Effects of 2,4-Dichlorophenoxyacetic acid on Rhizobium sp. membrane fluidity

The effects of 1 mM 2,4-Dichlorophenoxyacetic acid on Rhizobium sp. in pure culture was studied. In a previous work it was demonstrated that this herbicide produces an alteration on the saturated to unsaturated phospholipid acyl chains ratio. In the present paper, it was found that this alteration produces a modification on the membrane fluidity in bacteria that had achieved the stationary phase. The same results were obtained when determinations were done in liposomes from sonicated lipids of treated bacteria, indicating that changes in phospholipid acyl chains may be the main cause of membrane fluidity alteration. In addition, it was determined that leucine transport as well as Ca⁺⁺-ATPase activity (a membrane enzyme) was affected under the experimental conditions.     

Differential effects of antidepressant treatment on brain monoaminergic receptors

Chronic (21 days) antidepressant administration to rats results in a decrease in both serotonin and β-adrenergic but not cholinergic muscarinic, receptor binding in selected brain regions, with the frontal cortex appearing to be somewhat more sensitive to this effect. Neither nisoxetine nor fluoxetine, potent and specific inhibitors of norepinephrine and serotonin uptake respectively, caused receptor binding changes after chronic administration, suggesting that inhibition of transmitter uptake, in itself, in insufficient to cause receptor subsensitivity. In vitro experiments indicated that antidepressants are relatively weak α₂-receptor blocking agents, but some are potent on the α₁-receptor system indicating that the norepinephrine releasing potency of some antidepressants may not be mediated by blockade of presynaptic autoreceptors.     

The unresponsive regions of visual cortical receptive fields

We have recorded from simple and complex cells in area 17 of the cat cortex. Around the classical receptive field (regions within which a moving or flashing bar can elicit a response from a cell) there are large regions which dramatically influence the cell's responsiveness. In some cells these regions are facilitatory, in others, inhibitory. Since these regions do not respond in isolation to moving or flashing bars, we called them unresponsive regions of the receptive field. Both the inhibitory and facilitatory unresponsive regions show spatial-frequency selectivity. All the facilitatory unresponsive regions show orientation selectivity, while most of the inhibitory unresponsive regions are not orientation selective. Both the facilitatory and the inhibitory unresponsive regions contribute to the size-selectivity of the cell. The facilitatory unresponsive regions show a great influence on the orientation selectivity of the cell, in that they sharpen the orientation channel of the cell. The inhibitory unresponsive regions, on the contrary, have not such an effect.     

Semisynthetic studies on bovine pancreatic ribonuclease

The S-peptide of the enzyme bovine pancreatic ribonuclease has been used as a model for covalent semisynthesis. Methods for side-chain protection, enzymatic cleavage of the peptide chain at the level of the single arginine-10 and for selective deprotection of the α-carboxyl function of this residue, have been examined. The partially protected [1–10] sequence has been coupled to a solid-phase generated [11–15] sequence attached to the polymer. After deblocking from the solid-support, the [1–15] semisynthetic peptide was complexed with native S-protein to give a complex with high biological activity.     

The effect of 2,3-diphosphoglycerate on oxygen consumption burst in thrombin-stimulated platelets

2,3-Diphosphoglycerate (2,3-DPG) modifies platelet function; it diminishes aggregation and the release reaction. The hypothesis that this occurs through a modification of the intracellular level of cyclic AMP or through an alteration in the synthesis of prostaglandins has been proposed. Since the release reaction occurs simultaneously with a burst in the consumption of oxygen, the authors have studied the effect of 2,3-DPG on oxygen consumption after the addition of thrombin with or without the addition of substances which modify platelet metabolism (aspirin, theophylline, glucagon, etc.). It was observed that 2,3-DPG diminishes oxygen consumption induced by thrombin. This mechanism alters the platelet membrane function.