The precision of positron emission tomography: theory and measurement

The limits of quantitation with positron emission tomography (PET) are examined with respect to the noise propagation resulting from radioactive decay and other sources of random error. Theoretical methods for evaluating the statistical error have been devised but seldom applied to experimental data obtained on human subjects. This paper extends the analysis in several ways: (1) A Monte Carlo method is described for tracking the propagation of statistical error through the analysis of in vivo measurements; (2) Experimental data, obtained in phantoms, validating the Monte Carlo method and other methods are presented; (3) A difference in activation paradigm, performed on regional CBF (rCBF) data from five human subjects, was analyzed on 1.6-cm diameter regions of interest to determine the mean fractional statistical error in PET tissue concentration and in rCBF before and after stereotactic transformation; and (4) A linear statistical model and calculations of the various statistical errors were used to estimate the magnitude of the subject-specific fluctuations under various conditions. In this specific example, the root mean squared (RMS) noise in flow measurements was about three times higher than the RMS noise in the concentration measurements. In addition, the total random error was almost equally partitioned between statistical error and random fluctuations due to all other sources.     

Singlet oxygen induced cerebral vasospasm: an experimental study in rats

A new experimental model is described which can be used as an alternative to study the effects of subarachnoid hemorrhage (SAH) in rats. Vasospasm of the basilar artery is induced photochemically after transpalatal illumination of intracisternally injected rose bengal in two different rat strains. Singlet oxygen, generated in the subarachnoid space, elicits vasospasm which has been demonstrated angiographically at 90 min and 24 h after photosensitisation. Sprague Dawley rats responded better than Wistar rats. Dilution of rose bengal in water was more vasospastic than dilution of rose bengal in artificial CSF. Since the action of singlet oxygen is similar to that of free radicals, this experiment gives an argument for the hypothesis that free radicals play a leading role in the pathogenesis of cerebral vasospasm after subarachnoid hemorrhage.     

Multiple sclerosis in Galion, Ohio: prevalence and results of a case-control study.

An investigation of the occurrence of multiple sclerosis (MS) was undertaken in the City of Galion, Ohio, USA, because of a report of an increased number of cases. As of June 1, 1987, there were 18 living cases of MS in Galion and Polk Township, for a prevalence rate of 112 cases per 100,000 population. The expected rate is approximately 65-170 cases per 100,000. In a case-control study, residents of Galion or Polk Township who had MS were compared to residents who did not have MS. The controls were matched to the cases on age and sex and had lived in Galion for at least as long as their matched case. The cases and controls did not differ in the distribution of their present or past Galion addresses, occupational histories or workplace exposures. Cases were more likely to have graduated from high school and college than controls. Cases were more likely than controls to report a history of allergies, to recall two or more relatives who had neurologic diseases that began before their first MS symptoms, to report owning a cat that died of unexplained causes and to recall having received oral polio vaccine. Cases and controls had similar levels of antibodies to measles, chickenpox, cytomegalovirus and the human T-cell lymphotrophic virus I.     

Regulatory properties of brain glutamate decarboxylase (GAD): the apoenzyme of GAD is present principally as the smaller of two molecular forms of GAD in brain

The apoenzyme of glutamate decarboxylase [enzyme without bound cofactor, pyridoxal 5'-phosphate (pyridoxal-P)] serves as a reservoir of inactive glutamate decarboxylase (GAD) that can be activated when additional GABA synthesis is required. We have investigated which of two molecular forms of GAD is present as apoenzyme in synaptosomes and in cortex, caudate nucleus, hippocampus, and cerebellum of rat brain. Endogenous glutamate apodecarboxylase (apoGAD) was labeled by incubating extracts of synaptosomes or punches of each region with 32P-pyridoxal-P, followed by reduction with NaBH4, to link covalently the 32P-pyridoxal-P to GAD. Proteins were separated by SDS-PAGE. Punches from all four brain regions and forebrain synaptosomes contained two forms of GAD with apparent Mrs of 63 and 65 kDa as identified by immunoblotting with four antiGAD sera. Punches and synaptosomes contained a major 32P-pyridoxal-P-labeled band with an apparent Mr of 63 kDa that was stained on immunoblots by the antiGAD serum 1440 and the monoclonal antibody GAD-6, and a minor labeled band at 65 kDa that was stained by the 1440, 6799, and K2 antisera. Synaptosomes contained remarkably few other strongly labeled proteins, but punches contained several other labeled bands. Three additional lines of evidence indicate that the labeled 63-kDa protein is apoGAD: (1) it was purified by immunoaffinity chromatography with the GAD-1 monoclonal antibody; (2) it yielded one major labeled peptide when digested with chymotrypsin, and that peptide appeared identical in peptide-mapping experiments to the labeled active-site peptide isolated from chromatographically prepared rat brain GAD; and (3) its labeling was selectively blocked by 4-deoxypyridoxine 5'-phosphate, a competitive inhibitor of the binding of pyridoxal-P to GAD.(ABSTRACT TRUNCATED AT 250 WORDS)     

The role of adenosine in the vascular adaptation of neonatal cerebral blood flow during hypotension

This study investigated the potential role of adenosine in cerebral blood flow (CBF) regulation in the neonate during moderate and severe hypotension. Experiments were done in anesthetized, 1- to 3-day-old piglets. Regional CBF (determined by radiolabeled microsphere technique) and cerebral metabolic rate for O2 (CMRO2) were measured (a) during normotension and (b) during a 3-min period of moderate (58 +/- 9 mm Hg) or severe (36 +/- 7 mm Hg) hypotension produced by the inflation of a balloon catheter placed in the aortic root. Measurements of CBF and CMRO2 were performed successively after intracerebroventricular (i.c.v.) injections of vehicle (n = 17), the adenosine receptor blocker 8-phenyltheophylline (8-PT, 10 micrograms, n = 14), and the A2-receptor agonist 5'-N-(ethylcarboxamide)adenosine (NECA, 2 ng, n = 8). After i.c.v. administration of vehicle, none of the parameters studied was significantly altered by moderate hypotension, but severe hypotension decreased the total CBF (mean +/- SD) from 86 +/- 24 to 40 +/- 15 ml min-1 100 g-1 and CMRO2 from 3.2 +/- 0.8 to 1.8 +/- 1.0 ml min-1 100 g-1 (p less than 0.05). Administration of 8-PT did not alter these parameters during normotension, but significantly decreased CBF during moderate hypotension compared to postvehicle values (53 +/- 11 versus 81 +/- 12 ml min-1 100 g-1, p less than 0.05). This loss of autoregulation was completely reversed by NECA. During severe hypotension, 8-PT altered the CBF redistribution towards the brainstem.(ABSTRACT TRUNCATED AT 250 WORDS)     

Dopamine differentially regulates dynorphin, substance P, and enkephalin expression in striatal neurons: in situ hybridization histochemical analysis.

Dopamine regulation of the levels of dynorphin, enkephalin, and substance P messenger RNAs in rat striatal neurons was analyzed with in situ hybridization histochemistry (ISHH). Relative levels of peptide mRNA expression in the patch and matrix compartments of the dorsolateral striatum were compared among control rats, rats treated for 10 d with apomorphine, rats with unilateral 6-hydroxydopamine (6-OHDA) lesions of the nigrostriatal dopaminergic system, and rats with nigrostriatal dopaminergic lesions followed 2 weeks later by 10 d of apomorphine treatment. Image analysis of ISHH labeling demonstrated that the number of neurons expressing each peptide mRNA remained constant, whereas the relative level of peptide mRNA per neuron changed significantly, depending on the experimental treatment. Dynorphin mRNA expression increased following chronic apomorphine treatment: striatal patch neurons increased to an average of 100% above control values, whereas striatal matrix neurons showed only a 25% increase. Dynorphin mRNA expression decreased following 6-OHDA lesions: patch neurons showed an average 75% reduction in expression, whereas matrix neurons showed no significant change. In animals with 6-OHDA lesions followed by apomorphine treatment, both patch and matrix neurons showed an average increase in dynorphin expression of 300% above control levels. Changes in dynorphin mRNA levels with these treatments were matched by qualitative changes in dynorphin immunoreactivity both in the striatum and in striatonigral terminals in the substantia nigra. Neither substance P nor enkephalin mRNA levels showed a significant difference between the striatal patch and matrix compartments in any experimental condition (in the dorsolateral striatum). Substance P mRNA expression was increased an average of 50% after 10 d of apomorphine treatment and showed an average decrease of 75% following 6-OHDA lesions of the mesostriatal system. There was no significant change in the expression of substance P mRNA in striatal neurons compared to control values in rats with combined 6-OHDA lesion and apomorphine treatment. Enkephalin mRNA expression was not significantly altered by chronic apomorphine treatment but showed an average increase per cell of some 130% above control levels following 6-OHDA-induced lesions of the mesostriatal system. In animals with a 6-OHDA lesion and apomorphine treatment, enkephalin mRNA was also elevated but not significantly above the levels produced by the lesions alone. These data show that the expression of dynorphin, enkephalin, and substance P is differentially regulated by the mesostriatal dopaminergic system and, further, suggests that the mechanisms by which this regulation occurs may be different for the 3 peptide families.     

The impact of sequential quality assessment exercises on laboratory performance: the multicentre ECAT Angina Pectoris Study. Report from the European Concerted Action on Thrombosis and Disabilities (ECAT)

As an adjunct to a European multicentre prospective study, five quality assessment (QA) exercises, spanning a period of 2.5 years, were undertaken. In these, fifteen laboratories from eight countries each performed ten haemostatic factor assays. The design of the QA exercises allowed the between-duplicate, between-day and between-laboratory coefficients of variation (CVs) to be calculated. The between-duplicate CV decreased by a factor of one quarter, and the between-day CV by a factor of one third, over the five exercises. The activated partial thromboplastin time (APTT) assay consistently showed the lowest CVs, while there was notable improvement in the between-day CVs for von Willebrand factor related antigen (vWF R:Ag) and factor VIII clotting activity (VIII:C). However, the between-laboratory CV, assessing extent of agreement between the different laboratories, did not apparently improve over the five exercises. Thus, while QA exercises may be very useful in improving the performance of haemostatic assays according to criteria which an individual laboratory can assess, improving agreement on haemostatic assay results between laboratories may be more difficult to achieve.     

Neurobiology of obsessive compulsive disorder--a serotonergic basis of Freudian repression

Intrusive thoughts and images, often of a violent, horrific, or blasphemous nature are the hallmark of Obsessive Compulsive Disorder (OCD). OCD patients frequently also often have reductions in normal serotonergic (5-HT) function. This paper proposes a model of 5-HT function involving the routine filtering and suppression of violent or libidinal impulses. This model accounts for OCD as an instance of failed inhibition. The model also appears to resemble Freud's model of ego-id interactions at least in part, suggesting that it may be possible to psychobiologically substantiate a Freudian metaphor.     

Double-blind, placebo-controlled comparison of clonazepam and alprazolam for panic disorder

To test the reported antipanic efficacy of clonazepam, the authors randomized 72 subjects with panic disorder to 6 weeks of treatment with either alprazolam, clonazepam, or placebo. Endpoint analysis demonstrated a significant beneficial effect of both active treatments, but not placebo treatment, on the frequency of panic attacks, overall phobia ratings, and the extent of disability. Comparison of the two active treatments revealed no significant differences and no consistent tendency for one agent to be favored over another, although power to detect small differences was limited. Sedation and ataxia were the most common side effects reported, but these effects were mild and transient and did not interfere with treatment outcome. The results of this double-blind, placebo-controlled trial are consistent with previous reports of clonazepam's antipanic efficacy.     

Experimental isovolemic haemodilution-induced augmentation of carotid blood flow and oxygen transport through graded carotid stenoses.

The effect of haemodilution without volume expansion (isovolemic haemodilution) was assessed with respect to blood flow and oxygen transport across stenotic lesions of progressive severity in the dog carotid artery. As the mean haematocrit (Hct) was reduced from 40 +/- 1% (+/- SEM) to 32 +/- 0% (p less than 0.001), reductions in vascular resistance were significant across the 90% (p less than 0.001) and 95% (p less than 0.0003) relative carotid stenoses. Isovolemic haemodilution reduced fresh blood viscosity significantly by 27 +/- 3% (p less than 0.001) and 42 +/- 4% (p less than 0.001) at the low shear rates of 10 sec-1 and 1 sec-1 which are typical of low-flow states. Following a 20% reduction in Hct 30 to 35% increase (p less 0.001) in carotid blood flow occurred at non-critical degrees of stenosis while a mean 83% increase (p less than 0.001) occurred at the highly critical 95% relative stenosis. Oxygen transport after a 22% decrease in blood haemoglobin was significantly increased by 28% (p less than 0.01) at the 95% relative stenosis level. These data provide a physiologic rationale for the beneficial effects of haemodilution in acute cerebral ischaemia, cerebral vasospasm and cerebral revascularization or carotid endarterectomy.