Biomedical subjects

A Klaassen

Publications and source records attributed to A Klaassen.

3 recordsLinked to original sources

PubMed2001

Processing bottlenecks in dual-task performance: structural limitation or strategic postponement?

Recent evidence indicates that a central bottleneck causes much of the slowing that occurs when two tasks are performed at the same time. This bottleneck might reflect a structural limitation inherent in the cognitive architecture. Alternatively, the bottleneck might reflect strategic (i.e., voluntary) postponement, induced by instructions to emphasize one task over the other. To distinguish structural limitations from strategic postponement, we examine a new paradigm in which subjects are told to place equal emphasis on both tasks and to emit both responses at about the same time. An experiment using this paradigm demonstrated patterns of interference that cannot easily be attributed to strategic postponement, preparation effects, or conflicts in response production. The data conform closely to the predictions of structural central bottleneck models.

Adult↗

PubMed1998

Corticotropin-releasing factor receptor blockade enhances conditioned aversive properties of cocaine in rats.

The behavioral profile of corticotropin-releasing factor (CRF) in mediating anxiogenic-like and aversive responses to stressors may be particularly relevant for dependence and withdrawal in drug-experienced organisms. Moreover, stressful aspects of drug exposure in the drug naive organism may also induce CRF system activation. In the present studies, the dependence of aversive properties of cocaine on activation of endogenous CRF systems has been evaluated in rats using taste conditioning and runway self-administration paradigms. Systemic cocaine administration (20 mg/kg i.p.) produced a conditioned saccharin aversion which was dose-dependently potentiated by central administration of the CRF receptor antagonist, D-phe CRF (12 41). In addition, i.v. cocaine administration (0.75 mg/kg per injection i.v.) produced runway goal-box avoidance and conditioned place avoidance responses which were significantly accelerated by CRF antagonist treatment. In contrast, CRF receptor stimulation using CRF itself abolished cocaine-induced increases in goal latency in the runway paradigm. This generalized involvement of CRF systems in cocaine-related motivational/associative states is consistent with the comprehensive role of CRF in mediating emotional responses to non-drug stressors.

Animals↗

PubMed1980

Uptake of the lipophilic cation dibenzyldimethylammonium into Saccharomyces cerevisiae. Interaction with the thiamine transport system.

The distribution ratio of the lipophilic cation dibenzyldimethylammonium between the cells of Saccharomyces cerevisiae and the medium appears to reflect changes in the membrane potential in a way that is qualitatively correct: the addition of a proton conductor or of an agent which blocks metabolism causes an apparent depolarization of the cell membrane; monovalent cations cause also a lowering of the equilibrium distribution, whereas the addition of divalent cations results in an increase of the partition ratio. However, uptake of dibenzyldimethylammonium and probably also of other liophilic cations proceeds via the thiamine transport system of the yeast. Dibenzyldimethylammonium transport is inducible, like thiamine transport. A kinetic analysis of the mutual interaction between thiamine and dibenzyldimethylammonium uptake shows that these compounds share a common transport system; moreover, dibenzyldimethylammonium uptake is inhibited complete by thiamine disulfide, a competitive inhibitor of thiamine transport and dibenzyldimethylammonium uptake in a thiamine-transport mutant is reduced considerably. It is concluded that one should be cautious when using lipophilic cations to measure the membrane potential of cells of S. cerevisiae.

Biological Transport↗