Patient information leaflets for placebo-controlled surgical trials: a review of current practice and recommendations for developers.

INTRODUCTION: Informed consent for participation in an RCT is an important ethical and legal requirement. In placebo surgical trials, further issues are raised, and to date, this has not been explored. Patient information leaflets (PILs) are a core component of the informed consent process. This study aimed to investigate the key content of PILs for recently completed placebo-controlled trials of invasive procedures, including surgery, to highlight areas of good practice, identify gaps in information provision for trials of this type and provide recommendations for practice. METHODS: PILs were sought from trials included in a recent systematic review of placebo-controlled trials of invasive procedures, including surgery. Trial characteristics and data on surgical and placebo interventions under evaluation were extracted. Directed content analysis was applied, informed by published regulatory and good practice guidance on PIL content and existing research on placebo-controlled surgical trials. Results were analysed using descriptive statistics and presented as a narrative summary. RESULTS: Of the 62 eligible RCTs, authors of 59 trials were contactable and 14 PILs were received for analysis. At least 50% of all PILs included content on general trial design. Explanations of how the placebo differs or is similar to the surgical intervention (i.e. fidelity) were reported in 6 (43%) of the included PILs. Over half (57%) of the PILs included information on the potential therapeutic benefits of the surgical intervention. One (7%) included information on potential indirect therapeutic benefits from invasive components of the placebo. Five (36%) presented the known risks of the placebo intervention, whilst 8 (57%) presented information on the known risks of the surgical intervention. A range of terms was used across the PILs to describe the placebo component, including 'control', 'mock' and 'sham'. CONCLUSION: Developers of PILs for placebo-controlled surgical trials should carefully consider the use of language (e.g. sham, mock), be explicit about how the placebo differs (or is similar) to the surgical intervention and provide balanced presentations of potential benefits and risks of the surgical intervention separately from the placebo. Further research is required to determine optimal approaches to design and deliver this information for these trials.

Trial Forge Guidance 4: a guideline for reporting the results of randomised Studies Within A Trial (SWATs).

BACKGROUND: Evidence to support decisions on trial processes is minimal. One way to generate this evidence is to use a Study Within A Trial (SWAT) to test trial processes or explore methodological uncertainties. SWAT evidence relies on replication to ensure sufficient power and broad applicability of findings. Prompt reporting is therefore essential; however, SWAT publications are often the first to be abandoned in the face of other time pressures. Reporting guidance for embedded methodology trials does exist but is not widely used. We sought therefore to build on these guidelines to develop a straightforward, concise reporting standard, which remains adherent to the CONSORT guideline. METHODS: An iterative process was used to develop the guideline. This included initial meetings with key stakeholders, development of an initial guideline, pilot testing of draft guidelines, further iteration and pilot testing, and finalisation of the guideline. RESULTS: We developed a reporting guideline applicable to randomised SWATs, including replications of previous evaluations. The guideline follows the Consolidated Standards for Reporting Trials (CONSORT) statement and provides example text to ensure ease and clarity of reporting across all domains. CONCLUSIONS: The SWAT reporting guideline will aid authors, reviewers, and journal editors to produce and review clear, structured reports of randomised SWATs, whilst also adhering to the CONSORT guideline. TRIAL REGISTRATION: EQUATOR Network - Guidelines Under Development ( https://www.equator-network.org/library/reporting-guidelines-under-development/reporting-guidelines-under-development-for-clinical-trials/#SWAT ). Registered on 25 March 2021.

e-Consent in UK academic-led clinical trials: current practice, challenges and the need for more evidence.

BACKGROUND: During the COVID-19 pandemic, in-person healthcare visits were reduced. Consequently, trial teams needed to consider implementing remote methods for conducting clinical trials, including e-Consent. Although some clinical trials may have implemented e-Consent prior to the pandemic, anecdotes of uptake for this method increased within academic-led trials. When the increased use of this process emerged, representatives from several large academic clinical trial groups within the UK collaborated to discuss ways in which trialists can learn from one another when implementing e-Consent. METHODS: A survey of UKCRC-registered Clinical Trials Units (CTUs) was undertaken in April-June 2021 to understand the implementation of and their views on the use of e-Consent and experiences from the perspectives of systems programmers and quality assurance staff on the use of e-Consent. CTUs not using e-Consent were asked to provide any reasons/barriers (including no suitable trials) and any plans for implementing it in the future. Two events for trialists and patient and public involvement (PPI) representatives were then held to disseminate findings, foster discussion, share experiences and aid in the identification of areas that the academic CTU community felt required more research. RESULTS: Thirty-four (64%) of 53 CTUs responded to the survey, with good geographical representation across the UK. Twenty-one (62%) of the responding CTUs had implemented e-Consent in at least one of their trials, across different types of trials, including CTIMPs (Clinical Trial of Investigational Medicinal Product), ATIMPs (Advanced Therapy Medicinal Products) and non-CTIMPs. One hundred ninety-seven participants attended the two workshops for wide-ranging discussions. CONCLUSION: e-Consent is increasingly used in academic-led trials, yet uncertainties remain amongst trialists, patients and members of the public. Uncertainties include a lack of formal, practical guidance and a lack of evidence to demonstrate optimal or appropriate methods to use. We strongly encourage trialists to continue to share their own experiences of the implementation of e-Consent.

Twitter communication of the UK public on dental health and care during a COVID lockdown: "My kingdom for a dentist".

BACKGROUND: The COVID-19 pandemic forced a UK-wide closure of dental services. An understanding of public concerns about dental care was urgently needed to inform careful resumption of paused dental services. AIM: To describe public concerns about dental care during lockdown. BASIC RESEARCH DESIGN: Framework analysis of relevant Twitter posts identified collected using the Awario tool. RESULTS: Of 1863 tweets manually screened for eligibility, 285 were relevant, as they contained views expressed by the public. The number of tweets by country were proportionate to the population size. The key views expressed in tweets focused on: 'oral health impact' ('oral health and self-care', 'types of dental problems', 'managing symptoms at home', 'views on consequences of delaying treatment') and 'dental service or care provision' ('views on managing dental care response', 'experiences with access to dental care'). CONCLUSIONS: The impact of COVID-19 on dental services raised many physical and mental health concerns for the public, highlighting their importance. Online profiles and social media communication platforms can be used to provide convenient, and timely information on public perceptions of dental care.

Trials need participants but not their feedback? A scoping review of published papers on the measurement of participant experience of taking part in clinical trials.

BACKGROUND: Participant recruitment and retention are long-standing problems in clinical trials. Although there are a large number of factors impacting on recruitment and retention, some of the problems may reflect the fact that trial design and delivery is not sufficiently 'patient-centred' (i.e., sensitive to patient needs and preferences). Most trials collect process and outcome measures, but it is unclear whether patient experience of trial participation itself is routinely measured. We conducted a structured scoping review of studies reporting standardised assessment of patient experience of participation in a trial. METHODS: A structured search of Medline, PsycINFO, Embase and CINAHL (Cumulative Index to Nursing and Allied Health Literature) and hand searching of included studies were conducted in 2016. Additional sources included policy documents, relevant websites and experts. We extracted data on trial context (type, date and location) and measure type (number of items and mode of administration), patient experience domains measured, and the results reported. We conducted a narrative synthesis. RESULTS: We identified 22 journal articles reporting on 21 different structured measures of participant experience in trials. None of the studies used a formal definition of patient experience. Overall, patients reported relatively high levels of global satisfaction with the trial process as well as positive outcomes (such as the likelihood of future participation or recommendation of the trial to others). CONCLUSIONS: Current published evidence is sparse. Standardised assessment of patient experience of trial participation may provide opportunities for researchers to enhance trial design and delivery. This could complement other methods of enhancing the patient-centredness of trials and might improve recruitment, retention, and long-term patient engagement with trials.

Prioritizing research areas for antibiotic stewardship programmes in hospitals: a behavioural perspective consensus paper.

SCOPE: Antibiotic stewardship programmes (ASPs) are necessary in hospitals to improve the judicious use of antibiotics. While ASPs require complex change of key behaviours on individual, team organization and policy levels, evidence from the behavioural sciences is underutilized in antibiotic stewardship studies across the world, including high-income countries (HICs). A consensus procedure was performed to propose research priority areas for optimizing effective implementation of ASPs in hospital settings using a behavioural perspective. METHODS: A workgroup for behavioural approaches to ASPs was convened in response to the fourth call for leading expert network proposals by the Joint Programming Initiative on Antimicrobial Resistance (JPIAMR). Eighteen clinical and academic specialists in antibiotic stewardship, implementation science and behaviour change from four HICs with publicly funded healthcare systems (e.g. Canada, Germany, Norway and the UK) met face-to-face to agree on broad research priority areas using a structured consensus method. Question addressed and recommendations: The consensus process assessing the ten identified research priority areas resulted in recommendations that need urgent scientific interest and funding to optimize effective implementation of ASPs for hospital inpatients in HICs with publicly funded healthcare systems. We suggest and detail behavioural science evidence-guided research efforts in the following areas: (a) comprehensively identifying barriers and facilitators to implementing ASPs and clinical recommendations intended to optimize antibiotic prescribing; (b) identifying actors ('who') and actions ('what needs to be done') of ASPs and clinical teams; (c) synthesizing available evidence to support future research and planning for ASPs; (d) specifying the activities in current ASPs with the purpose of defining a control group for comparison with new initiatives; (e) defining a balanced set of outcomes and measures to evaluate the effects of interventions focused on reducing unnecessary exposure to antibiotics; (f) conducting robust evaluations of ASPs with built-in process evaluations and fidelity assessments; (g) defining and designing ASPs; (h) establishing the evidence base for impact of ASPs on resistance; (i) investigating the role and impact of government and policy contexts on ASPs; and (j) understanding what matters to patients in ASPs in hospitals. CONCLUSIONS: Assessment, revisions and updates of our priority-setting exercise should be considered at intervals of 2 years. To propose research priority areas in low- and middle-income countries, the methodology reported here could be applied.

Types of urethral catheter for reducing symptomatic urinary tract infections in hospitalised adults requiring short-term catheterisation: multicentre randomised controlled trial and economic evaluation of antimicrobial- and antiseptic-impregnated urethral catheters (the CATHETER trial).

BACKGROUND: Catheter-associated urinary tract infection (CAUTI) is a major preventable cause of harm for patients in hospital and incurs significant costs for health-care providers such as the UK NHS. Many preventative strategies and measures have been introduced to minimise CAUTI risk, including the use of antimicrobial catheters. However, there is considerable uncertainty regarding their usefulness in terms of reducing symptomatic CAUTI, and whether or not they are cost-effective. OBJECTIVES: Do antimicrobial catheters reduce the rate of symptomatic urinary tract infection (UTI) during short-term hospital use and is their use cost-effective for the UK NHS? DESIGN: A pragmatic multicentre UK randomised controlled trial comparing three catheters as they would be used in the UK NHS: antimicrobial-impregnated (nitrofurazone) and antiseptic-coated (silver alloy) catheters with the standard polytetrafluoroethylene (PTFE)-coated catheters. Economic evaluation used a decision model populated with data from the trial. Sensitivity analysis was used to explore uncertainty. SETTING: Relevant clinical departments in 24 NHS hospitals throughout the UK. PARTICIPANTS: Adults requiring temporary urethral catheterisation for a period of between 1 and 14 days as part of their care, predominantly as a result of elective surgery. INTERVENTIONS: Eligible participants were randomised 1 : 1 : 1 to one of three types of urethral catheter in order to make the following pragmatic comparisons: nitrofurazone-impregnated silicone catheter compared with standard PTFE-coated latex catheter; and silver alloy-coated hydrogel latex catheter compared with standard PTFE-coated latex catheter. MAIN OUTCOME MEASURES: The primary outcome for clinical effectiveness was the incidence of UTI at any time up to 6 weeks post randomisation. This was defined as any symptom reported during catheterisation, up to 3 days or 1 or 2 weeks post catheter removal or 6 weeks post randomisation combined with a prescription of antibiotics, at any of these times, for presumed symptomatic UTI. The primary economic outcome was incremental cost per quality-adjusted life-year (QALY). Health-care costs were estimated from NHS sources with QALYs calculated from participant completion of the European Quality of Life-5 Dimensions (EQ-5D). RESULTS: Outcome analyses encompassed 6394 (90%) of 7102 participants randomised. The rate of symptomatic UTI within 6 weeks of randomisation was 10.6% in the nitrofurazone group (n = 2153; -2.1% absolute risk difference), 12.5% in the silver alloy group (n = 2097; -0.1% absolute risk difference) and 12.6% in the PTFE group (n = 2144). The effect size {odds ratio (OR) [97.5% confidence interval (CI)]} was 0.82 (97.5% CI 0.66 to 1.01) for nitrofurazone (p = 0.037) and 0.99 (97.5% CI 0.81 to 1.22) for silver alloy (p = 0.92) catheters. The nitrofurazone catheters were more likely to cause discomfort during use and on removal. The primary economic analysis suggested that nitrofurazone-impregnated catheters would be, on average, the least costly (> £7 less than PTFE) and most effective option at current NHS prices. There was a 73% chance that nitrofurazone would be cost saving and an 84% chance that the incremental cost per QALY would be < £30,000. At the trial price (£6.46), silver alloy catheters were very unlikely to be cost-effective. These results were unchanged in sensitivity analyses, although when the length of stay cost was excluded the incremental cost per QALY for nitrofurazone against PTFE was £28,602. CONCLUSIONS: The trial estimate of clinical effectiveness for nitrofurazone-impregnated catheters was less than the pre-specified minimum absolute risk difference that we considered important (-3.3%), and the surrounding CI included zero, indicating that any reduction in catheter-associated UTI was uncertain. Economic analysis, although associated with uncertainty, suggested that nitrofurazone-impregnated catheters may be cost-effective for the NHS. The trial ruled out the possibility that silver alloy-coated catheters might reach the pre-set degree of clinical effectiveness and that their use was unlikely to be cost-effective. These findings should be considered by patients, clinicians and health-care policy-makers to determine whether or not a change in practice is worthwhile. Future research should be aimed at determining the minimum clinically important difference in terms of CAUTI prevention in comparative trials, and to identify reliable methods which can detect the impact of the intervention on quality of life and other drivers of cost, when the intervention is a subsidiary part of overall treatment plans.

Fates of the earliest generated cells in the developing murine neocortex.

In mammalian species studied to date, the first-born neocortical cells normally form two layers, one above and one below the cortical plate, called the marginal zone (future layer 1) and the subplate. In primates and carnivores, many of these first-born cells die early in postnatal life. Whether this also occurs in rodents is highly controversial. In this study, we injected pregnant mice with bromodeoxyuridine on embryonic days (E) 11-14 to label the earliest generated neocortical cells, and examined their fates between birth and postnatal day 21. At birth, most cells born on embryonic day 11 were below the cortical plate, and a smaller proportion were above it. Very few of these cells remained by postnatal day 3 and there were none at any depth in the neocortex at older ages. At birth, the largest proportion of cells born on embryonic days 12 and 13 were in the subplate and smaller proportions were in the cortical plate and marginal zone. At older ages, almost all of these cells had disappeared from the marginal zone and from below the cortical plate, although some were retained in the cortical plate. The density of the remaining E12- and E13-born cells decreased more than could be explained by neocortical expansion alone. As a control, we studied cells born on embryonic day 14. These cells were restricted to the cortical plate at birth. By postnatal day 21, their density had decreased by an amount that could be explained by neocortical expansion alone. We conclude that, as in other species, many of the earliest generated cells of the murine neocortex die.

Loss of plasmid-mediated oligopeptide transport system in lactococci: another reason for slow milk coagulation.

Fast milk-coagulating (Fmc+) strains of lactococci are known to segregate slow milk-coagulating (Fmc-) variants, which has been attributed to loss of proteinase (Prt) activity encoded by plasmid DNA. It was found that the Fmc- phenotype could also be due to loss of a plasmid encoding an oligopeptide permease (Opp) system. In Lactococcus lactis subsp. lactis (L. lactis) C2O, lactose metabolism (Lac) and Prt were linked to pJK550 and the Opp system to pJK430. In Lactococcus lactis subsp. cremoris SK11, known to possess Prt on a 78-kb plasmid, DNA sequence analysis of a 7.4-kb region from the Lac plasmid, pSK11L, revealed that it possessed the Opp system. The Lac plasmid in L. lactis C2 encoded both the Prt and Opp systems. Fmc- derivatives of L. lactis C2 were missing the prt genes and had Opp integrated into the chromosome, possibly due to transposition events. Growth studies showed the Opp systems were functional and, in combination with Prt, produced the Fmc+ phenotype.

Characterization and sequence analysis of a stable cryptic plasmid from Enterococcus faecium 226 and development of a stable cloning vector.

A small cryptic plasmid, pMBB1, isolated from Enterococcus faecium 226 was characterized. The plasmid contained an extremely stable replicon which has limited homology to the lactococcal plasmid pCI305. Sequence analysis of the replicon detected one open reading frame of 822 bp capable of encoding a 32-kDa protein. No detectable single-stranded intermediates were found for the replicon, suggesting that pMBB1 may be included in the same family as pCI305, although pCI305 exhibits a more narrow host range. A small stably maintained vector able to replicate in a variety of lactic acid bacteria, containing a large multiple cloning region, was constructed by using the pMBB1 replicon.

Arterial compliance may influence baroreflex function in athletes and hypertensives.

The present study investigated arterial compliance as a possible influence on mean arterial pressure-heart rate (MAP-HR) reflex function in athletes and hypertensives. Aortic stiffness and systemic arterial compliance (SAC) were estimated in 25 elite male athletes and 25 age-matched sedentary controls. Blood pressure did not vary between groups, but SAC was higher in the athletic compared with the sedentary group (0.46 +/- 0.04 vs. 0.37 +/- 0.02 arbitrary compliance units; P = 0.03). In five hypertensives and six age-matched normals and in a subgroup of seven athletes and seven age-matched controls the sigmoidal MAP-HR reflex was assessed using phenylephrine and nitroprusside. In athletes compared with sedentary subjects MAP-HR reflex sensitivity was the same; however, the maximum tachycardia in response to blood pressure reduction was lower in the athletic group (87.1.1 +/- 3.7 vs. 97.1 +/- 2.9 beats/min; P = 0.05). Athletes had a higher blood pressure corresponding to 95% of the HR range (64.2 +/- 3.2 vs. 54.0 +/- 2.1 mmHg; P = 0.02), but there was no difference in the blood pressure corresponding to 5% of the HR range. The blood pressure excursion necessary to traverse the baroreceptor transducer range (MAPd) was therefore less in athletes compared with normals. The beta-index of aortic stiffness correlated closely with MAPd (R = 0.70; P < 0.01). In hypertensives reflex sensitivity was reduced, the minimum HR was elevated, and the MAPd was 56% greater compared with normals.(ABSTRACT TRUNCATED AT 250 WORDS)

Cell migration and subplate loss in explant cultures of murine cerebral cortex.

We studied whether cortical cells migrate and subplate cells are lost in explants of murine cortex cultured for up to 14 days in defined serum-free medium. We gave bromodeoxyuridine (BrdU) to mice on embryonic days 12-13 (E12-13), to label subplate cells, or E17, to label cells destined for superficial cortical layers. We started culturing on E18-20. We left some mice to develop and provide in vivo data. At E18-20, most cells born on E17 lay below the cortical plate. During the following days in vitro, many of them moved to the cortical plate's superficial edge, although an abnormally high number remained in the ventricular zone. There was a selective loss of BrdU labelled cells from the subplate in culture; this occurred more rapidly than in vivo. Factors absent from our cultures may normally enhance migration and prolong the survival of subplate cells.

The fates of cells in the developing cerebral cortex of normal and methylazoxymethanol acetate-lesioned mice.

We are interested in the mechanisms that generate the mature cerebral cortex. We used bromodeoxyuridine (BrdU) to label cortical cells as they were being born. We followed the fates of specific sets of cortical precursors in normal mice and in mice in which other groups of cortical progenitors had been destroyed with the antimitotic agent methylazoxymethanol acetate (MAM Ac). In normal mice, most cells destined for the cerebral cortex were produced from embryonic day 12 (E12) to E16 in the expected inside-to-outside sequence (deep layers first, superficial layers last). Injection of MAM Ac at E13 killed cells that would normally have contributed to the deep cortical layers. As a consequence, the cortex was thinned by approximately 25% at postnatal day 21 (P21). However, all laminae were present and had normal connections with subcortical structures, although all were proportionately thinner. BrdU injected on E16 labelled a normally sized complement of cells that spanned a larger proportion of the depth of the thinned cortex. Thus, the deep cortical layers comprised many cells that were born several days later than normal. At embryonic ages prior to E12, a transient set of cells is produced in the early telencephalon. After injection with MAM Ac at E10, the cortex appeared histologically and histochemically normal at P21. However, many cells that would normally have contributed to superficial cortex (born on E15) were significantly deeper than normal. These results suggest that, during the early stages of cortical development, the nervous system is sufficiently plastic to compensate to some extent for the destruction of specific precursor cells by altering the fates of neurons born later. They indicate that the embryonic date on which a cortical cell is born does not necessarily determine its eventual phenotype.

Double-blind randomized multicenter study comparing Maalox TC tablets and ranitidine in healing of duodenal ulcers.

The efficacy of ranitidine 150 mg twice daily and Maalox TC three tablets four times daily were compared in patients with endoscopically confirmed duodenal ulcer. Seventy-nine patients were randomly allocated to double-blind, double-dummy treatment, stratified for smokers. Endoscopy was repeated after four weeks. Those unhealed continued treatment for a further two weeks before final endoscopy. Per protocol analysis in 53 patients showed ulcer healing rates at week 4 and at weeks 4 and 6 combined of 78 and 89% on Maalox TC, and of 81 and 91% on ranitidine, respectively. The same analysis gave overall healing rates of 81% in smokers and 100% in nonsmokers, irrespective of treatment. Both treatments provided early ulcer pain relief. Diarrhea was a commoner side effect in patients on Maalox TC. The study showed Maalox TC and ranitidine were equally effective in healing duodenal ulceration.

Nisin inhibits several gram-positive, mastitis-causing pathogens.

Organisms known to cause bovine mastitis, Enterococcus faecalis ssp. liquefaciens ATCC 27959, Staphylococcus aureus ATCC 29740, Streptococcus agalactiae ATCC 27956, Streptococcus equinus ATCC 27960, Streptococcus dysgalactiae ATCC 27957, Streptococcus uberis ATCC 27958, and the neotype Staphylococcus epidermidis ATCC 14990 were examined for their susceptibility to the small peptide antibiotic, nisin. Using a disc assay, minimum inhibitory concentrations of nisin ranged from 10 to 250 micrograms/ml among the strains. Examination of the antimicrobial effect of 50 micrograms/ml nisin in milk showed nisin inhibited all gram-positive pathogens tested.

Iron-sulfur centers involved in methanogenic electron transfer in Methanobacterium thermoautotrophicum (delta-H).

Utilizing a subcellular particulate preparation from Methanobacterium thermoautotrophicum (delta-H) which contains all detectable methanogenic electron transfer activity, we present the results of the effects of the anaerobic addition of oxidized factor F420 and of methyl coenzyme M plus ATP on the EPR signals from reduced iron-sulfur centers and a rapidly-relaxing radical species. Based on these results, we report the existence of a minimum of three iron-sulfur centers which are capable of donating electrons to these cofactors.

Membrane topography of the photosynthetic reaction center polypeptides of Rhodopseudomonas sphaeroides.

The topography of the photosynthetic reaction center (RC) polypeptides (H, M, and L) was investigated by proteolysis and radioiodination of membrane vesicles isolated from Rhodopseudomonas sphaeroides. Chromatophores, obtained from French-pressed cell lysates, are closed vesicles' and oriented inside out with respect to the cytoplasmic membrane (cytoplasmic side out). Spheroplast-derived vesicles (SDVs), obtained after osmotic lysis of lysozyme-treated cells, are oriented right side in (periplasmic side out). Alpha-Chymotrypsin treatment of chromatophores and trypsin treatment of SDVs resulted in cleavage of H. Alpha-Chymotrypsin treatment of SDVs did not cleave H, and trypsin treatment of chromatophores did not consistently cleave this polypeptide. M and L of both vesicles were apparently not affected by these proteases. The SDV trypsin cleavage product of H was identified by alpha-chymotryptic (125)I-labeled peptide mapping and had a molecular weight of 26 000. Membrane surface radioiodination with chloroglycoluril coated on glass tubes resulted in preferential labeling of H and M of SDVs and chromatophores. The radiospecific activities of H, M, and L were higher with labeling of SDVs as compared to labeling of chromatophores. Alpha-Chymotryptic (125)I-labeled peptide maps of H, M, and L from surface-radioiodinated SDVs differed from the corresponding maps of these polypeptides from surface-radioiodinated chromatophores. The results indicate the asymmetric exposure of H, M, and L on opposite surfaces of the R. sphaeroides membrane. Exposed iodination sites of these polypeptides are more abundant on the periplasmic surface than on the cytoplasmic surface of this membrane.

Molecular hybridization of RNA and DNA in situ" visualization at the electron microscope level.

Electron microscopic visualization of molecular hybrids formed in situ is feasible at the present time. It can be accomplished by two alternative approaches. In one, the in situ hybridization is carried out on ultrathin sections of target embedded in glycol methacrylate. In the other, whole cells are used for hybridization and they are subsequently prepared for electron microscopy. The choice of the method to be adopted depends on the type of target tissue. When there is a choice, the second approach seems preferable. Some of the important technical steps in the hybridization procedure, such as DNA denaturation in ultrathin sections, have been discussed and attention has been drawn to practical problems that may arise during the preparatory steps. Our light microscope experiments demonstrate that preparations made after glutaraldehyde fixation have a lower hybridization efficiency than those fixed with 3 : 1 methanol-acetic acid. Attempts are therefore being made to explore the possibility of using methanol-acetic acid for electron microscope in situ hybridization. First results of straight-forward fixation show that the preservation of nuclear structure may be fairly satisfactory for the purpose. However, the cumultative effects of subsequent treatments in the procedure still remain to be examined. For electron microscope autoradiograph (EM ARG) of hybridized preparations, the most suitable emulsion at present appears to be Ilford L4. Various factors conductive to optimum resolution consistent with maximum efficiency in this emulsion have been pointed out. Practical problems that may arise in autoradiographs of hybridized preparations such as background and variation of grain density in adjacent sections have also been considered.