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In this work an Electronic Control Unit for the management of a CFR engine will be described. The engine, which is used both for fuel octane rating (both in terms of RON and MON) and for research purpose, is equipped with a double injection system, with the aim to independently operate both with liquid and gaseous fuels. The developed ECU, hence, is able to control the injections of both kind of fuel, together with the spark ignition. Furthermore the system is also able to measure fuel’s consumption, instantaneous engine speed of rotation and air-fuel ratio, showing all the running parameters both on a local LCD display and on a PC based graphical user interface.

Il presente elaborato rappresenta il seguito del lavoro di tirocinio svolto presso il CNR ISSIA (Istituto dei Sistemi Intelligenti per l'Automazione) di Palermo, nel quale è stato effettuato il dimensionamento dell'elemento di accumulo con supercondensatore per tre tipologie di autoveicolo da strada, in grado di recuperare energia in fase di frenata e restituirla in fase di accelerazione. In questo elaborato è stata sviluppata la progettazione e la simulazione del convertitore bidirezionale DC/DC ad alta efficienza per veicoli ibridi con frenata rigenerativa, in modo da ottimizzare l'energia in gioco. L'obiettivo che si è prefissati è quello di ottenere un sistema elettronico di potenza in grado di gestire correnti elevate ma allo stesso tempo mantenere perdite ridotte. Nello studio, sono mostrate le varie strategie che consentono di intervenire sulle perdite, a partire dalla configurazione del convertitore, ai materiali, fino al controllo.

Purpose To address the tumorigenic potential of exposure to low/intermediate doses of ionizing radiation and to identify biological factors influencing tumor response in a mouse model highly susceptible to radiogenic cancer. Methods and Materials Newborn Ptc1 heterozygous mice were exposed to X-ray doses of 100, 250, and 500 mGy, and tumor development was monitored for their lifetime. Additional groups were irradiated with the same doses and sacrificed at fixed times for determination of short-term endpoints, such as apoptosis and early preneoplastic lesions in cerebellum. Finally, groups of Ptc1 heterozygous mice were bred on the C57BL/6 background to study the influence of common variant genes on radiation response. Results We have identified a significant effect of low-intermediate doses of radiation (250 and 500 mGy) in shortening mean survival and inducing early and more progressed stages of tumor development in the cerebellum of Ptc1 +/– mice. In addition, we show that age at exposure and heritable factors are potent modifiers of radiation-related cancer risk. Conclusions The Ptc1 knockout mouse model offers a highly sensitive system that may potentially help to improve understanding and quantification of risk at low doses, such as doses experienced in occupational and medical exposures, and clarify the complex interactions between genetic and environmental factors underlying cancer susceptibility.

The central dogma of radiation biology, that biological effects of ionizing radiation are a direct consequence of DNA damage occurring in irradiated cells, has been challenged by observations that genetic/epigenetic changes occur in unexposed “bystander cells” neighboring directly-hit cells, due to cell-to-cell communication or soluble factors released by irradiated cells. To date, the vast majority of these effects are described in cell-culture systems, while in vivo validation and assessment of biological consequences within an organism remain uncertain. Here, we describe the neonatal mouse cerebellum as an accurate in vivo model to detect, quantify, and mechanistically dissect radiation-bystander responses. DNA double-strand breaks and apoptotic cell death were induced in bystander cerebellum in vivo . Accompanying these genetic events, we report bystander-related tumor induction in cerebellum of radiosensitive Patched-1 ( Ptch1 ) heterozygous mice after x-ray exposure of the remainder of the body. We further show that genetic damage is a critical component of in vivo oncogenic bystander responses, and provide evidence supporting the role of gap-junctional intercellular communication (GJIC) in transmission of bystander signals in the central nervous system (CNS). These results represent the first proof-of-principle that bystander effects are factual in vivo events with carcinogenic potential, and implicate the need for re-evaluation of approaches currently used to estimate radiation-associated health risks.

We examined the effects of hair cycle phase on basal cell carcinoma (BCC) tumorigenesis induced by radiation in mice lacking one Patched allele (Ptc1neo67/+). Our results show that Ptc1neo67/+ mouse skin irradiated in early anagen is highly susceptible to tumor induction, as a 3.2-fold incidence of visible BCC-like tumors was observed in anagen-irradiated compared with telogen-irradiated mice. Microscopic nodular BCC-like tumors were also enhanced by irradiation during active hair-follicle growth phases. Interestingly, histologic examination of the tumors revealed a qualitative difference in BCC tumorigenesis depending on hair growth phase at the time of exposure. In fact, in addition to typical BCC-like tumors, we observed development of a distinct basal cell tumor subtype characterized by anti–cytokeratin 14 and anti–smooth muscle actin reactivity. These tumors showed relatively short latency and rapid growth and were strictly dependent on age at irradiation, as they occurred only in mice irradiated in early anagen phase. Examination of anatomic and immunohistochemical relationships revealed a close relation of these tumors with the follicular outer root sheath of anagen skin. In contrast, there are strong indications for the derivation of typical, smooth muscle actin–negative BCC-like tumors from cell progenitors of interfollicular epidermis. These results underscore the role of follicular bulge stem cells and their progeny with high self-renewal capacity in the formation of basal cell tumors and contribute to clarify the relationship between target cell and tumor phenotype in BCC tumorigenesis induced by radiation. (Cancer Res 2006; 66(13): 6606-14)

Loss-of-function mutations in Patched (Ptch1) are implicated in constitutive activation of the Sonic hedgehog pathway in human basal cell carcinomas (BCCs), and inherited Ptch1 mutations underlie basal cell nevus syndrome in which a typical feature is multiple BCC occurring with greater incidence in portals of radiotherapy. Mice in which one copy of Ptch1 is inactivated show increased susceptibility to spontaneous tumor development and hypersensitivity to radiation-induced tumorigenesis, providing an ideal in vivo model to study the typical pathologies associated with basal cell nevus syndrome. We therefore examined BCC development in control and irradiated Ptch1neo67/+ mice. We show that unirradiated mice develop putative BCC precursor lesions, i.e., basaloid hyperproliferation areas arising from both follicular and interfollicular epithelium, and that these lesions progress to nodular and infiltrative BCCs only in irradiated mice. Data of BCC incidence, multiplicity, and latency support the notion of epidermal hyperproliferations, nodular and infiltrative BCC-like tumors representing different stages of tumor development. This is additionally supported by the pattern of p53 protein expression observed in BCC subtypes and by the finding of retention of the normal remaining Ptch1 allele in all nodular, circumscribed BCCs analyzed compared with its constant loss in infiltrative BCCs. Our data suggest chronological tumor progression from basaloid hyperproliferations to nodular and then infiltrative BCC occurring in a stepwise fashion through the accumulation of sequential genetic alterations.

Experimental data on the incidence of solid tumors from various long-term mouse studies performed at the Casaccia laboratories over several years were reconsidered, limiting the analysis to the results available for doses equal to or less than 17 cGy of neutrons and 32 cGy of X rays since these dose limits are reasonably close to the generally accepted low-dose levels for high- and low-LET radiation (i.e. D(high-LET) < 5 cGy and D(low-LET) < 20 cGy, respectively). The following long-term experiments with BC3F1 mice were reviewed: (a) females treated with single doses of 1.5 MeV neutrons or 250 kVp X rays, (b) males treated with fractionated doses of fission neutrons, and (c) mice of both sexes irradiated in utero 17.5 days post coitus with single doses of fission neutrons or X rays. An experiment with CBA mice of both sexes treated with single doses of fission neutrons was also included in this study. Analysis was done on animals at risk; thus all incidences of tumor-bearing animals were expressed as the percentage excess incidence with respect to the controls. Ovarian tumors and other solid neoplasms were considered. The percentage frequencies and mean survival times of tumor-free mice were also recalculated. The results indicate the existence of a region at low doses where the final incidence of solid neoplasms is indistinguishable from the background incidence. These data reinforce the idea that at low doses the effectiveness of ionizing radiation in inducing solid neoplasms in laboratory mice is very low.

Outbred carcinogenesis-resistant (Car-R) and carcinogenesis-susceptible (Car-S) mouse lines were generated by phenotypic selection for resistance or susceptibility to two-stage skin carcinogenesis. These two Car mouse lines differ by100-fold in susceptibility. In the present study, we tested the hypothesis that a subset of genetic loci responsible for susceptibility or resistance to chemical skin tumorigenesis may also be involved in radiation-induced skin tumorigenesis. Skin tumorigenesis was tested in groups of Car-S/R mice after X-ray initiation and 12-O-tetradecanoylphorbol-13-acetate (TPA) promotion. We found that ionizing radiation can initiate skin tumors in Car-S mice but not in Car-R mice. In Car-S mice, the most effective radiation doses (6 and 10 Gy given in four fractions) gave a threefold increase in tumor multiplicity and a twofold increase in tumor incidence compared to a TPA-only control group. We performed a molecular analysis of Hras gene mutations in skin tumors of Car-S mice induced by X-ray initiation/TPA promotion or by TPA promotion alone. The most notable difference emerging from the comparison of these mutation patterns is the high incidence ( approximately 50%) of papillomas lacking Hras gene mutations in X-ray-initiated/TPA-promoted papillomas compared to 13% in papillomas induced by TPA alone, suggesting that lack of Hras gene mutations is a consistent feature of radiation-induced papillomas.

Medulloblastoma (MB) is the most common pediatric tumor of the CNS, representing ∼20% of all childhood CNS tumors. Although in recent years many molecular mechanisms that control MB development have been clarified, the effects of biological factors such as sex on this tumor remain to be explained. Epidemiological data, in fact, indicate a significant difference in the incidence of MB between the 2 sexes, with considerably higher susceptibility of males than females. Besides this different susceptibility, female sex is also a significant favorable prognostic factor in MB, with girls having a much better outcome. Despite these literature data, there has been little investigation into estrogen influence on MB development. In our study, we evaluated how hormone deficiency resulting from ovariectomy and hormone replacement influences the development of early and advanced MB stages in Patched1 heterozygous mice, a well-characterized mouse model of radiation-induced MB. Susceptibility to MB development was significantly increased in ovariectomized Ptch1(+/-) females and restored to levels observed in control mice after estrogen replacement. We next investigated the molecular mechanisms by which estrogen might influence tumor progression and show that ERβ, but not ERα, is involved in modulation of MB development by estrogens. Finally, our study shows that a functional interaction between estrogen- and IGF-I-mediated pathways may be responsible for the effects observed.

Gender-related differences in medulloblastoma (MB) development have been reported with a higher incidence in males (slightly above 60%) than in females, female gender being also a significantly favorable prognostic factor in MB. The present study focused on the evaluation of the mechanisms by which estrogens protect against MB formation. To this end, we used a well characterized mouse model of MB – the Patched1 heterozygous mice. Ovariectomized mice were treated with 2,3-bis(4-hydroxyphenyl)-propionitrile (DPN), a highly potent ERβ agonist, or 4,4′,4″-(4-propyl-[1H]-pyrazole-1,3,5-triyl) trisphenol (PPT), a highly potent ERα agonist. Our results show that the ERβ selective agonist DPN significantly inhibits development of MB preneoplastic lesions when compared with untreated ovariectomized mice, restoring the final incidence to that observed in the intact controls, and that these effects were achieved via activation of anti-proliferative and pro-apototic pathways. On the other hand, the ERα selective agonist PPT did not influence MB tumorigenesis relative to untreated ovariectomized mice.

Background Medulloblastoma is amongst the most common malignant brain tumors in childhood, arising from neoplastic transformation of granule neuron precursors (GNPs) of the cerebellum via deregulation of pathways involved in cerebellar development. Deregulation of the Sonic hedgehog/Patched1 (Shh/Ptc1) signaling pathway predisposes humans and mice to medulloblastoma. In the brain, insulin-like growth factor (IGF-I) plays a critical role during development as a neurotrophic and neuroprotective factor, and in tumorigenesis, as IGF-I receptor is often activated in medulloblastomas. Results To investigate the mechanisms of genetic interactions between Shh and IGF signaling in the cerebellum, we crossed nestin/IGF-I transgenic (IGF-I Tg) mice, in which transgene expression occurs in neuron precursors, with Ptc1 +/- knockout mice, a model of medulloblastoma in which cancer develops in a multistage process. The IGF-I transgene produced a marked brain overgrowth, and significantly accelerated tumor development, increasing the frequency of pre-neoplastic lesions as well as full medulloblastomas in Ptc1 +/- /IGF-I Tg mice. Mechanistically, tumor promotion by IGF-I mainly affected preneoplastic stages through de novo formation of lesions, while not influencing progression rate to full tumors. We also identified a marked increase in survival and proliferation, and a strong suppression of differentiation in neural precursors. Conclusions As a whole, our findings indicate that IGF-I overexpression in neural precursors leads to brain overgrowth and fosters external granular layer (EGL) proliferative lesions through a mechanism favoring proliferation over terminal differentiation, acting as a landscape for tumor growth. Understanding the molecular events responsible for cerebellum development and their alterations in tumorigenesis is critical for the identification of potential therapeutic targets.

The patched (Ptc1) protein is a negative regulator of sonic hedgehog signaling, a genetic pathway whose perturbation causes developmental defects and predisposition to specific malignant tumors. Humans and mice with mutated Ptc1 are prone to medulloblastoma and basal cell carcinoma (BCC), both tumors showing dependence on radiation damage for rapid onset and high penetrance. Poly(ADP-ribose) polymerase (PARP-1) is a nuclear enzyme that plays a multifunctional role in DNA damage signaling and repair. In healthy and fertile PARP-1-null mice, radiation exposure reveals an extreme sensitivity and a high genomic instability. To test for interactions between PARP-1 and sonic hedgehog signaling, PARP-1-null mice were crossed to Ptc1 heterozygous mice. PARP-1 deletion further accelerated medulloblastoma development in irradiated Ptc1(+/-) mice, showing that PARP-1 inactivation sensitizes cerebellar cells to radiation tumorigenic effects. In addition to increased formation and slowed down kinetics of disappearance of gamma-H2AX foci, we observed increased apoptosis in PARP-1-deficient granule cell progenitors after irradiation. Double-mutant mice were also strikingly more susceptible to BCC, with >50% of animals developing multiple, large, infiltrative tumors within 30 weeks of age. The results provide genetic evidence that PARP-1 function suppresses sonic hedgehog pathway-associated tumors arising in response to environmental stress.

We described previously a basal cell carcinoma (BCC) and medulloblastoma (MB) phenotype for CD1Ptch1neo67/+ mice exposed to ionizing radiation. Ptch1 heterozygous mice mimic the predisposition to BCC and MB development of patients affected by nevoid BCC syndrome that inherit a mutant Patched (Ptch1) allele. To examine the impact of genetic background on development of BCCs and other tumors we used two outbred mouse lines characterized by extremely high, carcinogenesis-susceptible (Car-S), and low, carcinogenesis-resistant (Car-R), susceptibility to skin carcinogenesis. Crosses between Ptch1neo67/+ mice and Car-S (F1S) or Car-R mice (F1R) were exposed to ionizing radiation. F1SPtch1neo67/+ mice were highly susceptible to radiation-induced BCCs, whereas F1RPtch1neo67/+ mice were completely resistant, indicating that tumor penetrance can be modulated by genetic background. Development of microscopic and macroscopic BCC lesions was influenced by Car-S and Car-R genotypes, suggesting a genetic-background effect on both initiation and progression of BCC. Susceptibility was additionally increased in N2 backcross mice (Car-S x F1SPtch1neo67/+), showing a contribution from recessive-acting Car-S modifiers. The modifying effects of Car-S-derived susceptibility alleles were tissue specific. In fact, despite higher susceptibility to BCC induction, Car-S-derived lines had lower MB incidence compared with CD1Ptch1neo67/+ mice. BCC-associated somatic events were not influenced by genetic background, as shown by similar rate of wild-type Ptch1 loss in BCCs from F1SPtch1neo67/+ (93%) and CD1Ptch1neo67/+ mice (100%). Finally, microsatellite analysis of BCCs showed Ptch1 loss through interstitial deletion. These results are relevant to humans, in which BCC is the commonest malignancy, because this model system may be used to study genes modifying BCC development.

Loss-of-function mutations in Patched (Ptch1) are implicated in constitutive activation of the Sonic hedgehog pathway in human basal cell carcinomas (BCCs), and inherited Ptch1 mutations underlie basal cell nevus syndrome in which a typical feature is multiple BCC occurring with greater incidence in portals of radiotherapy. Mice in which one copy of Ptch1 is inactivated show increased susceptibility to spontaneous tumor development and hypersensitivity to radiation-induced tumorigenesis, providing an ideal in vivo model to study the typical pathologies associated with basal cell nevus syndrome. We therefore examined BCC development in control and irradiated Ptch1(neo67/+) mice. We show that unirradiated mice develop putative BCC precursor lesions, i.e., basaloid hyperproliferation areas arising from both follicular and interfollicular epithelium, and that these lesions progress to nodular and infiltrative BCCs only in irradiated mice. Data of BCC incidence, multiplicity, and latency support the notion of epidermal hyperproliferations, nodular and infiltrative BCC-like tumors representing different stages of tumor development. This is additionally supported by the pattern of p53 protein expression observed in BCC subtypes and by the finding of retention of the normal remaining Ptch1 allele in all nodular, circumscribed BCCs analyzed compared with its constant loss in infiltrative BCCs. Our data suggest chronological tumor progression from basaloid hyperproliferations to nodular and then infiltrative BCC occurring in a stepwise fashion through the accumulation of sequential genetic alterations.

The two-stage skin carcinogenesis model of initiation and promotion in Carcinogenesis-susceptible (Car-S) mice has been used to investigate the pathways of promotional activity of 12- O -tetradecanoylphorbol-13-acetate (TPA), a phorbol ester tumor promoter, and benzoyl peroxide (BzPo), a free radical-generating compound. To test whether distinct populations of 9,10-dimethyl-1,2-benzanthracene (DMBA)-initiated epidermal keratinocytes are responsive to the two promoters, tandem experiments were performed. DMBA-initiated Car-S mice were promoted twice weekly with maximal promoting doses of TPA or BzPo. When the number of papillomas/mouse reached a plateau, promotion in the TPA and BzPo groups was switched to BzPo or TPA, respectively, until achievement of a new plateau. Mice promoted with BzPo developed 11.0±1.3 papillomas/mouse and subsequent TPA promotion induced 13.8 additional papillomas, for a total of 24.8±2.1 papillomas/mouse. TPA-promoted mice developed 23.3±1.1 papillomas/mouse, and subsequent BzPo promotion for 91 days did not promote additional papillomas. Our results show a less than additive tumor response after sequential promotion with BzPo and TPA, or vice versa, indicating that the pathways of promotional activity of TPA and BzPo are interacting. While the final papilloma yield was similar at the end of the two tandem promotion experiments independently of promoter sequence, the percentage of mice developing carcinomas was significantly higher in mice that were promoted with BzPo in the first stage. No significant differences in the frequency and type of c-Ha- ras mutations were observed in TPA- and BzPo-promoted tumors, suggesting that promotion of DMBA-initiated cells by BzPo requires introduction of additional molecular alterations compared to TPA.

Individuals affected with the Gorlin syndrome inherit a germ-line mutation of the patched (Ptc1) developmental gene and, analogously to Ptc1 heterozygous mice, show an increased susceptibility to spontaneous tumor development. Human and mouse Ptc1 heterozygotes (Ptc1(+/-)) are also hypersensitive to ionizing radiation (IR)-induced tumorigenesis in terms of basal cell carcinoma (BCC) induction. We have analysed the involvement of Ptc1 in the tumorigenic response to a single dose of 3 Gy X-rays in neonatal and adult Ptc1 heterozygous and wild type mice. We report that irradiation dramatically increased the incidence of medulloblastoma development (51%) over the spontaneous rate (7%) in neonatal but not adult Ptc1 heterozygotes, indicating that medulloblastoma induction by IR is subjected to temporal restriction. Analysis of Ptc1 allele status in the tumors revealed loss of the wild type allele in 17 of 18 medulloblastomas from irradiated mice and in two of three spontaneous medulloblastomas. To our knowledge, irradiated newborn Ptc1(+/-) heterozygous mice constitute the first mouse model of IR-induced medulloblastoma tumorigenesis, providing a useful tool to elucidate the molecular basis of medulloblastoma development.

As most occupational and environmental exposures to ionizing radiation are at low dose rates or in small dose fractions, risk estimation requires that the effects of the temporal distribution of dose are taken into account. Previous in vitro studies of oncogenic transformation, as well as in vivo studies of carcinogenesis induced by high-LET radiation, yielded controversial results concerning the presence of an inverse dose-rate effect. The present study tested the influence of one scheme of dose fractionation of monoenergetic neutrons on neoplastic transformation of C3H 10T1/2 cells. Neutrons of 0.5, 1.0 and 6.0 MeV were used. Cells were exposed to doses of 0.25 and 0.5 Gy, given acutely or in five fractions at 2-h intervals. The acute and fractionated irradiations with each energy were done on the same day. No significant difference between the two irradiation modes was found for both cell inactivation and neoplastic transformation at all energies. These results are in agreement with our data for fractionated fission-spectrum neutrons from the RSV-TAPIRO reactor.

An experimental study of male and female CBA/Cne mice was set up at Casaccia primarily to investigate the influence of sex on long-term survival and tumor induction after exposure to high- and low-LET radiation. Mice were whole-body-irradiated at 3 months of age with fission-neutron doses of 0.1, 0.2, 0.4, 0.8, 1.2 and 1.8 Gy at the RSV-TAPIRO reactor (mean neutron energy 0.4 MeV, in terms of kerma, y{sub D} = 51.5 KeV/{mu}m), or with 250 KVp X-ray doses of 1, 3, 5 and 7 Gy. Control and irradiated animals were then followed for their entire life span. As a general finding, male CBA/Cne mice appear more susceptible to tumori-genesis than females. In particular, the incidences of induced acute myeloid leukemia and malignant lymphomas are significant only in male mice. Benign and malignant solid tumors of many types are observed in mice of both sexes, the most frequent being in the lung, liver and ovary. However, evidence for a radiation response is limited to the case of Harderian gland neoplasms. In addition, a comparison of the observed frequency of all irradiated compared to unirradiated animals bearing solid tumors shows that the total tumor occurrence is not altered markedly by radiation exposure.more » A decrease in survival time is observed for both sexes and radiation types and correlates well with increasing dose. Moreover, both sex and radiation quality appear to influence the life shortening. A similar dose dependence of survival time is found when tumor-free animals alone are considered, suggesting a non-specific component of life-shortening. 18 refs., 3 figs., 5 tabs.« less

An experimental study of the biological effectiveness of multifractionated low doses of high-LET radiation was carried out using BC3F1 male mice. They were treated with whole-body irradiation with five equal daily fractions of fission neutrons to yield cumulative doses of 0.025, 0.05, 0.10, 0.17, 0.25, 0.36, 0.535 and 0.71 Gy at the RSV-TAPIRO reactor (mean neutron energy 0.4 MeV, in terms of kerma, y_D=51.5 keVμm, dose rate 0.004 Gy/min) and were followed for their entire life span. The statistical method described by Peto et al. (IARC Monograph, Suppl. 2, 1980) to establish the existence of a carcinogenic effect in long-term animal experiments was applied to the data sets. This analysis was done for myeloid leukemia and for the presence of selected solid tumors. Myeloid leukemia was absent in the control group and was rarely found in irradiated animals. However, a positive significant trend was found in the dose ranges 0-0.17 Gy and higher. Epithelial tumors were induced at doses from 0.17 Gy on. Tumor ...

was similar in the two cases, showing a steeply rising branch at doses up to 0.75 Gy followed by a maximum and an elevated plateau up to 4.00 Gy. A higher incidence of tumors in transplanted organs was apparent for doses up to the maximum, which was attributed to castration-induced hormonal imbalance. Specific death rate analysis of mice dying with ovarian tumors showed that in this system radiation acts essentially by decreasing tumor latency. Ovarian tumors were classified in various histological types and their development in time was followed by serial sacrifice. Separate analysis of death rate of animals carrying different tumor classes allowed further resolution of the various components of the tumor induction phenomenon. It was thus possible to show that the overall death rate analysis masks a true effect of induction of granulosa cell tumors in whole-body-irradiated animals. The transplantation technique offers little advantage for the study of radiation induction of ovarian tumor.

(C57BL/Cne x C3H/Cne)F1 mice were splenectomized at 3, 9, or 19 months of age (males) or at 4 months of age (females) and observed until spontaneous death. Their mean lifespans were only slightly increased by splenectomy, but the final incidence of and age-specific death rate from reticulum cell sarcoma (RCS) were significantly decreased; the latter effect was associated with prolonged latency times of neoplastic expression. Splenectomized females had a more pronounced decrease in incidence of and rate of death from RCS than did males. Lethally irradiated male mice were inoculated with isogeneic spleen cells from young (3 mo of age) or old (12-18 mo of age) untreated male donors, and the animals surviving acute radiation effects were also observed until spontaneous death. In spite of the fact that the mean life-spans of the spleen-repopulated animals were slightly shortened, age-specific death rate analysis showed that the rate of RCS incidence approached that of untreated controls of comparable ages. The combined results of splenectomy and spleen cell transplantation strongly indicated that some cells in the spleens of these mice have a high probability of being transformed into potentially neoplastic progenitor cells with long latency between cell transformation and overt tumor growth.

The average final incidence of reticulum cell sarcoma (RCS) in untreated control (C57BL/Cnefemale X C3H/Cnemale)F1 male mice was 57% and was not significantly changed by single acute whole-body doses of X-rays up to 400 rads. Higher doses sharply decreased this incidence to very low levels. In a syngeneic chimera system, however, irradiation (400 rads) of bone marrow prior to transplantation significantly increased the frequency and rate of RCS relative to transplantation of unirradiated marrow. An endogenous repopulating system was tested; marrow was irradiated in situ by a limb-shielding technique. The results indicated a biphasic dose-incidence curve with a peak at 500 rads. The rising part of the curve was in agreement with and extended the conclusion from the exogenous system, whereas the descending portion at higher doses paralleled the trend observed in the whole-body X-irradiated animals. Finally, the irradiation of two hind legs resulted in a higher frequency of RCS than did irradiation of only one leg at the same dose levels.

Biozzi mice selected for high (H) or low (L) antibody responsiveness to natural antigens have been followed for their entire life-span to examine their pathology at death. As previously found in selection I, shorter life-span and higher lymphoma incidence were observed in L responder mice than in H responder mice selected for antibody responsiveness to sheep red blood cells (selection II). In mice selected for antibody responsiveness to Salmonella flagellar antigens (selection III), similar life-span and similar lymphoma incidence were found in H and L responder mice. Natural killer (NK) cell activity, as assessed in spleen cells from young mice, was lower in L than in H responder mice of selection I but higher in L than in H responder mice of both selections II and III. All these results indicate that longevity and lymphoma incidence at death are independent of NK cell activity in mice selected for H or L antibody responsiveness to natural antigens. Furthermore, genetic selection for antibody responsiveness does not always appear to influence life-span and lymphoma incidence.

Dl MAJO, V., BALLARDIN, E., AND METALLI, P. Comparative Effects of Fission Neutron and X Irradiation on 7.5-Day Mouse Embryos. Radiat. Res. 87, 145-158 (1981). Fission spectrum neutrons (0-46.5 rad) were compared with 250-kV X rays (0-200 rad) for reduction of fetal weight and for embryolethal and teratogenic effects in mice. Animals were irradiated 7.5 days postcoitum (p.c.) and fetuses were examined 18.5 days p.c. Mortality showed a definite shoulder for both types of radiation. The shoulder was smaller for neutrons than for X rays, and at 20% mortality, the dose ratio was approximately 3. The relative biological effectiveness (RBE) for weight loss was 3.2 ? 0.8. The dose-effect relationships for major malformations after X irradiation showed a large shoulder (approximately 100 rad), while no apparent threshold could be seen in the neutron series, so that the relative efficiency of neutrons was dependent on the neutron dose. The equal effectiveness dose ratio estimated at 7% incidence of severe external malformations was 2.4, increasing to about 3.4 if more common head abnormalities were also included. In conclusion, fission neutrons induce the same types of effects as X rays in 7.5-day mouse embryos, being two to four times more effective than sparsely ionizing radiation at relatively high doses, except for major malformations where the RBE is higher with decreasing neutron doses.

(C57BL/Cne X C3H/Cne)F/sub 1/ male mice spontaneously develop reticulum cell sarcoma (RCS) with an average final incidence of 56%; neither myeloid leukemia (ML) nor thymic lymphoma (TL) has been observed in intact animals. X rays (4Gy, 250 kV) induce a few cases of ML but no TL. In increasing the dose to 6 Gy, we observed a few cases of TL, no ML, and a drastic reduction (8%) of RCS. The same dose of 6 Gy fractionated into four weekly doses of 1.5 Gy induced 24% of TL. By transplanting cells into appropriately preirradiated (4 Gy) syngeneic recipients we found evidence that four weekly doses of 1.5 Gy to donor animals caused an excess of ML and drastic changes of both TL and RCS incidences and rates in recipients as a function of time postirradiation at which the lymphohemopoietic tissues are transplanted. Furthermore, the same transplanted animals showed an evident acceleration of time of appearance of RCS and an enhanced incidence of NL; the latter effect is significant 10 days after the last X-ray fraction, but not thereafter. These data are in line with the hypothesis that committed cells for these two types of systemic tumors may be present amongmore » the irradiated transplanted tissues.« less