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Biomedical subjects

D Hofer

Publications and source records attributed to D Hofer.

35 records · Page 2Linked to original sources
PubMed1995

Computer-controlled flushing for long-term cannulation in freely moving rats.

An in vivo long-term perfusion system is presented, which is based on automated, computer-controlled high-frequency heparin (10 U/mL) flushing of the cannula inserted into the tail artery of freely moving rats. The short flushing intervals as achieved with this system guarantee stable conditions throughout an experiment of several days, and reduce blood clotting and the infiltration of fibroblasts. In addition, a specially developed software enables the periodical application of test substances into the blood stream under time-controlled conditions over long periods. The system can be used continuously to follow up blood parameters in single animals without significant elicitation of stress-sensitive plasma catecholamines for up to 12 days.

Animals↗
PubMed1992

Specific effects of the benzodiazepine midazolam on visual receptive fields in light and dark adapted human subjects.

Psychophysical experiments in humans have revealed similar characteristics of visual receptive fields as were found in cats and monkeys from retinal ganglion cell recordings. In addition, in some retinal ganglion cells of cats the GABA antagonist bicuculline decreases the activity of the inhibitory surround. These findings led to two predicitions: 1) benzodiazepines will selectively increase the inhibitory surround of human visual receptive fields, 2) after dark adaptation, no free GABA will be available in the synapses and benzodiazepines will have no effect on the visual system. Characteristics of human receptive fields were determined by subthreshold summation: the contrast threshold of a vertical line was measured dependent on the distance of two parallel flanking lines whose contrast was below threshold. Both hypotheses were confirmed: the threshold in the inhibitory region of receptive fields was specifically increased in a dose-dependent manner by midazolam PO (7.5 mg: P < 0.05; 15 mg: P < 0.01). In dark-adapted subjects no effect of midazolam was found. Control experiments with atropine (1 mg IV), sulpiride (100 mg IM), and levodopa (100 mg PO) showed no specific effect. The visual system may be a model to bridge the gap between animal and human psychopharmacology.

Adaptation, Ocular↗
PubMed1992

Continuous in vivo treatment with catecholamines suppresses in vitro reactivity of rat peripheral blood T-lymphocytes via alpha-mediated mechanisms.

A 20 h continuous treatment of rats with catecholamines, using subcutaneously implantable retard tablets, had either no (adrenaline, isoproterenol, midodrine) or a slight (noradrenaline) suppressive effect on the in vitro responsiveness of peripheral blood T-lymphocytes. A marked suppression of the mitogen response ensued when adrenaline, noradrenaline or midodrine, but not isoproterenol, was applied together with the beta-receptor blocker propranolol, whereas the combination with the alpha-receptor blocker phentolamine had no effect. The mitogen response of splenic lymphocytes was not affected by any of these treatments. This alpha-mediated adrenergic suppression of peripheral blood T-cells was not correlated with general metabolic alterations, shifts in white blood cell counts or CD4+/CD8+ subsets, or with elevated glucocorticoid levels. The data suggest that to consistently influence the reactivity of rat peripheral blood lymphocytes by chronic adrenergic stimuli in vivo requires both high catecholamine levels and a bias towards alpha-adrenergic receptivity.

Animals↗
PubMed1991

Professionals' placement recommendations to parents of a newborn with Down's syndrome.

The placement recommendations of 98 professionals to parents, relating to their newborn with Down's syndrome, were studied in respect to social variables relating to their decisions. Using a projective questionnaire with case vignettes it was found that social variables played a significant role in professionals' hypothetical placement recommendations to parents of a newborn with Down's syndrome. Furthermore, these placement recommendations varied according to professional categories (nurses differed from physicians and social workers) and personal attributes (age and professional experience).

Attitude of Health Personnel↗
PubMed1990

[Subconscious image recognition].

Two experiments demonstrate the influence of an unconscious form of information storage on behavior. In the learning phase, subjects see pictures in which other pictures or figures are embedded. The experimental procedure makes sure that these embedded figures cannot be seen (or consciously identified) by the subjects. Nevertheless, the results of a perceptual identification task in the test phase prove that information of these unidentified figures has been stored by the subjects: In a clarification task, subjects were shown the cut out, previously embedded figures and other pictures which they had to name as quickly as possible. The experimental group, which had seen the pictures with the embedded figures in the learning phase, was much quicker in responding to the naming task than the control group, which had not seen these pictures before. These results are discussed in terms of a distinction between sensori-perceptual and conceptual information storage in humans. Conceptual information is characterized as meaningful, symbolic, and accessible to conscious reasoning and remembering, while sensori-perceptual information is seen as nonsymbolic, modality-bound, and restricted to unconscious reactivations in data-driven process repetitions.

Attention↗
PubMed1980

The interactions between indomethacin and cytotoxic drugs in mice bearing B-16 melanomas.

We have compared the effects of indomethacin alone (100 microgram/mouse/day) with those of indomethacin plus adriamycin, 5-FU, nitrogen mustard, thioTEPA, and vincristine on B-16 tumor cell proliferation in vivo. As we have previously described, after four days of treatment with indomethacin, subcutaneous tumors were slightly smaller and lighter in weight, but contained more melanoma cells. Addition of indomethacin to cytotoxic regimens resulted in either no change or a decrease in the effectiveness of the chemotherapy. In previous studies we demonstrated that treatment of tumor-bearing mice with a long-acting synthetic analogue of PGE2 (di-M-PGE2) stimulated the synthesis of endogenous prostaglandins. In order to evaluate if these endogenously synthesized prostaglandins were responsible for the inhibition of B-16 growth in vivo, mice were treated with di-M-PGE2 or di-M-PGE2 plus indomethacin. Addition of indomethacin did not alter the tumor inhibitory effects of di-M-PGE2.

16,16-Dimethylprostaglandin E2↗