Assessment of practical tasks in the Phantom course of Conservative Dentistry by pre-defined criteria: a comparison between self-assessment by students and assessment by instructors

INTRODUCTION

Assessment of practical skills in undergraduate dental education has difficulties, including a lack of transparency/objectivity in student evaluations. This prospective study investigated whether agreement between student- and faculty-based assessments increased when students were trained to use the assessment criteria.

MATERIALS AND METHODS

Assessment criteria were available for 6 tasks in the Phantom course of Conservative Dentistry: Class II cavity preparation, composite restoration, gold and ceramic partial crown preparation, trepanation and access cavity preparation, and root canal filling. Forty-two students were allocated to three different assessment training groups. Students' self-assessments of practical tests were compared with instructors' assessments, depending on training intensity and task type (Pearson's rho, ANOVA, Tukey's post hoc test, Kruskal-Wallis test). Students/instructors were questioned regarding benefits/drawbacks of the criteria.

RESULTS

Student self-assessments showed either consent (24.2%), overestimation (31%) or underestimation (44.8%). Gender differences were negligible. Regarding passing/failing grades, more intensive training yielded significantly increased agreement only for preparation of gold partial crowns (rho = +0.313, P = 0.044). Ratings exhibited significant differences amongst tasks (P = 0.002), for example, trepanation assessment had significantly lower differences than gold or ceramic preparation assessments. These discrepancies decreased with increased training. Students consistently reported benefitting most from learning the criteria for gold preparations, followed by composite and ceramic preparations. They also reported that learning the criteria was beneficial for knowledge transfer/feedback. Instructors rated the criteria as helpful for task evaluation and feedback efficiency.

CONCLUSIONS

Pre-defined assessment criteria may increase consistency between student self-assessment and instructor assessment depending on the task, improving transparency and feedback in dental education.

Assessment of practical tasks in the Phantom course of Conservative Dentistry by pre-defined criteria: a comparison between self-assessment by students and assessment by instructors

INTRODUCTION

Assessment of practical skills in undergraduate dental education has difficulties, including a lack of transparency/objectivity in student evaluations. This prospective study investigated whether agreement between student- and faculty-based assessments increased when students were trained to use the assessment criteria.

MATERIALS AND METHODS

Assessment criteria were available for 6 tasks in the Phantom course of Conservative Dentistry: Class II cavity preparation, composite restoration, gold and ceramic partial crown preparation, trepanation and access cavity preparation, and root canal filling. Forty-two students were allocated to three different assessment training groups. Students' self-assessments of practical tests were compared with instructors' assessments, depending on training intensity and task type (Pearson's rho, ANOVA, Tukey's post hoc test, Kruskal-Wallis test). Students/instructors were questioned regarding benefits/drawbacks of the criteria.

RESULTS

Student self-assessments showed either consent (24.2%), overestimation (31%) or underestimation (44.8%). Gender differences were negligible. Regarding passing/failing grades, more intensive training yielded significantly increased agreement only for preparation of gold partial crowns (rho = +0.313, P = 0.044). Ratings exhibited significant differences amongst tasks (P = 0.002), for example, trepanation assessment had significantly lower differences than gold or ceramic preparation assessments. These discrepancies decreased with increased training. Students consistently reported benefitting most from learning the criteria for gold preparations, followed by composite and ceramic preparations. They also reported that learning the criteria was beneficial for knowledge transfer/feedback. Instructors rated the criteria as helpful for task evaluation and feedback efficiency.

CONCLUSIONS

Pre-defined assessment criteria may increase consistency between student self-assessment and instructor assessment depending on the task, improving transparency and feedback in dental education.

The transmitter release pattern of serotonin axons in rabbit brain cortex slices during short pulse trains

The release of serotonin was studied in superfused rabbit brain cortex slices that had been preincubated with [(3)H]serotonin. The slices were stimulated by single electrical pulses or by trains of 4 pulses delivered at 0.011, 1 or 100 Hz. The overflow of tritium elicited by these stimuli was calcium-dependent and tetrodoxin- and Mg(2+)-sensitive. When the superfusion medium contained nitroquipazine or fluvoxamine, the overflow elicited by 4 pulses at 0.011 or 1 Hz was about 2-fold, whereas the overflow elicited by 4 pulses/100 Hz was about 3.7-fold the single pulse-evoked overflow. Metitepin increased little the overflow of tritium elicited by single pulses or 4 pulses/100 Hz, but increased by up to about 150% the overflow evoked by 4 pulses at 1 or 0.011 Hz. Unlabelled serotonin inhibited the evoked overflow in a similar manner, irrespective of the stimulation conditions. When the superfusion medium did not contain serotonin uptake inhibitors, the overflow elicited by a single pulse was too low to be reliably measured. Metitepin increased only slightly the overflow at 4 pulses/0.011 Hz or 4 pulses/100 Hz but increased by up to about 160% the overflow at 4 pulses/1 Hz. The results indicate that the release of serotonin elicited by single pulses as well as by 4 pulses/100 Hz is subject to only a small tonic, stimulation-independent presynaptic autoinhibition, and under these conditions the three pulses following the first one at intervals of 10 ms release about the same amount of transmitter as does pulse No. 1. In contrast, stimulation-dependent presynaptic autoinhibition develops in trains of 4 pulses delivered at 0.011 Hz (only when serotonin re-uptake is blocked) or 1 Hz so that there is a marked fall in the release elicited by each pulse in the course of the train. The total release elicited by such short, autoinhibited trains is dominated by the large response to pulse No. 1. It seems possible that more presynaptic autoreceptors are available for exogenous agonists than for released serotonin.

Effectiveness of a novel endoscopy training concept

BACKGROUND AND STUDY AIMS

Training standards in gastrointestinal endoscopy are poorly defined even though different simulators are increasingly used for skills training. In 2001 a new training concept called "GATE--gastroenterological education-training endoscopy" was established, which provides a combination of background theory, video demonstrations, and simulator training. We aimed to evaluate the acceptance and training effect of this training model.

METHODS

In total, 98 physicians participating in four training courses were included. Data were collected on baseline characteristics, acceptance (5-point Likert scale), and pre- and post-course knowledge through a structured questionnaire (A-type and Pick-N multiple choice questions). A total of 13 trainees were randomly selected for additional simulator assessment of training effects on manual skills (5-point Likert scale).

RESULTS

A total of 78 trainees (80%) provided complete data sets. The evaluation showed a positive acceptance of the training program (value 1 and 2, Likert scale); for example, 88% of participants suggested the inclusion of the GATE course as an obligatory part of endoscopic education. There was a significant improvement in theoretical knowledge in the post-test set compared with the pre-test set (mean 3.27 ±1.30 vs. 1.69 ±1.01 points; P<0.001). The training effect on practical skill showed a significant reduction in time needed for a procedure (445 ±189 s vs. 274 ±129 s; P<0.01). The mean assessment rating for practical skills improved from 3.05 ±0.65 at baseline to 2.52 ±0.59 on Likert scale ( P=0.085).

CONCLUSIONS

The integrated GATE training improved theoretical knowledge and manual skill. The GATE courses have been accredited by the German Society of Gastroenterology, underlining the demand for implementing preclinical training courses in endoscopic training.

[The motivation to become a medical doctor - doctoral students in a formal academic study program compared with those pursuing their doctorate independently]

BACKGROUND AND OBJECTIVE

Weight and quality of medical doctoral theses have been discussed in Germany for years. Doctoral study programs in various graduate schools offer opportunities to improve quality of medical doctoral theses. The purpose of this study was to demonstrate distinctions and differences concerning motivation, choice of subject and the dissertation process between doctoral candidates completing the doctoral seminar for doctoral students in the Ludwig-Maximilians-University (LMU) Munich and doctoral candidates doing their doctorate individually.

METHODS

All 4000 medical students of the LMU obtained an online-questionnaire which was completed by 767 students (19 % response rate). The theoretical framework of this study was based upon the Self-Determination-Theory by Deci and Ryan.

RESULTS

Doctoral candidates completing the doctoral study program were more intrinsically motivated than doctoral candidates doing their doctorate individually; no difference was found in their extrinsic motivation. In regard to choice of subject and dissertation process the doctoral students in the seminar were distinguished from the individual group by having chosen a more challenging project. They anticipated a demanding dissertation process including conference participation, publishing of papers, etc. Intrinsic motivation correlates positively with choosing a challenging project and a demanding dissertation process.

CONCLUSION

High intrinsic motivation seems to be very important for autonomous scholarly practice. Our results suggest that doctoral study programs have a positive impact on intrinsic motivation and interest in research.

Is a PBL curriculum a better nutrient medium for student-generated learning issues than a PBL island?

Problem based learning (PBL) is often introduced in curricula in form of short segments. In the literature the value of these PBL-islands is doubted. In order to gain more insight in this curricular approach, we compared student generated learning issues, from a 7-week PBL-island introduced in a traditional curriculum (PBL-I), with the gold standard of a PBL-based model-curriculum (PBL-B) existing in parallel at the same University (Ruhr-University Bochum, Germany). Both tracks use five identical PBL-cases. Thousand seven hundred and three student-generated learning issues of 252 tutorial groups (193 PBL-I and 59 PBL-B groups with six to seven students per group) were analysed in seven different categories. Results showed that overall there were no substantial differences between both curricula. PBL-B students generated more problem-related and less basic science clinical learning issues than PBL-I students, but in both groups learning issues were related to the same number of different subjects. Furthermore, students in the PBL-curriculum tend to generate little less but slightly better phrased issues. Taken together, we found no substantial evidence with respect to student-generated learning issues that could prove that students cannot work with the PBL-method, even if it is introduced later in the curriculum and last only for a short period of time.

On the long-wavelength component of the light-harvesting complex of some photosynthetic bacteria

The effect of the presence of a minor antenna component in light-harvesting complexes of photosynthetic bacteria is investigated with numerical simulation employing the transition probability matrix method. A model antenna system of hexagonal symmetry is adopted, using as a working hypothesis that the minor component forms a ring around the trap. Three cases have been considered: (a) the minor component is isoenergetic with the trap, which is at lower energy than the antennas (the "supertrap"), (b) the minor component is at lower energy than the trap, which is at lower energy than the antennas (the "asymmetric gutter"), (c) the minor component is at lower energy than the trap, which is isoenergetic with the antennas (the "gutter"). It is found that the supertrap speeds up the fluorescence decay and enhances the trapping efficiency, whereas the gutter slows down the fluorescence decay and decreases the trapping efficiency. It is concluded that, in contrast to a recent suggestion (Bergström, H., R. van Grondelle, and V. Sundström. 1989. FEBS (Fed. Eur. Biochem. Soc.) Lett. 250:503-508), concentrating excitations in the vicinity of the trap by the so-called long-wavelength minor antenna component purportedly present in Rhodobacter sphaeroides and Rhodospirillum rubrum instead of improving trapping actually impedes trapping.

[Acceptance of case-based, interactive e-learning in veterinary medicine on the example of the CASUS system]

OBJECTIVE

New teaching methods such as e-learning, are increasingly used to support common methods such as lectures, seminars and practical training in universities providing education in veterinary medicine. In the current study, the acceptance of e-learning in the example of the CASUS system by veterinarians as well as students of veterinary medicine of all German-speaking universities was analyzed. Material und methods: For this purpose an online evaluation questionnaire was developed. Members of the target groups were informed by e-mail and references in professional journals, as well as through veterinarian exchange platforms on the internet. Additionally, 224 students' final anatomy marks were compared and correlated to the utilization of CASUS to gain an important insight for the development of new teaching practices in the teaching of veterinary medicine.

RESULTS

In total 1581 questionnaires were evaluated. A good acceptance regarding new teaching practices was found, although the classical textbook is still the most important instrument for imparting knowledge. The degree of utilization of e-learning strongly depends on its integration into the teaching content. CASUS is regarded as an efficient teaching method, with over 90% of the respondents indicating a strong desire to expand the number of case studies. Due to the present low degree of integration into the teaching content, no significant correlation could be found between the utilization of anatomy case studies and the final anatomy mark. However, based on their subjective perception, the students reported a high level of success in their study results with the likely effect of supporting increasing self-assurance in the situation of examinations.

CONCLUSION

With the help of e-learning, educational objectives can be achieved that are not attainable by traditional teaching methods, e.g. the review of individual improvements by using the integrated feedback-function of e-learning programs. However, e-learning is not able to completely replace current teaching practices and hence should be considered as an additional element in future teaching models.

Genomic instability and aging-like phenotype in the absence of mammalian SIRT6

The Sir2 histone deacetylase functions as a chromatin silencer to regulate recombination, genomic stability, and aging in budding yeast. Seven mammalian Sir2 homologs have been identified (SIRT1-SIRT7), and it has been speculated that some may have similar functions to Sir2. Here, we demonstrate that SIRT6 is a nuclear, chromatin-associated protein that promotes resistance to DNA damage and suppresses genomic instability in mouse cells, in association with a role in base excision repair (BER). SIRT6-deficient mice are small and at 2-3 weeks of age develop abnormalities that include profound lymphopenia, loss of subcutaneous fat, lordokyphosis, and severe metabolic defects, eventually dying at about 4 weeks. We conclude that one function of SIRT6 is to promote normal DNA repair, and that SIRT6 loss leads to abnormalities in mice that overlap with aging-associated degenerative processes.

Mammalian SIRT1 limits replicative life span in response to chronic genotoxic stress

The Saccharomyces cerevisiae chromatin silencing factor Sir2 suppresses genomic instability and extends replicative life span. In contrast, we find that mouse embryonic fibroblasts (MEFs) deficient for SIRT1, a mammalian Sir2 homolog, have dramatically increased resistance to replicative senescence. Extended replicative life span of SIRT1-deficient MEFs correlates with enhanced proliferative capacity under conditions of chronic, sublethal oxidative stress. In this context, SIRT1-deficient cells fail to normally upregulate either the p19(ARF) senescence regulator or its downstream target p53. However, upon acute DNA damage or oncogene expression, SIRT1-deficient cells show normal p19(ARF) induction and cell cycle arrest. Together, our findings demonstrate an unexpected SIRT1 function in promoting replicative senescence in response to chronic cellular stress and implicate p19(ARF) as a downstream effector in this pathway.

[Evaluation of a case-based computerized learning program (CASUS) for medical students during their clinical years]

BACKGROUND

Clinical undergraduate medical education at the Ludwig-Maximilians University in Munich (LMU) is supplemented by computerized case presentations. This educational strategy teaches problem-solving abilities and differential diagnostic reasoning, thus preparing the students for the management of actual clinical situations with real patients. This study describes the use of a case-based learning system and its acceptance in internal medicine from the students' perspective. Effects of age and gender were taken into account. The results are used for continually improving the system and the offered contents (cases).

METHODS

By means of qualitative and quantitative methods data on the integrated concept of the students' perceived learning success, their motivation and acceptance were assessed during 1999 to 2002. Connections between the different factors were evaluated and the reasons for not using the learning program were given particular attention. Data were obtained from on-line and printed questionnaires as well as electronic protocols. Results were obtained from 380 fourth year medical students, aged between 20 and 34 years. 47% of all registered students during the academic year 2001/2 were female, but they were 58% of those completing the written questionnaire part of the study.

RESULTS

The study showed a good acceptance rate and broad utilization of cases by the students. Case-based learning improved study motivation. Voluntary use of cases increased from 11% in 1999 to 31% in 2002. Male and older students were more motivated than female and younger students. In free comments the students pointed out the close link between this new learning method and real life and the chance of a useful learning experience.

CONCLUSION

Case-based computerized learning programs adapted to concurrent lectures assists in the self-assisted learning. Thus the integration concept contributes to the learning process.

[57-year-old patient with diplopia and headache]

A 57-year old patient presented with an 8 week history of headache and diplopia. Left-sided incomplete oculomotor nerve paresis was found, whereas further clinically relevant visual impairment was not seen. Magnetic resonance imaging of the head showed an extensive intra-, para- and suprasellar tumor which in combination with a markedly elevated serum prolactin level was identified as a macroprolactinoma. The symptoms began 7 years ago with a loss of libido and virility. The application of a dopamine agonist lead to a reduction of serum prolactin level to 0.5% of the initial value and a considerable tumor regression within three months. The development of oculomotor nerve paresis is an unusual manifestation of prolactinoma. By contrast, long-term medical history with slowly developing signs and symptoms of hypogonadotropic hypogonadism are often to be found in men. The delayed diagnosis is responsible for the high percentage of macroprolactinomas in male subjects.

Comparing health care delivery systems--initiating a student exchange project between Europe and the United States

BACKGROUND

Cross-cultural contact among different health care systems can provide a framework for identifying the strengths and weaknesses of one's own healthcare system. However, such contact has rarely had much impact upon medical education curricula. Despite intense debate on reforming the healthcare delivery systems (HCDS) in Europe and the United States, there is very little formal representation of this interdisciplinary field in our educational programs.

DESCRIPTION

To address this problem, a medical student exchange program was conducted in which students developed case studies that produced comparative analyses of HCDS in Germany, Sweden, Denmark and the United States. Each case is intended to highlight critical differences among the systems.

EVALUATION

Students and their faculty preceptors completed pre- and post-exchange questionnaires to assess perceived knowledge of the HCDS and the adequacy of time devoted to it in their curricula. Both perceived that too little attention was devoted to this content in their programs. Following the exchange, students described clear increases in perceived knowledge.

DISCUSSION

Our common interest in curriculum reform was key to implementing the exchange. The written cases generated by the students are being developed as course material in some of the schools and a conference is planned to disseminate the cases and the implementation strategies for their inclusion in medical curricula.

Do computers teach better? A media comparison study for case-based teaching in radiology

A prospective study was performed to better define the role of computers in teaching radiology to medical students. Two hundred twenty-five 3rd-year students were randomly assigned to one of four groups and exposed to 10 radiology cases as well as to a voluntary weekly radiology lecture. Group A used computer-based cases with interactive elements; group B used computer-based cases without interactive elements; group C used paper-based cases with interactive elements; and group D was not exposed to the cases and served as a control group. On a multiple-choice question test, groups A, B, and C showed significant improvement (+11.2%, +15.1%, and +13.0%, respectively), whereas group D did not (+0.6%). On an image interpretation test, group A showed the most improvement (+15.7% [P <.001]), followed by group B (+15.1% [P <.01]) and group C (+10.2% [P <.05]); group D showed no significant improvement (+8.5%). No significant differences in the learning outcome were found between the two interactive groups (computer based and paper based). Computer-based teaching with case studies (with or without interactivity) improves students' problem-solving ability in radiology.

[Computer-assisted instruction in medicine: a multicenter evaluation study in 7 German language media resource centers]

EVA, a multicentre study of seven computer resource centres (CRCs) in three German-speaking nations, was carried out over a period of six months to gather structural and process data regarding the use of computer-based instruction (CBI) applications in medicine, and to identify the factors contributing to a more successful integration of CBI into the medical curriculum. 618 machine-readable questionnaires from CRC users and seven questionnaires on structural data of the participating CRCs covering 51 computer stations were evaluated. For Macintosh workstations (n = 34), an additional digital log-protocol was analysed. In conclusion, it seems that so far less than 10% of medical students use CBI programs in German-speaking countries. The data show the presently still poor integration of CBI into the medical curriculum.

[Immunogenic hyperthyroidism with hyperdynamic heart failure and early cirrhotic transformation of the liver]

HISTORY AND CLINICAL FINDINGS

A 58-year-old woman was admitted because of jaundice, ascites and marked oedema. For three years she had suffered from nervousness, decreasing fitness and weight loss, which had been assumed as due to chronic alcoholism. Liver biopsy revealed extensive fibrosis, in part with early cirrhotic transformation. This was followed by cardiac failure with atrial fibrillation (ventricular rate 140/min) and marked pleural effusions. The thyroid was diffusely enlarged and there were signs of exophthalmos.

INVESTIGATIONS

Bilirubin concentration was 3 mg/dl, lactate dehydrogenase activity was 310 U/l, cholesterase 1.3 kU/l and the prothrombin test was 21%. The TSH level was 0.01 microU/ml while the free thyroxine level was 4.7 ng/dl and that of free triiodothyronine 13.5 pg/ml. Chest radiograph revealed cardiomegaly, bilateral peripheral pulmonary congestion and pleural effusions to midfield. Right heart catheterization excluded pulmonary hypertension; cardiac output was 10l/min. The thyroid was enlarged on ultrasound and diffusely echopoor, as in immune thyroid disease.

TREATMENT AND COURSE

Cardiac failure regressed and thyroid function normalized within ten days on propranolol, 4 x 40 mg and thiamazole 3 x 40 mg daily intravenously. Subtotal thyroidectomy was performed three weeks later with subsequent thyroid hormone substitution. Liver functions were normal six months later and ultrasound showed no signs of cirrhotic change and the ascites had resolved.

CONCLUSION

Hyperthyroidism is frequently associated with changes in liver functions. In extreme cases, high-output cardiac failure may occur, with liver congestion and clinical as well as histological changes like those in liver cirrhosis.

[CASUS model trial. A computer-assisted author system for problem-oriented learning in medicine]

The CASUS-project, a three year publicly funded effort to improve the quality of continuing medical education in Germany, has one major goal: The development and evaluation of an easy-to-handle author-system for problem-oriented learning in medicine. On the theoretical basis of the cognitive apprenticeship-approach, the concept of a teaching and learning database as a hypermedia system was built. The student should learn to manage authentical problems in the form of authentical clinical cases. The step-by-step learning process is expert-guided by the clinical authors of each case. The creation of various differential diagnoses by the learner is strongly supported in the process. The structure of the program can also be used for case-based examinations. In parallel to the technical development, a case-selection process for medical students students in internal medicine was initiated. About 120 relevant diseases were identified to be represented in the CASUS-case library. Prevalence, transferability of knowledge, treatability, urgence of treatment and preventive aspects were used as selection criteria. The system will be evaluated during the implementation of test cases and will then be available to be used by authors and students on a routine basis in 1997.

Data quality in computerized patient records. Analysis of a haematology biopsy report database

This paper addresses the problem of data quality in electronic patient records using a computerized haematology biopsy report system as an example. Physicians extracted five parameters from a traditional free text cytology report and encoded these parameters thus producing a computer processable report. The parameters were 1) the organ biopsied, 2) quality of specimen, 3) cytological diagnosis including 4) a modifier code for the main diagnosis code (i.e. status post chemotherapy, Y-code) and 5) an additional key describing the degree of remission obtained after chemotherapy of acute leukemias. From the various steps involved in generating the electronic record we selected two critical ones: encoding of free text terms by physician staff; entering of the coded terms into a computer by lab staff. We analyzed the rates of correct, incorrect and missing codes for each of the five parameters. Our findings indicate that in this model of an electronic patient record: 1) there is significant inaccuracy of physicians during the process of encoding the free text report with error rates between 3.2 and 28% and omission rates up to 64%. 2) lab staff entering these coded data into the computer introduce additional errors (0-7.8%) but rarely miss correctly encoded data (0-0.9%). 3) introducing a revised coding system data quality improved significantly (p < or = 0.001) with a fivefold increase of correct and a 75% reduction of missing codes. 4) the clinical relevance of the diagnoses encoded as perceived by clinicians is a significant factor affecting error and omission rates.(ABSTRACT TRUNCATED AT 250 WORDS)

Building a cytology report database: a computer-assisted system for documentation, evaluation and hospital-wide recall of haematological biopsy reports

Owing to an increasing number of biopsies from different organ systems in our institution and referring institutions there was need to develop a computer-based system to improve documentation, analysis and reports of pathological findings, as well as speed of transmission of information in a clinical haematology/oncology unit. As terminals connected to a central minicomputer are located on all wards of our hospital, we have now provided a faster way of moving information from the cytology reporting site to all hospital departments. Using the hospital's minicomputer we developed an easy-to-use system based on five different codes for each cytological specimen: organ biopsied, quality of specimen, cytological diagnosis including information as to status of patient (i.e. pretherapy), and an additional code describing the degree of remission obtained after chemotherapy of acute leukemias. After microscopic analysis of the specimen these five codes are read into a terminal; minutes after the diagnosis is made, a short version of the report can be accessed from all wards in the hospital.

13C magic angle spinning NMR study of the light-induced and temperature-dependent changes in Rhodobacter sphaeroides R26 reaction centers enriched in [4'-13C]tyrosine

Solid-state 13C magic angle spinning (MAS) NMR has been used to investigate detergent-solubilized photosynthetic reaction centers of Rhodobacter sphaeroides R26, selectively enriched in [4-13C]-tyrosine. The reaction centers were frozen, in the dark and while subject to intense illumination, and studied at temperatures between approximately 215 and approximately 260 K. The signal consists of at least seven narrow lines superimposed on a broad doublet. The chemical shift anisotropy is similar to that for crystalline tyrosine. The two narrowest resonances, corresponding to signals from individual tyrosines, are 28 +/- 5 Hz wide, comparable to what is observed for quaternary carbons in linearly elastic organic solids. The line width as well as the chemical shift of these signals is essentially independent of temperature. This provides strong evidence for an unusually ordered, well-shielded, and structurally, electrostatically, and thermodynamically stable interior of the protein complex without structural heterogeneities. As the temperature is lowered, additional signal from the labels develops and the natural abundance resonances from the detergent broaden, providing evidence for considerable flexibility at the exterior of the protein complex and in the detergent belt at the higher temperatures. In addition, the NMR provides evidence for an electrostatically uniform and neutral complex, since the total dispersion in isotropic shifts for the labels is < 5 ppm and corresponds to electron density variations of less than 0.03 electronic equivalents with respect to tyrosine in the solid state or in solution. When the sample is frozen while subject to intense illumination, a substantial part of the protein is brought into the charge-separated state P.+QA.-. At least three sharp resonances, including the narrowest lines, are substantially reduced in intensity. It is argued that this effect is caused by the electronic spin density associated with the oxidized primary donor P.+. These results strongly suggest that the environment of the special pair is extremely rigid and question the role of protein conformational distortions during the primary photoprocess.

Phentolamine blocks presynaptic serotonin autoreceptors in rabbit and rat brain cortex

Possible antagonist effects of phentolamine at presynaptic serotonin autoreceptors were studied in slices of the occipito-parietal cortices of the rabbit and the rat. The slices were preincubated with 3H-serotonin and then superfused and stimulated electrically with single pulses or pulse trains. Nitroquipazine 1 mumol/l, a compound that inhibits the high affinity neuronal uptake of serotonin, was present in the superfusion medium in all one pulse-experiments as well as in experiments in which the effect of unlabelled serotonin was examined. In rabbit cortical slices, unlabelled serotonin reduced the single pulse-evoked overflow of tritium. Its concentration-response curve was not changed by the selective alpha 2-adrenoceptor antagonist idazoxan 1 mumol/l but was shifted to the right by phentolamine 1 and 10 mumol/l. Phentolamine 10 mumol/l also shifted to the right the concentration-inhibition curve of the selective 5-HT1-receptor agonist 5-carboxamidotryptamine. When the slices were stimulated by trains of 30 pulses at 3 Hz, phentolamine 1 and 10 mumol/l but not 0.1 mumol/l increased the evoked overflow of tritium, the maximal increase amounting to 178%; its effect was enhanced in the presence of nitroquipazine 1 mumol/l plus idazoxan 10 mumol/l (a drug combination that, when given alone, slightly increased the evoked overflow of tritium). The serotonin receptor antagonist metitepin at concentrations of 0.01-1 mumol/l also increased the overflow of tritium elicited by 30 pulses/3 Hz, the maximal increase amounting to 280%; its effect was potentiated in the presence of nitroquipazine 1 mumol/l plus idazoxan 10 mumol/l but was abolished or almost abolished in the presence of nitroquipazine 1 mumol/l plus phentolamine 10 mumol/l (a drug combination that, given alone, greatly increased the evoked overflow of tritium). When slices were stimulated by trains of 360 pulses at 3 Hz, there was no apparent antagonism of phentolamine 10 mumol/l against the inhibitory effect of unlabelled serotonin. In rat brain cortex slices, unlabelled serotonin reduced the overflow of tritium elicited by 4 pulses delivered at 100 Hz. Again, phentolamine 10 mumol/l shifted the concentration-response curve to the right. It is concluded that phentolamine blocks presynaptic serotonin autoreceptors in rabbit and rat brain cortex with pA2 values of 6.44 and 5.95, respectively. Previous failures to detect the antagonistic effect against exogenous agonists were probably due to stimulation conditions that led to marked endogenous autoinhibition of serotonin release.(ABSTRACT TRUNCATED AT 400 WORDS)