Neural coding of speech sound in the telencephalic auditory area of the mynah bird

Summary The responses of neurons in field L in the auditory neostriatum of the mynah bird, Gracula religiosa, were recorded during presentation of intact or manipulated mimic voices. A typical mimic voice konnichiwa elicited responses in most of the neurons. Neurons in the input layer (L2) of field L showed many peaks on peristimulus time histograms while those in other layers (L1 and L3) exhibited only one or two peaks. Several neurons in L1 and L3 responded only to the affricative consonant /t/ in the intact mimic voices. They did not respond to the affricative consonant in the isolated segment or to the one in the playbacked voice in reverse. Forty-five percent of the neurons (33/ 73) decreased in firing rates at the affricative consonant in the isolated segment compared with in the intact voice. Some of these neurons, in which neither the affricative consonant in the isolated segment nor bursts of noise alone elicited responses, exhibited clear phasic responses to /t/ in the case when bursts of noise with particular central frequencies preceded the affricative consonant. The responsiveness of these neurons appears to receive temporal facilitation. These results suggest that these neurons code the temporal relationship of speech sound.Abbreviations HVc hyperstriatum ventrale, pars caudale - TFN temporally facilitated neuron - TSN temporally suppressed neuron     

青海省海北地区高寒草甸鸟类群落结构的季节变化

本研究地区,高寒草甸鸟类群落由22种鸟组成,它们隶属于2目9科,其中留鸟11种,迁徙鸟8种。在当地繁殖的鸟19种,冬候鸟2种。各项鸟类群落指标呈现明显季节变化,一般从早春开始上升,到夏季达到高峰,然后逐渐下降至隆冬的最低点。     

绿尾虹雉生态学研究

绿尾虹雉Lophophorus lhuysti生态和生物学研究是中国科学院重点科研课题——“中国珍稀濒危难类生态生物学”——部分工作。 本文为作者对绿尾虹雉所作的生态和生物学系统研究首次报道。绿尾虹雉主要牺息于海拔3,500—4,000米亚高山灌丛和草甸。杂食性鸟类,以植物性食物为主,亦食昆虫。营巢于岩洞或灌丛地面上,每窝产3—4,多达11枚卵。种群密度1.32—1.58只/km~2。目前数量急剧下降,处于濒危,急待保护。     

Induced reversion of a Chinese hamster ovary triple auxotroph. Validation of the system with several mutagens

A Chinese hamster ovary triple auxotroph (CHO AUXB1) requires glycine, adenosine, and thymidine (GAT) for growth and survival due to a defect in the structural gene for folylpolyglutamate synthetase (FPGS). This auxotroph and others like it contain less than 3% of the parental amounts of FPGS activity. In order to develop a reverse mutation assay with CHO AUXB1, we determined the optimal conditions for measuring reversion and characterized some of the revertants. We also obtained quantitative mutagenicity data for several direct-acting mutagens for comparison to the parental CHO-S/HGPRT locus. Induced revertants appear in the culture immediately following 20-22 h exposures in +GAT complete medium, indicative of dominant genetic changes. They are maximally expressed after 2 population doublings and can be conveniently selected after 44-48 h of expression growth by plating 1 X 10(6) cells/100-mm dish into -GAT-deficient medium and incubating 12-13 days. Plating reconstruction experiments show that the cloning efficiencies of revertants in -GAT medium are not influenced by the presence of up to 1 X 10(6) CHO AUXB1 cells. Dose-dependent increases above the spontaneous revertant frequency (average = 5 X 10(7)) are induced with cis-Pt(NH3)2Cl2 (14-fold) (but not trans-Pt(NH3)2Cl2), PtCl4(10-fold), Pt(SO4)2 (14-fold), K2CrO4 (8-fold), EMS (10-fold), 4-NQO (53-fold), ICR-191 (60-fold), and ICR-170 (30-fold). All of the revertants that have been isolated are stable to repeated subculturing in -GAT medium; 40 out of 42 that have been analyzed are characterized by an increased 72-h growth incorporation of labeled folate and their extracts contain 5-94% as much FPGS as the original, parental CHO-S line. Spontaneous and induced reversion to the GAT+ phenotype primarily reflects mutations involving the FPGS gene locus. But the re-acquisition by most of the revertants of much less than normal amounts of FPGS activity suggests that they arise from compensatory second-site mutations within this gene. Comparison of the mutagenicity patterns of the foregoing compounds as a function of the applied concentration and the relative percent survival reveals some interesting similarities, as well as differences, between the CHO AUXB1/FPGS and CHO-S/HGPRT loci. In particular, the FPGS locus is rather insensitive to EMS (or other simple alkylating agents). However, it seems to be quite susceptible to reversion by other chemicals that are known to react selectively with guanine bases in DNA. CHO AUXBI is a useful supplemental mammalian assay system for assessing quantitatively the generally weak mutagenic activities of metal compounds.     

Cellular systems for the study of the biosynthesis of polyamines and ethylene,as well as of virus multiplication

Leaves of Chinese cabbage from healthy plants or from those infected with turnip yellow mosaic virus yield protoplasts which convert methionine to protein, S-adenosylmethionine, decarboxylated S-adenosylmethionine, spermidine, spermine and 1-aminocyclopropane-1-carboxylate. The enzyme spermidine synthase is entirely cytosolic and has been purified extensively. An inhibitor of this enzyme, dicyclohexylamine, blocks spermidine synthesis in intact protoplasts, and in so doing stimulates spermine synthesis. Aminoethoxyvinylglycine blocks the conversion of S-adenosylmethionine to 1-aminocyclopropane-1-carboxylate, the precursor to ethylene, in protoplasts. This inhibitor markedly stimulates the synthesis of both spermidine and spermine. Essentially all the protoplasts obtained from new leaves of plants infected 7 days earlier are infected. On incubation, such protoplasts convert exogenous methionine to viral protein and viral spermidine whose specific radioactivity is twice that of total cell spermidine. Exogeneous spermidine is also converted to cell putrescine and viral spermidine and spermine. Normal and virus-infected cells are being studied for their content of phenolic acid amides of the polyamines.     

1-Methylguanine and 7-methylguanine increase cell agglutinability

Summary 1-Methylguanine and 7-methylguanine, both metabolic products of tRNA degradation, are known to induce transformation of Chinese hamster fibroblasts in culture. The effects of these compounds on the cell membrane have been studied by the method of Concanavalin A-mediated hemadsorption. 1-Methylguanine or 7-methylguanine induced a 50% increase of Con A-mediated hemadsorption within 20 hours of exposure of the cells to the agent at a concentration of 10^-5 M. This alteration was reversed within 13 days when the cells were grown in the control medium. Prolonged treatment with 1-methylguanine or 7-methylguanine resulted in changes which were only slowly reversed during growth of the cells in the control medium. The effect of the methylated purines on the cell membrane could be completely inhibited by simultaneous addition of dibutyryl-cAMP at a concentration of 10^-5 M. The possible mechanism of cell membrane alteration by methylated purines and its relevance to transformation in vitro are discussed.     

Poly(ADP-ribose) metabolism appears normal in EM9, a mutagen-sensitive mutant of CHO cells

EM9 is a mutagen-sensitive CHO cell whose phenotype resembles that of normal CHO cells exposed to 3-aminobenzamide, an inhibitor of poly(ADP-ribose) synthesis. This phenotype suggested that EM9 might be defective in poly(ADP-ribose) metabolism, but we now cannot find any abnormality in the synthesis or in the degradation of poly(ADP-ribose) in permeabilized EM9 cells. Thus the effects of 3-aminobenzamide on wild-type cells may be due to the inhibition of processes other than poly(ADP-ribose) synthesis. 3-Aminobenzamide enhances the cytotoxicity of EMS toward EM9 and control cells to the same degree.     

The relationship between the levels of DNA-hydrocarbon adducts and the formation of sister-chromatid exchanges in Chinese hamster ovary cells treated with derivatives of polycyclic aromatic hydrocarbons

The frequencies of the induction of sister-chromatid exchanges and the levels of deoxyribonucleoside-hydrocarbon adducts formed in Chinese hamster ovary cells that had been treated with either dihydrodiols or a diol-epoxide derived from polycyclic aromatic hydrocarbons were determined. Up to 6-fold increases in the incidence of these exchanges were observed when the cells were treated either with the dihydrodiols, trans-3,4-dihydro-3,4-dihydroxy-7-methylbenz[a]anthracene,trans-7,8-dihydro-7,8-dihydroxybenzo[a]pyrene or the diol-epoxide, (±)-r-7, t-8dihydroxy-t-9,10-oxy-7,8,9,10-tetrahydrobenzo[a] pyrene but when the cells were transferred to media free of these compounds, there were rapid reductions in the frequency of these exchanges. When the exchanges were induced by the diol-epoxide, the decreases in frequency were paralleled by decreases in the levels of deoxyribonucleoside-diol-epoxide adducts that were present in hydrolysates of DNA isolated from the cells. There thus appears to be a close relationship between the frequency of sister-chromatid exchanges and the levels of deoxyribonucleoside-diol-epoxide adduct formation.     

The possible involvement of gibberellins and calcium in tipburn of Chinese cabbage: Study of intact plants and detached leaves

Spraying Chinese cabbage seedlings [Brassica pekinensis (Lour.) Rupr.] with the growth retardant daminozide (succinic acid-2,2-dimethylhydrazide) reduced tipburn of the mature plants. As the concentration of daminozide increased, the reduction in tipburn damage was correlated with increased calcium content in young susceptible leaves. This effect was much more pronounced in plants that were misted once a day during the head formation period.Incubation of detached Chinese cabbage leaves for 48 h (in the dark) in solutions which contained either EDTA or EGTA caused characteristic lesions at the leaf tips. The extent of the damage was reduced by including CaCl₂ in the solutions. Leaves which were incubated in a solution of EDTA+GA₃ or EGTA+GA₃ were severely affected, with the latter solution being the more harmful. GA₃ alone did not enhance tipburn. CaCl₂ greatly reduced the effect of a complex of chelating agents and GA₃. Leaves derived from daminozide-treated plants which were incubated in EDTA+GA₃ were less affected with tipburn lesions than leaves of control plants treated with the same solutions. When detached leaves were water-stressed for 24 h prior to incubation in these solutions, the severity of tipburn symptoms increased. The possible interactions between GA, calcium chelation and tipburn development are discussed.Contribution no. 1171-E, 1984 series, from the ARO, The Volcani Center Bet Dagan, Israel.