Effect of low-dose treatment with selegiline on dopamine transporter (DAT) expression and amphetamine-induced dopamine release in vivo

1. Chronic treatment with low doses of the selective monoamine oxidase (MAO) type B inhibitors selegiline [(-)-deprenyl] and rasagiline, causes elevation in extracellular level of 3,4-dihydroxyphenylethylamine (dopamine) in the rat striatum in vivo (Lamensdorf et al., 1996). The present study was carried out to determine whether this effect of selegiline could be the result of an inhibition of the high-affinity dopamine neuronal transport process. 2. Changes in activity of the dopamine transporter (DAT) in vivo following selegiline treatment were evaluated indirectly by microdialysis technique in the rat, from the change in striatal dopamine extracellular concentration following systemic amphetamine administration (4 mg kg(-1), i.p.). Striatal levels of the DAT molecule were determined by immunoblotting. Uptake of [3H]-dopamine was determined in synaptosomes from selegiline-treated animals. 3. Amphetamine-induced increase in striatal extracellular dopamine level was attenuated by one day and by chronic (21 days) treatment with selegiline (0.25 mg kg(-1), s.c.). 4. Striatal levels of DAT were elevated after 1 and 21 days treatment with selegiline, but were not affected by clorgyline, rasagiline, nomifensine or amphetamine. 5. The increase in DAT expression, and attenuation of amphetamine-induced dopamine release, were not accompanied by a change in [3H]-dopamine uptake in synaptosomes of selegiline-treated animals. 6. The results suggest that a reversible inhibition of dopamine uptake occurs following chronic low dose selegiline treatment in vivo which may be mediated by an increase in endogenous MAO-B substrates such as 2-phenylethylamine, rather than by the inhibitor molecule or its metabolites. Increased DAT expression appears to be a special property of the selegiline molecule, since it occurs after one low dose of selegiline, and is not seen with other inhibitors of MAO-A or MAO-B. The new DAT molecules formed following selegiline treatment appear not to be functionally active.     

Selective monoamine oxidase subtype inhibition and striatal extracellular dopamine in the guinea-pig

Striatal microdialysate levels of dopamine (DA) in conscious guinea-pigs were measured following acute (1 day) and chronic (21 days) treatment with deprenyl (2 and 0.25 mg kg(-1) s.c., respectively) or clorgyline (4 and 1 mg kg(-1) s.c., respectively), as well as by combination treatment using the same doses of the two inhibitors. These treatments caused selective inhibition of monoamine oxidase type B (MAO-B) or monoamine oxidase type A (MAO-A) respectively. Neither acute nor chronic treatments with deprenyl or clorgyline increased basal or KCl-induced DA levels. Acute and chronic clorgyline treatments were accompanied by significant reductions in striatal microdialysate 3,4-dihydroxyphenylacetic acid (DOPAC) and homovanillic acid (HVA). On the other hand, both acute and chronic deprenyl treatments were accompanied by significant increases in microdialysate HVA with no effect on DOPAC levels. Acute or chronic combined treatment with clorgyline and deprenyl increased tissue but not microdialysate DA levels. The combination treatment given chronically also reduced KCl-induced DA release but enhanced amphetamine-induced DA release. Microdialysate DA levels increased to a smaller extent in guinea-pig than in rat following local striatal infusion of GBR-12909 (100 microM). The difference between guinea-pigs and rats in the response to GBR-12909, could be the result of a lower dopaminergic innervation and/or density of DA transporter. This difference may explain why striatal microdialysate DA levels increased following chronic deprenyl treatment in the rat but not in the guinea-pig.     

Orbital porencephalic cyst following penetrating orbitocranial trauma

In a 10-year-old boy an orbitocranial penetrating wound produced by an umbrella tip caused an orbital roof bone fragment to penetrate up to the anterior part of the third ventricle behind the left foramen of Monro. Hemorrhages and encephalomalacia developed along the trajectory of the fragment and subsequently a porencephalic cyst was formed at this site. Six months after the trauma, increased pressure developed in the left ventricular system due to obstructive hydrocephalus and consequently the porencephalic cyst herniated into the orbit through the orbital roof fracture, producing intermittent diplopia, left exophthalmos, and palpebral swelling. A ventriculo-peritoneal shunt led to shrinkage of the orbital cyst content and resolution of the symptoms.     

Effect of glipizide on dopamine synthesis, release and metabolism in PC12 cells

Sulfonylureas block ATP-dependent K(+) channels (K/ATP channels) in pancreatic beta cells and brain gamma-aminobutyric acid (GABA) containing neurons causing depolarization-evoked insulin or GABA release. In high concentrations, sulfonylureas also inhibit catecholamine release from bovine adrenal chromaffin cells and isolated guinea pig aorta. In this study, we examined the effect of glipizide, a sulfonylurea, on dopamine release from PC12 cells and found that neither basal nor K(+)-stimulated dopamine release was affected. Although PC12 cells expressed mRNA for the K/ATP channel, functional K/ATP channels could not be demonstrated electrophysiologically, consistent with the lack of effect of glipizide on dopamine release. Glipizide did, however, increase cytoplasmic retention of the acidic dopamine metabolites, 3, 4-dihydroxyphenylacetic acid (DOPAC) and homovanillic acid (HVA), indicating blockade of their outward transport. The cellular accumulation of DOPAC was accompanied by reduced tyrosine hydroxylase activity and reduced formation of dopamine and its metabolites presumably by a negative feedback effect of the increased cytoplasmic concentrations of DOPAC.     

Acidic dopamine metabolites are actively extruded from PC12 cells by a novel sulfonylurea-sensitive transporter

Incubation of PC 12 cells with the sulfonylurea drug, glipizide (1-100 microM), increased intracellular levels of the acidic metabolites of dopamine, 3,4-dihydroxyphenylacetic acid (DOPAC) and homovanillic acid (HVA). The levels of these acids in the medium were decreased, indicating the presence of a sulfonylurea-sensitive organic anion transporter. In the present study, we demonstrate that the sulfonylurea-sensitive transport of acidic dopamine metabolites is unidirectional, ATP dependent, unaffected by ouabain or by tetrodotoxin and blocked by drugs that interact with the multidrug-resistance protein-1 (MRP1). However, over-expression of MRP1 did not affect transport of the acid metabolites. The pharmacological profile and ion dependence of the transporter also differs from that of known ATP-binding cassette (ABC) family members. Using microdialysis, we also demonstrated a sulfonylurea-sensitive transport process in the striatum of freely moving rats. These results show that acidic dopamine metabolites are actively secreted from dopaminergic cells into surrounding extracellular fluid by a previously undescribed transporter.     

Attenuation of methamphetamine induced dopaminergic neurotoxicity by flupirtine: microdialysis study on dopamine release and free radical generation

Summary. Flupirtine is a triaminopyridine derived centrally acting analgetic, which has been found to display neuroprotective effects in models of excitotoxic cell damage, global, and focal ischemia, but no direct interaction with any component of the N-methyl-d-aspartate (NMDA) and glutamate triggered Ca²⁺-channel. Additionally flupirtine shows potent antioxidant effects in isolated mitochondria and cell culture. Work in models of monoamine depletion and neuroleptic induced catalepsy in rats suggests a interaction of flupirtine with the dopaminergic neurotransmitter system as well. This prompted us to examine the effect of flupirtine on methamphetamine toxicity in mice and to investigate the influence on dopamine release and free radical formation in the rat striatum by microdialysis that may explain methamphetamine neurotoxicity. Pretreatment of C57-BL mice with flupirtine (4 × 10 mg/kg) significantly attenuated the striatal dopamine loss after methamphetamine application (4 × 5 mg/kg). In rats, a single injection of 10 mg/kg flupirtine reduced the methamphetamine induced striatal dopamine release by almost 50%, as measured by in vivo microdialysis. Flupirtine, however, did not influence the increase of free radical formation after methamphetamine infusion, which was assayed after infusion of salicylic acid by quantification of 2,3- and 2,5-dihydroxybenzoic acid. This suggests that other mechanisms rather than dopamine metabolism and autoxidation, may contribute to methamphetamine neurotoxicity. Received March 12, 2002; accepted August 22, 2002 Published online December 9, 2002 Acknowledgements The authors acknowledge the support of ASTA Medica (Frankfurt/Main, Germany), the Goldings Parkinson Fund (Technion, Haifa, Israel), and the National Parkinson Foundation (USA). MG thanks the Minerva Foundation (Heidelberg, Germany) for his postdoctoral fellowship an National Parkinson Foundation, Miami. We also wish to thank Ms. B. Pinchasi for experimental support. Authors' address: Prof. M. B. H. Youdim, Eve Topf and NPF Centers and Department of Pharmacology, Faculty of Medicine, Technion, P.O. Box 9649, Haifa 31096, Israel, e-mail: youdim@tx.technion.ac.il Abbreviations DOPAC 2,3-dihydroxyphenylacetic acid; HVA homovanillic acid; MPTP N-Methylphenyltetrahydropyridine; NMDA N-Methyl-D-aspartate; VDAC voltage dependent anion channel.     

Forceful endoscopic extraction of ureteral calculi

Two hundred seventy cases of stone manipulation are reviewed. Manipulation was successful in 68 per cent and 9 per cent had to have open ureterolithotomy. There were no serious complications. An aggressive approach to the treatment of lower ureteral calculi is recommended. Manipulation is indicated if the patient is incapacitated. If certain rules are followed, the risk of complications should be minimal.     

Use of transvaginal endosonography in the evaluation of women with stress urinary incontinence.

Hypermobility of the bladder neck in response to increased intra-abdominal pressure is the anatomical cause of uncomplicated stress urinary incontinence in women. Transvaginal endosonography is a reliable, minimally invasive technique for demonstrating bladder neck hypermobility in patients with genuine stress urinary incontinence. Of 279 patients with genuine stress urinary incontinence evaluated during a 24-month period 271 (97%) had bladder neck hypermobility demonstrated by transvaginal endosonography. Resolution of stress urinary incontinence after surgical bladder neck suspension correlated with stabilization of bladder neck mobility on ultrasound examination. The technique is painless and easily performed in the office setting.