bluuebunny/crossref_metadata_2025_split huggingface dataset:
Melatonin Biosynthesis in Drosophila: Its Nature and Its Effects
Authors: Finocchiaro L. , Callebert J. , Launay J. M. , Jallon J. M. 
Published: October 2006

Abstract Drosophila melanogaster homogenates incubated with tritiated 5‐hydroxytryptophan, 5‐hydroxytryptamine, or N‐acetylserotonin have the ability of converting them into labelled indolamines, including melatonin. All these compounds were characterized by two‐dimensional thinlayer chromatography by comparison with nonradiolabelled standards, and melatonin by mass spectrometry and radioimmunoassay. On the other hand, the injection of pharmacological doses of melatonin into 2‐day‐old female flies diminishes the mating speed and the oviposition rate.
Racemization of Individual Aspartate Residues in Human Myelin Basic Protein
Authors: Shapira Raymond , Wilkinson Keith D. , Shapira Gary 
Published: October 2006

AbstractHuman myelin basic protein (MBP), a long‐lived brain protein, undergoes gradual racemization of its amino acids, primarily aspartic acid and serine. Purified protein was treated at neutral pH with trypsin to yield peptides that were separated by HPLC using a C18 column. Twenty‐nine peptides were isolated and analyzed for amino acid composition and aspartate racemization. Each aspartate and asparagine in the protein was racemized to a different extent, ranging from 2.2 to 17.1% D isomer. When the racemization was examined in terms of the β‐structure model of MBP, a correlation was observed in which six aspartate/ asparagine residues assumed to be associated with myelin membrane lipids showed little racemization (2.2–4.9% D isomer), whereas five other aspartate residues were more highly racemized (9.9–17.1% D isomer). Although the observed aspartate racemization may be related to steric hindrance by neighboring residues and/or the protein secondary structure, interaction of aspartates with membrane lipids may also be a major factor. The data are compatible with a model in which each MBP molecule interacts with adjacent cytoplasmic layers of myelin membrane through a β‐sheet on one surface and loops and helices on the other surface, thereby stabilizing the myelin multilamellar structure.
In Vivo Electrical Stimulation of the Sympathetic Nerve of the Eye Increases Inositol Phosphate Production and Prostaglandin Release in the Rabbit Iris Muscle
Authors: Yousufzai Sardar Y. K. , Gracy Ronald A. , Aboul‐Khair Hisham S. , Abdel‐Latif Ata A. 
Published: October 2006

AbstractThe effects of in vivo electrical stimulation of the sympathetic nerve of the eye on phosphatidylinositol 4,5‐bisphosphate (PIP2) hydrolysis in rabbit iris and release of arachidonate and prostaglandin (PG) E2 into aqueous humor were investigated. myo‐[3H]Inositol or [l‐14C]ara‐chidonate was injected intracamerally into each eye 3 h before electrical stimulation of one of the sympathetic trunks. Tissue phosphoinositides were determined by TLC, and 3H‐Iabeled inositol phosphates were analyzed by either ion‐exchange chromatography or HPLC. The aqueous humor was analyzed for 14C‐labeled arachidonate and PGE2 by radiochromatography and for unlabeled PGE2 by radioimmunoassay. The results obtained from this study can be summarized as follows: (a) The rates of in vivo incorporation of myo‐[3H]inositol into phosphoinositides and accumulation of 3H‐labeled inositol phosphates in the iris muscle increased with time and then leveled off between 3 and 5 h. (b) Distribution of 3H radioactivity in inositol phosphates, as determined by HPLC, showed that of the total radioactivity in inositol phosphates, 53.6% was recovered in myo‐inositol 1‐phosphate. 36% in myo‐inosi‐tol bisphosphate, 0.95% in myo‐inositol 1,3,4‐trisphosphate (1,3,4‐IP3), and 2.6% in 1,4,5‐IP3. (c) Electrical stimulation of the sympathetic nerve resulted in a significant loss of 3H radioactivity from PIP2 and a concomitant increase of that in IP3, an observation indicating that PIP2 is the physiological substrate for α1‐adrenergic receptors in this tissue, (d) Release of IP3 and liberation of arachidonate for PGE2 synthesis are dependent on the duration of stimulation and the intensity (voltage) of stimulus. We conclude that IP3 accumulation and arachidonate release are produced in the iris muscle under in vivo conditions that produce contraction, i.e., electrical stimulation of the sympathetic nerve. These observations add further support to the concept that PIP2 and its derived second messengers are involved in excitation‐contraction coupling in the smooth muscle cells of the iris.
Ionic Requirements for the Specific Binding of [3H]GBR 12783 to a Site Associated with the Dopamine Uptake Carrier
Authors: Bonnet J.‐J. , Benmansour S. , Vaugeois J.‐M. , Costentin J. 
Published: October 2006

AbstractAt 0°C, when Na+ was the only cation present in the incubation medium, increasing the Na+ concentration from 3 to 10 mM enhanced the affinity of [3H]l‐[2‐(di‐phenylmethoxy)ethyl]‐4‐(3‐phenyl‐2‐propenyl)piperazine ([3H]GBR 12783) for the specific binding site present in rat striatal membranes without affecting the 5max. For higher Na+ concentrations, specific binding values plateaued and then slightly decreased at 130 mM Na+. In a 10 mM Na+ medium, the KD and the Bmax were, respectively, 0.23 nM and 12.9 pmol/mg of protein. In the presence of 0.4 nM [3H]GBR 12783, the half‐maximal specific binding occurred at 5 mM Na+. A similar Na+ dependence was observed at 20°C. Scatchard plots indicated that K+, Ca2+, Mg2+, and Tris+ acted like competitive inhibitors of the specific binding of [3H]GBR 12783. The inhibitory potency of various cations (K+, Ca2+, Mg2+, Tris+, Li+ and choline) was enhanced when the Na+ concentration was decreased from 130 to 10 mM. In a 10 mM Na+ medium, the rank order of inhibitory potency was Ca2+ (0.13 mM) > Mg2+ > Tris+ > K+ (15 mM). The requirement for Na+ was rather specific, because none of the other cations acted as a substitute for Na+. No anionic requirement was found: Cl‐, Br‐, and F‐ were equipotent. These results suggest that low Na+ concentrations are required for maximal binding; higher Na+ concentrations protect the specific binding site against the inhibitory effect of other cations.
Phorbol Ester Inhibition of Current Responses and Simultaneous Protein Phosphorylation in Xenopus Oocyte Injected with Brain mRNA
Authors: Kato Ken‐ichi , Kaneko Shuji , Nomura Yasuyuki 
Published: October 2006

AbstractThe role of protein kinase C activation in a coupling of Ca2+‐mobilizing receptors/GTP‐binding protein/ phospholipase C was examined using Xenopus oocytes before and after microinjection of mRNA purified from rat brains. Under voltage‐clamp conditions, although the phorbol ester TPA per se never elicited any changes in ionic conductance, chloride current responses of mRNA‐injected cells to 5‐hydroxytryptamine and acetylcholine (ACh) were suppressed by an 8‐min pretreatment of 12‐O‐tetradeca‐noyl‐4β‐phorbol‐13‐acetate (TPA), at nanomolar concentrations. Native ACh response in intact follicular oocytes was also inhibited by the TPA treatment. However, similar current responses triggered by the direct activation of their intracellular signalling pathway with guanosine‐5′‐O‐(3‐thio)triphosphate or Ca2+ were not affected by TPA. Biochemical analyses indicated that phosphorylation of 33,000‐ and 45,000‐dalton proteins was markedly enhanced by TPA in vivo, and that stimulation of receptors with agonists as well as TPA treatment increased phospho‐proteins in the membrane fraction of mRNA‐injected oocytes. These observations suggest that protein kinase C may switch off the signal transduction from receptors to GTP‐binding proteins and may participate in the negative feedback modulation of receptor‐operated ion channel responses.
Acylgalactosylceramides in Developing Dysmyelinating Mutant Mice
Authors: Theret N. , Boulenguer P. , Fournet B. , Fruchart J. C. , Bourre J. M. , Delbart C. 
Published: October 2006

AbstractAcylgalactosylceramides (AGC) from forebrains of normal and dysmyelinating (quaking and shiverer) mice were purified by Florisil column chromatography and preparative TLC. These procedures resolved the AGC on the basis of their Rf values into two main fractions which co‐nigrate with their homologs from rat forebrains. In control animals, AGC were detectable in mouse forebrains from the eighth postnatal day and reached maximal values within 20 days. The same developmental pattern was obtained in dysmyelinating shiverer mice but the AGC content was reduced to approximately 30% of control values. In quaking mutants, the AGC were hardly detected. They were also present in sciatic nerve of normal mice and to a lesser extent in trembler mice. Gas chromatography‐mass spectrometry analysis of both ester‐ and amide‐linked fatty acids isolated from AGC of normal and shiverer mice shows that the shiverer mutant AGC display a chemical structure similar to that of normal AGC. AGC constituents of control myelin are reduced by approximately 70% in shiverer myelin, indicating that these molecules can be considered as early markers of oligodendrocyte differentiation. The early arrest of myelinogenesis in the quaking animals and the near absence of AGC are in good agreement with this proposal. Moreover, the reduced amount of AGC in the trembler PNS indicates that AGC could also be early markers for differentiation of the Schwann cell.
Interaction of l‐Prolyl‐l‐Leucyl Glycinamide with Dopamine D2 Receptor: Evidence for Modulation of Agonist Affinity States in Bovine Striatal Membranes
Authors: Srivastava Lalit K. , Bajwa Samina B. , Johnson Rodney L. , Mishra Ram K. 
Published: October 2006

AbstractThe role of the hypothalamic tripeptide l‐prolyl‐l‐leucyl‐glycinamide (PLG) in modulating the agonist binding to bovine striatal dopamine D2 receptor was investigated using a selective high‐affinity agonist, n‐propylnor‐apomorphine (NPA). PLG caused an enhancement in [3H]NPA binding in striatal membranes in a dose‐dependent manner, the maximum effect being observed at 10‐‐7‐‐10‐‐6M concentration of the tripeptide. The Scat‐chard analysis of [3H]NPA binding to membranes preincu‐bated with 10‐‐6M PLG revealed a significant increase in the affinity of the agonist binding sites. In contrast, there was no effect of PLG on the binding pattern of the antagonist [3H]spiroperidol. The antagonist versus agonist competition curves analyzed for agonist high‐ and low‐affinity states of the receptor displayed an increase in the population and affinity of the high‐affinity form of the receptor with PLG treatment. The low‐affinity sites concomitantly decreased with relatively small change in the affinity for the agonists. Almost similar results were obtained when either NPA or apomorphine was used in the competition experiments. A partial antagonistic effect of PLG on 5′‐guanylyl‐imidodiphosphate [Gpp(NH)p]‐induced inhibition of high‐affinity agonist binding was also observed, as the ratio of high‐ to low‐affinity forms of the receptor was significantly higher in the PLG‐treated membranes compared to the controls. Direct [3H]NPA binding experiments demonstrated that PLG attenuated the Gpp(NH)p‐induced inhibition of agonist binding by increasing the EC50 of the nu‐cleotide (concentration that inhibits 50% of the specific binding). No effect of PLG on high‐affinity [3H]NPA binding, however, could be observed when the striatal membranes were preincubated with Gpp(NH)p. The binding of antagonists and agonists to α2 adrenergic receptors, negatively coupled to adenylate cyclase in the striatum. was not affected by PLG. The results suggest that PLG modulates the affinity states of the dopamine D2 receptor, possibly by enhancing its interaction with the guanine nucleotide regulatory protein.
Age‐Related Changes of Ribonuclease Activities in Various Regions of the Rat Central Nervous System
Authors: Alberghina M. , Stella A. M. Giuffrida 
Published: October 2006

AbstractAcid (pH 5.5), free, and latent alkaline (pH 7.4) RNases were assayed in homogenates of temporal cortex, hypothalamus, hippocampus, and cervicothoracic segments of spinal cord of rats at three different ages (5,14, and 25 months old). Free alkaline RNase activity was lower (two‐ to fivefold) than the acid activity. Both free and inhibitor‐bound alkaline RNases remained unchanged with age in all CNS regions examined. This result also indirectly indicates no change of RNase‐inhibitor complex throughout aging. In contrast, the acid RNase activity showed a significant increase during aging in all tissues, with exception of the hypothalamus. Because this enzyme is localized mainly in the lysosomes, this result might be due to an increased lysosomal activity and/or to the release of hydro‐lases into the cytoplasm from these organelles, undergoing shrinkage and degeneration in aged animals.
Bicuculline Up‐Regulation of GABAA Receptors in Rat Brain
Authors: Ito Yoshihisa , Lim Dong Koo , Hoskins Beth , Ho Ing K. 
Published: October 2006

AbstractEffects of acute and subacute administration of Dicuculline on [3H]muscimol, [3H]flunitrazepam, and t‐[35S]butylbicyclophosphorothionate ([35S]TBPS) binding to various brain regions were studied in Sprague‐Dawley rats. Acute administration of bicuculline affected neither the KD nor the Bmax of the three receptor sites. In rats treated sub‐acutely with bicuculline (2 mg/kg, i.p., daily for 10 days), [3H]muscimol binding was increased in the frontal cortex, cerebellum, striatum, and substantia nigra. Scatchard analysis revealed that subacute treatment of rats with bicuculline resulted in a significantly lower KD of high‐affinity sites in the striatum and in a significantly lower KD of high‐ and low‐affinity sites in the frontal cortex. In the cerebellum, two binding sites were apparent in controls and acutely treated animals; however, only the high‐affinity site was defined in subacutely treated animals, with an increase in the Bmax value. Triton X‐100 treatment of frontal cortical membranes eliminated the difference in [3H]muscimol binding between control and subacute bicuculline treatments. On the other hand, [3H]muscimol binding was significantly increased in the cerebellum from bicuculline‐treated animals even after Triton X‐100 treatment. The apparent Ki of bicuculline for the GABAA receptor was also decreased in the frontal cortex and the striatum following the treatment. However, subacute administration of bicuculline affected neither the KD nor the Bmax of [3H]‐flunitrazepam and [35S]TBPS binding in the frontal cortex and the cerebellum. These results suggest that GABAA receptors are up‐regulated after subacute administration of bicuculline, with no change in benzodiazepine and picro‐toxin binding sites.
Exchange of Guanine Nucleotides Between Tubulin and GTP‐Binding Proteins That Regulate Adenylate Cyclase: Cytoskeletal Modification of Neuronal Signal Transduction
Authors: Rasenick Mark M. , Wang Nan 
Published: October 2006

AbstractTubulin, the primary constituent of microtubules, is a GTP‐binding protein with structural similarities to other GTP‐binding proteins. Whereas microtubules have been implicated as modulators of the adenylate cyclase system, the mechanism of this regulation has been elusive. Tubulin, polymerized with the hydrolysis‐resistant GTP analog, 5′‐guanylylimidodiphosphate [Gpp(NH)p], can promote inhibition of synaptic membrane adenylate cyclase which persists subsequent to washing. Tubulin with Gpp(NH)p bound was slightly less potent than free Gpp(NH)p in the inhibition of adenylate cyclase, but tubulin without nucleotide bound had no effect on the enzyme. A GTP‐binding protein from the rod outer segment (transducin), with Gpp(NH)p bound, was also without effect on adenylate cyclase. Tubulin (regardless of the nucleotide bound to it) did not alter the activity of the adenylate cyclase catalytic unit directly. When tubulin was polymerized with the hydrolysis‐resistant photoaffinity GTP analog, [32P]P3(4‐azidoanilido)‐P1‐5′‐GTP ([32P]AAGTP), and this protein was added to synaptic membranes, AAGTP was transferred from tubulin to the inhibitory GTP‐binding protein, Gi. This transfer was blocked by prior incubation of the membranes with Gpp(NH)p or covalent binding of AAGTP to tubulin prior to exposure of that tubulin to membranes. Incubation of membranes with Gpp(NH)p subsequent to incubation with tubulin‐AAGTP results in a decrease in AAGTP bound to Gi and a compensatory increase in AAGTP bound to the stimulatory GTP‐binding protein, Gs. Likewise, persistent inhibition of adenylate cyclase by tubulin‐Gpp(NH)p could be overridden by the inclusion of 100 μM Gpp(NH)p in the assay inhibition. Whereas Gpp(NH)p promotes persistent inhibition of synaptic membrane adenylate cyclase without incubation at elevated temperatures, tubulin [with AAGTP or Gpp(NH)p bound] requires 30 s incubation at 23°C to effect adenylate cyclase inhibition. Photoaffinity experiments yield parallel results. These data are consistent with synaptic membrane tubulin regulating neuronal adenylate cyclase by transferring GTP to Gi and, subsequently, to Gs.
Evidence for the Presence of Serotonin Receptors Negatively Coupled to Adenylate Cyclase in the Rabbit Iris‐Ciliary Body
Authors: Tobin A. B. , Osborne N. N. 
Published: October 2006

AbstractSerotonin has no obvious effect on basal cyclic AMP levels but reduces the forskolin‐, isoproterenol‐, and vasoactive intestinal peptide‐induced stimulation of cyclic AMP levels in a dose‐dependent manner. Serotonergic, cholinergic, muscarinic, α‐adrenergic, and dopaminergic antagonists have no effect on the serotonin response. Topical Application of a serotonin/pargyline solution to the living eye causes desen‐sitisation of the serotonin response in the iris‐ciliary body, an observation confirming the presence of specific serotonergic receptors linked to adenylate cyclase. The 5‐HT1A[5‐hy‐droxytryptamine (serotonin) type 1A] receptor agonists 8‐hydroxy‐2‐(di‐n‐propylamino)tetralin and bujspirone mimic the serotonin response in reducing the forskolin‐stimulated cyclic AMP levels, as do the indole derivatives 5‐methoxy‐ tryptamine, 5‐hydroxtryptophan, and tryptamine. However, the ineffectiveness of the 5‐HT1Aagonist ipsapirone and the inability of spiroxatrine to block the serotonin response show that classical 5‐HT1Areceptors are not involved. The serotonin response is blocked by pertussis toxin and is insensitive to the phosphodiesterase inhibitor theophylline, which indicates the involvement of an inhibitory guanine regulatory protein in the coupling of the serotonin receptor to the adenylate cyclase catalytic unit.
Developmental Changes in the Calcium Dependency of γ‐Aminobutyric Acid Release from Isolated Growth Cones: Correlation with Growth Cone Morphology
Authors: Taylor Joanne , Gordon‐Weeks Phillip R. 
Published: October 2006

AbstractWe have investigated the development of Ca2+‐dependent ‐γ‐[3H]aminobutyric acid ([3H]GABA) release in superfused growth cone fractions isolated from rats between the postnatal ages of 1 and 11 days. We have compared this release with the overall morphology of the subcellular fractions, and identified those structures taking up [3H]GABA by electron microscopical autoradiography. In fractions isolated from rats between 1 and 5 days, K+‐evoked [3H]GABA release was completely independent of extracellular Ca2+. After 5 days a Ca2+ dependency appeared, wfiich increased with age, such that by 10 days approximately 50% of the K+‐evoked release was Ca2+ dependent. Electron microscopical analysis showed that, at all ages, large numbers of GABAergic growth cones were present in the subcellular fractions. Up to postnatal day 5, the growth cones were synaptic vesicle sparse but, after this age, increasing numbers of synaptic vesicle‐containing growth cones were seen. These results suggest that during maturation of GABAergic growth cones into synapses there is, initially, a mechanism for release that is independent of extracellular Ca2+ and that the appearance of a Ca2+‐dependent [3H]GABA release from growth cones correlates with the appearance of synaptic vesicles.
Effect of Halide Ions on t‐[35S]Butylbicyclophosphorothionate Binding
Authors: Garrett Kennon M. , Blume Arthur J. , Abel Marc S. 
Published: October 2006

AbstractThe binding of t‐[35S]butylbicyclophosphoro‐thionate ([35S]TBPS) to a site on the GABAA receptor complex is ion dependent. This study was conducted to determine the effects of ion species and concentration on the time course, affinity, and number of sites of [35S]TBPS binding. At a concentration of 200 mM ion, the time to equilibrium for [35S]TBPS binding was shortest for I‐, followed by Br‐< CI‐< F‐. A similar rank order was observed for the concentration of ion required to produce half‐maximal [35S]TBPS binding. Saturation binding experiments were conducted to evaluate the effect of increasing ion concentration on the KD and Bmax of [35S]TBPS binding. The Bmax was independent of both ion species and concentration. The receptor affinity, however, increased with increasing concentration for each ion. Calculated maximal affinity values were not different between ions; however, the EC50 to produce those values was different among ions and ranked in the same order as that for time course and maximal binding data. Association and dissociation rates for [35S]TBPS binding were greater in I‐ than in Cl‐. These data emphasize the importance of ion selection and incubation times on [35S]TBPS binding.
Clinical Concentrations of Volatile Anesthetics Reduce Depolarization‐Evoked Release of [3H]Norepinephrine, but Not [3H]Acetylcholine, from Rat Cerebral Cortex
Authors: Bazil Carl W. , Minneman Kenneth P. 
Published: October 2006

AbstractWe compared the potencies of halothane, enflurane, and methoxyflurane in producing unconsciousness in vivo and in inhibiting the release of [3H]norepinephrine and [3H]acetylcholine in vitro. Rats were anesthetized with various concentrations of each anesthetic, and responsiveness was determined by a hemostat tail pinch. Slices of cerebral cortex were equilibrated with similar concentrations of each agent in vitro, and potassium‐evoked release of [3H]norepinephrine and [3H]acetylcholine was determined. For both studies, brain concentrations of the anesthetics were determined by heptane extraction and gas chromatography. Using this method, we found that brain concentrations of all three agents which caused unconsciousness in vivo also reduced depolarization‐evoked release of [3H]norepinephrine by approximately 30% in vitro. The release of [3H]acetylcholine was unaffected b/similar concentrations of these anesthetics. Such selective interference with stimulus‐secretion coupling in central noradrenergic, and possibly other, neurons might contribute to the depressant actions of volatile anesthetics. The differential effects on norepinephrine and acetylcholine release also suggest differences in the mechanisms by which these two transmitters are released.