Assessment of individual tumor buds using keratin immunohistochemistry: moderate interobserver agreement suggests a role for machine learning

Tumor budding is a promising and cost-effective biomarker with strong prognostic value in colorectal cancer. However, challenges related to interobserver variability persist. Such variability may be reduced by immunohistochemistry and computer-aided tumor bud selection. Development of computer algorithms for this purpose requires unequivocal examples of individual tumor buds. As such, we undertook a large-scale, international, and digital observer study on individual tumor bud assessment. From a pool of 46 colorectal cancer cases with tumor budding, 3000 tumor bud candidates were selected, largely based on digital image analysis algorithms. For each candidate bud, an image patch (size 256 × 256 µm) was extracted from a pan cytokeratin-stained whole-slide image. Members of an International Tumor Budding Consortium (n = 7) were asked to categorize each candidate as either (1) tumor bud, (2) poorly differentiated cluster, or (3) neither, based on current definitions. Agreement was assessed with Cohen's and Fleiss Kappa statistics. Fleiss Kappa showed moderate overall agreement between observers (0.42 and 0.51), while Cohen's Kappas ranged from 0.25 to 0.63. Complete agreement by all seven observers was present for only 34% of the 3000 tumor bud candidates, while 59% of the candidates were agreed on by at least five of the seven observers. Despite reports of moderate-to-substantial agreement with respect to tumor budding grade, agreement with respect to individual pan cytokeratin-stained tumor buds is moderate at most. A machine learning approach may prove especially useful for a more robust assessment of individual tumor buds.

Fission time measurements: a new probe into superheavy element stability

Reaction mechanism analyses performed with a 4pi detector for the systems 208Pb + Ge, 238U + Ni and 238U + Ge, combined with analyses of the associated reaction time distributions, provide us with evidence for nuclei with Z=120 and 124 living longer than 10(-18) s and arising from highly excited compound nuclei. By contrast, the neutron deficient nuclei with Z=114 possibly formed in 208Pb + Ge reactions have shorter lifetimes, close to or below the sensitivity limit of the experiment.

Review article: the diagnosis and management of Crohn's disease in populations with high-risk rates for tuberculosis

BACKGROUND

Distinguishing Crohn's disease from intestinal tuberculosis in endemic areas is challenging as both conditions have overlapping clinical, radiological, endoscopic and histological characteristics. Furthermore, high rates of latent tuberculosis confer a considerable risk of reactivation once therapy for established Crohn's disease is started.

AIM

To review current strategies in differentiating these two conditions, and in managing Crohn's disease, in populations with high rates of tuberculosis.

METHODS

Literature review and clinical experience.

RESULTS

While various clinical, radiological, endoscopic and histological parameters may aid in differentiating Crohn's disease from intestinal tuberculosis, these remain imperfect and as treatment options differ misdiagnosis has grave consequences. We propose a diagnostic algorithm, based on currently available evidence and experience, to aid in this dilemma. We also discuss approaches to the management of Crohn's disease, including agents targeting tumour necrosis factor-alpha, in patients at risk of developing tuberculosis.

CONCLUSIONS

A diagnosis of Crohn's disease in individuals at risk for tuberculosis should only be made after careful interpretation of clinical signs, abdominal imaging and systematic endoscopic and histological assessment. Newer techniques for the diagnosis of latent tuberculosis still need to be validated in this environment, and guidelines on the treatment of latent tuberculosis in this setting require clarification.

Comparative evaluation of 2D time-of-flight and 3D elliptic centric contrast-enhanced MR venography in patients with presumptive cerebral venous and sinus thrombosis

We retrospectively evaluated an elliptic centric ordered 3D (ec 3D) magnetic resonance venography (MRV) technique in comparison to 2D time-of-flight (2D TOF) MRV in patients with presumptive cerebral venous sinus thrombosis (CVST). Twenty-five patients (mean age 40.6 +/- 16.5 years) with presumptive CVST underwent cerebral MRI including 2D TOF and ec 3D MRV. Radiologic findings and clinical outcome were correlated. MRV studies were evaluated by two neuroradiologists in a blinded manner for image quality, assessment of various sinus, internal cerebral veins (ICV), vein of Labbé and Galen (VL/VG) as well as for additional imaging procedures required. Sensitivity/specificity of ec 3D MRV amounted to 85.7%/97.2% as compared with 2D TOF 71.4%/55.6 %. Ec 3D MRV performed superior in terms of image quality as well as assessment of all sinus and veins except for the straight sinus. Additional imaging procedures were less often required in ec 3D MRV studies (28% vs. 66% for 2D TOF MRV; P < 0.001). Interobserver agreement was significantly increased by using ec 3D MRV (93.1% vs. 70.9% of readings). The results of our study provide additional evidence for the superiority of ec 3D compared with 2D TOF MR venography for the diagnosis or exclusion of acute CVST in daily clinical practice.

Role of colonoscopic biopsy in distinguishing between Crohn's disease and intestinal tuberculosis

BACKGROUND

The histological differential diagnosis of Crohn's disease and intestinal tuberculosis can be very challenging, as both are chronic granulomatous disorders with overlapping histological features.

AIM

To evaluate selected clinical and histological parameters in colonic biopsy specimens for their ability to discriminate between Crohn's disease and intestinal tuberculosis.

METHODS

25 patients with Crohn's disease and 18 patients with intestinal tuberculosis were selected for this study on the basis of established clinical, radiological and histological criteria. Clinical data and selected histological parameters in colonoscopic biopsy specimens were assessed retrospectively. A total of 103 and 41 biopsy sites were evaluated in patients with Crohn's disease and intestinal tuberculosis, respectively.

RESULTS

Clinical parameters helpful in differentiating intestinal tuberculosis from Crohn's disease included chest radiographic features of tuberculosis (56% v 0%), perianal fistulae (0% v 40%) and extraintestinal manifestations of Crohn's disease (0% v 40%). Histopathological features that seemed to reliably differentiate between intestinal tuberculosis and Crohn's disease included confluent granulomas, > or =10 granulomas per biopsy site and caseous necrosis (in biopsy samples of 50%, 33% and 22% of patients with intestinal tuberculosis, respectively, v 0% of patients with Crohn's disease). Features that were observed more often in patients with intestinal tuberculosis than in those with Crohn's disease included granulomas exceeding 0.05 mm(2) (67% v 8%), ulcers lined by conglomerate epithelioid histiocytes (61% v 8%) and disproportionate submucosal inflammation (67% v 10%).

CONCLUSION

Clinical features and selected histological parameters in colonoscopic biopsy specimens can help in differentiating between Crohn's disease and intestinal tuberculosis.

Measurement of vacuum-assisted photoionization at 1 GeV for Au and Ag targets

We report a measurement of photon impact ionization of K and L shell of Au and K shell of Ag targets in the 1-GeV energy range. We show that the cross section is dominated by a contribution from a new channel called vacuum-assisted photoionization. In this process the energy-momentum balance associated with the removal of the innershell electron is obtained by conversion of a high-energy photon into an electron-positron pair. This measurement is consistent with the theoretical prediction that vacuum-assisted photoionization is the most probable ionization mechanism at very high energies.

Effects of stimulated hip extension moment and position on upper-limb support forces during FNS-induced standing--a technical note

This study explores the effects of active hip extension moment produced by electrical stimulation on the support forces the arms must exert through an assistive device during quiet erect standing with functional neuromuscular stimulation (FNS) in individuals with spinal cord injuries (SCI). A static sagittal plane biomechanical model of human standing was developed to predict the effects of stimulated hip extension moment and sagittal plane hip angle on the arm support necessary to maintain an upright posture. Two individuals with complete thoracic SCI were then tested while they stood with continuous stimulation to the knee and trunk extensors. The steady-state active extension moment exerted at the hip was varied by activating different combinations of hip extensor muscles with continuous stimulation while steady-state support forces applied to the arms and feet during standing were measured. The steady-state support forces imposed on the arms during quiet standing decrease with increased stimulated hip extension moment and are highly dependent upon hip flexion angle, as predicted by the biomechanical simulations. Experimentally, the combination of gluteus maximus and semimembranosus stimulation produced three times more steady-state hip extension moment than did stimulation of the gluteus maximus and adductor magnus. This resulted in a ten-fold decrease in body weight supported on the arms. More vertical postures (smaller hip flexion angles) improve the effectiveness of the hip extensor muscles in reducing the support forces placed on the arms. A single Newton-meter of stimulated hip extension moment with the hips fixed at 5 degrees of flexion results in almost five times the reduction in arm support forces as with the hips at 20 degrees. To minimize the forces applied by the arms on an assistive device for support while standing with FNS, these preliminary results suggest that (1) efforts should be made to assume the most erect postures possible and (2) muscles and stimulation paradigms that maximize active hip extension moment should be chosen.

Strong evidence for enhanced multiple electron capture from surfaces in 46 MeV/u Pb81+ collisions with thin carbon foils

Strong evidence has been found for enhanced multiple electron capture into 46 MeV/u Pb81+ with a significant contribution from the entrance surface of thin carbon foils. Capture of up to five electrons has been observed. The multiple electron capture yield is found to increase with decreasing target thickness for thin targets. A simple model describing the data and showing the importance of capture from surfaces is discussed. Further evidence is found for a pronounced asymmetry between electron capture at the entrance and the exit surfaces. Absolute yields for multiple electron capture and projectile ionization are presented. The experimental total cross sections for single capture and ionization agree well with theory.

Do cognitively normal children with epilepsy have a higher rate of injury than their nonepileptic peers?

The objective of this study was to determine if cognitively normal children with epilepsy have higher accidental injury rates than their age- and sex-matched friends without epilepsy and what factors may predict this. Patients 5 to 16 years old, with a developmental quotient >70, without major motor or sensory impairments, with a 1-year history of epilepsy and who either had a seizure or had been on antiepileptic drugs within the past year, were identified from the pediatric neurology database of the Royal University Hospital. Twenty-five of 31 cases and their best friend controls agreed to participate. Seizure-related factors including type, duration, frequency, timing, date of diagnosis, antiepileptic drug initiation and discontinuation, and specific types and total antiepileptic drugs used were assessed by interview. Questionnaires about accidental injury including type, number, severity, and, if applicable, injuries resulting from seizures, as well as general safety practices, activity restrictions, and presence of attention-deficit hyperactivity disorder, were completed by cases and controls. No significant differences in injury numbers (specific types or total) or severity were found, although a small number of epileptic children were very predisposed to injury. Seizure-related factors did not predict injury in cases. Safety practices were similar, and restrictions in cases were not excessive. Children with attention-deficit hyperactivity disorder had a higher injury rate, both in cases and controls. Cognitively normal children with epilepsy do not have a higher injury rate than their nonepileptic peers. If consciousness is impaired in seizures, extra supervision for swimming and bathing and restricted climbing heights are suggested. All other safety restrictions for epileptic children should follow those appropriate to nonepileptic children to allow a normal lifestyle.

Patients with stable uncomplicated cirrhosis have normal neutrophil function

BACKGROUND

Neutrophil function has been reported to be abnormal in patients with cirrhosis. In order to evaluate the relative contribution of hepatocellular dysfunction and portalsystemic shunting of blood to these abnormalities, neutrophil function was studied in 18 patients with cirrhosis and portal hypertension. Nine patients, with extrahepatic portal hypertension (EPH) caused by portal vein thrombosis, who had no clinical, biochemical or histologic evidence of liver disease were also studied.

METHODS

Superoxide generation, phagocytosis, degranulation, leukotriene B4 release, candidacidal activity and quantitative and qualitative expression of the cell surface adhesive marker CD11b/CD18 were measured in these patients as well as in age- and gender-matched controls.

RESULTS

Patients with cirrhosis were found to have a small but statistically significant decrease in the expression of the CD18 component of MAC1 in N-formyl-methionyl-leucyl-phenylalanine-stimulated neutrophils (P = 0.04). No significant differences were found between either of the two patient groups and the control group for any of the other parameters of neutrophil function tested.

CONCLUSIONS

These were unexpected findings in the light of data published elsewhere, which indicate impaired neutrophil function in patients with cirrhosis. The study suggests that patients with stable, uncomplicated cirrhosis and patients with EPH have normal neutrophil function.

Long-term daily melatonin infusion induces a large increase in N-acetyltransferase activity, hydroxyindole-O-methyltransferase activity, and melatonin content in the Harderian gland and eye of pinealectomized male Siberian hamsters (Phodopus sungorus)

The effects of long-term daily melatonin infusions on the melatonin synthetic pathway in the Harderian glands and eyes of male Siberian hamsters were studied. Hamsters were pinealectomized (PX) and infused daily for 8 hr with either melatonin (6 microg/hr) or vehicle for 7 days in short photoperiod (SP, 10L:14D), followed by 14 wk in either SP (SP group) or in constant darkness (DD group). After the infusion period (15 wk), the infusion was stopped and animals were transferred into SP for 3 wk. The hamsters were then killed at midday or midnight. Exogenous melatonin infusion caused an increase in the Harderian gland weight, which was still evident 3 wk after the end of the treatment. In addition, exogenous melatonin increased endogenous melatonin concentrations (4-fold) and hydroxyindole-O-methyltransferase (HIOMT) activity (2-fold). N-acetyltransferase (NAT) activity, however, was not increased, and no day/night difference in melatonin content and HIOMT activity was observed in the Harderian glands. In the eye, melatonin infusions significantly increased day and night-time melatonin levels (up to 3-fold) and both NAT and HIOMT activities (up to 3.5-fold). This effect of melatonin treatment was observed in both SP and DD groups. These observations demonstrate that exogenously-infused melatonin at relatively high doses activates the synthesis of endogenous melatonin in the Harderian gland and eye of the Siberian hamster. Circulating levels of melatonin were also markedly increased, indicating that in these conditions melatonin may be released from extra-pineal sites.

Organization of rat circadian rhythms during daily infusion of melatonin or S20098, a melatonin agonist

Daily administration of melatonin or S20098, a melatonin agonist, is known to entrain the free-running circadian rhythms of rats. The effects of the duration of administration on entrainment were studied. The animals demonstrated free-running circadian rhythms (running-wheel activity, body temperature, general activity) in constant darkness. Daily infusions of melatonin or S20098 for 1, 8, or 16 h entrained the circadian rhythms to 24 h. Two daily infusions of 1 h (separated by 8 h) entrained the activity peak within the shorter time interval. The entraining properties of melatonin and S20098 were similar and were affected neither by pinealectomy nor by infusion of 1- or 8-h duration. However, with 16-h infusion, less than half of the animals became entrained. Once entrained, the phase angle between the onset of infusion and the rhythms (onset of activity or acrophase of body temperature) increased with the duration of infusion. Before entrainment, the free-running period increased with the duration of infusion, an effect that was not predictable from the phase response curve.

Genes in two major histocompatibility complex class I regions control selection, phenotype, and function of a rat Ly-49 natural killer cell subset

We have generated a monoclonal antibody (STOK2) which reacts with an inhibitory MHC receptor on a subset of alloreactive NK cells in the rat. This receptor, termed the STOK2 antigen (Ag), belongs to the Ly-49 family of lectin-like molecules and displays specificity for the classical MHC class I molecule RT1-A1c of PVG rats. Here, we have investigated the influence of the MHC on the selection, phenotype and function of the STOK2+ NK subset in a panel of MHC congenic and intra-MHC recombinant strains. STOK2 receptor density was influenced by the presence of its classical MHC I ligand RT1-A1c, as evidenced by a reduction of STOK2 Ag on the surface of NK cells from RT1-A1c+, as compared with RT1-A1c-, strains. In addition, a role for nonclassical MHC I RT1-C/E/M alleles in the selection of the STOK2 Ag was demonstrated. The relative number of STOK2+ NK cells was fivefold higher in rats expressing the RT1-C/E/M(av1) as compared with those expressing the RT1-C/E/M(u) class Ib haplotype. The STOK2 ligand RT1-A1c inhibited cytotoxicity of STOK2+ NK cells regardless of effector cell MHC haplotype. Allospecificity of STOK2+ NK cells varied markedly with effector cell MHC, however, and suggested that inhibitory MHC I receptors apart from STOK2 were variably co-expressed by these cells. These data provide evidence for the MHC-dependent regulation of the allospecific repertoire within a subset of potentially autoreactive Ly-49+ rat NK cells.

In vitro selection for different mutational patterns in the HIV-1 reverse transcriptase using high and low selective pressure of the nonnucleoside reverse transcriptase inhibitor HBY 097

In vitro resistance of HIV-1 against high levels of HBY 097 ((S)-4-isopropoxycarbonyl-6-methoxy-3-(methylthiomethyl)-3, 4-dihydro-quinoxaline-2(1H)-thione) and other quinoxaline nonnucleoside reverse transcriptase inhibitors (NNRTIs) is characterized by a specific amino acid substitution in the reverse transcriptase (RT), Gly 190Glu. This change results in decreased RT polymerase activity and in reduced growth properties of the corresponding viral variant. Here we show that the appearance of the crippling mutation at codon 190 can be prevented by lowering the selective pressure exerted by HBY 097. Under low selective pressure an accumulation of other NNRTI-specific mutations is observed. Up to five NNRTI-specific substitutions were detected in some of these virus lineages. In addition, we report novel RT amino acid changes which were not observed previously, including Val106lle, Val106Leu, and Gly190Thr. HBY 097 selects for different mutational patterns under high and low selective pressure conditions, respectively. Thus, the type of mutations which appear in HIV-infected patients undergoing therapy may be determined by the levels of the selecting drug.

Selective pressure of a quinoxaline nonnucleoside inhibitor of human immunodeficiency virus type 1 (HIV-1) reverse transcriptase (RT) on HIV-1 replication results in the emergence of nucleoside RT-inhibitor-specific (RT Leu-74-->Val or Ile and Val-75-->Leu or Ile) HIV-1 mutants

The quinoxaline nonnucleoside RT inhibitor (NNRTI) (S)-4-isopropoxycarbonyl-6-methoxy-3-(methylthiomethyl)-3,4- dihydroquinoxaline-2(1H)-thione (HBY 097) was used to select for drug-resistant HIV-1 variants in vitro. The viruses first developed mutations affecting the NNRTI-binding pocket, and five of six strains displayed the RT G190-->E substitution, which is characteristic for HIV-1 resistance against quinoxalines. In one variant, a new mutant (G190-->Q) most likely evolved from preexisting G190-->E mutants. The negative charge introduced by the G190-->E substitution was maintained at that site of the pocket by simultaneous selection for V179-->D together with G190-->Q. After continued exposure to the drug, mutations at positions so far known to be specific for resistance against nucleoside RT inhibitors (NRTIs) (L74-->V/I and V75-->L/I) were consistently detected in all cultures. The inhibitory activities of the cellular conversion product of 2',3'-dideoxyinosine (ddI, didanosine), 2',3'-dideoxyadenosine (ddA) and of 2',3'-didehydro-3'-deoxythymidine (d4T, stavudine) against these late-passage viruses were shown to be enhanced with the L74-->V/I RT mutant virus as compared with the wild-type (wt) HIV-1MN isolate. Clonal analysis proved linkage of the codon 74 and codon 75 mutations to the NNRTI-specific mutations in all RT gene fragments. The nonnucleoside- and nucleoside-resistance mutation sites are separated by approximately 35 A. We propose that the two sites "communicate" through the template-primer which is situated in the DNA-binding cleft between these two sites. Quinoxalines cause high selective pressure on HIV-1 replication in vitro; however, the implication of these findings for the treatment of HIV-1 infection has yet to be determined.

The photoperiodic response in Syrian hamster depends upon a melatonin-driven circadian rhythm of sensitivity to melatonin

The pineal gland, via the daily pattern of melatonin (MEL) secretion, is directly involved in the conduction of photoperiodic information. The duration of MEL secretion is proportional to the duration of the dark period and, whatever the photoperiod is, MEL synthesis occurs 3 or 4 h after the dark onset in Syrian hamsters. In order to determine the relative importance of the duration or the coincidence hypothesis, a daily infusion protocol was used in sexually active pinealectomized hamsters. Long duration of MEL infusion (10 h) completely inhibit testes whereas short duration infusion (5 h) had no effect. When the animals were infused twice within 2 h 30 min separated by 3 h, they presented a complete gonadal atrophy, similar to the one observed with the 10 h infusion. Measurement of plasma MEL during the infusion and separation periods revealed that MEL reached physiological nighttime values during the infusion period and fell to daytime values 1 h after the end of an infusion period. Thus, the results could not be due to a time additive action of the two MEL pulses. An intermediate response was observed when the 2 signals were applied across the light/dark transition. Gonadal regression did not occur when the 2 periods of infusion were separated by 5 h 30 min. The efficiency of this type of infusion was not dependent on the ambiant photoperiod since similar results were obtained in long and short photoperiods. The infusion was also as effective during the day as well as during the night. These results suggest that there is a rhythm of sensitivity to MEL, based on the coincidence hypotheses, that are important for transmission of photoperiodic information. This rhythm of sensitivity to MEL seems to be entrained by MEL itself, since the efficiency of the two pulses of MEL is not dependent of time of application and/or of photoperiod.

Preclinical evaluation of HBY 097, a new nonnucleoside reverse transcriptase inhibitor of human immunodeficiency virus type 1 replication

HBY 097 [(S)-4-isopropoxycarbonyl-6-methoxy-3-(methylthiomethyl)-3, 4-dihydroquinoxaline-2(1H)-thione] was selected from a series of quinoxalines as a nonnucleoside inhibitor of human immunodeficiency virus type 1 (HIV-1) reverse transcriptase (NNRTI). HBY 097 was shown to be a highly potent inhibitor of HIV-1 induced cell killing and HIV-1 replication in a variety of human cell lines as well as in fresh human peripheral blood lymphocytes and macrophages. The compound was also active against a variety of clinical isolates of HIV-1 including different HIV-1 subtypes and viruses resistant to 3'-deoxy-3'-azidothymidine. Mutant reverse transcriptases which arise as a consequence of treatment with other nonnucleoside inhibitors of HIV-1 reverse transcriptase were still inhibited by HBY 097 at relatively low concentrations. An HIV-1MN variant resistant to inhibition by HBY 097 displayed in the reverse transcriptase gene a mutation causing a substitution at position 190 of a glutamic acid for a glycine residue (G190 --> E), which is characteristic for quinoxaline derivatives. The drug was demonstrated to possess a favorable toxicity profile and to show good oral bioavailability in both mice and dogs. As a consequence of its outstanding properties, HBY 097 was selected for further development and is at present undergoing clinical trials.

New systematically active antimycotics from the beta-blocker category

Candida albicans secretes phospholipases, which are considered to be one of the mediators of cell penetration. It is known that other phospholipases from mammalian cells can be inhibited by lipophilic beta-blocking structures. As the result of a synthesis programme of several years' duration, structures deriving from beta-hydroxyethylamines were introduced. In vitro and in vivo results with these compounds are presented in comparison with standard antimycotics. In combination with fluconazole, several of the compounds can prevent death in mice infected with lethal inocula of C. albicans. Histological examinations confirm the inhibitory effect of the beta-blocker-like structures on tissue penetration. The structures therefore constitute new antimycotics that are endowed with extensive in vitro effectiveness against fungi and also definite in vivo effects in the animal model.

Expression of daily torpor in the Djungarian hamster (Phodopus sungorus) is correlated with the testosterone-driven vasopressin content in the lateral septum

In the Djungarian hamster (Phodopus sungorus), torpor bouts appear after exposure to short photoperiods (SP) for 11 weeks. Castration accelerates the occurrence of daily torpor when performed between the 1st week before and the 4th week after transfer to SP. In animals castrated 8 weeks before transfer to SP, daily torpor was observed nearly at the same time as in the control group. Vasopressin-immunoreactivity (VP-ir) in the lateral septum (LS) of the Djungarian hamster was examined. Dense VP-ir was seen in sexually active and in sexually inactive hamsters implanted with testosterone (T) capsules. No VP-ir could be detected in sexually inactive animals. Thus, the presence of VP-ir in the LS depends on circulating T levels. In control animals exposed to SP, complete disappearance of VP-ir in the LS was observed after 8 weeks. Castration on the day of transfer to SP reduced this period to 6 weeks. In these animals, the early occurrence of daily torpor is related to the quick disappearance of VP-ir in the LS. When castrated animals were maintained under long photoperiods the disappearance of VP-ir was not complete. However, VP-ir disappeared completely after transfer to SP. The results suggest that the SP message acts on daily torpor indirectly via testicular regression but also 'directly' via VP septal innervation.

Mutational analysis of residue 190 of human immunodeficiency virus type 1 reverse transcriptase

S-2720 and other members of the quinoline/quinoxaline class of HIV-1-specific nonnucleoside reverse transcriptase inhibitors (NNRTIs) select for a glycine to glutamate substitution at residue 190 (Gly 190 Glu) of the reverse transcriptase (RT), when drug-resistant viruses are generated in cell culture. This mutation has not been described to appear upon selection for resistant viral variants using derivatives of any other class of NNRTIs. Notably, the RNA-dependent DNA polymerase activity of the Gly 190 Glu mutant enzyme is drastically diminished with respect to the wild-type RT. We describe here the effects of other amino acid substitutions at position 190 of the RT that were introduced by using site-directed mutagenesis. Polymerase activities and sensitivities to inhibition by a number of NNRTIs were determined for the different RT mutants. In general, an inverse correlation was found between the enzymatic activity and increasing length of the side chain, whereas the size of the residue and the level of resistance to NNRTIs appeared to be positively related. Double mutants, which contain the Gly 190 Glu mutation together with substitutions that confer resistance to other RT inhibitors, were all shown to possess severely diminished polymerase activity.

Search for rhythmicity during hibernation in the European hamster

Temporal patterns of hibernation were studied by continuous monitoring of body temperature by radiotelemetry over 6 months in European hamsters, Cricetus cricetus, at constant temperature and photoperiod. Entrances into hibernation occurred mostly at the end of the night (0000-0800 hours), while arousals were randomly distributed between day and night. This is at variance with a control of bout duration by a clock with a period of 24 h. Consequently, the timing of entrances implies a phase-resetting of the circadian clock on each arousal. Persistence of circadian rhythmicity with a period different from 24 h during deep hibernation was investigated examining whether the durations of torpor bouts were integer multiples of a constant period. A non-parametric version of the classical contingency test of periodicity was developed for this purpose. Periods ranging from 21 to 29 h were tested. Nine animals out of ten showed at least one significant period in this range (P < 0.01), either below 24 h (21.8 +/- 0.5 h, n = 4) or above (27.3 +/- 0.5 h, n = 7). However, we have found a theoretical model of bout durations for which the contingency test of periodicity sometimes gives false significant results. This indicates that the power of the test is weak. With this reservation our results suggest that a circadian oscillator controls the duration of a bout of hibernation, which would occur after an integer, but variable and possibly temperature-dependent number of cycles.

Induction of arousal in hibernating European hamsters (Cricetus cricetus L.) by vasopressin infusion in the lateral septum

Vasopressin immunostaining in the lateral septum of the European hamster (Cricetus cricetus L.) disappears in autumn, at the time of the first appearance of hypothermic periods characteristic to hibernation. Previous results have shown that chronic administration of vasopressin in the lateral septum during winter prevents the expression of hypothermic periods, suggesting a role for this peptide in hibernation. It is now observed that acute infusion of vasopressin, and in 50% of the cases, of a specific vasopressin V1 receptor agonist, during a hypothermic period results in an immediate termination of hypothermia. Infusion of oxytocin or a vasopressin V2 receptor agonist were without effect. The results indicate that the seasonal variation in central vasopressin activity, possibly through an interaction with V1 receptors, may play an important role in the expression of hibernation in the European hamster.

The effects of inhibition of plasma cholinesterase activity on systemic toxicity and blood catecholamine levels from cocaine infusion in pigs

We investigated systemic effects and possible mechanisms for lethality of intravenously infused cocaine in spontaneously breathing and mechanically ventilated unconscious Landrace male pigs weighing about 26 kg (25.75 +/- 0.25 kg) that were pretreated with either saline solution (groups 1 and 3) or iso-ompa (tetraisopropyl pyrophosphoramide), a specific plasma cholinesterase inhibitor (groups 2 and 4). Pigs were made unconscious with sodium thiopental and ventilated with 70% nitrous oxide and 30% oxygen. A carotid arterial cannula and a Swan-Ganz catheter were inserted for hemodynamic monitoring. Pigs in groups 1 and 2 were then allowed to breathe spontaneously and groups 3 and 4 were mechanically ventilated. After obtaining a stable state, as judged by cardiovascular and respiratory parameters, the pigs were infused intravenously with cocaine hydrochloride (0.8 mg/kg/min) until the time of cardiac arrest. Respiratory and cardiovascular parameters, blood temperature, and sodium and potassium levels were monitored. The times of occurrence of respiratory arrests (RA), cardiac arrests (CA), and convulsions were recorded. Our results showed that RA is the primary cause of death in spontaneously breathing pigs and that mechanical ventilation significantly delayed the occurrence of CA (p < 0.05). Significant decreases in cardiac output, mean blood pressure, and heart rate as well as significant increases in systemic and pulmonary vascular resistances, central venous and pulmonary wedge pressures, and blood K+ levels were noted in mechanically ventilated pigs (p < 0.05). Variable hemodynamic responses were noticed in spontaneously breathing pigs. Our results also showed that no significant changes occurred in blood catecholamine levels when compared with baseline values associated with the infusion of toxic doses of cocaine.(ABSTRACT TRUNCATED AT 250 WORDS)

Allosteric inhibition of human lymphoblast and purified porphobilinogen deaminase by protoporphyrinogen and coproporphyrinogen. A possible mechanism for the acute attack of variegate porphyria

Variegate porphyria (VP) is characterized by photocutaneous lesions and acute neuropsychiatric attacks. Decreased protoporphyrinogen oxidase activity results in accumulation of protoporphyrin (ogen) IX and coproporphyrin (ogen) III. During acute attacks delta-aminolevulinic acid and porphobilinogen also increase, suggesting that porphobilinogen deaminase (PBG-D) may be rate limiting. We have examined the effects of porphyrinogens accumulating in VP on PBG-D activity in Epstein-Barr virus-transformed lymphoblast sonicates from 12 VP and 12 control subjects. Protoporphyrinogen oxidase activity was decreased and protoporphyrin increased in VP lymphoblasts. PBG-D in control lymphoblasts obeyed Michaelis-Menten kinetics (Vmax 28.7 +/- 1.8 pmol/mg per h, Hill coefficient 0.83 +/- 0.07). VP sonicates yielded sigmoidal substrate-velocity curves that did not obey Michaelis-Menten kinetics. Vmax was decreased (21.2 +/- 2.0 pmol/mg per h) and the Hill coefficient was 1.78 +/- 0.17. Addition of protoporphyrinogen IX and coproporphyrinogen III to control sonicates yielded sigmoidal PBG-D substrate-velocity curves and decreased PBG-D Vmax. Addition of porphyrins or uroporphyrinogen III did not affect PBG-D activity. Removal of endogenous porphyrin (ogens) from VP sonicates restored normal PBG-D kinetics. Purified human erythrocyte PBG-D obeyed Michaelis-Menten kinetics (Vmax 249 +/- 36 nmol/mg per h, Km 8.9 +/- 1.5 microM, Hill coefficient 0.93 +/- 0.14). Addition of protoporphyrinogen yielded a sigmoidal curve with decreased Vmax. The Hill coefficient approached 4. These findings provide a rational explanation for the increased delta-aminolevulinic acid and porphobilinogen during acute attacks of VP.