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Working memory contents are represented in neural activity patterns across multiple regions of the cortical hierarchy. A division of labor has been proposed where more anterior regions harbor increasingly abstract and categorical representations while the most detailed representations are held in primary sensory cortices. Here, using fMRI and multivariate encoding modeling, we demonstrate that for color stimuli categorical codes are already present at the level of extrastriate visual cortex (V4 and VO1), even when subjects are neither implicitly nor explicitly encouraged to categorize the stimuli. Importantly, this categorical coding was observed during working memory, but not during perception. Thus, visual working memory is likely to rely at least in part on categorical representations. Significance statement: Working memory is the representational basis for human cognition. Recent work has demonstrated that numerous regions across the human brain can represent the contents of working memory. We use fMRI brain scanning and machine learning methods to demonstrate that different regions can represent the same content differently during working memory. Reading out the neural codes used to store working memory contents, we show that already in sensory cortex, areas V4 and VO1 represent color in a categorical format rather than a purely sensory fashion. Thereby, we provide a better understanding of how different regions of the brain might serve working memory and cognition.

Randomness is a fundamental property of human behavior. It occurs both in the form of intrinsic random variability, say when repetitions of a task yield slightly different behavioral outcomes, or in the form of explicit randomness, say when a person tries to avoid being predicted in a game of rock, paper and scissors. Randomness has frequently been studied using random sequence generation tasks (RSG). A key finding has been that humans are poor at deliberately producing random behavior. At the same time, it has been shown that people might be better randomizers if randomness is only an implicit (rather than an explicit) requirement of the task. We therefore hypothesized that randomization performance might vary with the exact instructions with which randomness is elicited. To test this, we acquired data from a large online sample (n = 388), where every participant made 1,000 binary choices based on one of the following instructions: choose either randomly, freely, irregularly, according to an imaginary coin toss or perform a perceptual guessing task. Our results show significant differences in randomness between the conditions as quantified by conditional entropy and estimated Markov order. The randomization scores were highest in the conditions where people were asked to be irregular or mentally simulate a random event (coin toss) thus yielding recommendations for future studies on randomization behavior.

Workers in occupational settings are usually exposed to numerous sources of electromagnetic fields (EMF) and to different physical agents. Risk assessment for industrial workplaces concerning EMF is not only relevant to operators of devices or machinery emitting EMF, but also to support-workers, bystanders, service and maintenance personnel, and even visitors. Radiofrequency EMF guidelines published in 2020 by the International Commission on Non-Ionizing Radiation Protection (ICNIRP) may also be indirectly applied to assess risks emerging from EMF sources at workplaces by technical standards or legislation. To review the applicability and adequacy to assess exposure to EMF in occupational settings in the European Union, the most current ICNIRP guidelines on radiofrequency EMF are reviewed. Relevant ICNIRP fundamentals and principles are introduced, followed by practical aspects of exposure assessment. To conclude, open questions are formulated pointing out gaps between the guidelines' principles and occupational practice, such as the impact of hot and humid environments and physical activity or controversies around ICNIRPS's reduction factors in view of assessment uncertainty in general. Thus, the article aims to provide scientific policy advisors, labor inspectors, or experts developing standards with a profound understanding about ICNIRP guidelines' applicability to assess hazards related to radiofrequency EMF in occupational settings.

Representations of sensory working memory can be found across the entire neocortex. But how are verbal working memory (VWM) contents retained in the human brain? Here we used fMRI and multi-voxel pattern analyses to study Chinese native speakers (15 males, 13 females) memorizing Chinese characters. Chinese characters are uniquely suitable to study VWM because verbal encoding is encouraged by their complex visual appearance and monosyllabic pronunciation. We found that activity patterns in Broca's area and left premotor cortex carried information about the memorized characters. These language-related areas carried (1) significantly more information about cued characters than those not cued for memorization, (2) significantly more information on the left than the right hemisphere and (3) significantly more information about Chinese symbols than complex visual patterns which are hard to verbalize. In contrast, early visual cortex carries a comparable amount of information about cued and uncued stimuli and is thus unlikely to be involved in memory retention. This study provides evidence for verbal working memory maintenance in a distributed network of language-related brain regions, consistent with distributed accounts of WM. The results also suggest that Broca's area and left premotor cortex form the articulatory network which serves articulatory rehearsal in the retention of verbal working memory contents.

Techniques of multivariate pattern analysis (MVPA) can be used to decode the discrete experimental condition or a continuous modulator variable from measured brain activity during a particular trial. In functional magnetic resonance imaging (fMRI), trial-wise response amplitudes are sometimes estimated from the measured signal using a general linear model (GLM) with one onset regressor for each trial. When using rapid event-related designs with trials closely spaced in time, those estimates are highly variable and serially correlated due to the temporally extended shape of the hemodynamic response function (HRF). Here, we describe inverse transformed encoding modelling (ITEM), a principled approach of accounting for those serial correlations and decoding from the resulting estimates, at low computational cost and with no loss in statistical power. We use simulated data to show that ITEM outperforms the current standard approach in terms of decoding accuracy and analyze empirical data to demonstrate that ITEM is capable of visual reconstruction from fMRI signals.

Abstract Background This study investigates the prediction of mild cognitive impairment‐to‐Alzheimer's disease (MCI‐to‐AD) conversion based on extensive multimodal data with varying degrees of missing values. Methods Based on Alzheimer's Disease Neuroimaging Initiative data from MCI‐patients including all available modalities, we predicted the conversion to AD within 3 years. Different ways of replacing missing data in combination with different classification algorithms are compared. The performance was evaluated on features prioritized by experts and automatically selected features. Results The conversion to AD could be predicted with a maximal accuracy of 73% using support vector machines and features chosen by experts. Among data modalities, neuropsychological, magnetic resonance imaging, and positron emission tomography data were most informative. The best single feature was the functional activities questionnaire. Conclusion Extensive multimodal and incomplete data can be adequately handled by a combination of missing data substitution, feature selection, and classification.

Currently, it is unclear whether pediatric multiple sclerosis (PMS) is a pathoetiologically homogeneous disease phenotype due to clinical and epidemiological differences between early and late onset PMS (EOPMS and LOPMS). Consequently, the question was raised whether diagnostic guidelines need to be complemented by specific EOPMS markers. To search for such markers, we analyzed cerebral MRI images acquired with standard protocols using computer-based classification techniques. Specifically, we applied classification algorithms to gray (GM) and white matter (WM) tissue probability parameters of small brain regions derived from T2-weighted MRI images of EOPMS patients (onset

Runtime reconfigurable system-on-chip designs for FPGAs pose manifold demands on the underlying system architecture and design tool capabilities. The system architecture has to support varying communication needs of a changing number of processing units mapped onto diverse locations. Design tools should support an arbitrary placement of processing modules and the adjustment of boundaries of reconfigurable regions to the size of the actually instantiated processing modules. While few works address the design of flexible system architectures, the adjustment of boundaries of reconfigurable regions to the size of the actually instantiated processing modules is hardly ever considered due to design tool limitations. In this paper, a technique for circumventing this restriction is presented. It allows for a rededication of the reconfigurable area to a different number of individually sized reconfigurable regions. This technique is embedded in the design flow of a runtime reconfigurable system architecture for Xilinx Virtex-4 FPGAs. The system architecture will also be presented to provide a realistic application example.

Background: Central nervous system fungal infections (FI) are important complications and a cause of mortality in patients who receive hematopoietic stem cell transplantation (HSCT)., Aims: To study the clinical aspects of fungal encephalitis (FE)., Settings and Design: The study was carried out at the HSCT Center of the Hospital de Clínicas, Federal University of Paraná, Curitiba, Brazil., Materials and Methods: Clinical records and autopsy reports from patients submitted to HSCT with a diagnosis of FE., Results: Twelve patients were diagnosed with FE presenting with lowered level of consciousness, hemiparesis and seizures. We were able to identify two subgroups regarding susceptibility to FE: (1) patients with early onset FI and severe leucopenia, and (2) patients with later onset FI with graft-versus-host disease using immunosuppressive drugs. Eleven of the patients died directly due to the neurological complication, all had post-mortem confirmation of the diagnosis of FI., Conclusions: These clinical, paraclinical and temporal patterns may provide the opportunity for earlier diagnosis and interventions.

The chronic inflammatory demyelinating polyradiculoneuropathy (CIDP) is an unusual but important complication of hematopoietic stem cell transplantation (HSCT) rarely reported to date. We describe a 17-year-old woman with a diagnosis of acute myeloid leukemia due to Fanconi's anemia who was submitted to allogeneic HSCT and developed CIDP as part of graft-versus-host disease. Investigation showed high cerebrospinal fluid protein; electrophysiological studies revealed sensory-motor demyelinating polyradiculoneuropathy; muscle and nerve biopsy were compatible with CIDP.

Rippling muscle disease (RMD) is a benign myopathy with symptoms and signs of muscular hyperirritability. We report a 17-year-old patient who presented with muscular hypertrophy, local mounding on percussion, and a rippling phenomenon. Needle electromyography showed electrical silence during the rippling phenomenon. Muscle protein immunohistochemical analysis showed a partial deficiency of caveolin-3. Molecular analysis revealed a novel heterozygous A>C transition at nucleotide position 140 in exon 2 of the caveolin-3 gene. We associated this novel mutation with RMD.

The Emery-Dreifuss muscular dystrophy is a form of muscular dystrophy that frequently presents early contractures and cardiac conduction defects, caused by emerin deficiency in the inner nuclear membrane of the muscular fibers. A 19-years-old man it presented muscle weakness and hypotrophy in the proximal upper and lower limbs, dysphagia and early contractures in elbows and ankles, with familiar history compatible with X-linked inheritance form. The investigation showed increased serum creatinekinase levels electrocardiogram had a first degree atrioventricular block and right bundle branch block normal electromyography and nerve conduction study muscle biopsy disclosed myopathic characteristics and nuclear protein immunohystochemical analysis showed deficiency of emerin. The clinical and genetics manifestations, laboratorial and electromyography changes, as well as, the study of the pattern of inheritance for genetic counseling are discussed.

The National Council on Radiation Protection and Measurements (NCRP) in NCRP Report Number 106 recommended a limit of 10(10) beta particles emitted from radioactive particles with sizes less than 1 mm (hot particles) to prevent acute deep ulceration. This recommendation was determined, in part, by regressing the diameter of the scabs induced by fissioned 235UC2 hot particles as a function of the logarithm of the number of beta particles emitted from the sources for one study. To validate this recommendation and the approach used by the NCRP, external irradiations of pig skin using radioactive sources of less than 600 microm in the largest dimension were carried out. The hot particles used included fissioned 235UC2 and activated 170Tm, 175Yb, and 46Sc. Results indicated a strong correlation between scab diameter and dose for scabs induced using fissioned 235UC2, activated 170Tm, and 46Sc, but not for 175Yb. The correlation value decreased with decreasing beta particle energy, with the exception of 46Sc, which had scabs with diameters greater than twice the maximum beta particle range. The larger scabs from 46Sc are thought to be due to dose contributions from the gamma rays. The results also give an ulceration threshold less than that given by NCRP to prevent acute deep ulceration. It was concluded that regression analysis of scab diameter as a function of either number of beta particles emitted from the hot particles or dose did not yield either precise or accurate thresholds but was useful in determining probable ranges of doses which lead to scab induction.

External irradiations of pig skin using radioactive sources of less than 600 microm in the largest dimension (hot particles) were carried out. The objective of the study was to determine a threshold for scab induction. Hot particles used included fissioned 235U and activated 170Tm, 17SYb, and 46Sc with maximum beta-particle energies of approximately 1.8 (average), 0.97, 0.47, and 0.35 MeV, respectively. The photon emissions from the fissioned 235U were about 1 MeV per disintegration. The photon emissions from 46Sc were 0.89 and 1.12 MeV, with 100% abundance. Photon emissions from 170Tm and 175Yb were negligible. Responses followed cumulative normal probability distributions; thus, no true thresholds could be determined. Hence, 10% and 50% scab incidence rates (ED10 and ED50, respectively) were determined using probit analysis. For dose averaged over 1 cm2 at a depth of 70 microm, the ED10 (and 95% confidence limits) were 5.1 (2.7-7.2) Gy for 46Sc, 1.3 (0.89-1.8) Gy for 175Yb, 2.8 (1.9-3.5) Gy for 170Tm, 8.5 (5.7-9.8) Gy for on-skin fissioned UC2, and 4.5 (0.9-7.2) Gy for off-skin fissioned UC2. The ED50 values were 12 (8.8-17) Gy for 46Sc, 6.0 (4.3-9.7) Gy for 175Yb, 5.9 (5.1-6.7) Gy for 170Tm, 11 (9.9-19) Gy for on-skin fissioned 235UC2, and 11 (6.2-14) Gy for off-skin fissioned 235UC2.

Effective half-lives (T(e)) for radiolabeled antibodies can be much longer than that of traditional radiopharmaceuticals, potentially resulting in larger doses to members of the public. Clearance-rate data from patients treated with radio-labeled antibodies (RABs) were obtained from ten institutions. Calculations were made to determine if a single- or bi-exponential clearance-rate model was statistically justified; the results indicated that the former model was justified for more than 95% of the data. Values of T(e) for the different RABs are summarized. To plan actions to limit doses to less than 5 mSv annually for individuals continuously close to the patient (at 1 m), dose rates from patients at the time of release also are given as a function of T(e).

During the past decade, a large number of radiobiological studies have become available for tritium--many of them focusing on the relative biological effectiveness of tritium beta rays. These and previous studies indicate that tritium in body water produces the same spectrum of radiogenic effects (e.g., cancer, genetic effects, developmental abnormalities, and reproductive effects) observed following whole-body exposure to penetrating radiations such as gamma rays and x rays. However, tritium beta rays are of greater biological effectiveness than gamma rays and x rays. For example, tritium in the oxide form is about 2 to 3 times more effective at low doses or low dose rates than gamma rays from 137Cs or 60Co. When tritium is bound to organic molecules, relative biological effectiveness values may be somewhat larger than those for tritium in oxide form. Tritium administered to animals or to cells in vitro as tritiated amino acids results in relative biological effectiveness values that appear similar to those obtained for tritium in oxide form; however, if administered as tritiated thymidine, the relative biological effectiveness values appear to be about two-fold higher. It is clear from the wealth of tritium data now available that relative biological effectiveness values for tritium beta rays are higher than the quality factor of unity generally used in radiation protection.

Nonuniform distribution of absorbed dose is frequently encountered in the irradiated mammal; the degree of nonuniform distribution is generally more severe as the size of the animal increases and the energy or penetrating power of the radiation decreases. However, acute mortality under these conditions, e.g., from the hematopoietic syndrome, appears not to be consistently predictable from the dose at any given location or locations within the animal. It is thus reasonable to seek a biological quantity that may be adequate for this purpose. Accordingly, it was postulated that, in animals dying from the bone marrow syndrome, survival is determined by the total number of viable stem cells remaining in the entire body, independent of their distribution. To test this hypothesis, the LD50/30 value for mice exposed to nonuniform irradiation of varying degrees of severity was obtained, as was that for mice receiving uniform total-body irradiation. The distribution of bone marrow in transverse segments of tissue along the spinal axis was determined, as was the dose to each of the segments. The data were analyzed by multiplying, for each segment, the fraction of stem cells in the fraction of cells surviving, as determined from the dose and a survival curve for stem cells determined separately. The sum of these products yielded the surviving number of stem cells in the total mouse, for both the uniformly and nonuniformly exposed animals. The surviving fraction was found to differ by no more than 20%; this was taken to be reasonable evidence that, based on the number of surviving stem cells, it is possible to predict the mortality rate for both uniform and markedly nonuniform irradiation.

Equipment designed for simultaneous exposure of rodents to 60-Hz electric and magnetic fields is described. Three identical systems were constructed, each capable of continuous exposure of 256 rats or 640 mice to a nominal electric field at less than 50 kV/m, and to horizontal and vertical magnetic fields at less than 1 mT. Design features, construction details, and results of various tests of the systems are described. Tests were made: of phase relations between electric and magnetic fields; of uniformity of electric and magnetic fields; of changes across time in electric-field intensity as a result of animals' soiling of cages and various washing routines; of resistance of bedding material during humid and dry conditions; and of acoustic noise due to background, to field-generation equipment, and to air conditioning equipment. The results demonstrated that fields were effectively generated but that significant and troublesome changes in electric-field intensity occurred because of cage-soiling. However, when cages were frequently cleaned, field intensities were consistent from one exposure to another.

Proliferation and differentiation of human granulocytes were studied in a diffusion chamber (DC) culture system. Evaluation of the nucleated marrow cells of normal volunteers revealed that the granulocytic precursors continue differentiation in the DC as they do in vivo. Generation time of the granulocytes in the multiplicative pool in DC was determined by the autoradiographic mean grain count halving method. With tritiated thymidine (3HTdR) the half-time was 67 h, where as with 125Iododeoxyuridine it was 47 h. The longer half-time with 3HTdR supports the notion that a fraction of nuclear 3HTdR from dead cells is reutilized by the newly proliferating cells. The 3HTdR labeling index of granulocytic precursors in the multiplicative pool during the first 10 days in DC is not constant, suggesting a variation in the rate of proliferation. The DNA synthesis time in DC, determined by double isotope labeling technique, showed that it was relatively constant. Simultaneous evaluation of rate of transition of granulocytes in DC from one stage to the next of one patient with chronic myelocytic leukemia and another with myeloid metaplasia with myelofibrosis indicated a more rapid transition in the DC than in vivo in man.

The residual injury to the proliferation capability of hemopoietic stem cells (CFU-S) which results from their exposure to leukemogenic agents was evaluated in mice given a single leukemogenic dose of methyl nitrosourea (MNU 50 mg/kg body weight, i.v.). Bone marrow cellularity, splenic weight, number of CFU-S and the proportion of cycling to noncycling CFU-S were measured in an effort to detect and acute and residual injury to the CFU-S from mice given MNU 21 and 3 days earlier. Marrow cells were also transferred into lethally irradiated mice to observe the self-renewal capability of the CFU-S in the recipient spleen and bone marrow. The results of these measurements show that the CFU-S in marrow from mice given 50 mg/kg of MNU 21 days earlier still have a defective ability for self-renewal, although the total cellularity, number of CFU-S and proportion of cycling and noncycling CFU-S in the donor have returned to the normal range. The relationship of this self-renewal defect to the development of leukemia after this leukemogenic dose of MNU is not known.

A summary of all the findings to date is given in Table 2. It appears from this information that it is possible to detect somatic, cytogenetic, and genetic effects resulting from exposures at 33 to 100 times the mpc's for HTO. Similar effects also result from exposure to external gamma rays at an equivalent dose. The reduction in bone marrow cells in animals maintaining normal total cellularity is of interest since it demonstrates both the presence of an effect at the primitive cell level and the animal's ability to compensate for this effect by recruiting stem cells from the G0 resting state. This evidence of damage together with the observed cytogenetic changes leads one to contemplate the possible importance of radiation exposures at these levels for the induction of leukemia or other blood dyscrasias. Studies to investigate this question are now under way. As predicted on the basis of established principles of radiobiology, exposure to tritium beta rays from HTO ingestion results in measurable effects on several animal systems. The importance of position of incorporation of H into molecules of biological importance has not been well defined, nor have the low-dose portions of the dose-response curve for several effects of interest. Experiments designed to address these questions and measure H turnover as a means for analysis of cell kinetics in several systems are now under way.

Radiation damage to the right femoral artery was studied in mice 7--8 weeks old. Single X-ray exposures of 500 to 10 000 rad were used. The animals, except for the right upper legs, were shielded from exposure. The unexposed left femoral arteries served as 'controls'. Animals were killed at post-irradiation times of up to 120 days. Pathological changes in the irradiated arteries were scored on an arbitrary scale of 0 to 5 for individual tunica. The overall arterial damage was scored on a scale of 0 to 15. Radiation doses of 1000 to 10 000 rad produced quantitative histological changes in the three individual tunica and the degree of damage was dose-dependent. The tunica adventitia showed the maximum radiation injury, followed by tunica media and tunica intima in decreasing magnitude of injury. The combined effects on the artery followed closely the effects on media and adventitia.

The spleen-colony technique has been used for determining the relative biological effectiveness (r.b.e.) for several energies of neutron radiation. Donor mice were exposed for fission and accelerator-generated neutrons at a variety of doses and energies. Immediately after exposure, donor bone-marrow was removed from the hind legs, and standard amounts were injected intravenously into lethally X-irradiated recipients. After 7 days the recipients spleens were evaluated for surface colonies. Dose-response curves were obtained for each type of radiation and the Do was determined. The neutron r.b.e. values from the Do compared with 250kVp X-rays were: reactor 1.58, 252Cf 1:59, and accelerator varied from 2.85 at 1.0 Mev to 0.85 at 13.4 MeV.

Female mice were given different dosages (0, 3.0, 7.5, 15.0, or 30 muCi/ml) of tritium in their drinking water continuously from 3 to 7 weeks of age to assess the effects on germ cell chromosomes. At 8-9 weeks of age, mice were superovulated and metaphase II oocytes were processed and C-banded for cytogenetic analyses. Chromatid acentric fragments were the only type of structural aberration detected, and their incidence was higher in controls than in any of the tritiated water (HTO) groups. Analysis of numerical chromosomal aberrations revealed that the incidence of hypoploid (N = 19) oocytes was higher in oocytes from mice who drank HTO as compared with controls. However, the effects of HTO upon aneuploidy induction was not definitive due to the increase the incidence of aberrations in mouse oocytes can be related to the low dose rate resulting from chronic HTO exposure and possibly death of tritium-damaged cells.

The effect of X-rays and different-energy neutrons on human bone-marrow cells was studied using two different cell-culture techniques--diffusion chamber (DC) growth and colony formation in vitro (CFU-C). Based on the survival of proliferative granulocytes in DC on day 13, the D0 value was 80 rad with X-rays, and 117 rad as measured by the CFU-C assay. The D0 values for neutrons depended on the radiation source and the energy level. The r.b.e. values, which dropped with increasing energy levels of mono-energetic neutrons, were (i) 0.44 MeV; DC 3.7, CFU-C 4.1; (ii) 6 MeV; DC 1.8, CFU-C 2.0; (iii) 15 MeV; DC 1.6, CFU-C 1.6; (iv) fission neutrons; DC 2.6, CFU-C 2.4.

To obtain concentrated suspensions of pluripotent hematopoietic stem cells *CFUS) from murine bone marrow, density gradient centrifugal sedimentation (DGCS) was combined with counterflow centrifugal elutriation (CE). This combination provided a 7.6 fold enrichment of the CFUS concentration. For DGCS, Percoll a suspension of silica particles coated with polyvinylpyrrolidone was used. For fractionation by the CE an elutriator rotor (JE-6, Beckman) was used for further concentration of the cells harvested from the DGCS. Bone marrow erythropoiesis was suppressed by transfusion plethora initiated 5-6 days before the bone marrow was harvested. These two physical separation procedures combined with transfusion plethora to suppress erythropoiesis are effective in producing an enriched fraction of CFUS without change in distribution of the histologic type of colonies.

In order to investigate some characteristics of Millipore diffusion chamber cultures (DCC) and their potential for the quantitation of tumor cell growth kinetics, HeLa S-3-cells were grown in diffusion chambers implanted i.p. in mice. HeLa cells grew pseudologarithmically in DCC with a population-doubling time of approximately 2.8 days when 9.2 to 12.0 X 10(5) cells were placed in the chambers initially. The population-doubling time varied as a function of the initial innocula size but was always longer than the in vitro population-doubling time of 1.2 days. Comparable harvests of cells from experiment to experiment varied quantitatively by no more than a factor 1.8. This variaton somewhat limits the use of DCC for the quantitation of subtle effects. The fate and morphology of HeLa cells in DCC were determined from scanning electron microscopy. DCC might be exploited in clinical studies of the growth of patients' tumors and the effects of various therapies in a host-mediated system.

The long term somatic and genetic effects of chronic tritium (3H) ingestion have been measured in mice. Second generation animals, who with their parents were maintained on drinking water containing 3 muCi/ml of HTO, have been bred and the number of dominant lethal mutations measured. The increase in dominant lethal mutations in treated animals as compared to tap water controls is significant at the 1% level. The stem cell content of the bone marrow has been measured throughout the lifetime of the animals. A slight reduction in colony forming units in the bone marrow of treated animals is evident beginning after approximately 12 weeks, increasing in severity throughout the lifetime of the animals. The distribution of tritium in tissue water protein fractions was determined, and the relative contribution to tissue dose calculated. The differential incorporation into protein fractions was not found to be significant.

The distribution of tritium among the amino acids of serum proteins in mice chronically exposed to tritiated water was determined by ion exchange chromatography of the protein hydrolysate. The specific activity of nonexchangeable tritium in these amino acids relative to the specific activity of tritium in the tissue water of mice ranged from 0.04 for phenylalanine and threonine to 1.0 for glycine and alanine. Since tritium from tissue water can enter the nonexchangeable positions of amino acids only as the result of metabolic processing, the relative specific activity of tritium in each amino acid is an indicator of the extent of such processing. The tritium content of tyrosine and all the amino acids required in the diet for survival is quite low, except for histidine, and can be entirely accounted for by transamination or, in the case of methionine, by transmethylation. The tritium content of the other amino acids is too high to result from such minor processing and must reflect primarily the fraction synthesized de novo. The implications of these findings with respect to the radiobiological consequences of a diet containing tritiated proteins are discussed.

The turnover of DNA and histones in the livers and brains of mice has been determined. These mice had been exposed to constant levels of tritiated water from conception until they were 8 months old. At this point, exposure to tritium was discontinued, and the tritium remaining in DNA and histones was measured at various intervals afterward. The half-lives calculated for these components (with 95% confidence limits given in parentheses) were 117 (85-188) days for liver histone, 318 (241-466) days for liver DNA, 159 (129-208) days for brain histone and 593 (376-1406) days for brain DNA. The difference between histone and DNA turnover is statistically significant for both tissues and indicates that histone turnover within tissues cannot be solely accounted for by cell turnover within the tissue but also must include histone turnover within living cells. The half-life of histone within cells is estimated to be 117 (88-178) days in liver and 223 (187-277) days in brain.

Nucleated cells obtained from blood and/or bone marrow of patients with myelofibrosis with myeloid metaplasia (MMM) were cultured in diffusion chambers (DC) implanted into the peritoneal cavities of irradiated mice. A total of five blood studies and two bone marrow studies were performed using cells obtained from five patients. The DC were harvested at intervals from the host mice and the total and differential cellularity of DC contents were evaluated. The results obtained from MMM cultures were compared with those from similar cultures of blood cells and marrow cells of four and six normal individuals respectively. The proliferation and maturation of the granulocytic, erythrocytic, and megakaryocytic lines in MMM cultures occurred in an orderly fashion as they occur in vivo. The patterns of proliferation and maturation of the three cell lines in cultures after day 7 suggest that they primarily originate from progenitor cells. The numbers of granulocytes in the multiplicative pool, recognizable red cell precursors, and megakaryocytes recovered were significantly greater from the MMM cultures than those from the normal blood or marrow cultures. These results suggest that the blood and marrow cells of MMM patients have increased numbers of progenitors for granulocytes, erythrocytes, and megakaryocytes.

A DC with Nuclepore filter wall has been described. Recovery of in vitro incubated human nucleated peripheral blood cells and in vivo growth of mouse bone marrow cells in intraperitoneally implanted DCs were improved when compared to the growth obtained in the more commonly used Millipore filter chambers.

A transplanted tumor that induces granulocytosis and produces colony stimulating factor (CSF) was studied in mice during several passages. The sequence of events leading to granulocytosis was characterized. Band granulocytes were increased 3 days after tumor inoculation, while simultaneously CFU-s and CFU-c in bone marrow and spleen were transitorily low. This was followed by rapid accumulation of CFU-c and CFU-s in spleen, and by successive waves of increased mitotable and non-mitotable granulocytes in spleen and marrow. In contrast, marrow CFU-c and CFU-s remained normal or slightly decreased.

These studies have addressed firstly the effect of single small doses of x-rays upon murine hematopoietic stem cells to obtain a better estimate of the Dq. It is small, of the order of 20 rad. Secondly, a dose fractionation schedule that does not kill or perturb the kinetics of hemopoietic cell proliferation was sought in order to investigate the leukemogenic potential of low level radiation upon an unperturbed hemopoietic system. Doses used by others in past radiation leukemogenesis studies clearly perturb hemopoiesis and kill a detectable fraction of stem cells. The studies reported herein show that 1.25 rad every day decrease the CFU-S content of bone marrow by the time 80 rads are accumulated. Higher daily doses as used in published studies on radiation leukemogenesis produce greater effects. Studies on the effect of 0.5, 1.0, 2.0, and 3.0 rad 3 times per week are under way. Two rad 3 times per week produced a modest decrease in CFU-S content of bone marrow after an accumulation of 68 rad. With 3.0 rad 3 times per week an accumulation of 102 rad produced a significant decrease in CFU-S content of bone marrow. Dose fractionation at 0.5 and 1.0 rad 3 times per week has not produced a CFU-S depression after accumulation of 17 and 34 rad. Radiation leukemogenesis studies published to date have utilized single doses and chronic exposure schedules that probably have significantly perturbed the kinetics of hematopoietic stem cells. Whether radiation will produce leukemia in animal models with dose schedules that do not perturb kinetics of hematopoietic stem cells remains to be seen.

These studies were to evaluate the effects of humoral factors on amplification of nonrecognizable erythrocytic and granulocytic precursors by the in vivo plasma clot diffusion chamber and the in vitro plasma clot culture methods. Changes in the plasma erythropoietin levels in the reticulocyte concentration and hematocrits of irradiated and nonirradiated Long-Evans rats exposed to hypoxia were also determined. While erythropoietin plasma concentrations appeared to affect BFU-E and CFU-E growth, results suggest erythropoietin may not be the sole regulator of red cell production and that inhibitors of chalone-like mechanisms may be involved. Measurements made on granulocyte precursors treated with colony stimulating factor (CSF) containing L-cell-conditioned medium revealed granulocytic colonies and burst-like formations similar to those seen for erythrocytic growth. There is strong evidence suggesting that CSF is a regulator of granulopoiesis; however, it is not the sole regulator and it appears that inhibitors may play an in vivo role. Growth of colonies with cell numbers not a power of 2 implies either asymmetric mitosis due to loss of genetic information required for continuing division, or differences in concentrations of, or ability to recognize, inhibitory factors. These possibilities are examined in the light of results from in vivo and in vitro culture techniques.

Effects of benzene inhalation on mouse pluripotent hematopoietic stem cells have been evaluated. Male mice 8--12 wk old were exposed to 400 ppm benzene for 6 h/d, 5 d/wk, for up to 9 1/2 wk. At various time intervals exposed and control animals were killed, and cardiac blood was evaluated for changes in white blood cell (WBC) and red blood cell (RBC) content. In addition, femora and tibiae were evaluated for total marrow cellularity, stem cell content (as measured by the spleen colony technique), and the percent of stem cells in DNA synthesis (as determined by the tritiated thymidine cytocide technique). Exogenous spleen colonies grown from marrow of exposed animals were counted, identified, and scored by histological type. Exposure to benzene caused significant depressions of RBCs and WBCs throughout the exposure period, which continued for at least 14 d after exposure. Bone marrow cellularity and stem cell content were also depressed in exposed animals throughout the study. Tritiated thymidine cytocide of spleen colony-forming cells was generally increased in exposed animals, perhaps indicating a compensatory response to the reduction of circulating cells. Spleen colonies of all types were depressed after exposure to benzene. The significance of the reduction in cellularity, stem cell content, and changes in morphology of spleen colonies is discussed in relation to cellular toxicity and residual injury.

The ability of tritium to induce sister chromatid exchanges (SCEs) has been investigated in male mice of the Hale-Stoner-Brookhaven strain maintained on drinking water containing 3.0 microCi/ml tritiated water (HTO). At selected intervals after 28-261 days of consuming HTO, the frequency of SCEs and the kinetics of cellular proliferation were measured in bone marrow cells of animals maintained on HTO, and in age-matched control groups, by 5-bromo-2'-deoxyuridine labelling methods. A statistically significant (1 percent level) elevation of SCEs was observed after 81, 163, 192, 247 and 261 days of HTO ingestion. The frequency of induced SCEs increased linearly with the ingestion time. These results are of particular interest since ionizing radiation is generally not considered to be an efficient inducer of SCEs.

A survey of the literature to date on the enzyme histochemistry of intracellular organelles has not yielded any reference to the presence of acid phosphatase reaction products in the mammalian mitochondria of the central nervous system. A combination of Gomori's acid phosphatase mehtod, however, with standard electron microscopy has disclosed the presence of enzyme reaction products in the mitochondria of the central nervous system of rats from 2 hr to 22 weeks after x-ray irradiation, as well as in a cerebral biopsy performed on a patient affected by Huntington's chorea. No enzyme reaction products, on the other hand, were observed in serial sections that had been incubated in substrates either containing sodium fluoride or lacking in beta-glycerophosphate. The abnormal mitochondrial enzyme reaction (chemical lesion) is considered to be the consequenco of the pathologic process affecting the ultrastructural-chemical organization of the organelle.