Regulation of calmodulin content in synaptic plasma membranes by glucocorticoids

Synaptic plasma membranes (SPM) from the brain are known to have specific binding sites for several steroid hormones, but the mechanisms of membrane transduction of steroid signals is not understood. In this study, corticosterone was found to prevent temperature-dependent dissociation of endogenous calmodlin (CaM) from highly purified SPM from rat cerebral cortex. The steroid stabilizes Ca²⁺-dependent membrane binding of endogenous CaM (78% of total CaM), whereas Ca²⁺-independent binding of CaM (the other 22%) is not affected. The stabilization of membrane binding of endogenous CaM by corticosterone is concentration-dependent, with the maximal effect occurring at steroid concentration of 1 M. The EC₅₀ is estimated as 130 nM, which is almost identical to the K_d of specific binding of the steroid to SPM (120 nM) reported previously. The effect in stabilizing membrane binding of CaM is specific to corticosterone and other glucocorticoids (cortisol, dexamethasone and triamcinolone); gonadal steroids (17-estradiol, progesterone and testosterone) are ineffective. Furthermore, corticosterone administration in vivo (2 mg/kg, i.p.) produced a rapid increase of CaM content in SPM, occurring within 5 min after steroid injection and persisting for at least 20 min. Since CaM mediates a variety of biochemical processes in synaptic membranes, we hypothesize that the effect of glucocorticoids in promoting membrane binding of CaM may lead to a cascade of consequences in synaptic membrane function.Special issue dedicated to Dr. Sidney Ochs.     

Effects of Ca(II) ions on Mn(II) dynamics in chick glia and rat astrocytes: Potential regulation of glutamine synthetase

Previous studies have demonstrated that in glia and astrocytes Mn(II) is distributed with ca. 30–40% in the cytoplasm, 60–70% in mitochondria. Ca(II) ions were observed to alter both the flux rates and distribution of Mn(II) ions in primary cultues of chick glia and rat astrocytes. External (influxing) Ca(II) ions had the greatest effect on Mn(II) uptake and efflux, compared to internal (effluxing) or internal-external equilibrated Ca(II) ions. External (influxing) Ca(II) ions inhibited the net rate and extent of Mn(II) uptake but enhanced Mn(II) efflux from mitochondria. These observations differ from Ca(II)–Mn(II) effects previously reported with brain (neuronal) mitochondria. Overall, increased cytoplasmic Ca(II) acts to block Mn(II) uptake and enhance Mn(II) release by mitochondria, which serve to increase the cytoplasmic concentration of free Mn(II). A hypothesis is presented involving external L-glutamate acting through membrane receptors to mobilize cell Ca(II), which in turn causes mitochondrial Mn(II) to be released. Because the concentration of free cytoplasmic Mn(II) is poised near the K_d for Mn(II) with glutamine synthetase, a slight increase in cytoplasmic Mn(II) will directly enhance the activity of glutamine synthetase, which catalyzes removal of neurotoxic glutamate and ammonia.     

Incorporation of [3H]ethanolamine into acetylcholine by a human cholinergic neuroblastoma clone

Human neuroblastoma cholinergic LA-N-2 cells were used as an experimental model to test the possibility that the methylation of phosphoethanolamine (PEtn) to phosphocholine (PCho) and free choline (Cho) (Andriamampandry et al. 1989) could contribute to acetylcholine (AcCho) synthesis. LA-N-2 cells were incubated with [³H]Cho for 90 min and 22.7% of the radioactivity was present in PCho, 18.5% in free Cho and 4.8% as AcCho. The ratio of Cho/AcCho, however, was of about 1 after 16 hours of incubation. The incorporation of 10M [³H]ethanolamine (Etn) into MeEtn, PMeEtn, PMe₂Etn and their corresponding phospholipids was reduced in cells incubated in medium containing 7.2M choline as compared to cells incubated in medium devoid of choline indicating that the lack of Cho from the incubation medium stimulated the conversion of PEtn to Cho water soluble derivatives. Incubation of LA-N-2 cells with [³H]Etn led to the labelling of [³H]AcCho. Cultures incubated in parallel with [³H]Cho showed that roughly 10% of [³H]AcCho obtained after 16 hrs of incubation with the Cho label derived from [³H]Etn. The synthesis of Cho and AcCho from Etn may be enhanced after cellular differentiation induced by the growth of the cells in the presence of retinoic acid (RA). The results indicate that the methylation of [³H]Etn and/or of [³H]PEtn may be used by cholinergic neurons as precursor for AcCho.Abbreviations Etn ethanolamine - MeEtn monomethylethanolamine - Me₂Etn dimethylethanolamine - P- phosphoryl - AcCho acetylcholine - Ptd phosphatidyl - LPtd lysophosphatidyl - RA retinoic acid     

Spawning ofConger oceanicus andConger triporiceps (Congridae) in the Sargasso Sea and subsequent distribution of leptocephali

Synopsis Distribution of leptocephali ofConger in the Western North Atlantic Ocean was studied using specimens from our collections, specimens from other collections, and various existing collection records. The presence of leptocephali ofConger oceanicus andConger triporiceps < 30 mm long over deep water in the southwestern Sargasso Sea in autumn and winter implies a protracted spawning period there. The subtropical convergence zone, meandering east-west across the Sargasso Sea, is probably the northern limit of spawning of both species. Spawning may also occur close to the Bahamas and Antilles.C. triporiceps may spawn also in the Caribbean Sea judging by the capture of small leptocephali in the western Caribbean and of the more southerly continental distribution of its juveniles. The claim of Johannes Schmidt in 1931 that the EuropeanC. conger spawns across the North Atlantic into the western Sargasso Sea is probably incorrect, because leptocephali ofConger are rare in the eastern Sargasso Sea and becauseC. triporiceps, with myomere numbers overlapping those ofC. conger, was recently described in the western North Atlantic. With increasing size, leptocephali ofC. oceanicus and a portion ofC. triporiceps spread westward and northward in the Florida Current and Gulf Stream, but larger leptocephali especially ofC. triporiceps are found also in the Caribbean and Gulf of Mexico. Spawning ofC. oceanicus in the Sargasso Sea indicates that adults cross the Florida Current-Gulf Stream, and successful leptocephali cross the current in the opposite direction to colonize juvenile habitat on the continental shelf, a migratory pattern similar to that of the American eelAnguilla rostrata (Anguillidae).     

Fish species composition before and after construction of a main stem reservoir on the White River,Colorado

Synopsis The completion in the fall of 1984 of Taylor Draw Dam on the White River, Colorado, formed Kenney Reservoir — thus impounding the last significant free-flowing tributary in the Upper Colorado River Basin. Fishes were sampled above and below the dam axis prior to closure of the dam and in the reservoir and river downstream following impoundment. While immediate effects of the dam to the ichthyofauna included blockage of upstream migration to 80 km of documented range for endangered Colorado squawfish, the reservoir also proved to have profound delayed effects on the river's species composition. Pre-impoundment investigations in 1983–1984 showed strong domination by native species above, within, and below the reservoir basin. By 1989–1990, non-native species comprised roughly 90% of the fishes collected in the reservoir and 80% of the fishes collected in the river below the dam. Initially, fathead minnow, whose numbers quickly increased in the new reservoir, dominated all post-impoundment collections, but red shiner became the most abundant fish collected in the river below the dam by 1989–1990. While agency stocking programs for the reservoir sought to emphasize a sport fishery for salmonids, primarily rainbow trout, local enthusiasm for warmwater sport fishes resulted in illicit transfers of these species from nearby impoundments. Several species, formerly rare or unreported in the White River in Colorado, including white sucker, northern pike, green sunfish, bluegill, largemouth bass and black crappie, were present in the river following impoundment. Our investigation indicates smaller-scale, main-stem impoundments that do not radically alter hydrologic or thermal regimes can still have a profound influence on native ichthyofauna by facilitating establishment and proliferation of nonnative species.Cooperators are the U.S. Fish and Wildlife, the Colorado Division of Wildlife, and Colorado State University     

Genetic diversity in and phylogenetic relationships of the Brazilian endemic cotton,Gossypium mustelinum (Malvaceae)

Gossypium mustelinum, one of five tetraploid species in the cotton genus, is geographically restricted to a few states in NE Brazil. Allozyme analysis was used to assess levels and patterns of genetic diversity inG. mustelinum and its relationship to the other tetraploid species. Genetic variation was low, with only 6 of 50 loci examined being polymorphic, a mean of 1.14 alleles per locus and a mean panmictic heterozygosity of 0.08. These estimates are low relative to other tetraploid cotton species, but are typical of island endemics. Interpopulational genetic identities were uniformly high, lending support to the concept of there being only one wild species of Brazilian cotton. The limited allelic diversity observed was correlated with geographical distribution, although variability is so limited in the species that geographically marginal populations are electrophoretically ordinary. Phylogenetic and phenetic analyses demonstrate thatG. mustelinum is isolated among polyploid cotton species, occupying one of the three basal clades resulting from an early radiation of polyploid taxa subsequent to polyploid formation. We suggest thatG. mustelinum represents a paleoendemic that presently exists as a series of widely scattered, relictual populations. Despite several centuries of sympatric cultivation ofG. barbadense andG. hirsutum, there was little evidence of interspecific introgression of alleles from cultivated cottons intoG. mustelinum.     

樟脊网蝽生物学特性观察

樟脊网蝽是香樟的重要害虫,在上海1年发生4代。4月下旬越冬卵始孵,9月下旬开始出现越冬卵。成虫末见期在11月中旬。经室内饲养,樟脊网蝽第三代各龄若虫历期为：一龄61．45±7．8h,二龄48．00±7．6h,三龄43．43±7．6h,四龄51．00±8．0h,五龄70．50±7．5h,整个若虫期历期为281．92±14．8h。第三代野外雌雄比为1：4．07。第三代每雌产2～96粒。日最高产卵量为34粒／头,孤雌可产卵。10％灭百可2000倍稀释液和50％杀螟松2000倍稀释液喷雾防治效果可达93％以上。     

离体条件下诱导番茄果实状结构的再生

以番茄（Ｌｙｃｏｐｅｒｓｉｃｏｎ ｅｓｃｕｌｅｎｔｕｍ Ｍｉｌｌ．）雌蕊和幼果的组织作外植体可以诱导果实状结构的再生。这种果实状结构在离体条件下能培养成熟,成熟时具红色。解剖观察表明：果实状结构由果肉和包围在外面的果皮组成,无种子和胎座。外源激素和外植体年龄的试验揭示：１．以雌蕊组织作外植体时,仅附加外源细胞分裂素就可以诱导果实状结构的再生,外源生长素似乎不是必需的,最高的诱导频率（５０．０％ ）出现在仅附加玉米素０．５ ｍ ｇ／Ｌ的组合。２．从直径４—１２ ｍ ｍ 的幼果上分离的外植体在附加外源激素的培养基上均可诱导果实状结构的再生,但只有从直径８ ｍ ｍ 的果实分离的组织块作外植体并将它们培养在６－ＢＡＰ ２ ｍ ｇ／Ｌ,ＮＡＡ０．１ ｍ ｇ／Ｌ的培养基上时,果实状结构的诱导频率最高（６２．５％ ）。为了探讨在果实状结构再生中表现出来的细胞全能性的表达,提出了植物细胞全能性的部分表达（Ｐａｒｔｉａｌｅｘｐｒｅｓｓｉｏｎ ｏｆｐｌａｎｔ ｃｅｌｌｔｏｔｉｐｏｔｅｎｃｙ）的概念并进行了讨论。     

河西走廊不同生态型芦苇核酸代谢季节动态研究

分布在甘肃河西走廊的４ 种生态型芦苇（Ｐｈｒａｇｍ ｉｔｅｓｃｏｍ ｍ ｕｎｉｓＴｒｉｎ．）的核酸代谢季节变化有差异。盐化草甸芦苇ＲＮＡ 含量持续增加,ＤＮＡ 含量相对稳定,其它３ 种生态型芦苇的ＲＮＡ 和ＤＮＡ 含量以５月份为最高。过渡带芦苇的ＲＮＡ 含量、沼泽芦苇及沙丘芦苇的ＤＮＡ含量９ 月份略有增高。盐化草甸芦苇与过渡带芦苇的ＤＮａｓｅ和ＲＮａｓｅ的活性７ 月份最高,沼泽芦苇与沙丘芦苇的ＤＮａｓｅ和ＲＮａｓｅ活性５—９ 月份呈增高趋势。盐化草甸芦苇的ＤＮＡ 和ＲＮＡ 合成活性不断升高,过渡带芦苇和沼泽芦苇的ＤＮＡ 和ＲＮＡ 合成活性及沙丘芦苇的ＲＮＡ 合成活性５—９月份均降低,仅沙丘芦苇的ＤＮＡ合成活性增强。ＲＮＡ 聚丙烯酰胺梯度凝胶电泳分析结果表明,４ 种生态型芦苇均含有２５Ｓ、２３Ｓ、１８Ｓ、１６Ｓ大分子量ｒＲＮＡ 和小分子量５．８Ｓ、５Ｓ、４．５ＳｒＲＮＡ 及４ＳｔＲＮＡ。大分子量ＲＮＡ 的含量高于小分子量ＲＮＡ 含量。不同生态型及同一生态型芦苇的不同发育时期,相同的ＲＮＡ 组分含量各不相同。且发育过程中２３Ｓ、１８Ｓ、１６ＳｒＲＮＡ 在不同月份发生不同程度的降解。由此,我们认为,核酸代谢的差异性是４ 种生态型由生长转入衰