bluuebunny/crossref_metadata_2025_split huggingface dataset:
Indirect determination of ephedrine in urine by differential pulse polarography
Authors: Hernandez L. , Zapardiel A. , Bermejo E. , Perez J. A. , Chicharro M. , Garijo M. J. 
Published: May 2005

AbstractThe nitrosation of ephedrine and the electrochemical reduction of N‐nitrosoephedrine were investigated by differential pulse polarography and have been optimized in order to attain the optimum analytical signal. Reduction of the N‐nitrosoephedrine was carried out in one irreversible, diffusion‐controlled step using potassium chloride‐hydrochloric acid. In 0.1 M hydrochloric acid the N‐nitrosoephedrine shows a well‐defined reduction peak at −0.77 V (vs. Ag/AgCl/ 3 M KCl). An indirect differential‐pulse polarographic method is described for the determination of ephedrine at levels higher than 2.5 μg per mL of urine. An extraction procedure with C18 cartridge and a fast and easy nitrosation reaction with sodium nitrite in 0.2 M phthalate potassium hydrogen is also described. Determination of 5 μg/mL of N‐nitrosoephedrine in urine samples of 4 mL was possible using the standard addition method, with a relative error of −4.0% and relative standard deviations no higher than 2.1%.
Amperometric sensor for fish freshness based on immobilized multi‐enzyme modified electrode
Authors: Hu Shengshui , Liu Chung‐Chiun 
Published: May 2005

AbstractAn amperometric biosensor for the determination of fish freshness has been developed by immobilizing 5′‐nucleotidase (NT), nucleoside phosphorylase (NP) and xanthine oxidase (XO) enzymes on a Nafion‐paraquat chemically modified glassy‐carbon working electrode. The sensing principle is based on the oxygen consumption in the enzymatic reaction catalyzed by xanthine oxidase immobilized in the matrix. The quantity of hypoxanthine (Hx), the combined amount of inosine (HxR) and Hx and the total quantity of inosine 5′‐monophosphate (IMP), HxR and Hx can be determined, respectively, by changing the medium conditions. This sensor system can be used to determine the freshness of fish. An indicator of fish freshness, K1, is defined as K1 = {[HxR] + [Hx]}/{[IMP] + [HxR] + [Hx]}. This biosensor prowides a reliable means for determining of Hx, HxR and IMP in fish samples and the freshness of the fish meat.
Electrochemistry of hexacoordinate silicon(IV) porphyrin complexes
Authors: Lorenz Carrie R. , Dewald Howard D. , Lemke Frederick R. 
Published: May 2005

AbstractCyclic voltammetry was used to characterize the oxidation‐reduction behavior of a series of novel hexacoordinate silicon(IV) porphyrin complexes. Each (Por)SiX2 [Por = the dianions of the porphyrins: tetrakis(p‐tolyl)porphyrin (TTP), tetraphenylporphyrin (TPP), tetrakis(p‐trifluoromethylphenyl)porphyrin (TTFP), octaethylporphyrin (OEP), × = F, Cl, O3SCF3] complex undergoes one to two oxidations and one to two reductions, all occurring at the porphyrin ring. No silicon(IV) reduction is observed for any of the porphyrin complexes. The effects of solvent, supporting electrolyte, substituents on the porphyrin ring, axial ligands, certral metal, and ruffling of the porphyrin ring are described.
Electrochemical detection of disodium 3,3′‐azobis‐(6‐hydroxy‐) benzoate (olsalazine sodium)
Authors: Eriksson Alf , Nyholm Leif 
Published: May 2005

AbstractElectrochemical detection of disodium 3,3′‐azobis‐(6‐hydroxy‐)benzoate, olsalazine sodium, in reversed phase liquid chromatography is shown to provide a detection limit of 40 fmol and a linear range extending up to 4 nmol for an injection volume of 20 μL. The method has been used for the determination of the solubility of olsalazine sodium in aqueous solutions. The solubility was found to be 2 × 10−8 M and 4 × 10−6 M at pH 1.0 and 3.5, respectively.
Voltammetric study of kinetin in a carbon fiber microelectrode. Determination by adsorptive stripping in apple extracts
Authors: Hernández Pedro , Patón Fernando , Hernández Lucas 
Published: May 2005

AbstractThis article presents an electroanalytical method of kinetin analysis using a carbon fiber microelectrode. Kinetin is one of the growth regulators in plants and belongs to the group of cytokinins. The adsorption process of the hormone to the microelectrode surface, previously subjected to electrochemical activation, permits a high degree of sensitivity in the quantification of kinetin in plant extracts.
A glucose amperometric sensor based on covalent immobilization of glucose oxidase in poly‐2‐aminoaniline film via chloranil on platinized platinum electrode
Authors: Losada José , Armada M. Pilar García 
Published: May 2005

AbstractThe construction and response of the immobilized enzyme chemically modified electrode as an amperometric sensor is described. Glucose oxidase (GOx) has been covalently bound to poly‐2‐aminoaniline (PAANI) film, formed onto a platinized Pt surface via a tetrachloro‐1,4‐p‐benzoquinone linkage. The steady‐state amperometric response of the sensor is investigated as a function of the glucose concentration, applied potential and platinum loading. The working potential for glucose determinations was +250mV (vs. SCE) and the biosensor exhibited a linear response in the range 0.2–20 mM with a response time that does not exceed 5 s.
Electrochemical quartz crystal microbalance study of the electrochemical behavior of riboflavin at gold electrodes
Authors: Wang Ying , Xu Bo , Zhu Guoyi , Wang Erkang 
Published: May 2005

AbstractThe electrochemical and adsorption behaviors of riboflavin (RF) at gold electrodes has been studied by using an electrochemical quartz crystal microbalance (EQCM). Useful information is obtained not only about electrochemical behavior but also about mass changes on the electrode surface. The electrochemical properties and frequency shifts were investigated in RF solutions at different pH values, concentrations and scan rates. Reversible voltammograms were observed for pH ⩽ 9.71. There was no electrochemical reaction for pH > 9.71. The maximum current response was obtained at about pH 8. The current response was proportional to the square root of scan rates when the concentration of RF was lower than 1.0 × 10−4 molL−1 (pH 6.92). On the contrary, at concentrations higher than 1.0 × 10−4 mol L−1 (pH 6.92), it was proportional to the scan rates.
Potentiometry with perchlorate and fluoroborate ion‐selective carbon paste electrodes
Authors: Ježková Jitka , Musilová Jarmila , Vytřas Karel 
Published: May 2005

AbstractPerchlorate and tetrafluoroborate ion‐selective carbon paste electrodes based on different moditied pasting liquids were prepared and their basic characteristics were tested in direct potentiometric measurements. Although the slopes of calibration plots, detection limits as well as selectivity coefficients were similar to those obtained with commercial liquid/plastic membrane type ion‐selective electrodes, the carbon pastes offered some advantages as more rapid response and very low ohmic resistance. The resulting electrodes were successfully applied in ion‐pair formation‐based potentiometric titrations of perchlorate, fluororate and iodide ions with cetylpyridinium chloride.
Selective effects of aniracetam across receptor types and forms of synaptic facilitation in hippocampus
Authors: Xiao Peng , Staubli Ursula , Kessler Markus , Lynch Gary 
Published: May 2005

AbstractAniracetam reversibly increased synaptic responses mediated by the AMPA but not the NMDA subclass of glutamate receptors in hippocampus and was considerably more potent than structurally similar nootropics. The drug had greater effects on field excitatory postsynaptic potentials (EPSPs) in the dentate gyrus and CA1 region than it did in the CA3 region, suggesting that it differentiates between variants of the AMPA receptor. Ligand binding to glutamate receptors in synaptosomal membrane fractions was minimally changed by aniracetam. Finally, the percent facilitation produced by aniracetam in the CA1 region was not reduced by any of three treatments (4‐aminopyridine, changes in extracellular calcium concentrations, paired‐pulse stimulation) that affect release but, in accord with a previous report, was substantially decreased by long‐term potentiation. These results support the conclusion that aniracetam selectively increases the conductance of a subgroup of synaptic AMPA receptors in hippocampus and suggest that receptor changes underlie the expression of long‐term potentiation.
Linear relationship between the maintenance of hippocampal long‐term potentiation and retention of an associative memory
Authors: Doyère Valérie , Laroche Serge 
Published: May 2005

AbstractThe hypothesis that the maintenance or decay of an associative memory trace after an extended retention interval is a function of the residual strength of the synapses originally strengthened during learning was examined in a classical conditioning paradigm in which high‐frequency stimulation of a hippocampal input—the medial perforant path—served as a conditioned stimulus. Rats received perforant path stimulus‐foot shock pairings while engaged in a previously acquired food‐motivated lever‐pressing task. Conditioned suppression of lever pressing was the behavioral measure of learning and retention of the association. Stimulus trains to the perforant path at an intensity above the threshold for eliciting a population spike induced long‐term potentiation of synaptic transmission in the dentate gyrus. Synaptic potentials recorded extracellularly in the dentate gyrus were subsequently monitored for 31 days to examine quantitatively the decay of synaptic potentiation, a period after which retention of the learned association was assessed. All rats learned the association to a similar extent and displayed equivalent amounts of long‐term potentiation by the end of conditioning. A slowly decaying function of synaptic potentiation was observed in remembering rats, i. e., rats with high retention performance after the 31‐day learning‐to‐retention interval, while forgetting was associated with a rapid decay of long‐term potentiation. Behavioral performance at the long‐term memory test was linearly correlated with the amplitude of long‐term potentiation maintained just prior to the retention test. The results favor the hypothesis that long‐term associative memory depends, at least in part, on the maintenance of elevated synaptic strengths in the pathway activated during learning and suggest a role for the lasting component of long‐term potentiation in the maintenance of memory.
Bilateral knife cuts to the perforant path disrupt spatial learning in the Morris water maze
Authors: Skelton Ronald W. , McNamara Robert K. 
Published: May 2005

AbstractBoth the hippocampus and the entorhinal cortex are known to be crucial for spatial learning, but the contribution of the pathway linking the two structures, the perforant path (PP), has never been tested in a spatial learning paradigm. The present study examined the role of the PP in spatial learning using the Morris water maze. Seven days after bilateral transection of the PP with a fine‐bladed knife, rats were habituated to the pool, then trained to swim from varying start locations to a platform submerged in a fixed location. After 28 training trials over 5 days, probe trials (without any platform present) were given to assess spatial memory for the location. Compared to sham‐operated controls, lesioned rats showed slower learning and poorer asymptotic performance in terms of both swim path distance and escape latency, and less preference for the correct quadrant during probe trials. When the platform location was “reversed” to the opposite quadrant, the lesioned rats again showed poorer learning, poorer asymptotic performance, and reduced preference for the correct quadrant on the probe trial. When tested with a visible platform whose position varied from trial to trial, lesioned rats performed as well as controls. These results are congruent with previous analyses of the contributions of the entorhinal cortex and hippocampus to spatial learning and suggest that for spatial learning, the PP is a critical functional link between these two structures.
Fast (beta) rhythms in the hippocampus: A review
Authors: Leung L. Stan 
Published: May 2005

AbstractSpontaneous or evoked brain activity in the hippocampus showed a 20–70 Hz beta rhythm under some conditions, typically during behavioral activation and accompanied by a theta rhythm. Beta rhythms are generated locally, perhaps by a recurrent feedback loop involving pyramidal cells and inhibitory interneurons. Modulation of the local circuit and rhythm by cholinergic inputs has also been demonstrated. Under some behavioral states, neural impulses modulated at the beta frequency may transmit preferentially through the trisynaptic circuit in the hippocampus. It is suggested that the beta rhythm may serve to establish transient physiological connections, reflected in coherence at the beta frequency, among neurons in the hippocampus and related structures. Thus, the beta rhythm may play an essential role in hippocampal function.
Maintained saturation of hippocampal long‐term potentiation does not disrupt acquisition of the eight‐arm radial maze
Authors: Robinson Gilbert B. 
Published: May 2005

AbstractThe present experiment examined the anterograde effect of bilateral saturation of long‐term potentiation (LTP) of the rat perforant path‐granule cell response on acquisition of the eight‐arm radial maze. To ensure maintained saturation, high‐frequency stimulation was applied to the perforant path immediately prior to each trial. LTP did not significantly increase the number of trials required for acquisition of the standard eight‐arm radial maze task. Furthermore, the magnitude of LTP did not correlate with the rate of acquisition. LTP also did not significantly affect the number of either working or reference memory errors during subsequent training with only four of the eight arms baited; both control and LTP rats made significantly more reference memory than working memory errors, with the number of both types of errors decreasing as training progressed. These results indicate that prior saturation of LTP within the perforant path‐dentate granule cell circuit does not affect acquisition of either the reference or working memory components of the radial maze task. The results are discussed in relation to the role of LTP in acquisition of the eight‐arm radial maze.
Structural synaptic plasticity associated with the induction of long‐term potentiation is preserved in the dentate gyrus of aged rats
Authors: Geinisman Yuri , de Toledo‐Morrell Leyla , Morrell Frank , Persina Inna S. , Rossi Marvin 
Published: May 2005

AbstractChanges in synaptic numbers were examined in the hippocampal dentate gyrus of aged (28 months old) rats following the induction of long‐term potentiation (LTP) by high‐frequency stimulation of the medial perforant path carried out on each of 4 consecutive days. Potentiated animals were sacrificed 1 hour after the fourth stimulation. Stimulated but not potentiated and implanted but not stimulated rats of the same chronological age served as controls. Synapses were analyzed in the middle (MML) and inner (IML) molecular layer of the dentate gyrus. Using the stereological dissector technique, unbiased estimates of the number per neuron were obtained for the following morphological varieties of synapses: axodendritic synaptic junctions involving dendritic shafts, nonperforated axospinous synapses having a continuous postsynaptic density (PSD), and perforated ones distinguished by a fenestrated, horseshoe‐shaped, or segmented PSD. The induction of LTP resulted in a selective increase in the number of synapses with segmented PSDs. This change was detected only in the potentiated synaptic field (MML), but not in an immediately adjacent one (IML), which was not directly stimulated during the induction of LTP. Comparison of these data with the results of our previous LTP study in young adult rats (Geinisman, Y. et al., 1991, Brain Res. 566:77–88) showed that the only significant difference in the absolute number of synaptic contacts per neuron between potentiated animals of the two chronological ages was an age‐related reduction in segmented synapses of the MML. Relative increases in the number of segmented synapses per neuron were, however, virtually of the same magnitude in potentiated rats of both ages as compared with their respective controls. This finding may explain why senescent rats can be potentiated to the same extent as young ones.
Hippocampal morphology and spatially related behavior in long‐evans and CFY rats
Authors: Schwegler Herbert , Mueller Gary G. , Crusio Wim E. , Szemes Laszlo , Seress Laszlo 
Published: May 2005

AbstractBehavioral responses to novelty in an open field and spatial learning in a radial maze with four arms out of eight reinforced were tested in male and female CFY and Long‐Evans rats. Subsequently, the sizes of the total hippocampi and of various hippocampal cell layers and terminal fields at the midseptotemporal level were measured in Timm‐stained sections. No strain differences were found in the open field (except for defecation). In the radial maze, Long‐Evans rats showed better spatial reference memory capabilities than rats of the CFY strain. The relative sizes of the intra‐ and infrapyramidal mossy fiber (IIP‐MF) projections did not differ between the strains. Within the more variable CFY strain, a positive correlation between the size of the IIPMF projection and radial maze performance was found. The absolute sizes of the entire hippocampi and all hippocampal layers at the midseptotemporal level were larger in the CFY strain. The size of the suprapyramidal mossy fiber projection was related to the number of granule cells and to the ratio between granule and CA3 pyramidal cells. In contrast, the size of the IIP‐MF projection did not correlate with either of these variables. The results indicate that the size of the mossy fiber projection may be determined mainly by the available postsynaptic surface on the dendrites of CA3 pyramidal neurons. Furthermore, an increased number of granule cells and their larger projection to the apical dendrites of pyramidal neurons does not appear to result in physiological changes with behavioral consequences. The results also indicate that hippocampal size or the numbers of hippocampal neurons as shown in particular bird and rodent populations is not an indicator of spatial learning capacity in commonly used laboratory rodent strains.
Adenosine‐induced suppression of synaptic responses and the initiation and expression of long‐term potentiation in the CA1 region of the hippocampus
Authors: Mitchell John B. , Miller Karen , Dunwiddie Thomas V. 
Published: May 2005

AbstractThe results of several previous studies have suggested that pretreatment with adenosine can block the induction of long‐term potentiation (LTP), although other studies have found no effect of adenosine on the induction of LTP. The interaction of adenosine with the induction of LTP in the rat hippocampal slice was investigated. Inhibition of synaptic responses by adenosine either prior to or immediately after high‐frequency or theta‐burst stimulation did not affect LTP measured after washout of the adenosine. The only conditions under which adenosine blocked the development of LTP was when it was given 3–5 minutes prior to the stimulation train. To understand how it was possible to induce LTP, during the period 1–3 minutes following adenosine when synaptic responses were virtually eliminated, evoked responses during the 100 Hz stimulation train were recorded. Although synaptic responses to low‐frequency stimulation were virtually eliminated by adenosine, they reappeared during high‐frequency stimulation. These results suggest that although adenosine can depress synaptic responses, an increase in neurotransmission during a high‐frequency train can partially overcome this effect of adenosine, and the hypothesis that adenosine can selectively block LTP is not supported.
Induction of long‐term potentiation at perforant path dentate synapses does not affect place learning or memory
Authors: Sutherland Robert J. , Dringenberg Hans C. , Hoesing Janice M. 
Published: May 2005

AbstractIn two experiments the authors failed to detect an effect of inducing bilateral, long‐lasting synaptic potentiation at perforant path dentate synapses on spatial learning by rats in the Morris place navigation task. Daily sessions of high‐frequency stimulation of perforant path axons produced large increases to an asymptotic level in population spike and field excitatory postsynaptic potential recorded in ipsilateral dentate gyrus. Place learning proceeded normally 24 hours after the last of 14 high‐frequency stimulation sessions in rats that had previously mastered the procedural aspects of place navigation (Experiment 1) and in rats that were naive (Experiment 2).
Transduction of a protein kinase C‐generated signal into the long‐lasting facilitation of glutamate release
Authors: Terrian David M. , Ways D. Kirk , Gannon Robert L. , Zetts Debbie A. 
Published: May 2005

AbstractThe present study investigated the delayed and persistent effects of 4β‐phorbol 12, 13‐dibutyrate (PDBu) on the K+ ‐evoked release of endogenous glutamate and dynorphin B‐like immunoreactivity from a subcellular fraction (P3) that is enriched in hippocampal mossy fiber synaptosomes. It is demonstrated that the alpha, beta, gamma, epsilon, and zeta isoforms of protein kinase C (PKC) are present in the P3 fraction obtained using the guinea pig hippocampus as starting tissue. The K+ ‐evoked release of glutamate was found to be selectively enhanced when mossy fiber‐enriched synaptosomes were preincubated with PDBu for 15 minutes and extensively washed with a PDBu‐free medium. The persistent enhancement of glutamate release observed under this condition was not reversed by the protein kinase inhibitor staurosporine and was desensitized to the potentiating effects of an acute reexposure to PDBu. The overall content and activity of PKC was not substantially altered during the initial 15 minutes of treatment with PDBu (10 μM). More prolonged pretreatments with PDBu altered the substrate specificity of PKC and decreased the content of all PKC isoforms, but did not reverse the facilitation of glutamate release that followed preincubation in the presence of PDBu. It is concluded that the persistent activation of PKC enhances K+ ‐evoked glutamate release from hippocampal mossy fiber‐enriched synaptosomes and that, once established, this presynaptic facilitation is sustained by a process that is no longer directly dependent on continued PKC phosphotransferase activity.
Hippocampus minor and man's place in nature: A case study in the social construction of neuroanatomy
Authors: Gross Charles G. 
Published: May 2005

AbstractIn mid‐19th century Britain the possibility of evolution and particularly the evolution of man from apes was vigorously contested. Among the leading antievolutionists was the celebrated anatomist and paleontologist Richard Owen and among the leading defenders of evolution was Thomas Henry Huxley. The central dispute between them on human evolution was whethe or not man's brain was fundamentally unique in having a hippocampus minor (known today as the calcar avis), a posterior horn in the lateral ventricle, and a posterior lobe. The author considers the background of this controversy, the origin and fate of the term hippocampus minor, why this structure became central to the question of human evolution, and how Huxley used it to support both Darwinism and the political ascendancy of Darwinians. The use of ventricular structures to distinguish humans from other animals appears to reflect an importance given to the ventricles that stretches back to ancient Greek medicine. This account illustrates both the extraordinary persistence of ideas in biology and the role of the political and social matrix in the study of the brain.