Neurochemical evidence for two types of presynaptic alpha2-adrenoceptors

Neurochemical and pharmacological evidence has been obtained that noradrenergic varicosities (in mouse and rat vas deferens) and cholinergic varicosities (in the Auerbach's plexus) contain heterogenous alpha₂-adrenoceptors through which the release of [³H]noradrenaline and [³H]acetylcholine can be modulated. The quantitative data also support the hypothesis that different noradrenaline and xylazine sensitive alpha₂-adrenoceptors are present prejunctionally in the vas deferens and Auerbach's plexus preparations. Prazosin, although it has a presynaptic inhibitory effect on alpha₂-adrenoceptors of noradrenergic axon terminals, has no effect on cholinergic axon terminals. These data suggest that there are two different types of alpha₂-adrenoceptors at the presynaptic axon terminals.Special Issue Dedicated to Dr. Abel Lajtha     

Relative cytotoxicity of psychotropic drugs in cultured rat hepatocytes

The relative cytotoxic effects of ten psychotropic drugs were assessed in rat hepatocyte monolayer cultures. Clear concentration-related toxicity was seen in the narrow range of 10^–5M to S × 10^–5M. The four cytotoxicity endpoints chosen were: release of the cytosolic enzyme, lactate dehydrogenase, and impairment of biosynthesis and secretion of proteins, bile acids and glycerolipids. LDH leakage and inhibition of protein secretion into the culture medium proved to be the parameters which allowed the best differentiation between the test compounds. The inhibition of glycerolipid secretion was the most sensitive test in relation to concentration and time of exposure. Based on the effects of these endpoints, the following ranking of relative in vitro toxicity, using equimolar drug concentrations, could be established: clomipramine > imipramine = thioridazine > chlorpromazine > amitriptyline = fluperlapine > haloperidol > promazine > clozapine sulpiride. This ranking order of in vitro cytotoxicity correlated well with the potential of the drugs to impair liver function in man. Only clozapine had to be classified as a false negative. There was, however, no correlation between the cytotoxicity and the intracellular accumulation of the test drugs. Furthermore, the comparison of the data obtained with psychotropics with the data from five other amphiphilic cationic drugs was consistent with the widely accepted concept of a direct toxic interaction of the drugs with cytomembranes. This nonspecific toxicity of the membrane-active drugs was further corroborated by a positive correlation between their potential to induce LDH leakage in hepatocytes and their ability to induce hemolysis in red cells. In conclusion, the results obtained in our study strongly suggest that it is possible to assess the relative cytotoxicity of psychotropic drugs in rat hepatocyte cultures. It is proposed that this in vitro system provides a useful tool to evaluate new drugs at an early stage of their development, and to identify the most promising candidates within a class of structurally related compounds. In addition, it allows information to be obtained on possible mechanisms of cytotoxicity.Abbreviations AIB aminoisobutyric acid - AMT amitriptyline - BSA bovine serum albumin - CLP clomipramine - CLZ clozapine - CPZ chlorpromazine - FLU fluperlapine - HAL haloperidol - HC₅₀ dose causing 50% hemolysis - IMP imipramine - LDH lactate dehydrogenase - PZ promazine - SUL sulpiride - TCA trichloroacetic acid - TRZ thioridazine     

Cloning and nucleotide sequence of the Salmonella typhimurium LT2 gnd gene and its homology with the corresponding sequence of Escherichia coli K12

Summary The complete nucleotide sequence of the Salmonella strain LT2 gnd gene for 6-phosphogluconate dehydrogenase was determined. The gene contains 1404 bases and encodes a 468 amino acid polypeptide, which is the same as for Escherichia coli K12. The DNA sequence shows 14.8% difference between the two and the amino acid sequence 3.6% difference. Changes are mostly in the third codon base and most of the amino acid changes are conservative.     

Tagging of a maize gene involved in kernel development by an activated Uq transposable element

Summary A quiescent Uq transposable element has been activated in a maize plant treated with 5-aza-2-deoxycyti-dine. This activated Uq cosegregates with a heritable dominant miniature (Mn) kernel phenotype, indicating its physical association with a maize miniature locus (Mn:: Uq). The Mn:: Uq mutant is dominant in producing a miniature seed phenotype of variable size and in reducing seedling vigor in the early growth stage. Genetic experiments indicate that the Mn:: Uq mutant also affects the activity of the male gametophyte, whereby pollen germination is inhibited, thus lacking pollen tube growth resulting in the male nontransmissibility of this mutant. Proof for the Uq element in this mutant is derived by its ability to transactivate the standard a-ruq reporter allele to yield spotted aleurone tissue. However, the Mn:: Uq mutant does not transactivate a normally Uq-responsive c-ruq allele, suggesting a structural difference between the two ruq receptors at the A1 and C1 loci. It is anticipated that cloning of the Uq transposable element would facilitate the molecular cloning and characterization of the maize miniature gene.Journal Paper No. J-13425 of the Iowa Agriculture and Home Economics Experiment Station, Ames, Iowa 50011, USA, Project No. 2850     

The effect of sucrose on the levels of abscisic acid, indoleacetic acid and zeatin/zeatin riboside in wheat ears growing in liquid culture

The influence of a varied sucrose supply on grain size and hormonal contents of detached wheat ears ( Triticwn aestivum L. cv. Schirokko) was investigated throughout grain development. In ears led limited amounts, or no sucrose, grain weights in both proximal and distal grain positions of the ear were reduced. Radioimmunoassay for abscisic acid, indoleacetic acid and zeatin/zeatin riboside showed that the changes in the levels of these hormones in grains and bracts were comparable to intact ears when detached ears were well supplied with sucrose. Under conditions of limited sucrose supply, higher abscisic acid levels in the distal and proximal grains of detached ears were found compared to ears supplied with adequate sucrose. Limiting sucrose supply to the ear did not alter the levels of indoleacetic acid or zeatin/zeatin riboside in either the grains or bracts of detached ears.     

The seed dimorphism of Spergularia marina in relation to dispersal by wind and water

Summary The seeds of the halophyte Spergularia marina differ both within and between individuals in that they either possess or lack a membranaceous border. This paper presents a morphological study of the length, weight and area of the seed types, and their dispersal characteristics under experimental conditions of wind and water dispersal. The winged seeds are shown to be larger both by length and by weight. Their rate of descent increases with wing loading. If the wing is lacking, however, the rate of descent increases with weight only. The distance of dispersal is equal for both seed types except at low wind speeds, when the winged seeds disperse farther. If the seed wing is removed, the excised seeds have shorter dispersal distances. When dispersed by water, a difference in the distance seeds are dispersed can only be detected in the presence of vegetation. The winged seeds are more frequently trapped in the vegetation as compared to the unwinged seeds. The hypothesis that the seed dimorphism is an adaptation for differential dispersal distances is discussed.