Self-organization of an oscillatory neural system

Hebbian dynamics is used to derive the differential equations for the synaptic strengths in the neural circuitry of the locomotive oscillator. Initially, neural connection are random. Under a specified arborization hypothesis relating to the density of neural connections, the differential equations are shown to model the self-organization and the stability of the oscillator.     

Acoustic response properties of single neurons in the central posterior nucleus of the thalamus of the goldfish,Carassius auratus

Acoustic responses were recorded extracellularly from single neurons in the thalamic central posterior nucleus (CP). Spontaneous activity, best sensitivity, and sharpness of tuning (Q_10db) of CP neurons ranged from 0 to 36 spikes/s, -40 to 5 dB re: 1 dyne/cm², and 0.18 to 1.80, respectively. The distribution of characteristic frequency (CF) was nonuniform with a mode at 195 Hz. Temporal response patterns of CP neurons (N = 60) were categorized into three groups: phasic (25%), tonic chopper-like (22%), and tonic nonchopper-like (53%) on the basis of peri-stimulus time and inter-spike interval histograms. Most CP neurons (90%) did not phase-lock to tones, and none phase-locked strongly. The properties of CP neurons are similar to those of the midbrain torus semicircularis neurons in spontaneous rates, best sensitivities, nonuniform CF distributions, and in exhibiting level-independent best frequencies. Both CP and toral neurons show a diversity of response patterns resembling those found in the mammalian central auditory system. However, CP neurons have broader tuning and less phase-locking than toral neurons, suggesting different roles in auditory processing. While peripheral frequency analysis is enhanced at the midbrain level, the integration of frequency-selective channels in the thalamus may function in the processing of wideband spectra characteristic of natural sound sources.Abbreviations BF best frequency - BS best sensitivity - CF characteristic frequency - CP central posterior nucleus - ISIH inter-spike interval histogram - PSTH peri-stimulus-time histogram - RA response area     

Molecular mapping of wheat. Homoeologous group 2.

A molecular-marker map of bread wheat having many markers in common with other grasses in the Gramineae family is a prerequisite for molecular level genetic studies and breeding in this crop species. We have constructed restriction fragment length polymorphism maps of the A-, B-, and D-genome chromosomes of homoeologous group 2 of hexaploid wheat (Triticum aestivum L. em. Thell) using 114 F7 lines from a synthetic x bread wheat cross and clones from 11 libraries. Chromosomes 2A, 2B, and 2D comprise 57, 60, and 56 markers and each spans about 200 cM. Comparisons between chromosomes are facilitated by 26 sets of homoeoloci. Genes mapped include a heterologous abscisic acid responsive locus cloned as pBS128, the epidermal waxiness inhibitor W21, and two presumed leaf rust and stem rust resistance genes. Anomalies suggesting ancestral rearrangements in chromosome 2B are pointed out and features of wheat group 2 chromosomes that are common to barley (Hordeum vulgare L.), rice (Oryza spp.), and T. tauschii are discussed.     

Dynamic properties of some β-chain mutant hemoglobins

The thermal behavior of the Soret band relative to the carbonmonoxy derivatives of some β-chain mutant hemoglobins is studied in the temperature range 300–10 K and compared to that of wild-type carbonmonoxy hemoglobin. The band profile at various temperatures is modeled as a Voigt function that accounts for homogeneous broadening and for the coupling with high- and low-frequency vibrational modes, while inhomogeneous broadening is taken into account with a gaussian distribution of purely electronic transition frequencies. The various contributions to the overall bandwidth are singled out With this analysis and their temperature dependence, in turn, gives information on structural and dynamic properties of the system studied. In the wildtype and mutant hemoglobins, the values of homogeneous bandwidth and of the coupling constants to high-frequency vibrational modes are not modified with respect to natural human hemoglobin, thus indicating that the local electronic and vibrational properties of the heme–CO complex are not altered by the recombinant procedures. On the contrary, differences in the protein dynamic behavior are observed. The most relevant are those relative to the “polar isosteric” βVal-67(Ell) →Thr substitution, localized in the heme pocket, which results in decreased coupling with low-frequency modes and increased anharmonic motions. Mutations involving residue βLys-144(HC1) at the C-terminal and residue βCys-112(G14) at the α₁β₁ interface have a smaller effect consisting in an increased coupling with low-frequency modes. Mutations at the β-N-terminal and at the α₁β₂ interface have no effect on the dynamic properties of the heme pocket. © 1995 Wiley-Liss, Inc.     

生态环境对白芷产量质量的影响

生态环境对白芷产量质量的影响陈兴福,丁德蓉,刘岁荣,卢进,黄文秀（四川省中医药研究院药物种植研究所,南川６４８４０８）ＥｆｆｅｃｔｏｆＥｃｏ－ＥｎｖｉｒｏｎｍｅｎｔｏｎＤａｈｕｒｉａｎＡｎｇｅｌｉｃａＹｉｅｌｄａｎｄＩｔｓＱｕａｌｉｔｙ￥ＣｈｅｎＸｉ...     

大鼠烫伤后延髓孤束核β－内啡肽含量的变化及其抗血清的作用

大鼠背部２０％体表面积接触沸水２０ｓ,形成Ⅲ度烫伤后,延髓孤束核推挽灌流液中β－内啡肽免疫活性物质的含量显著升高,在烫后１、４ｈ两次达到峰值。烫后立即向弧束核微量注射０．４μｌβ－内啡肽抗血清（滴度１：３００００）,可在一定程度上改善心功能指标,延缓血压和心率的下降,但未能延长动物的存活时间。提示孤束核的β－内啡肽在烫伤休克的病理过程中起作用,其含量的过量升高有抑制心血管功能的作用,从而不利于烫伤休克的恢复。     

Purification and characterization of two essential cytochromes of the thiosulphate-oxidizing multi-enzyme system from Thiobacillus A2 (Thiobacillus versutus)

Four c-type cytochromes were purified by several procedures including chromatography on DEAE-Sepharose CL-6B, Phenyl-Sepharose CL-4B and Sephadex G-75, G-100 and G-200 and chromatofocusing. Cytochrome c-551 had a pI value of 5.2 and an M_r of 260 000 consisting of six non-covalently bound polypeptides each with an M_r of 43 000, and contained four to five haems. Cytochrome c-552.5 had a pI value of 4.8 and an M_r of 56 000 consisting of two polypeptides with the same M_r 29 000, and contained two haems. Cytochromes c-551 and c-552.5 were reduced by ascorbate to about 70 and 60% of the fully dithionite-reduced values, respectively, and both were essential components in the thiosulphate-oxidizing multi-enzyme system (other components of the system were ‘enzyme A’, ‘enzyme B’ and sulphite: cytochrome c oxidoreductase). These two cytochromes functioned as electron carriers and effectors in the oxidation of thiosulphate. Some evidence suggested that cytochrome c-551 might be a specialized electron transfer component for sulphonate-sulphur oxidation. Both cytochromes could be reduced by thiosulphate in the presence of enzymes A and B. Cytochrome c-550 (basic) and cytochrome c-550 (acidic) were small proteins with M_r 15 000 and 14 000 and pI values of over 8 and 5, respectively. Their physiological role is uncertain.     

Dimethyl sulfoxide: A solvent for cytokinins in theAmaranthus bioassay

Dimethyl sulfoxide present in the agar medium at concentration 0.2 % (v/v) and lower does not inhibit cytokinin-induced betacyanin synthesis in theAmaranthus caudatus seedlings. The activity of kinetin, N⁶-(Δ²-isopentenyl)adenine andtrans- zeatin is the same when these cytokinins are dissolved in either water or dimethyl sulfoxide and incorporated into the medium after autoclaving. A simple method is described which allows the cytokinin activity of slightly water-soluble and thermolabile compounds,e.g. aromatic urea and thiourea derivatives, to be determined in theAmaranthus bioassay.     

Hepatic microsomal epoxide hydrase. Chemical evidence for a single polypeptide chain.

Highly purified hepatic microsomal epoxide hydrase, which had been purified in the presence of proteolytic enzyme inhibitors, was subjected to carboxypeptidase Y digestion, automated Edman degradation, and carbohydrate analysis. Carboxypeptidase Y digestion resulted in the near stoichiometric release of leucine, the COOH-terminal amino acid. Automated Edman degradation permitted the identification of the first 20 amino acid residues of epoxide hydrase. Methionine was identified as the NH2-terminal residue. The NH2-terminal region of epoxide hydrase is similar in hydrophobicity to the NH2-terminal precursor segments of several secretory proteins and the NH2-terminal regions of several microsomal cytochromes P-450. Carbohydrate analyses of the enzyme revealed the presence of 0.5 to 1.0 mol of mannose/50,000 g of protein. These results provide evidence for the presence of a single polypeptide chain in our purified enzyme preparations and suggest that there may be only one enzymic form of epoxide hydrase in microsomes from phenobarbital-treated rats.