DNA sequence-specific reading by echinomycin: role of hydrogen bonding and stacking interactions

The binding of echinomycin to DNA hexamers of the form GpApXpZpTpC, where the central XpZ step can be CpG, TpA, GpC, or ApT, has been studied by molecular modeling and molecular mechanics techniques. Interaction energies have also been calculated for the complexation of echinomycin with sequences containing the preferred central CpG step and different flanking base pairs. Besides, two more sets of sequences incorporating either 2,6-diaminopurine (DAP) or hypoxanthine in place of adenine or guanine, respectively, have been examined. The aim of this work was to evaluate the relative importance of hydrogen-bonding and stacking interactions in the association of echinomycin with DNA and further rationalize the experimental evidence. The results of these calculations are in consonance with available data from footprinting experiments and appear to support our previous hypothesis that, in addition to the crucial intermolecular hydrogen bonds in the central region, the stacking interactions involving the quinoxaline-2-carboxamide chromophores of the drug and the DNA base pairs play an important role in modulating the binding specificity of this bisintercalating antitumor antibiotic. This is most clearly seen when sequences with similar minor-groove environments are compared (e.g. CpI vs TpA or CpG vs TpDAP). The dipole moment of N-methylquinoxaline-2-carboxamide has been measured (mu = 4.15 +/- 0.03 D) and compares very well with the calculated value (mu = 4.14 D). The fact that G:C, I:C, A:T, and DAP:T base pairs are shown to be endowed with distinct van der Waals and electrostatic stacking properties with respect to this heteroaromatic ring system could have important implications for the design of novel DNA mono- and bis-intercalating agents.

Chronic eosinophilic pneumonia as a presenting feature of Churg-Strauss syndrome

We report on a case of Churg-Strauss syndrome in a 30 year old male with a history of perennial rhinitis. The syndrome began nine months earlier with clinico-radiological features typical of chronic eosinophilic pneumonia. Diagnosis of vasculitis was made by skin biopsy, and at that time there was multisystemic involvement with pulmonary, cardiac, renal, cutaneous and muscular disease, and right vocal chord paralysis, which improved with corticosteroids and cyclophosphamide. This case report illustrates the possible overlap of chronic eosinophilic pneumonia and the Churg-Strauss syndrome.

Chronic eosinophilic pneumonia as a presenting feature of Churg-Strauss syndrome

We report on a case of Churg-Strauss syndrome in a 30 year old male with a history of perennial rhinitis. The syndrome began nine months earlier with clinico-radiological features typical of chronic eosinophilic pneumonia. Diagnosis of vasculitis was made by skin biopsy, and at that time there was multisystemic involvement with pulmonary, cardiac, renal, cutaneous and muscular disease, and right vocal chord paralysis, which improved with corticosteroids and cyclophosphamide. This case report illustrates the possible overlap of chronic eosinophilic pneumonia and the Churg-Strauss syndrome.

Performance and learning during voluntary control of breath patterns

Fourteen subjects learned to adjust their breath pattern to two target breaths displayed on a video screen, by using visual feedback, during two sessions 24 h apart. These two targets were respectively the smallest and the largest breaths of a ten-breath sample previously recorded from each subject's resting spontaneous breathing. Performances were significantly better for the large than for the small target breath. This cannot be directly inferred from current knowledge related to the control of movement time and amplitude, but rather it may be inferred from the periodic character of breathing, to the higher mental load during the small breath task, or to the presumably different frequencies of target breaths in the whole span of spontaneous breathing. In the second session, performance on the two targets levelled out as a result of learning.

Learned activation of thoracic inspiratory muscles in tetraplegics

The aim of this study was to determine whether tetraplegics can learn to activate accessory inspiratory muscles of the upper rib cage, and how this learning affects respiratory motion. Ten tetraplegics with lesional levels ranging from C5 to C7 were trained to increase the upper rib cage expansion during nine 20-min sessions. They were shown an electromyogram (EMG) feedback of the inspiratory muscles of the upper thorax and a signal indicating their current breathing phase (inspiration or expiration). The subjects were instructed to increase EMG during inspiration and to decrease it during expiration. Analysis of variance with session and respiratory phase as factors showed that the subjects progressively learned to increase inspiratory EMG. Thoracic motion, tidal volume and minute ventilation were correlated with inspiratory EMG and tended to increase as a function of practice. These preliminary results lend some support to the clinical use of EMG feedback in breathing therapy aimed at increasing thoracic motion and preventing or reducing paradoxical breathing in tetraplegics.

Abstraction of covariation in category learning: a critical note on K. Richardson's studies

Several studies directed by K. Richardson (Richardson, 1986, 1987; Richardson & Carthy, 1989, 1990) claimed that people are able to abstract imperfect covariations among feature variables defining artificial categories, and to use that information in various subsequent tasks. We challenge this claim on a twofold basis. First, a large part of the performance variance Richardson attributed to covariation knowledge may be accounted for by a very simple exemplar model, which assumes no abstractive processes. Second, the residual influence of relational information on performance may be attributed to the knowledge subjects have acquired in real-world situations before their training with the study exemplars.

A molecular dynamics study of the bis-intercalation complexes of echinomycin with d(ACGT)2 and d(TCGA)2: rationale for sequence-specific Hoogsteen base pairing

The behavior of the complexes of echinomycin with the DNA tetramers d(ACGT)2 and d(TCGA)2, in which the terminal AT base pairs are in either a Hoogsteen or a Watson-Crick conformation, has been explored by molecular dynamics taking into account experimental data from NMR studies (Gao and Patel. Biochemistry 1988, 27, 1744-1751). The DNA binding specificity of echinomycin appears to be the result of a subtle balance between stabilizing and destabilizing forces. Among the former is a number of hydrogen bonds between the alanine residues of echinomycin and both the N3 and 2-amino groups of the guanine bases which decisively determine the strong affinity of the antibiotic for CpG steps. On the other hand, there appears to be an unfavorable dipolar interaction between the chromophores of the antibiotic and the CpG step. This electrostatic component of the stacking interactions also contributes to explaining the conformational preferences of the flanking sequences: upon Hoogsteen pairing, the dipole moment of an AT base pair is found to increase significantly and alter its relative orientation. In the d(ACGT)2:echinomycin complex, this arrangement helps to improve the stacking interactions with the quinoxaline-2-carboxamide system, but would lead to unfavorable dipolar interactions in the d(TCGA)2 complex. The bearing of these findings on the binding of echinomycin to several sequences as well as on the altered binding selectivity of other members of the quinoxaline family of antibiotics is also discussed.

The effect of voluntary breathing on reaction time

The effect of voluntary changes in inspiratory duration on reaction time was studied in 17 normal subjects. All received a visual feedback on inspiratory duration and successively adjusted this variable to two target values which were respectively higher and slightly lower than resting level. The order of the two tasks was counterbalanced across subjects. Reaction times to auditory stimuli were measured during a key-pressing task immediately after voluntary breathing. Voluntary control of inspiration induced concomitant changes in breathing period and minute ventilation. Per cent changes in these breathing variables and in reaction times under the two conditions were analysed. Correlations were significant for period not for minute ventilation. This effect was probably due to neuromuscular rather than humoral factors.

Prevention of the acute neurotoxic effects of phenytoin on rat peripheral nerve by H7, an inhibitor of protein kinase C

The neurotoxic effects of a single dose of phenytoin (150 mg/kg body weight) alone or 30 min after H7 (a protein kinase C inhibitor) injection (20 mg/kg body weight) were investigated in terms of peripheral neuromuscular function and Na+,K(+)-ATPase activity of the sciatic nerve. This intraperitoneal injection of phenytoin induced complete blockade of muscle action potentials in the dorsal segmental muscles of the rat tail evoked by electric stimulation of the caudal nerve and a 40% decrease in the Na+,K(+)-ATPase activity of the rat sciatic nerve when compared with control values, measured as the difference between total and ouabain-insensitive ATPase activity. Prior administration of H7 resulted in the complete prevention of both effects. Implications of protein kinase C inhibition in phenytoin neurotoxicity are discussed.

Implications of a consensus recognition site for phosphatidylcholine separate from the active site in cobra venom phospholipases A2

A model structure of Naja naja kaouthia cobra venom phospholipase A2 has been constructed by utilizing molecular modeling techniques. Analysis of the model and available biochemical data reveal the presence in this enzyme of a putative recognition site for choline derivatives in loop 57-70 made up of residues Trp-61, Tyr-63, Phe-64, and Lys-65, together with Glu-55. The magnitude and shape of the electrostatic potential in this binding site are approximately 80% similar to that in the McPC603 antibody binding site specifically recognizing phosphocholine. Docking studies indicate that the recognition site we now describe and the phosphocholine head of an n-alkylphosphocholine molecule are complementary both sterically and electronically, mainly due to anion-cation and cation-pi interactions. Moreover, binding enthalpies of n-heptylphosphocholine to this site are found to parallel the catalytic rate of pancreatic, mutant pancreatic, and cobra venom phospholipase A2 enzymes acting on dihexanoylphosphatidylcholine micelles, suggesting that it behaves as an activator site. This proposal is in keeping with the "dual phospholipid" model put forward to account for the phenomenon of interfacial activation. This novel site is also shown to be able to discriminate choline derivatives from ethanolamine derivatives, in accord with experimental data. On the basis of the results obtained, two functions are assigned to this putative activator site: (i) desolvation of the lipid-enzyme interface, particularly the surroundings of tyrosine at position 69 (Tyr-63), and (ii) opening of the entrance to the active site by means of a conformational change of Tyr-63 whose chi 2 angle rotates nearly 60 degrees.

Unusual foreign bodies in the urethra and bladder

We report 8 cases of self-inserted unusual foreign bodies in the lower urinary tract, all being treated from 1976 to 1990. Three of them were located in the urethra and 5 in the bladder. Several objects were found (electric cable, tweezers, hairpin, drawing pin, pebbles, paper clip). In 4 cases the objects were inserted for masturbatory purposes. Five of the patients were psychologically ill or handicapped. The most common reason for consultation was dysuria, and the treatment procedures were endoscopy in 5 patients and cystotomy in the other 3.

[Treatment of obstruction caused by prostatic hypertrophy with prazosin. 1-year follow-up]

Since Caine demonstrated the presence of alpha-adrenergic receptors in prostate tissue in 1975, an alpha-blocker capable of producing maximum relaxation of prostatic tissue with minimum side effects has been sought. Prazosin, a selective alpha-1 blocking agent, must meet these requirements. We report the results of a study undertaken in 28 patients with benign hyperplasia of the prostate demonstrated by flowmetry, clinically and by ultrasound. A significant improvement was observed in all patients except for the ultrasound measured prostate size, which remained unchanged. Undesired effects were observed in 36% of the patients. Despite the initial improvement, 89.3% had abandoned treatment at 1 year principally owing to deterioration of the clinical picture and because they were submitted to surgery (the majority) or treatment with other drugs. We can conclude from our results that prazosin is useful for short-term therapy; i.e., until the patient can be referred for surgery.

Electromyographic feedback for learning to activate thoracic inspiratory muscles

The utility of EMG feedback for modifying the muscular pattern of breathing was investigated in twenty-four subjects divided into two groups (feedback, no feedback. Each took part in three 20-min training sessions, 24 h apart. All the subjects were instructed to increase the thoracic contribution of inspired gas. The feedback subjects were shown an EMG signal of the inspiratory muscles of the upper thorax and a signal indicating their current breathing phase (inspiration or expiration). The no feedback subjects only saw the breathing phase signal. The subjects' ability to control muscular activity was assessed as the relative increase in EMG from expiration to the subsequent inspiration. Analysis of variance with group and session as factors showed that feedback subjects performed significantly better, although the improvement in performance over the sessions by the two groups was not significantly different. These results lend some support to the clinical use of EMG feedback in breathing therapy aimed at changing the thoracoabdominal distribution of ventilation. However, further research for improving learning is necessary.

Assessing attentional control of breathing by reaction time

The reaction time (RT) to an auditory stimulus was measured in 27 subjects during spontaneous breathing and during controlled breathing, which consisted of maintaining a set inspiratory duration. During spontaneous breathing, reaction times were unrelated to the time the stimulus was delivered during the breathing cycle. During controlled breathing, reaction times were longer than during spontaneous breathing. Peak reaction times were observed at the transition from inspiration to expiration. After the end of controlled breathing, reaction times gradually became shorter until they reached their initial level. The findings are discussed in terms of varying allocation of attentional resources to breathing. It is argued that probe RT methodology provides a suitable means for investigating attentional control of breathing.

Classical conditioning of ventilatory responses in humans

A classical conditioning experiment, in which an auditory stimulus was paired with a hypoxic stimulus, was carried out on 34 normal subjects assigned to two groups (experimental and control). Each subject took part in one session divided into two phases, acquisition and test. In the acquisition phase, eight hypoxic and eight auditory stimuli were paired in the experimental group and unpaired in the control group. In the test phase, which was identical for the two groups, the hypoxic stimuli were suppressed and three purely auditory stimuli were presented. Significant differences between the two groups in ventilatory response to these auditory stimuli provided evidence for conditioning. In the control group, no significant changes were elicited by the auditory stimuli, whereas a conditioned increase in total cycle duration was observed in the experimental group. The conditioned response closely resembled the first component of the hypoxic response. Analysis of the pattern of the conditioned response, along with postexperimental interviews, strongly suggests that this response was not mediated by volitional factors.

Effect of practice on the voluntary control of a learned breathing pattern

Changes in orientation of attention and ventilatory data were examined in three normal volunteers who practiced a learned ventilatory pattern over eight training sessions. The breathing task was a voluntary increase of inspiratory duration up to a given target with the aid of informative feedback on this variable. The orientation of attention was investigated through reaction time (RT) to auditory stimuli presented at different points in inspiration and expiration, during either automatic or voluntary control of breathing. Findings show that RTs are longer during voluntary than automatic breathing throughout the experiment, and that they decrease across sessions in both conditions. In the first sessions, RTs were longer during expiration than inspiration but this difference cancels out in the last sessions. The results are discussed in terms of attentional demands of control of breathing, automatization, and the connection between automatic and voluntary control of breathing. This work shows that after eight practice sessions, the orientation of attention displays significant changes; however, the control of breathing remains attention demanding.

Carcinoma of prostatic ducts

Carcinoma of prostatic ducts is a rare clinical feature. We have reviewed 398 histories of patients with histologic diagnosis of prostatic carcinoma and found 10 patients with the ductal variety (2.51%). Four had pure ductal transitional cell carcinoma, 5 had mixed acinar adenocarcinoma plus ductal transitional cell carcinoma, and the last one had mixed acinar and ductal adenocarcinoma. Age, symptoms, physical findings, and imaging diagnoses were similar to those of acinar carcinoma. Rectal examination disclosed hard prostate in 9 patients. The metastatic way depended on the histologic elements present in each patient. Cystoscopy showed a malignant-resembling image in 4 cases. The mean survival (23 months) was lower than that of patients with acinar carcinoma. Early diagnosis and radical surgery still are the only way to increase the expectation of life of patients affected by this pathology.

Temperature dependence of the toxic effects of phenytoin on peripheral neuromuscular function of the rat tail

We studied the acute effects of a single dose of phenytoin (250 mg/kg) on peripheral neuromuscular function. The evoked muscle action potentials of the dorsal segmental muscles in the rat tail, and the conduction velocity of the dorsal nerve trunk which innervates them, were measured before and after the intraperitoneal injection of phenytoin. The experiments were performed at different temperatures, 27 (physiological tail temperature), 36 and 37 degrees C (physiological central temperature) in different groups of animals. The amplitudes of the evoked muscle action potentials in the treated groups showed no significant modifications at 27 degrees C, at 36 degrees C a small nonsignificant decrease could be observed, and a complete block occurred at 37 degrees C. The mean blocking time was approximately one hour. No significant variations of conduction velocity were observed at 27 and 36 degrees C, whereas it decreased significantly after 30 minutes at 37 degrees C. The results presented confirm phenytoin toxicity. How far these results, especially the decrease of nerve conduction velocity observed at 37 degrees C, confirm a previous hypothesis which supported that peripheral and central nervous system are affected by phenytoin by similar mechanisms, is discussed.

'Carrusel': an expert system for vestibular diagnosis

Neuro-otology is the only field of otolaryngology in which diagnoses are mainly deductive. Although many technological advances have indeed occurred, the patient history still remains the most important part of the evaluation of a patient complaining of vertigo and/or dizziness. The use of artificial intelligence methods as an aid for the solution of clinical problems is not new. "Carrusel" is a Prolog build-up expert system dealing with the diagnosis of vestibular disorders that achieves a success rate of 97% when compared to the human experts involved in its design.

[Approximation to the epidemiology of salt intake and arterial pressure. Study on a community of Toledo]

The relationship between salt intake and Blood Pressure (BP) is studied in a random sample of adults from 25 to 64 years of age in a urban community in Toledo, by means of a semiquantitative determination with a reactive (Saltex strip). Of the 3,824 people included in the census (1984), 384 were selected, regarding whom, in addition to the Cl- NaCl in the night fraction of urine being studied, the average BP of two samples, the body mass index (BMI), chronic communicable diseases, the use of tobacco, alcohol and drugs, as well as other social variables of the population were studied. Data was collected regarding the salt intake of 238 individuals and the BP of 236 individuals. A prevalence of high blood pressure (BP greater than 140 and/or 90 mmHg) in 14% was observed, and 81% of the sample studied ingested over 11 g of salt daily. The results were analyzed in strata, by age and BMI to avoid factors resulting in confusion, no relationship between salt intake, BP and rest of the variables studied being found in our community.