alcoholic subjects had a blunted response to lorazepam that was specific to certain brain regions. The association between cerebellar metabolism and response to lorazepam suggests that the cerebellum may contribute to the decreased sensitivity to lorazepam which was seen in the alcoholic subjects.

Abscess scintigraphy with 99mTc-human immunoglobulin (IgG) using a one-step labeling method

It was shown earlier that non-specific human gamma globulin (IgG) labeled with 111In can be used as an agent for abscess localization. We describe experimental results with 99mTc-IgG in animals bearing abscesses and tumors using a one-step labeling method with 99mTc. We studied this compound in several animal models: mice bearing turpentine abscesses and subcutaneously transplanted sarcomas, in rats with turpentine or E. coli abscesses and intracerebrally implanted gliomas and in rabbits with E. coli or turpentine abscesses. Blood clearance was studied in dogs. It was found that the absolute concentration of 111In-IgG in abscess and tumor was higher than that of 99mTc-IgG. However, the abscess-to-tumor ratio was higher for 99mTc-IgG. The 99mTc-IgG images were of high quality and abscesses could be detected as early as 30 min post-injection (p.i.). It appears that 99mTc-IgG has many potential advantages over 111In-IgG because of better physical properties of 99mTc, simpler preparation, lower cost and greater availability and the possibility of using higher 99mTc doses.

Functional importance of ventricular enlargement and cortical atrophy in healthy subjects and alcoholics as assessed with PET, MR imaging, and neuropsychologic testing

The authors assessed the relationship between ventricular enlargement, cortical atrophy, regional brain glucose metabolism, and neuropsychologic performance in 10 alcoholics and 10 control subjects. Regional brain glucose metabolism was measured with fluorine-18 fluorodeoxyglucose (FDG) and positron emission tomography (PET). Cortical atrophy and ventricular size were evaluated quantitatively with magnetic resonance (MR) imaging. Alcoholics had decreased brain glucose metabolism and more cortical atrophy but did not have significantly greater ventricular size than did control subjects. The degree of ventricular enlargement and of cortical atrophy was associated with decreased metabolism predominantly in the frontal cortices and subcortical structures in both alcoholics and control subjects. There were no significant correlations between neuropsychologic performance and MR imaging structural changes, whereas various subtest scores were significantly correlated with frontal lobe metabolism. These data show that F-18 FDG PET is a sensitive technique for detecting early functional changes in the brain due to alcohol and/or aging before structural changes can be detected with MR imaging.

A comparison of magnetic resonance imaging to bone scintigraphy in early traumatic ischemia of the femoral head

In adult rabbits, a unilateral subcapital osteotomy of the femoral neck was performed to induce avascularity. One half of the osteotomy sites were fixed with a magnetic resonance imaging (MRI) compatible absorbable pin and the other osteotomies had no fixation. The femoral heads were studied at three, five, and 12 days with roentgenographs, bone scintigraphy, and MRI, and MRI only at four weeks and six weeks after osteotomy. Histologic studies were performed after imaging to evaluate the viability of the femoral heads. At three, five, and 12 days after osteotomy, bone scintigraphy showed a decrease in uptake of radioisotope in the region of the femoral head on the operated side relative to the acetabulum and greater trochanter in 17 of 18 rabbits. A comparison of the surgically treated hip to the normal hip in fixed and unfixed osteotomies showed no change in the signal behavior of T1- or T2-weighted images in all rabbits Days 3, 5, and 12 (n = 18) after operation. The rabbit femoral heads with fixation of the osteotomy 28 days after operation showed a decrease in signal intensity in the subcapital region of the femoral head. Six weeks after operation, the fixed femoral head shows a loss of signal in a portion of the femoral head near the osteotomy. The MRI signal intensity appears to increase in the unfixed femoral heads six weeks after operation.(ABSTRACT TRUNCATED AT 250 WORDS)

Alcohol intoxication does not change [11C]cocaine pharmacokinetics in human brain and heart

There is increasing evidence that the combined use of cocaine and alcohol produces enhanced behavioral and toxic effects. We have used PET and tracer doses of [11C]cocaine in 7 normal human volunteers to assess if the distribution and clearance of cocaine are altered by alcohol intoxication. Each subject received 2 PET studies with [11C]cocaine (3-11 micrograms), one before and one during alcohol intoxication (1 g/kg). Regions of interest included the brain (n = 3) and heart (n = 4). Arterial plasma was assayed for unchanged cocaine and for labeled cocaethylene, a metabolite of cocaine found in individuals using cocaine and alcohol in combination (Hearn et al., 1991a). Alcohol intoxication did not change uptake and clearance or the steady-state distribution volume of [11C] cocaine in brain (striatum, thalamus, and cerebellum) or in heart. Moreover, labeled cocaethylene was not detected in the 10 minute plasma sample. These results suggest that the acute enhancement of behavior and toxicity associated with the combined use of cocaine and alcohol is not due to an alteration in cocaine's organ distribution or to cocaethylene formation but may be related to an additive effect resulting from the direct actions of each of these drugs.

Decreased brain metabolism in neurologically intact healthy alcoholics

OBJECTIVE

The extent to which cerebral dysfunction in alcoholics is related to the direct effects of alcohol in the brain rather than to indirect mechanisms and/or alcohol withdrawal remains unclear. The purpose of this study was to evaluate whether healthy alcoholics with no evidence of alcohol-associated complications showed changes in brain glucose metabolism.

METHOD

Positron emission tomography and [18F]-fluorodeoxyglucose were used to measure regional brain metabolism. The study group consisted of 22 normal, healthy, right-handed volunteers and 22 neurologically intact, healthy, right-handed alcoholics tested 6 to 32 days after alcohol discontinuation.

RESULTS

Alcoholics showed significantly lower whole brain metabolism than normal control subjects. Normalization of regional metabolic values to the whole brain metabolic rate revealed that the left parietal and right frontal cortices were the most affected regions. Although the whole brain metabolic rate was correlated with the amount of time since alcohol discontinuation, the "normalized" decreases in left parietal and right frontal glucose metabolism were not.

CONCLUSIONS

These findings support the contribution of the direct effect of alcohol as well as alcohol withdrawal on the changes in regional brain metabolism seen in alcoholics. They also provide evidence of cerebral changes in neurologically intact healthy alcoholics.

Long-term frontal brain metabolic changes in cocaine abusers

Neurological complications from cocaine use are well recognized. We propose that chronic cocaine use can also cause clinically silent brain dysfunction. We investigated brain glucose metabolism with positron emission tomography (PET) and 2-deoxy-2[18F] fluoro-D-glucose (FDG) in 21 neurologically intact chronic cocaine abusers (C) and 18 normal controls (N). The cocaine abusers were tested 1-6 weeks after the last use of cocaine and seven were retested after a 3 month drug-free period. Global cerebral glucose metabolism was not significantly different between controls and cocaine abusers (N = 38.4 +/- 3, C = 36.5 +/- 5 mumol/100 g of tissue, min). However, cocaine abusers had significantly (P less than 0.05) lower metabolic activity in 16 of the 21 left frontal regions and 8 of the 21 right frontal regions. These decreases persisted after 3-4 months of detoxification and were correlated with the dose (P less than or equal to 0.01) and the years of cocaine use (P less than or equal to 0.05). This study shows reduced rates of frontal metabolism in neurologically intact cocaine abusers that persist even after 3-4 months of detoxification.

Effect of light scatter on the pattern reversal visual evoked response: comparison with psychophysical results

The effect of light scatter on the pattern reversal visual evoked response (PVER) was studied in 6 normal subjects. The results were compared with contrast visual acuity, contrast sensitivity function, and glare disability. Light scatter was induced by translucent acrylic sheets. Visual acuity measured with the low-contrast charts decreased significantly (P < 0.0001) even with a small degree of light scatter. Contrast sensitivity decreased with a small degree of light scatter especially for high spatial frequencies. PVER amplitudes decreased especially at the smaller checks with its peak shifted to larger checks. PVER was equally sensitive to light scatter compared to psychophysical tests.

Brain imaging of an alcoholic with MRI, SPECT, and PET

A medically healthy chronic alcoholic without evidence of neurological and neuropsychological impairment was studied with magnetic resonance imaging (MRI), single photon emission computerized tomography (SPECT), and positron emission tomography (PET). An age-matched normal volunteer was evaluated with the same scans for comparison. The MRI of the alcoholic revealed prominent ventricles and mild cortical atrophy. SPECT and PET revealed predominant involvement of the frontal cortex as shown by decreased frontal blood flow and metabolism. This case illustrates the sensitivity of brain imaging techniques in detecting cerebral abnormalities even in the absence of neurologic and/or neuropsychological impairments.

Distribution and kinetics of carbon-11-cocaine in the human body measured with PET

The extent to which the toxic properties of cocaine are related to its accumulation in various organs is not known. This study investigates cocaine uptake in the human body using 11C-cocaine and PET in 14 healthy males. The rate of uptake and clearance of 11C-cocaine varied among organs: peak uptake occurred in the lungs at 45 sec, in the heart and kidneys at 2-3 min, in the adrenals at 7-9 min, and in the liver at 10-15 min. Half-peak clearances were 90 sec in the lungs, 10 min in the heart and kidneys and 22 min in the adrenals. Liver radioactivity plateaued 10-15 min after injection and remained constant thereafter (40 min). Lung radioactivity paralleled that of plasma. The average uptake at peak was 0.007% (s.d., 0.001) dose/cc in the heart, 0.014% (s.d., 0.002) dose/cc in the kidney, 0.014% (s.d., 0.002) dose/cc in the liver and 0.034% (s.d., 0.001) dose/cc in the adrenals. The significant accumulation of cocaine in human heart, kidneys, adrenals and liver could contribute to its toxicity.

Mechanical failure of hydroxyapatite- and polysulfone-coated titanium rods in a weight-bearing canine model

Three types of material that have shown potential as coatings for orthopaedic implants were studied. Using a weight-bearing canine model, Ti-6A1-4V femoral intramedullary rods coated with (1) sintered titanium beads, (2) plasma-sprayed hydroxyapatite, and (3) silyl coupled polysulfone beads were evaluated for mechanical strength and bone ingrowth. The model was designed to secure optimal prosthetic stability by obtaining maximal bony ingrowth during an initial non-weight-bearing phase, then stressing the implant during a full-weight-bearing phase. None of the rods coated with titanium beads failed. All 17 polysulfone-coated rods failed, 13 of them at the interface between the polysulfone coating and the titanium core. Of 18 rods coated with hydroxyapatite, 15 suffered implant breakdown at the interface between the hydroxyapatite coating and the titanium core. This may be due to dissolution of the plasma-sprayed hydroxyapatite in vivo. Testing of retrieved specimens from both hydroxyapatite- and polysulfone-coated implants showed that the shear strength at the coating-rod interface had decreased to less than 40% of the shear strength at manufacture. Despite mechanical failure, histologic study showed extensive bone ingrowth or apposition onto both the polysulfone and hydroxyapatite coatings.

Contrast visual acuities in cataract patients. I. Comparison with normal subjects

Contrast sensitivity and glare sensitivity are often abnormal in cataract patients. However, despite significant subjective complaints, relatively good visual acuities often are obtained with high-contrast optotypes. Using Variable-Contrast Visual Acuity Charts (VCVAC), we measured visual acuities of 40 eyes of 24 normal subjects (visual acuity greater than or equal to 1.0) aged 41 to 72 years, and 40 eyes of 28 cataract patients (visual acuity greater than or equal to 0.6) aged 44 to 81 years. The VCVAC consists of 4 different charts (1-4). The contrast is 90% in charts 1 and 4, 15% in chart 2 and 2.5% in chart 3. Chart 4 is the reverse polarity of chart 1. The decrease of visual acuity compared with the high-contrast chart (chart 1) was larger in the cataract group with both in the 15% contrast (0.52 vs. 0.71 octave) and the 2.5% contrast (1.21 vs. 1.75 octaves). In cataract group, 23/40 eyes (57.5%) showed better visual acuity with chart 4 than that of chart 1. In addition to high-contrast optotypes, acuity measurements using intermediate- to low-contrast optotypes, combined with the reverse polarity chart, seem effective in analyzing the visual disabilities caused by early cataract.

Identification of a Fab interaction footprint site on an icosahedral virus by cryoelectron microscopy and X-ray crystallography

Biological processes frequently require the formation of multi-protein or nucleoprotein complexes. Some of these complexes have been produced in homogeneous form, crystallized, and analysed at high resolution by X-ray crystallography (for example, see refs 1-3). Most, however, are too large or too unstable to crystallize. Individual components of such complexes can often be purified and analysed by crystallography. Here we report how the coordinated application of cryoelectron microscopy, three-dimensional image reconstruction, and X-ray crystallography provides a powerful approach to study large, unstable macromolecular complexes. Three-dimensional reconstructions of native cowpea mosaic virus (CMPV) and a complex of CPMV saturated with a Fab fragment of a monoclonal antibody against the virus have been determined at 23 A resolution from low-irradiation images of unstained, frozen-hydrated samples. Despite the nominal resolution of the complex, the physical footprint of the Fab on the capsid surface and the orientation and position of the Fab have been determined to within a few ångstroms by fitting atomic models of CPMV4 and Fab (Kol)5 to reconstructed density maps.

A convenient method of measuring the thermal conductivity of biological tissue

The basic principle of the thermal conductivity probe is described. Thin probes were developed based on this principle, with a reproducibility of 5.3% and relative error less than 6.0%. Each measurement can be completed in 90 s and the temperature increase can be controlled within 2 degrees C. Using the probes, the thermal conductivities of pig fat, meat, liver, kidney and live and dead snake head were measured and it was found that water content plays an important role in influencing the magnitude of the thermal conductivity of biological tissues. The probe can be used over a temperature range from -40 to 150 degrees C.

[Effects of alpha-dimethylamino-cyclohexoxyl-dimethyl gallium on ultrastructure of erythrocytic stage of Plasmodium berghei and P yoelii]

The effects of alpha-dimethylamino-cyclohexoxyl-dimethyl gallium (DCDG), a new antimalarial drug developed in China, on the ultrastructure of murine malaria parasites in vivo was studied in comparison with those of chloroquine (CQ) and artemisinin (Art). All these 3 antimalarials were administered ig to mice at dosages of 1-3, 40-80, and 200-400 mg.kg-1 for DCDG, CQ, and Art respectively, based on a similar intensity of morphological changes in the parasites. Blood samples were collected for electron microscopy from 15 min to 48 h after medication. The results showed that DCDG killed the malaria parasites (both asexual and sexual forms) rapidly. The most prominent changes in DCDG-treated parasites were serious dilation of perinuclear space, endoplasmic reticulum, mitochondrion and some other vesicles or intermembranous spaces. These led to the formation of large autophagic vacuoles containing some membranous materials, which were subsequently extruded. Then the parasite cells became more concentrated, finally pyknotic and died. The mode of action was very different from that of CQ and Art.

Structural variation of La Crosse virions under different chemical and physical conditions

La Crosse (LAC) virions exposed to different pHs (7.3, 6.2, and 5.4) and temperatures (37 degrees, 20 degrees, and 4 degrees) were preserved in thin layers of vitreous ice and observed by electron cryomicroscopy. Our results indicate that, at lower pH, virus particles interact with each other to form aggregates. In some cases, particles could be interpreted to have fused together. At neutral pH and higher temperatures morphological changes consistent with deformation in some particles were observed. We suggest that low pH conditions are sufficient for membrane fusion events to occur with LAC virions.

Imaging of cocaine-induced global and regional myocardial ischemia

Severe and often fatal cardiac complications have been reported in cocaine users with narrowed coronary arteries caused by atherosclerosis as well as in young adults with normal coronaries. We have found that in normal dogs cocaine induces severe temporary hypoperfusion of the left ventricle as indicated by a significantly lower 201Tl concentration compared to the baseline state. The most significant decrease in uptake occurred 5 min after injection and was more pronounced in the septal and apical segments. Following intravenous administration of cocaine, instead of gradual disappearance of 201Tl from the left ventricle, there was continuous increase in 201Tl concentration in the left ventricle. These imaging experiments indicate that the deleterious effects of cocaine on the heart are probably due to spasm of the coronaries and decreased myocardial perfusion. Since spasm of the large subpericardial vessels does not seem to explain the magnitude of the increased coronary resistance and decreased coronary flow after cocaine as described in the literature, it is suggested that microvascular spasm of smaller vessels plays a major role in the temporary decrease in perfusion. The data may also suggest that severe temporary myocardial ischemia is probably the initiating factor for the cardiac complications induced by cocaine.

[Preliminary observation on lymphocyte function with radioisotope incorporation in asthmatic patients]

Twenty-five asthmatic patients and 54 normal subjects were included in this study. The results of our study showed that among the asthmatic group, no obvious decrease was observed in the uptake of 3H-TdR by T-lymphocyte stimulated with PHA, whereas there was markedly depressed uptake of 14C-UR by T-lymphocyte. The latter finding demonstrated that the asthmatic patients had a decrease of RNA synthesis during the course of T-lymphocyte transformation. The mean 3H-TdR uptake by T-lymphocyte was less in the patients whose first attack of asthma occurred after 30 years of age, when compared to those before 30 years of age, but statistically not significant. There was a slightly lower uptake of 3H-TdR by T-lymphocyte in the mild attack group than that in the remission group. B-lymphocyte transformation ability reflected in the uptake of 3H-tyrosine by B-lymphocyte stimulate with LPS was apparently increased in the asthmatic group, as compared to normal subjects. This study supports the hypothesis that the abnormal function of cell-mediated immunity may play a role in the pathogenesis of asthma.

A monoclonal antibody reacting with platelets for monitoring thrombolysis

Thrombus immunoscintigraphy with radiolabeled monoclonal antibodies are presently undergoing intense clinical evaluations. Reports on clinical trials of radiolabeled antifibrins are very encouraging and results of antiplatelet antibody evaluations are forthcoming. Animal studies with antiplatelet antibodies indicate that a diagnosis can be made within the critical "lytic window" of 4-6 h, and thus the imaging procedure may be used as an adjunct to thrombolytic therapy, i.e. screening of patients. We now report on a potentially new application of monoclonal antibodies, immunoimaging for monitoring thrombolysis. In vitro studies were performed with "standardized clots" incubated with 99mTc 50H.19 and re-incubated with streptokinase (SK), urokinase (UK) or recombinant tissue plasminogen activator (rt-PA). The decrease in clot-bound 99mTc 50H.19 activity after SK, UK or rt-PA incubation was proportional to the decrease in clot weight (r = 0.90-0.98). The direct effects of these thrombolytic agents on the labeled antibody and the possible interference of aspirin, warfarin and heparin in thrombus immunoimaging were also investigated. Aspirin, heparin and warfarin did not interfere with clot-binding of 99mTc 50H.19. Thrombolytic agents did not affect the stability of the radiolabel or immunoreactivity of 50H.19. These results indicate that 99mTc 50H.19 is a promising agent that may enable monitoring thrombolysis in addition to thrombus immunoimaging.

A new set of variable-contrast visual acuity charts

Using a computer plotting technique, we designed four variable-contrast visual acuity charts. The contrast of the first 3 is 90, 15, and 2.5%, respectively. The fourth is 90%, but the luminance of the optotypes and background are the reverse of the first chart. The main features of these charts are as follows. Both contrast sensitivity and spatial frequency are in geometric gradation, which observes the laws of Weber and Fechner. The mean average luminance, (Lmax + Lmin)/2, is constant for all four charts, which follows the concept of contrast sensitivity function (CSF). Charts 1 and 4, which have the same contrasts but different glare backgrounds, measure the glare that is related to the transparency of the refractive media of the eye. Because the charts are rotatable, patient memorization and guessing are minimized. Results compared with those of the conventional visual acuity test and are understandable by patients and eye care practitioners. The charts, which are simple, easy, and require little time, are inexpensive and portable.