Postinhibitory unit response of crustacean stretch receptors after direct and recurrent inhibition

The postinhibitory response of a slowly adapting neuron was investigated in experiments on an isolated preparation of crustacean stretch receptor and abdominal nerve chain. The structural features of this preparation are such that this response can be regarded as the response of the postsynaptic membrane to synaptic inhibition and not the action of synaptic excitation. IPSPs arise in the slowly adapting neuron in response to stimulation of the abdominal nerve chain (direct inhibition) or to excitation of the neuron itself (recurrent inhibition). The postinhibitory response consists of the development of action potentials or an increase in their amplitude and frequency. The magnitude of the response is determined by the duration of the inhibition and the state of the neuron membrane. The postinhibitory response was strongest when IPSPs were superposed on cathodal depression. IPSPs and an intracellular hyperpolarizing current evoke similar postinhibitory responses. Repetitive excitation of an inhibitory neuron may result in the appearance of a regular spike discharge from a previously inactive neuron through the mechanism of the postinhibitory response. Activation of a chain of recurrent inhibition increases the duration of the postinhibitory response evoked by direct inhibition or by a hyperpolarizing current. The existence of a chain of recurrent inhibition prevents the cessation of firing by a neuron during increasing cathodal depression. A mechanism of postinhibitory rebound lies at the basis of this phenomenon.     

Analysis of theta-rhythms recorded in an isolated strip of rabbit sensomotor cortex

To test the possibility that the theta-rhythm may spread passively from the hippocampus into the neocortex in rabbits and to analyze the properties of these rhythms recorded from the surface of the neocortex, an investigation was made of activity recorded simultaneously from the hippocampus and various points of the neocortex, including from a strip of the sensomotor cortex isolated completely with respect to its nervous connections. The use of special correlation methods showed that an appreciable contribution to the potentials recorded from the isolated strip can be made by the passive conduction of hippocampal activity (provided that it generates a regular high-amplitude theta-rhythm). At the same time, potentials in a theta-rhythm may be generated in the isolated strip itself. The theta-rhythm recorded in the intact rabbit cortex may thus be of combined genesis: generated in the neocortex itself and spreading passively from the hippocampus through the brain tissues as through a volume conductor.     

Callus induction and shoot regeneration in Sempervivum tectorum

Leaf and shoot explants of Sempervivum tectorum L., taken from 14- and 30-day-old plants germinated in vitro, have been studied by using Murashige-Skoog and White basal media with cytokinins (benzyladenine, kinetin) and auxins (indoleacetic acid, naphthaleneacetic acid, indolebutyric acid) in various concentrations. Explants taken from 14-day-old plants died but 30-day-old leaves and shoots produced yellow and soft, as well as green and hard calluses on Murashige-Skoog medium with 4.4–8.8 M benzyladenine and 0.57 M indoleacetic acid. Shoot organogenesis was induced from green, hard callus in a medium with 2.2 M benzyladenine plus either 1.1 M indoleacetic acid or 2.5 M indolebutyric acid. Whole plants were grown on Murashige-Skoog medium without plant growth regulators. On the other hand, White medium was not suitable for raising Sempervivum tectorum in vitro.Abbreviations BA benzyladenine - IAA indoleacetic acid - IBA indolebutyric acid - MS Murashige-Skoog - NAA napthaleneacetic acid - W White     

Changes in ion fluxes and the energy demand during spore development inPhytophthora infestans zoospores

Cell-free supernatant of pelleted zoospores was found to be more suitable for maintaining viable zoospores and developed cysts than the supernatant of mature cysts. Conductivity and pH measurements indicated quantitative changes in the ionic composition of a suspension ofP. infestans zoospores during their conversion into cysts. An increase in conductivity in the incipient cyst suspension was followed by a decrease of conductivity in the maturing cyst suspension. The conductivity changes correlated closely with K⁺ fluxes which, in turn, coincided with the reverse, but stoichiometrically smaller, H⁺ fluxes. Zoospores treated with 1.5 μmol/L DCCD (an inhibitor of plasma membrane H⁺-ATPase) or 100 mmol/L Li⁺ (an inhibitor of cell motility) released predominantly K⁺ and other cations and their O₂ consumption decreased. The H⁺/K⁺ exchange is therefore very probably associated with an operation of the plasma membrane H⁺-ATPase. The differential decrease in respiration caused by DCCD and Li⁺ was used to estimate the energy demand for cell motility and spore development.     

Relations between stomatal closure, leaf turgor and xylem vulnerability in eight tropical dry forest trees

This study examined the linkage between xylem vulnerability, stomatal response to leaf water potential (Ψ_L), and loss of leaf turgor in eight species of seasonally dry tropical forest trees. In order to maximize the potential variation in these traits species that exhibit a range of leaf habits and phenologies were selected. It was found that in all species stomatal conductance was responsive to Ψ_L over a narrow range of water potentials, and that Ψ_L inducing 50% stomatal closure was correlated with both the Ψ_L inducing a 20% loss of xylem hydraulic conductivity and leaf water potential at turgor loss in all species. In contrast, there was no correlation between the water potential causing a 50% loss of conductivity in the stem xylem, and the water potential at stomatal closure (Ψ_SC) amongst species. It was concluded that although both leaf and xylem characters are correlated with the response of stomata to Ψ_L, there is considerable flexibility in this linkage. The range of responses is discussed in terms of the differing leaf‐loss strategies exhibited by these species.     

Activation of RAT erythrocyte phosphofructokinase by AMP and by non-physiological concentrations of Cyclic AMP

Summary Cyclic AMP (300µ m) activates phosphofructokinase from dialyzed haemolysates of mature rat erythrocytes. The main conclusions are: a) Cyclic AMP, at pH 7.1 and low concentrations of fructose-6-phosphate, is able to reverse the inhibition produced by different amounts of ATP (up to 1.5mm). b) The cyclic nucleotide is a positive allosteric effector of the enzyme as shown by the displacement of sigmoidal fructose-6-phosphate saturation curve to hyperbolic kinetics in the presence of inhibitory concentrations (1.5mm) of ATP. c) Cyclic AMP has no significant influence as deinhibitor of phosphofructokinase either at pH 7.1 and non-inhibitory levels (0.25mm) of ATP or at pH 8.1 and inhibitory (1.5mm) of non-inhibitory (0.25mm) concentrations of ATP. Similar conclusions were obtained with 300µ m AMP but not at a lower concentration (3µ m) with both nucleotides.The comparison of cyclic AMP results with those obtained under similar concentrations of AMP suggest that cyclic AMP is really only an in vitro modulator of the enzyme from rat erythrocytes, presumably at an AMP regulatory site, since non-physiological concentrations are required to act as deinhibitor.     

The role of N-acyl groups in the inhibitory activity of LH-RH analogues

Inhibitory analogues of luteinizing hormone-releasing hormone (LH-RH) were prepared with formyl-D-Trp¹, acetyl-D-Trp¹, valeryl-D-Trp¹, tartaryl-D-Trp¹, diacetyl-tartaryl-D-Trp¹, acetyl-Gly¹, and acetyl-Sar¹ successively replacing the position one in the analogue [D-Trp¹, D-p-Cl-Phe², D-Trp³, D-Phe⁶, D-Ala¹⁰]-LH-RH. The formyl-D-Trp¹ and acetyl-D-Trp¹ analogues yielded 100% blockade of ovulation at the 10 μg dose; the others were less potent and inhibited ovulation at the 50 μg dose. The inhibitory potency seems to correlate with the polarity of the acyl group.     

Le Crocodilien Diplocynodon (Eusuchia,Alligatoridae) dans la«série du gypse d'Aix à Venelles (Bouches-du-Rhône,France)

A crocodilian skeleton from the «série du gypse d'Aix (basal Aquitanian) at Venelles (Bouches-du-Rhône) is described and referred to Diplocynodon cf. rateli. The specimen seems to have been mutilated by scavengers before burial. The occurrence of the freshwater crocodilian Diplocynodon in the «série du gypse d'Aix is in agreement with recent reconstructions of the depositional environment, which suggest a basin with a fluctuating, but usually low, salinity.     

Ant versus bird exclusion effects on the arthropod assemblage of an organic citrus grove

1. Predation‐exclusion experiments have highlighted that top‐down control is pervasive in terrestrial communities, but most of these experiments are simplistic in that they only excluded a single group of predators and the effect of removal was evaluated on a few species from the community. The main goal of our study was to experimentally establish the relative effects of ants and birds on the same arthropod assemblage of canopy trees. 2. We conducted 1‐year long manipulative experiments in an organic citrus grove intended to quantify the independent effects of bird and ant predators on the abundance of arthropods. Birds were excluded with plastic nets whereas ants were excluded with sticky barriers on the trunks. The sticky barrier also excluded other ground dwelling insects, like the European earwig Forficula auricularia L. 3. Both the exclusion of ants and birds affected the arthropod community of the citrus canopies, but the exclusion of ants was far more important than the exclusion of birds. Indeed, almost all groups of arthropods had higher abundance in ant‐excluded than in control trees, whereas only dermapterans were more abundant in bird‐excluded than in control trees. A more detailed analysis conducted on spiders also showed that the effect of ant exclusion was limited to a few families rather than being widespread over the entire diverse spectrum of spiders. 4. Our results suggest that the relative importance of vertebrate and invertebrate predators in regulating arthropod populations largely depends on the nature of the predator–prey system.     

Heme induces significant neutrophil adhesion in vitro via an NFκB and reactive oxygen species-dependent pathway

Molecular and Cellular Biochemistry - Intravascular hemolysis, a major manifestation of sickle cell disease (SCD) and other diseases, incurs the release of hemoglobin and heme from red blood cells,...