Molecular mechanisms protecting centromeres from self-sabotage and implications for cancer therapy

Centromeres play a crucial role in DNA segregation by mediating the cohesion and separation of sister chromatids during cell division. Centromere dysfunction, breakage or compromised centromeric integrity can generate aneuploidies and chromosomal instability, which are cellular features associated with cancer initiation and progression. Maintaining centromere integrity is thus essential for genome stability. However, the centromere itself is prone to DNA breaks, likely due to its intrinsically fragile nature. Centromeres are complex genomic loci that are composed of highly repetitive DNA sequences and secondary structures and require the recruitment and homeostasis of a centromere-associated protein network. The molecular mechanisms engaged to preserve centromere inherent structure and respond to centromeric damage are not fully understood and remain a subject of ongoing research. In this article, we provide a review of the currently known factors that contribute to centromeric dysfunction and the molecular mechanisms that mitigate the impact of centromere damage on genome stability. Finally, we discuss the potential therapeutic strategies that could arise from a deeper understanding of the mechanisms preserving centromere integrity.

Myostatin gene inactivation increases post-mortem calpain-dependent muscle proteolysis in mice

Myostatin deficiency leads to extensive skeletal muscle hypertrophy, but its consequence on post-mortem muscle proteolysis is unknown. Here, we compared muscle myofibrillar protein degradation, and autophagy, ubiquitin-proteasome and Ca²⁺-dependent proteolysis relative to the energetic and redox status in wild-type (WT) and myostatin knock-out mice (KO) during early post-mortem storage. KO muscles showed higher degradation of myofibrillar proteins in the first 24 h after death, associated with preserved antioxidant status, compared with WT muscles. Analysis of key autophagy and ubiquitin-proteasome system markers indicated that these two pathways were not upregulated in post-mortem muscle (both genotypes), but basal autophagic flux and ATP content were lower in KO muscles. Proteasome and caspase activities were not different between WT and KO mice. Conversely, calpain activity was higher in KO muscles, concomitantly with higher troponin T and desmin degradation. Altogether, these results suggest that calpains but not the autophagy, proteasome and caspase systems, explain the difference in post-mortem muscle protein proteolysis between both genotypes.

Study on Female Refugees – A Representative Research Study on Refugee Women in Germany

Introduction

Germany is one of the European countries that receive the highest number of refugees for the last years, with around 468 thousand asylum seekers in the first half of 2016. However, the increase in the speed of short-term procedures regarding refugees may at the same time overlook the risks regarding specific populations. Moreover, women and children constitute the most vulnerable groups during war and conflicts and the worst effects, in terms of physical, mental and social consequences, develop on these groups.

Objectives

To understand deeply the psychosocial situation of female refugees that have arrived in Federal German Republic, to assess their challenges and resources before, during and after the displacement and to propose recommendations for policy changes.

Methods

The study consists of two modules, taking place in five states in Federal German Republic, including Berlin, Mecklenburg-Vorpommern, Bayern, Hessen und Mainz. In the first step, a representative stratified sample of female refugees from Syria, Iraq, Iran, Afghanistan, Somali and Eritrea are recruited. The quantitative study instrument include a socio-demographic question form and HSCL-Hopkins checklist, Harvard Trauma questionnaire, Beck depressions inventory, EUROHIS–QOL and SCL-14. In the second step, a qualitative in-depth analysis of focus group meetings is conducted.

Results and conclusions

There is an urgent need to take action for the mental health problems of refugees. This study constitutes one of the most extensive researches, especially on a subpopulation of refugees that requires specific attention. Challenges faced throughout the protocol and detailed results will be shared as presentation.

Disclosure of interest

The authors have not supplied their declaration of competing interest.

Protective effect of Rhus coriaria fruit extracts against hydrogen peroxide-induced oxidative stress in muscle progenitors and zebrafish embryos

Background and Purpose

Oxidative stress is involved in normal and pathological functioning of skeletal muscle. Protection of myoblasts from oxidative stress may improve muscle contraction and delay aging. Here we studied the effect of R. coriaria sumac fruit extract on human myoblasts and zebrafish embryos in conditions of hydrogen peroxide-induced oxidative stress.

Study Design and Methods

Crude ethanolic 70% extract (CE) and its fractions was obtained from sumac fruits. The composition of sumac ethyl acetate EtOAc fraction was studied by ¹H NMR. The viability of human myoblasts treated with CE and the EtOAc fraction was determined by trypan blue exclusion test. Oxidative stress, cell cycle and adhesion were analyzed by flow cytometry and microscopy. Gene expression was analyzed by qPCR.

Results

The EtOAc fraction (IC₅₀ 2.57 µg/mL) had the highest antioxidant activity and exhibited the best protective effect against hydrogen peroxide-induced oxidative stress. It also restored cell adhesion. This effect was mediated by superoxide dismutase 2 and catalase. Pre-treatment of zebrafish embryos with low concentrations of the EtOAc fraction protected them from hydrogen peroxide-induced death in vivo. ¹H NMR analysis revealed the presence of gallic acid in this fraction.

Conclusion

Rhus coriaria extracts inhibited or slowed down the progress of skeletal muscle atrophy by decreasing oxidative stress via superoxide dismutase 2 and catalase-dependent mechanisms.

NORM management in the oil and gas industry

It has been established that naturally occurring radioactive material (NORM) may accumulate at various locations along the oil and gas production process. Components such as wellheads, separation vessels, pumps, and other processing equipment can become contaminated with NORM, and NORM can accumulate in the form of sludge, scale, scrapings, and other waste media. This can create a potential radiation hazard to workers, the general public, and the environment if certain controls are not established. Saudi Aramco has developed NORM management guidelines, and is implementing a comprehensive strategy to address all aspects of NORM management that aim to enhance NORM monitoring; control of NORM-contaminated equipment; control of NORM waste handling and disposal; and protection, awareness, and training of workers. The benefits of shared knowledge, best practice, and experience across the oil and gas industry are seen as key to the establishment of common guidance. This paper outlines Saudi Aramco's experience in the development of a NORM management strategy, and its goals of establishing common guidance throughout the oil and gas industry.

Altered cross-bridge characteristics following haemodynamic overload in rabbit hearts expressing V3 myosin

1. Our goal in this study was to evaluate the effect of haemodynamic overload on cross-bridge (XBr) kinetics in the rabbit heart independently of myosin heavy chain (MHC) isoforms, which are known to modulate kinetics in small mammals. We applied a myothermal-mechanical protocol to isometrically contracting papillary muscles from two rabbit heart populations: (1) surgically induced right ventricular pressure overload (PO), and (2) sustained treatment with propylthiouracil (PTU). Both treatments resulted in a 100 % V3 MHC profile. 2. XBr force-time integral (FTI), evaluated during the peak of the twitch from muscle FTI and tension-dependent heat, was greater in the PO hearts (0.80 +/- 0.10 versus 0.45 +/- 0.05 pN s, means +/- S.E.M., P = 0.01). 3. Within the framework of a two-state XBr model, the PO XBr developed more force while attached (5.8 +/- 0.9 versus 2.7 +/- 0.3 pN), with a lower cycling rate (0.89 +/- 0.10 versus 1.50 +/- 0.14 s(-1)) and duty cycle (0.14 +/- 0.03 versus 0.24 +/- 0.02). 4. Only the ventricular isoforms of myosin light chain 1 and 2 and cardiac troponin I (cTnI) were expressed, with no difference in cTnI phosphorylation between the PO and PTU samples. The troponin T (TnT) isoform compositions in the PO and PTU samples were significantly different (P = 0.001), with TnT2 comprising 2.29 +/- 0.03 % in PO hearts versus 0.98 +/- 0.01 % in PTU hearts of total TnT. 5. This study demonstrates that MHC does not mediate dramatic alterations in XBr function induced by haemodynamic overload. Our findings support the likelihood that differences among other thick and thin filament proteins underlie these XBr alterations.

Correlation of p53 and the proto-oncogene eIF4E in larynx cancers: prognostic implications

p53 abnormalities constitute the most frequent genetic alterations identified in larynx cancers. p53 overexpression in histologically "tumor-free" surgical margins correlates with a high recurrence rate. However, only 50-60% of tumors overexpress p53. The tumor marker eIF4E is overexpressed in 100% of larynx cancers, and overexpression of eIF4E in histologically "tumor-free" margins predicts a significantly higher recurrence. We undertook this study to correlate the expression of p53 and eIF4E in the tumors and surgical margins of squamous cell cancers of the larynx and to determine their prognostic value. A retrospective analysis was performed on 54 patients who underwent surgery for squamous cell cancers of the larynx. Patient and tumor characteristics were reviewed, and the time to recurrence was noted. Paraffin-embedded sections from the tumors and surgical margins were immunostained with antibodies to eIF4E and p53, and a qualitative analysis was performed. All 54 patients (100%) overexpressed eIF4E in the primary tumor, whereas 25 of 53 patients (47%) were p53 positive. Thirty-two of the 54 patients (59%) had eIF4E-positive margins. All 6 of 53 patients (11%) with p53-positive margins also overexpressed eIF4E in the margins. There was a significant correlation between p53 and eIF4E being positive in the margins (Spearman's correlation coefficient, P = 0.03). Twenty-one of the 25 patients (84%) that recurred, including the 6 patients with p53-positive margins, had eIF4E-positive margins. Hence, although the univariate analysis showed that nodal status and both eIF4E and p53 expression in the margins were significant predictors of recurrence (P < 0.05), in the multivariate analyses only nodal status (P < 0.001) and eIF4E in the margins (P < 0.001) were significant predictors of recurrence. Kaplan-Meier analysis demonstrated that the disease-free intervals for eIF4E-positive margins were significantly shorter than eIF4E-negative margins (P = 0.0007). There was no additional effect to the combination of positive p53 and eIF4E margins (P = 0.21). The overexpression of eIF4E in the margins appears to be a more sensitive indicator of recurrence and may be an earlier event in the process of tumorigenesis than p53.

Soluble complement receptor-1 protects heart, lung, and cardiac myofilament function from cardiopulmonary bypass damage

BACKGROUND

Host defense system activation occurs with cardiopulmonary bypass (CPB) and is thought to contribute to the pathophysiological consequences of CPB. Complement inhibition effects on the post-CPB syndrome were tested with soluble complement receptor-1 (sCR1).

METHODS AND RESULTS

Twenty neonatal pigs (weight 1.8 to 2.8 kg) were randomized to control and sCR1-treated groups. LV pressure and volume, left atrial pressure, pulmonary artery pressure and flow, and respiratory system compliance and resistance were measured. Preload recruitable stroke work, isovolumic diastolic relaxation time constant (tau), and pulmonary vascular resistance were determined. Pre-CPB measures were not statistically significantly different between the 2 groups. After CPB, preload recruitable stroke work was significantly higher in the sCR1 group (n=5, 46.8+/-3.2x10(3) vs n=6, 34.3+/-3.7x10(3) erg/cm(3), P=0.042); tau was significantly lower in the sCR1 group (26.4+/-1.5, 42.4+/-6. 6 ms, P=0.003); pulmonary vascular resistance was significantly lower in the sCR1 group (5860+/-1360 vs 12 170+/-1200 dyn. s/cm(5), P=0.009); arterial PO(2) in 100% FIO(2) was significantly higher in the sCR1 group (406+/-63 vs 148+/-33 mm Hg, P=0.01); lung compliance and airway resistance did not differ significantly. The post-CPB Hill coefficient of atrial myocardium was higher in the sCR1 group (2.88+/-0.29 vs 1.88+/-0.16, P=0.023).

CONCLUSIONS

sCR1 meaningfully moderates the post-CPB syndrome, supporting the hypothesis that complement activation contributes to this syndrome.

Analysis of surgical margins with the molecular marker eIF4E: a prognostic factor in patients with head and neck cancer

PURPOSE

Complete excision of cancer is guided by histologic assessment of surgical margins. Molecular markers may be more sensitive in identifying malignant cells. eIF4E, a eukaryotic protein synthesis initiation factor, is found elevated in all head and neck squamous cell cancers (HNSCC). In a preliminary study using Western blots and a retrospective study using immunohistochemistry, eIF4E elevation in histologically tumor-free surgical margins correlated with a higher local-regional recurrence. We wanted to confirm this hypothesis in a prospective study.

PATIENTS AND METHODS

Immunohistochemical analysis of surgical margins and tumors with an antibody to eIF4E was performed on all newly diagnosed HNSCC patients who underwent surgical resection for their disease between January 1996 and December 1997.

RESULTS

All 65 patients had elevated levels of eIF4E in the tumors. Thirty-six patients (55%) had elevated eIF4E in histologically tumor-free margins, and 20 of these patients (56%) have had local-regional recu rrences. Twenty-nine patients (45%) had no elevation of eIF4E in the margins, and only two of these patients (6.9%) have had recurrences. Cox regression analysis showed that elevated eIF4E in the margins was an independent prognostic factor (P =.009) for recurrence. The Kaplan-Meier curves for the probability of nonrecurrence were significantly different for positive and negative eIF4E margins (P =. 0001, log-rank test).

CONCLUSION

In histologically tumor-free surgical margins, elevated levels of eIF4E predict a significantly increased risk of recurrence. Elevated levels of eIF4E in tumor margins may identify patients who could benefit from additional therapy.

Expression of eIF4E during head and neck tumorigenesis: possible role in angiogenesis

OBJECTIVE

The translation initiation factor eIF4E (4E) when overexpressed in mammalian cells results in their oncogenic transformation. 4E facilitates the synthesis of two powerful tumor angiogenic factors (VEGF and FGF-2) by selectively enhancing their translation. 4E is overexpressed not only in all head and neck squamous cell cancers but also in some dysplastic margins. Tumorigenesis in the head and neck is proposed to be a multistep process preceded by clinically evident precancerous lesions. Molecular events underlie the histological changes that herald transformation. We wanted to study the role of 4E in tumorigenesis and further elucidate its causal role in angiogenesis.

METHODS

An immunohistochemical analysis with antibodies to 4E, VEGF, and basic (b)-FGF was performed on 115 specimens of the head and neck representing various stages of histological progression of malignancy. This was correlated with mean vessel density (MVD) using factor VIII.

RESULTS

There were 41 cases of hyperplasia and low-grade dysplasia, 40 cases of high-grade dysplasia and 34 cases of cancer. There was a significant increase in the percent of cases expressing 4E from low-grade dysplasia through tumor. However, for VEGF and b-FGF the significant increase was only seen between the tumor group and dysplastic groups and no significant increase was noted between low-grade and high-grade dysplasia There was a significant increase in MVD from low- (10.7+/-1) to high-grade grade dysplasia (18.0+/-2.3). This increase was even more striking for the 4E positive cases.

CONCLUSION

4E elevation is correlated with progressive cell transformation in the head and neck. Its correlation with VEGF, b-FGF, and MVD potentiates its possible role in angiogenesis.

Microfabrication techniques using focused ion beams and emergent applications

The application of focused ion beam (FIB) machining in several technologies aimed at microstructure fabrication is presented. These emergent applications include the production of micromilling tools for machining of metals and the production of microsurgical tools. An example of the use of microsurgical manipulators in a circulatory system measurement is presented. The steps needed to transform the laboratory fabrication of these tools and manipulators into a routine FIB production process are discussed. The ion milling of three-dimensional cavities by the exact solution of a mathematical model of the FIB deflection is demonstrated. A good agreement between the model calculation and the ion beam control has been obtained for parabolic and cosine cross-section features with planes of symmetry.

Detection of the proto-oncogene eIF4E in larynx and hypopharynx cancers

BACKGROUND

The proto-oncogene eIF4E has been found to be elevated in head and neck squamous cell carcinomas. In an earlier prospective study overexpression of eIF4E, detected by Western blot analysis, in histologically normal surgical margins correlated with an increased local-regional recurrence rate during a 1-year follow-up.

OBJECTIVE

To test the reverse hypothesis that absence of overexpression of eIF4E in the surgical margins is a predictor for long-term survival in patients with squamous cell carcinoma of the head and neck.

DESIGN

A retrospective analysis was performed on 31 patients who underwent surgery for squamous cell carcinoma of the larynx or hypopharynx. Immunohistochemical analysis was used to detect eIF4E on paraffin embedded sections of the tumor and the histologically negative surgical margins.

RESULTS

All 31 patients overexpressed eIF4E in the tumors. Thirteen patients had no detectable level of eIF4E in the margins, and only 1 had a local-regional recurrence. The average disease-free interval in this group of patients was 82.08 months. The remaining 18 patients all overexpressed eIF4E in the surgical margins (eIF4E score range, 5-80). Twelve (67%) of these patients developed a recurrence; the average disease-free interval was 31.95 months. Cox regression analysis showed that eIF4E in the margin (P= .01), nodes (P= .06), site (P= .02), and age (P= .02) had significant effects on the disease-free interval. The Kaplan-Meier survival curves were significantly different for eIF4E-positive and eIF4E-negative margins (P = .002).

CONCLUSIONS

eIF4E in the surgical margins is an independent prognostic factor and its absence in surgical margins may predict long-term survival. Detecting eIF4E in the margins may improve survival by determining which patients would benefit from further resection or adjuvant therapy.

Clinical outcome in stage I to III breast carcinoma and eIF4E overexpression

OBJECTIVE

The objective of this study is to determine if high eukaryotic initiation factor 4E (eIF4E) overexpression (sevenfold elevation or more over benign breast tissue) is associated with a worse clinical outcome.

SUMMARY BACKGROUND DATA

Dysregulation of cellular functions by selective overexpression of specific proteins can lead to malignant transformation. The overexpression of eIF4E preferentially increases translation of mRNAs with long, G-C rich 5'-untranslated regions. Selective gene products, such as tumor neoangiogenic factors, ornithine decarboxylase, and cyclin D1, are upregulated.

METHODS

One hundred fourteen breast specimens were analyzed and eIF4E overexpression was quantified by Western blot analysis. Quantification for eIF4E protein level was accomplished using a rabbit anti-eIF4E antibody and colorimetric development of Western blots using nitro blue tetrazolium and 5-bromo-4-chloro-3-indolyl phosphate. The blots were scanned and analyzed by densitometry. Treatment, pathologic, and clinical outcome data variables were analyzed. Statistical analysis was performed to determine if eIF4E overexpression is associated with breast cancer clinical outcome.

RESULTS

In the 55 benign specimens, the mean eIF4E expression was 1.1+/-0.4 fold (mean +/- standard deviation). All 59 malignant breast carcinoma specimens were noted to have eIF4E overexpression (range, 1.9-fold to 30.6-fold), with a mean overexpression of 10.8+/-6.3-fold. The mean level of eIF4E expression in malignant specimens was higher than benign specimens (p < 0.05, unpaired t test). The degree of eIF4E overexpression appears to be independent of T and N stage. In the 21 patients with eIF4E overexpression of less than sevenfold, there was one cancer recurrence but no cancer-related deaths. In the 38 patients with high eIF4E overexpression (sevenfold or more), 14 patients had breast cancer recurrences (p = 0.03, log rank test), of whom 11 have died from the disease (p = 0.04, log rank test). The average follow-up interval in this study was 40 months.

CONCLUSIONS

Patients with stage I to III breast cancer and high eIF4E overexpression had a higher rate of cancer recurrence and a higher rate of cancer-related death when compared to similar-stage breast cancer patients with low eIF4E overexpression. Therefore, eIF4E protein overexpression may be of prognostic value in stage I to III breast carcinoma.

Cardiac troponin T isoform expression correlates with pathophysiological descriptors in patients who underwent corrective surgery for congenital heart disease

BACKGROUND

This study examined cardiac troponin T (cTnT) isoform expression in patients who had undergone surgery at Duke University Medical Center (Durham, NC) between December 1, 1993, and January 31, 1995, to correct congenital heart defects. The human heart expresses four cTnT isoforms (cTnT1 through cTnT4) whose sequence differences result from combinatorial alternative splicing of two exons. We have previously shown that cTnT4 is expressed at higher levels in severely failing hearts from transplant patients. In this study, we tested the hypothesis that congenital heart defects that have a more negative effect on myocardial function increase cTnT4 expression. We used the presence or absence of drug treatment for heart failure or congested circulation before surgery and the duration of inotropic support after corrective surgery as indicators of the pathophysiological state of the heart just before surgery.

METHODS AND RESULTS

Right atrial appendage tissue was collected from 34 patients, 6 days to 35 years old (median age, 3.4 months). The amounts of the cTnT1 through cTnT4 isoforms, measured as a percentage of total cTnT, were determined from Western blots probed with MAb13-11, a cTnT-specific monoclonal antibody. We found that cTnT4 expression correlated positively with the duration of inotropic support and was higher in patients who received drug treatment before surgery than in those who did not. Furthermore, we found that the percent of cTnT4 was significantly higher in hearts with congenital defects that caused congestive failure than in hearts with tetralogy of Fallot.

CONCLUSIONS

These findings suggest that in patients with congenital cardiac defects, cTnT4 expression is modulated by heart failure and is increased in hearts that are more hemodynamically stressed.

C2C12 cells: biophysical, biochemical, and immunocytochemical properties

We examined the myofibril biochemical, structural, and biophysical properties of C2C12, a mouse skeletal muscle cell line (American Type Culture Collection), to assess whether force development and the sensitivity of the myofilaments to calcium could be measured in C2C12 myotubes and whether a cardiac contractile protein, troponin T, is expressed and incorporated into C2C12 myofibrils. When myoblasts fused and differentiated into myotubes, expression of myofilament proteins was initiated. Multiple cardiac and skeletal muscle troponin T isoforms were coexpressed. Cardiac troponin T expression increased and then decreased with time. Fluorescence immunocytochemistry demonstrated incorporation of cardiac troponin T isoforms into the myofibrils. At the time of the biophysical studies, mean myotube diameter was 12 microns (range 5-25 microns), and mean length was 290 microns (range 130-520 microns). The estimated maximum force developed by chemically skinned myotubes at 6-7 days poststarvation, 0.88 +/- 0.12 microN (mean +/- 95% confidence interval, n = 5), was significantly less (P < 0.05) than that at 10-13 days poststarvation, 1.12 +/- 0.12 microN (n = 7). The force-pCa relation yielded a Hill coefficient of 2.9 +/- 0.6 (n = 7) and half-maximal activation at pCa of 5.77 +/- 0.20. The demonstration that the biophysical properties of C2C12 cells can be measured and that cardiac and skeletal muscle troponin T isoforms are incorporated and colocalized into myofibrils suggest that these cells could be a useful model to assess the effects of exogenous native and mutated cardiac and skeletal contractile protein isoforms on myofilament function.

A hemodynamic excitatory response to veratridine in the in utero lamb

The inhibitory hemodynamic effects of the Bezold-Jarisch reflex in the adult animal, which play a role in the response to disease states, are elicited by veratridine and are mediated by vagal afferents. We tested whether the reported excitatory response to veratridine in the fetal animal may be caused by a maturational phase in the Bezold-Jarisch response. The effects of proprananol and atropine on the hemodynamic response to veratridine were examined at 124-141 d (mean, 133 d) of gestation in 11 fetal lambs instrumented long-term (instrumentation, 111-129 d of gestation). Seven lambs had intact vagal nerves, and four had bilateral cervical vagotomies. Veratridine injected into the superior vena cava (0.3 to 2.8 micrograms/kg) and the left atrium (0.2 to 0.8 microgram/kg) increased heart rate, arterial pressure, and left ventricular output, with the responses to left atrial injections occurring more rapidly. Propranolol markedly inhibited the increase in arterial pressure; atropine had no effect. Neither carbocaine, perfused around the cervical vagi, nor bilateral transection of the vagal nerves altered the hemodynamic excitatory response to veratridine. These findings demonstrate that the fetal excitatory response to veratridine is not mediated by vagal afferents, indicating the Bezold-Jarisch reflex does not undergo a maturational change from an excitatory reflex to an inhibitory one and suggesting the maturational loss of a sympathetically mediated hemodynamic reflex.

Differential development of autoreceptor subsensitivity and enhanced dopamine release during amphetamine sensitization

Various changes in the function of dopamine neurons have been proposed to underly the development of behavioral sensitization to the locomotor stimulant effects of d-amphetamine. The present study examined the relative importance of two such mechanisms after both short (3-4 days off) and longer (10-14 days off) withdrawals from repeated amphetamine or saline injection (1 mg/kg/day, days 1-5 and 8-12). First, single-unit recording was used to examine the sensitivity of impulse-regulating somatodendritic autoreceptors located on mesoaccumbens dopamine neurons in the rat ventral tegmental area. Second, in vivo microdialysis was used to examine the ability of amphetamine challenge to increase extracellular dopamine levels in the rat nucleus accumbens. Amphetamine-treated rats exhibited robust behavioral sensitization at both time points as compared to saline-treated rats. At 3 to 4 days off, autoreceptor subsensitivity was observed in the ventral tegmental area of amphetamine-treated rats, but there was no significant change in the ability of amphetamine to increase extracellular dopamine levels in nucleus accumbens. However, after 10 to 14 days off, autoreceptor subsensitivity was no longer observed, but amphetamine challenge resulted in a significantly greater increase in extracellular dopamine levels in amphetamine-treated as compared to saline-treated rats. These findings suggest that autoreceptor subsensitivity is a transient effect which may be related to the development of sensitization, whereas enhancement of amphetamine-stimulated dopamine release does not accompany early stages of behavioral sensitization, but may be involved in the persistence of the phenomenon after longer withdrawal periods.

A stimulus timing device for capturing fast physiologic events by quick-freezing

A timing device was designed that, in conjunction with an impact type of quick-freezing apparatus and an externally-triggerable stimulus generator, allows the application of an electrical stimulus to a muscle preparation at a selected time interval before quick-freezing and the measurement of the interval with submillisecond precision. This is needed for stopping fast physiological events in calcium release and excitation-contraction coupling and allows studying the morphological parameters (by freeze-fracture and freeze-substitution) and elemental distributions (by x-ray microanalysis) as a function of time after stimulation. The device should be adaptable for use with most equipment designed for quick-freezing electrically excitable tissue by impact on a cold solid surface.

Analysis of the spectrum of mutations induced by the rad3-102 mutator allele of yeast

The product of the RAD3 gene of Saccharomyces cerevisiae is required for mitotic cell viability and excision repair of UV-induced pyrimidine dimers. Certain rad3 mutant alleles (originally called rem1) increase the rates of both spontaneous mitotic recombination and mutation. The increase in mutation rates is not dependent upon the presence of the RAD6 error-prone pathway. The mutator phenotype suggests that the wild-type RAD3 gene product may be involved in the maintenance of fidelity of DNA replication in addition to its known role in excision repair. To investigate the role that RAD3 might play in mutation avoidance, we have utilized a well-characterized shuttle vector system to study the mutational spectrum occurring in rad3-102 strains and compare it to that seen in RAD3 strains. The results put constraints on the role that the rad-102 mutant gene product must play if the RAD3 protein is a component of the replication complex. Alternatively, the mutational spectrum is consistent with the hypothesis that the rad3-102 mutant protein interferes with postreplication mismatch repair.

Cryopreservation evaluated with mitochondrial and Z line ultrastructure in striated muscle

Single, intact, frog skeletal muscle fibres and whole frog hearts were quick-frozen on a polished, liquid-He-cooled copper block and examined in the electron microscope after freeze-substitution and freeze-fracture. In both kinds of striated muscle, collapse of the peripheral and intracristal membrane spaces in mitochondria was found to increase with increasing distance from the point of first impact (PFI) of the muscle cells on the cold copper block. The changes correlated with a previously described gradient of Z line and A band cryodamage occurring with distance from the PFI. The findings in thin sections from freeze-substituted preparations were confirmed by freeze-fracture preparations. It is concluded that, since the mitochondrial membrane changes are concurrent with, and follow the same spatial distribution of, other manifest cryoartefacts, the cryoartefactual nature of the mitochondrial changes must be excluded before functional significance is attributed to them. The collapse of mitochondrial membrane spaces as a sensitive indicator of quality of cryopreservation may apply to non-muscle cells as well.

Force-pCa relation and troponin T isoforms of rabbit myocardium

We have previously reported the existence of at least four troponin T isoforms in rabbit ventricular muscle and described the changes in their distribution with development. In this report we test whether the proportions of the troponin T isoforms are related to the sensitivity of the myofilaments to calcium. We measured the force-pCa relations in 12 detergent-skinned ventricular strands of cardiac muscle from newborn (2-5-day-old) rabbits. We determined from each strand the amount of each troponin T isoform relative to the total amount of troponin T by using sodium dodecyl sulfate-polyacrylamide gel electrophoresis and densitometric scans of Western blots probed with a cardiac-specific troponin T monoclonal antibody, MAb 13-11. To assess the presence of different relative amounts of cardiac and slow skeletal troponin I among the strands, we determined the amount of cardiac troponin I relative to tropomyosin. We determined the Hill coefficient and the pCa for half-maximal force, pCa50, for each strand. pCa50 was related directly to the relative amount of troponin T2 (pslope = 0.037). Our results do not indicate a relation between the Hill coefficient and troponin T2. We also did not find a relation between pCa50 and the cardiac troponin I/tropomyosin ratio, which suggests that the correlation between pCa50 and troponin T2 was not a result of changes in the relative amounts of cardiac and slow skeletal muscle troponin I. Our findings indicate that a relation exists between the force-pCa characteristics of rabbit myocardium and the troponin T isoforms that it expresses, suggesting a role for troponin T in modulating the sensitivity of cardiac myofilaments to calcium.

The in utero left ventricle of the fetal sheep: the effects of isoprenaline

1. Isoprenaline was infused into in utero fetal lambs to examine the effect of this beta-adrenoceptor agonist on left ventricular stroke volume and left ventricular output and test the generally held assumption that the fetal ventricle is markedly limited in its ability to increase ventricular output. 2. Seven in utero lambs (121-133 days of gestation) were instrumented with left ventricular dimension transducers, an ascending aortic electromagnetic flow transducer, a brachiocephalic arterial catheter and electrocardiographic and atrial pacing electrodes. 3. On the day of study, 5-8 days following surgery and 129-137 days of gestation, each lamb received infusions of isoprenaline, via the superior vena cava or left atrium, at rates which ranged from 0.005-0.5 microgram kg-1 min-1. 4. Heart rate and left ventricular stroke volume, output and end-diastolic and end-systolic dimensions were measured under control conditions and during various levels of isoprenaline infusion, with and without controlling heart rate. 5. Analysis of variance was done using the mean cell model. Least-square means and standard errors of the least-square means are reported. F ratios were calculated from type III sums-of-squares; P less than 0.05 was considered significant. 6. The mean heart rate increased with isoprenaline (P less than 0.0001) from a mean control level of 169 +/- 8 to 281 +/- 9 beats min-1 (+/- S.E.M.). 7. Mean left ventricular end-diastolic and end-systolic minor axis dimensions decreased significantly with isoprenaline from 16.7 +/- 0.1 mm (control) to 15.7 +/- 0.2 mm (P less than 0.0004) and from 11.7 +/- 0.1 mm (control) to 10.4 +/- 0.2 mm (P less than 0.0001) respectively. When heart rate was controlled with atrial pacing, mean end-diastolic dimension increased significantly at the higher isoprenaline doses from 14.6 +/- 0.1 mm (control) to 15.3 +/- 0.2 mm (control) (P = 0.0002), while mean end-systolic dimension fell significantly from 10.9 +/- 0.1 to 10.5 +/- 0.1 mm (P less than 0.003). Inasmuch as stroke volume increased, the increase in end-diastolic dimension and the fall in end-systolic dimension indicate an increase in venous return to the left ventricle. 8. During spontaneous rhythm, isoprenaline increased stroke volume from 2.45 +/- 0.06 ml (control) to 2.63 +/- 0.09 ml, not statistically significant. When heart rate was controlled, stroke volume increased with isoprenaline dose from 1.68 +/- 0.06 ml (control) to 2.40 +/- 0.08 ml (P less than 0.0001).(ABSTRACT TRUNCATED AT 400 WORDS)

Cardiac muscle following quick-freezing: preservation of in vivo ultrastructure and geometry with special emphasis on intercellular clefts in the intact frog heart

Intact frog, mouse and finch hearts were quick-frozen on a liquid He-cooled copper block. Adjacent frozen samples from the same heart were processed by freeze-substitution (followed by embedding and thin sectioning), freeze-fracture/etch (followed by platinum/carbon replication) and frozen sectioning (followed by freeze-drying), respectively, and examined with the electron microscope for fidelity of reproducing the in vivo state of heart muscle geometry, especially that of the narrow intercellular clefts between frog cardiac muscle cells. It was concluded that quick-freezing followed by the above procedures accomplishes that and that, therefore, narrow intercellular clefts are an invariant feature of the normal anatomy of frog cardiac muscle, which must be considered in physiological experiments. The methodology showed that quick-freezing through the epicardial surface is capable of producing superb cryopreservation for ultrathin cryosections, as well.