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Biomedical subjects

B Fischer

Publications and source records attributed to B Fischer.

At least 307 records · Page 17Linked to original sources
PubMed1987

E. coli maltodextrin phosphorylase: primary structure and deletion mapping of the C-terminal site.

The complete 796 residue amino acid sequence of maltodextrin phosphorylase was deduced from the E. coli malP nucleotide sequence. The calculated molecular weight of 90,500, including pyridoxal phosphate, is significantly larger than experimentally determined values. Enzymatically active and inactive mutants following deletion or exchange of up to 8 codons (7 amino acids) at the 3' end (C-terminus) confirm the size of the mature native enzyme and disclose the essential functional or structural role of the highly conserved C-terminal region of phosphorylases.

Amino Acid Sequence↗
PubMed1987

Development retardation in cultured preimplantation rabbit embryos.

Day 3 to Day 5 preimplantation rabbit embryos were cultured for 24 h in chemically defined media which are widely used in early embryo culture (BSM II and Ham's F-10) supplemented with BSA or homologous serum. For the next 24 h, the embryos were left in the same culture medium, placed in freshly made medium, or cultured in medium which was supplemented with uterine flushings. In addition, 24-h cultured embryos were transferred into uteri of synchronous recipients for 1 day. After culture or transfer, development was assessed by cell proliferation evaluated by incorporation of tritiated thymidine. In comparison to non-cultured controls, thymidine incorporation demonstrated a considerably impaired cell proliferation after culture in defined media irrespective of medium, supplement, or replenishment with fresh medium. For Day 3 embryos, there was a developmental retardation amounting to about 1 day after 2 days in culture. Compared to Day 3 embryos, delay was clearly more pronounced in Day 4 and Day 5 blastocysts, i.e. in stages which had been retrieved from the uterus before culture. Supplementation with uterine flushings markedly promoted blastocyst cell proliferation (P less than 0.001). Incorporation data examined after transfer showed that impairment of cell proliferation caused by 1 day in culture had been compensated for to a large extent within 1 day in utero.

Animals↗
PubMed1986

Further observations on the occurrence of express-saccades in the monkey.

Express-saccades, i.e. goal directed eye movements with extremely short saccadic reaction times (SRT) have recently been observed in rhesus monkey (70-80 ms) and human subjects (around 100 ms). In the gap task which has been used so far, a central fixation point (Fp) was turned off a short time before a new target (Tg) in the near periphery was presented. Therefore, express-saccades occurred when the goal of fixation was no longer visible. To determine whether or not the absence of the Fp is a necessary condition for the execution of an express-saccade, we used an overlap task in which the monkeys had to change the direction of gaze in the presence of the Fp. The results for this overlap task were compared to those found in the gap task. Three major observations have emerged from the present study. Even though the Fp remained visible, a suddenly appearing peripheral target could be reached by an express-saccade. Express-saccades persisted if the location as well as the time of the appearance of the target was randomized. It appears that for an express-saccade to occur, the process of interruption of previous active fixation must be completed at the time when a new target becomes visible. The spectrum of the monkey's saccadic reaction times contains at least three different peaks: express-saccades with reaction times below 100 ms, fast regular saccades with reaction times around 130 ms, and slow regular saccades with reaction times around 180 ms.

Animals↗
PubMed1986

Regeneration of the uterine epithelium in later stages of pseudopregnancy in the rabbit. An ultrastructural study.

Morphological changes of the uterine epithelium in later stages of pseudopregnancy in the rabbit have been studied using different morphological methods. The highly proliferated mucosa with numerous symplasms of a pseudopregnant animal returns to the morphology of a nonpregnant animal by apoptosis, moderate necrosis and lytic transformation of symplasms back to typical endometrial cells without desquamation of cells. The first signs of lytic transformation are observed on Day 8 of pseudopregnancy. Enhanced regeneration with apoptosis and lysis of the symplasmic nuclei is observed between Day 14 and Day 16. Full restoration of the epithelium with reappearance of ciliated cells, typical columnar and partly mucified epithelial cells is not completed earlier than Day 24 p. hCG. This epithelium, however, differs clearly from the epithelium of a virgin rabbit due to several residues of epithelial transformation. Thus, from a morphological point of view, pseudopregnancy in the rabbit lasts up to or even longer than Day 28 p. hCG with persisting ultrastructural remnants of the preceding cycle.

Animals↗
PubMed1986

Human express saccades: effects of randomization and daily practice.

When human subjects are asked to execute saccades from a fixation point to a peripheral target, if the fixation point is turned off some time (200 ms) before the target is turned on, the distribution of the saccadic reaction times is bimodal. The first peak occurs at about 100 ms and represents the population of express saccades. If the target location is kept constant the express saccades have reaction times of about 100 ms. If the target location is randomized between right and left (distance from fixation point constant at 4 deg) the reaction times of the express saccades are increased by about 15 ms. If the target location is randomized between 4 deg and 8 deg (direction constant to the right) no increase of the reaction time is observed. The proportion of express saccades increases with daily practice and their reaction times decrease slightly from 105 ms to 98 ms. If an anticipatory saccade was made after reaction times below 75 ms, it frequently undershot the target by more than 20% and was followed by a corrective saccade. The corrections could be executed at times where usually an express saccade would have occurred such that all of these corrections began at about the same time, i.e. 100 ms after target onset, implying intersaccadic intervals between 100 ms and zero (!)

Adult↗
PubMed1986

Eye-hand-coordination in man: a reaction time study.

Reaction time measurements were used to test the possibility that an eye and a reach movement both aimed at the same visual target share a common final motor command. This hypothesis predicts highly correlated pairs of reaction times on a trial by trial basis. The experiments were based on the earlier observation that long saccadic reaction times (above 200 ms) with a large scatter (150-300 ms) are obtained if the central fixation point remained visible through out a trial (overlap paradigm), whereas extremely short saccadic reaction times (around 120 ms) with a small scatter (100-150 ms) occur if the fixation point was turned off some time (200 ms) before the target appeared (gap paradigm). In the overlap paradigm high correlations (coefficients up to 0.95) between saccadic and reach reaction times were obtained and the corresponding linear regression lines had a slope of almost one. In the gap paradigm, however, correlations were almost absent even though the mean reach reaction times were considerably decreased. These observations clearly contradict the "common command" hypothesis, but can be explained by the assumption that the execution of the reach movement depends on the completion of the preparation of the saccade but not vice versa ("one way synchronization" hypothesis).

Dominance, Cerebral↗
PubMed1986

Eye-hand-coordination: a model for computing reaction times in a visually guided reach task.

A model is described which provides a simple algorithm to compute the reaction times of saccadic eye movements and reach movements aimed at a single visual target. It is assumed, that the two movements are prepared in parallel and initiated independently unless the preparation of the saccade for some reason takes longer than the preparation of the reach movement. In the latter case the final command to execute the reach movement is synchronized with that to execute the eye movement and therefore the corresponding reaction times are highly correlated in a one-to-one relationship. Random variables are used to predict sets of data that are directly comparable with the experimental results. The algorithm includes the effects of daily practice (learning). The structure of the model and its computational results will be compared with the physiological data from monkey and man.

Algorithms↗
PubMed1986

The role of fixation and visual attention in the occurrence of express saccades in man.

The differential influence of fixation and directed visual attention on reaction times of goal-directed saccades and especially on the occurrence of express saccades was investigated. In all the experiments the subjects were instructed first to keep their direction of gaze at the center of a translucent screen with or without a central fixation point. When a new stimulus appeared, the subjects had to look at it as soon as possible. In some control experiments the subjects had to direct their gaze to the screen center and simultaneously direct their attention to a peripheral light spot before the target for the saccade appeared. Many express saccades occurred when either active fixation of a central fixation point or attention directed to a peripheral visual target (regardless of its position) was interrupted 200 ms before the target for the saccade appeared. Express saccades were almost completely abolished in the presence of fixation and/or directed visual attention at the moment in which the saccade target appeared. We conclude that express saccades occur if visual attention has already been released at the moment when the target for the saccade appears. This disengagement needs some time which adds to the reaction time.

Adult↗
PubMed1986

The mutagenic activity of agaritine--a constituent of the cultivated mushroom Agaricus bisporus--and its derivatives detected with the Salmonella/mammalian microsome assay (Ames Test).

Purified agaritine (N'-(gamma-L(+)-glutamyl)-p-hydroxymethylphenylhydrazine) isolated from Agaricus bisporus, p-hydrazinobenzoic acid (its presumptive precursor) and some agaritine-degradation products were tested for mutagenic activity with the Salmonella/mammalian microsome assay (Ames test). Consistent with the literature, agaritine showed a distinct direct-acting mutagenicity with the strain TA1537 (30 revertants/mumol) and with TA97. Incubation of agaritine at alkaline pH increased the mutagenic effect. Pre-incubation of agaritine with gamma-glutamyl transferase (GT) during 10 h at room temperature (pH 8.2) even enhanced the mutagenicity by a factor of 8 to 16 depending on the strain. In accordance with this finding, synthetic p-hydroxymethylphenylhydrazine (the presumptive product of the GT catalyzed degradation) showed also a distinct direct-acting mutagenicity, but the increase was only about 3- to 6- times compared with agaritine. The hypothetical ultimate mutagenic metabolite of agaritine, the p-hydroxymethylbenzenediazonium ion, a compound occurring naturally in A. bisporus, showed the highest mutagenic activity (with TA1537 approximately 300 to 1,000 revertants/mumol).

Agaricales↗
PubMed1986

Alcohol consumption: effect of gender and psychopathology.

Alcohol consumption, when corrected for body weight, was not related to age and did not differ from male and female alcoholics, when compared within subtype of alcoholism. Regardless of gender, alcoholics with antisocial personality diagnosis drank significantly more alcohol than non-antisocial personality alcoholics.

Adolescent↗
PubMed1986

Transformation of endometrium and fertility in late stages of pseudopregnancy in the rabbit.

Ovulation was induced in rabbits between Days 14 and 18 of pseudopregnancy by an intravenous injection of hCG. Induction of ovulation from Day 16 onwards led to normal progestational endometrial transformation. In rabbits injected on Day 14 or 15, a normal preimplantation endometrial morphology developed, but not earlier than 7 days after hCG (Day 14/15 + 7). Uteroglobin secretion was advanced during the second pseudopregnancy. After mating or artificial insemination, fertility was greatest on Day 18 of pseudopregnancy. Conception failed on Day 14 and embryo transfers were unsuccessful on Day 14 + 1. Transfers performed on Day 14 + 3, however, led to implantation and offspring, even though endometrial morphology did not correspond to the normal Day 3 preimplantational morphology at the time of transfer. We conclude that endometrial transformation typical of normal pseudopregnancy can be induced by ovulation during the regeneration phase of pseudopregnancy from Day 16 onwards; fertilization and implantation can be achieved as early as Day 15 of pseudopregnancy; an oestrous period with high mating activity and fertility occurs about 3 days later; and Day 14 after hCG represents a limited time of functional change from pseudopregnancy to a fertile uterine cycle in the rabbit.

Animals↗
PubMed1985

Antilipolytic effects of N6-phenylisopropyladenosine and prostaglandin E2 in fat-cells of obese volunteers before and during energy restriction.

The antilipolytic effects of N6-phenylisopropyladenosine and of prostaglandin E2 were studied with adipocytes of obese volunteers before and after 4 weeks of severe energy restriction [1250 kJ (300 cal)/day] in the presence and absence of adenosine deaminase (1.6 micrograms/ml, corresponding to 320 m-units/ml). The studies were undertaken to define more clearly the role that local modulators might play in adaptation of lipid mobilization to starvation in humans. Starvation was associated with an approx. 3-fold increase in non-stimulated lipolysis. Removal of endogenous adenosine resulted in a similar increase in basal glycerol release under both conditions, averaging 2 and 2.2 mumol/180 min per 10(6) cells respectively. The sensitivity of the cells to N6-phenylisopropyladenosine and to prostaglandin E2 was not changed by starvation in the presence of adenosine deaminase. These results are discussed in terms of the possible role that local regulators might play during dietary adaption in human fat-cells in vitro.

Adenosine↗
PubMed1985

Peripheral attention versus central fixation: modulation of the visual activity of prelunate cortical cells of the rhesus monkey.

Single unit activity was monitored in the prelunate gyrus of monkeys trained to execute or suppress goal-directed saccades to a peripheral target in the presence or absence of a central fixation spot. Throughout the experiments in the dimming paradigm was used. We observed the previously reported spatially selective enhancement of the visual on-response and the extra activation before saccades to a continuously visible target. However, we also observed a sudden increase of activity when the central fixation spot was extinguished in the presence of a peripheral target which the monkey decided not to look at, although he could detect its dimming correctly. This activity is also spatially selective: it occurs only if the peripheral target is within the receptive field of the cell. The presence or absence of just any foveal spot, which is behaviourally not relevant, does not make any difference. The activity occurs about 220 ms after fixation point offset. Thus it can be interpreted as a sign of the animal having directed attention to the peripheral target and/or having stopped active fixation being ready for the next goal-directed saccade without necessarily executing it.

Animals↗
PubMed1985

Reaction times of the eye and the hand of the monkey in a visual reach task.

Two monkeys were trained to execute saccadic eye movements and reach movements with the hand from a central fixation point to a peripheral target. Reaction times for both movements were compared on a trial-by-trial basis. If the fixation point was extinguished before the target appeared (gap condition), extremely short latency saccades (85 ms) (express saccades) were obtained, that were followed by short latency reach movements (250 ms), but there was no correlation between them on a trial-by-trial basis. If the fixation point remained visible (overlap condition), very short (100 ms) and rather long (220 ms) latency saccades were observed. Long saccadic latencies correlated strongly with the reach reaction times. Short latency saccades were followed by reach movements of reaction times longer than those observed after express saccades in the gap condition; there was no correlation between them. All reaction times varied systematically with practice.

Animals↗