The varied sources of faculae-forming brines in Ceres' Occator crater emplaced via hydrothermal brine effusion.

Before acquiring highest-resolution data of Ceres, questions remained about the emplacement mechanism and source of Occator crater's bright faculae. Here we report that brine effusion emplaced the faculae in a brine-limited, impact-induced hydrothermal system. Impact-derived fracturing enabled brines to reach the surface. The central faculae, Cerealia and Pasola Facula, postdate the central pit, and were primarily sourced from an impact-induced melt chamber, with some contribution from a deeper, pre-existing brine reservoir. Vinalia Faculae, in the crater floor, were sourced from the laterally extensive deep reservoir only. Vinalia Faculae are comparatively thinner and display greater ballistic emplacement than the central faculae because the deep reservoir brines took a longer path to the surface and contained more gas than the shallower impact-induced melt chamber brines. Impact-derived fractures providing conduits, and mixing of impact-induced melt with deeper endogenic brines, could also allow oceanic material to reach the surfaces of other large icy bodies.

Landslides on Ceres: Diversity and Geologic Context.

Landslides are among the most widespread geologic features on Ceres. Using data from Dawn's Framing Camera, landslides were previously classified based upon geomorphologic characteristics into one of three archetypal categories, Type 1(T1), Type 2 (T2), and Type 3 (T3). Due to their geologic context, variation in age, and physical characteristics, most landslides on Ceres are, however, intermediate in their morphology and physical properties between the archetypes of each landslide class. Here we describe the varied morphology of individual intermediate landslides, identify geologic controls that contribute to this variation, and provide first-order quantification of the physical properties of the continuum of Ceres's surface flows. These intermediate flows appear in varied settings and show a range of characteristics, including those found at contacts between craters, those having multiple trunks or lobes; showing characteristics of both T2 and T3 landslides; material slumping on crater rims; very small, ejecta-like flows; and those appearing inside of catenae. We suggest that while their morphologies can vary, the distribution and mechanical properties of intermediate landslides do not differ significantly from that of archetypal landslides, confirming a link between landslides and subsurface ice. We also find that most intermediate landslides are similar to Type 2 landslides and formed by shallow failure. Clusters of these features suggest ice enhancement near Juling, Kupalo and Urvara craters. Since the majority of Ceres's landslides fall in the intermediate landslide category, placing their attributes in context contributes to a better understanding of Ceres's shallow subsurface and the nature of ground ice.

The superstatistical nature and interoccurrence time of atmospheric mercury concentration fluctuations.

The probability density function (PDF) of the time intervals between subsequent extreme events in atmospheric Hg0 concentration data series from different latitudes has been investigated. The Hg0 dynamic possesses a long-term memory autocorrelation function. Above a fixed threshold Q in the data, the PDFs of the interoccurrence time of the Hg0 data are well described by a Tsallis q-Exponential function. This PDF behavior has been explained in the framework of superstatistics, where the competition between multiple mesoscopic processes affects the macroscopic dynamics. An extensive parameter µ, encompassing all possible fluctuations related to mesoscopic phenomena, has been identified. It follows a χ 2-distribution, indicative of the superstatistical nature of the overall process. Shuffling the data series destroys the long-term memory, the distributions become independent of Q, and the PDFs collapse on to the same exponential distribution. The possible central role of atmospheric turbulence on extreme events in the Hg0 data is highlighted.

Drug-repositioning screening identified piperlongumine as a direct STAT3 inhibitor with potent activity against breast cancer.

Signal transducer and activator of transcription (STAT) 3 regulates many cardinal features of cancer including cancer cell growth, apoptosis resistance, DNA damage response, metastasis, immune escape, tumor angiogenesis, the Warburg effect and oncogene addiction and has been validated as a drug target for cancer therapy. Several strategies have been used to identify agents that target Stat3 in breast cancer but none has yet entered into clinical use. We used a high-throughput fluorescence microscopy search strategy to identify compounds in a drug-repositioning library (Prestwick library) that block ligand-induced nuclear translocation of Stat3 and identified piperlongumine (PL), a natural product isolated from the fruit of the pepper Piper longum. PL inhibited Stat3 nuclear translocation, inhibited ligand-induced and constitutive Stat3 phosphorylation, and modulated expression of multiple Stat3-regulated genes. Surface plasmon resonance assay revealed that PL directly inhibited binding of Stat3 to its phosphotyrosyl peptide ligand. Phosphoprotein antibody array analysis revealed that PL does not modulate kinases known to activate Stat3 such as Janus kinases, Src kinase family members or receptor tyrosine kinases. PL inhibited anchorage-independent and anchorage-dependent growth of multiple breast cancer cell lines having increased pStat3 or total Stat3, and induced apoptosis. PL also inhibited mammosphere formation by tumor cells from patient-derived xenografts. PL's antitumorigenic function was causally linked to its Stat3-inhibitory effect. PL was non-toxic in mice up to a dose of 30 mg/kg/day for 14 days and caused regression of breast cancer cell line xenografts in nude mice. Thus, PL represents a promising new agent for rapid entry into the clinic for use in treating breast cancer, as well as other cancers in which Stat3 has a role.

Efficacy of sodium thiosulfate for the treatment for calciphylaxis.

BACKGROUND/AIMS: Calciphylaxis is a rare condition with dismal prognosis that affects patients with ESRD. Sodium thiosulfate (STS) may play a therapeutic role but its proposed efficacy is based on case reports and thus subject to publication bias. METHODS: We identified all patients who received STS for any indication over a 5-year period through pharmacy records of 4 hospitals, retrospectively reviewing medical records for risk factors, laboratory values, the response of skin lesions to STS, and mortality. RESULTS: 14 patients received STS for calciphylaxis over 5 years. Following STS administration, pain decreased in 71% of patients, and 70% had an improvement in their lesions. Those who did not improve or stabilize their skin lesions tended to have more advanced skin lesions, were on renal replacement therapy longer, were more obese and received less total dose of STS. However, despite STS, there was a 71% mortality rate, with 50% of subjects dying within 6 months. CONCLUSION: We conclude in this study of all subjects who received STS at our Institution that STS is an effective treatment for the pain and skin lesions of calciphylaxis if given in the early stages of disease and for a consistent period of time. However, there is little impact on overall mortality compared to historical published cohorts.

LMO4 is an essential mediator of ErbB2/HER2/Neu-induced breast cancer cell cycle progression.

ErbB2/HER2/Neu-overexpressing breast cancers are characterized by poor survival due to high proliferation and metastasis rates and identifying downstream targets of ErbB2 should facilitate developing novel therapies for this disease. Gene expression profiling revealed the transcriptional regulator LIM-only protein 4 (LMO4) is upregulated during ErbB2-induced mouse mammary gland tumorigenesis. Although LMO4 is frequently overexpressed in breast cancer and LMO4-overexpressing mice develop mammary epithelial tumors, the mechanisms involved are unknown. In this study, we report that LMO4 is a downstream target of ErbB2 and PI3K in ErbB2-dependent breast cancer cells. Furthermore, LMO4 silencing reduces proliferation of these cells, inducing a G2/M arrest that was associated with decreased cullin-3, an E3-ubiquitin ligase component important for mitosis. Loss of LMO4 subsequently results in reduced Cyclin D1 and Cyclin E. Further supporting a role for LMO4 in modulating proliferation by regulating cullin-3 expression, we found that LMO4 expression oscillates throughout the cell cycle with maximum expression occurring during G2/M and these changes precede oscillations in cullin-3 levels. LMO4 levels are also highest in high-grade/less differentiated breast cancers, which are characteristically highly proliferative. We conclude that LMO4 is a novel cell cycle regulator with a key role in mediating ErbB2-induced proliferation, a hallmark of ErbB2-positive disease.

Ovarian hyperstimulation induces centrosome amplification and aneuploid mammary tumors independently of alterations in p53 in a transgenic mouse model of breast cancer.

Aneuploidy and genomic instability are common features of human cancers, including breast cancer; however, mechanisms by which such abnormalities develop are not understood. The exquisite dependence of the mammary gland on hormones for growth and development as well as hormonal contributions to breast cancer risk and progression suggest that tumorigenic mechanisms in the breast should be considered in the context of hormonal stimulation. We used transgenic mice that overexpress luteinizing hormone with subsequent ovarian hyperstimulation as a model to identify mechanisms involved in hormone-induced mammary cancer. Tumor pathology in these mice is highly variable, suggesting individual tumors undergo distinct initiating or promoting events. Supporting this notion, hormone-induced tumors display considerable chromosomal instability and aneuploidy, despite the presence of functional p53. The presence of extensive centrosome amplification in tumors and hyperplastic glands prior to tumor formation suggests that alterations in the ovarian hormonal milieu dysregulate the centrosome cycle in mammary epithelial cells, leading to aneuploidy and cancer.

Sustained trophism of the mammary gland is sufficient to accelerate and synchronize development of ErbB2/Neu-induced tumors.

Epidemiological studies indicate that parity enhances HER2/ErbB2/Neu-induced breast tumorigenesis. Furthermore, recent studies using multiparous, ErbB2/Neu-overexpressing mouse mammary tumor virus (MMTV-Neu) mice have shown that parity induces a population of cells that are targeted for ErbB2/Neu-induced transformation. Although parity accelerates mammary tumorigenesis, the pattern of tumor development in multiparous MMTV-Neu mice remains stochastic, suggesting that additional events are required for ErbB2/Neu to cause mammary tumors. Whether such events are genetic in nature or reflective of the dynamic hormonal control of the gland that occurs with pregnancy remains unclear. We postulated that young age at pregnancy initiation or chronic trophic maintenance of mammary epithelial cells might provide a cellular environment that significantly increases susceptibility to ErbB2/Neu-induced tumorigenesis. MMTV-Neu mice that were maintained pregnant or lactating beginning at 3 weeks of age demonstrated accelerated tumorigenesis, but this process was still stochastic, indicating that early pregnancy does not provide the requisite events of tumorigenesis. However, bitransgenic mice that were generated by breeding MMTV-Neu mice with a luteinizing hormone-overexpressing mouse model of ovarian hyperstimulation developed multifocal mammary tumors in an accelerated, synchronous manner compared to virgin MMTV-Neu animals. This synchrony of tumor development in the bitransgenic mice suggests that trophic maintenance of the mammary gland provides the additional events required for tumor formation and maintains the population of cells that are targeted by ErbB2/Neu for transformation. Both the synchrony of tumor appearance and the ability to characterize a window of commitment by ovariectomy/palpation studies permitted microarray analysis to evaluate changes in gene expression over a defined timeline that spans the progression from normal to preneoplastic mammary tissue. These approaches led to identification of several candidate genes whose expression changes in the mammary gland with commitment to ErbB2/Neu-induced tumorigenesis, suggesting that they may either be regulated by ErbB2/Neu and/or contribute to tumor formation.

Ontogenic development of brown adipose tissue in Angus and Brahman fetal calves.

Brahman calves experience greater neonatal mortality than Angus calves if cold-stressed. To establish a developmental basis for this, three fetuses of each breed type were taken at 96, 48, 24, 14, and 6 d before expected parturition, and at parturition. Overall fetal BW tended (P = 0.08) to be greater for Angus than for Brahman fetuses. There was no difference between breed types in total brown adipose tissue (BAT) mass or grams of BAT/kg BW. Brown adipocyte density decreased 56%, whereas lipogenesis from acetate and glucose in vitro decreased 97% during the last 96 d of gestation in both breed types. Glycerolipid synthesis from palmitate declined by 85% during the last trimester but still contributed 98% to total lipid synthesis at birth. The fetal age x breed interaction was significant for lipogenesis from glucose (P = 0.05) and palmitate (P = 0.005); rates were higher at 96 d before birth in Brahman BAT but declined to similar rates by birth. Uncoupling protein-1 (UCP1) mRNA tripled during gestation in both breed types (P = 0.002), whereas mitochondrial cross-sectional area did not change (P = 0.14) during gestation. Neither the breed nor the age x breed effect was significant (P > or = 0.24) for UCP1 mRNA concentration or mitochondrial cross-sectional area. In both breed types, a marked decrease in BAT UCP1 mRNA between 24 and 14 d prepartum was associated with a similar reduction in lipogenesis from palmitate and a noticeable change in BAT mitochondrial morphology, as the mitochondria became more elongated and the cristae became more elaborate. Uncoupling protein-1 mRNA initially was elevated in Angus tailhead s.c. adipose tissue, but was barely detectable by birth, and tended to be greater overall (P = 0.09) in Angus than in Brahman BAT. If uncoupling protein activity in s.c. adipose tissue persists after birth, then s.c. adipose tissue may contribute more to thermogenesis in Angus newborn calves than in Brahman calves. In contrast, we did not observe differences in ontogenic development of perirenal BAT that could explain the documented differences in thermogenic capacity between Angus and Brahman newborn calves.

Effects of dietary L-arginine on structure and function of flow-restricted vein grafts.

PURPOSE: Experiments were designed to determine effects of dietary supplementation with L -arginine on structure and function of flow-restricted vein grafts. METHODS: Saphenous veins were placed as bilateral interposition grafts in femoral arteries of two groups of adult male mongrel dogs; one group was maintained on a normal diet (control), the other group supplemented with L -arginine (200 mg/kg per day) beginning 1 week before surgery. In each dog, flow was reduced by 50% in one graft by placing an adjustable clamp on the artery distal to the distal anastomosis. Plasma amino acids and oxidized products of nitric oxide (NO(x )) were measured before and after L -arginine feeding. At postoperative week 4, grafts were removed and prepared for organ chamber studies to determine functions of the endothelium or smooth muscle and for histology. RESULTS: Plasma L -arginine increased within 3 hours after feeding and increased from 141 +/- 8 nmol/mL to 169 +/- 11 nmol/mL (n = 6) after 5 weeks of supplementation. Plasma ornithine and citrulline paralleled arginine, whereas circulating NO(x ) was unchanged. Maximal contractions to 60 mmol/L KCl were reduced in grafts from L -arginine-fed dogs. Endothelium-dependent relaxations to the calcium ionophore A23187 and relaxations of the smooth muscle NO were reduced in grafts from L -arginine-fed dogs. Neointimal hyperplasia was increased in grafts with reduced flow and not affected by arginine feeding. CONCLUSIONS: Dietary supplementation with L -arginine did not increase plasma NO in dogs with peripheral vein grafts or increase endothelium-dependent relaxations in control or flow-restricted grafts. Therefore, dietary supplementation with L -arginine may not improve long-term functions of flow-restricted peripheral bypass grafts.

Isolated visceral angioedema: an underdiagnosed complication of ACE inhibitors?

Angiotensin-converting enzyme (ACE) inhibitors are known to cause potentially fatal peripheral angioedema in some patients. ACE inhibitors may also cause isolated visceral angioedema, a rarely reported complication. This article describes 2 patients who experienced this complication. Both patients came to medical attention with episodes of recurrent abdominal symptoms that had occurred while taking ACE inhibitors for hypertension. Each patient had undergone surgical procedures for symptoms that persisted after surgery and were ultimately relieved with cessation of their ACE inhibitors. These cases call attention to what may be an underappreciated cause of abdominal pain in patients presenting to emergency departments.

Rapid upregulation of caspase-3 in rat spinal cord after injury: mRNA, protein, and cellular localization correlates with apoptotic cell death.

Although the precise mechanisms explaining loss of, and failure to regain, function after spinal cord injury are unknown, there is increasing interest in the role of "secondary cell death." One prevalent theme in cell loss in other regions of the CNS involves apoptosis executed by the intracellular caspase proteases. A recent study demonstrated that spinal cord injury rapidly increased the activation of caspase-3. Our previous studies demonstrated peak apoptosis in three of four cellular compartments 3 days after controlled contusion in the rat. We have extended these analyses to include enzyme and substrate studies of caspase subfamilies both in rostral and in caudal adjacent segments compared to the lesion site. Although presumed activation of programmed proenzyme is considered the mechanism for enhanced caspases, our novel analyses were designed to detect upregulation of gene expression. We surveyed traumatically injured spinal cord for caspase family messages with a modified differential mRNA display approach and found that the caspase-3 (CASP3) message was present and upregulated severalfold after injury. Our results clearly demonstrate that cell death in the spinal cord occurs after posttranslational activation of caspases that follow, at least for caspase-3, initial upregulation of CASP3 mRNA levels.

Effects of dietary L-arginine on the reactivity of canine coronary arteries.

Experiments were designed to determine the effects of supplemental dietary L-arginine on the endothelial and smooth muscle function of canine coronary arteries. One group of dogs was fed the standard laboratory chow while another group was supplemented with 250 mg/kg per day L-arginine. All dogs had undergone bilateral reversed interposition saphenous vein grafting and received 325 mg/day oral aspirin. After 5 weeks of arginine feeding, left circumflex coronary arteries were removed, cut into rings, and suspended for the measurement of isometric force in organ chambers. Concentration-response curves were obtained to L-arginine, UK-14,304 (alpha2-adrenergic agonist) and A23187 (calcium ionophore) in the absence and presence of N(G)-monomethyl-L-arginine (L-NMMA) and tetraethylammonium (TEA) alone or in combination. Serum concentrations of L-arginine increased by about 20% following 2 weeks of arginine feeding and remained elevated throughout the study. In rings with and without endothelium contracted with prostaglandin F2alpha, L-arginine caused concentration-dependent contractions in rings from control animals but no significant change in tension in rings from arginine-fed animals. Contractions to L-arginine in control animals were reduced by either L-NMMA or TEA. Endothelium-dependent relaxations to the alpha2-adrenergic agonist were decreased with arginine feeding while relaxations to the calcium ionophore and the endothelium-derived factor nitric oxide were similar among groups. Relaxations to UK-14,304 were reduced by L-NMMA in both groups but by TEA only in rings from control animals. These results suggest that dietary supplementation with L-arginine modifies reactivity of endothelium and smooth muscle by at least two mechanisms: one associated with activation of potassium channels and the other with receptor-coupled release of nitric oxide.

alpha-Melanocyte-stimulating hormone signaling regulates expression of microphthalmia, a gene deficient in Waardenburg syndrome.

The pituitary peptide alpha-melanocyte-stimulating hormone (alpha-MSH) stimulates melanocytes to up-regulate cAMP, but the downstream targets of cAMP are not well understood mechanistically. One consequence of alpha-MSH stimulation is increased melanization attributable to induction of pigmentation enzymes, including tyrosinase, which catalyzes a rate-limiting step in melanin synthesis. The tyrosinase promoter is a principle target of the melanocyte transcription factor Microphthalmia (Mi), a factor for which deficiency in humans causes Waardenburg syndrome II. We show here that both alpha-MSH and forskolin, a drug that increases cAMP, stimulate a rapid increase in Mi mRNA and protein levels in both melanoma cell lines and primary melanocytes. This up-regulation requires a cAMP-responsive element within the Mi promoter, and the pathway leading to Mi stimulation is subject to tight homeostatic regulation. Although cAMP signaling is ubiquitous, the Mi promoter was seen to be cAMP-responsive in melanocytes but not in nonmelanocytes. Moreover, dominant negative interference with Mi impeded successful alpha-MSH stimulation of tyrosinase. The regulation of Mi expression via alpha-MSH thus provides a direct mechanistic link to pigmentation. In addition, because the human melanocyte and deafness condition Waardenburg syndrome is sometimes caused by haploinsufficiency of Mi, its modulation by alpha-MSH suggests therapeutic strategies targeted at up-regulating the remaining wild type Mi allele.

Long-term survival and late complications after repair of ruptured abdominal aortic aneurysms.

PURPOSE: Long-term survival and late vascular complications in patients who survived repair of ruptured abdominal aortic aneurysms (RAAA) is not well known. The current study compared late outcome after repair of RAAA with those observed in patients who survived elective repair of abdominal aortic aneurysms (AAA). METHODS: The records of 116 patients, 102 men and 14 women (mean age: 72.5 (8.3 years), who survived repair of RAAA (group I) between 1980 to 1989 were reviewed. Late vascular complications and survival were compared with an equal number of survivors of elective AAA repair matched for sex, age, surgeon, and date of operation (group II). Survival was also compared with the age and sex-matched white population of west-north central United States. RESULTS: Late vascular complications occurred in 17% (20/116) of patients in group I and in 8% (9/116) in group II. Paraanastomotic aneurysms occurred more frequently in group I than in group II (17 vs. 8, p = 0.004). At follow-up, 32 patients (28%) were alive in group I (median survival: 9.4 years) and 53 patients (46%) were alive in group II (median survival: 8.7 years). Cumulative survival rates after successful RAAA repair at 1, 5, and 10 years were 86%, 64%, and 33%, respectively. These were significantly lower than survival rates at the same intervals after elective repair (97%, 74%, and 43%, respectively, p = 0.02) or survival of the general population (95%, 75%, and 52%, respectively, p < 0.001). Coronary artery disease was the most frequent cause of late death in both groups. Vascular and graft-related complications caused death in 3% (3/116) in group I and 1% (1/116) in group II. Cox proportional hazards modeling identified age (p = 0.0001), cerebrovascular disease (p = 0.009), and number of days on mechanical ventilation (p = 0.01) to be independent prognostic determinants of late survival in group I. CONCLUSIONS: Late vascular complications after repair of RAAA were higher and late survival rates lower than after elective repair. These data support elective repair of AAA. As two-thirds of the patients discharged after repair of RAAA are alive at 5 years, aggressive management of RAAA remains justified.

Effect of preoperative donation of autologous blood on deep-vein thrombosis following total joint arthroplasty of the hip or knee.

The effect of preoperative donation of autologous blood on postoperative deep-vein thrombosis was retrospectively studied in men who had been managed consecutively with elective total joint replacement of the hip or knee because of osteoarthrosis. The patients had, on the average, two of nine considered risk factors for deep-vein thrombosis. Two hundred and thirty-seven patients were evaluated postoperatively with ascending venography, and they form the basis of this study. Fifty-four patients had venographic evidence of deep-vein thrombosis of the lower extremity, with most having asymptomatic clots distal to the knee. The prevalence of deep-vein thrombosis was nineteen (16 per cent) of 116 after total hip arthroplasty, compared with thirty-five (29 per cent) of 121 after total knee arthroplasty (chi square=4.6, p=0.03). Deep-vein thrombosis developed in twenty-eight (17 per cent) of the 161 patients who had donated blood preoperatively, compared with twenty-six (34 per cent) of the seventy-six patients who had not donated blood preoperatively (chi square=7.7, p=0.006). Through logistic regression analysis, the donation of autologous blood was shown to reduce significantly the development of postoperative deep-vein thrombosis for patients managed with total knee arthroplasty (p<0.01) but not for patients managed with total hip arthroplasty. Additional neural network analysis showed the donation of autologous blood to be the most important prognostic factor in predicting the absence of postoperative deep-vein thrombosis. In addition to diminishing the need for transfusion of homologous blood after total joint arthroplasty, preoperative donation of autologous blood appears to protect against postoperative deep-vein thrombosis after total knee arthroplasty.

Modification of an automated method for determining plasma and erythrocyte cholinesterase activity in laboratory animals.

By altering the analytical parameters on an automated analyzer, analytical precision for measuring cholinesterase (ChE) activity in hemolysates was markedly improved in samples from several species. Manual and automated spectrophotometric analyses of plasma and erythrocyte ChE activity were optimized for use in rats, mice and dogs. Replicate ChE analyses were performed on plasma samples and on hemolysates made from whole blood or packed erythrocytes to determine the precision of the manual ChE method and 4 modifications of the automated method. Large method-related differences in precision were observed for the erythrocyte assay, but not the plasma assay. The addition of a nonionic detergent to make hemolysates was beneficial in determining erythrocyte ChE activity in the rat, but not in the mouse or dog. Species specific temperature conversion factors were necessary for comparing results from methods using different analytical temperatures. Analysis of whole blood hemolysates provided similar or better precision for determining erythrocyte ChE activity compared to using hemolysates made from packed erythrocytes. Comparisons of erythrocyte ChE results obtained from assays with even minor methodological differences should be approached with caution because of the many analytical factors which can affect results.

Removal of excess nuclear protein from cells heated in different physiological states.

The relationship between heat-induced cell kill and alterations in nuclear protein content was investigated by heating quiescent 66 mouse mammary adenocarcinoma cells in three different physiological states: (1) quiescent, nutrient deprived cells (Q); (2) Q cells placed in fresh medium 2 h prior to heating (QM); and (3) Q cells made thermotolerant by a previous heat treatment (QTT). Although cell survival varied by a factor of 80, the increase in nuclear protein after a 30 min exposure to 45 degrees C was similar in Q, QM and QTT cells. Removal of the excess nuclear protein from cells in the three physiological states differed both in the percentage of the population that could remove the protein and the rate at which the protein was removed. While all of the QM and QTT cells removed the excess nuclear protein, approximately 30% of the Q cells did not remove the excess nuclear protein, and continued to accumulate protein over the 48 h after the heat treatment. The time for complete removal of the excess protein (Q, 32 h: QM, 18 h: QTT, 8 h) was directly correlated with cell survival. Therefore, these data support the hypothesis that the removal of excess nuclear protein after heat treatment is related to and, perhaps, a determinant of, cell survival.

Alterations of neuronal nuclear matrix and chromatin structure after irradiation under aerobic and anoxic conditions.

This study was undertaken to determine if structural alterations of the bulk chromatin and the amount of protein associated with the nuclear matrix in cerebellar neurons depend on radiation dose and a cell's state of oxygenation. After irradiation with 2.5 to 25.0 Gy under both aerobic and anoxic conditions, the sensitivity of the neuronal chromatin to m. nuclease digestion increase linearly with dose up to about 5 Gy, beyond which there was no further increase. The same increase in accessibility of chromatin to micrococcal nuclease digestion was observed when neuronal nuclei were irradiated at 4 degrees C. Neuronal nuclei were stained with propidium iodide (PI) for DNA and with fluorescein isothiocyanate (FITC) for protein, both before and after complete digestion with DNase I, and analyzed by flow cytometry. There was no change in either the PI (P greater than 0.4) or the FITC (P greater than 0.9) fluorescence of undigested nuclei after irradiation. For the DNase I digested nuclei, the PI fluorescence was unchanged after irradiation (P greater than 0.4), but the FITC fluorescence increased significantly (P less than 0.02). This increase in the FITC fluorescence was linear with dose up to about 5 Gy, beyond which there was no further increase. The flow cytometry results from DNase I digested nuclei were identical for neurons irradiated under aerobic or anoxic conditions, indicating that this phenomenon is oxygen independent. This increase in FITC fluorescence after irradiation was inhibited at ice-cold temperatures and probably reflects an increase in protein content at the nuclear matrix that requires metabolism. This may explain our previously observed resistance of nuclear matrix-associated DNA to digestion by DNase I. This protein increase at the nuclear matrix appears to follow "saturation" kinetics identical to that previously reported for repair of DNA strand breaks in cerebellar neurons. However, the exact molecular nature of this process and its role in DNA repair or cell survival remains to be determined.