bluuebunny/crossref_metadata_2025_split huggingface dataset:
In Vitro Release of Endogenous Dopamine from the Striatum of the Weaver Mutant Mouse
Authors: Simon J. R. , Yu H. , Richter J. A. , Vasko M. R. , Ghetti B. 
Published: October 2006

Abstract: The weaver mutant mouse has a genetically determined defect in the nigrostriatal dopaminergic system. The present study was undertaken to test the hypothesis that in the weaver mutant mouse, striatal nerve terminals undergo compensatory changes in response to this deficiency. To test this hypothesis, we studied the basal and stimulated release of dopamine from striatal slices of weaver mutant mice and matched controls. By using a superfusion system and concentrating the superfusate by passage over alumina, resting dopamine release could be determined in the weaver mutant despite the fact that striatal tissue content of dopamine in these mice is reduced by >75% compared with control mice. Fractional resting release of dopamine in weaver striatal slices was significantly elevated compared with that in controls, suggesting that the release mechanisms in the weaver may be adapting to overcome the dopamine deficit. Potassium‐evoked release (24 and 48 mM potassium) was not significantly different between the two genotypes. In contrast, amphetamine‐evoked release (1 μM) was significantly greater in the weaver mice than in controls. In both genotypes, release evoked by amphetamine was completely inhibited by cocaine, implicating the dopamine uptake carrier in this release process. These findings suggest that fundamental differences in dopamine release mechanisms exist between weaver and control mice and support the hypothesis that compensatory mechanisms may develop in neurons in response to dopamine deficits.
Metabolism of Extracellular Adenine Nucleotides by Cultured Rat Brain Astrocytes
Authors: Lai Kam‐Ming , Wong Patrick C. L. 
Published: October 2006

Abstract: Intact astrocytes cultured from newborn rat cerebral cortex rapidly converted extracellular ATP to ADP. The ATPase responsible was apparently not saturated, even at 750 μM ATP. In contrast, the conversion of ADP to AMP was slow, and the reaction was limiting for the subsequent dephosphorylation process. Adenosine formation was the only fate for AMP. The reaction was catalyzed by S'‐nucleotidase with an apparent Km of 55 μM for AMP and appeared to be inhibited by high concentrations of ATP and ADP.Astrocytes were able to take up adenosine with an apparent Km value of 45 μM. Uptake was inhibited by dipyridamole but not by anti‐5′‐nucleotidase IgG. The results support the proposal that astrocytes play a role in modulating synaptic events involving ATP and adenosine.
Effect of Loading Doses of l‐Valine on Relative Contributions of Valine Derived from Protein Degradation and Plasma to the Precursor Pool for Protein Synthesis in Rat Brain
Authors: Smith C. Beebe , Sun Y. , Deibler G. E. , Sokoloff L. 
Published: October 2006

Abstract: “Flooding” amino acid pools with high doses of labeled amino acids of low specific activity has been proposed to minimize the effects of recycling of amino acids derived from protein degradation on the specific activity of the amino acid precursor pool for protein synthesis. We have examined the influence of recycling on the precursor pool for protein synthesis under conditions in which plasma valine concentrations were normal (0.19 mM) and “flooded” (10‐28 mM) by comparing the steady‐state specific activity of the tRNA‐bound valine with that of the plasma valine. Under normal and “flooding” conditions, the relative contributions of valine from protein degradation to the precursor pool were 63 and 26%, respectively; “flooding” with a plasma level of 28 mM raised the brain acid‐soluble pool level to 3.1 mM but was no more effective in decreasing the relative contribution of valine from protein degradation to the precursor pool than “flooding” with a plasma level of 17 mM valine, which raised the brain acid‐soluble level only to 2.3 mM. The results of these studies show that “flooding” amino acid pools does indeed reduce the effect of recycling on the precursor amino acid pool for protein synthesis, but it does not totally eliminate it.
Proteolysis of Microtubule‐Associated Protein 2 and Tubulin by Cathepsin D
Authors: Johnson Gail V. W. , Litersky Joel M. , Whitaker John N. 
Published: October 2006

Abstract: The in vitro degradation of microtubule‐associated protein 2 (MAP‐2) and tubulin by the lysosomal aspartyl endopeptidase cathepsin D was studied. MAP‐2 was very sensitive to cathepsin D‐induced hydrolysis in a relatively broad, acidic pH range (3.0–5.0). However, at a pH value of 5.5, cathepsin D‐mediated hydrolysis of MAP‐2 was significantly reduced and at pH 6.0 only a small amount of MAP‐2 was degraded at 60 min. Interestingly, the two electro‐phoretic forms of MAP‐2 showed different sensitivities to cathepsin D‐induced degradation, with MAP‐2b being significantly more resistant to hydrolysis than MAP‐2a. To our knowledge, this is the first clear demonstration that MAP‐2 is a substrate in vitro for cathepsin D. In contrast to MAP‐2, tubulin was relatively resistant to cathepsin D‐induced hydrolysis. At pH 3.5 and an enzyme‐to‐substrate ratio of 1: 20, only 35% of the tubulin was degraded by cathepsin D at 60 min. The cathepsin D‐mediated hydrolysis of tubulin was optimal only at pH 4.5. These results demonstrate that MAP‐2 and tubulin are unequally susceptible to degradation by cathepsin D. These data also imply a potential for rapid degradation of MAP‐2 in vivo by cathepsin D either in lysosomes or perhaps autophagic vacuoles of the neuron.
Ultrastructural Changes Induced by 12‐O‐Tetradecanoylphorbol 13‐Acetate in Pure Cholinergic Synaptosomes of Torpedo Electric Organ
Authors: Egea Gustavo , Guitart Xavier , Marsal Jordi 
Published: October 2006

Abstract: We have studied the morphological changes induced by the phorbol ester 12‐O‐tetradecanoylphorbol 13‐acetate (TPA) treatment on pure cholinergic synaptosomes from Torpedo electric organ. These changes were studied by both ultrathin sections and freeze‐fracture techniques We found that after a treatment with TPA, a redistribution of synaptic vesicles inside the nerve endings and exocytotic images could be observed. Also, TPA, under conditions that induced the acctylcholme release, did not change the density of mtramembrane particles at the synaptosomal protoplasmic hemimembrane leaflet. Similar results were found when calcium was not present in the extrasynaptosomal medium, and our results suggest that acetylcrioline release induced by phorbol ester is probably mediated by exocytosis of synaptic vesicles.
Genomic Organization of Drosophila Choline Acetyltransferase
Authors: Sugihara Hidemitsu , Andrisani Veronica , Salvaterra Paul M. 
Published: October 2006

Abstract: Choline acetyltransferase (ChAT; acetyl‐CoA:cho‐line‐O‐acetyltransferase; EC 2.3.1.6) is the enzyme responsible for the synthesis of the neurotransmitter acetylcholine and is thus the genetic determinant of neurons with a cholinergic phenotype. We have screened a Drosophila genomic library using a cRNA probe, transcribed from Drosophila ChAT cDNA, and isolated three independent clones representing all the exons of this gene. The gene spans more than 26 kb of DNA and is organized into eight exons containing 594, 80,192, 759, 408, 147, 201, and 1,612 nucleotides. All inserts that hybridized with a cRNA probe have been subcloned and the sequence of intron/exon boundaries determined. The only part of the ChAT gene not represented in our clones is a part of the first intron. A minimum size for this uncloned DNA has been deduced from Southern analysis of Drosophila genomic DNA. We also have probed the transcripts of the ChAT gene by northern analysis of total Drosophila RNA using two different exon‐specific antisense RNA probes. An exon I probe detected two bands of RNA whereas an exon VHI probe hybridized with only the smaller band, previously identified as ChAT mRNA. These results indicate a complex transcription pattern for the ChAT locus in Drosophila.
Specific Brain Protein Changes Correlated with Behaviourally Effective Brain Transplants
Authors: Wets Kathleen M. , Sinden John , Hodges Helen , Allen Yvonne , Marchbanks R. M. 
Published: October 2006

Abstract: The objective of this study was to identify cellular proteins that are associated with foetal brain transplants effective in reinstating memory function in adult rats with brain lesions. Quantitative memory deficits can be created in rats by lesioning the cholinergic projection system, using ibotenic acid. Previous work suggested that injection of cell suspensions prepared from presumptive cholinergic cells of foetal basal forebrain into adult brain, after such lesions, are most effective in restoring cognitive function. It was not clear, however, whether it was the cholinergic nature of the transplants that was critical for their success or whether other factors were involved. In this study, the proteins present in transplanted tissues and control brains were analysed by two‐dimensional polyacrylamide gel electrophoresis to identify markers for the cells that were specifically correlated with restoration of cognitive function. On each gel, the relative optical densities of the same 33 selected proteins were measured on an interactive computerised image analyser. The amount of each protein was compared between treatment groups and correlated with four behavioural measurements. Seven of the proteins analysed had levels of expression that were either related to transplantation or correlated with behavioural performance. The proteins of interest were divided into the following three groups: (1) transplant‐related proteins, (2) cholinergic transplant‐specific proteins, and (3) behaviour‐related proteins. Notable among the proteins of interest was one of the cholinergic transplant‐specific proteins that was positively correlated with three of the four behavioural measurements and was also the only protein among those analysed that was significantly correlated with choline acetyltransferase (ChAT) levels. This has been identified, by immunoblotting, as glial fibrillary acidic protein, an astrocytic cell marker. These results suggest, therefore, that at least two cell types, astrocytes and ChAT+‐staining cells, play an important role in the successful recovery of cognitive function. This study also identified possible protein markers for cognitive performance. The level of expression of two of the proteins analysed was not affected by lesioning or transplantation, but was significantly correlated with behaviour. One of these proteins, whose amounts correlated negatively with behavioural measurements, has been identified as neurone‐specific enolase, a brain‐specific neuronal cell marker.
Conservation of Docosahexaenoic Acid in Rod Outer Segments of Rat Retina During n‐3 and n‐6 Fatty Acid Deficiency
Authors: Wiegand Rex D. , Koutz Cynthia A. , Stinson Ann M. , Anderson Robert E. 
Published: October 2006

Abstract: We investigated the mechanism by which rat retina conserves docosahexaenoic acid during essential fatty acid deficiency. Weanling female albino rats were fed diets containing either 10% by weight hydrogenated coconut oil, safflower oil, or linseed oil for 15 weeks. Plasma and rod outer segment (ROS) membranes were prepared for fatty acid and phospholipid molecular species analysis. In addition, retinas were removed for morphometric analysis. We found the following: (1) Plasma phospholipids and cholesterol esters from coconut oil, safflower oil, and linseed oil diet groups were enriched in 20:3(n‐9), 20:4(n‐6), and 20:5(n‐3), respectively. The levels of these 20‐carbon fatty acids in the ROS, however, were only slightly affected by diet. (2) The fatty acids and molecular species of ROS phospholipids from the safflower oil and coconut oil groups showed a selective replacement of 22:6(n‐3) with 22:5(n‐6), as evidenced by a reduction of the 22:6(n‐3)‐22:6(n‐3) molecular species and an increase in the 22:5(n‐6)‐22:6(n‐3) species. (3) The renewal rate of ROS integral proteins, determined by autoradiography, was 10% per day for each diet group. (4) Morphometric analysis of retinas showed no differences in the outer nuclear layer area or in ROS length between the three groups. We conclude that the conservation of 22:6(n‐3) in ROS is not accomplished through reductions in the rate of membrane turnover, the total amount of ROS membranes, or in the number of rod cells. The retina may conserve 22:6(n‐3) through recycling within the retina or between the retina and the pigment epithelium, or through the selective uptake of 22‐carbon poly‐unsaturated fatty acids from the circulation.
Interactions of Glutamate Receptor Agonists Coupled to Changes in Intracellular Ca2+ in Rat Cerebellar Granule Cells in Primary Culture
Authors: Holopainen Irma , Louve Michael , Åkerman Karl E. O. 
Published: October 2006

Abstract: Changes in cytosolic free Ca2+ concentrations in response to glutamate receptor agonists and their interactions were studied in rat cerebellar granule cells grown on cover‐slips. The intracellular Ca2+ as measured with fura‐2 increased by applying kainate (KA), quisqualate (QU), and N‐methyl‐d‐aspartate (NMDA). The effect of KA could not be blocked by the NMDA receptor blocker 2‐amino‐5‐phosphonovalenc acid (APS). The KA‐and QU‐induced increase in intracellular free Ca2+ was also observed in a Na+‐free medium, indicating that this response is not secondarily due to the depolarization. The effect of 10 μM QU on the KA‐induced changes in cytosolic free Ca2+ was additive only at low KA concentrations, but QU at 0.1 mM totally blocked the response to KA. In the presence of 10 μM KA, the dose‐response curve of QU became biphasic, whereas with 50 μM KA, a reduction of the response was seen around 1–100 μM QU. The effect of NMDA on the QU‐induced response was additive only at low QU concentrations. It is proposed that rat cerebellar granule cells in primary culture express separate receptor‐channel complexes for NMDA, QU, and KA, but interactions between agonists for these receptor sites exist. Thus, QU when present at intermediate concentrations seems to interact with the KA type of receptor, causing its desensitization. At high QU concentrations, an interaction of QU with the NMDA receptor site is apparent.
The Posttranslational Arginylation of Proteins in Different Regions of the Rat Brain
Authors: Hallak Marta E. , Bongiovanni Guillermina , Barra Héctor S. 
Published: October 2006

Abstract: The posttranslational incorporation of arginine into proteins catalyzed by arginyl‐tRNA protein transferase was determined in vitro in different rat brain regions. The incorporation was found in all the regions studied, although with different specific activities (pmol [14C]arginine incorporated/mg protein). Of the regions studied, hippocampus had the highest specific activity followed by striatum, medulla oblongata, cerebellum, and cerebral cortex. Electrophoretic analysis of the [14C]arginyl proteins from the different regions followed by autoradiography and scanner densitometry showed at least 13 polypeptide bands that were labeled with [14C]arginine. The radioactive bands were qualitatively coincident with protein bands revealed by Coomassie Blue. There were peaks that showed different proportions of labeling in comparison with peaks of similar molecular mass from total brain. Most notable because of their high proportions were those of molecular mass 125 kDa in hippocampus, striatum, and cerebral cortex; 112 and 98 kDa in striatum and cerebellum; and 33 kDa in hippocampus and striatum. In lower proportions than in total brain were the peaks of 33 kDa in medulla oblongata and cerebral cortex and of 125 kDa in medulla oblongata.
Acute Regulation of the Epidermal Growth Factor Receptor in Response to Nerve Growth Factor
Authors: Brown Alice B. , Carpenter Graham 
Published: October 2006

Abstract: PC12 cells possess specific receptors for both nerve growth factor and epidermal growth factor, and by an unknown mechanism, nerve growth factor is able to attenuate the propagation of a mitogenic response to epidermal growth factor. The differentiation response of PC12 cells to nerve growth factor, therefore, predominates over the proliferative response to epidermal growth factor. We have observed that the addition of nerve growth factor to PC12 cells rapidly produces a decrease in surface 125I‐epidermal growth factor binding capacity. Unlike previously described nerve growth factor effects on 125I‐epidermal growth factor binding capacity, which required several days of nerve growth factor exposure, the decreases we report occur within minutes of nerve growth factor addition: A 50% decrease in 125I‐epidermal growth factor binding capacity is evident at 10 min. This rapid nerve growth factor response is concentration dependent; inhibition of 125I‐epidermal growth factor binding is detectable at nerve growth factor levels as low as 0.2 ng/ml and is maximal at approximately 50 ng/ml, consistent with known ranges of biological activity. No demonstrable differences in the rate of epidermal growth factor receptor synthesis or degradation were observed in cells acutely exposed to nerve growth factor. Scatchard analysis revealed that acute nerve growth factor treatment decreased the number of both high‐and low‐affinity 125I‐epidermal growth factor binding sites, while the receptor affinity remained unchanged. We have also investigated the involvement of various potential intracellular mediators of nerve growth factor action and of known intracellular modulatory systems of the epidermal growth factor receptor for their capacity to participate in this nerve growth factor activity.
Effects of Chronic and Subchronic Nicotine on Tyrosine Hydroxylase Activity in Noradrenergic and Dopaminergic Neurones in the Rat Brain
Authors: Smith Katherine M. , Mitchell Stephen N. , Joseph Michael H. 
Published: October 2006

Abstract: Chronic nicotine (0.8 mg/kg by daily subcutaneous injection) over a 7 to 28‐day period was found to increase the activity of tyrosine hydroxylase in predominantly noradrenergically innervated regions but not in dopaminergic projection areas. Increases in tyrosine hydroxylase activity were observed in dopaminergic cell body regions only after nicotine treatment for 3 to 5 days. The increase in tyrosine hydroxylase activity in noradrenergic neurones was evident first in the cell bodies in the locus coeruleus from 3 to 7 days, reaching 223% of control activities, and was followed by increases of up to 205% in the terminals up to 3 weeks later. It was then established that nicotine for 7 days was sufficient to increase the activity of the enzyme to the same extent in the terminals at 21 days even without further nicotine administration. This is consistent with axonal transport preceded by induction of the enzyme in noradrenergic cell bodies, whereas “delayed activation” might account for the transient effect seen in dopaminergic cell body regions. The response in the locus coeruleus to nicotine for 7 days was completely blocked by daily preinjection with mecamylamine but not with hexamethonium, which is consistent with the effect of nicotine on tyrosine hydroxylase being mediated by central nicotinic receptors.
Regulation of Five Tubulin Isotypes by Thyroid Hormone During Brain Development
Authors: Aniello Francesco , Couchie Dominique , Gripois Daniel , Nunez Jacques 
Published: October 2006

Abstract: Nucleic acid probes derived from the 3’noncoding region of five tubulin cDNAs were used to study the effects of thyroid hormone deficiency on the expression of the mRNAs encoding two α (α1 and α2)‐and three β (β2, β4, and β5)‐tubulin isotypes in the developing cerebral hemispheres and cerebellum. The content of α1, which markedly declines during development in both brain regions, is maintained at high levels in the hypothyroid cerebellum, whereas it is decreased in the cerebral hemispheres. The α2 level also declines during development and is decreased in both regions by thyroid hormone deficiency, but only during the two first postnatal weeks. Thyroid hormone deficiency slightly increases at all stages the β2 level in the cerebellum, whereas a decrease is observed at early stages in the cerebral hemispheres. The ft level seems to be independent of thyroid hormone in the cerebral hemispheres, whereas it decreases at early stages in the hypothyroid cerebellum. Finally, the expression of the brain‐specific β4 isotype is markedly depressed by thyroid hormone deficiency, particularly in the cerebellum. These data suggest that the genes encoding the tubulin isotypes are, directly or not, differently regulated by thyroid hormone during brain development This might contribute to abnormal neurite outgrowth seen in the hypothyroid brain and therefore to impairment in brain functions produced by thyroid hormone deficiency.
Autoradiographic Localization of Dopaminergic and Noradrenergic Receptors in the Bovine Pineal Gland
Authors: Simonneaux V. , Happe H. K. , Ebadi M. , Murrin L. C. 
Published: October 2006

Abstract: Dopamine and norepinephrine are involved in regulation of melatonin synthesis in the pineal gland. In bovine pineal gland, D1‐and D2‐dopaminergic and α1‐adrenergic receptors have been characterized pharmacologically in several laboratories, while β1‐adrenergic receptors have been studied using physiological techniques. The current study presents a quantitative autoradiographic analysis of these four dopaminergic and noradrenergic receptors in bovine pineal gland. The density order of the receptors is D1 > α1 > D2β1. The Bmax of dopamine D1 receptors is about 5 to 6 times higher than the Bmax for α1adrcnergic receptors and about 20 times higher than the Bmax values for β1adrenergic and D2‐dopaminergic receptors. Dopamine D1 receptors are significantly denser in the pineal cortex than in the medulla. Both dopamine receptors are more concentrated in the distal area than in the proximal area (close to the habenula), whereas both noradrenergic receptors are homogeneously distributed along the longitudinal axis. Only D1‐dopaminergic receptors display a heterogeneous distribution between the superior and the inferior areas, being denser in the inferior area. The observation of a much higher concentration of D1‐dopaminergic receptors relative to the other receptors suggests an important role for dopamine in the regulation of bovine pineal physiology.
Phorbol Ester Pretreatment Desensitizes the Inhibition of Ca2+ Channels Induced by k‐Opiate, α2‐Adrenergic, and Muscarinic Receptor Agonists
Authors: Attali Bernard , Nah Seung‐Yeol , Vogel Zvi 
Published: October 2006

Abstract: Acute treatment of rat spinal cord‐dorsal root ganglion cocultured neurons with 12‐O‐tetradecanoylphorbol 13‐acetate (TPA), a known activator of protein kinase C, inhibited the dihydropyridinc‐sensitive voltage‐dependent 45Ca2+ influx measured in these cells (IC50 of⋍100 nM, 66% inhibition at 1 νM TPA). However, prolonged preincubation (24 h) of the cells with 100 nM TPA followed by extensive washing completely abolished, i.e., desensitized, the capacity of a second application of TPA to inhibit the activity of the voltage‐dependent Ca2+ channels. Moreover, this treatment also abolished the inhibition of Ca2+ influx produced by k‐opiate as well as by α2‐adrenergic and muscarinic receptor agonists. Substantial desensitization was already observed following a 1‐h pretreatment with 100 nMTPA. In contrast to TPA, an inactive phorbol ester (4β‐phorbol 13‐acetate) did not affect the inhibition of the voltage‐dependent Ca2+ influx by these receptor agonists. These results suggest that protein kinase C may have a role in the modulation of Ca2+channels by k‐opiate, α2‐adrenetgic, and muscarinic receptor agonists.