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M F Brown

Publications and source records attributed to M F Brown.

At least 55 records · Page 3Linked to original sources
PubMed1996

Surface plasmon resonance spectroscopy studies of membrane proteins: transducin binding and activation by rhodopsin monitored in thin membrane films.

Surface plasmon resonance (SPR) spectroscopy can provide useful information regarding average structural properties of membrane films supported on planar solid substrates. Here we have used SPR spectroscopy for the first time to monitor the binding and activation of G-protein (transducin or Gt) by bovine rhodopsin incorporated into an egg phosphatidylcholine bilayer deposited on a silver film. Rhodopsin incorporation into the membrane, performed by dilution of a detergent solution of the protein, proceeds in a saturable manner. Before photolysis, the SPR data show that Gt binds tightly (Keq approximately equal to 60 nM) and with positive cooperativity to rhodopsin in the lipid layer to form a closely packed film. A simple multilayer model yields a calculated average thickness of about 57 A, in good agreement with the structure of Gt. The data also demonstrate that Gt binding saturates at a Gt/rhodopsin ratio of approximately 0.6. Moreover, upon visible light irradiation, characteristic changes occur in the SPR spectrum, which can be modeled by a 6 A increase in the average thickness of the lipid/protein film caused by formation of metarhodopsin II (MII). Upon subsequent addition of GTP, further SPR spectral changes are induced. These are interpreted as resulting from dissociation of the alpha-subunit of Gt, formation of new MII-Gt complexes, and possible conformational changes of Gt as a consequence of complex formation. The above results clearly demonstrate the ability of SPR spectroscopy to monitor interactions among the proteins associated with signal transduction in membrane-bound systems.

Animals↗
PubMed1996

Control of choice by the spatial configuration of goals.

Rats gathered pellets from the tops of 15.5-cm-tall poles. In a matrix of poles, bait was located on the tops of poles arranged in either a square (Experiment 1) or linear (Experiment 2) configuration. The specific locations of baited poles varied unpredictably from trial to trial. The data show that the rats' choices were controlled by the spatial configuration of baited locations. This indicates that the rats represented the geometric pattern formed by the locations of food.

Animals↗
PubMed1996

Causes of gastrointestinal hemorrhage in neonates and children.

The causes of gastrointestinal hemorrhage in children were detailed in 1964 by Spencer. We investigated the causes of gastrointestinal hemorrhage in 165 children seen at our institution over a 13-year period. The most common causes of gastrointestinal hemorrhage in the hospitalized patients were necrotizing enterocolitis (44%), anal fissures (23%), and guaiac-positive stools of unknown cause (16%). The mortality rate was 5.4%. Necrotizing enterocolitis was the most common cause of death. Only 16 patients required surgery. Gastrointestinal hemorrhage is an infrequent cause of mortality and morbidity in hospitalized pediatric patients.

Adolescent↗
PubMed1995

Preoperative vein mapping for coronary artery bypass operations.

High-resolution, real-time ultrasonographic imaging of the greater saphenous veins was performed preoperatively in 100 patients undergoing coronary artery bypass grafting. Vein diameters were measured by ultrasound at four locations in the leg, and the course of the vein in the leg was marked on the overlying skin. Veins removed at operation were measured at the same locations at initial dissection and after vein preparation. The mapped and in situ vein diameters correlated closely, whereas the distended vein diameter was approximately 1.5 mm larger. When greater saphenous veins were absent or diseased, lesser saphenous veins were mapped. No differences in measurements were demonstrated for a variety of patient and operator variables. Major branches or duplications were predicted correctly in 11 patients and venous disease in 13 patients. Mapping influenced the surgeon's choice of the venectomy site in 13 patients. Vein mapping is a simple, accurate, and noninvasive method of imaging the saphenous vein preoperatively. It is useful in demonstrating areas of venous anomalies and disease, and predicts the course of the vein in the leg.

Coronary Artery Bypass↗
PubMed1995

Successful prenatal management of hydrops, caused by congenital cystic adenomatoid malformation, using serial aspirations.

Congenital cystic adenomatoid malformation (CCAM) is a lung lesion that is now commonly diagnosed in utero with fetal ultrasonography. The described treatment of this lesion includes observation with treatment delivery, a single aspiration, thoraco-amniotic shunts, and fetal resection. This patient had an in utero diagnosis of a Stocker type I CCAM associated with hydrops. Fetal resection was not an option because of patient refusal. The fetus was treated with multiple serial aspirations. There was marked improvement of the anasarca, and subsequently the baby was born without respiratory distress. On the second day of life the CCAM began to expand, and the right lower lobe was resected. The baby's postoperative course was uneventful. CCAM with hydrops is associated with a high mortality rate. Current recommended therapy for these lesions is fetal resection or thoracoamniotic shunt. The authors' patient was treated with serial fetal thoracocenteses, with an excellent outcome. This therapy may be an alternative to fetal surgery or an adjunct to fetal surgery in selected cases.

Adult↗
PubMed1995

Monoclonality of parathyroid tumors in chronic renal failure and in primary parathyroid hyperplasia.

The pathogeneses of parathyroid disease in patients with uremia and nonfamilial primary parathyroid hyperplasia are poorly understood. Because of multigland involvement, it has been assumed that these common diseases predominantly involve polyclonal (non-neoplastic) cellular proliferations, but an overall assessment of their clonality has not been done. We examined the clonality of these hyperplastic parathyroid tumors using X-chromosome inactivation analysis with the M27 beta (DXS255) DNA polymorphism and by searching for monoclonal allelic losses at M27 beta and at loci on chromosome band 11q13. Fully 7 of 11 informative hemodialysis patients (64%) with uremic refractory hyperparathyroidism harbored at least one monoclonal parathyroid tumor (with a minimum of 12 of their 19 available glands being monoclonal). Tumor monoclonality was demonstrable in 6 of 16 informative patients (38%) with primary parathyroid hyperplasia. Histopathologic categories of nodular versus generalized hyperplasia were not useful predictors of clonal status. These observations indicate that monoclonal parathyroid neoplasms are common in patients with uremic refractory hyperparathyroidism and also develop in a substantial group of patients with sporadic primary parathyroid hyperplasia, thereby changing our concept of the pathogenesis of these diseases. Neoplastic transformation of preexisting polyclonal hyperplasia, apparently due in large part to genes not yet implicated in parathyroid tumorigenesis and possibly including a novel X-chromosome tumor suppressor gene, is likely to play a central role in these disorders.

Adult↗
PubMed1995

Elephantiasis nostras verrucosa.

Elephantiasis is an uncommon disease in the United States. We present a case of nonfilarial elephantiasis nostras verrucosa in a 14-year-old girl. Most commonly, the upper and lower extremities are affected; the disease, in this patient, was confined to the buttock. The patient has done well after excision and primary closure. The patient is currently undergoing pressure therapy 1 year after surgery. She has no evidence of recurrence. We present this case and review the literature.

Adolescent↗
PubMed1994

Conformational changes in rhodopsin probed by surface plasmon resonance spectroscopy.

Surface plasmon resonance (SPR) spectroscopy has been used to follow incorporation and light-induced conformational changes in bovine rhodopsin reconstituted into an egg phosphatidylcholine bilayer deposited on a thin silver film. The magnitude of the SPR spectral changes caused by light varies with pH in a manner paralleling that in flash photolysis experiments, which monitor formation of metarhodopsin II. Irradiation produces an increase of approximately 4 A in the average thickness of the proteolipid layer, consistent with exposure of recognition sites for the G protein. The results demonstrate that the SPR technology described herein may be used to monitor conformational events in membrane-associated receptors such as rhodopsin.

Animals↗
PubMed1994

Modulation of rhodopsin function by properties of the membrane bilayer.

A prevalent model for the function of rhodopsin centers on the metarhodopsin I (MI) to metarhodopsin II (MII) conformational transition as the triggering event for the visual process. Flash photolysis techniques enable one to determine the [MII]/[MI] ratio for rhodopsin in various recombinant membranes, and thus investigate the roles of the phospholipid head groups and the lipid acyl chains systematically. The results obtained to date clearly show that the pK for the acid-base MI-MII equilibrium of rhodopsin is modulated by the lipid environment. In bilayers of phosphatidylcholines the MI-MII equilibrium is shifted to the left; whereas in the native rod outer segment membranes it is shifted to the right, i.e., at neutral pH near physiological temperature. The lipid mixtures sufficient to yield full photochemical function of rhodopsin include a native-like head group composition, viz, comprising phosphatidylcholine (PC), phosphatidylethanolamine (PE), and phosphatidylserine (PS), in combination with polyunsaturated docosahexaenoic acid (DHA; 22:6 omega 3) chains. Yet such a native-like lipid mixture is not necessary for the MI-MII conformational transition of rhodopsin; one can substitute other lipid compositions having similar properties. The MI-MII transition is favored by relatively small head groups which produce a condensed bilayer surface, viz, a comparatively small interfacial area as in the case of PE, together with bulky acyl chains such as DHA which prefer a relatively large cross sectional area. The resulting force imbalance across the layer gives rise to a curvature elastic stress of the lipid/water interface, such that the lipid mixtures yielding native-like behavior form reverse hexagonal (HII) phases at slightly higher temperatures. A relatively unstable membrane is needed: lipids tending to form the lamellar phase do not support full native-like photochemical function of rhodopsin. Thus chemically specific properties of the various lipids are not required, but rather average or material properties of the entire assembly, which may involve the curvature free energy of the membrane-lipid water interface. These findings reveal that the membrane lipid bilayer has a direct influence on the energetics of the conformational states of rhodopsin in visual excitation.

Animals↗
PubMed1994

Evidence for spatial working memory in honeybees (Apis mellifera).

Spatial working memory (the ability to represent multiple locations in a flexible, dynamic manner) has been studied in a range of vertebrate species. The results of 3 experiments indicate that this ability also exists in at least one invertebrate (honeybees; Apis mellifera). Individual honeybees collected sugar solution from a matrix of 6 locations. They avoided revisits to locations previously depleted of solution more accurately than expected by chance. The results rule out several nonmemorial explanations for this ability, and it is therefore best explained by a spatial working memory system that allows discrimination of previously visited locations from those not yet visited. These results substantially expand the range of species in which spatial working memory has been demonstrated.

Animals↗
PubMed1993

Curvature, order, and dynamics of lipid hexagonal phases studied by deuterium NMR spectroscopy.

Solid-state deuterium (2H) NMR spectroscopy enables one to study both equilibrium and dynamical properties of membrane constituents at the molecular level and can yield significant insights regarding the organization of non-bilayer lipid aggregates. We have investigated a representative unsaturated phosphatidylethanolamine, viz., 1-perdeuteriopalmitoyl-2-linoleoyl-sn-glycero- 3-phosphoethanolamine, PLPE-d31, in the lamellar, or L alpha, phase and the reversed hexagonal, or HII, phase. Phosphorus-31 (31P) NMR studies of PLPE-d31 in the HII phase revealed that the chemical shift anisotropy of the phosphoethanolamine head groups, delta sigma, was scaled by the expected geometrical factor of -1/2 relative to the lamellar state. However, we found the occurrence of a further reduction in the 2H NMR quadrupolar splittings, delta vQ, of the 2H-labeled palmitoyl acyl chain segments. These observations point toward the role of interfacial curvature with regard to properties of reverse hexagonal phase lipids, and indicate that the pivotal position or neutral surface of approximately constant area may lie near the glycerol or polar head group region. Variations in the acyl chain packing due to curvature of the aqueous interface yield significant differences in the segmental order profiles as determined by 2H NMR spectroscopy. The latter reflect the local orientational order of the acyl chains and can be used together with simple statistical theories to extract positional or structural information. Average projected acyl chain lengths and mean interfacial or cross-sectional areas for PLPE-d31 in the different phases have been calculated. In addition, we describe a new means of estimating the radius of curvature of HII phase lipid aggregates utilizing 2H NMR spectroscopy, which is based on the difference between the lamellar and hexagonal phase order profiles. Here the radius of curvature, Rc, is defined as the distance from the center of the water core to the lipid/water interface, near the carbonyl segments of the acyl chains, giving Rc = 25.4-28.1 A for PLPE-d31 in the HII phase at 60 degrees C. This value is in good agreement with previous X-ray diffraction studies of 1,2-dioleoyl-sn-glycero-3-phosphoethanolamine (DOPE). Alternatively, the data yield for the radius of the central water core that Rw = 17.8-20.5 A at 60 degrees C. The differences in geometry also lead to higher quadrupolar echo relaxation rates (R2e) for the lipid acyl segments closest to the aqueous interface in the HII versus the L alpha phase.(ABSTRACT TRUNCATED AT 400 WORDS)

Chemical Phenomena↗
PubMed1993

Lipid headgroup and acyl chain composition modulate the MI-MII equilibrium of rhodopsin in recombinant membranes.

A current paradigm for visual function centers on the metarhodopsin I (MI) to metarhodopsin II (MII) conformational transition as the trigger for an intracellular enzyme cascade leading to excitation of the retinal rod. We investigated the influences of the membrane lipid composition on this key triggering event in visual signal transduction using flash photolysis techniques. Bovine rhodopsin was combined with various phospholipids to form membrane recombinants in which the lipid acyl chain composition was held constant at that of egg phosphatidylcholine (PC), while the identity of the lipid headgroups was varied. The ratio of MII/MI produced in these recombinants by an actinic flash at 28 degrees C was studied as a function of pH. The results were compared to the photochemical function observed for rhodopsin in native retinal rod outer segment (ROS) membranes, in total native ROS lipid recombinants, and in dimyristoylphosphatidylcholine (DMPC) recombinants. In membrane recombinants incorporating lipids derived from egg PC, as well as in the total ROS lipids control and the native ROS disk membranes, MI and MII were found to coexist in a pH-dependent, acid-base equilibrium on the millisecond time scale. The recombinants of rhodopsin with egg PC, either alone or in combination with egg PC-derived phosphatidylethanolamine (PE) or phosphatidylserine (PS), exhibited substantially reduced photochemical activity at pH 7.0. However, all recombinants comprising phospholipids with unsaturated acyl chains were capable of full native-like MII production at pH 5.0, confirming previous results [Gibson, N.J.. & Brown, M.F. (1990) Biochem. Biophys. Res. Commun. 169, 1028-1034]. It follows that energetic constraints on the MI and MII states imposed by egg PC-derived acyl chains can be offset by increased activity of H+ ions. The data reveal that the major effect of the membrane lipid composition is to alter the apparent pK for the MI-MII conformational equilibrium of rhodopsin [Gibson, N.J., & Brown, M.F. (1991) Biochem. Biophys. Res. Commun. 176, 915-921]. Recombinants containing only phosphocholine headgroups exhibited the lowest apparent pK values, whereas the presence of either 50 mol % PE or 15 mol % PS increased the apparent pK. The inability to obtain full native-like function in recombinants having egg PC-derived chains and a native-like headgroup composition indicates a significant role of the polyunsaturated docosahexaenoic acid (DHA) chains (22:6 omega 3) of the native retinal rod membrane lipids. Temperature studies of the MI-MII transition enabled an investigation of lipid influences on the thermodynamic parameters of a membrane protein conformational change linked directly to function.(ABSTRACT TRUNCATED AT 400 WORDS)

Acid-Base Equilibrium↗
PubMed1993

The effects of ischemia and reperfusion on intestinal motility.

The interdigestive migrating motor complex (MMC) has been demonstrated to be a reliable indicator of intestinal motility and function. The effects of low perfusion on the MMC have never been studied. Fourteen newborn Yorkshire piglets (5 to 18 days old, weighing 2.9 +/- 0.4 kg) underwent celiotomy under general anesthesia with placement of four jejunal electrodes (50 cm apart) as well as a superior mesenteric artery (SMA) Doppler flow probe and a pericardial catheter. Group 1 (n = 5) had operation alone. Group 2 (n = 9) had nonocclusive mesenteric ischemia induced by reversible cardiac tamponade for 5 hours between postoperative days 6 to 12. All subjects had MMC phase III electrical activity, cycling time, and propagation velocity recorded daily. In group 2 MMCs were recorded prior to and during ischemia, and during reperfusion. Group 2 animals had 75% +/- 4% decrease in SMA flow during the tamponade period. During the ischemic period, the MMC cycling time (CT) increased from 67 +/- 10 (mean +/- SEM) to 98 +/- 12 minutes (P < .05) and MMC propagation velocity (PV) decreased to 4.2 +/- 2.2 from a baseline value of 10.5 +/- 1.5 cm/min (P < .05). During reperfusion CT and PV values were not significantly different from baseline. The validity of this model is confirmed by the comparable baseline recordings in groups 1 and 2, and by the return of MMC to baseline values within 4 to 7 hours of reperfusion, as seen in group 2.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1993

Mesenteric ischemia in hypoplastic left heart syndrome.

Hypoplastic left heart syndrome (HLHS) has been widely viewed as a uniformly fatal form of congenital heart disease. Between January 1984 and December 1990, 387 patients with the diagnosis of HLHS were treated at this institution. Mesenteric ischemia was clinically diagnosed in 31 patients (8% incidence) and confirmed by pathology or surgery in 25 of those patients. The mean age at the time of onset was 17.5 +/- 5.4 weeks and only 13% were premature newborns. In 80% of the patients a low perfusion state and significant hypotension were documented within 48 hours prior to the diagnosis of bowel ischemia. Nine patients (29%) required operative intervention (bowel resection 4, diffuse ischemia 3, and simple drainage 2). Overall, at operation or at autopsy, nine patients (29%) had diffuse gastrointestinal ischemia. Of 31 patients with mesenteric ischemia, 26 children (84%) died shortly after onset of the gastrointestinal symptoms regardless of means of management. Five patients (10%) initially improved with aggressive medical and/or surgical management; however, 4 subsequently died secondary to complications of their primary cardiac disease. Therefore, the overall mortality of patients with mesenteric ischemia was 97%. Previous reports have estimated that up to 7% of full-term newborns with symptomatic congenital heart disease may develop necrotizing enterocolitis (NEC). Our unique group of patients with HLHS is comprised mostly of full-term infants who developed onset of mesenteric ischemia at a mean age of 4 months associated with an underlying low perfusion state. This mesenteric ischemia has been erroneously identified as NEC.(ABSTRACT TRUNCATED AT 250 WORDS)

Diagnosis, Differential↗
PubMed1993

Ovarian masses in children: a review of 91 cases of malignant and benign masses.

Ovarian masses in children are uncommon. We reviewed all cases of ovarian masses presenting to this hospital from 1979 to 1990. Ninety-one patients fulfilled the criteria and had medical records available. All patients were less than 18 years old. Four were diagnosed antenatally. Thirty-four tumors presented prior to 8 years of age and 1 (2.9%) was malignant. Fifty-eight tumors presented after 8 years of age and 18 (33%) were malignant. Seventy-two patients had benign disease and 19 had malignant tumors. Of those with benign disease 22 had simple or epithelial cysts, 25 had teratomas, 13 had torsion with cyst formation, 3 had granulosa cell tumors, and 9 had other less common lesions. Analysis of symptoms could not distinguish between benign and malignant lesions; however, age was less (P < .03) and tumor size smaller (P < .001) in patients with benign lesions. Benign lesions presented at a mean age of 8.8 years. Fifty-four patients had an ultrasound, all were diagnostic: simple mass (14), complex mass (8), or cyst (32). Mean size of the masses was 9.5 x 7.7 cm. Fourteen patients had a contralateral ovarian cyst. The malignant lesions included 14 germ cell tumors (4 endodermal sinus, 4 teratoma, 2 choriocarcinoma, 2 dysgerminoma, 1 embryonal, and 1 mixed), 4 epithelial tumors (1 mucinous cystadenocarcinoma, papillary cystadenocarcinoma, papillary serous cystadenocarcinoma, and endometrioid adenocarcinoma), and one patient with leukemic infiltration (ALL). Germ cell tumors presented at a mean age of 11.8 years. Eight of these patients had an ultrasound and all showed a mass (7) or cyst (1).(ABSTRACT TRUNCATED AT 250 WORDS)

Adolescent↗
PubMed1993

Mesenteric, omental, and retroperitoneal cysts in children: a clinical study of 22 cases.

Cystic lesions of the mesentery, omentum, and retroperitoneum are rare; from 1956 to 1990, 22 patients had operative treatment for such lesions at our institution. They ranged in age from 1 month to 14 years; 75% were younger than 5 years. All had either an acute abdomen or, more commonly, a silent abdominal mass. In all cases, the histologic diagnosis was lymphangioma. Abdominal ultrasonography was done in all cases after 1977 except for two patients who had an acute abdomen requiring emergency exploration. A cystic abdominal mass was diagnosed in 94% of these cases, but the correct diagnosis of lymphangioma was made prior to surgery in only 24%. Mesenteric cysts are most common in the small bowel mesentery. Omental cysts usually occur singly and are easily resected, but multiple cysts predominate in the mesentery and retroperitoneum. Complete resection was accomplished in 82% of our cases. Two patients required partial bowel resection, and four had partial excision with marsupialization of the cysts. With a mean follow-up of 23 months, we have had three recurrences, but none necessitated reexploration. Extra-abdominal lesions, mainly cutaneous lymphangiomas, developed in two cases. Prognosis is good after surgical excision, but long-term follow-up is advisable because of the possibility of recurrence, even during adulthood.

Adolescent↗
PubMed1993

Spatial guidance of choice behavior in the radial-arm maze.

In 6 experiments, the performance of male rats in a 12-arm radial maze was examined. The focus of study was the extent to which the spatial location of individual baited maze arms was determined before the rat was exposed to the extramaze visual cues corresponding to the arm, and thereby guided the rat toward the location of baited arms. Such spatial guidance of choice behavior implies a spatially organized cognitive representation of maze arms (i.e., a cognitive map). A higher level of spatial guidance was found when visual access to extramaze cues was restricted than when it was unrestricted. There was no evidence of a difference between the level of spatial guidance in the context of working memory performance and reference memory performance. Some evidence that intramaze cues contributed to microchoice guidance was found. However, spatial guidance, under at least some conditions, is best explained in terms of cognitive mapping.

Animals↗