Dopamine Synthesis in Synaptosomes: Relation of Autoreceptor Functioning to pH, Membrane Depolarization, and Intrasynaptosomal Dopamine Content

Abstract: Factors affecting dopamine (DA) synthesis in rat striatal synaptosomes were examined by measuring the conversion of [³H]tyrosine (Tyr) to [³H]DA. Any [³H]DA that was synthesized was extracted into a toluene-based scintillation cocktail and quantitated by liquid scintillation spectrometry. The extraction was facilitated using di-(2-ethylhexyl) phosphoric acid (DEHP), a liquid cation exchanger. DA, apomorphine, and other DA agonists were much less potent inhibitors of DA synthesis in striatal synaptosomes at pH 6.2 than at pH 7.2. 3-(3-Hydroxyphenyl)- N - n -propylpiperidine (3-PPP), a putative DA autoreceptor agonist, was inactive at pH 6.2. However, at pH 7.2, 3-PPP did inhibit DA synthesis. This inhibition was reversed by sulpiride, a DA receptor antagonist, but not by benztropine, a DA uptake blocker, suggesting that 3-PPP inhibits DA synthesis by stimulating the DA autoreceptor. DA release from synaptosomes was much greater at pH 6.2 than at pH 7.2, most probably because the synaptosomal membrane appears to be depolarized at pH 6.2, as measured by the accumulation of [³H]tetraphenylphosphonium ions. Since tyrosine hydroxylase is inhibited by DA, this finding suggested that low assay buffer pH (i.e., pH 6.2) might interfere with the ability of 3-PPP and other DA agonists to inhibit DA synthesis, by promoting DA release. Likewise, reserpine and tetrabenazine, compounds which disrupt vesicular DA storage, were much less effective inhibitors of DA synthesis at pH 6.2 (high basal DA release). Moreover, d -amphetamine and high buffer potassium concentrations, treatments which promote DA release, also interfered with the ability of 3-PPP to inhibit DA synthesis. Thus, modulation of the release of DA in equilibrium with tyrosine hydroxylase may be a mechanism by which the DA autoreceptor regulates DA synthesis.     

Reactions of the adult female of the soft scale Kilifia acuminata to some physical factors in laboratory experiments (Homoptera: Coccoidea: Coccidae)

The soft scale insect, Kilifia acuminata (Signoret) reacts positively to light. The simple eyes are the photoreceptors by means of which the insect can sum up the light from various directions and steers in a path towards the high intensity beam. The insect reacts skototactically towards dark objects.
The linear velocity of the insect significantly increases with the increase of temperature. It has a zone of thermopreferendum extending between 22° and 32°C. Above 37°C, the insect is sensitive to small temperature differences of 2°C.
At different humidity combinations below 75% R.H., the insect prefers the moist side, while in the upper range above 83% R.H., it usually prefers the dry side. The preferred zone of humidity extends between 75 and 83%.
Orthokinesis, klinokinesis and klinotaxis are the main mechanisms regulating the insect reaction towards different physical factors.
The insect behaviour and its correlation to the normal environment is also discussed.     

Development of some lepidopterous cotton pests as affected by exposure to sublethal levels of endotoxins of Bacillus thuringiensis for different periods

Three spore-δ-endotoxin preparations from Bacillus thuringiensis vars. kurstaki and entomocidus including a commercial biological insecticide, Thuricide, were studied with respect to their biological interactions with the lepidopterous cotton pests, Spodoptera littoralis, Spodoptera exigua, and Heliothis armigera. The biological effects of sublethal doses and the length of exposure time to low endotoxin concentrations were assessed during and after removal of toxin from the diet. Retardation in larval development, reduction in egg production of the moths, and fertility of the egg were observed together with significant reduction in pupal weight and appearance of deformities in both pupae and moth populations. The influence of exposure to sublethal toxin concentrations was also manifested in term of decreasing the adult emergence, fecundity reduction, and prolonging the generation period. In the exposed insects, the precentage of larvae that survived and succeeded to pupate increased with the decrease in the toxin concentration and with the decrease in exposure time. The reduction of the pupal weight significantly increased with the increase in either toxin concentration or the duration of exposure. The longevity of the moths was not affected by larval treatment and the data showed no clear correlation with the concentration and time of larval exposure to the toxin.     

Enhanced Ca2+ uptake and ATPase activity of sarcoplasmic reticulum in the presence of diethyl ether

The presence of diethyl ether enhances the rates of both Ca2+ uptake and ATPase activity in sarcoplasmic reticulum vesicles (SR) isolated from rabbit skeletal muscle. Stopped-flow measurements of Ca2+ transport in SR show that, in the absence of oxalate and other calcium-complexing anions, the initial velocity of the ATP-dependent Ca2+ uptake increases from 60 to 107 nmol of Ca2+/s/mg of protein when 5% (v/v) diethyl ether is present. Similar concentrations of diethyl ether increase steady state levels of Ca2+ accumulation by over 80%. Parallel to the enhancement of the rate of Ca2+ transport, diethyl ether induces an increased rate of Ca2+-dependent ATPase activity. Among four other ether compounds tested, three enhanced the rate of Ca2+ uptake, but none as effectively as diethyl ether, and a fourth reduced the rate of Ca2+ transport by the SR. These results contrast with previous observations concerning the effect of diethyl ether on ATP-dependent Ca2+ transport by SR and are now consistent with a direct pharmacological action of ether as a muscle relaxant at the level of SR Ca2+ transport.     

G1 cyclin degradation: the PEST motif of yeast Cln2 is necessary, but not sufficient, for rapid protein turnover.

The 545-residue Cln2 protein, like the other G1 cyclins of Saccharomyces cerevisiae, is a very unstable protein. This instability is thought to play a critical role in regulating cell cycle progression. The carboxyl-terminal domains of Cln2 and the other G1 cyclins contain sequences rich in Pro, Glu (and Asp), Ser, and Thr (so-called PEST motifs) that have been postulated to make up the signals that are responsible for the rapid degradation of these and other unstable proteins. To test this hypothesis, the carboxyl-terminal 178 residues of Cln2 were fused to the C terminus of a reporter enzyme, a truncated form of human thymidine kinase (hTK delta 40). The resulting chimeric protein (hTK delta 40-Cln2) retained thymidine kinase activity but was markedly less stable than hTK, hTK delta 40, or an hTK-beta-galactosidase fusion protein, as judged by enzyme assay, immunoblotting with anti-hTK antibodies, pulse-chase analysis of the radiolabeled polypeptides, and ability to support the growth of a thymidylate auxotroph (cdc21 mutant) on thymidine-containing medium. Thus, the presence of the Cln2 PEST domain was sufficient to destabilize a heterologous protein. Furthermore, the half-life of hTK delta 40-Cln2 was similar to that of authentic Cln2, and the rate of degradation of neither protein was detectably enhanced by treatments known to cause G1 arrest, including exposure of MATa haploids to alpha-factor mating pheromone and shifting cdc28ts and cdc34ts mutants to the restrictive temperature. These results suggest that the major signals responsible for Cln2 instability are confined to its C-terminal third. Because hTK delta 40-Cln2 and Cln2 were expressed from heterologous promoters yet their half-lives both in asynchronous cultures and when arrested at various cell cycle stages were always similar, the Cln2 PEST domain contains a signal for rapid protein turnover that is constitutively active and operative throughout the cell cycle. Removal of the 37 codons that encode the most prominent PEST-like segment from either hTK delta 40-Cln2 or Cln2 decreased the turnover rate of the resulting proteins, as expected; however, an hTK delta 40 chimera containing only this 37-residue segment was not detectably destabilized, suggesting that this PEST sequence, when removed from its normal context, is not a self-contained determinant of protein instability.     

海马内注射脑啡肽对细胞免疫功能及脑内IL－1α基因表达的影响

本文研究了海马内微量注射脑啡肽对大鼠细胞免疫功能及海马内白细胞介素－１α（ＩＬ－１α）基因表达的影响。结果发现：（１）双侧海马内微量注射甲硫－脑啡肽或亮－脑啡肽各１μｌ（１８ｍｍｏｌ／Ｌ）能明显增强ＣｏｎＡ刺激的脾淋巴细胞增殖活性,而双侧海马内微注射脂多糖各１μｌ（５０ｎｇ／μｌ）则起抑制作用。切除双侧肾上腺后,海马内注射脑啡肽仍可增强脾淋巴细胞增殖反应。低浓度亮－及甲硫－脑啡肽（１０￣（－１０）,１０￣（－１１）ｍｏｌ／Ｌ）直接作用于体外培养的大鼠脾淋巴细胞,也明显增强ＣｏｎＡ刺激的细胞增殖活性。（２）双侧海马内微量注射脂多糖各１μｌ（５０ｎｇ／μｌ）,于９０ｍｉｎ后用逆转录－聚合酶链反应技术检测到海马结构内ＩＬ－１α基因表达,而海马内甲硫或亮脑啡肽注射３０ｍｉｎ后再给予脂多糖,则未检测到ＩＬ－１αｃＤＮＡ的扩增条带。上述结果表明,海马结构对机体免疫功能的调节中脑啡肽起着重要作用,其机制可能与抑制海马结构ＩＬ－１α基因表达有关。     

Biology and development of some stored grain pests as affected by δ‐endotoxin and β‐exotoxin of Bacillus thuringiensis

Exposure of Plodia interpunctella and Sitotroga cerealella to sublethal concentrations of Dipel 2X® (Bacillus thuringiensis var.kurstaki‐HD‐1)with its spores and endotoxin crystals led to an increase in the sum of larval‐pupal duration. A decrease in moth emergence, egg production and fertility was observed with increase of Dipel 2X concentration, while the longevity of the moths was not affected by treatment. Sublethal concentrations of β‐exotoxin (ABG‐6162 A) had no significant effect on the sum of larval—pupal duration of either insect species. Percentage of moth emergence decreased with the increase of β‐exotoxin concentrations. The longevity of both male and female adults of P. interpunctella and of females of S. cerealella were shorter at high concentrations. Egg production in P. interpunctella was reduced by all concentrations of the β‐exotoxin, and hatching of eggs was reduced by concentrations of 15 ppm and above.     

Characterization of the Quisqualate Receptor Linked to Phosphoinositide Hydrolysis in Neurocortical Cultures

Activation of phosphoinositide metabolism is an early event in signal transduction for a number of neurotransmitters and hormones. In primary cultures of rat neurocortical cells, various excitatory amino acids stimulate inositol phosphate production with a rank order of potency of quisqualate greater than ibotenate greater than glutamate greater than kainate, N-methyl-D-aspartate greater than alpha-amino-3-hydroxyl-5-methyl-4-isoxazole propionate. This response to excitatory amino acids was insensitive to a variety of excitatory amino acid antagonists including 6-cyano-7-nitroquinoxaline-2,3-dione, 3-3(2-carboxypiperazine-4-yl)propyl-1-phosphonate, and 2-amino-4-phosphonobutyrate. The individual responses of quisqualate-, ibotenate-, and kainate-stimulated inositol phosphate production were not additive. These results suggest that phosphoinositide metabolism activated by excitatory amino acids is mediated by a unique quisqualate-preferring receptor that is not antagonized by known N-methyl-D-aspartate and non-N-methyl-D-aspartate antagonists, and is relatively insensitive to alpha-amino-3-hydroxyl-5-methyl-4-isoxazole propionate.     

Fibrinolytic activity of some fungi isolated from self-heated composted fertilizer

Mesophilic fungi isolated from organic fertilizer compost samples accounted for 70.94% of the total fungal count, while thermophilic and thermotolerant fungi constituted 29.05% of that count. Eight mesophilic fungal species, namelyAspergillus niger, Monilia sitophila, Paecilomyces divaricata, Penicillium chrysogenum, P. fellutanum, Scopulariopsis brevicaulis, S. brumptii andZygorhynchus japonicus; two thermophilic fungiHumicola grisea andOidiodendron flavum and three thermotolerant speciesAspergillus fumigatus, Thermomyces lanuginosus andZygorhynchus vuilleminii were isolated during the study. Most of the tested fungi showed a proteolytic activity and liquified gelatin in the test tube method and in cup plates. The thermophilic fungusO. flavum was the most potent proteolytic fungus. The comparative fibrinolytic assay revealed the following sequence in the ability of the tested fungi to hydrolyse fibrin:O. fiavum>S. brevicaulis>H. grisea>A. fumigatus>T. lanuginosus.