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Biomedical subjects

D R Buck

Publications and source records attributed to D R Buck.

At least 19 recordsLinked to original sources
PubMed1998

Excitation delocalization in the bacteriochlorophyll c antenna of the green bacterium Chloroflexus aurantiacus as revealed by ultrafast pump-probe spectroscopy.

Room temperature absorption difference spectra were measured on the femtosecond through picosecond time scales for chlorosomes isolated from the green bacterium Chloroflexus aurantiacus. Anomalously high values of photoinduced absorption changes were revealed in the BChl c Qy transition band. Photoinduced absorption changes at the bleaching peak in the BChl c band were found to be 7-8 times greater than those at the bleaching peak in the BChl a band of the chlorosome. This appears to be the first direct experimental proof of excitation delocalization over many BChl c antenna molecules in the chlorosome.

Bacterial Proteins↗
PubMed1998

Energy transfers in the B808-866 antenna from the green bacterium Chloroflexus aurantiacus.

Energy transfers within the B808-866 BChl a antenna in chlorosome-membrane complexes from the green photosynthetic bacterium Chloroflexus aurantiacus were studied in two-color pump-probe experiments at room temperature. The steady-state spectroscopy and protein sequence of the B808-866 complex are reminiscent of well-studied LH2 antennas from purple bacteria. B808-->B866 energy transfers occur with approximately 2 ps kinetics; this is slower by a factor of approximately 2 than B800-->B850 energy transfers in LH2 complexes from Rhodopseudomonas acidophila or Rhodobacter sphaeroides. Anisotropy studies show no evidence for intra-B808 energy transfers before the B808-->B866 step; intra-B866 processes are reflected in 350-550 fs anisotropy decays. Two-color anisotropies under 808 nm excitation suggest the presence of a B808-->B866 channel arising either from direct laser excitation of upper B866 exciton components that overlap the B808 absorption band or from excitation of B866 vibronic bands in nontotally symmetric modes.

Anisotropy↗
PubMed1997

Pump-probe anisotropies of Fenna-Matthews-Olson protein trimers from Chlorobium tepidum: a diagnostic for exciton localization?

Exciton calculations on symmetric and asymmetric Fenna-Matthews-Olson (FMO) trimers, combined with absorption difference anisotropy measurements on FMO trimers from the green bacterium Chlorobium tepidum, suggest that real samples exhibit sufficient diagonal energy disorder so that their laser-excited exciton states are noticeably localized. Our observed anisotropies are clearly inconsistent with 21-pigment exciton simulations based on a threefold-symmetric FMO protein. They are more consistent with a 7-pigment model that assumes that the laser-prepared states are localized within a subunit of the trimer. Differential diagonal energy shifts of 50 cm(-1) between symmetry-related pigments in different subunits are large enough to cause sharp localization in the stationary states; these shifts are commensurate with the approximately 95 cm(-1) inhomogeneous linewidth of the lowest exciton levels. Experimental anisotropies (and by implication steady-state linear and circular dichroism) likely arise from statistical averaging over states with widely contrasting values of these observables, in consequence of their sensitivity to diagonal energy disorder.

Anisotropy↗
PubMed1997

Ultrafast absorption difference spectra of the Fenna-Matthews-Olson protein at 19 K: experiment and simulations.

We describe simulations of absorption difference spectra in strongly coupled photosynthetic antennas. In the presence of large resonance couplings, distinctive features arise from excited-state absorption transitions between one- and two-exciton levels. We first outline the theory for the heterodimer and for the general N-pigment system, and we demonstrate the transition between the strong and weak coupling regimes. The theory is applied to Fenna-Matthews-Olson (FMO) bacteriochlorophyll a protein trimers from the green photosynthetic bacterium Prosthecochloris aestuarii and then compared with experimental low-temperature absorption difference spectra of FMO trimers from the green bacterium Chlorobium tepidum.

Bacterial Proteins↗
PubMed1992

Peritoneal carcinomatosis: preoperative CT with intraperitoneal contrast material.

Thirty-five abdominal computed tomographic (CT) scans of 27 patients with peritoneal metastases from a mucin-producing tumor of the appendix, colon, small bowel, or ovary were retrospectively reviewed. Fifteen scans were obtained of 15 patients after CT with intraperitoneal infusion of contrast material (IP), and 20 scans were obtained of 16 patients with CT without IP. Subsequent exploratory laparotomy revealed that all 27 patients had multi-focal spread of peritoneal metastases. The sensitivity of CTIP and CT without IP for detection of peritoneal metastases at all sites of involvement was 61% and 59%, respectively. For CTIP, the highest sensitivity was in the right subphrenic space (88%), splenic hilum (86%), and left subphrenic space (83%). For CT without IP, the highest sensitivity was noted in the splenic hilum (100%), left subphrenic space (75%), and left paracolic gutter (75%). CTIP and CT without IP had low sensitivity for detection of disease in the greater omentum (50% each) and small-bowel mesentery (38% and 59%, respectively), two areas that had the highest frequency of metastases.

Appendiceal Neoplasms↗
PubMed1991

Effects of ischemia and hemoglobin on vascular function in isolated rabbit aortas.

The vascular endothelium is important in the modulation of vascular tone via production of endothelium-derived relaxing and contracting factors. The abdominal aortas of five groups of rabbits were subjected to varying lengths of ischemia (0, 1, 2, 3, or 4 hours), removed, sectioned into transverse rings, and placed in tissue baths containing Krebs' buffer at 37 degrees C and aerated with 95% O2/5% CO2. After equilibration the rings were tested for endothelium-dependent vasodilation with methacholine and nonendothelium-dependent vasodilation with nitroprusside. Endothelium-dependent relaxation as elicited by methacholine was impaired at 3 and 4 hours of ischemia but was not significantly different at 1 and 2 hours as compared to control, whereas endothelium-independent vasodilation remained normal throughout the different periods of ischemia. The addition of 1 x 10(-6) mol/L rabbit hemoglobin reduced the time needed to demonstrate significant impairment of endothelial function to 2 hours. Endothelium-independent vasodilation was not affected by hemoglobin. We conclude that hemoglobin exacerbates ischemia vascular dysfunction in the rabbit aorta.

Animals↗
PubMed1984

Evaluation of sonography in the initial assessment of the gynecologic patient.

Although the importance of sonography in modern obstetrics is undisputed, its role in the evaluation of the patient with gynecologic disease is less clear. We evaluated the role of pelvic sonography in the initial assessment of gynecologic patients. Standardized pelvic sonography was performed on patients scheduled to undergo laparoscopy or celiotomy. These examinations were evaluated by a radiologist who was not informed of the clinical diagnosis and the findings of physical examination. The overall performance of sonography was inferior to clinical examination and was notable for a high number of false positive diagnoses. We conclude that sonography should be reserved for specific indications.

Fallopian Tube Diseases↗
PubMed1983

Prevalence of increased intraocular pressure in Graves' disease--evidence of frequent subclinical ophthalmopathy.

Graves' exophthalmos is frequently associated with elevated intraocular pressure on upgaze. Eighty patients with Graves' disease were evaluated prospectively by applanation tonometry to assess the prevalence of ophthalmopathy in this disorder. Whereas 21 (26 per cent) of the 80 patients had exophthalmos, 61 (76 per cent) had abnormal intraocular pressure (delta greater than or equal to 3 mm Hg). All patients with exophthalmos had elevated intraocular pressure on upgaze; 40 (68 per cent) of 59 patients without proptosis had abnormal pressure readings. The mean interval between the onset of Graves' disease and this study was 6.3 +/- 1.0 years (S.E.M.) for those patients who had exaggerated positional changes in intraocular pressure, as compared with 3.0 +/- 1.0 years for those with normal intraocular pressure (P less than 0.005). All but 1 of 15 patients in whom the diagnosis of Graves' disease had been documented 10 or more years earlier had increased intraocular pressure on upgaze. We conclude that Graves' ophthalmopathy is more common than is recognized clinically and that eye involvement is an inevitable complication of the disease.

Adult↗
PubMed1983

Maternal dietary magnesium effects on lactation success and on milk yield and composition in the rat.

Maternal dietary magnesium (Mg) intake during lactation is known to affect the growth and development of the newborn. We fed three groups of lactating rats diets containing 125, 500 and 900 mg Mg/kg, and observed pup growth, milk yield, and milk Mg, calcium, protein, fat, lactose and energy concentrations on maternal dietary Mg; milk calcium decreased. Other milk constituents and yield did not appear to be directly affected, although deficient dams ate less food which did depress milk yield. Deficient dams also developed swollen and distended teats when milked. We conclude that less than a normally recommended amount of Mg in the maternal diet depresses pup growth, while more than a normal amount accelerates it. No clear connection was identified between the growth response and any milk constituent.

Animals↗
PubMed1982

Visual loss from cavernous hemangiomas of the middle cranial fossa.

We studied a case of cavernous hemangioma of the middle cranial fossa. This rare tumor, of which only nine prior cases have been recorded, is characterized by insidious visual loss, multiple cranial nerve pareses, proptosis, papilledema, and bitemporal hemianopsia. Pituitary dysfunction has been noted in the more advanced cases. The female-male ratio has been 8:2; ages ranged from 30 to 62 years. The hemangiomas may occur on either side. Contrast-enhanced computed tomography can clearly demonstrate the presence of these lesions, but is not diagnostically specific. High-quality angiograms using magnification and subtraction techniques may show areas of dye retention in the cavernous spaces of the lesion. This tumor is amenable to successful excision, and early removal may prevent progressive visual loss.

Female↗
PubMed1979

Effects of cerebral intraventricular magnesium injections and a low magnesium diet on nonspecific excitability level, audiogenic seizure susceptibility and serotonin.

Cerebral intraventricular injections of 17 and 50 microgram magnesium in artificial cerebrospinal fluid progressively depressed the Non-specific Excitability Level of permanently cannulated 150--200 g rats fed a low magnesium diet for 21 days. Compared with control diet, a low Mg diet caused an increase in brain serotonin. Weanling rats fed a low Mg diet for 2 weeks, then injected with 25 microgram Mg via acute cannulations, displayed reduced audiogenic seizure susceptibility compared with sham-injected controls.

Acoustic Stimulation↗
PubMed1979

Retrorenal cysts.

Three patients are presented in whom computed tomography incidentally demonstrated low density masses posterior to, but separate from, the right kidney. In two, these were proven to represent unilocular cysts, and the third is presumed cystic. Possible etiologies are discussed.

Aged↗
PubMed1978

Preliminary report on the magnesium deficient rat as a model of epilepsy.

Weanling male rats fed a low magnesium diet for 14 days were protected from audiogenic seizures by administration of phenobarbital and diphenylhydantoin. Amphetamine, levo-dopa, and magnesium chloride injected 45 minutes prior to testing did not prevent the seizures. In contrast to weanling male rats which became mortally seizure prone, 3--5 week-old female rats fed a low magnesium diet for 17--21 days varied as to their susceptibility to audiogenic seizures. If thrown into seizures by a loud noise, the females frequently could be revived for subsequent testing, thus affording the opportunity to design experiments using fewer animals.

Age Factors↗
PubMed1976

Effect of magnesium deficiency on nonspecific excitability level (NEL) and audiogenic seizure susceptibility.

Magnesium deficiency in weanling rats caused an increase in NEL and in audiogenic seizure susceptibility. These behavioral effects were apparent after eight days of magnesium restriction and could be reversed by dietary rehabilitation. Serum magnesium declined rapidly from 1.87 +/- 0.10 mEq/L to 0.91 +/- 0.24 mEq/L in two days. Cerebrospinal fluid (CSF) magnesium decreased gradually from 1.86 mEq/L, becoming significantly lower (1.44 +/- 0.23 mEq/L) after eight days. When deficient rats were injected IP with MgCl2, raising the serum magnesium concentration to 6.6 mEq/L, NEL decreased to normal while audiogenic seizure susceptibility remained. Both NEL and audiogenic seizure susceptibility in rats reflect central nervous system magnesium concentration, except when serum magnesium concentration is very high. Very high serum magnesium concentration lowers NEL but does not reduce audiogenic seizure susceptibility if CSF magnesium is low.

Animals↗
PubMedDate not supplied

Fluoroscopically guided peritoneal catheter placement for intraperitoneal chemotherapy.

PURPOSE: Surgical placement of intraperitoneal catheters for intraperitoneal chemotherapy is associated with bowel perforation, peritonitis, and catheter occlusion. The authors evaluated the safety and efficacy of fluoroscopically guided placement of temporary intraperitoneal catheters for chemotherapy. PATIENTS AND METHODS: Two hundred one intraperitoneal catheter placements were attempted in 88 patients with peritoneal carcinomatosis or sarcomatosis. The peritoneum was punctured with 22-gauge needles and exchange was made with use of Seldinger technique and liberal injections of contrast material at each step for 8.3- or 8.5-F multiple-side-hole catheters. Placement sites included all four quadrants and the midline. Computed tomographic (CT) peritoneography was performed prior to chemotherapy. RESULTS: One hundred ninety (94.5%) of 201 attempted catheter insertions were technically successful. Results of CT peritoneography were available in 175 cases and showed free distribution of peritoneal contrast material in 39% (n = 69), partial loculation in 38% (n = 67), and extensive loculation in 22% (n = 39). Catheters remained in place for a median of 5 days (range, 2-6 days). Significant complications occurred in 11 procedures (5.5%). There were seven unintended bowel intubations; all were treated conservatively except one that required surgical repair. One other patient developed necrotizing fasciitis requiring surgical débridement. Three other patients (1.5%) developed mild peritonitis responsive to antibiotics. Technical success, complications, and peritoneal distribution of contrast material did not correlate with the site of catheter placement. CONCLUSION: Percutaneous catheter placement with use of small-gauge needles for initial puncture is safe and efficacious in patients requiring short-term peritoneal access for chemotherapy.

Adult↗