Detecting neuroinflammation in the brain following chronic alcohol exposure in rats: A comparison between in vivo and in vitro TSPO radioligand binding

Excessive alcohol consumption is associated with neuroinflammation, which likely contributes to alcohol-related pathology. However, positron emission tomography (PET) studies using radioligands for the 18-kDa translocator protein (TSPO), which is considered a biomarker of neuroinflammation, reported decreased binding in alcohol use disorder (AUD) participants compared to controls. In contrast, autoradiographic findings in alcohol exposed rats reported increases in TSPO radioligand binding. To assess if these discrepancies reflected differences between in vitro and in vivo methodologies, we compared in vitro autoradiography (using [3 H]PBR28 and [3 H]PK11195) with in vivo PET (using [11 C]PBR28) in male, Wistar rats exposed to chronic alcohol-vapor (dependent n = 10) and in rats exposed to air-vapor (nondependent n = 10). PET scans were obtained with [11 C]PBR28, after which rats were euthanized and the brains were harvested for autoradiography with [3 H]PBR28 and [3 H]PK11195 (n = 7 dependent and n = 7 nondependent), and binding quantified in hippocampus, thalamus, and parietal cortex. Autoradiography revealed significantly higher binding in alcohol-dependent rats for both radioligands in thalamus and hippocampus (trend level for [3 H]PBR28) compared to nondependent rats, and these group differences were stronger for [3 H]PK11195 than [3 H]PBR28. In contrast, PET measures obtained in the same rats showed no group difference in [11 C]PBR28 binding. Our in vitro data are consistent with neuroinflammation associated with chronic alcohol exposure. Failure to observe similar increases in [11 C]PBR28 binding in vivo suggests the possibility that a mechanism mediated by chronic alcohol exposure interferes with [11 C]PBR28 binding to TSPO in vivo. These data question the sensitivity of PBR28 PET as a methodology to assess neuroinflammation in AUD.

Regional differences in distribution volume of I-123 IMP in the human brain: effect on CBF calculated by ARG method

OBJECTIVE

Two methods of quantitating cerebral blood flow (CBF) with iodine-123-labeled N-isopropyl-p-iodoamphetamine (I-123 IMP) and a two-compartment model had been proposed; one is the table look-up (TLU) method and the other is the autoradiographic (ARG) method. The TLU method provides values of the cerebral blood flow (CBF) values and distribution volume of I-123 IMP (Vd) independently. In the ARG method, a fixed Vd is applied for the entire brain to calculate CBF. Our purpose was to evaluate regional differences in Vd in the human brain, or possible effects of regional differences in Vd on CBF calculated by the ARG method.

METHODS

In the present study, two SPECT scans were acquired from each of eight normal subjects (aged 44.0 +/- 16.7) at 40 min and 180 min of mid-scan-time after intravenous 1 min infusion of 111 MBq IMP. A single arterial blood sampling was performed 10 min after the IMP infusion. All images were anatomically normalized and analyzed with SPM99 and Matlab. We generated CBF and Vd images for each subject by the TLU method and evaluated differences in Vd among brain structures. We subsequently generated another set of CBF images by the ARG method and examined differences between CBF calculated by the TLU method and that by the ARG method.

RESULTS

Significant main effects of subject and brain structure in Vd were observed (two-way ANOVA). Vd values were higher in the deep gray matter than in the cerebral cortical regions. Among the cerebral cortical regions, no significant difference in Vd was observed. In spite of the significant differences in Vd among the brain structures, the voxel-by-voxel analyses as well as the ROI analyses revealed no statistically significant difference between CBF calculated by the TLU method and that by the ARG method.

CONCLUSIONS

Although regional differences in Vd were observed, the present results support the assumption that a fixed Vd does not cause significant error in the calculation of CBF by the ARG method.

Precision of measurement of tissue concentrations by RLG

Existing investigations about the precision of radioluminography (RLG) are restricted to descriptive analysis of the tissue samples. The aim of the present experiments was to obtain a general prospective statement about the precision that the RLG method can achieve. Several pharmaceutical companies in Europe participated in the experiments. Albino rats of various strains were dosed with various (14)C-labeled compounds. Whole-body sections were produced, and blood calibration scales were set up with standard radioactivity sources of dog or rat blood. Photostimulated luminescence was detected using Fuji imaging plate BAS-III. For each organ separately, variability was investigated on each of the levels: rat, section of rat, region within section, and residual, with the help of variance components. The producing company was seen as a fixed factor and adjusted for. A mixed linear model was fitted to the log-transformed data. The variance component (SD estimate) for the residual term gave the desired prospective statement about the achievable precision of the RLG method. Exponential back transformation from the logarithmic to the natural scale transformed the SD estimates to multiplication factors. In total, 29 organs were investigated. The RLG method was comparable in precision to the dissection/combustion method.

Technical validation of radioluminography systems

More and more laboratories are forced to document evidently that experimental results were achieved compliant with the regulatory of Good Laboratory Pratice (GLP). Thus, also for the imaging plate technique, which is widely used in whole-body autoradiography, it is necessary to provide procedures for formal validation and continuous quality control. Therefore, several European pharmaceutical companies agreed to carry out a project on this subject. This part considers the technical validation. Methods to prove uniform sensitivity and resolution of the technique were developed and are suggested as standard operation procedures and demonstrated, as well, by examples using the isotope (14)C. The high linearity of the detection method is shown by performing a calibration of the image data to the applied radioactivity.

Quantitative whole-body autoradiography: recommendations for the standardization of the method

The objective of this article is to identify the best conditions for preparing, handling, and exposing radioactive sections by using the Fujix BAS 2000 system for quantitative radioluminography. Regarding the influence of thickness of sections, thicker sections may allow shorter exposure times due to the increased radioactivity, but on the other hand they take more time for the freeze-drying process, resolution will be reduced, and the recovery of radioactivity will be lower due to increased self-absorption particularly in organs like bones or teeth. The pretreatment of the sections should depend on the method of exposure. Powdering with talcum is the most recommendable method when vacuum packaging the imaging plates and sections. Spraying with Nobecutan is recommended when using the cartridge method. Particularly for low concentrations, the vacuum-contact method should be the method of choice. To avoid a flare effect, the geometrical arrangement of the sections on the imaging plate (IP) should always be vertical to the scanning direction of the laser. An exposure time longer than 10 days is not recommended and the time between the end of exposure and start of scanning should be as short as possible. In order to reduce the background signal, it is necessary to expose the IPs in a shielding box in a cold environment. No positive chemographic effects of sections were found.

Quantification of tissue self-absorption of weak beta-radiation in lyophilized whole-body sections of rats

Whole-body autoradiography has been widely used in the investigation of the distribution of radiolabeled compounds in animals. The newly introduced radioluminography offers a reliable way of quantifying the radioactivity distribution within whole-body sections. Since the radioactivity is distributed over the entire depth of the section, self-absorption of beta-radiation in tissues is supposed to relevantly affect the detection of radioactivity at the section surface. The self-absorption of radiation energy ((14)C) was investigated in 28 organs/tissues of routinely produced lyophilized rat sections. Nonradioactive whole-body sections with different thickness between 20 and 120 microm were placed between a homogeneous (14)C source and the imaging plates to detect the transmitted radioactivity. The self-absorption was expressed in terms of percentage of transmission of the radioactivity through the sections. Transmission decreased with increasing section thickness, e.g., from 44% (20 microm) to 28% (120 microm) for blood. Comparison of three complete sets of data disclosed intertissue variations of up to about 30% (i.e., +/-15%) disregarding bone. A defined bandwidth of +/-15% around the blood transmission would cover the transmission of almost all tissues. Thus, for most organs radioactivity can be quantified by direct comparison with radioactive blood calibration samples.

Quantitative distribution studies in animals: cross-validation of radioluminography versus liquid-scintillation measurement

The results of a cross-validation of the radioluminography (RLG) and liquid scintillation counting (LSC) methods are presented. The methods for the determination of radioactivity concentrations were compared in 16 organs, after administration of (14)C-labeled substances to rats. LSC measurements of two kinds were used as reference methods for RLG: (1) quantitative determination of radioactivity after conventional dissection (interindividual comparison) and (2) quantitative determination of radioactivity in tissue punches taken from the whole-body sections after they had undergone RLG measurement (intraindividual comparison). Blood standards containing known concentrations were used for calibration. For statistical evaluation log-linear regression analysis of paired concentration values and organ-specific 95% confidence intervals of the log-transformed RLG/LSC concentration quotients were compared. For most organs, the slopes of the regression lines and the means of the concentration quotients were within the defined equivalence range of 0.80-1.25. Deviations were distinctly smaller in the intraindividual comparison. For some organs, however, it became clear that found concentrations were affected by self-absorption (RLG) and by differences in sample preparation (LSC). In conclusion, quantification with RLG is a reliable and reproducible method with comparable measurement precision and greater accuracy in respect of tissue localization, compared to LSC (dissection).

Quantitative whole-body radioluminography-future strategy for balance and tissue distribution studies

The present routine to conduct balance and/or tissue dissection distribution studies has now and then been questioned, because the way they are generally conducted does not produce information in proportion to the spending of animal and personnel resources. Usually only total radioactivity is measured and due considerations are not always taken to the metabolic fate of the label. In this study a different strategy is presented-integrating quantitative whole-body radioluminography and different chromatographic methods on extracts of tissue pieces punched from the whole-body sections. In addition to the saving in cost and time, the proposed integrated whole-body radioluminographic/metabolic profile protocol will provide (i) a detailed picture of the distribution of radioactivity at selected dose levels and time points in male, female, and pregnant animals; (ii) the time course of radioactivity in blood/plasma and tissues selected from the images (approximate half-life and AUC); (iii) accumulated urinary and fecal excretion of radioactivity and an estimate of the proportion of radioactive metabolites; (iv) tissue information about the proportion of parent drug versus metabolites of pieces punched from the whole-body sections; and (v) indications of possible tissue binding.

Autoradiographic characterisation of beta-adrenoceptors in chick brain using [3H]CGP 12177

An autoradiographic method for labelling beta(1)- and beta(2)-adrenoceptors using [3H]CGP 12177 as a radioligand is described as well as the procedure for an autoradiographic saturation kinetic study. The method afforded higher quality autoradiographs as well as an improvement in the tissue preservation when assayed in birds and chick embryos. The results confirmed the K(d) values previously reported for membrane homogenate binding. The use of different radioligands to characterise beta-adrenoceptors, the higher B(max) values found with autoradiography than those obtained by the membrane homogenate binding method and the typical errors in quantifying autoradiography are discussed. It is concluded that the method described here considerably improves autoradiographic beta-adrenergic characterisation.

Sensitivity of radioluminography using (14)C-labeled tracers in whole-body sections of rats

Radioluminography using photostimulated luminescence recently became popular for the quantitation of radioactivity in whole-body sections. In order to estimate the limits of the method, the sensitivity was investigated using routinously prepared blood standards with known amounts of radioactivity. The blood standards underwent the typical steps similar to conventional whole-body autoradiography including freezing, sectioning, and lyophilizing. The limit of detection, defined as 3 times the standard deviation of background values, decreases with exposure time from 18 Bq/g wet tissue for 1 day of exposure to 6 Bq/g for 7 days of exposure. The respective limit of quantitation defined as 10 times the standard deviation of background is 60 to 20 Bq/g. A similar sensitivity is found when the quantitation limit is defined as reproducible measurement with coefficients of variance below 20%: 60 Bq/g can be quantified if the measure area is above 3.5 mm(2).

Proposition for assessment of quantitative whole-body autoradiography

To assess recent improvements in quantitative whole-body autoradioluminography (QWBA), the entire QWBA procedure was divided into five processes. Each process was then investigated carefully to determine whether there were any problems in defining a clear standard operating procedure. Results show that use of two instruments, Macro-Cut, Leica, Germany, and the Bioimaging Analyzer with IP, Fuji Photo Film, was essential to produce macroautoradiographs for QWBA data. The remaining problems include the process for freezing the animal carcass and the process for freeze-drying or lyophilizing the frozen sections of the biomaterials. In addition, a desirable standard operating procedure (SOP) must be developed for assessing QWBA. This article proposes satisfactory SOPs with sufficient clarification and experimental proofs to ensure regulatory compliance for the QWBA technique.

No difference between estimated mean nuclear volumes of various types of neurons in the mouse brain obtained on either isotropic uniform random sections or conventional frontal or sagittal sections

Whenever using modern stereological methods for estimating number-weighted or volume-weighted mean volumes of biological particles such as cell nuclei, either 'isotropic uniform random' (IUR) tissue sections or 'vertical' ones had to be used. However, with the currently available procedures and tools it was virtually impossible to prepare such sections from small specimens such as the mouse brain. Here, a modification of the 'isector' is presented, which allows the embedding of mouse brain halves into paraffin spheres as a useful basis for preparing IUR sections. By using this modified isector it could be shown for various types of neurons in the hippocampus and cerebellum of young adult mice, that there are no differences between estimated mean nuclear volumes obtained on IUR sections and those obtained on conventional frontal or sagittal ones. This result may be used to expand the interpretation of estimated mean nuclear volumes of the types of neurons investigated here.

Interlaboratory comparison of autoradiographic DNA profiling measurements. 2. Measurement uncertainty and its propagation

Identifying the intrinsic sources of measurement uncertainty greatly facilitates control and further optimization of a measurement system. We have developed a model which quantitatively describes the observed interlaboratory variability of autoradiographic DNA band sizing. The model focuses on optical imaging measurements of band position and the calibration techniques used to convert measured band position to reported band size. The imaging component of measurement variability is described as a 0.05-0.2% standard deviation in determining the relative location of sample and calibration bands on a given film image. While developed solely with optical imaging information, the model is consistent with interlaboratory band sizing measurement variability observed with pristine samples. This interlaboratory variability can be modeled as a 0.2-0.4% standard deviation in the relative positions of sample and calibration bands across different electrophoretic gels. Further band sizing protocol standardization among laboratories would thus be expected to achieve at best a 2-fold reduction in interlaboratory band sizing variability.

Quantitative and qualitative genetic variation in two-dimensional DNA gels of human lymphocytoid cell lines

There is a continuing need for more efficient methods to examine human (and other) populations for altered germinal and somatic cell mutation rates. To this end, we have explored the potential usefulness of two-dimensional (2-D) electrophoresis of human DNA fragments obtained from restriction-enzyme-digested genomic DNA, using samples from father/mother/child trios. On a single 2-D DNA preparation, approximately 2000 DNA fragments varying in size from 1.0 to 5.0 kbp in the first dimension and 0.3 to 2.0 kbp in the second dimension are visualized. To enter into a genetic analysis of quantitative variation, these fragments must exhibit positional and quantitative stability. With respect to the latter, if spots that are the product of two homologous DNA fragments are to be distinguished with the requisite accuracy from spots that are the product of only one fragment, the coefficient of variation of spot intensity should be approximately < or = 0.12. At present, 482 of the spots in our preparations meet these standards. In an examination of preparations based on three Japanese mother/father/child trios, 43 of these 482 spots were found to exhibit variations that segregated within families according to Mendelian principles. Additionally, of the 2000 spots, 1114 (of which the aforementioned 482 are a subset) were deemed appropriate for the study of qualitative variation. A total of 142 variable spots were identified; the heterozygosity index for these DNA fragments was 4.4%. The genetic nature of the additional variants was again established by their segregation according to Mendelian principles. We have established the feasibility of cloning fragments from such gels and determining their nucleotide sequence. This technology should be highly efficient in monitoring for mutation resulting in loss/gain/rearrangement events in DNA fragments distributed throughout the genome.

Local glucose utilization and local blood flow in hearts of awake rats

Local cardiac glucose utilization and local cardiac blood flow in rat heart were measured in vivo by quantitative autoradiographic techniques with 2-[14C] deoxyglucose and [14C] iodoantipyrine, respectively. [14C]methylmethacrylate standards were calibrated for quantitative autoradiography of dried sections of heart tissue; the calibration values for heart tissue differed from those for brain by 8%, probably because of differences in self-absorption within the tissues. The lumped constant required by the deoxyglucose method was determined in isolated, perfused, working rat hearts and found to be 1.11 +/- 0.36 (mean +/- SD, n = 21). The heart: blood partition coefficient for iodoantipyrine required by the [14C]iodoantipyrine method was measured and found to be 1.25. The results obtained in awake rats showed: 1) overall cardiac glucose utilization varied considerably among animals with a mean of 53 (left ventricle) and 30 (right ventricle) mumol/100 g/min; 2) cardiac blood flow was less variable among animals with a mean of 592 (left ventricle) and 420 (right ventricle) ml/100 g/min; 3) glucose utilization was found to be particularly high in the papillary muscle; 4) systematic gradients of glucose utilization or blood flow in the ventricular wall were not observed; 5) glucose utilization and blood flow were not closely correlated on a local level. It is concluded that autoradiographic methods are suitable for the quantification of local glucose utilization and local blood flow in the rat heart in vivo. These methods could not demonstrate transmural gradients for glucose utilization and blood flow between epi- and endocardium in awake rats.

Criteria of applicability for autoradiography of tritium

Autoradiography is an effective tool for the imaging of radionuclide distributions in various samples. In sophisticated applications with special preparation and development of sample-emulsion combinations and subsequent grain counts it can be highly quantitative, but it requires carefully controlled conditions and a variety of counter-checks, for example through scintillation spectroscopy. Less refined applications use X-ray films as detectors, and their seeming simplicity tends to invite artefacts and misinterpretations. Particular care needs to be taken, if one deals, or presumes to deal, with the low-energy beta-emitter tritium. Because of the short electron ranges the film must be in intimate contact with the sample, which tends to produce chemographic artefacts; without added spectroscopic measurements it is impossible to discriminate the spurious signals from a blackening of the film due to tritium. Recent statements concerning autoradiographic tritium measurements in tree samples have created considerable public concern and have demonstrated the pitfalls of uncritical use. This paper presents order-of-magnitude criteria for the detection threshold in the autoradiography of tritium; they can serve as an exclusion principle for some of the more extravagant misinterpretations.

Measurement of lymphocyte proliferation: critical analysis of radioactive and photometric methods

Different methods of lymphocyte proliferation are compared to identify a non-radioactive alternative to 3H-thymidine-test. The enzymatic assays evaluating the turnover of mitochondrial dehydrogenases (MTT-test) and lysosomal hexosaminidase (NAG-test) proved not sensitive enough to substitute for 3H-thymidine incorporation. The incorporation of the nucleotide analog 5-bromodeoxyuridine (BrdU) can be exploited using an ELISA-system (enzyme linked immunosorbent assay) employing a monoclonal anti-BrdU antibody to measure cell proliferation. An optimized test protocol of the BrdU-ELISA which fulfills the requirements for a sensitive and practicable non-radioactive alternative to 3H-thymidine-test is presented.

In situ amplification of single copy gene segments in individual cells by the polymerase chain reaction

A method is described using the polymerase chain reaction (PCR) to amplify defined nucleic acid strands in individual cells in situ in conventional smears of bone marrow and peripheral cells. Using radioactively labeled precursors, the incorporation into newly synthesized strands by PCR can be detected by microautoradiography. The specificity of the method can be monitored by gel electrophoresis of the material shed into the reaction mixture. Thus it could be shown that even single genes in individual cells can be amplified to visibility. In a mixture of HIV infected and non infected cells both can be clearly distinguished from one another.

The calibration of 35S or 32P with 14C-labeled brain paste or 14C-plastic standards for quantitative autoradiography using LKB Ultrofilm or Amersham Hyperfilm

The relationship between 14C-labeled brain paste or plastic standards and 35S- or 32P-labeled brain paste was characterized with quantitative autoradiography. Film was exposed to both sets of 14C-labeled standards and 35S- and 32P-labeled standards for 15-148 h and the film was analyzed with computer densitometry. Subsequently, the tissue pastes were scraped from the slides, dissolved in tissue solubilizer and radioactivity determined by scintillation spectroscopy. A linear relationship was observed between the plastic and brain paste 14C standards as well as between both sets of 14C-labeled standards and 35S-labeled brain paste standards. The 32P-labeled standards demonstrated a poor linear relationship with the 14C-labeled standards and greater variability in the autoradiographic estimates than was seen with 35S or 14C. Results were similar for both Ultrofilm and Hyperfilm with all the radioisotopes. These findings demonstrate a simple linear relationship between plastic and brain paste 14C-labeled standards and between either 14C-labeled standards and 35S-labeled brain paste for use in quantitative autoradiography.

Quantitative assessment and reduction of long-term autoradiographic background

Quantitative autoradiography can measure distribution patterns in an animal exposed to radiolabeled compounds. A comparison of autoradiographs of rat brain containing low levels of 14C showed that a highly variable background signal had been produced. This resulted in several overexposed autoradiographs which could not be quantitatively compared. The background, believed to be produced by light emanating from the phosphor coating in the X-ray cassette, was a major impediment because it hindered correct analysis of the specimen. This article details our experiments demonstrating the sources of variance contributing to background and offers methods for its reduction. We found that placement of black polyethylene plastic between the slides and phosphor in the X-ray film cassette minimized autoradiographic background and effectively eliminated the effects caused by inherently different levels of radioactivity in the glass slides.

A new method to measure brain serotonin synthesis in vivo. II. A practical autoradiographic method tested in normal and lithium-treated rats

We describe here a practical autoradiographic method to estimate the rate of serotonin synthesis in brain. A two-time point method (60 and 150 min after injection of alpha-[14C]methyl-L-tryptophan) was first evaluated in 14 normal rats (7 at each time point). After this the method was tested in lithium-treated rats. In normal rats the rate of serotonin synthesis measured by the two-time point method generally correlated with known concentrations of tryptophan hydroxylase. The rate of synthesis in lithium-treated rats was compared with that in sham-treated rats (NaCl treatment). The results showed a significant increase in the synthesis rate in some cerebral structures. The greatest increases in the serotonin synthesis rate, attributable to the lithium treatment, were observed in the parietal cortex (52%) and caudate nucleus (47%). This is the first investigation to demonstrate, with autoradiographic resolution (approximately 100 microns), the differential changes in the rate of serotonin synthesis in the brain. Lithium had no significant effect on the rate of synthesis in the pineal gland.

Validity of tissue paste standards for quantitative whole-body autoradiography using short-lived radionuclides

A method of preparing radioactive standards for quantitative whole-body autoradiography (WBARG) using short-lived radionuclides is described and evaluated. Radioactive standards were prepared from bovine brain paste which was mixed with serial dilutions of the radionuclide being studied. Homogeneous distribution of the radionuclide in the brain paste was verified by direct counting and autoradiographic techniques. In addition, there was good agreement between the amounts of radioactivity obtained from quantitative WBARG and tissue counting in all of the major tissues sampled. Therefore, this method is effective for quantitative analysis of WBARG using short-lived radionuclides, for which permanent reference standards are unavailable.

Calibration of 125I-polymer standards with 125I-brain paste standards for use in quantitative receptor autoradiography

125I-Polymer standards were calibrated by interpolation of their optical densities in [125I]-brain paste standard curves to obtain dpm/mg protein. There was a linear relationship between the calibrated polymer standards and the dpm/mg polymer, as provided by the manufacturer. One dpm/mg polymer was equivalent to 7.34 +/- 0.22 dpm/mg protein. Receptor quantification in selected rat brain areas with comparison to either brain paste or calibrated polymer standards yielded similar results.

Calibration of [14C]plastic standards for quantitative autoradiography of [125I]labeled ligands with Amersham Hyperfilm beta-max

The densitometric response of Hyperfilm beta-max (HFBM) to [14C]plastic standards was calibrated to tissue-equivalent concentrations of [125I]. Plastic sections with standard concentrations of [125I] and [14C] were apposed to HFBM for 1, 3, 5, and 9 days, with liver and muscle slices (20 microns thick) labeled with [125I]insulin. The relative optical densities (ROD = log 10 [1/gray level x 256(-1)] produced by [125I]- and [14C]plastic standards were converted to equivalent tissue [125I] concentrations (dpm/mm2). The response of HFBM to the [125I]- and [14C]plastic standards was similar (P less than 0.001). Standard curves of tissue [125I] (dpm/mm2) vs plastic [14C] (microCi/g) concentrations fit second order polynomials (r2 = 0.995-0.999). The results show that [14C]plastic standards are valid for measuring [125I] radioactivity in tissue slices by autoradiography with HFBM.

Measurement of absolute myocardial blood flow with H215O and dynamic positron-emission tomography. Strategy for quantification in relation to the partial-volume effect

An in vivo technique was developed for measuring the absolute myocardial blood flow with H215O and dynamic positron-emission tomography. This technique was based on a new model involving the concept of the tissue fraction, which was defined as the fraction of the tissue mass in the volume of the region of interest. The myocardium was imaged dynamically by positron-emission tomography, starting at the time of intravenous bolus injection of H215O. The arterial input function was measured continuously with a beta-ray detector. A separate image after C15O inhalation was also obtained for correction of the H215O radioactivity in the blood. The absolute myocardial blood flow and the tissue fraction were calculated for 15 subjects with a kinetic technique under region-of-interest analysis. These results seem consistent with their coronary angiographic findings. The mean value of the measured absolute myocardial blood flows in normal subjects was 0.95 +/- 0.09 ml/min/g. This technique detected a diffuse decrease of myocardial blood flow in patients with triple-vessel disease.

An improved calibration procedure for computer-based quantitative autoradiography utilizing a mathematical model for the non-linear response of camera and film

A mathematical model which accounts for the non-linear response of both the camera and film in computer-aided quantitative autoradiography is derived. This model and the algorithm to fit the data for radioactive standards by a non-linear least-squares procedure to this model are described. The usefulness of this technique is demonstrated by employing it to analyze a set of 14C-labeled brain paste standards which were exposed to Ultrofilm in such a way that the full response range of the film was used. This technique can be readily implemented on most commercially available image analysis systems and is compatible with most types of video cameras.

The use of 14C-labeled tissue paste standards for the calibration of 125I-labeled ligands in quantitative autoradiography

The relationship between the exposure of Ultrofilm to 5-30-microns slices of 14C-labeled or 125I-labeled brain paste standards was characterized using quantitative autoradiography. After exposing these slices to Ultrofilm for 24, 48 or 72 h, the autoradiograms from the 14C-labeled brain pastes were used to generate standard curves with computerized densitometry. These autoradiographic standard curves were then used to estimate the level of radioactivity present in brain paste slices containing known amounts of 125I, which also had been exposed to the film for the same length of time. The relationship between the calculated concentration of 125I and the radioactivity of 125I as determined by direct gamma counting of slices scraped from slides was a direct linear one. The use of 14C-labeled, as opposed to 125I-labeled, standards obviates the major disadvantage of using 125I-radioligands for quantitative autoradiographic studies.

Maximizing precision in quantitative autoradiographic determination of tissue tracer concentration using exposure optimization

The relationships between tissue tracer concentrations, length of time of tissue contact with film, and the darkness of resulting autoradiographic images were explored. Operational equations were then developed relating ranges of film darkening to the ranges of tracer concentration contained within the sections. These equations were solved and used to define ranges of optical density that are optimal for precise determination of tracer concentration using digital image analyzers. The solutions indicated that optimal optical densities are a function of the range of tracer concentrations in the sections. For autoradiograms of typical cerebral blood flow and metabolism tracers, exposure should be controlled to produce images that are significantly less dark than what is generally considered pleasing to the eye.

Quantitative autoradiographic characterization of receptors for angiotensin II and other neuropeptides in individual brain nuclei and peripheral tissues from single rats

Autoradiographic techniques coupled with computerized microdensitometry and comparison with 125I standards were used to characterize and quantitate receptors for neuropeptides in rat brain and adrenal and pituitary glands. These techniques are rapidly performed, anatomically precise, and more sensitive than membrane binding techniques. They permit the determination of complete saturation curves and Scatchard analysis in discrete nuclei of the rat brain and in single rat pituitary and adrenal glands. Angiotensin II (AII) receptors were quantitated after incubation of 16-micron tissue sections with the AII agonist 125I-[Sar1]-AII. High-affinity, high-density AII receptors were present in the organon subfornicalis, organon vasculosum laminae terminalis and nuclei triangularis septalis, suprachiasmatis, and paraventricularis of the rat and in rat adrenal capsule-zona glomerulosa area, adrenal medulla, and anterior pituitary. These techniques could be used for precise localization and quantitation of other neuropeptide receptors in single rat brain nuclei, after optimizing the assay conditions and provided that suitable 125I ligands are available.

Quantitative film autoradiography for tritium: methodological considerations

The details of quantitative film autoradiography for tritium using tritium plastic standards were examined with respect to 3 issues: tritium tissue equivalent (TE) calibration; correction of autoabsorption differences for gray and white matter; and the use of carbon-14 standard sources as a method for quantifying tritium tissue images. Both 3H-tissue and 3H-plastic sources produced linear log-log relationships of 3H-concentration (nCi/mg source weight) vs source optical density (OD) over a reproducible OD range (0.080-0.800). The curves for both 3H-tissue and 3H-plastic were parallel; uncalibrated 3H-plastic standards exhibited a 4-fold higher autoabsorption over 3H-tissue sources for OD values in the linear range. Using chloroform extraction of brains from rats treated with either [14C]deoxyglucose ([14C]DG) or [3H]deoxyglucose ([3H]DG), we found neither isotope loss nor redistribution after defatting (30% reduction of tissue dry weight). After chloroform extraction, the OD values from both gray and white matter structures containing carbon-14 were unaltered. Gray matter OD values increased by 28.7 +/- 5.6% (mean +/- S.D.) in structures containing tritium; white matter structures containing tritium exhibited a 115.9 +/- 29.3% increase in OD after chloroform extraction. The increase in OD after chloroform extraction was a fixed percent for any given tritium OD value from unextracted tissue when the value was within the linear range of 0.080-0.800 OD units. The magnitude of the higher white matter autoabsorption for tritium was confirmed using tritium impregnated cow brain pastes of variable gray/white mixtures. Chloroform extraction of tissue from [3H]DG treated rats was therefore a suitable procedure for direct correction of regionally heterogeneous autoabsorption of tritium. Finally, the rates of image generation for tritium and carbon-14 sources were compared. The rate of increase of OD with increasing exposure time was found to be equal for 3H-tissue and 3H-plastic images; sources of carbon-14 in plastic, however, exhibited more accelerated rates of image generation when compared to tritium sources (i.e. 3H- and 14C-images did not covary with exposure time). The effect of non-covariance on tritium TE calibrated standards was the overestimation of OD values for 14C-plastic standards with increasing times of exposure (comparison of 4 week images to 1 week images showed errors of 35-40%). Use of carbon-14 sources to quantify tritium-generated images therefore required recalibration of 14C-plastic for all exposure times of interest.

Autoradiography and epifluorescence microscopy combined for the determination of number and spectrum of actively metabolizing bacteria in natural water

A technique is described for the determination of bacterial numbers and the spectrum of actively metabolizing cells on the same microscopic preparation by a combined autoradiography/epifluorescence microscopy technique. Natural bacterial populations incubated with [(3)H]glucose were filtered onto 0.2-mum Nuclepore polycarbonate membranes. The filters were cut into quarters and fixed on the surface of glass slides, coated with NTB-2 nuclear track emulsion (Kodak), and exposed to the radiation. After processing, the autoradiographs were stained with acridine orange. A combination of overstaining on the slightly alkaline side and gradual destaining on the acid side of neutrality gave the best results. Epifluorescence microscopy revealed bright-orange fluorescent cells with dark-silver grains associated against a greenish-to-grayish background. Based on the standardization curves, detection of actually metabolizing cells was optimal when cells were incubated with 1 to 5 muCi of [(3)H]glucose per ml of sample for 4 h and the autoradiographs were exposed to NTB-2 emulsion at 7 degrees C for 3 days. In water samples taken immediately above sandy sediments at beaches of the Kiel Fjord and the Kiel Bight (Baltic Sea, FRG), between 2.3 and 56.2% (average, 31.3%) of the total number of bacteria were actually metabolizing cells. Spearman rank correlation analysis revealed significant interrelationships between the number of active bacteria and the actual uptake rate of glucose.

[Bactericidal power of polymorphonuclear neutrophils. Trials for standardization of a micromethod using autoradiography (author's transl)]

A 50 mul sample of blood is placed successively in the presence of staphylococci, then of tritiated thymidine. Stripping film autoradiography permits identification of living intracellular bacteria which metabolize the marked precursor. In our experimental conditions, the percentage of marked intracellular bacteria is: -- 15,4 +/- 3,7% (x +/- 1s) among adults -- 14,6 +/- 3,2% among children.

The radioautographic transfer function and its implications for radioautographic methodology

A function was developed to relate the radioautographic detectability of tritiated thymidine to its incorporation into nuclear DNA under various experimental and specimen processing conditions. The implications of this function for the interpretation of cell kinetic studies were outlined, and its implications for radioautographic methodology were discussed. The standardization of radioautographic methods for facilitation of comparisons of data obtained from different sources under dissimilar experimental conditions was discussed.