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Biomedical subjects

A Mack

Publications and source records attributed to A Mack.

At least 37 records · Page 2Linked to original sources
PubMed1987

Relationship between orthogonal arrays of particles and tight junctions as demonstrated in cells of the ventricular wall of the rat brain.

Ependymal cells in the ventricular wall and in several circumventricular organs of the rat were compared by means of freeze-fracturing. In principle, tight junctions and orthogonal arrays of particles (OAP) do not coexist in the cells bordering the ventricular wall: (1) Ordinary ependymal cells of the rat possess OAP and are devoid of tight junctions. (2) Epithelial cells of the rat choroid plexus are connected by tight junctions; OAP are lacking here. In some cases, however, tight junctions and OAP coexist in the same cell. In the boundary zone between choroid plexus and ependyma of the rat, the density of OAP is very low, whereas the tight junctions are well developed. In the subfornical and the subcommissural organ (SCO) of the rat both structures are poorly developed; in the SCO they occur segregated in different membranous areas. An overview of the literature confirms that tight junctions and OAP mostly exclude each other. The possibility that in astrocytes and ependymal cells tight junctions may have been replaced by OAP during phylogeny is briefly discussed.

Animals↗
PubMed1987

Motion aftereffects associated with pursuit eye movements.

Contrary to an earlier report [Anstis and Gregory, Q. Jl exp. Psychol. 17, 173-174 (1965)], we find that the sustained retinal motion caused by tracking a moving target over a stationary grating does not result in a motion aftereffect (MAE) which is equivalent to that resulting from comparable retinal motion caused by actual motion of a grating. The MAE associated with tracking generally occurs in elements falling on areas not previously exposed to retinal motion. It is in the same direction as the previous retinal motion in the display and is apparently an induced MAE caused by a weak, below threshold MAE in the elements stimulating areas that were previously exposed to retinal motion. Based on an analysis of eye movement records, we do not believe that the weakness of the tracking MAE is primarily a function of the poor quality of the tracking eye movements. Other possible reasons for the weakness of the MAE are suggested.

Adaptation, Ocular↗
PubMed1987

Effect of regulatory withdrawal of drugs and prescription recommendations on the pattern of self-poisonings in Oslo.

A two-year prospective study of 1350 admissions for self-poisoning, covering the Oslo area was undertaken to identify the sources of the toxic agents. After the first year of the study, four barbiturates were withdrawn from the Norwegian market and recommendations were made by the Health Authorities to promote more restrictive attitudes when prescribing psychoactive drugs. The patterns of self-poisonings in the two periods were compared. The withdrawal of four barbiturates resulted in a 55% decrease in the rate of barbiturate poisonings in general (p less than 0.001). No increase could be detected in the rate of self-poisoning with benzodiazepines and other hypnotics, but the incidence of self-poisonings with antidepressants (p less than 0.01) and neuroleptics (p less than 0.01) was found to have increased significantly. The regulations and recommendations resulted in a significant decrease in drugs obtained from doctors randomly consulted (p less than 0.01), and a significant increase in drugs prescribed by psychiatrists (p less than 0.01). Drugs obtained from non-medical sources increased from 28% in the first period to 33.2% in the second. The total number of admissions and toxic agents taken remained unaltered. Thus, regulatory measures can influence the pattern of self-poisoning but do not seem to influence the tendency to abuse drugs or to take an overdose.

Adolescent↗
PubMed1986

Heterogeneity of glial membranes in the rat olfactory system as revealed by freeze-fracturing.

The membranes of glial cells in the adult rat olfactory system were investigated by freeze-fracture. The astroglia-related glial cells in the olfactory nerve are interconnected by gap and tight junctions. Their membranes are free of orthogonal arrays of particles (OAP) which are generally believed to be reliable markers of astrocytes within the central nervous system. Likewise, the membranes of the superficial glial cells in the olfactory bulb which ensheath the olfactory fiber bundles lack OAP. In contrast, the astrocytes in the olfactory bulb reveal OAP. The results are discussed with regard to the role of glial membrane architecture in the process of central fiber regeneration.

Animals↗
PubMed1985

Perceived position and saccadic eye movements.

Data are reported which support the conclusion that saccades which occur 600 msec or more after the brief, presentation of a target stimulus are directed to its perceived position when that differs from both its retinal and spatial position.

Animals↗
PubMed1985

Induced motion and oculomotor capture.

Three experiments investigating the basis of induced motion are reported. The proposition that induced motion is based on the visual capture of eye-position information and is therefore a subject-relative, rather than object-relative, motion was explored in the first experiment. Observers made saccades to an invisible auditory stimulus following fixation on a stationary stimulus in which motion was induced. In the remaining two experiments, the question of whether perceived induced motion produces a straight ahead shift was explored. The critical eye movement was directed to apparent straight ahead. Because these saccades partially compensated for the apparent displacement of the induction stimulus, and saccades to the auditory stimulus did not, we conclude that induced motion is not based on oculomotor visual capture. Rather, it is accompanied by a shift in the judged direction of straight ahead, an instance of the straight ahead shift. The results support an object-relative theory of induced motion.

Attention↗
PubMed1984

13-cis-retinoic acid in conglobate acne. A follow-up study of 14 trial centers.

A follow-up was done on the patients of the German multicenter study with severe conglobate acne who had been treated with different dosages of 13-cis-retinoic acid. Eighty-seven patients were monitored from 12 to 21 months. Optimal long-term therapeutic effects were obtained with an initial dose of 1.0 mg/kg body weight, for 3 months, followed by another 3-month-treatment period with 0.2 mg/kg body weight. Six months after the termination of therapy 96% of the patients were still in remission and 81% after 12 months. Comparative figures for the administration of doses were 84% as opposed to 47% (0.5----0.2 mg/kg body wt.) and 74% as opposed to 37% (0.2----0.2 mg/kg body wt.), respectively. It is suggested from the present data that a high initial dosage of 13-cis-retinoic acid be chosen in order to obtain optimal long-term therapeutic effects. Transiently elevated lipid levels as well as other tolerable side effects return to normal within 3 months at the latest after discontinuation of treatment.

Acne Vulgaris↗
PubMed1982

Is perceived motion a stimulus for smooth pursuit.

Previous investigations have challenged the generality of the claim that perceived motion in an effective stimulus for smooth pursuit eye movements. The experiments extend the scope of these investigations. Three experiments test the hypothesis that perceived motion can serve as the stimulus for pursuit when the eye movement does not generate constraining retinal error information. Observers viewed retinally stabilized displays that elicited the perception that a stationary target was moving or that a moving target was moving faster than it was actually moving. The results failed to confirm the hypothesis. Relevant literature is reviewed. We conclude that perceived movement can act as a stimulus for pursuit only when the "perceptual target" has no retinal counterpart.

Eye Movements↗
PubMed1981

Saccadic programming and perceived location.

The retinal location of a saccadic target was made discrepant with its perceived position by means of an induced displacement. If localizing the target required information stored in memory, the eye was directed to the perceived target position. Otherwise, it was directed to its retinal location. These findings do not conform to either a strictly retinotopic or spatiotopic model of oculomotor control. Rather they suggest that the position information used to program saccades may be either perceptual or retinal/spatial depending upon whether the information must be accessed from memory.

Eye Movements↗
PubMed1980

The effect of axial tension on the load bearing capacity of traction pins.

Skeletal traction is often used in the conservative treatment of fractures. Although a small diameter traction pin causes less trauma, its use is limited by the strength of the pin and the holding power of the bone. Both theoretical analysis and in vitro experiments were conducted to investigate the bending resistance of traction pins subjected to an applied traction force. The results of this study indicate that thin K-wires could be prevented by applying tension. The possibility of a pin cutting through bone is minimal if the cortical bone structure of the patient is normal. However, further in vivo study is necessary to ascertain whether necrosis might occur due to excessive contact stress between the pin and the bone.

Bone and Bones↗
PubMed1979

Smooth pursuit eye movements: is perceived motion necessary?

It has recently been shown that perceived motion, in the absence of any appropriate retinal motion, is a sufficient stimulus to generate smooth pursuit eye motions. This raises the question of whether perceived motion is necessary for pursuit. In three experiments we obtained a negative answer to this question: retinal motion always governed pursuit.

Eye Movements↗
PubMed1979

The effect of an injectable progestogen contraceptive on blood coagulation and fibrinolysis.

In 26 women receiving either medroxyprogesterone acetate (Depo-Provera) injections or combined oestrogen-progestogen pills for contraception, tests of coagulation and fibrinolysis were performed before treatment, and after 8, 16 and 24 weeks of therapy. In the medroxyprogesterone group no significant changes were induced in fibrinogen, the vitamin K-dependent factors, or antithrombin III. Plasminogen levels fell during therapy, and were significantly lower than pre-treatment values after 16 and 24 weeks. By contrast, the 13 women receiving oral contraceptives showed raised levels of fibrinogen and plasminogen after 8 weeks of treatment, and of factors VII and X after 24 weeks. These data suggest that medroxyprogesterone acetate injections induce fewer changes in the blood coagulation system than oral contraceptives.

Adult↗
PubMed1975

Implant assessment.

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Dental Implantation↗