bluuebunny/crossref_metadata_2025 huggingface dataset:
The biogeography of prediction error: why does the introduced range of the fire ant over‐predict its native range?
Authors: Fitzpatrick Matthew C. , Weltzin Jake F. , Sanders Nathan J. , Dunn Robert R.
Published: December 2006

Aim  The use of species distribution models (SDMs) to predict biological invasions is a rapidly developing area of ecology. However, most studies investigating SDMs typically ignore prediction errors and instead focus on regions where native distributions correctly predict invaded ranges. We investigated the ecological significance of prediction errors using reciprocal comparisons between the predicted invaded and native range of the red imported fire ant (Solenopsis invicta) (hereafter called the fire ant). We questioned whether fire ants occupy similar environments in their native and introduced range, how the environments that fire ants occupy in their introduced range changed through time relative to their native range, and where fire ant propagules are likely to have originated.

Location  We developed models for South America and the conterminous United States (US) of America.

Methods  We developed models using the Genetic Algorithm for Rule‐set Prediction (GARP) and 12 environmental layers. Occurrence data from the native range in South America were used to predict the introduced range in the US and vice versa. Further, time‐series data recording the invasion of fire ants in the US were used to predict the native range.

Results  Native range occurrences under‐predicted the invasive potential of fire ants, whereas occurrence data from the US over‐predicted the southern boundary of the native range. Secondly, introduced fire ants initially established in environments similar to those in their native range, but subsequently invaded harsher environments. Time‐series data suggest that fire ant propagules originated near the southern limit of their native range.

Conclusions  Our findings suggest that fire ants from a peripheral native population established in an environment similar to their native environment, and then ultimately expanded into environments in which they are not found in their native range. We argue that reciprocal comparisons between predicted native and invaded ranges will facilitate a better understanding of the biogeography of invasive and native species and of the role of SDMs in predicting future distributions.
Differential effects of past climate warming on mountain and flatland species distributions: a multispecies North American mammal assessment
Authors: Guralnick Robert
Published: December 2006

Aim The magnitude of predicted range shifts during climate change is likely to be different for species living in mountainous environments compared with those living in flatland environments. The southern edges of ranges in mountain species may not shift northwards during warming as populations instead migrate up available elevational gradients; overall latitudinal range appears therefore to expand. In contrast, flatland species should shift range centroids northwards but not expand or contract their latitudinal range extent. These hypotheses were tested utilizing Late Pleistocene and modern occurrence data.

Location North America.

Methods The location and elevation of modern and Late Pleistocene species occurrences were collected from data bases for 26 species living in mountain or flatland environments. Regressions of elevation change over latitude, and southern and northern range edges were calculated for each species for modern and fossil data sets. A combination of regressions andanovas were used to test whether flatland species shift range edges and latitudinal extents more than mountain species do.

Results Flatland species had significantly larger northward shifts at southern range edges than did mountain‐dwelling species from the Late Pleistocene to the present. There was also a significant negative correlation between the amount of change in the latitude of the southern edge of the range and the amount of elevational shifting from the Late Pleistocene to the present. Although significant, onlyc. 25% of the variance could be explained by this relationship. In addition, there was a weak indication that overall range expansion was less in flatland‐dwelling than in mountain‐dwelling species.

Main conclusions The approach used here was to examine past species’ range responses to warming that occurred after the last ice ages as a means to better predict potential future responses to continued warming. The results confirm predictions of differential southern edge and overall range shifts for species occupying mountain and flatland regions in North America. The findings may be broadly applicable in other regions, thus allowing better modelling of future range and distribution related responses.
The role of land cover in bioclimatic models depends on spatial resolution
Authors: Luoto Miska , Virkkala Raimo , Heikkinen Risto K.
Published: December 2006

Aim  We explored the importance of climate and land cover in bird species distribution models on multiple spatial scales. In particular, we tested whether the integration of land cover data improves the performance of pure bioclimatic models.

Location  Finland, northern Europe.

Methods  The data of the bird atlas survey carried out in 1986–89 using a 10 × 10 km uniform grid system in Finland were employed in the analyses. Land cover and climatic variables were compiled using the same grid system. The dependent and explanatory variables were resampled to 20‐km, 40‐km and 80‐km resolutions. Generalized additive models (GAM) were constructed for each of the 88 land bird species studied in order to estimate the probability of occurrence as a function of (1) climate and (2) climate and land cover variables. Model accuracy was measured by a cross‐validation approach using the area under the curve (AUC) of a receiver operating characteristic (ROC) plot.

Results  In general, the accuracies of the 88 bird–climate models were good at all studied resolutions. However, the inclusion of land cover increased the performance of 79 and 78 of the 88 bioclimatic models at 10‐km and 20‐km resolutions, respectively. There was no significant improvement at the 40‐km resolution. In contrast to the finer resolutions, the inclusion of land cover variables decreased the modelling accuracy at 80km resolution.

Main conclusions  Our results suggest that the determinants of bird species distributions are hierarchically structured: climatic variables are large‐scale determinants, followed by land cover at finer resolutions. The majority of the land bird species in Finland are rather clearly correlated with climate, and bioclimate envelope models can provide useful tools for identifying the relationships between these species and the environment at resolutions ranging from 10 km to 80 km. However, the notable contribution of land cover to the accuracy of bioclimatic models at 10–20‐km resolutions indicates that the integration of climate and land cover information can improve our understanding and model predictions of biogeographical patterns under global change.
Patterns in species richness and endemism of European freshwater fish
Authors: Reyjol Yorick , Hugueny Bernard , Pont Didier , Bianco Pier Giorgio , Beier Ulrika , Caiola Nuño , Casals Frederic , Cowx Ian , Economou Alcibiades , Ferreira Teresa , Haidvogl Gertrud , Noble Richard , De Sostoa Adolfo , Vigneron Thibault , Virbickas Tomas
Published: December 2006

Aim  To analyse the patterns in species richness and endemism of the native European riverine fish fauna, in the light of the Messinian salinity crisis and the Last Glacial Maximum (LGM).

Location  European continent.

Methods  After gathering native fish faunistic lists of 406 hydrographical networks, we defined large biogeographical regions with homogenous fish fauna, based on a hierarchical cluster analysis. Then we analysed and compared the patterns in species richness and endemism among these regions, as well as species–area relationships.

Results  Among the 233 native species present in the data set, the Cyprinidae family was strongly dominant (> 50% of the total number of species). Seven biogeographical regions were defined: Western Peri‐Mediterranea, Central Peri‐Mediterranea, Eastern Peri‐Mediterranea, Ponto‐Caspian Europe, Northern Europe, Central Europe and Western Europe. The highest regional species richness was observed for Central Peri‐Mediterranea and Ponto‐Caspian Europe. The highest endemic richness was found in Central Peri‐Mediterranea. Species–area relationships were characterized by high slope values for Peri‐Mediterranean Europe and low values for Central and Western Europe.

Main conclusions  The results were in agreement with the ‘Lago Mare’ hypothesis explaining the specificity of Peri‐Mediterranean fish fauna, as well as with the history of recolonization of Central and Western Europe from Ponto‐Caspian Europe following the LGM. The results also agreed with the mechanisms of speciation and extinction influencing fish diversity in hydrographical networks. We advise the use of the seven biogeographical regions for further studies, and suggest considering Peri‐Mediterranean Europe and Ponto‐Caspian Europe as ‘biodiversity hotspots’ for European riverine fish.
Does versatility as measured by geographic range, bathymetric range and morphological variability contribute to taxon longevity?
Authors: Liow Lee Hsiang
Published: December 2006

Aim  This paper aims to examine the relationship between versatility as measured by geographic range, bathymetric range and morphological variability (species and subspecies richness and the occurrence of morphologically highly variable populations), and the geologic longevities of trachyleberidid ostracode species and genera, while accounting for sampling biases and other confounding factors.

Location  Global.

Methods  A large database of occurrence records of species of the family Trachyleberididae s.l. was analysed. The relationships between genus and species longevity and the above mentioned variables were examined singly and in concert. Re‐analyses of subsets of data and rarefaction techniques were employed to account for sampling biases, while randomization was used to account for autocorrelation of variables.

Results  The mean number of occurrence records, and latitudinal and longitudinal ranges, were strongly and positively correlated with genus and species longevities. The number of bathymetric zones occupied by genera had no consistent bearing on their longevities, but species data subsets tended to indicate significant positive relationships between bathymetric range and longevities. Species richness was significantly and positively correlated with genus longevities. Species and genera with subspecies and species with high morphological variability all had significantly greater longevities. Genus‐level characteristics can be explained largely by species‐level characteristics, including longevity, latitudinal ranges and bathymetric ranges to a lesser degree. However, genus longevity was best explained by species richness and genus age, even for extinct genera, while species longevity was best explained by species latitudinal range.

Main conclusions  In spite of the incompleteness of the fossil record, we can control for biasing factors and still confidently draw the conclusion that both ecological and evolutionary versatility contribute to lineage longevity, beyond the shorter temporal observation windows available to most ecological studies.
Modification of 5′‐Nucleotidase Activity by Divalent Cations and Nucleotides
Authors: Mallol Josefa , Bozal Jorge
Published: December 2006

Abstract: The 5′‐nucleotidase activity of the purified cytoplasmic fraction preparation of bovine brain does not depend on the presence of the divalent metal ions Mg2+, Ca2+, and Cu2+ in the incubation medium. The Zn2+ ion (0.5 mM) causes total enzyme inhibition. Although EDTA and 8‐hydroxyquinoline inhibit the 5′‐nucleotidase from this source, it has not been possible to show the existence of metal ions in the enzyme molecule. The inhibition of 5′nucleotidase by EDTA is progressive and irreversible; when the enzyme is not preincubated with EDTA, the inhibition is overridden by metal ions. The purines (except xanthine, 0.3 mM), pyrimidines, and their nucleosides do not affect the 5′‐nucleotidase activity. The nucleoside di‐ and triphosphates are competitive enzyme inhibitors against 5′‐AMP as substrate. The K1 values of the diphosphates are lower than those determined for the corresponding triphosphates. The inhibition caused by the above nucleotides is reversed, partly or wholly, by Mg2+, depending on the molar ratio between the effectors. The inhibitory action of the ‐SH group reagents on the 5′‐nucleotidase activity is weak and reversible.
Characterization and Biosynthesis of Soluble and Membrane‐Bound Carbonic Anhydrase in Brain
Authors: Sapirstein Victor S. , Strocchi Paola , Wesolowski Mary , Gilbert Jeffrey M.
Published: December 2006

Abstract: Carbonic anhydrase from both the cytoplasmic and membrane fractions of the forebrains of rats was characterized with respect to enzymatic activity, immunoreactivity, and in vitro biosynthesis. A procedure for the rapid purification of both membrane‐bound and soluble brain carbonic anhydrase is presented that permits retention of full enzymatic activity. Both forms of the enzyme were found to show specific activities of approximately 5500 Units/mg protein when CO2 hydrating activity was determined. In addition, they exhibited similar esterase activity when assayed with p‐nitrophenyl acetate. The membrane‐bound form, although requiring detergent for extraction from membranes, was freely soluble in aqueous buffers after purification. The molecular weights of both soluble and membrane‐bound carbonic anhydrase are 30,000 daltons, and mixing experiments failed to show any significant differences with respect to size. The two forms also exhibit isoelectric points of 7.2. However, the two proteins were found to differ in two respects. Complement fixation indicated that antibodies to soluble carbonic anhydrase had a higher affinity for the soluble form than for the membrane‐bound form. The failure to observe any precursor‐product relationship between these two proteins with pulse chase studies and the establishment that carbonic anhydrase‐like proteins are synthesized on both free polysomes and the rough endoplasmic reticulum indicated that these proteins are synthesized by two separate mechanisms. In vitro synthesis on both free and bound polysomes was determined by two independent methods using different antibodies and different analytical procedures. The basis for these findings and their physiologic importance are discussed.
High‐Affinity Uptake of [3H]Norepinephrine by Primary Astrocyte Cultures and Its Inhibition by Tricyclic Antidepressants
Authors: Kimelberg Harold K. , Pelton E. Williams
Published: December 2006

Abstract: Primary astrocyte cultures from neonatal rat brains show uptake of [3H]norepinephrine ([3H]NE). This uptake has a high‐affinity component with an apparent Km of approximately 3 × 10−7 M. At 10−7 M [3H]NE both the initial rate of uptake and steady‐state content of [3H]NE is inhibited by up to 95% by omission of external Na+. The Na+‐dependent component of this uptake is totally inhibited by the tricyclic antidepressants desipramine (DMI) and amitryptyline with IC50 values of 2 × 10−9 and 4 × 10−8 M, respectively. Inhibition of [3H]NE uptake by DMI shows competitive kinetics. These characteristics are essentially identical to those found for high‐affinity uptake of NE in total membrane or synaptosome fractions from rodent brains and suggests that such uptake in neural tissue is not exclusively neuronal.
Phospholipid Synthesis in the Squid Giant Axon: Incorporation of Lipid Precursors
Authors: Gould R. M. , Pant H. , Gainer H. , Tytell M.
Published: December 2006

Abstract: The squid giant axon and extruded axoplasm from the giant axon were used to study the capacity of axoplasm for phospholipid synthesis. Extruded axoplasm, suspended in chemically defined media, catalyzed the synthesis of phospholipids from all of the precursors tested. 32P‐Labeled inorganic phosphate and γ‐labeled ATP were actively incorporated into phosphatidylinositol phosphate, while [2‐3H]myo‐inositol and l‐[3H(G)]serine were actively incorporated into phosphatidylinositol and phosphatidylserine, respectively. Though less well utilized, [2‐3H]glycerol was incorporated into phosphatide acid, phosphatidylinositol, and triglyceride, and [methyl‐3H]choline and [1‐3H]ethanolamine were incorporated into phosphatidylcholine and phosphatidylethanolamine, respectively. Isolated squid giant axons were incubated in artificial seawater containing the above precursors. The axoplasm was extruded following the incubations. Although most of the product lipids were recovered in the sheath (composed of cortical axoplasm, axolemma, and surrounding satellite cells), significant amounts (4–20%) were present in the extruded axoplasm. With tritiated choline and myo‐inositol, the major labeled phospholipids found in both the extruded axoplasm and the sheath were phosphatidylcholine and phosphatidylinositol, respectively. With both glycerol and phosphate, phosphatidylethanolamine was a major labeled lipid in both axoplasm and sheath. These findings demonstrate that all classes of phospholipids are formed by endogenous synthetic enzymes in axoplasm. In addition, we feel that the different patterns of incorporation by intact axons and extruded axoplasm indicate that surrounding sheath cells contribute lipids to axoplasm. A comprehensive picture of axonal lipid metabolism should include axoplasmic synthesis and glial‐axon transfer as pathways complementing the axonal transport of perikaryally formed lipids.
Phospholipid Synthesis in the Squid Giant Axon: Enzymes of Phosphatidylinositol Metabolism
Authors: Gould R. M. , Spivack W. D. , Robertson D. , Poznansky M. J.
Published: December 2006

Abstract: We examined the properties of several enzymes of phospholipid metabolism in axoplasm extruded from squid giant axons. The following synthetic enzymes, CDP‐diglyceride: inositol transferase (EC 2.7.8.11), ATP:diglyceride phosphotransferase, diglyceride kinase (EC 2.7.2.‐), and phosphatidylinositol kinase (EC 2.7.1.67), were all present in axoplasm. Phospholipid exchange proteins, which catalyzed the transfer of phosphatidylinositol and phosphatidylcholine between membrane preparations and unilamellar lipid vesicles, were also found. However, we did not find conditions under which the synthesis of CDP‐diglyceride, phosphatidyl serine, and phosphatidylinositol‐4,5‐diphosphate could be measured. Subcellular fractionation by differential centrifugation showed that the axoplasmic inositol transferase and phosphatidylinositol kinase activities were largely “microsomal,” while the diglyceride kinase and exchange protein activities were primarily “cytosolic.”
Effects of Monensin on Posttranslational Processing of Myelin Proteins
Authors: Townsend Laurace E. , Benjamins Joyce A.
Published: December 2006

Abstract: Rat brain slices were incubated with [3H]palmitic acid and [14C]glycine to label the lipid and protein moieties, respectively, of myelin proteolipid protein (PLP). The effects of monensin on posttranslational processing of proteins were examined by measuring the appearance of [14C]glycine‐ and [3H]palmitate‐labeled proteins in myelin and myelin‐like fractions. At 0.01 and 0.10 μM, monensin did not appreciably affect total lipid or protein synthesis; higher concentrations caused increased inhibition. Monensin at 0.10 μM markedly decreased the appearance of [14C]glycine‐labeled PLP in myelin, but had little effect on the 14C basic proteins or the incorporation of [3H]palmitic acid into total or myelin PLP. The same relative effect was apparent at higher monensin concentrations. In the myelin‐like fraction, monensin at 0.10 μM also depressed entry of [14C]glycine into protein comigrating with PLP, and again had no effect on incorporation of [3H]palmitic acid. In addition, monensin increased the [3H]palmitate label associated with two high‐molecular‐weight proteins in the myelin‐like fraction with no concomitant increase in [14C]glycine label.
Pyruvate Dehydrogenase Phosphate (PDHb) Phosphatase in Brain: Activity, Properties, and Subcellular Localization
Authors: Sheu Kwan‐Fu Rex , Lai James C. K. , Blass John P.
Published: December 2006

Abstract: The activity of pyruvate dehydrogenase phosphate (PDHb) phosphatase in rat brain mitochondria and homogenate was determined by measuring the rate of activation of purified, phosphorylated (i.e., inactive) pyruvate dehydrogenase complex (PDHC), which had been purified from bovine kidney and inactivated by phosphorylation with Mg·ATP. The PDHb phosphatase activity in purified mitochondria showed saturable kinetics with respect to its substrate, the phospho‐PDHC. It had a pH optimum between 7.0 and 7.4, depended on Mg and Ca, and was inhibited by NaF and K‐phosphate. These properties are consistent with those of the highly purified enzyme from beef heart. On subcellular fractionation, PDHb phosphatase copurified with mitochondrial marker enzymes (fumarase and PDHC) and separated from a cytosolic marker enzyme (lactate dehydrogenase) and a membrane marker enzyme (acetylcholinesterase), suggesting that it, like its substrate, is located in mitochondria. PDHb phosphatase had similar kinetic properties in purified mitochondria and in homogenate: dependence on Mg and Ca, independence of dichloroacetate, and inhibition by NaF and K‐phosphate. These results are consistent with there being only one type of PDHb phosphatase in rat brain preparations. They support the validity of the measurements of the activity of this enzyme in brain homogenates.
On the Ability of Galactose to Influence Hexose and Amino Acid Uptake by Isolated Rat Brain Capillaries
Authors: Segal Stanton , Hwang Shing Mei
Published: December 2006

Abstract: The uptake of glucose, 2‐deoxyglucose, proline, methionine, and α‐methylamino isobutyric acid was studied in brain capillaries preincubated with 50 mM galactose either in vitro or isolated from galactose‐fed rats. The uptake was not decreased in both cases. The linear rate of glucose oxidation by capillaries was also not altered by preincubation with galactose.
Protein Components of the Purified Sodium Channel from Rat Skeletal Muscle Sarcolemma
Authors: Barchi Robert L.
Published: December 2006

Abstract: Sensitive detection systems have been used to study the protein components of the sodium channel purified from rat skeletal muscle sarcolemma. This functional, purified sodium channel contains at least three subunits on 7–20% gradient sodium dodecyl sulfate (SDS)‐polyacrylamide gel electrophoresis: a large glycoprotein which migrates anomalously in the high‐molecular‐weight range, a 45,000 molecular weight polypeptide, and a third protein often seen as a doublet at 38,000. The large glycoprotein runs as a diffuse band and stains very poorly with Coomassie blue, but is adequately visualized with silver staining or iodination followed by autoradiography. This glycoprotein exhibits anomalous electrophoretic behavior in SDS‐polyacrylamide gels. The apparent molecular weight of the center of the band varies from ∼230,000 on 13% acrylamide gels to ∼130,000 on 5% gels; on 7–20% gradient gels a value of 160,000 is found. Plots of relative migration versus gel concentration suggest an unusually high apparent free solution mobility. Lectin binding to purified channel peptides separated by gel electrophoresis indicates that the large glycoprotein is the only subunit that binds either concanavalin A or wheat germ agglutinin, and this component has high binding capacity for both lectins. The smaller channel components run consistently at 45,000 and 38,000 molecular weight in a variety of gel systems and do not appear to be glycosylated.
Acetylcholine Synthesis and Accumulation in the CNS of Drosophila Larvae: Analysis of shibirets, a Mutant with a Temperature‐Sensitive Block in Synaptic Transmission
Authors: Wu Chun‐Fang , Berneking James M. , Barker David L.
Published: December 2006

Abstract: A radiochemical method is applied to the study of neurotransmitter metabolism in Drosophila. The larval CNS is a favorable system for analyzing acetylcholine (ACh) metabolism, since the pool of [3H]ACh rapidly reaches a steady state with a high ratio of intracellular [3H]ACh to [3H]choline. A temperature‐sensitive paralytic mutant, shibirets, shows reduced [3H]ACh accumulation at the restrictive temperature. This reduction is not the result of decreased synthesis of [3H]ACh, but rather an abnormally rapid rate of release, which is not prevented by blocking tetrodotoxin‐sensitive nerve activity.
Characterization, Development, and Localization of the Deoxycytidine Phosphorylating Systems in Mammalian Brain
Authors: Spector Reynold , Huntoon Sheryl
Published: December 2006

Abstract: The accumulation of deoxycytidine by rabbit and mouse brain was studied in vitro. Brain slices from brain stem, cerebellum, and forebrain of rabbits of various ages (1 day to 2.5 years) and forebrain from adult mice were incubated for various times in artificial CSF containing 6 nM [3H]deoxycytidine at 37°C under 95% O2/5% CO2. Rabbit and mouse brain slices of all ages accumulated [3H]deoxycytidine by a saturable system (IC50 = 4 μM) and converted it to [3H]deoxycytidine phosphates and [3H]DNA. When slices from all brain regions of 1‐day‐old rabbits were incubated in 6 nM [3H]deoxycytidine for 30 min, tissue‐to‐medium ratios of 3H were between 1.2 and 2.5 and declined with age, except in cortex; the percentages of total 3H in perchloric acid homogenates of brain slices as [3H]DNA were 10–24% and declined to low levels in middle age. However, at all ages and in all regions tested, 30–85% of the [3H]deoxycytidine within the slices was phosphorylated. After homogenization and subcellular fractionation of the brain slices incubated in [3H]deoxycytidine for 30 min, the highest percentage of [3H]deoxycytidine phosphates plus [3H]DNA was present in the nuclear and mitochondrial fractions of all brain regions. Deoxycytidine phosphates were synthesized from deoxycytidine in all brain regions tested into middle age.
Hyperthermia Induces the Synthesis of a Heat Shock Protein by Polysomes Isolated from the Fetal and Neonatal Mammalian Brain
Authors: Brown Ian R.
Published: December 2006

Abstract: Analysis of the cell‐free translation products of polysomes isolated from fetal brain and other organs indicates that elevation of maternal body temperature induces the synthesis of a heat shock protein of molecular weight 74,000 (74K). The newborn mammal is particularly sensitive to induction of the 74K protein. As early postnatal development proceeds, higher body temperatures are required to induce synthesis of the 74K heat shock protein.
Localization of Membrane‐Bound Catechol‐O‐Methyltransferase
Authors: Rivett A. Jennifer , Francis Andrew , Roth Jerome A.
Published: December 2006

Abstract: Previous studies of the distribution of catechol‐O‐methyltransferase (COMT) have concentrated on the soluble enzyme activity. In this study the activity of the membrane‐bound enzyme was determined in different brain regions and peripheral tissues of the rat. Membrane‐bound COMT, like the soluble enzyme, has a general distribution with high levels in liver, kidney, and vas deferens. However, the ratio of membrane‐bound to soluble activity varies almost 30‐fold in different tissues, with the highest ratio in brain. Membrane‐bound activity varies twofold within brain. In view of their different localization and kinetic properties, it seems likely that the two forms of COMT have different functions in vivo.
Barium Evokes Glutamate Release from Rat Brain Synaptosomes by Membrane Depolarization: Involvement of K+, Na+, and Ca2+ Channels
Authors: Sihra Talvinder S. , Piomelli Daniele , Nichols Robert A.
Published: December 2006

Abstract: During K+ ‐induced depolarization of isolated rat brain nerve terminals (synaptosomes), 1 mM Ba2+ could substitute for 1 mM Ca2+ in evoking the release of endogenous glutamate. In addition, Ba2+ was found to evoke glutamate release in the absence of K+‐induced depolarization. Ba2+ (1–10 mM) depolarized synaptosomes, as measured by voltage‐sensitive dye fluorescence and [3H]‐tetraphenylphosphonium cation distribution. Ba2+ partially inhibited the increase in synaptosomal K+ efflux produced by depolarization, as reflected by the redistribution of radiolabeled 86Rb+. The release evoked by Ba2+ was inhibited by tetrodotoxin (TTX). Using the divalent cation indicator fura‐2, cytosolic [Ca2+] increased during stimulation by approximately 200 nM, but cytosolic [Ba2+] increased by more than 1 μM. Taken together, our results indicate that Ba2+ initially depolarizes synaptosomes most likely by blocking a K+ channel, which then activates TTX‐sensitive Na+ channels, causing further depolarization, and finally enters synaptosomes through voltage‐sensitive Ca2+channels to evoke neurotransmitter release directly. Though Ba2+‐evoked glutamate release was comparable in level to that obtained with K+‐induced depolarization in the presence of Ca2+, the apparent intrasynaptosomal level of Ba2+ required for a given amount of glutamate release was found to be several‐fold higher than that required of Ca2+.
Neuropeptide γ‐(l‐9)‐Peptide: A Major Product of the Posttranslational Processing of γ‐Preprotachykinin in Rat Tissues
Authors: Wang Yunxia , Bockman Charles S. , Lovas Sandor , Abel Peter W. , Murphy Richard F. , Conlon J. Michael
Published: December 2006

Abstract: γ‐Preprotachykinin mRNA is the most abundant tachykinin mRNA in rat tissues, but the pathway of posttranslational processing of its translation product is unknown. An antiserum was raised against the synthetic peptide Asp‐Ala‐Gly‐His‐Gly‐Gln‐lle‐Ser‐His [neuropeptide γ‐(1‐9)‐peptide, equivalent to γ‐preprotachykinin‐(72‐80)‐peptide], that showed <1% reactivity with intact neuropeptide γ and other tachykinins. Neuropeptide γ‐(1‐9)‐peptide was detected by radioimmunoassay in relatively high concentrations in extracts of regions of rat brain and gastrointestinal tract. These concentrations correlated with (r = 0.99), but were significantly (p < 0.05) less than, the concentrations of neurokinin A‐like immunoreactivity. The neuropeptide γ‐(1‐9)‐like immunoreactivity in an extract of rat brain was eluted from a reverse‐phase HPLC column in a single fraction with the same retention time as synthetic neuropeptide γ‐(1 ‐9)‐peptide. The synthetic peptide did not contract or relax isolated rat trachea, superior mesenteric artery, stomach fundus, or ileum, and the peptide did not affect the ability of neuropeptide 7 to contract the rat fundus. It is concluded that, in rat tissues, Lys70‐Arg71 in 7‐preprotachykinin is a major site of posttranslational processing, but the resulting product, neuropeptide γ‐(1‐9)‐peptide, is neither an agonist nor an antagonist at the neurokinin‐2 (NK‐2) receptor.
Identification of an Annexin‐Like Protein and Its Possible Role in the Aplysia Eye Circadian System
Authors: Raju Uma , Nunez‐Regueiro Marta , Cook Richard , Kaetzel Marcia A. , Yeung Sai‐Ching Jim , Eskin Arnold
Published: December 2006

Abstract: Light and serotonin regulate the phase of the circadian rhythm of the isolated eye of Aplysia. To screen for possible protein components of the eye circadian oscillator, we identified a number of proteins whose synthesis was altered in opposite ways by light and serotonin. The cellular function of one of these proteins was investigated by obtaining a partial amino acid sequence of it and by examining its immunoreactivity. A 38‐amino acid sequence was obtained from a 40‐kDa (isoelectric point 5.6) protein. A greater than 60% amino acid identity existed between this sequence and sequences of a family of calcium/phospholipid‐binding proteins called annexins. Furthermore, the 40‐kDa protein reacted with antibodies generated against a conserved amino acid sequence of annexins and with antibodies raised against human annexin I. The identification of the 40‐kDa, light‐ and serotonin‐regulated protein as an annexin led us to hypothesize that arachidonic acid metabolism plays a role in the Aplysia eye circadian system. To test this hypothesis, we examined the ability of an inhibitor of the arachidonic acid metabolic pathway to perturb the eye rhythm. Pulse treatments of isolated eyes with a lipoxygenase inhibitor, nordihydroguaiaretic acid, phase shifted the rhythm. The phase‐shifting ability of nordihydroguaiaretic acid suggests that arachidonic acid and some of its metabolites may play a role in the eye circadian system. The results of our studies raise the possibility that links may exist between the 40‐kDa annexin‐like protein, arachidonic acid metabolism, and the circadian oscillator.
D1 Dopamine Receptor Binding and mRNA Levels Are Not Altered After Neonatal 6‐Hydroxydopamine Treatment: Evidence Against Dopamine‐Mediated Induction of D1 Dopamine Receptors During Postnatal Development
Authors: Duncan Gary E. , Breese George R. , Criswell Hugh E. , Johnson Kevin B. , Schambra Uta B. , Mueller Robert A. , Caron Marc G. , Fremeau Robert T.
Published: December 2006

Abstract: The role of dopaminergic innervation on the postnatal developmental expression of D1 dopamine receptors was investigated. Bilateral destruction of dopa‐mine‐containing neurons was achieved by treating rats intracisternally with 6‐hydroxydopamine (6‐OHDA) on postnatal day 3, and rats were killed on day 21. To ensure effective reduction of D1 receptor activation by residual dopamine, a group of 6‐OHDA‐lesioned rats was given twice daily injections of the D1 receptor antagonist SCH‐23390, from day 4 to 20. D1 dopamine receptor binding was assessed in the caudate—putamen, nucleus accumbens, and olfactory tubercle by quantitative autoradiographic analysis of [3H]SCH‐23390 binding. In addition, the relative amount of D1A receptor mRNA was assessed by in situ hybridization of a 35S‐labeled riboprobe. In the developing rats, neither the amount of [3H]SCH‐23390 binding nor the amount of D1A receptor mRNA was altered by 6‐OHDA lesioning followed by chronic treatment with SCH‐23390. Thus, bilateral destruction of dopamine‐containing neurons and treatment with SCH‐23390 in neonatal rats did not interfere with the developmental expression of D1 receptors or alter the levels of mRNA that code for this receptor protein. Treatment of intact rats with SCH‐23390 from postnatal day 4 to 20 also did not alter [3H]SCH‐23390 binding or levels of D1 receptor mRNA. However, adult rats treated chronically with SCH‐23390 exhibited increased [3H]SCH‐23390 binding but did not show a significant change in D1 receptor mRNA levels.
Chronic Electroconvulsive Seizures Increase the Expression of Serotonin2 Receptor mRNA in Rat Frontal Cortex
Authors: Butler Marcus O. , Morinobu Shigeru , Duman Ronald S.
Published: December 2006

Abstract: The present study examines the influence of electroconvulsive seizure (ECS), as well as antidepressant drugs, on levels of serotonin2 (5‐HT2) receptor mRNA in rat frontal cortex. Using a sensitive RNase protective assay, preliminary studies demonstrated the predicted regional distribution for the 5‐HT2 receptor mRNA: levels of 5‐HT2 mRNA were highest in frontal cortex (2.58 amol/μg of total RNA), intermediate in neostriatum, thalamus, and midbrain, and lowest in hippocampus, cerebellum, and choroid plexus. Chronic (10 or 14 days), but not acute (1 or 3 days), ECS treatment significantly increased levels of 5‐HT2 receptor mRNA. ECS treatment resulted in a similar time‐dependent up‐regulation of 5‐HT2 receptor ligand binding; chronic, but not acute, ECS treatment significantly increased levels of [3H]ketanserin ligand binding, confirming previous reports. Northern blot analysis demonstrated that 5‐HT2 receptor mRNA occurs as two bands (∼5 and 6 kb in size), both of which were increased by chronic ECS treatment. The influence of antidepressant drug treatments on 5‐HT2 receptor mRNA was also examined. Chronic fluoxetine treatment increased levels of 5‐HT2 receptor mRNA, although levels of [3H]ketanserin ligand binding were not altered. In contrast, chronic administration of imipramine, mianserin, and tranylcypromine, treatments that decreased ligand binding, did not decrease levels of 5‐HT2 receptor mRNA. In fact, mianserin treatment caused a small, but significant, increase in levels of receptor mRNA. The results suggest that ECS up‐regulation of 5‐HT2 receptor mRNA could underlie the increased density of 5‐HT2 receptor binding sites in response to this treatment, but that other mechanisms likely operate in the down‐regulation of 5‐HT2 receptor ligand binding by antidepressant drug treatments.
A Neural Gene from Drosophila melanogaster with Homology to Vertebrate and Invertebrate Glutamate Decarboxylases
Authors: Phillips A. Marie , Salkoff Lawrence B. , Kelly Leonard E.
Published: December 2006

Abstract: Cross‐species hybridization has been used to isolate a second Drosophila gene, with homology to a feline glutamate decarboxylase (Gad) cDNA. The gene differs in sequence, chromosomal location, and spatial expression from the previously reported Drosophila Gad gene, but both encode proteins of 58 kDa. The derived amino acid sequence reveals a typical pyridoxal phosphate binding site and sequence homology consistent with a glutamate decarboxylase function. The protein includes an amino‐terminal polyasparagine sequence, and a /β‐pleated sheet region, with regularly spaced glutamine and arginine residues, not found in other decarboxylases. Expression in the adult is limited to the neuropil of the first optic ganglion and to regions of the thoracic musculature that may correspond to the location of motor neuron axons. This is consistent with a glial localization for the transcript. There is no overlap with the reported expression of Drosophila Gad. Although the molecular evidence suggests that this gene encodes a pyridoxal phosphate‐dependent decarboxylase, glutamate decarboxylase activity associated with this gene could not be demonstrated, and the in vivo substrate is unknown. It is possible that the protein encoded by this gene is novel, not only in sequence and spatial expression, but also in substrate specificity.
Low Selenium Diet Affects Monoamine Turnover Differentially in Substantia Nigra and Striatum
Authors: Castaño Angélica , Cano Josefina , Machado Alberto
Published: December 2006

Abstract: Turnover of dopamine, noradrenaline. serotonin, and their metabolites has been measured in striatum and substantia nigra of adult female rats that were fed control or selenium‐deficient diets for 15 days. In addition, the glutathione peroxidase activity has been studied. The most striking result was the increase of dopamine turnover (63%) and 3‐ methoxytyramine turnover (55%) in substantia nigra between control and experimental animals. On the other hand, no changes were found in the turnover rate of dopamine and its metabolites in the striatum. Likewise, no changes were found in noradrenaline turnover in substantia nigra. In the striatum, there was a significant increase of serotonin turnover versus no change for 5‐hydroxy‐3‐indoleacetic acid. However, in the substantia nigra, serotonin turnover did not show significant changes, whereas 5‐hydroxy‐3‐indoleacetic acid turnover decreased. At the same time, glutathione peroxidase activity significantly decreased in both structures after selenium‐deficient diets. These results suggest that a selenium‐deficient diet for a short period of time decreases brain protection. principally in the substantia nigra, against oxidative damage.
Selective Dephosphorylation of the Subunits of Skeletal Muscle Calcium Channels by Purified Phosphoprotein Phosphatases
Authors: Lai Yvonne , Peterson Blaise Z. , Catterall William A.
Published: December 2006

Abstract: Multiple sites on the α1 and β subunits of purified skeletal muscle calcium channels are phosphorylated by cyclic AMP‐dependent protein kinase, resulting in three different tryptic phosphopeptides derived from each subunit. Phosphoprotein phosphatases dephosphorylated these sites selectively. Phosphoprotein phosphatase 1 (PP1) and phosphoprotein phosphatase 2A (PP2A) dephosphorylated both α1 and β subunits at similar rates, whereas calcineurin dephosphorylated β subunits preferentially. PP1 dephosphorylated phosphopeptides 1 and 2 of the α1 subunit more rapidly than phosphopeptide 3. In contrast, PP2A dephosphorylated phosphopeptide 3 of the α1 subunit preferentially. All three phosphoprotein phosphatases preferentially dephosphorylated phosphopeptide 1 of the β subunit and dephosphorylated phosphopeptides 2 and 3 more slowly. Mn2+ increased the rate and extent of dephosphorylation of all sites by calcineurin so that >80% dephosphorylation of both α1 and β sub‐units was obtained. The results demonstrate selective dephosphorylation of different phosphorylation sites on the α1 and β subunits of skeletal muscle calcium channels by the three principal serine/threonine phosphoprotein phosphatases.
Absence of 6‐Hydroxydopamine in the Rat Brain After Treatment with Stimulants and Other Dopaminergic Agents: A Mass Fragmentographic Study
Authors: Karoum Farouk , Chrapusta Stanislaw J. , Egan Michael F. , Wyatt Richard Jed
Published: December 2006

Abstract: Formation of 6‐hydroxydopamine (6‐OHDA) from dopamine has been hypothesized to mediate neuro‐degeneration induced by some psychostimulants. Although the emergence of a 6‐OHDA‐like substance was reported in the striatum of methamphetamine‐treated rats, this substance has not been identified by a direct approach. We used mass fragmentography to search for 6‐OHDA in the rat frontal cortex and striatum after the administration of a number of drugs including 3,4‐dihy‐droxyphenyl‐L‐alanine, methamphetamine, amphetamine, and cocaine, all of which increase synaptic dopamine. No 6‐OHDA was detected after the acute systemic administration of these agents. Intraventricular administration of 6‐OHDA (10 μg/rat.) produced measurable concentrations of 6‐OHDA that were higher in the striatum than in the frontal cortex. Intraventricular administration of 2,4,5‐trihydroxy‐phenyl‐D,L‐alanine (6‐OHDOPA; 10 μg/rat) produced similar concentrations of 6‐OHDA in both regions. Pargyline, but not carbidopa (α‐methyldopahydrazine), enhanced the effect of intraperitoneal 6‐OHDOPA administration (80 mg/kg). We conclude that (1) 6‐OHDOPA can cross the blood‐brain barrier and is converted to 6‐OHDA in the brain, (2) 6‐OHDA is a substrate for monoamine oxidase(s) and therefore a search for its purported deaminated metabolite is warranted, and (3) acute treatment with the above stimulants either does not lead to the formation of 6‐OHDA or produces concentrations below the detection limit of the assay (<34 pg/mg of protein).
Posttranslational Processing of Carboxypeptidase E, a Neuropeptide‐Processing Enzyme, in AtT‐20 Cells and Bovine Pituitary Secretory Granules
Authors: Fricker Lloyd D. , Devi Lakshmi
Published: December 2006

Abstract: Carboxypeptidase E (CPE) functions in the posttranslational processing of peptide hormones and neurotransmitters. Like other peptide processing enzymes, CPE is present in secretory granules in soluble and membrane‐associated forms that arise from posttranslational processing of a single precursor, “proCPE.” To identify the intracellular site of proCPE processing, the biosynthesis and posttranslational processing were investigated in the mouse anterior pituitary‐derived cell line, AtT‐20. Following a 15‐min pulse with [35S]Met, both soluble and membrane‐bound forms of CPE were identified, indicating that the posttranslational processing event that generates these forms of CPE occurs in the endoplasmic reticulum or early Golgi apparatus. The relative proportion of soluble and membrane‐bound forms of CPE changed when cells were chased for 2 h at 37°C but was unaffected when cells were chased at either 20 or 15°C, suggesting that further processing of membrane forms to the soluble form occurs in a post‐Golgi compartment. Treatment of the cells with chloroquine did not alter the relative distribution of soluble and membrane forms, suggesting that an acidic compartment is not required for this processing event. Overexpression of CPE did not influence the distribution of soluble and membrane forms of CPE, indicating that the CPE‐processing enzymes are not rate‐limiting. To examine directly CPE‐processing enzymes, bovine anterior pituitary secretory vesicles were isolated. An enzyme activity that releases the membrane‐bound form of CPE was detected in the purified secretory vesicle membranes. This enzyme, which removes the C‐terminal region of CPE, is partially inhibited by EDTA and phenylmethylsulfonyl fluoride and is activated by CaCI2. Together, the data indicate that posttranslational processing of CPE occurs in secretory granules and that this activity may be mediated by a prohormone convertase‐like enzyme.
Further Characterization of the Long‐Term Effect of RU24722 on Tyrosine Hydroxylase in the Rat Locus Coeruleus
Authors: Schmitt Pascal , Reny‐Palasse Véronique , Bourde Odile , Garcia Christine , Pujol Jean‐Francois
Published: December 2006

Abstract: Recent data have indicated that the long‐lasting increase in tyrosine hydroxylase (TH) protein could be differently expressed in the anterior and posterior locus coeruleus (LC) after a single intraperitoneal injection of RU24722, which has been proposed as a potent activator of catecholaminergic systems. In the present study, we have evaluated the dose and time course responses and the effect of a repeated treatment with RU24722 at 3‐day intervals on TH protein level in the anterior and posterior rat LC. The results showed that RU24722 induces a long‐lasting increase of TH protein level in the anterior and posterior LC that was maximal 3 days following a single injection of 30 mg/kg. The increase in TH protein was maintained at a constant level after repeated administrations of RU24722 at 3‐day intervals. Furthermore, we have investigated whether the effect of the drug on TH protein could be modulated via several hormonal systems. The long‐term increase of TH steady‐state content after RU24722 was still observed 15 days after castration, adrenalectomy, hypophysectomy, and thyroidectomy. The initial steady‐state TH protein level was significantly higher in the anterior LC of thyroid‐ or hypophysectomized and in the posterior LC of hypophysectomized rats. However, this increase was reversed when animals were housed at 28°C.