Proprioceptor distribution and control of a muscle reflex in the tibia of spider legs

In spiders, retrograde cobalt staining was used to clarify the distribution and detailed innervation of the three types of proprioceptors in the tibio-metatarsal leg joint: internal joint receptors, lyriform slit sense organs, and cuticular spines and hairs. The axons of all these receptors run in just two lateral, ascending nerves, which had previously been associated only with the internal receptors. Each nerve contains several hundred axons ranging in diameter from 0.1 micron to ca. 10 micron. Each slit of the four tibial lyriform organs is innervated by two bipolar sensory neurons. The lateral nerves are entirely sensory and run just beneath the cuticle, a convenient site for electrophysiological recording. We demonstrate simultaneous nerve and muscle recordings from intact spiders; these, in combination with selective sensory ablations, show that a resistance reflex in the flexor metatarsi muscles is elicited by internal joint-receptor units.     

Spatiotemporal receptive fields: a dynamical model derived from cortical architectonics

We assume that the mammalian neocortex is built up out of some six layers which differ in their morphology and their external connections. Intrinsic connectivity is largely excitatory, leading to a considerable amount of positive feedback. The majority of cortical neurons can be divided into two main classes: the pyramidal cells, which are said to be excitatory, and local cells (most notably the non-spiny stellate cells), which are said to be inhibitory. The form of the dendritic and axonal arborizations of both groups is discussed in detail. This results in a simplified model of the cortex as a stack of six layers with mutual connections determined by the principles of fibre anatomy. This stack can be treated as a multi-input-multi-output system by means of the linear systems theory of homogeneous layers. The detailed equations for the simulation are derived in the Appendix. The results of the simulations show that the temporal and spatial behaviour of an excitation distribution cannot be treated separately. Further, they indicate specific processing in the different layers and some independence from details of wiring. Finally, the simulation results are applied to the theory of visual receptive fields. This yields some insight into the mechanisms possibly underlying hypercomplexity, putative nonlinearities, lateral inhibition, oscillating cell responses, and velocity-dependent tuning curves.     

Pyruvate decarboxylase--potentially inactive in the absence of the substrate

Using two independent methods, it was shown that pyruvate decarboxylase of brewer's yeast/EC 4.1.1.1./showing a sigmoidal v/S-shape and a corresponding activation phase in the product formation is potentially inactive in the absence of its substrate-pyruvate.     

Regeneration in Hydrozoa: distal versus proximal transformation in Hydractinia

Summary Polyps of mature colonies of Hydractinia echinata obey the rule of distal transformation by regenerating heads but not stolons. However, this rule is not valid for young polyps as these regenerate stolons from proximal cut ends. Also, small cell aggregates and even small fragments excised from full-grown polyps are capable of stolon formation. Aggregates produced from dissociated cells undergo either distal or proximal transformation depending on their size, speed of head regeneration in the donor used for dissociation and the positional derivation of the cells. The latent capability of stolon formation is released under conditions that cause loss of morphogens and depletion of their sources. However, internal regulative processes can also lead to gradual proximal transformation: regenerating segments of polyps sometimes form heads at both ends and the distal pattern is duplicated. Subsequently, all sets of proximal structures, including stolons, are intercalated. In contrast to distal transformation, proximal transformation is a process the velocity of which declines with the age and size of the cell community.     

Metabolism and non-random occurrence of nonnascent short chains in the DNA of Ehrlich ascites cells

The DNA of Ehrlich ascites cells was labeled with radioactive thymidine using different labeling schedules: Incubation periods between 15 s and 4 h; pulse/pulse-chase experiments with pulses in the range of a few minutes; longtime incubation followed by a longtime chase (both in the range of 1 cell generation). From the purified DNA of the labeled cells a fraction (0.3-0.4%) of short chains was separated and partially fractionated by means of a hydroxyapatite thermochromatography procedure. The evaluation of the labelling patterns of the short chains indicated that less than 5% of them can be regarded as replication intermediates ('Okazaki pieces'). The rest, termed nonnascent pieces, exhibited a slow turnover. The life span of the nonnascent pieces was estimated to be about 1 cell generation. On helical DNA, nonnascent pieces were distributed in a non-random manner. Their preferential localisation was nearby sites which caused binding of the DNA, after purification, to nitrocellulose and which occurred about every 60-80 microns on the nuclear DNA of the cells.     

Regulation of citrate synthase in facultative methylotrophic bacteria

Commonly the TCA cycle fulfils an anabolic and a catabolic function in case of aerobic chemoorganoheterotrophic nutrition. In methylotrophic growth the TCA cycle is dispensable as a bioenergetic pathway. This is reflected by properties of citrate synthase in facultative methylotrophic bacteria. Two citrate synthases, a "chemoorganoheterotrophic" one, which is inhibited by NADH (or ATP in Acetobacter MB 58), and a "methylotrophic" one, which is not or less affected by energy indicators, were found in Pseudomonas oleovorans, Pseudomonas MS, Pseudomonas MA, and Acetobacter MB 58. The concentration of these citrate synthases depends on the manner of nutrition. Bacteria with ICL-negative-variant of the serine pathway and with ribulosebisphosphate pathway seem to possess only a "chemoorganoheterotrophic" citrate synthase. Possibly the anabolic function of this citrate synthase can be realized by metabolites.     

Estimation of pyruvate decarboxylation in perfused rat skeletal muscle

A total of 46 E. coli strains showing mannose-resistant, P-blood-group independent hemagglutination of human erythrocytes were tested for binding to neuraminic acid. Nine of the strains completely lost their hemagglutination activity after the erythrocytes were treated with neuraminidase. To characterize the receptor structure, different neuraminic acid containing glycoproteins, their desialylated derivatives and neuraminyl oligosaccharides were tested for hemagglutination inhibition. These studies showed that the nine strains had binding specificity for alpha 2-3 linked neuraminic acid.     

A comparison of some procedures of salt extraction of nucleic acids from pollen. Elimination of interfering substances from extracts

Some methods were studied which use hot 10% NaCl solution for the extraction of both RNA and DNA from pollen. The raw salt extracts were precipitated with perchloric acid, trichloroacetic acid or ethanol and purified according to the described methods. The nucleic acid hydrolysates were obtained in several ways. In all the samples spectra in the UV-region were measured and the nucleic acid contents were determined according to the absorbance at 260 nm. In order to ascertain the extent of contaminants, the contents of phosphorus, saccharides and proteins were determined. It was found that by the methods studied it is possible to remove some impurities from extracts, but that the extractions of nucleic acids from pollen are not quite quantitative. A part of nucleic acids remained unextracted after the salt extraction in pollen, but it was possible to obtain it only by an additional extraction with 1 N perchloric acid at 75°C.     

Untersuchungen über die Bindung pflanzlicher Wuchsstoffe an verschiedene Komponenten des Chromatins in vitro

Summary Several growth substances (IAA, -NAA) are able to reduce thermal stability of artificially reconstituted nucleoproteins without splitting off measurable amounts of protein from DNA. This effect is not shown by substances structurally related to auxins (-NAA, tryptophan), but other growth substances (GA, KI) also reduce thermal stability of several reconstituated nucleoproteins.The effect of growth substances on the Tm of nucleoproteins strongly depends upon the concentration of the growth substances. The effective concentrations of IAA are lowered by increasing acidity of the protein component in the nucleoprotein. IAA and GA diminish the binding capacity of histones and residual nucleoproteins to DNA at different concentrations.Nucleoproteins containing histones and residual nuclear proteins (DNA/resid. prot. 1:0,5: 0,5) exhibited different thermal stability depending on whether part of the histones or residual nuclear proteins were first bound to DNA. Furthermore, these nucleoproteins showed different thermal stability after treatment with growth substances.