Modulatory Action of Taurine on the Release of GABA in Cerebellar Slices of the Guinea Pig

Abstract: For the purpose of demonstrating the action of taurine as a neuromodulator in addition to its suggested neurotransmitter function, the effects of taurine and muscimol on the depolarization-induced Ca-dependent release of [³H]γ-aminobutyric acid (pH]GABA) and l -[³H]glutamate in cerebellar slices from guinea pigs were investigated. The release of [³H]GABA was found to be greatly decreased by a GABA agonist, muscimol, and by taurine, but not by glycine. The release of l -[³H]glutamate was little affected by taurine. The release of [³H]GABA was enhanced by bicuculline and strychnine, but not by picrotoxin, and the suppressive action of muscimol on the GABA release was antagonized by bicuculline, picrotoxin, and strychnine, suggesting the possible existence of presynaptic autoreceptors for GABA in the cerebellum. The suppressive action of taurine on the release of [³H]GABA, on the other hand, was blocked only by bicuculline. These results suggest that taurine reduced the release of [³H]GABA from cerebellar slices by acting on the GABA autoreceptors or, more likely, on other types of receptors that are sensitive to bicuculline. As a possible mechanism for this modulatory action of taurine, the blockade by this amino acid of the influx of Ca²⁺ into cerebellar tissues was tentatively suggested.     

Halothane Anesthesia Affects NMDA-Stimulated Cholinergic and GABAergic Modulation of Striatal Dopamine Efflux and Metabolism in the Rat In Vivo

Microdialysis of the striatum of halothane-anesthetized rats was used to study the participation of local cholinergic and GABAergic neurotransmission in NMDA receptor-modulated striatal dopamine release and metabolism. Reverse dialysis.of NMDA (1 mM) evoked a 10-fold increase in dopamine efflux and reduced DOPAC and HVA to > 20% of basal values. The effect of NMDA on dopamine efflux was abolished by atropine (10 microM) but unaffected by (+)-bicuculline (50 microM). NMDA-induced decrease in DOPAC (but not HVA) efflux was potentiated by atropine, whereas (+)-bicuculline attenuated the decrease in DOPAC and HVA. Compared to our previous studies in unanesthetised rats, our data suggest that halothane anesthesia alters the balance between NMDA-stimulated cholinergic and GABAergic influences on striatal dopamine release and metabolism. Differential sensitivity to halothane of NMDA receptors expressed by the neurones mediating these modulatory influences, or loss of specific NMDA receptor populations through voltage-dependent Mg2+ block under anesthesia, could underlie these observations.     

Environmental implications of recombinant DNA technology

Applications of recombinant DNA technology are discussed as a backdrop for evaluation of the environmental impacts of this technology. Some of applications include using traditional biological techniques for specific purposes, including nitrogen fixation, microbial pesticides, and waste treatment. In these instances the final product lies along a continuum, beginning with an organism marginally performing its function, and ending with one that is highly specialised and very efficient in what it does. One may move along this continuum toward the ‘perfect’ microorganism by using traditional methodologies of mutagenesis and selection, recombinant DNA technology, or a combination of the two.     

Spontaneous Release of γ-Aminobutyric Acid Formed from Putrescine and Its Enhanced Ca2+-Dependent Release by High K+ Stimulation in the Brains of Freely Moving Rats

The spontaneous release of [3H] gamma-aminobutyric acid ([3H]GABA) in various areas of rat brain injected with [3H]putrescine was examined using a push-pull perfusion technique. The release in a 25-min perfusate was highest in the caudate-putamen. The effect of high K+ stimulation on the release of [3H]GABA formed from [3H]putrescine was examined in the caudate-putamen. The release was enhanced by high K+ solution in a Ca2+-dependent manner.     

Compensation in pre-synaptic dopaminergic function following nigrostriatal damage in primates

Clinical symptoms of Parkinson's disease only become evident after 70-80% reductions in striatal dopamine. To investigate the importance of pre-synaptic dopaminergic mechanisms in this compensation, we determined the effect of nigrostriatal damage on dopaminergic markers and function in primates. MPTP treatment resulted in a graded dopamine loss with moderate to severe declines in ventromedial striatum (approximately 60-95%) and the greatest reductions (approximately 95-99%) in dorsolateral striatum. A somewhat less severe pattern of loss was observed for striatal nicotinic receptor, tyrosine hydroxylase and vesicular monoamine transporter expression. Declines in striatal dopamine uptake and transporter sites were also less severe than the reduction in dopamine levels, with enhanced dopamine turnover in the dorsolateral striatum after lesioning. The greatest degree of adaptation occurred for nicotine-evoked [(3)H]dopamine release from striatal synaptosomes, which was relatively intact in ventromedial striatum after lesioning, despite > 50% declines in dopamine. This maintenance of evoked release was not due to compensatory alterations in nicotinic receptor characteristics. Rather, there appeared to be a generalized preservation of release processes in ventromedial striatum, with K(+)-evoked release also near control levels after lesioning. These combined compensatory mechanisms help explain the finding that Parkinson's disease symptomatology develops only with major losses of striatal dopamine.     

Enhancement effect of hematite nanoparticles on fermentative hydrogen production

The effects of hematite nanoparticles concentration (0-1600 mg/L) and initial pH (4.0-10.0) on hydrogen production were investigated in batch assays using sucrose-fed anaerobic mixed bacteria at 35 °C. The optimum hematite nanoparticles concentration with an initial pH 8.48 was 200 mg/L, with the maximum hydrogen yield of 3.21 mol H₂/mol sucrose which was 32.64% higher than the blank test. At 200 mg/L hematite nanoparticles concentration, further initial pH optimization experiments indicated that at pH 6.0 the maximum hydrogen yield reached to 3.57 mol H₂/mol sucrose and hydrogen content was 66.1%. The slow release of hematite nanoparticles had been recorded by transmission electron microscopy (TEM). In addition, TEM analysis indicated that the hematite nanoparticles can affect the shape of bacteria, namely, its length increased from ca. 2.0-3.6 μm to ca. 2.6-5.6 μm, and width became narrower.     

Stereoselective drug release from Ketoprofen and Ricobendazole matrix tablets

Crystalline characteristics of racemic, pure R and S enantiomers and physical mixtures of Ketoprofen (KET) have been studied by DSC and X‐ray diffractometry. Aqueous solubilities were 182.6 ± 9.1 μg/ml for racemic KET, 259.6 ± 6.6 μg/ml for R‐KET, and 304.3 ± 2.7 μg/ml for S‐KET. Matrix tablets made with racemic and physical mixtures of KET show stereoselective drug release, which is faster for S‐KET than for R‐KET. This effect is more marked when the chiral excipient hydroxypropylmethylcellulose (HPMC) is used in place of the achiral Eudragit RL. Stereoselectivity of release is also affected by the amount of KET. Similar results were obtained when another chiral drug with low solubility, Ricobendazole (RBZ), is used. Depending on the excipient and drug dosage, more or less marked stereoselective drug release is obtained in RBZ matrix tablet formulations. Chirality 11:611–615, 1999. © 1999 Wiley‐Liss, Inc.     

Calcium‐induced calcium release contributes to somatic secretion of serotonin in leech Retzius neurons

We analyzed the contribution of calcium (Ca²⁺)‐induced Ca²⁺ release to somatic secretion in serotonergic Retzius neurons of the leech. Somatic secretion was studied by the incorporation of fluorescent dye FM1‐43 upon electrical stimulation with trains of 10 impulses and by electron microscopy. Quantification of secretion with FM1‐43 was made in cultured neurons to improve optical resolution. Stimulation in the presence of FM1‐43 produced a frequency‐dependent number of fluorescent spots. While a 1‐Hz train produced 19.5 ± 5.0 spots/soma, a 10‐Hz train produced 146.7 ± 20.2 spots/soma. Incubation with caffeine (10 mM) to induce Ca²⁺ release from intracellular stores without electrical stimulation and external Ca²⁺, produced 168 ± 21.7 spots/soma. This staining was reduced by 49% if neurons were preincubated with the Ca²⁺‐ ATPase inhibitor thapsigargin (200 nM). Moreover, in neurons stimulated at 10 Hz in the presence of ryanodine (100 μM) to block Ca²⁺‐induced Ca²⁺ release, FM1‐43 staining was reduced by 42%. In electron micrographs of neurons at rest or stimulated at 1 Hz in the ganglion, endoplasmic reticulum lay between clusters of dense core vesicles and the plasma membrane. In contrast, in neurons stimulated at 20 Hz, the vesicle clusters were apposed to the plasma membrane and flanked by the endoplasmic reticulum. These results suggest that Ca²⁺‐induced Ca²⁺ release produces vesicle mobilization and fusion in the soma of Retzius neurons, and supports the idea that neuronal somatic secretion shares common mechanisms with secretion by excitable endocrine cells. © 2004 Wiley Periodicals, Inc. J Neurobiol, 2004     

Partial alanine scan of mast cell degranulating peptide (MCD): importance of the histidine- and arginine residues.

The influence of the two histidine and two arginine residues of mast cell degranulating peptide (MCD) in activity and binding was studied by replacing these amino acids in the MCD sequence with L-alanine. Their histamine releasing activity was determined on rat peritoneal mast cells. Their binding affinity to the FcepsilonRIalpha binding subunit of the human mast cell receptor protein, was carried out using fluorescence polarization. The histamine assay showed that replacement of His13 by Ala o ccurred without loss of activity compared with the activity of MCD. Alanine substitutions for Arg7 and His8 resulted in an approximately 40 fold increase, and for Arg16 in a 14-fold increase in histamine-releasing activity of MCD. The binding affinities of the analogs were tested by competitive displacement of bound fluorescent MCD peptide from the FcepsilonRIalpha binding protein of the mast cell receptor by the Ala analogs using fluorescence polarization. The analogs Ala8 (for His) and Ala16 (for Arg) showed the same binding affinities as MCD, whereas analog Ala7 (for Arg) and analog Ala13 (for His) showed slightly better binding affinity than the parent compound. This study showed that the introduction of alanine residues in these positions resulted in MCD agonists of diverse potency. These findings will be useful in further MCD structure-activity studies.     

Studies on the isolation of penicillin acylase from Escherichia coli by aqueous two-phase partitioning

A method of enzyme release and aqueous two-phase extraction is described for the separation of penicillin acylase from Escherichia coli cells. Butyl acetate, 12% (v/v), treatment combined with freeze-thawing gives up to 70% enzyme release. For polyethylene glycol (PEG) + phosphate two-phase extraction systems the enzyme purity and yield were rather low. Modified PEG, including PEG-ampicillin, PEG-aniline, PEG-phosphate, and PEG-trimethylamine, were synthesized and used in aqueous two-phase systems; PEG-trimethylamine is the most satisfactory. A system containing 12% (w/w) PEG4000, 8% (w/w) of which is PEG-trimethylamine, with 0.7M potasium phosphate at pH 7.2, resulted in the enzyme selective partition being greatly enhanced by charge directed effects. Possible mechanisms for the separation process are discussed. (c) 1992 John Wiley & Sons, Inc.