Swim Stress Increases the Potency of Glycine at the N-Methyl-d-Aspartate Receptor Complex

Abstract: We have previously demonstrated that chronic administration of antidepressants results in a reduction in the potency of glycine to displace 5,7-[³H]dichlorokynurenic acid (5,7-[³H]-DCKA) from the strychnine-insensitive glycine recognition site of the NMDA receptor complex. We now report that exposure of rats to the forced swim test results in a 56% increase in the potency of glycine to displace 5,7-[³H]DCKA from frontal cortical homogenates. These data are consistent with the hypothesis that the forced swim test, a preclinical screen sensitive to acute administration of antidepressant drugs and NMDA receptor antagonists, also results in adaptation of the NMDA receptor complex. Moreover, these data lend further support to the hypothesis that glutamatergic pathways are involved in the neurobiological response to stress and, potentially, in the pathophysiology of depression.     

Pre-existence and emergence of drug resistance in HIV-1 infection.

Antiviral treatment of HIV-1 infection often fails because of the rapid emergence of resistant virus within weeks of the start of therapy. This raises the question of whether resistant viruses pre-exist in drug-naive patients or whether it is produced after the start of therapy. Here we compare the likelihood of pre-existence with the likelihood of production of resistant virus during therapy. We show that provided resistant virus pre-exists, then a stronger therapy may lead to a greater initial reduction of virus load, but will also cause a faster rise of resistant virus. In this case the total benefit of treatment is independent of the degree of inhibition of sensitive virus. If, on the other hand, resistant mutants do not pre-exist, then the emergence of resistance during treatment depends on the efficacy of the drug. If the drug is sufficiently potent to eradicate sensitive virus, then the probability that resistant mutants first appear during therapy is smaller than the probability that they existed before therapy. If the drug cannot eradicate the sensitive virus, then after sufficiently long time resistant mutants will appear. However, mutants that are unlikely to pre-exist may taken long time to appear.     

Human immunodeficiency virus drug therapy and virus load.

Analysis of the short-term dynamics of human immunodeficiency virus (HIV) type 1 infection in response to drug therapy has elucidated crucial kinetic properties of viral dynamics in vivo (D. D. Ho et al., Nature 373:123-126, 1995; A. S. Perelson et al., Science 271:1582-1586, 1996; X. Wei et al., Nature 373:117-122, 1995). Here we investigated long-term changes in virus load in patients treated with a combination of lamivudine and zidovudine to identify principal factors responsible for the observed 10- to 100-fold sustained suppression of virus load in vivo. Interestingly, most standard accounts of virus dynamics cannot explain a large sustained reduction without shifting the virus very close to extinction. The effect can be explained by taking into consideration either (i) the immune response against HIV, (ii) the killing of uninfected CD4 cells, or (iii) the differential efficacies of the drugs in different cell populations.     

Automata,repeated games and noise

We consider two-state automata playing repeatedly the Prisoner's Dilemma (or any other 2 × 2-game). The 16 × 16-payoff matrix is computed for the limiting case of a vanishingly small noise term affecting the interaction. Some results concerning the evolution of populations of automata under the action of selection are obtained. The special role of win-stay, lose-shift-strategies is examined.     

Decrease of collagen biosynthesis ability of rat kidney fibroblasts transformed with SV-40 virus

Summary Rat kidney fibroblasts transformed with SV-40 produce in vitro a significantly lower amount of hydroxyproline-containing material which is collagenase sensitive as compared to normal cells. In contrast to normal fibroblast cultures, no collagenous material was found by histochemical methods in intercellular spaces of transformed cultures.     

THE PERMISSIVE ROLE OF HYPERTHERMIA IN THE DISAGGREGATION OF BRAIN POLYSOMES BY l-DOPA OR d-AMPHETAMINE1

Abstract— l -DOPA or d -amphetamine administration disaggregates brain polyribosomes in animals maintained in an environment warm enough (26°C) so that the drugs concurrently elevate their body temperatures to above 39°C. The production of equivalent hyperthermia (by keeping control rats at ambient temperatures of 40–44° C) does not cause similar disaggregation of brain polysomes. Hence, the role of hyperthermia in the drug-induced disaggregation is permissive.     

Reciprocal cooperative effects of multiple ligand binding to pyruvate kinase

The formation of multiple ligand complexes with muscle pyruvate kinase was measured in terms of dissociation constants and the standard free energies of formation were calculated. The binding of Mn2+ to the enzyme (KA = 55 +/- 5 X 10(-6) M; deltaF degrees = -5.75 +/- 0.05 kcal/mol) and to the enzyme saturated with phosphoenolpyruvate (conditional free energy) KA' = 0.8 +/- 0.4 X 10(-6) M; deltaF degrees = -8.22 +/- 0.34 kcal/mol) has been measured under identical conditions giving a free energy of coupling, delta(deltaF degrees) = -2.47 +/- 0.34 kcal/mol. Such a large negative free energy of coupling is diagnostic of a strong positively cooperative effect in ligand binding. The binding of the substrate phosphoenolpyruvate to free enzyme and the enzyme-Mn2+ complex was, by necessity, measured by different methods. The free energy of phosphoenolpyruvate binding to free enzyme (KS = 1.58 +/- 0.10 X 10(-4)M; deltaF degrees = -5.13 +/- 0.04 kcal/mol) and to the enzyme-Mn2+ complex (K3 = 0.75 +/- 0.10 X 10(-6)M; deltaF degrees = -8.26 +/- 0.07 kcal/mol) also gives a large negative free energy of coupling, delta(deltaF degrees) = -3.16 +/- 0.08 kcal/mol. Such a large negative value confirms reciprocal binding effects between the divalent cation and the substrate phosphoenolpyruvate. The binding of Mn2+ to the enzyme-ADP complex was also investigated and a free energy of coupling, delta(deltaF degrees) = -0.08 +/- 0.08 kcal/mol, was measured, indicative of little or no cooperativity in binding. The free energy of coupling with Mn2+ and pyruvate was measured as -1.52 +/- 0.14 kcal/mol, showing a significant amount of cooperativity in ligand binding but a substantially smaller effect than that observed for phosphoenolpyruvate binding. The magnitude of the coupling free energy may be related to the role of the divalent cation in the formation of the enzyme-substrate complexes. In the absence of the activating monovalent cation, the coupling free energies for phosphoenolpyruvate and pyruvate binding decrease by 40-60% and 25%, respectively, substantiating a role for the monovalent cation in the formation of enzyme-substrate complexes with phosphoenolpyruvate and with pyruvate.     

Affinity chromatography purification of Pseudomonas aeruginosa exotoxin A on specifically linked NAD agarose.

The specific binding of P. aeruginosa exotoxin A to NAD was exploited for the rapid purification of the toxin. Affinity chromatography on a column of agarose-N6-(aminohexyl)carbamoylmethyl-NAD resulted in an enzymatically, biologically, and immunologically active purified toxin preparation. Other NAD-agarose resins were not efficient substrates for toxin purification.