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Biomedical subjects

D Bracher

Publications and source records attributed to D Bracher.

9 recordsLinked to original sources
PubMed1992

Strictosidine synthase from Rauvolfia serpentina: analysis of a gene involved in indole alkaloid biosynthesis.

The gene for strictosidine synthase (str1), the enzyme which catalyzes the stereospecific condensation of tryptamine and secologanin to form the key indole alkaloid 3 alpha(S)-strictosidine has been isolated from genomic libraries prepared from Rauvolfia serpentina (India) and from Rauvolfia mannii (West Africa). The gene, str1, contained no introns and showed 100% nucleotide sequence homology over 1180 bp, encompassing the entire reading frame, between the two species. Transcription of the R. serpentina gene was found to start 81 nucleotides upstream from the AUG (26 nucleotides downstream from the TATA box). Transient expression assays in Nicotiana plumbaginifolia protoplasts of the R. serpentina str1 5'-noncoding region fused to the beta-glucuronidase reporter gene revealed promoter activity equivalent to 4 +/- 2% of that of 35 S CaMV promoter control. A series of truncated segments of the str1 promoter region indicated the presence of three areas of slight, but reproducible, negative control. Gel retardation assays demonstrated that several regions of the 5'-flanking sequences specifically bound nuclear protein from R. serpentina and that at least one region does not bind R. mannii nuclear protein. A survey of the expression of str1 in the R. serpentina plant suggested that strictosidine synthase poly(A)+ RNA was present predominantly, but not exclusively, in the root. This result correlated well with the distribution of both enzyme activity and indole alkaloids which were also predominant in the root, but, in general, distributed throughout the shrub.

Amino Acid Sequence↗
PubMed1983

Changes in corneal DC-potentials associated with changes in pupillary diameter.

Using light-emitting diodes we stimulated monocularly with light intensities of between 7.5 and 1,800 cd/m2, and recorded simultaneously the Dc-electroretinogram and pupillary movements of the stimulated and the contralateral eye. In some investigations, the visual evoked potential and the activity from the periorbicular muscles were also recorded. Various drugs acting on the autonomous nervous system were topically applied and their efforts studied. In the eye with an untreated pupil, stimulated or contralateral, a corneo positive potential coincident with pupillary constriction was seen (cu-wave), provided the pupil was large beforehand, a corneonegative deflection dominated, which was also coincident with pupillary constriction (mu-wave). Parasympathicolytics or -mimetics abolished both the cu and mu-wave. We conclude that the cu-wave is related to depolarization of the sphincter pupillae during constriction, whereas the mu-wave might be related to a modification of the potential distribution between the pigment epithelium and the tissue surrounding the eye in the case where the pupil is constricted beyond a critical point.

Adult↗
PubMed1983

Central retinal arteries in hyperoxemia, and a possible role of fundusscopy in prevention of retrolental fibroplasia (retinopathia praematurorum).

Width and tortuosity of the central retinal arteries have been measured on fundus photographs of 9 full-term newborns under intensive care taken at least once in normoxemia and once in inadvertent hyperoxemia. In agreement with previous investigators no correlation was found between the actual paO2 and width of the arterioles. This is newly explained as a modification of the effect of paO2 on the vessel through acute asphyxia and adaptational phenomena. In opposition to the commonly accepted view on prevention of retrolental fibroplasia it is felt that the use of fundusscopy during intensive care should be reconsidered.

Asphyxia Neonatorum↗
PubMed1982

Changes in peripapillary tortuosity of the central retinal arteries in newborns. A phenomenon whose underlying mechanisms need clarification.

The phenomenon of tortuosity of the central retinal arteries (CRA) and the changes within a few hours are documented by photographs centered on the disc of different newborns. Tortuosity is more marked in the temporal than in the nasal branches: it may be sinusoidal, but is more often irregular inasmuch as bends alternate with straight parts. In the latter, there is no rule for the distance of the bend from the disc, for the length of its chord, or for the steepness of the ascending and descending parts. With regard to pathophysiology, tortuosity is seen in, and a few hours after, fetal or neonatal circulatory distress, but the anatomy causing a vessel to become tortuous is not understood. In an appendix we propose rules on how to obtain a quantitative value of tortuosity for a single artery if it is irregular, and how to calculate a value we term mean temporonasal tortuosity for interindividual comparison.

Female↗
PubMed1981

Central retinal arteries in the full-term newborn: decrease in width and tortuosity during uneventful adaptation.

The fundi of 87 full-term newborns were repeatedly photographed from 2 to 144 h of life. At 2 h of life the width of the temporal arteries in the peripapillary area was about 100 micrometers and that of the nasal arteries about 70 micrometers, and all gradually decreased by about 30% during uneventful adaptation in room air. This decrease did not correlate with concomitant tcpO2 and blood pressure measurements. In most babies the arteries were slightly tortuous at 2 h of life and gradually straightened during adaptation. In some babies, however, there was marked tortuosity at 2 h of life, and this finding was significantly correlated with fetal risk factors. We conclude that marked tortuosity is a sign of passed acute fetal distress and that funduscopy in risk babies should be promoted.

Blood Pressure↗
PubMed1979

Measurement of vessel width on fundus photographs.

Many factors play a role in determining the width of retinal vessels, based on fundus photographs. We have tried to estimate their influence by comparing experimentally six different measuring methods, taking into account film and developer, intra- and interindividual reproducibility of results under short- and long-term conditions, and training in measuring technique. Our method of choice was tenfold projection of the negatives on a fine-grained wax layer screen and use of a very narrow marker line to be aligned with the vessel borders. Width determinations on pictures of good definition, yet low contrast, repeated by a trained observer on consecutive days, lay with a 95% probability within an interval of about 9 micron on the retina. The width so determined is, of course, relative and only a rough approximation to the absolute width, because of photographic bias, interobserver difference, and uncertainly of the refractive power of the eye. The method appears to be especially suitable for the study of intraindividual variations; however, because of photographic bias, conclusions should be drawn only when based on several pictures.

Adult↗
PubMed1979

Measurement of vessel tortuosity on fundus photographs.

Quantitative measurement of vessel tortuosity and its variation on fundus photographs is a sensitive means of obtaining information about the course of an asphyctic event in newborns, virtually independent of bias produced by the photographic process. We subdivide a tortuous vessel into single arcs and measure the chord length and the arrow height (Pfeilhöhe) of every arc on a projected image of the film. From these figures, a fairly accurate value for the relative length increase of the arc, as compared with the chord, can be derived by a simple approximation formula [Eq. (5)]. It is shown that neglect of the third dimension, not visible on an ordinary photograph, entails only a small error. Trained observers achieve results reproducible to about 1% in relative length variation.

Asphyxia Neonatorum↗
PubMed1976

Fundus photography in neonates, an approach to obtain indirect information on cerebral blood flow.

In view of the possibility to obtain indirect information on the interdependency between brain tissue metabolish and the diameter of the intraparenchymatous arterioles through measurement of systemic blood gases and blood pressure on one hand and the diameter of the central retinal artery on the other, we describe a modified method of fundus photography which is practical for neonatologists owing to the simplification brought about by the use of a special contact lens. In an appendix the relevant optical data are analyzed. Fundus photographs of neonates suffering from cardiac malformation or asphyxia are shown.

Cerebrovascular Circulation↗