Sustained sensitivity modifications induced by brief length perturbations in the crayfish slowly adapting stretch receptor

These experiments in the slowly adapting stretch receptor of crayfish test the effects of brief length perturbations (i.e., pulses) when presented in isolation at different constant elongations or superimposed on trapezoidal stretches of different amplitudes. Within "in vivo" lengths, during static responses, perturbations reduced firing rates to below control values and, in extreme cases, could silence the receptor. This effect, or "down-step," was sustained, occurred above a threshold pulse amplitude and background stretch, and increased with both stimulus characteristics, but was not present during dynamic responses. Beyond "in vivo" lengths, and in a few cases within those limits but close to the extremes, the receptor was silent but perturbations could restore activity. Lengthening pulses were more effective than shortening ones in generating after-effects. Perturbations change, during indefinitively long periods, the receptor's length or static sensitivity acting as a negative feedback which tends to maintain the discharge rate within fixed values. Perturbations disclose marked nonlinearities, which suggest that the classical view of a proportional control in the reflex loop in which the receptor participates may not operate in natural conditions.     

Meiotic behaviour of Un,D and R genomes in the amphiploid Aegilops ventricosa -Secale cereale and the parental species

Summary Meiotic pairing frequencies of the Un and D genomes of Ae. ventricosa and the R of S. cereale could be easily established at metaphase I in Aegilops ventricosa — Secale cereale amphiploid plants as well as in its parental species by using the C-banding technique procedure. The results show a high diminution of chromosome pairing for all genomes in the amphiploid with respect to its parental species probably due to C-heterochromatin content and/or genotypic or cryptic interactions between the three genomes.     

In vitro synthesis of full-length influenza virus complementary RNA.

Influenza virus-specific RNA has been synthesized in vitro, using cytoplasmic or microsomal fractions of influenza virus-infected MDCK cells. The RNA polymerase activity was stimulated 5-30 times by priming with ApG. About 20-30% of the product was polyadenylated. Most of the in vitro product was of positive polarity, as shown by hybridization to strand specific probes and by T1 fingerprinting of the poly(A)+ and poly(A)- RNA segments encoding haemagglutinin and nucleoprotein. The size of poly(A)- RNA segments, determined on sequencing gels, was indistinguishable from that of virion RNA, whereas poly(A)+ RNA segments contain poly(A) tails approximately 50 nucleotides long. The size of in vitro synthesized RNA segments was also determined by gel electrophoresis of S1-treated double-stranded RNAs, obtained by hybridization of poly(A)+ or poly(A)- RNA fractions with excess of unlabelled virion RNA. The results of these experiments indicate that poly(A)- RNA contains full-length complementary RNA. This conclusion is further substantiated by the presence of additional oligonucleotides in the T1 fingerprints of in vitro synthesized poly(A)- haemagglutinin or nucleoprotein RNA, selected by hybridization to cloned DNA probes corresponding to the 3' termini of the genes.     

Isolation of complement-fragment-iC3b-binding proteins by affinity chromatography. The identification of p150,95 as an iC3b-binding protein.

The proteins from labelled human spleen membranes and polymorphonuclear leucocytes which bind to the iC3b fragment of complement component C3 were prepared by iC3b-Sepharose chromatography in the presence of bivalent cations. Complement receptor type 3(CR3) was eluted from iC3b-Sepharose by removal of bivalent cations. Complement receptors type 1 and 2 (present in spleen but not in polymorphonuclear leucocytes) were sequentially eluted by an NaCl gradient. An additional protein of Mr 135 000 was eluted from iC3b-Sepharose under the same conditions as those used to elute CR3. Preabsorption of the starting material on an anti-(CR3 beta-subunit) antibody column before iC3b-Sepharose chromatography removed the alpha- and beta-chains of CR3 and the 135 000-Mr protein. Preabsorption with iC3b-Sepharose before the anti-(CR3 beta-subunit) antibody column showed that iC3b binds CR3 and p150,95, the smallest member of the group of three homologous proteins that share the same beta-subunit.     

Kinin-converting aminopeptidase from human urine. Further purification and characterization through kinetic and inhibitory studies

An aminopeptidase from human urine (HUA) able to hydrolyze L-aminoacyl-2-naphthylamides, L-Leu-p-nitroanilide and to convert both MLBK and LBK to BK has been further purified and characterized. The preparation now obtained showed a 3-fold higher specific activity than the previously described one and a single active protein band in 7% polyacrylamide gel electrophoresis accounting for 86% of total protein. Kinetic constants for this kinin-converting enzyme were determined using L-aminoacyl-2-naphthylamides, L-Leu-p-nitroanilide and LBK. The Km values for different naphthylamides were in the 10(-5) M range while that for L-Leu-p-nitroanilide was 3.6 X 10(-4) M. With LBK as substrate the aminopeptidase activity showed the highest catalytic efficiency in spite of a Km in the mM range. The enzyme was poorly inhibited by -SH and -S-S- group reagents. Some L-aminoacids, as well as mono- and diamines, indomethacin, puromycin and bestatin were equipotent competitive inhibitors of both arylamidase and aminopeptidase activities. Results obtained in this paper are compatible with our conclusion that human urine, unlike other enzyme sources, contains only one aminopeptidase, and that this enzyme displays both arylamidase and kinin-converting activities. The enzyme's action may be important in the metabolism of kinins, yielding peptides which could interact with both B-1 and B-2 kinin receptors in the kidney.     

Division of temperature-sensitive Streptococcus faecium mutants after return to the permissive temperature

The regrowth of 27 temperature-sensitive division mutants of Streptococcus faecium ATCC 9790 was examined after various periods of incubation at the nonpermissive temperature. Several of the mutants blocked at various stages of septum formation or of daughter-cell separation divided in a partially or completely synchronous way after a short incubation at the nonpermissive temperature. All four lytic mutants blocked early in the cell division cycle divided at a normal rate after a brief lag.     

Location of O-acetyl groups in the acidic d-xylan of mimosa scabrella (bracatinga). A study of O-acetyl group migration

Extraction with dimethyl sulfoxide of wood-meal of the stem of bracatinga (Mimosa scabrella), a south Brazilian hardwood, that was defatted and delignified by treatment with aqueous chlorine at 0–5° followed by extraction with cold ethanol, gave a soluble O-acetylated 4-O-methyl-d-glucurono-d-xylan having (1→4)-linked β-d-xylopyranosyl residues that were unsubstituted (65%) and 2-O-(14%), 3-O- (16%), and 2,3-di-O-acetylated (5%), as determined by methylation analysis. Another preparation obtained by use of refluxing ethanol in the delignification process showed neither removal nor migration of acetyl groups. By comparison with synthetic, partly O-acetylated d-xylans of known composition, ¹³C-n.m.r. spectroscopy indicated that O-acetyl group migration does not occur during treatment with cold aqueous chlorine, refluxing ethanol, or water at 70°. Methyl 2-O-acetyl-4-O-methyl-β-d-xylopyranoside (6) was also unaffected by aqueous chlorine. O-Acetyl group migration took place more readily in aqueous and dimethyl sulfoxide solutions of 6 than of O-acetyl-d-xylans. The lowest temperatures at which migration was observed in monosaccharides was at 50 and 70° for solutions in D₂O and (CD₃)₂SO, respectively.     

Antagonism of diazepam-induced feeding in rats by antisera to opioid peptides

Diazepam-induced feeding in rats is antagonized not only by the opiate antagonist naloxone but also intraventricular administration of specific antisera to the endogenous opioid peptides met-enkephalin or beta-endorphin. Pituitary beta-endorphin is probably not implicated in the diazepam effect since blockade with the glucocorticoid dexamethasone of the release of beta-endorphin from the anterior pituitary does not modify the diazepam-induced feeding, which is however prevented by TRH, a suggested physiological antagonist of some of the effects of opioid peptides. The possible central participation of both beta-endorphin and met-enkephalin in the ingestive behavior induced by diazepam gives further support to the postulated physiological role of endogenous opioids in appetite regulation.     

Antiepileptic effects of amphetamine may require GABA (benzodiazepine) activity

Secondary components of visual evoked potentials (slow negative wave-SNW, and photically-evoked sensory afterdischarge-SAD) are known to be precursors of experimentally activated wave-spike discharges, similar to wave-spikes of petit mal epilepsy. Both SNW and SAD may be potently suppressed wither by amphetamine or GABAergic compounds such as diazepam and sodium valproate. A hypothesis was tested in the present study, that amphetamine-induced suppression of wave-spike discharges may require GABA-benzodiazepine activity for its expression.Electrocortical activity was recorded and averaged in unrestrained albino rats with chronically implanted epicortical electrodes. SNW and SAD obtained in habituated rats in the predrug state were potently suppressed by amphetamine (1 mg/kg, i.p.). Fifteen minutes after amphetamine injection, a challenging drug (metrazol, picrotoxin, convulsant benzodiazepine, Ro 5-3663, or imidazodiazepine, Ro 15-1788) was administered intraperitoneally. Subconvulsive doses of metrazol (10 mg/kg) reversed amphetamine suppression; imidazodiazepine (20 mg/kg) and picrotoxin (1.5 mg/kg) reliably opposed the SNW suppression; convulsant benzodiazepine, Ro 5-3663 (2 mg/kg), showed modest and nonsignificant effect in the same direction. It is proposed that the antiepileptic potency of amphetamine may be associated with its ability, apparently via modulatory effect of norepinephrine, to facilitate the activation of benzodiazepine-GABA receptors.