Mechanism by which brain-derived neurotrophic factor increases dopamine release from the rabbit retina.
(17/185)
PURPOSE: To determine whether BDNF modulates the release of dopamine from amacrine cells in the rabbit retina. METHODS: Isolated retinas from rabbits killed with pentobarbital were incubated in Krebs bicarbonate medium containing pargyline, nomifensine, and bovine serum albumin. The medium was changed at 10-minute intervals, and the dopamine in the resultant samples measured by HPLC. Five samples were collected to establish the spontaneous resting release of dopamine, and then the retina was exposed to BDNF for a further two collection periods. Double-label immunohistochemistry was used to identify tyrosine hydroxylase containing neurons and to localize TrkB (BDNF) receptors. RESULTS: Exposure of the retina to BDNF (70-150 ng/mL) caused a concentration-dependent increase in the release of dopamine. The maximum effect was produced by 150 ng/mL BDNF, which almost doubled the release. The BDNF-evoked release was abolished in low-calcium/high-magnesium medium. It was also prevented by the tyrosine kinase inhibitors k252a and genistein, the phospholipase inhibitor U73122, and the sarco/endoplasmic reticulum Ca(2+)-ATPase (SERCA) inhibitors thapsigargin and cyclopiazonic acid. Antagonists of gamma-aminobutyric acid (GABA) and glutamate did not affect the BDNF-evoked release of dopamine. ELISA assay confirmed the presence of BDNF in the retina, and immunohistochemistry revealed that some tyrosine hydroxylase-containing neurons possessed TrkB receptors. CONCLUSIONS: BDNF quickly (within minutes) increases the release of dopamine from amacrine cells in the rabbit retina by an action that is likely to involve TrkB receptors. The mechanism linking TrkB receptor activation to the release of dopamine involves activation of phospholipase-Cgamma, with the subsequent production of IP(3) and calcium release from the endoplasmic reticulum. The resultant capacitative entry of calcium seems to be the actual trigger for BDNF-induced release of dopamine. (+info)
Effects of mazindol, a non-phenylethylamine anorexigenic agent, on biogenic amine levels and turnover rate.
(18/185)
1 Mazindol is a new anorexigenic agent which possesses a different chemical structure from that of phenylethylamines, but shows a pharmacological profile similar to that of (+)-amphetamine. 2 Mazindol neither altered whole brain monoamine levels (noradrenaline (NA), dopamine, 5-hydroxytryptamine (5-HT)) nor changed NA levels in the hypothalamus or dopamine levels in the caudate nucleus. 3 Mazindol enhanced dopamine turnover rate in the caudate nucleus, as shown by the increased rate of dopamine decline after blockade of catecholamine synthesis by alpha-methyl-p-tyrosine and decreased the conversion index of (3H)-tyrosine into brain NA. 4 Mazindol administration did not modify pargyline-induced decline of 5-hydroxyindoleacetic acid suggesting that 5-HT turnover is not altered by this drug. (+info)
Uptake of 5-hydroxytryptamine in different parts of the brain of the rabbit after intraventricular injection.
(19/185)
1 The uptake of 5-hydroxytryptamine (5-HT) was investigated in different areas of the rabbit brain (anterior hypothalamus, the raphe, the region of the substantia nigra, several cortical areas and the medulla oblongata) after intraventricular injection in pargyline pretreated animals by the formaldehyde-induced histochemical fluorescence method. 2 The distribution of fluorescence showed that the uptake of 5-HT, after circulation in the cerebrospinal fluid, caused a general increase in intensity of green yellow to yellow background fluorescence. There was an increased fluorescence in the nerve terminals, but no uptake occurred either in the cell bodies of neurones or in the glial cells. (+info)
Effects of various drugs on serum free and total tryptophan levels and brain tryptophan metabolism in rats.
(20/185)
Various drugs known to bind to serum albumin were examined to determine whether or not they influenced the level of free tryptophan in serum in vitro and in vivo. Possible relationships between the serum free tryptophan level and serotonin (5-HT) synthesis in the brain and the hypothermic effects of these drugs were investigated. Of the drugs examined, sodium salicylate, sodium benzoate and indomethacin caused a significant increase in the concentration of serum free tryptophan and stimulated the synthesis of 5-HT in the brain. Hypothermia induced by salicylate and indomethacin was potentiated by pretreatment with pargyline, a monoamine oxidase inhibitor. Administration of benzoate did not cause any change in body temperature, but after pargyline a hypothermia did occur. However, pretreatment with parachlorophenylalanine, an inhibitor of 5-HT synthesis, did not influence the hypothermia induced by salicylate and indomethacin. Relationship between the hypothermic effect and the increase of 5-HT synthesis in the brain after a large dose of salicylate and indomethacin is discussed. (+info)
Effects of reboxetine on sympathetic neuroeffector transmission in rabbit carotid artery.
(21/185)
The effect of reboxetine on sympathetic neuroeffector transmission in rabbit isolated carotid artery was examined. Reboxetine (10-8-3 x 10-6 M) and cocaine (10-6-3 x 10-5 M), but not desipramine (10-8-3 x 10-7 M), increased contractions evoked by electrical field stimulation. At higher concentrations, reboxetine (10-4 M), cocaine (3 x 10-4 M), and desipramine (3 x 10-7-10-5 M) inhibited the neurogenic contractions. The enhancement seen with reboxetine and cocaine was partially reversible, whereas the inhibition was readily reversible. Reboxetine (10-7 M) and cocaine (10-5 M) prevented the inhibitory action of bretylium (10-6 M). Reboxetine (10-8-10-5 M), desipramine (10-7-10-4 M), and cocaine (10-6-10-5 M) increased the stimulation-evoked [3H]norepinephrine release. Pargyline (5 x 10-4 M) augmented the facilitatory effect of reboxetine (3 x 10-9-10-6 M) and cocaine (10-7-3 x 10-5 M). Reboxetine (10-8-10-6 M), desipramine (10-8-10-6 M), and cocaine (3 x 10-8-10-5 M) reduced the [3H]norepinephrine (10-8 M) uptake. Reboxetine (10-7 M) and cocaine (10-5-2 x 10-4 M) enhanced the contractions evoked by phenylephrine and norepinephrine. Higher concentrations of reboxetine antagonized the contractions. Reboxetine (10-5-6 x 10-5 M) antagonized the contractions evoked by potassium. The contractions evoked by tyramine (3 x 10-6-10-3 M) was reduced by reboxetine (3 x 10-8-10-6 M) and by cocaine (10-7-10-5 M). We conclude that reboxetine inhibits the membrane amine pump (uptake-1) in the terminals of postganglionic adrenergic neurons in a cocaine-like manner. (+info)
Structural comparison of human monoamine oxidases A and B: mass spectrometry monitoring of cysteine reactivities.
(22/185)
Monoamine oxidases (MAO) A and B are approximately 60-kDa outer mitochondrial membrane flavoenzymes catalyzing the degradation of neurotransmitters and xenobiotic arylalkyl amines. Despite 70% identity of their amino acid sequences, both enzymes exhibit strikingly different properties when exposed to thiol-modifying reagents. Human MAO A and MAO B each contain 9 cysteine residues (7 in conserved sequence locations). MAO A is inactivated by N-ethylmaleimide (NEM) much faster (tau(1/2) = approximately 3 min) than MAO B (tau(1/2) = approximately 8 h). These differences in thiol reactivities are also demonstrated by monitoring the NEM modification stoichiometries by electrospray mass spectrometry. Inactivation of either enzyme with acetylenic inhibitors results in alterations of their thiol reactivities. Cys5 and Cys266 were identified as the only residues modified by biotin-derivatized NEM in clorgyline-inactivated MAO A and pargyline-inactivated MAO B, respectively. The x-ray structure of MAO B (Binda, C., Newton-Vinson, P., Hubalek, F., Edmondson, D. E., and Mattevi, A. (2002) Nat. Struct. Biol. 9, 22-26) shows that Cys5 is located on the surface of the molecule opposite to the membrane-binding region. Cys266 in MAO A is predicted to be located in the same region of the molecule. These thiol residues are also modified by biotin-derivatized NEM in the mitochondrial membrane-bound MAO A and MAO B. This study shows that the MAO A structure is "more flexible" than that of MAO B and that clorgyline and pargyline inactivation of MAO A and B, respectively, increases the structural stability of both enzymes. No evidence is found for the presence of disulfide bonds in either enzyme, contrary to a previous suggestion. (+info)
Intracellular patch electrochemistry: regulation of cytosolic catecholamines in chromaffin cells.
(23/185)
Alterations in the cytosolic pool directly affect neurotransmitter synthesis and release and are suggested to be key factors in various neurodegenerative disorders. Although this cytosolic pool is the most metabolically active, it is miniscule compared with the amount of vesicular transmitter and has never been quantified separately. Here, we introduce intracellular patch electrochemistry (IPE), a technique that for the first time provides direct measurements of cytosolic oxidizable molecules in single mammalian cells. In amperometric mode, IPE detects total catechols, whereas in cyclic voltammetric mode, it preferentially measures catecholamines. In cultured chromaffin cells, the total cytosolic catechol concentration was 50-500 microm, of which approximately 10% were catecholamines. Reserpine, a vesicular monoamine transporter inhibitor, had no effect on the catecholamine pool but increased total catechols by fourfold to fivefold. Combined with pargyline, a monoamine oxidase inhibitor, reserpine increased catecholamine levels in the cytosol by approximately sixfold. Amphetamine induced a transient approximately fivefold accumulation of cytosolic catecholamines and a slow increase of total catechols. In cells incubated with 3,4-dihydroxy-L-phenylalanine (L-DOPA), catecholamines increased by approximately 2.5-fold and total catechols increased by approximately fourfold. Cytosolic catecholamines returned to control levels +info)
The insertion of monoamine oxidase A into the outer membrane of rat liver mitochondria.
(24/185)
Human monoamine oxidase A that had been synthesized in a reticulocyte lysate translation system was capable of binding to and inserting into either rat liver mitochondria or isolated mitochondrial outer membranes. The inserted form was as resistant to proteinase K as endogenous mitochondrial monoamine oxidase A. The insertion, but not the binding, of monoamine oxidase A was prevented by depleting the reaction mixture of either ATP (with apyrase) or ubiquitin (with purified antibodies against this polypeptide). Addition of ATP or ubiquitin, respectively, to these depleted mixtures restored the insertion of the enzyme. In the absence of mitochondria, in vitro synthesized monoamine oxidase A did not catalyze its own alkylation by the mechanism-based inhibitor, [3H]clorgyline. However, both monoamine oxidase A that had been membrane-inserted in vitro and monoamine oxidase A that had been bound to the mitochondria under conditions of ATP depletion catalyzed adduct formation. Furthermore, reaction of either clorgyline or another mechanism-based inhibitor, pargyline, with the membrane-bound enzyme during ATP depletion inhibited the insertion of monoamine oxidase A when ATP was restored. These observations indicate that monoamine oxidase A acquired a catalytically active conformation on interaction with the mitochondrial outer membranes prior to its ATP and ubiquitin-dependent insertion into the membrane. (+info)