Computer simulation of an ideal lateral inhibition function

A model for lateral inhibition is presented in the context of the auditory channel. The mechanical analyzing system of the inner ear cannot alone account for the frequency resolution of hearing. Some additional mechanism, possibly lateral inhibition located in the auditory neural network, is needed to achieve the frequency selectivity observed in electrophysiological and psychoacoustical experiments. In a computer simulation study, the shape of an ideal lateral inhibition function was obtained. Such a function is applicable to all sensory modalities. In hearing, this function permits the sharpest possible frequency resolution as it can completely remove the frequency desharpening effect of the mechanical properties of the basilar membrane. In vision, it can compensate for abberations caused by the imperfections of the optical system of the eye.An expanded version of a paper presented at the XIth Intenational Congress on Acoustics, Paris, 1983     

Nitrogenase activity,hydrogen evolution and biomass production in different Casuarina symbioses

Nitrogenase activity, hydrogen evolution, biomass production and nodulation were studied in threeCasuarina species,C. equisetifolia Forst.,C. glauca Sieber ex Spreng andC. obesa Miq., either inoculated with a crushed nodule inoculum prepared fromC. glauca nodules or inoculated with the pure cultureHFP CcI3. Nodulation was also studied inC. cristata Miq. inoculated with the above mentionedFrankia sources. C. equisetifolia, C. glauca andC. obesa were nodulated when inoculated with both of theFrankia inoculum, whileC. cristata was very poorly nodulated. Nitrogenase activity per plant and on a nodule dry weight basis was significantly highest inC. glauca inoculated withC. glauca inoculum after 150 days from planting. This difference decreased and at 217 days from planting there was no significant difference between the symbioses, except forC. obesa inoculated withC. glauca inoculum which showed the significantly lowest nitrogenase activity. After 150 days from planting relative efficiency of nitrogenase was lowest inC. equisetifolia inoculated withHFP CcI3 and inC. equisetifolia inoculated withC. glauca inoculum. Biomass production was similar inC. glauca inoculated withC. glauca inoculum, inC. equisetifolia inoculated withHFP CcI3 and inC. obesa inoculated withHFP CcI3 at the final harvest. The data presented here show that there is a strong interrelationship between host plant and endobiont. This interrelationship is of considerable importance when introducing Casuarina symbioses for production of fuel wood.     

M-MuLV-induced leukemogenesis: Integration and structure of recombinant proviruses in tumors

M-MuLV-specific DNA probes were used to establish the state of integration and amplification of recombinant proviral sequences in Moloney virus-induced tumors of Balb/Mo, Balb/c and 129 mice. The somatically acquired viral sequences contain both authentic M-MuLV genomes and recombinants of M-MuLV with endogenous viral sequences. All reintegrated genomes carry long terminal repeat (LTR) sequences at both termini of their genome. In the preleukemic stage a large population of cells exhibiting a random distribution of reintegrated M-MuLV genomes are seen, but during outgrowth of the tumor, selection of cells occurs leaving one or a few clonal descendants in the outgrown tumor. In this latter stage recombinant genomes can be detected. Although these recombinants constitute a heterogeneous group of proviruses, characteristic molecular markers are conserved among many individual proviral recombinants, lending credence to the notion that a certain recombinant structure is a prerequisite for the onset of neoplasia. The structure of these recombinants shows close structural similarities to the previously described mink cell focus-inducing (MCF)-type viruses.     

Angiotensin III and IV activation of the brain AT1 receptor subtype in cardiovascular function

The present investigation determined that native angiotensins II and III (ANG II and III) were equipotent as pressor agents when ICV infused in alert rats, whereas native angiotensin IV (ANG IV) was less potent. An analogue of each of these angiotensins was prepared with a hydroxyethylamine (HEA) amide bond replacement at the N-terminus, yielding additional resistance to degradation. These three angiotensin analogues, HEA-ANG II, HEA-ANG III, and HEA-ANG IV, were equivalent with respect to maximum elevation in pressor responses when ICV infused; and each evidenced significantly extended durations of effect compared with their respective native angiotensin. Comparing analogues, HEA-ANG II had a significantly longer effect compared with HEA-ANG III, and HEA-ANG IV, whereas the latter were equivalent. Pretreatment with the AT₁ receptor subtype antagonist, Losartan (DuP753), blocked subsequent pressor responses to each of these analogues, suggesting that these responses were mediated by the AT₁ receptor subtype. Pretreatment with the specific AT₄ receptor subtype antagonist, Divalinal (HED 1291), failed to influence pressor responses induced by the subsequent infusion of these analogues. These results suggest an important role for Ang III, and perhaps ANG IV, in brain angiotensin pressor responses mediated by the AT₁ receptor subtype.     

Diethyl phthalate, a chemotactic factor secreted by Helicobacter pylori.

The structure of a small-molecule, non-peptide chemotactic factor has been determined from activity purified to apparent homogeneity from Helicobacter pylori supernatants. H. pylori was grown in brucella broth media until one liter of solution had 0.9 absorbance units. The culture was centrifuged, and the bacteria re-suspended in physiological saline and incubated at 37 degrees C for 4 h. A monocyte migration bioassay revealed the presence of a single active chemotactic factor in the supernatant from this incubation. The chemotactic factor was concentrated by solid phase chromatography and purified by reverse phase high pressure liquid chromatography. The factor was shown to be indistinguishable from diethyl phthalate (DEP) on the basis of multiple criteria including nuclear magnetic resonance spectroscopy, electron impact mass spectroscopy, UV visible absorption spectrometry, GC and high pressure liquid chromatography retention times, and chemotactic activity toward monocytes. Control experiments with incubated culture media without detectable bacteria did not yield detectable DEP, suggesting it is bacterially derived. It is not known if the bacteria produce diethyl phthalate de novo or if it is a metabolic product of a precursor molecule present in culture media. DEP produced by H. pylori in addition to DEP present in man-made products may contribute to the high levels of DEP metabolites observed in human urine. DEP represents a new class of chemotactic factor.     

Synthesis and structure-activity relationship of 2-(aminoalkyl)-2,3,3a,8-tetrahydrodibenzo[c,f]isoxazolo[2,3-a]azepine derivatives: a novel series of 5-HT(2A/2C) receptor antagonists. Part 2.

Following the programme started at Janssen Research Foundation searching for 5-HT(2A/2C) antagonists, we now report on the synthesis of a series of substituted 2-(Dimethylaminomethyl)-2,3,3a,8-tetrahydrodibenzo[c,f]isoxazolo[2,3-a]azepine derivatives. The 5-HT(2A), 5-HT(2C) and H(1) receptor affinities as well as the mCPP antagonistic activity of the compounds synthesised is described.     

Tetracycline production byStreptomyces aureofaciens: the time lag of production

Summary The exact time course of phosphate consumption in a tetracycline production byStreptomyces aureofaciens has been determined. The data have been compared with model simulations according to a model proposed by Votruba et al. (1984). This led to a revision of his equation for the rate of phosphate consumption and to the proposal that phosphate is consumed proportionally to the growth rate. In contradiction to the model simulations it was found that the length of the time lag of the production is independent of the initial phosphate concentration. While the model explains the time lag through inhibition of the production by phosphate, the measured data show that there must be another or an additional reason for the lag. Simultaneously with the start of the production the organism changes from an organic substrate to ammonia as nitrogen source.All experiments have been carried out in a bubble column of 651 working volume as fed batch fermentation. An autoanalyzer and a HPLC was coupled to the reactor for automatic measurement of phosphate, ammonia, sucrose and products in short intervals. Composition of the outlet gas, pH, pO₂, temperature and weight of the substrate flasks were monitored on-line.     

EFFECT OF CYANIDE AND ELECTRICAL STIMULATION ON PHOSPHOINOSITIDE METABOLISM IN LOBSTER NERVES

The contents of phosphoinositides, ATP, glucose and lactate in leg and claw nerves of the lobster were determined. Nerves were also analysed after cyanide poisoning, after electrical stimulation, and 1 h after removing the leg from the lobster. Cyanide poisoning decreased the levels of ATP and glucose and increased the content of lactate but did not alter the levels of phosphoinositides. Nerves left in situ for 1 h after disconnection from the central nervous system exhibited a decrease in the content of tri-phosphoinositides (TPI) of 50 per cent, without changes in ATP, glucose or lactate. The TPI change was reversed after incubation for 1 h in oxygenated seawater. Nerves labelled in vivo with ³²P were removed and stimulated at 50 Hz for 5 min. The turnover of TPI phosphorus increased on stimulation in both normal and cyanide-poisoned nerves. In contrast, turnover of ATP increased after stimulation in normal nerves but not in cyanide-treated nerves. We sought to determine whether polyphosphoinositides play a greater role in resting metabolism of the nerve or in the conducting mechanisms. Our results make more likely the involvement of TPI in permeability changes of neural membranes during excitation.