Biomedical subjects

A Mogilner

Publications and source records attributed to A Mogilner.

28 records · Page 2Linked to original sources

PubMed1998

Force generation in RNA polymerase.

RNA polymerase (RNAP) is a processive molecular motor capable of generating forces of 25-30 pN, far in excess of any other known ATPase. This force derives from the hydrolysis free energy of nucleotides as they are incorporated into the growing RNA chain. The velocity of procession is limited by the rate of pyrophosphate release. Here we demonstrate how nucleotide triphosphate binding free energy can rectify the diffusion of RNAP, and show that this is sufficient to account for the quantitative features of the measured load-velocity curve. Predictions are made for the effect of changing pyrophosphate and nucleotide concentrations and for the statistical behavior of the system.

Adenosine Triphosphatases↗

PubMed1998

Nocardia abscess of the choroid plexus: clinical and pathological case report.

OBJECTIVE: Cerebral Nocardia abscesses are rare, accounting for approximately 1 to 2% of all cerebral abscesses. Prompt aggressive surgical treatment involving craniotomy and excision of these lesions has been advocated by many authors, because these lesions have significantly higher morbidity and mortality rates than do most other cerebral abscesses. We report an atypical presentation of cerebral nocardiosis localized to the choroid plexus of the lateral ventricle. CLINICAL PRESENTATION: A 56-year-old man presented with a 3-week history of fever, cough, and progressive headache and an ensuing 3-day history of progressive lethargy, confusion, and gait ataxia. Radiographic studies demonstrated a loculated contrast-enhancing left lateral ventricular lesion with significant perilesional parenchymal edema that was thought preoperatively to be a neoplasm. INTERVENTION: The patient underwent a craniotomy for resection of the lesion. Intraoperatively, a reddish gray lesion with purulent exudate was encountered within the left lateral ventricle intimately adherent to the choroid plexus as well as to the ependyma and subependymal veins. A frozen section demonstrated an organizing abscess wall. The lesion was resected in its entirety, and multiple cultures were sent for analysis. CONCLUSION: Microbiology cultures grew Nocardia asteroides. A course of intravenous antibiotics was started, which included trimethoprim-sulfamethoxazole, amikacin, and ceftriaxone. Two weeks after surgery, at the time of discharge, the patient's neurological status had improved considerably. Although Nocardia abscesses have been documented to occur throughout the central nervous system, the presentation of a lesion confined to the choroid plexus of the lateral ventricle with significant parenchymal edema is unusual and demonstrates that Nocardia abscesses must be considered in the differential diagnosis of a contrast-enhancing intraventricular mass lesion involving the choroid plexus.

Brain Abscess↗

PubMed1998

Unemployment and underemployment in 1996 graduates of New York City gastroenterology training programs.

OBJECTIVE: Based on anecdotal reports of young gastroenterologists facing extreme difficulty in finding a job, we sought to gain information about the success of newly trained gastroenterologists in finding employment in their subspecialty, and to find any possible predictors of unemployment. METHODS: We surveyed all fellows finishing basic or advanced gastroenterology fellowship training in New York City in June 1996. Data were collected on unemployment, underemployment (practicing less than half-time gastroenterology), and also type of job, employment terms, training program, medical school, gender, and satisfaction with job plans. RESULTS: Of the 59 study subjects who sought gastroenterology employment in the United States, data were collected on all of them (100%). Fifteen subjects (25%) were unemployed. An additional 10 subjects (17%) were underemployed. Of the 24 subjects expecting to be associates in a group practice, eight (33%) had either no signed contract, were underemployed, or both. Programs that did not participate in the National Residency Matching Program were more likely to have both unemployed and underemployed graduates. CONCLUSION: Unemployment among newly trained gastroenterologists in New York City is very high. Also, there is substantial underemployment, and this phenomenon needs to be taken into account when studying the workforce.

Data Collection↗

PubMed1996

Cell motility driven by actin polymerization.

Certain kinds of cellular movements are apparently driven by actin polymerization. Examples include the lamellipodia of spreading and migrating embryonic cells, and the bacterium Listeria monocytogenes, that propels itself through its host's cytoplasm by constructing behind it a polymerized tail of cross-linked actin filaments. Peskin et al. (1993) formulated a model to explain how a polymerizing filament could rectify the Brownian motion of an object so as to produce unidirectional force (Peskin, C., G. Odell, and G. Oster. 1993. Cellular motions and thermal fluctuations: the Brownian ratchet. Biophys. J. 65:316-324). Their "Brownian ratchet" model assumed that the filament was stiff and that thermal fluctuations affected only the "load," i.e., the object being pushed. However, under many conditions of biological interest, the thermal fluctuations of the load are insufficient to produce the observed motions. Here we shall show that the thermal motions of the polymerizing filaments can produce a directed force. This "elastic Brownian ratchet" can explain quantitatively the propulsion of Listeria and the protrusive mechanics of lamellipodia. The model also explains how the polymerization process nucleates the orthogonal structure of the actin network in lamellipodia.

Actins↗

PubMed1996

Central motor loop oscillations in parkinsonian resting tremor revealed by magnetoencephalography.

A variety of clinical and experimental findings suggest that parkinsonian resting tremor results from the involuntary activation of a central mechanism normally used for the production of rapid voluntary alternating movements. However, such central motor loop oscillations have never been directly demonstrated in parkinsonian patients. Using magnetoencephalography, we recorded synchronized and tremor-related neuromagnetic activity over wide areas of the frontal and parietal cortex. The spatial and temporal organization of this activity was studied in seven patients suffering from early-stage idiopathic Parkinson's disease (PD). Single equivalent current dipole (ECD) analysis and fully three-dimensional distributed source solutions (magnetic field tomography, MFT) were used in this analysis. ECD and MFT solutions were superimposed on high-resolution MRI. The findings indicate that 3 to 6 Hz tremor in PD is accompanied by rhythmic subsequent electrical activation at the diencephalic level and in lateral premotor, somatomotor, and somatosensory cortex. Tremor-evoked magnetic activity can be attributed to source generators that were previously described for voluntary movements. The interference of such slow central motor loop oscillations with voluntary motor activity may therefore constitute a pathophysiologic link between tremor and bradykinesia in PD.

Aged↗

PubMed1996

Selecting a common direction. II. Peak-like solutions representing total alignment of cell clusters.

The problem of alignment of cells (or other objects) that interact in an angle-dependent way was described in Mogilner and Edelstein-Keshet (1995). In this sequel we consider in detail a special limiting case of nearly complete alignment. This occurs when the rotational diffusion of individual objects becomes very slow. In this case, the motion of the objects is essentially deterministic, and the individuals or objects tend to gather in clusters at various orientations. (Numerical solutions show that the angular distribution develops sharp peaks at various discrete orientations.) To understand the behaviour of the deterministic models with analytic tools, we represent the distribution as a number of delta-like peaks. This approximation of a true solution by a set of (infinitely sharp) peaks will be referred to as the peak ansatz. For weak but nonzero angular diffusion, the peaks are smoothed out. The analysis of this case leads to a singular perturbation problem which we investigate. We briefly discuss other applications of similar techniques.

Animals↗

PubMed1994

Neuromagnetic studies of the lip area of primary somatosensory cortex in humans: evidence for an oscillotopic organization.

Magnetic trigeminal somatosensory responses from human subjects were recorded using a 14-channel magnetoencephalographic system. Sensory stimuli comprising a 15-ms vibration at frequencies of 50 Hz, 150 Hz and 250 Hz were given at randomized interstimulus intervals. Using a single dipole model, the neuronal sources of the evoked responses were determined, and mapped onto magnetic resonance images of each subject. Source localization analysis was based on the main peak of the averaged signal (M55). All of the sources were located deep in the anterior bank of the postcentral gyrus, corresponding to area 3b of somatosensory cortex SI. In all cases, the source for the upper lip was significantly higher in the vertical axis (0.6-1.1 cm) than for the lower lip, while the lower lip stimulation produced a larger response than the upper lip. Furthermore, statistically significant differences were found between the locations of the dipoles evoked by different frequency stimulation. The location of the response shifted with change in stimulation frequency, showing a trend among all subjects with medial shift between 150 and 250 Hz for both upper and lower lip. The accuracy of source localization calculated from magnetic fields ranged between +/- 0.9 and +/- 3.0 mm (SEM). These results demonstrate (1) that a large area of the somatosensory cortex is utilized for lip representation and (2) that the spatial displacement of the trigeminal somatosensory response may be related to the discrimination of frequency.

Adult↗

PubMed1993

Somatosensory cortical plasticity in adult humans revealed by magnetoencephalography.

Microelectrode recordings in adult mammals have clearly demonstrated that somatosensory cortical maps reorganize following peripheral nerve injuries and functional modifications; however, such reorganization has never been directly demonstrated in humans. Using magnetoencephalography, we have been able to demonstrate the somatotopic organization of the hand area in normal humans with high spatial precision. Somatosensory cortical plasticity was detected in two adults who were studied before and after surgical separation of webbed fingers (syndactyly). The presurgical maps displayed shrunken and nonsomatotopic hand representations. Within weeks following surgery, cortical reorganization occurring over distances of 3-9 mm was evident, correlating with the new functional status of their separated digits. In contrast, no modification of the somatosensory map was observed months following transfer of a neurovascular skin island flap for sensory reconstruction of the thumb in two subjects in whom sensory transfer failed to occur.

Adult↗

PubMed1991

Magnetic field tomography of coherent thalamocortical 40-Hz oscillations in humans.

This paper introduces the use of magnetic field tomography (MFT), a noninvasive technique based on distributed source analysis of magnetoencephalography data, which makes possible the three-dimensional reconstruction of dynamic brain activity in humans. MFT has a temporal resolution better than 1 msec and a spatial accuracy of 2-5 mm at the cortical level, which deteriorates to 1-3 cm at depths of 6 cm or more. MFT is used here to visualize the origin of a spatiotemporally organized pattern of coherent 40-Hz electrical activity. This coherence, initially observed during auditory input, was proposed to be generated by recurrent corticothalamic oscillation. In support of this hypothesis, we illustrate well-defined 40-Hz coherence between cortical-subcortical sites with a time shift that is consistent with thalamocortical conduction times. Studies on Alzheimer patients indicate that, while a similar activity pattern is present, the cortical component is reduced in these subjects.

Adult↗

PubMedDate not supplied

Awareness and attitudes concerning BRCA gene testing.

BACKGROUND: The availability of a commercial test for the breast cancer susceptibility genes, BRCA1 and BRCA2, has generated interest in both the medical community and the general public. METHODS: Patients and family members were approached in the waiting room and asked to fill out an anonymous questionnaire about their awareness of breast cancer genes and breast cancer gene testing, and their desire to be tested. chi2 analysis was used to analyze frequencies between groups. RESULTS: A total of 354 women completed a questionnaire concerning the breast cancer genes BRCA1 and BRCA2. The very young, the very old, and African-Americans were the least informed in terms of awareness of the genes and the availability of testing for the breast cancer susceptibility genes. Jewish people, people with a college education or beyond, people earning more than $30,000 a year, and Caucasians were more aware of the genes and of testing for these genes. Interest in being tested was similar in all groups, except for participants over 60 and those who had only an elementary-school education. CONCLUSIONS: Information concerning the breast cancer susceptibility genes has not reached the general public uniformly. A concerted effort is needed if this information is to be passed on to those people at risk.

Adult↗