Systematic review and meta-analysis of the efficacy and safety of amfepramone and mazindol as a monotherapy for the treatment of obese or overweight patients

The aim of this study was to evaluate efficacy and safety of amfepramone, fenproporex and mazindol as a monotherapy for the treatment of obese or overweight patients. A systematic review of primary studies was conducted, followed by a direct meta-analysis (random effect) and mixed treatment comparison. Medline and other databases were searched. Heterogeneity was explored through I2 associated with a p-value. Of 739 identified publications, 25 were included in the meta-analysis. The global evaluation of Cochrane resulted in 19 studies with a high level of bias and six with unclear risk. Due to the lack of information in primary studies, direct meta-analyses were conducted only for amfepramone and mazindol. Compared to placebo, amfepramone resulted in higher weight loss in the short-term (<180 days; mean difference (MD) -1.281 kg; p<0.05; I2: 0.0%; p=0.379) and long-term (≥180 days; MD -6.518 kg; p<0.05; I2: 0.0%; p=0.719). Only studies with long-term follow up reported efficacy in terms of abdominal circumference and 5-10% weight reduction. These results corroborated the finding that the efficacy of amfepramone is greater than that of placebo. Treatment with mazindol showed greater short-term weight loss than that with placebo (MD -1.721 kg; p<0.05; I2: 0.9%; p=0.388). However, metabolic outcomes were poorly described, preventing a meta-analysis. A mixed treatment comparison corroborated the direct meta-analysis. Considering the high level of risk of bias and the absence of important published outcomes for anti-obesity therapy assessments, this study found that the evaluated drugs showed poor evidence of efficacy in the treatment of overweight and obese patients. Robust safety data were not identified to suggest changes in their regulatory status.

Structural basis for action by diverse antidepressants on biogenic amine transporters

The biogenic amine transporters (BATs) regulate endogenous neurotransmitter concentrations and are targets for a broad range of therapeutic agents including selective serotonin reuptake inhibitors (SSRIs), serotonin-noradrenaline reuptake inhibitors (SNRIs) and tricyclic antidepressants (TCAs). Because eukaryotic BATs are recalcitrant to crystallographic analysis, our understanding of the mechanism of these inhibitors and antidepressants is limited. LeuT is a bacterial homologue of BATs and has proven to be a valuable paradigm for understanding relationships between their structure and function. However, because only approximately 25% of the amino acid sequence of LeuT is in common with that of BATs, and as LeuT is a promiscuous amino acid transporter, it does not recapitulate the pharmacological properties of BATs. Indeed, SSRIs and TCAs bind in the extracellular vestibule of LeuT and act as non-competitive inhibitors of transport. By contrast, multiple studies demonstrate that both TCAs and SSRIs are competitive inhibitors for eukaryotic BATs and bind to the primary binding pocket. Here we engineered LeuT to harbour human BAT-like pharmacology by mutating key residues around the primary binding pocket. The final LeuBAT mutant binds the SSRI sertraline with a binding constant of 18 nM and displays high-affinity binding to a range of SSRIs, SNRIs and a TCA. We determined 12 crystal structures of LeuBAT in complex with four classes of antidepressants. The chemically diverse inhibitors have a remarkably similar mode of binding in which they straddle transmembrane helix (TM) 3, wedge between TM3/TM8 and TM1/TM6, and lock the transporter in a sodium- and chloride-bound outward-facing open conformation. Together, these studies define common and simple principles for the action of SSRIs, SNRIs and TCAs on BATs.

Time-course of SKF-81297-induced increase in glutamic acid decarboxylase 65 and 67 mRNA levels in striatonigral neurons and decrease in GABA(A) receptor alpha1 subunit mRNA levels in the substantia nigra, pars reticulata, in adult rats with a unilateral 6-hydroxydopamine lesion

Striatal projection neurons use GABA as their neurotransmitter and express the rate-limiting synthesizing enzyme glutamic acid decarboxylase (GAD) and the vesicular GABA transporter vGAT. The chronic systemic administration of an agonist of dopamine D1/D5-preferring receptors is known to alter GAD mRNA levels in striatonigral neurons in intact and dopamine-depleted rats. In the present study, the effects of a single or subchronic systemic administration of the dopamine D1/D5-preferring receptor agonist SKF-81297 on GAD65, GAD67, PPD and vGAT mRNA levels in the striatum and GABA(A) receptor alpha1 subunit mRNA levels in the substantia nigra, pars reticulata, were measured in rats with a unilateral 6-hydroxydopamine (6-OHDA) lesion. After a single injection of SKF-81297, striatal GAD65 mRNA levels were significantly increased at 3 but not 72 h. In contrast, striatal GAD67 mRNA levels were increased and nigral alpha1 mRNA levels were decreased at 72 but not 3 h. Single cell analysis on double-labeled sections indicated that increased GAD or vGAT mRNA levels after acute SKF-81297 occurred in striatonigral neurons identified by their lack of preproenkephalin expression. Subchronic SKF-81297 induced significant increases in striatal GAD67, GAD65, preprodynorphin and vGAT mRNA levels and decreases in nigral alpha1 mRNA levels. In the striatum contralateral to the 6-OHDA lesion, subchronic but not acute SKF-81297 induced a significant increase in GAD65 mRNA levels. The other mRNA levels were not significantly altered. Finally, striatal GAD67 mRNA levels were negatively correlated with nigral alpha1 mRNA levels in the dopamine-depleted but not dopamine-intact side. The results suggest that different signaling pathways are involved in the modulation by dopamine D1/D5 receptors of GAD65 and GAD67 mRNA levels in striatonigral neurons. They also suggest that the down-regulation of nigral GABA(A) receptors is linked to the increase in striatal GAD67 mRNA levels in the dopamine-depleted striatum.

The dopamine agonist piribedil with L-DOPA improves attentional dysfunction: relevance for Parkinson's disease

Cognitive deficits are often associated with motor symptoms in Parkinson's disease. This study investigates the ability of piribedil ([(methylenedioxy-3,4 benzyl)-4 pyperazinyl-1]-2 pyrimidine), a D(2)/D(3) dopamine (DA) receptor agonist with antagonist activity at alpha(2A)-adrenoceptors, to restore motor and attentional deficits in nigrostriatal 6-hydroxydopamine-lesioned rats. Subjects were trained to depress a lever, detect a stimulus occurring after variable foreperiods, and release the lever quickly afterward. Striatal DA depletions produce deficits in the timing of foreperiods and prolong reaction times. Although a subchronic treatment with piribedil (0.1-2 mg/kg) is not effective, a dose of 0.3 mg/kg administered for 3 weeks significantly reverses the akinetic deficits produced by the striatal dopamine depletion and progressively improves attentional deficits. When coadministered with the dopamine prodrug l-3,4-dihydroxyphenylalanine (l-DOPA) (3 mg/kg), piribedil (0.3 mg/kg) promotes a rapid and full recovery of preoperative performance. These results suggest that administration of l-DOPA in combination with piribedil in a chronic treatment as either initial or supplemental therapy for Parkinson's disease might improve cognitive functions while reducing the risk for motor complications.

Endothelin-1 inhibits the neuronal norepinephrine transporter in hearts of male rats

OBJECTIVE

Endothelin-1 (ET-1) potentiates norepinephrine (NE)-induced contractile responses. An impairment of cardiac NE re-uptake by the neuronal NE transporter (NET) contributes to an increased NE net release in failing hearts. We hypothesized that both phenomena are caused by ET-1-mediated inhibition of NET.

METHODS

[3H]-NE-uptake, electrical field stimulation-evoked NE overflow and left ventricular contractility (LV-dp/dt(max)) were measured in isolated perfused rat hearts. NET density on cardiac plasma membranes was determined by [3H]-mazindol binding. Experimental heart failure in rats was induced by transverse aortic constriction (TAC).

RESULTS

ET-1 inhibited cardiac [3H]-NE-uptake in a concentration- and time-dependent manner. The endothelin A receptor (ET(A)) antagonist BQ123 but not the endothelin B receptor (ET(B)) antagonist BQ788 abolished ET-1-induced reduction of [3H]-NE-uptake. Likewise, ET-1, but not the ET(B) agonist sarafotoxin S6c, enhanced the stimulated overflow of endogenous NE. In contrast, ET-1 inhibited the stimulated NE overflow during NET blockade (exocytotic NE release) via activation of ET(B). In isovolumically contracting healthy hearts, ET-1 potentiated the NE- but not isoprenaline-induced increase in LV-dp/dt(max). Since isoprenaline is not a NET substrate, the enhanced LV-dp/dt(max) response to NE thus depends on NET. In TAC rats, ET(A) antagonism by darusentan improved both impairment of cardiac [3H]-NE-uptake and reduction of [3H]-mazindol binding sites.

CONCLUSION

ET-1 inhibits cardiac NE re-uptake via ET(A) but attenuates exocytotic NE release via ET(B), resulting in opposite effects on cardiac NE net release. In healthy hearts, ET(A)-mediated inhibition of NE re-uptake exceeds ET(B)-mediated silencing of NE release and potentiates the NE-induced increase in left ventricular contractility. In TAC rats, endogenous ET-1 impairs NE re-uptake and promotes sympathetic overstimulation of failing hearts.

Perinatal heptachlor exposure increases expression of presynaptic dopaminergic markers in mouse striatum

Although banned in the 1970s, significant levels of the organochlorine pesticide heptachlor are still present in the environment raising concern over potential human exposure. In particular, organochlorine pesticides have been linked to an increased risk of Parkinson's disease. Studies from our laboratory and others have demonstrated that exposure of laboratory animals to heptachlor alters the levels and function of the dopamine transporter (DAT), an integral component of dopaminergic neurotransmission and a gateway for the dopaminergic neurotoxin MPTP. In this study, we examined the effects of developmental exposure to heptachlor on DAT, and other key components of the dopaminergic system, including the vesicular monoamine transporter 2 (VMAT2), tyrosine hydroxylase (TH), and aromatic amino acid decarboxylase (AADC). Female C57BL/6J mice received 0 or 3mg/kg heptachlor in peanut butter every 3 days for 2 weeks prior to breeding and throughout gestation and lactation until the offspring were weaned on postnatal day (PND) 21. On postnatal day 28, DAT, VMAT2, and TH levels were increased by 100, 70, and 30%, respectively, with no change in AADC levels or total dopamine levels. The ratio of DAT:VMAT2 was increased 29%. Since an increase in the DAT:VMAT2 ratio appears to predict susceptibility of brain regions to Parkinson's disease (PD) and results in increased toxicity of MPTP, these results suggest that alterations of the dopaminergic system by developmental heptachlor exposure may increase the susceptibility of dopamine neurons to toxic insult.

Neurochemical effects of chronic dietary and repeated high-level acute exposure to chlorpyrifos in rats

Very little is known about the effects of chronic exposure to relatively low levels of anticholinesterase insecticides or how the effects of chronic exposure compare to those of higher, intermittent exposure. To that end, adult male rats were fed an anticholinesterase insecticide, chlorpyrifos (CPF), for 1 year at three levels of dietary exposure: 0, 1, or 5 mg/kg/day (0+oil, 1+oil, and 5+oil). In addition, half of each of these groups also received a bolus dosage of CPF in corn oil ("spiked" animals; 60 mg/kg initially and 45 mg/kg thereafter) every 2 months (0+CPF, 1+CPF, 5+CPF). Animals were analyzed after 6 or 12 months of dosing, and again 3 months after cessation of dosing (i.e., "recovery" animals-six experimental groups with n = 4-6/group/time point). Cholinesterase (ChE) activity was measured in retina, whole blood, plasma, red blood cells, diaphragm, and brain [pons, striatum, and the rest of the brain (referred to simply as "brain")]. Muscarinic receptor density was assessed in retina, pons, and brain, whereas dopamine transporter density and the levels of dopamine and its metabolites were assessed in striatum. Cholinesterase activity at 6 and 12 months was not different in any of the tissues, indicating that a steady state had been reached prior to 6 months. The 1+oil group animals showed ChE inhibition only in the blood, whereas the 5+oil group exhibited > or = 50% ChE inhibition in all tissues tested. One day after the bolus dose, all three groups (0+CPF, 1+CPF, 5+CPF) showed > or = 70% ChE inhibition in all tissues. Muscarinic receptor density decreased only in the brain of the 5+oil and 5+CPF groups, whereas dopamine transporter density increased only at 6 months in all three spiked groups. Striatal dopamine or dopamine metabolite levels did not change at any time. Three months after CPF dosing ended, all end points had returned to control levels. These data indicate that, although chronic feeding with or without intermittent spiked dosages with CPF produces substantial biochemical changes in a dose- and tissue-related manner, there are no persistent biochemical changes.

Recognition of benztropine by the dopamine transporter (DAT) differs from that of the classical dopamine uptake inhibitors cocaine, methylphenidate, and mazindol as a function of a DAT transmembrane 1 aspartic acid residue

Binding of cocaine to the dopamine transporter (DAT) protein blocks synaptic dopamine clearance, triggering the psychoactive effects associated with the drug; the discrete drug-protein interactions, however, remain poorly understood. A longstanding postulate holds that cocaine inhibits DAT-mediated dopamine transport via competition with dopamine for formation of an ionic bond with the DAT transmembrane aspartic acid residue D79. In the present study, DAT mutations of this residue were generated and assayed for translocation of radiolabeled dopamine and binding of radiolabeled DAT inhibitors under identical conditions. When feasible, dopamine uptake inhibition potency and apparent binding affinity K(i) values were determined for structurally diverse DAT inhibitors. The glutamic acid substitution mutant (D79E) displayed values indistinguishable from wild-type DAT in both assays for the charge-neutral cocaine analog 8-oxa-norcocaine, a finding not supportive of the D79 "salt bridge" ligand-docking model. In addressing whether the D79 side chain contributes to the DAT binding sites of other portions of the cocaine pharmacophore, only inhibitors with modifications of the tropane ring C-3 substituent, i.e., benztropine and its analogs, displayed a substantially altered dopamine uptake inhibition potency as a function of the D79E mutation. A single conservative amino acid substitution thus differentiated structural requirements for benztropine function relative to those for all other classical DAT inhibitors. Distinguishing the precise mechanism of action of this DAT inhibitor with relatively low abuse liability from that of cocaine may be attainable using DAT mutagenesis and other structure-function studies, opening the door to rational design of therapeutic agents for cocaine abuse.

Inhibiting BDNF expression by antisense oligonucleotide infusion causes loss of nigral dopaminergic neurons

Brain derived neurotrophic factor (BDNF) expression is significantly reduced in the Parkinson's disease substantia nigra. This neurotrophin has potent affects on dopaminergic neuron survival protecting them from the neurotoxins MPTP and 6-hydroxydopamine (6-OHDA) commonly used to create animal models of Parkinson's disease and also promoting dopaminergic axonal sprouting. In this study, we demonstrate that an antisense oligonucleotide infusion (200 nM for 28 days) to prevent BDNF production in the substantia nigra of rats mimics many features of the classical animal models of Parkinson's disease. 62% of antisense treated rats rotate (P < or = 0.05) in response to dopaminergic receptor stimulation by apomorphine. 40% of substantia nigra pars compacta tyrosine hydroxylase immunoreactive neurons are lost (P < or = 0.00001) and dopamine uptake site density measured by (3)H-mazindol autoradiography is reduced by 34% (P < or = 0.005). Loss of haematoxylin and eosin stained nigral neurons is significant (P < or = 0.0001) but less extensive (34%). These observations indicate that loss of BDNF expression leads both to down regulation of the dopaminergic phenotype and to dopaminergic neuronal death. Therefore, reduced BDNF mRNA expression in Parkinson's disease substantia nigra may contribute directly to the death of nigral dopaminergic neurons and the development of Parkinson's disease.

Differential effects of prolonged high frequency stimulation and of excitotoxic lesion of the subthalamic nucleus on dopamine denervation-induced cellular defects in the rat striatum and globus pallidus

This study examined the effects of prolonged (4 days) high frequency stimulation (HFS) of the subthalamic nucleus (STN), in comparison with those of STN lesion, on the dopamine denervation-mediated cellular changes in the basal ganglia in a Wistar rat model of Parkinson's disease. STN HFS counteracted the dopamine lesion-induced increase in GAD67 mRNA expression in the output structures of the basal ganglia, as shown previously after STN lesion, providing cellular support for the similar antiparkinsonian benefits produced by the two surgical procedures. The dopamine denervation-induced increase in GAD67 mRNA levels in the globus pallidus was partially antagonized after HFS and totally reversed after ibotenate-induced STN lesion. The overexpression of striatal enkephalin mRNA tended to be further increased by HFS but was antagonized by STN lesion. The decrease in striatal substance P mRNA levels was affected neither by STN HFS nor lesion. As STN HFS for two hours was previously found not to interfere with the effects of dopamine lesion in the globus pallidus and striatum, the present data provide strong evidence that the effects of STN surgery in these structures involve long-term adaptive processes and that the rearrangements mediated by HFS and lesion are, at least in part, different.

A model of L-DOPA-induced dyskinesia in 6-hydroxydopamine lesioned mice: relation to motor and cellular parameters of nigrostriatal function

L-DOPA-induced dyskinesia is a major complication of L-DOPA pharmacotherapy in Parkinson's disease, and is thought to depend on abnormal cell signaling in the basal ganglia. In this study, we have addressed the possibility to model L-DOPA-induced dyskinesia in the mouse at both the behavioral and the molecular level. C57BL/6 mice sustained unilateral injections of 6-hydroxydopamine (6-OHDA) either in the medial forebrain bundle (MFB) or in the sensorimotor part of the striatum. Both types of lesion produced a similar degree of forelimb akinesia on the contralateral side of the body. The lowest dose of L-DOPA that could significantly relieve this akinetic deficit (i.e., 6 mg/kg) did not differ between MFB and intrastriatal lesions. The L-DOPA threshold dose for the induction of dyskinesia did however differ between the two lesion types. A daily dose of 6 mg/kg L-DOPA caused MFB lesioned mice to develop abnormal movements affecting orofacial, trunk, and forelimb muscles on the side contralateral to the lesion, whereas a daily dose of 18 mg/kg was required to produce comparable dyskinetic effects in the intrastriatally lesioned animals. The development of abnormal movements was accompanied by a striatal induction of DeltaFosB-like proteins and prodynorphin mRNA, that is, molecular markers that are associated with L-DOPA-induced dyskinesia in both rats and nonhuman primates. We conclude that 6-OHDA lesioned mice exhibit behavioral and cellular features of akinesia and L-DOPA-induced dyskinesia that are similar to those previously characterized in rats. The mouse model of L-DOPA-induced dyskinesia will provide a useful tool to study the molecular determinants of this movement disorder in transgenic mice strains.

Binding of [3H]mazindol to cardiac norepinephrine transporters: kinetic and equilibrium studies

The norepinephrine transporter (NET) is the carrier that drives the neuronal norepinephrine uptake mechanism (uptake1) in mammalian hearts. The radioligand [3H]mazindol binds with high affinity to NET. In this study, the kinetics of [3H]mazindol binding to NET were measured using a rat heart membrane preparation. Results from these studies were used to set up saturation binding assays designed to measure cardiac NET densities (Bmax) and competitive inhibition assays designed to measure inhibitor binding affinities (KI) for NET. Saturation binding assays measured NET densities in rat, rabbit, and canine hearts. Assay reproducibility was assessed and the effect of NaCl concentration on [3H]mazindol binding to NET was studied using membranes from rat and canine hearts. Specificity of [3H]mazindol binding to NET was determined in experiments in which the neurotoxin 6-hydroxydopamine (6-OHDA) was used to selectively destroy cardiac sympathetic nerve terminals in rats. Competitive inhibition studies measured KI values for several NET inhibitors and substrates. In kinetic studies using rat heart membranes, [3H]mazindol exhibited a dissociation rate constant koff=0.0123+/-0.0007 min(-1) and an association rate constant kon=0.0249+/-0.0019 nM(-1)min(-1). In saturation binding assays, [3H]mazindol binding was monophasic and saturable in all cases. Increasing the concentration of NaCl in the assay buffer increased binding affinity significantly, while only modestly increasing Bmax. Injections of 6-OHDA in rats decreased measured cardiac NET Bmax values in a dose-dependent manner, verifying that [3H]mazindol binds specifically to NET from sympathetic nerve terminals. Competitive inhibition studies provided NET inhibitor and substrate KI values consistent with previously reported values. These studies demonstrate the high selectivity of [3H]mazindol binding for the norepinephrine transporter in membrane preparations from mammalian hearts.

Destruction of midbrain dopaminergic neurons by using immunotoxin to dopamine transporter

1. The ability to target specific neurons can be used to produce selective neural lesions and potentially to deliver therapeutically useful moieties for treatment of disease. In the present study, we sought to determine if a monoclonal antibody to the dopamine transporter (anti-DAT) could be used to target midbrain dopaminergic neurons. 2. The monoclonal antibody recognizes the second, large extracellular loop of DAT. The antibody was conjugated to the "ribosome-inactivating protein"; saporin, and stereotactically pressure microinjected into either the center of the striatum or the left lateral ventricle of adult, male Sprague-Dawley rats. 3. Local intrastriatal injections produced destruction of dopaminergic neurons in the ipsilateral substantia nigra consistent with suicide transport of the immunotoxin. Intraventricular injections (i.c.v.) produced significant loss of dopaminergic neurons in the substantia nigra and ventral tegmental area bilaterally without evident damage to any other aminergic structures such as the locus coeruleus and raphe nuclei. To confirm the anatomic findings, binding of [3-H]mazindol to DAT in the striatum and midbrain was assessed using densitometric analysis of autoradiograms. Anti-DAT-saporin injected i.c.v. at a dose of 21 microg, but not 8 microg, produced highly significant decreases in mazindol binding consistent with loss of the dopaminergic neurons. 4. These results show that anti-DAT can be used to target midbrain dopaminergic neurons and that anti-DAT-saporin may be useful for producing a lesion very similar to the naturally occurring neural degeneration seen in Parkinson's disease. Anti-DAT-saporin joins the growing list of neural lesioning agents based on targeted cytotoxins.

Chronic intoxication with 3-nitropropionic acid in rats induces the loss of striatal dopamine terminals without affecting nigral cell viability

3-Nitropropionic acid (3NP) is a succinate dehydrogenase inhibitor allowing the generation of animal models of Huntington's disease. In the present study, we found that a 5-day continuous chronic infusion of 3NP produces loss of [3H]mazindol binding and tyrosine hydroxylase (TH) immunoreactivity in the striatal area of degeneration. This loss of dopamine terminals was not due to a loss of nigral neurons since the expression of TH as well as the number of TH-expressing neurons remained unaltered in the substantia nigra of rats treated by 3NP. This suggests that the 3NP-induced dopamine terminal loss is secondarily related to the striatal degeneration andlor to a direct effect of 3NP on striatal terminals and not to a primary effect on nigral cells.

Changes in GABA(B) receptor mRNA expression in the rodent basal ganglia and thalamus following lesion of the nigrostriatal pathway

Loss of striatal dopaminergic innervation in Parkinson's disease (PD) is accompanied by widespread alterations in GABAergic activity within the basal ganglia and thalamus. Accompanying changes in GABA(B) receptor binding have been noted in some basal ganglia regions in parkinsonian primates, suggesting that plasticity of this receptor may also occur in PD. However, the molecular mechanisms underlying the changes in receptor binding and the manner and extent to which different GABA(B) receptor mRNA subunits and splice-variants are affected remain unknown. This study used in situ hybridisation to examine the full profile of changes in expression of the known rat GABA(B) receptor genes and gene variants in the basal ganglia and thalamus of rats, brought about by degeneration of the nigrostriatal tract. All of the GABA(B) mRNA species examined showed unique expression patterns throughout the basal ganglia and thalamus. In addition, all exhibited a marked loss of expression (between 46 and 80%) in the substantia nigra pars compacta of animals bearing a complete 6-hydroxydopamine-induced lesion of the nigrostriatal tract, confirming the presence of these variants in dopaminergic neurones in this region. Further analysis of autoradioagrams revealed additional changes only in GABA(B(1a)) mRNA in discrete anatomical regions. Expression of the GABA(B(1a)) variant was significantly increased in the substantia nigra pars reticulata (33+/-2%), entopeduncular nucleus (26+/-1%) and the subthalamic nucleus (16+/-1%). Since these regions all receive reduced GABAergic innervation following nigrostriatal tract lesioning, it is possible that the increased expression occurs as a compensatory measure. In conclusion, these data demonstrate that GABA(B) receptor genes exhibit regional- and subunit/variant-specific plasticity at the molecular level under parkinsonian conditions.

Dual effects of intermittent or continuous L-DOPA administration on gene expression in the globus pallidus and subthalamic nucleus of adult rats with a unilateral 6-OHDA lesion

Intermittent oral doses of levodopa (L-DOPA) are routinely used to treat Parkinson's disease, but with prolonged use can result in adverse motor complications, such as dyskinesia. Continuous administration of L-DOPA achieves therapeutic efficacy without producing this effect, yet the molecular mechanisms are unclear. This study examined, by in situ hybridization histochemistry, the effects of continuous or intermittent L-DOPA administration on gene expression in the globus pallidus and subthalamic nucleus of adult rats with a unilateral 6-hydroxydopamine (6-OHDA) lesion of the nigrostriatal pathway. Results were compared to 6-OHDA-treated rats receiving vehicle. Our results provide original evidence that continuous L-DOPA normalizes the 6-OHDA-lesion-induced increase in mRNA levels encoding for the 67 kDa isoform of glutamate decarboxylase in neurons of the globus pallidus and cytochrome oxidase subunit I mRNA levels in the subthalamic nucleus. The extent of normalization did not differ between the continuous and intermittent groups. In addition, intermittent L-DOPA induced an increase in the mRNA levels encoding for the 65 kDa isoform of glutamate decarboxylase in globus pallidus neurons ipsilateral to the lesion and a bilateral increase in c-fos mRNA expression in the subthalamic nucleus. These results suggest that continuous L-DOPA tends to normalize the 6-OHDA-lesion-induced alterations in cell signaling in the pallido-subthalamic loop. On the other hand, we propose that chronic intermittent L-DOPA exerts a dual effect by normalizing cell signaling in a subpopulation of neurons in the globus pallidus and subthalamic nucleus while inducing abnormal signaling in another subpopulation.

Rapid reduction of ATP synthesis and lack of free radical formation by MPP+ in rat brain synaptosomes and mitochondria

MPTP is a neurotoxin thought to damage dopaminergic neurons through free radical formation. MPTP is metabolized in the brain to MPP(+), which is taken up into dopaminergic neurons via the dopamine transporter and assumed to impair mitochondrial function. We used striatal synaptosomes and telencephalic mitochondria to further investigate MPP(+) mechanism of action. For comparison, the respiratory toxins FCCP, a cyanide analog that uncouples mitochondrial ATP production, and rotenone, a NADH dehydrogenase inhibitor, were also tested. FCCP, MPP(+) and rotenone caused a rapid but stable decrease in [3H]dopamine (DA) uptake by striatal synaptosomes. Two free radical scavengers, the salen-manganese complex EUK-134, and the spin trap s-PBN, did not prevent MPP(+)-induced decrease in DA uptake. However, addition of ATP during synaptosome preparation resulted in partial recovery of MPP(+)-induced [3H]DA uptake decrease. Generation of oxygen free radicals by treatment of telencephalic mitochondria with MPP(+), FCCP, or rotenone, was evaluated by measuring DCF fluorescence, while light emission by the luciferin-luciferase complex was used to determine ATP levels. MPP(+), unlike rotenone, did not produce oxygen free radicals, but rather blocked ATP production in mitochondria, as did FCCP and rotenone. Taken together, these results suggest that MPP(+) toxicity, at least during its initial stages, is primarily due to a decrease in ATP synthesis by mitochondria and not to free radical formation.

Alterations in m-RNA expression for Cu,Zn-superoxide dismutase and glutathione peroxidase in the basal ganglia of MPTP-treated marmosets and patients with Parkinson's disease

Alterations occurring in the antioxidant enzymes, copper, zinc-dependent superoxide dismutase (Cu,Zn-SOD) and glutathione peroxidase (GPX) following nigral dopaminergic denervation are unclear. We now report on the distribution and levels of m-RNA for Cu,Zn-SOD and GPX in basal ganglia of normal and 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP)-treated common marmosets, and in normal individuals and patients with Parkinson's disease (PD) using in situ hybridization histochemistry and oligodeoxynucleotide (single-stranded DNA) probes. Cu,Zn-SOD and GPX m-RNA was present throughout basal ganglia (nucleus accumbens, caudate-putamen, globus pallidus, substantia nigra) in the common marmoset, with the highest levels being in substantia nigra (SN). Following MPTP induced nigral cell loss, Cu,Zn-SOD m-RNA levels were decreased in all areas but the SNr, and particularly in SNc (71%, P<0.001). MPTP-treatment had no effect on GPX m-RNA expression in any area of basal ganglia. Cu,Zn-SOD and GPX m-RNA was also present in the normal human SN. In PD, however, Cu,Zn-SOD m-RNA was significantly decreased (89%, P<0.005) in SNc, and there was a near-complete loss of GPX m-RNA in both SNc (100%, P<0.005) and SNr (88%, P<0.005). The loss of Cu,Zn-SOD m-RNA in SNc in MPTP-treated marmosets and patients with PD suggests that it is primarily located in dopaminergic neuronal cell bodies. The loss of GPX m-RNA in SNc in PD also suggests a localisation to dopaminergic cell bodies, but the similar change in SNr may indicate its presence in dopaminergic neurites. In contrast, the absence of change in GPX m-RNA in MPTP-treated primates appears to rule out its presence in dopaminergic cells in this species, but this may only be apparent and may reflect increased expression in glial cells following acute toxin treatment.

2,3-Disubstituted quinuclidines as a novel class of dopamine transporter inhibitors

There is considerable interest in developing dopamine transporter (DAT) inhibitors as potential therapies for the treatment of cocaine abuse. We report herein our pharmacophore-based discovery and molecular modeling-assisted rational design of 2,3-disubstituted quinuclidines as potent DAT inhibitors with a novel chemical scaffold. Through 3-D-database pharmacophore searching, compound 12 was identified as a very weak DAT inhibitor with K(i) values of 7.3 and 8.9 microM in [3H]mazindol binding and in inhibition of dopamine reuptake, respectively. Molecular modeling-assisted rational design and chemical modifications led to identification of potent analogues (-)-29 and 34 with K(i) values of 14 and 32 nM for both compounds in binding affinity and inhibition of dopamine reuptake, respectively. Behavioral pharmacological evaluations in rodents showed that 34 has a profile very different from cocaine. While 34 is substantially more potent than cocaine as a DAT inhibitor, it is approximately four times less potent than cocaine in mimicking the discriminative stimulus properties of cocaine in rat. On the other hand, 34 (3-30 mg/kg) lacks either the locomotor stimulant or stereotypic properties of cocaine in mice. Importantly, 34 blocks locomotor stimulant activity induced by 20 mg/kg cocaine in mice, with an estimated ED(50) of 19 mg/kg. Taken together, our data suggest that 34 represents a class of potent DAT inhibitors with a novel chemical scaffold and a behavioral pharmacological profile different from that of cocaine in rodents. Thus, 34 may serve as a novel lead compound in the ultimate development of therapeutic entities for cocaine abuse and/or addiction.

Unilateral infusion of a dopamine transporter antisense into the substantia nigra protects against MDMA-induced serotonergic deficits in the ipsilateral striatum

The present study was designed to elucidate the consequences of antisense oligonucleotide-mediated knockdown of striatal dopamine reuptake transporters on 3,4-methylenedioxymethamphetamine (MDMA)-induced neurotoxicity. Antisense oligonucleotide complementary to the mRNA translational start site of the rat dopamine transporter was delivered by constant (7 days) intranigral infusion with an osmotic minipump. Delivery of the antisense oligonucleotide by this method resulted in a 70% reduction in the density of the dopamine transporter in the ipsilateral striatum, as measured by [(3)H]mazindol binding. The effect of this transporter knockdown on MDMA-induced serotonergic neurotoxicity was then examined. MDMA (2x20 mg/kg, s.c., given 12 h apart) administered to control rats produced hyperthermia following the first dose and led to a 45-50% reduction in striatal serotonin, 5-hydroxyindoleacetic acid, and serotonin reuptake transporter density 1 week after the second dose. Conversely, in antisense-, but not missense-treated rats, a significant attenuation of MDMA-induced neurotoxicity was observed only in the ipsilateral striatum. The hyperthermic response elicited by MDMA was not altered by prior administration of antisense. In vivo microdialysis revealed that the antisense treatment attenuated MDMA-induced dopamine release in the ipsilateral striatum. These results suggest that the dopamine transporter plays an essential role in the neurodegeneration induced by MDMA, and provides additional support for the hypothesis that extracellular dopamine is involved in the neurotoxic process, at least in the striatum.

Assessment of mazindane, a pro-drug form of mazindol, in assays used to define cocaine treatment agents

The current studies compared mazindane (5-(4-chlorophenyl)-2,3-dihydro-5H-imidazo [2,1a] isoindole) hydrogen sulfate, a water soluble pro-drug of mazindol (5-(4-chlorophenyl-2,3-dihydro-5H-imidazo [2,1-a] isoindol-5-ol), with mazindol in assays used to define cocaine treatment agents. Both compounds enhanced motor activity (LMA) in Swiss Webster mice with ED(50) values of 2.5 mg/kg i.p. for mazindane and 3.9 mg/kg i.p. for mazindol. At 25 mg/kg mazindane displayed toxic effects and death while mazindol was effect/death free at 50 mg/kg. In Sprague-Dawley rats trained to discriminate cocaine from saline both compounds fully substituted for cocaine with mazindane being fourfold more potent in the total session (0.33 vs. 1.3 mg/kg i.p.) and first reinforcer (0.29 vs. 1.2 mg/kg i.p). Complete substitution was observed in rhesus monkeys trained to discriminate cocaine from saline with ED(50) values for mazindane (0.134 mg/kg i.m.) and mazindol (0.119 mg/kg i.m.). Mazindol exhibited little or no activity at 10(-5) M in inhibiting radioligand binding at 14 neurotransmitter sites while mazindane gave weak activity at the histamine H(1) and 5-hydroxytryptamine 5-HT(3) sites. These results demonstrate that mazindane could be a useful alternative to mazindol as a pharmacological tool because of its similar profile of activity and enhanced water solubility.

Three-dimensional quantitative structure-activity relationships of mazindol analogues at the dopamine transporter

A three-dimensional quantitative structure-activity relationship (3D-QSAR) study was performed on a series of mazindol analogues using the comparative molecular field analysis (CoMFA) method with their corresponding binding affinities for the displacement of [(3)H]WIN 35 428 from rat caudate putamen tissue. The cross-validated CoMFA models were derived from a training set of 50 compounds, and the predictive ability of the resulting CoMFA models was evaluated against a test set of 21 compounds. A set of alignment rules was derived to superimpose these compounds onto a template structure, mazindol (1). These CoMFA models yielded significant cross-validated r(2)(cv) values. Inclusion of additional descriptors did not improve the significance of the CoMFA models; thus, steric and electrostatic fields are the relevant descriptors for these compounds. The best QSAR model was selected on the basis of the predictive ability of the activity on the external test set of compounds. The analysis of coefficient contour maps provided further insight into the binding interactions of mazindol analogues with the DAT. The aromatic rings C and D are involved in hydrophobic interactions in which ring D may bind in a large hydrophobic groove. The relative orientation of these two rings is also important for high binding affinity to the DAT.

High-resolution phosphor imaging: validation for use with human brain tissue sections to determine the affinity and density of radioligand binding

This study investigated the suitability of high-resolution storage phosphor imaging for the quantitative analysis of radioligand binding to human brain tissue. Hence, the binding of [(3)H]mazindol to the dopamine transporter in caudate-putamen tissue homogenates or frozen tissue sections apposed to either autoradiographic film or phosphor imaging plates was measured. Estimates of binding affinity were similar for homogenate studies and phosphor imaging plates (Kd=6.44+/-0.14 and 6.91+/-0.47 nM, respectively), but higher values were obtained with film autoradiography (Kd=11.31+/-0.82 nM). The density of binding was similar for both autoradiographic techniques (Bmax=371.9+/-30.8 fmol/mg estimated tissue equivalent, ETE (imaging plate) and 425+/-13.77 fmol/mg ETE (film)), although lower values were obtained from tissue homogenates (Bmax=64.27+/-6.74 fmol/mg wet weight). These results suggest that high resolution phosphor imaging can be used to analyse radioligand binding parameters in human brain tissue. Moreover, the reduced exposure time of phosphor imaging plates (e.g. 7 days vs 5 weeks) allows results to be obtained more rapidly than with conventional film autoradiography.

Chronic high dose L-DOPA alone or in combination with the COMT inhibitor entacapone does not increase oxidative damage or impair the function of the nigro-striatal pathway in normal cynomologus monkeys

Parkinson's disease (PD) is characterised by a loss of pigmented dopaminergic neurones in the zona compacta of substantia nigra. The mechanisms underlying nigral cell death remain unknown but may involve oxidative damage. There has been concern that L-DOPA treatment may accelerate nigral pathology in PD through chemical and enzymatic oxidation to reactive oxygen species. In the present study, we examined tissues from normal macaque monkeys treated for 13 weeks with high doses of L-DOPA (in combination with the peripheral decarboxylase inhibitor, carbidopa) and/or the COMT inhibitor, entacapone. Plasma was analysed for changes in protein carbonyls as a marker of oxidative damage to protein. Cortical tissue was examined for changes in levels of protein carbonyls, lipid peroxidation and oxidative damage to DNA. The integrity of the nigro-striatal pathway was assessed by nigral tyrosine hydroxylase mRNA levels and specific [(3)H]mazindol binding to dopaminergic terminals in caudate-putamen. No alterations in plasma protein carbonyls were observed in any treatment group. An increase was found in the levels of protein carbonyls, lipid peroxidation and 5-OH uracil, but not other products of oxidative DNA damage, in cerebral cortex of monkeys treated with L-DOPA plus carbidopa or with L-DOPA plus carbidopa and entacapone but this was only statistically significant in the latter group. There was no change in nigral tyrosine hydroxylase mRNA levels or specific striatal [(3)H]mazindol binding in brain tissue from monkeys treated with either L-DOPA plus carbidopa or L-DOPA plus carbidopa and entacapone. The results show that in the normal monkeys L-DOPA does not provoke marked oxidative damage even at high doses, and that there is little or no potentiation of its effects by entacapone. Neither L-DOPA plus carbidopa nor L-DOPA plus carbidopa and entacapone led to obvious damage to the nigro-striatal pathway.

Decreased densities of dopamine and serotonin transporters and of vesicular monoamine transporter 2 in severely kainic acid lesioned subregions of the striatum

Fifteen days after a striatal kainic acid (KA) injection, we have examined presynaptic modifications of dopamine and serotonin terminals in the striatum through (i) autoradiographic labeling of dopamine, serotonin and vesicular monoamine transporters respectively with 3H-mazindol, 3H-citalopram and 3H-dihydrotetrabenazine, and (ii) determination of the contents in dopamine, serotonin and their metabolites. Acetylcholinesterase histochemical labeling enabled the definition of severely and moderately KA-lesioned subregions within the striatum. A significant decrease of the three transporters labeling density was observed only in the severely lesioned subregions. The strong decrease in serotonin transporter labeling revealed here has not been described until now. Besides, the striatal contents of homovanillic acid (dopamine metabolite) and 5-hydroxyindolacetic acid (serotonin metabolite) were significantly increased in the lesioned striatum. The whole data evidence an incomplete sparing of dopamine and serotonin terminals in the striatum 15 days after a KA injection, especially in the areas where the degeneration of postsynaptic neurons was the most extensive.

6-Hydroxydopamine-lesioning of the nigrostriatal pathway in rats alters basal ganglia mRNA for copper, zinc- and manganese-superoxide dismutase, but not glutathione peroxidase

The effects of nigrostriatal pathway destruction on the mRNA levels of copper, zinc-dependent superoxide dismutase (Cu,Zn-SOD), manganese-dependent superoxide dismutase (Mn-SOD), and glutathione peroxidase in basal ganglia of adult rat were investigated using in situ hybridization histochemistry and oligodeoxynucleotide (single-stranded complementary DNA) probes. The 6-hydroxydopamine (6-OHDA)-induced destruction of the nigrostriatal pathway resulted in contralateral rotation to apomorphine and a marked loss of specific [(3)H]mazindol binding in the striatum (93%; P<0.05) and of tyrosine hydroxylase mRNA in substantia nigra pars compacta (SC) (93%; P<0.05) compared with control rats. Levels of Cu,Zn-SOD mRNA were decreased in the striatum, globus pallidus, and SC on the lesioned side of 6-OHDA-lesioned rats compared with sham-lesioned rats (P<0.05). Levels of Mn-SOD mRNA were increased in the nucleus accumbens (P<0.05), but decreased in the SC (P<0.05) on the lesioned side of 6-OHDA-treated rats compared with sham-lesioned rats. Lesioning with 6-OHDA had no effect on glutathione peroxidase mRNA levels in any region of basal ganglia examined. The significant changes in Cu,Zn-SOD and Mn-SOD mRNA indicate that SOD is primarily expressed by dopaminergic neurons of the nigrostriatal pathway, and that the Mn-SOD gene appears to be inducible in rat basal ganglia in response to both physical and chemical damage 5 weeks after 6-OHDA-lesioning. These findings may clarify the status of antioxidant enzymes, particularly Mn-SOD, in patients with Parkinson's disease and their relevance to disease pathogenesis.

Pharmacophore-based discovery of 3,4-disubstituted pyrrolidines as a novel class of monoamine transporter inhibitors

3,4-Disubstituted pyrrolidines were discovered as a novel class of monoamine transporter inhibitors through 3-D database pharmacophore searching using a new pharmacophore model. The most potent analogue 12 has Ki values of 0.084 microM in [3H]mazindol binding, 0.20, 0.23, and 0.031 microM in inhibition of dopamine (DA), serotonin (SER), and norepinephrine (NE) reuptake, respectively. Functional antagonism testing in vitro showed that 11 and 12 are weak cocaine antagonists.

Differential sensitivity to NaCl for inhibitors and substrates that recognize mutually exclusive binding sites on the neuronal transporter of dopamine in rat striatal membranes

Addition of NaCl (90--290 mM) to a 10 mM Na(+) medium did not significantly modify B(max) and K(d) values for [3H]mazindol binding to the dopamine neuronal transporter (DAT) studied on rat striatal membranes at 20 degrees C. Addition of NaCl differentially affected the ability of other uptake inhibitors and substrates to block the [3H]mazindol binding. Ratios of 50% inhibiting concentrations calculated for 290 and 90 mM NaCl allowed to distinguish three groups of agents: substrates which were more potent in the presence of 290 mM NaCl (group 1; ratio < 1) and two groups of uptake inhibitors displaying ratio values either ranging around two (group 2: WIN 35,428, cocaine, methylphenidate, pyrovalerone) or close to unity (group 3: BTCP, mazindol, benztropine, nomifensine). However, agents from these three groups recognize mutually exclusive binding sites since in interaction studies the presence of WIN 35,428 (group 2) or mazindol (group 3) increased the 50% inhibiting concentrations of D-amphetamine (group 1) and WIN 35,428 on the [3H]mazindol binding to theoretical values expected for a competition of all of these compounds for the same binding domain on the DAT.

GDNF reverses priming for dyskinesia in MPTP-treated, L-DOPA-primed common marmosets

Parkinson's disease (PD) is associated with a progressive loss of dopamine neurons in the substantia nigra and degeneration of dopaminergic terminals in the striatum. Although L-DOPA treatment provides the most effective symptomatic relief for PD it does not prevent the progression of the disease, and its long-term use is associated with the onset of dyskinesia. In rodent and primate studies, glial cell line-derived neurotrophic factor (GDNF) may prevent 6-OHDA- or MPTP-induced nigral degeneration and so may be beneficial in the treatment of PD. In this study, we investigate the effects of GDNF on the expression of dyskinesia in L-DOPA-primed MPTP-treated common marmosets, exhibiting dyskinesia. GDNF or saline was administered by two intraventricular injections, 4 weeks apart, to MPTP-treated, L-DOPA-treated common marmosets primed to exhibit dyskinesia. Prior to GDNF or saline administration, all animals displayed marked dyskinesia when treated with L-DOPA. GDNF administration produced a significant improvement in motor disability and, following the second injection of GDNF, a significant improvement in the locomotor activity was observed. Following the administration of L-DOPA there was a greater reversal of disability and a reduction in the intensity of L-DOPA-induced dyskinesia in GDNF-treated animals compared to saline-treated controls. However, there was no significant difference in L-DOPA's ability to increase locomotor activity between GDNF-treated and saline-treated animals. GDNF treatment caused a significant increase in the number of tyrosine hydroxylase-positive neurons in the substantia nigra, but no change in [(3)H]mazindol binding to dopamine terminals was found in the striatum of GDNF-treated animals compared to saline-treated controls. In GDNF-treated animals a small but significant reduction in enkephalin mRNA was observed in the caudate nucleus but not in the putamen or the nucleus accumbens. Substance P mRNA expression was equally reduced in the caudate nucleus and the putamen of the GDNF-treated animals but not in the nucleus accumbens. Intraventricular administration of GDNF improved MPTP-induced disability and reversed dopamine cell loss in the substantia nigra. GDNF also diminished L-DOPA-induced dyskinesia, which may relate to its ability to partly restore nigral dopaminergic transmission or to modify the activity of striatal output pathways.

Biochemical and immunohistological changes in the brain of 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP)-treated mouse

We investigated neurochemically and neuropathologically the utility of 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP)-treated mice as a model of Parkinson's disease. The changes in dopamine D1 and D2 receptors and dopamine uptake sites were determined by quantitative autoradiography using [3H]SCH23390, [3H]raclopride and [3H]mazindol, respectively. Dopamine and 3,4-dihydroxyphenyl acetic acid (DOPAC) contents in the striatum were measured by high-performance liquid chromatography. The distribution of nigral neurons and reactive astrocytes was determined by immunohistochemical staining with antibody against tyrosine hydroxylase (TH) and glial fibrillary acidic protein (GFAP). The mice received four intraperitoneal injections of MPTP (10 mg/kg) at 1-h intervals and then the brains were analyzed at 3 and 7 days after the treatments. No significant change in dopamine D1 receptors was observed in the striatum and substantia nigra after acute treatment with MPTP. Dopamine D2 receptors were reduced significantly in the substantia nigra only 7 days after the MPTP treatment, whereas striatum showed no significant change in the binding throughout the experiments. In contrast, dopamine uptake sites were reduced markedly in the striatum and substantia nigra 3 and 7 days after the MPTP treatment. Dopamine and DOPAC content were also reduced in the striatum 3 and 7 days after the MPTP treatment. An immunohistochemical study indicated a loss of the number of TH-positive neurons in the substantia nigra 7 days after the MPTP treatment. In contrast, numerous GFAP-positive astrocytes were evident in the striatum 7 days after the MPTP treatment. These results provide valuable information for the pathogenesis of acute stage of Parkinson's disease.

Binding of uptake blockers to the neuronal dopamine transporter: further investigation about cationic and anionic requirements

Effects of ions on the binding of uptake blockers to the rat dopamine transporter (rDAT) labelled with [3H]WIN 35,428 [2beta-carbomethoxy-3beta-(4-fluorophenyl)-[3H] tropane] and [3H]mazindol were studied at 20 degrees C. [3H]WIN 35,428 binding increased with Na+ concentrations of up to 10-60 mM and decreased at higher concentrations. At pH 7.4, incubation media containing NaCl and/or Na2HPO4/NaH2PO4 were less stimulant than an NaHCO3/NaH2PO4 medium and they shifted maximal binding values to higher ionic concentrations. In an NaHCO3/NaH2PO4-buffered medium, Na+ concentrations >10 mM decreased the binding of 0.2 nM [3H]WIN 35,428, but an increase of the radioligand concentration shifted this decrease to the right. [3H]Mazindol binding was stimulated by Na+ concentrations < or =10 mM and was rather unaffected at higher concentrations. The inhibition of [3H]WIN 35,428 binding produced by 130 mM Na+ was independent of the nature of the anion; in contrast, isothionate and H2PO4-/HCO3 produced a more pronounced inhibition of the [3H]mazindol binding than Cl- and Br-, whereas I- tended to be a stimulant. Ca2+ and Mg2+ more potently inhibited the [3H]WIN 35,428 binding than K+. All these cations recognize a site which is not mutually exclusive with that of the radioligand since they induced the dissociation of the [3H]WIN 35,428-rDAT complex, an effect which was reduced (K+) or modified (Ca2+) when the Na+ concentration was increased. This site is likely to be the Na+ site by which low Na+ concentrations allosterically stimulate the uptake blocker binding. However, the intensity of the cation-induced dissociations was moderate and the main component of the binding inhibition that these cations produced results from the occupancy of a cation site, mutually exclusive with that of the radioligand. Thus, the WIN 35,428 binding inhibition produced by Ca2+, K+ and Na+ was competitive, and Na+ reduced the inhibitory potency of Ca2+ and K+. This reduction was more intense for Ca2+ and Mg2+ than for K+, suggesting that occupancy of the cation site by a divalent cation activated a strong negative allosteric interaction between this site and the Na+ site. Decrease in the Na+ concentration from 10 mM to 5 mM, or replacement of 5 mM HCO3-/H2PO4- by an equimolar concentration of isethionate or Cl- did not modify [3H]WIN 35,428 binding dissociation. Level(s) at which anions stimulate and inhibit the binding of uptake blockers remain uncertain and could be specific for each radioligand.

Chronic supranigral infusion of BDNF in normal and MPTP-treated common marmosets

BDNF or vehicle were administered by unilateral supranigral infusion in normal and chronically lesioned MPTP-treated common marmosets (Callithrix jacchus) for four weeks and locomotor activity, disability and response to apomorphine were assessed with nigral TH, GFAP and GAD immunoreactivity and striatal [3H]mazindol autoradiography. Selective contraversive orientation and ipsilateral neglect evolved in MPTP-treated marmosets receiving BDNF with no significant difference in disability or locomotor activity when compared to the vehicle-infused group. Apomorphine produced an ipsiversive rotational bias in BDNF-treated animals. In normal animals infused with BDNF contralateral neglect, ipsiversive turning, postural instability and ataxia rapidly evolved. In MPTP-treated marmosets BDNF caused increased ipsilateral striatal [3H]mazindol binding with increased somatic size and staining intensity in GAD-immunoreactive cells and a 10-20% loss of nigral TH-immunoreactive cells with increased GFAP staining. In normal common marmosets, both vehicle and BDNF infusion decreased nigral TH-immunoreactivity. Chronic supranigral infusion of BDNF alters motor behaviour and spatial attention in MPTP-treated marmosets which may reflect altered function in residual nigral dopaminergic neurons and brainstem GABAergic neurons and in normal animals produces behavioural and histological signs of nigrostriatal hypofunction.

An enantioselective synthesis and biobehavioral evaluation of 7-fluoro-3-(p-fluorophenyl)-2-propyltropanes

Optically pure 7-fluorotropanes 3a-c, were synthesized as structural probes of the dopamine transporter. The synthesis of these compounds was accomplished through the asymmetric 1,3-dipolar cycloaddition reaction of the oxidopyridinium betaine 4 with the chiral dipolarophile (R)-p-tolyl vinyl sulfoxide. In the preliminary analysis, tropane 3a was found to reduce the rewarding effects of cocaine in the brain stimulation reward paradigm.

Antiparkinsonian and neuroprotective effects of modafinil in the mptp-treated common marmoset

The psychostimulant drug, modafinil, protects rodents against 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) toxicity, striatal ischemia and partial transection of the nigro-striatal pathway. We now report on the ability of modafinil to reverse motor disability in MPTP-treated common marmosets and to prevent MPTP-induced nigral cell death in this species. In the initial experiments, adult common marmosets were treated with MPTP to produce stable motor deficits. The subsequent administration of modafinil (10, 30 or 100 mg/kg/day, p.o.) produced a dose-dependent reversal of motor disability. In a subsequent experiment, normal common marmosets were concurrently treated with 10, 30 or 100 mg/kg of modafinil once daily by gavage during acute MPTP administration (daily for 5 days), continuing for 2 weeks after the last dose of MPTP. Modafinil dose-dependently prevented the decline in motor activity normally produced by MPTP treatment. MPTP treatment caused a 76% loss of nigral tyrosine-hydroxylase-immunoreactive cells in placebo-treated animals, and this was dose-dependently prevented by modafinil. At the highest dose (100 mg/kg/day) of modafinil, there was no significant loss of tyrosine-hydroxylase-immunoreactive cells in the substantia nigra compared with normal animals. MPTP treatment also reduced striatal dopamine uptake sites by 95%, as measured by specific [3H]-mazindol binding, compared with normal controls. Modafinil treatment dose-dependently reduced the loss of specific [3H]-mazindol binding. Behavioural and morphological evidence in the present study indicate a potential antiparkinsonian and neuroprotective role for modafinil, which may form a new pharmacological approach to the treatment of Parkinson's disease.

Localization of dopaminergic markers in the human subthalamic nucleus

The potential role for dopamine in the subthalamic nucleus was investigated in human postmortem tissue sections by examining; (1) immunostaining for tyrosine hydroxylase, the rate-limiting enzyme in catecholamine synthesis; (2) binding of [(3)H]-SCH23390 (D1-like), [(3)H]-YM-09151-2 (D2-like), and [(3)H]-mazindol (dopamine uptake); and (3) expression of dopamine D1 and D2 receptor mRNAs. Immunostaining for tyrosine hydroxylase was visualized in Bouin's-fixed tissue by using a monoclonal antibody and the avidin-biotin-complex method. The cellular localization of the dopamine D1 and D2 receptor mRNAs was visualized by using a cocktail of human specific oligonucleotide probes radiolabeled with (35)S-dATP. Inspection of immunostained tissue revealed a fine network of tyrosine hydroxylase-immunostained fibers traversing the nucleus; no immunopositive cells were detected. Examination of emulsion-coated tissue sections processed for D1 and D2 receptor mRNA revealed, as expected, an abundance of D1 and D2 mRNA-positive cells in the caudate nucleus and putamen. However, no D1 or D2 receptor mRNA-expressing cells were detected in the subthalamic nucleus. Further, semiquantitative analysis of D1-like, D2-like and dopamine uptake ligand binding similarly revealed an enrichment of specific binding in the caudate nucleus and putamen but not within the subthalamic nucleus. However, a weak, albeit specific, signal for [(3)H]-SCH23390 and [(3)H]-mazindol was detected in the subthalamic nucleus, suggesting that the human subthalamic nucleus may receive a weak dopaminergic input. As weak D1-like binding is detected in the subthalamic nucleus, and subthalamic neurons do not express dopamine D1 or D2 receptor mRNAs, together these data suggest that the effects of dopaminergic agents on the activity of human subthalamic neurons may be indirect and mediated via interaction with dopamine D1-like receptors.

D2 autoreceptors are not involved in the down-regulation of the striatal dopamine transporter caused by alpha-methyl-p-tyrosine

The mechanisms by which the brain dopamine neuronal transporter is regulated by chronic alteration of dopamine transmission are not well understood. It has been shown previously that chronic inhibition of dopamine synthesis decreases dopamine transporter (DAT) density and function. The purpose of the present study was to determine whether these effects involve dopamine D2 receptors. Chronic treatment with alpha-methyl-p-tyrosine decreased binding of [3H]mazindol and dopamine release by d-amphetamine. The down-regulation of the DAT by alpha-methyl-p-tyrosine was not altered by co-treatment with a D2 receptor agonist or antagonist. However, chronic treatment with a D2 agonist, quinpirole, also decreased mazindol binding and amphetamine-induced release of dopamine. The results indicate that chronic inhibition of dopamine synthesis and stimulation of D2 receptors have similar, but independent, effects on DAT binding and function.

Autoradiographic study of striatal dopamine re-uptake sites and dopamine D1 and D2 receptors in a 6-hydroxydopamine and quinolinic acid double-lesion rat model of striatonigral degeneration (multiple system atrophy) and effects of embryonic ventral mesencephalic, striatal or co-grafts

The influence of embryonic mesencephalic, striatal and mesencephalic/striatal co-grafts on amphetamine- and apomorphine-induced rotation behaviour was assessed in a rat model of multiple system atrophy/striatonigral degeneration type using dopamine D1 ([3H]SCH23390) and D2 ([3H]spiperone) receptor and dopamine re-uptake ([3H]mazindol) autoradiography. Male Wistar rats subjected to a sequential unilateral 6-hydroxydopamine lesion of the medial forebrain bundle followed by a quinolinic acid lesion of the ipsilateral striatum were divided into four treatment groups, receiving either mesencephalic, striatal, mesencephalic/striatal co-grafts or sham grafts. Amphetamine- and apomorphine-induced rotation behaviour was recorded prior to and up to 10 weeks following transplantation. 6-Hydroxydopamine-lesioned animals showed ipsiversive amphetamine-induced and contraversive apomorphine-induced rotation behaviour. Amphetamine-induced rotation rates persisted after the subsequent quinolinic acid lesion, whereas rotation induced by apomorphine was decreased. In 11 of 14 animals receiving mesencephalic or mesencephalic/striatal co-grafts, amphetamine-induced rotation scores were decreased by >50% at the 10-week post-grafting time-point. In contrast, only one of 12 animals receiving non-mesencephalic (striatal or sham) grafts exhibited diminished rotation rates at this time-point. Apomorphine-induced rotation rates were significantly increased following transplantation of mesencephalic, striatal or sham grafts. The largest increase of apomorphine-induced rotation rates approaching post-6-hydroxydopamine levels were observed in animals with striatal grafts. In contrast, in the co-graft group, there was no significant increase of apomorphine-induced rotation compared to the post-quinolinic acid time-point. Morphometric analysis revealed a 63-74% reduction of striatal surface areas across the treatment groups. Striatal [3H]mazindol binding on the lesioned side (excluding the demarcated graft area) revealed a marked loss of dopamine re-uptake sites across all treatment groups, indicating missing graft-induced dopaminergic re-innervation of the host. In eight (73%) of the 11 animals with mesencephalic grafts and reduced amphetamine-induced circling, discrete areas of [3H]mazindol binding ("hot spots") were observed, indicating graft survival. Dopamine D1 and D2 receptor binding was preserved in the remaining lesioned striatum irrespective of treatment assignment, except for a significant reduction of D2 receptor binding in animals receiving mesencephalic grafts. "Hot spots" of dopamine D1 and D2 receptor binding were observed in 10 (83%) and nine (75%) of 12 animals receiving striatal grafts or co-grafts, consistent with survival of embryonic primordial striatum grafted into a severely denervated and lesioned striatum. Our study confirms that functional improvement may be obtained from embryonic neuronal grafts in a double-lesion rat model of multiple system atrophy/striatonigral degeneration type. Co-grafts appear to be required for reversal of both amphetamine- and apomorphine-induced rotation behaviour in this model. We propose that the partial reversal of amphetamine-induced rotation asymmetry in double-lesioned rats receiving mesencephalic or mesencephalic/striatal co-grafts reflects non-synaptic graft-derived dopamine release. The changes of apomorphine-induced rotation following transplantation are likely to reflect a complex interaction of graft- and host-derived striatal projection pathways and basal ganglia output nuclei. Further studies in a larger number of animals are required to determine whether morphological parameters and behavioural improvement in the neurotransplantation multiple system atrophy rat model correlate.

Effect of unilateral 6-hydroxydopamine lesions of the nigrostriatal pathway on GABA(A) receptor subunit gene expression in the rodent basal ganglia and thalamus

In Parkinson's disease, changes in GABAergic activity occurring downstream of the striatal dopamine loss are accompanied by reciprocal changes in GABA(A) receptor binding, the underlying molecular mechanisms for which are unknown. This study examined whether changes in expression of the genes encoding known GABA(A) receptor subunits (alpha(1-4), beta(1-3), gamma(1-3) and delta) could account for this receptor plasticity using a rodent model of Parkinson's disease with a 6-hydroxydopamine-induced nigrostriatal lesion. Analysis of autoradiograms of the basal ganglia and thalamus revealed changes in expression of only four of the 11 subunits studied. Expression of alpha1 and beta2 subunit genes was altered in a parallel manner following a 6-hydroxydopamine lesion; messenger RNA levels for both were significantly increased in the substantia nigra pars reticulata (11 +/- 4% and 17 +/- 1%, respectively), and significantly reduced in the globus pallidus (18 +/- 3% and 16 +/- 3%, respectively) and parafascicular nucleus (19 +/- 3% and 16 +/- 5%, respectively). Smaller changes in the messenger RNA levels encoding the alpha1 subunit in the lateral amygdala (8 +/- 1% decrease) and the alpha4 and gamma2 subunits in the striatum (10 +/- 2% and 6 +/- 1% increase, respectively) were also observed. No changes in expression were noted for any other subunits in any region studied. Clearly, both region- and subunit-specific regulation of GABA(A) receptor subunit gene expression occurs following a nigrostriatal tract lesion. The changes in expression of the alpha1 and beta2 subunit genes probably contribute to the documented changes in GABA(A) receptor binding following striatal dopamine depletion. Moreover, they provide a molecular basis by which the pathological changes in GABAergic activity in Parkinson's disease may be partially compensated.

Methamphetamine- and 1-methyl-4-phenyl- 1,2,3, 6-tetrahydropyridine-induced dopaminergic neurotoxicity in inducible nitric oxide synthase-deficient mice

Previous studies have suggested a role for the retrograde messenger, nitric oxide (NO), in methamphetamine (METH)- and 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP)- induced dopaminergic neurotoxicity. Since evidence supported the involvement of the neuronal nitric oxide synthase (nNOS) isoform in the dopaminergic neurotoxicity, the present study was undertaken to investigate whether the inducible nitric oxide synthase (iNOS) isoform is also associated with METH- and MPTP-induced neurotoxicity. The administration of METH (5mg/kg x 3) to iNOS deficient mice [homozygote iNOS(-/-)] and wild type mice (C57BL/6) resulted in significantly smaller depletion of striatal dopaminergic markers in the iNOS(-/-) mice compared with the wild-type mice. METH-induced hyperthermia was also significantly lower in the iNOS(-/-) mice than in wild-type mice. In contrast to the outcome of METH administration, MPTP injections (20 mg/kg x 3) resulted in a similar decrease in striatal dopaminergic markers in iNOS(-/-) and wild-type mice. In the set of behavioral experiments, METH-induced locomotor sensitization was investigated. The acute administration of METH (1.0 mg/kg) resulted in the same intensity of locomotor activity in iNOS(-/-) and wild-type mice. Moreover, 68 to 72 h after the exposure to the high-dose METH regimen (5 mg/kg x 3), a marked sensitized response to a challenge injection of METH (1.0 mg/kg) was observed in both the iNOS(-/-) and wild-type mice. The finding that iNOS(-/-) mice were unprotected from MPTP-induced neurotoxicity suggests that the partial protection against METH-induced neurotoxicity observed was primarily associated with the diminished hyperthermic effect of METH seen in the iNOS(-/-) mice. Moreover, in contrast to nNOS deficiency, iNOS deficiency did not affect METH-induced behavioral sensitization.

Long-term effects of pergolide and (-)-deprenyl on 3H-mazindol and 3H-spiperone binding in rat brain

The effects of long-term administration of the putative neuroprotective agents pergolide and (-)-deprenyl was assessed by studying 3H-mazindol and 3H-spiperone binding at 12 and 20 months in the major dopamine brain regions. Male Wistar rats were treated from 3 to 20 months, together with their respective untreated and saline injected control groups. The main findings were: 1) there was a decrease in both 3H-mazindol and 3H-spiperone binding with age between 12 and 20 months; 2) there were no differences at 20 months between the pergolide or the (-)-deprenyl treated groups and their controls, thus providing no evidence for long-term neuroprotection; and 3) there was a marked decrease in 3H-mazindol binding in the injected controls compared with the untreated controls at both 12 and 20 months. This raises the possibility that mild chronic stress may accelerate the aging of the dopamine system.

Recovery of dopamine neuronal transporter but lack of change of its mRNA in substantia nigra after inactivation by a new irreversible inhibitor characterized in vitro and ex vivo in the rat

1. In vitro, the ability of DEEP-NCS {1-[2-(diphenylmethoxy)ethyl]-4-[2-(4-isothiocyanatophenyl)ethyl]- piperazine} to inhibit [3H]-dopamine uptake by rat striatal synaptosomes was concentration-dependent and inversely related to the protein concentration. This inhibition was irreversible and resulted from changes in Vmax and KM. DEEP-NCS was less potent on noradrenaline, serotonin and choline transport. 2. One day after intrastriatal injections of DEEP-NCS (100 and 1000 pmol) in 20% dimethylsulphoxide, moderate decreases in the ex vivo dopamine uptake were observed in synaptosomes obtained from striatum injected with DEEP-NCS or solvent, and the contralateral uninjected striatum. 3. In similar conditions, 300 pmol DEEP-NCS in 45% 2 hydroxypropyl-gamma-cyclodextrin - 0.5% dimethylsulphoxide solution sub-totally reduced ex vivo dopamine uptake and mazindol binding, and moderately decreased choline and serotonin transport. These reductions were specific to DEEP-NCS-injected striata. A clomipramine pretreatment (16 mg kg-1 i.p. 1 h before) was performed in following experiments, since it reduced the DEEP-NCS-elicited decrease in serotonin uptake without affecting other indices. 4. One day after intrastriatal injection, DEEP-NCS elicited similar dose-dependent decreases in ex vivo dopamine uptake and mazindol binding (ID50=6.9-8 ng striatum-1). Changes in KM and Vmax for ex vivo dopamine transport produced by DEEP-NCS disappeared according to similar time-courses. 5. The t(1/2) for transporter recovery was 6. 1 days. This value should correspond to its actual turnover rate in vivo, since no change in transporter mRNA level was observed in substantia nigra ipsilateral to 300 pmol DEEP-NCS-injected striatum. 6. The results indicate that DEEP-NCS behaves as a potent, quite selective, irreversible inhibitor of the DAT, in vitro and in vivo. Its use in vivo suggests that the physiological half-life of the rat striatal DAT is close to 6 days.

Striatal preproenkephalin gene expression is upregulated in acute but not chronic parkinsonian monkeys: implications for the contribution of the indirect striatopallidal circuit to parkinsonian symptomatology

This study examined the extent of striatal dopamine (DA) denervation and coincident expression of preproenkephalin (PPE) mRNA in monkeys made parkinsonian by 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) administration. Some animals (n = 4) became moderately parkinsonian after receiving large doses of MPTP over short periods of time and were symptomatic for only a short period of time (1-3 months; acute parkinsonian group). Other animals became moderately parkinsonian after receiving either escalating doses of MPTP over long periods (4-6 months; n = 5) or a high dose of MPTP over a short period (<1 month; n = 1) and remained symptomatic for an extended period (>8 months; chronic parkinsonian group). Despite similar symptomatology and similar degrees of striatal DA denervation at the time of their deaths, only acute parkinsonian animals had significantly increased PPE expression in sensorimotor striatal regions. PPE expression in chronic parkinsonian animals was either not changed or significantly decreased in most striatal regions. These findings suggest that the duration and not the extent of striatal DA denervation is a critical factor in modulating changes in striatal PPE expression. Furthermore, these results question the role of increased activity in the enkephalin-containing indirect striatopallidal pathway in the expression of parkinsonian symptoms.

Synthesis of 8-Oxa analogues of norcocaine endowed with interesting cocaine-like activity

In order to further explore the importance of cocaine's bridge nitrogen atom in binding to the dopamine transporter (DAT), we have synthesized the previously known racemic 8-oxa-norcocaines 3-6 in which the nitrogen atom has been replaced by oxygen. Additionally, to avoid incorrect interpretations of biological data that may stem from the use of racemic materials, several of these analogues were synthesized and tested in non-racemic form. (-)-8-Oxa-norcocaine (3) was found to bind to the cocaine recognition site and to inhibit the dopamine transporter with potencies only about 8-fold and 4-fold, respectively, less than those of norcocaine (2). (-)-8-Oxa-pseudonorcocaine (4) as well as (+)-8-oxa-norcocaine (3) were found to be comparable in activity to (-)-oxa-norcocaine. These pharmacological findings support our earlier suggestion that cocaine is likely to bind in its neutral form to the DAT.

Increases in [3H]FK-506 and [3H]L-N(G)-nitro-arginine binding in the rat brain after nigrostriatal dopaminergic denervation

Receptor autoradiographic technique was studied to investigate sequential changes in FK-506 binding proteins, nitric oxide synthase and dopamine uptake sites in the brain 1 week to 8 weeks after unilateral 6-hydroxydopamine injection of the medial forebrain bundle in rats. [3H]FK-506, [3H]L-N(G)-nitro-arginine and [3H]mazindol were used to label FK-506 binding proteins (immunophilin), nitric oxide synthase and dopamine uptake sites, respectively. [3H]FK-506 binding showed about 13-25% increase in the ipsilateral striatum from 2 to 8 weeks after degeneration of nigrostriatal pathway. However, no significant change in [3H]FK-506 binding was observed in the ipsilateral substantia nigra during the postlesion periods. In the contralateral side, [3H]FK-506 binding also showed about 13-25% increase in the striatum from 2 to 8 weeks postlesion. The substantia nigra showed a 21% increase in [3H]FK-506 binding only 2 weeks after the lesioning. On the other hand, [3H]L-N(G)-nitro-arginine binding showed about 21-31% increase in the parietal cortex and striatum 1 week or 2 weeks postlesion. In the contralateral side, a 21% increase in [3H]L-N(G)-nitro-arginine binding was found in the dorsolateral striatum only 1 week postlesion. In contrast, degeneration of nigrostriatal pathway caused a conspicuous loss of [3H]mazindol binding in the ipsilateral striatum (87-96%), substantia nigra (36-73%) and ventral tegmental area (91-100%) during the postlesion periods. In the contralateral side, no significant changes in [3H]mazindol binding were observed in these areas up to 8 weeks after the postlesion. The present study demonstrates that unilateral injection of 6-hydroxydopamine into the medial forebrain bundle of rats can cause a significant increase in [3H]FK-506 and [3H]L-N(G)-nitro-arginine bindings in the brains. In contrast, a marked reduction in [3H]mazindol binding is observed in the brains after the lesioning, indicating severe damage to nigrostriatal dopaminergic pathway. These results suggest that immunophilin and nitric oxide synthase may play some role in the pathogenesis of neurodegenerative disorders such as Parkinson's disease.

Effect of repeated L-DOPA, bromocriptine, or lisuride administration on preproenkephalin-A and preproenkephalin-B mRNA levels in the striatum of the 6-hydroxydopamine-lesioned rat

Abnormal involuntary movements, or dyskinesias, plague current symptomatic approaches to the treatment of Parkinson's disease. The neural mechanisms underlying the generation of dyskinesia following repeated l-3,4-dihydroxyphenylalanine (L-DOPA) or dopamine agonist administration in Parkinson's disease remain unknown. However, de novo administration of bromocriptine or lisuride to either l-methyl-4-phenyl-1,2,3,6-tetrahydropyridine-lesioned primates or patients can alleviate parkinsonian symptoms without the development of dyskinesia. In this study, we have investigated behavioral responses and alterations in the expression of opioid neuropeptide precursors preproenkephalin-A (PPE-A, encoding methionine- and leucine-enkephalin) and preproenkephalin-B (PPE-B), the precursor encoding dynorphins (dynorphin A1-17 and B1-13, leucine-enkephalin, and alpha-neoendorphin) in striatal output pathways of the 6-hydroxydopamine (6-OHDA)-lesioned rat model of Parkinson's disease. Expression was assessed following repeated L-DOPA, bromocriptine, or lisuride administration. Given the functional organization of basal ganglia circuitry into anatomically discrete parallel circuits, we investigated alterations in peptide expression with reference to the detailed topography of the striatum. Following repeated L-DOPA administration (6.5 mg/kg, b.d., 21 days) in the 6-OHDA-lesioned rat a rotational response was observed. This became markedly enhanced with repeated treatment. We have previously characterized the pharmacology of this enhanced response and have suggested that it is a useful model for the elucidation of the cellular and molecular mechanisms underlying L-DOPA- and dopamine agonist-induced dyskinesia. In contrast to l-DOPA, de novo administration of bromocriptine (1 or 5 mg/kg, b.d., 21 days) or lisuride (0.01 or 0.1 mg/kg, b.d., 21 days) did not lead to an enhanced behavioral response. In vehicle-treated, 6-OHDA-lesioned animals, PPE-A expression was elevated rostrally and dorsally, while PPE-B expression was reduced in the striatum at all rostrocaudal levels. Repeated l-DOPA administration was accompanied by elevations in striatal PPE-B mRNA levels and a further elevation, above lesion-induced levels, in PPE-A expression. This further elevation was restricted to the dorsolateral striatum. However, following repeated bromocriptine or lisuride administration no increase in PPE-B expression was observed and the lesion-induced increase in PPE-A expression was normalized to prelesion levels. Increased PPE-A and PPE-B levels may, through decreasing GABA and glutamate release, respectively, in output nuclei of the basal ganglia, play a role in the development of L-DOPA- and dopamine-agonist induced dyskinesia in Parkinson's disease. These studies suggest that anti-parkinsonian treatments which are not associated with an elevation in PPE-B and/or normalize elevated PPE-A precursor expression, such as NMDA-receptor antagonists or long-acting dopamine D2 receptor agonists, e.g., cabergoline or ropinirole, may reduce dyskinesia in Parkinson's disease.

Alteration of neurotensin receptors in MPTP-treated mice

We examined the sequential changes in neurotensin receptors in the striatum and substantia nigra of mouse brains lesioned with 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) by receptor autoradiography, in comparison with the alterations in dopamine uptake sites. The mice received four intraperitoneal injections of MPTP (10 mg/kg) at 1-h intervals and then the brains were analyzed at 6 h and 1, 3, 7, and 21 days after the treatments. [3H]Neurotensin and [3H]mazindol were used to label neurotensin receptors and dopamine uptake sites, respectively. [3H]Neurotensin binding was significantly decreased in the striatum from 6 h to 21 days after MPTP treatment. In the substantia nigra, pars reticulata also showed a significant decrease in [3H]neurotensin binding from 3 to 21 days post-MPTP treatment. However, no significant change in [3H]neurotensin binding was observed in the pars compacta even after 21 days. On the other hand, [3H]mazindol binding was markedly decreased in the striatum and substantia nigra from 6 h to 21 days after MPTP treatment. These results indicate that neurotoxin MPTP can produce a severe decrease in neurotensin receptors and dopamine uptake sites in the striatum and substantia nigra of mice. Thus, our findings provide evidence that the dysfunction in neurotensin receptors may be involved in the degenerative processes causing Parkinson's disease.

Long-term changes in brain following continuous phencyclidine administration: an autoradiographic study using flunitrazepam, ketanserin, mazindol, quinuclidinyl benzilate, piperidyl-3,4-3H(N)-TCP, and AMPA receptor ligands

Phencyclidine induces a model psychosis which can persist for prolonged periods and presents a strong drug model of schizophrenia. When given continuously for several days to rats, phencyclidine and other N-methyl-D-aspartate (NMDA) antagonists induce neural degeneration in a variety of limbic structures, including retrosplenial cortex, hippocampus, septohippocampal projections, and piriform cortex. In an attempt to further clarify the mechanisms underlying these degeneration patterns, autoradiographic studies using a variety of receptor ligands were conducted in animals 21 days after an identical dosage of the continuous phencyclidine administration employed in the previous degeneration studies. The results indicated enduring alterations in a number of receptors: these included decreased piperidyl-3,4-3H(N)-TCP (TCP), flunitrazepam, and mazindol binding in many of the limbic regions in which degeneration has been reported previously. Quinuclidinyl benzilate and (AMPA) binding were decreased in anterior cingulate and piriform cortex, and in accumbens and striatum. Piperidyl-3,4-3H(N)-TCP binding was decreased in most hippocampal regions. Many of these long-term alterations would not have been predicted by prior studies of the neurotoxic effects of continuous phencyclidine, and these results do not suggest a unitary source for the neurotoxicity. Whereas retrosplenial cortex, the structure which degenerates earliest, showed minimal alterations, some of the most consistent, long term alterations were in structures which evidence no immediate signs of neural degeneration, such as anterior cingulate cortex and caudate nucleus. In these structures, some of the receptor changes appeared to develop gradually (they were not present immediately after cessation of drug administration), and thus were perhaps due to changed input from regions evidencing neurotoxicity. Some of these findings, particularly in anterior cingulate, may have implications for models of schizophrenia.

There is a limited critical period for dopamine's effects on D1 receptor expression in the developing rat neostriatum

Neonatal lesions of the dopamine (DA) system have different behavioral and neurochemical effects than lesions made in adulthood. Previous data from this laboratory have indicated that in the early postnatal period, lesions to the DA system induced by instrastriatal 6-hydroxydopamine (6-OHDA) result in a rapid and permanent loss of striatal D1 binding sites, but D2 receptor binding is unaffected. The length of the postnatal period within which neonatal instrastriatal 6-OHDA administration is effective in modulating D1 receptor binding is not known. To determine when D1 and D2 receptors are vulnerable to lesions of the DA system, we administered 6-OHDA intrastriatally to damage the DA innervation at different ages in the early postnatal period, at day of birth/postnatal day 1 (P0/1), P7 or P15 and examined DA receptor binding at P90 with quantitative autoradiography. Using [3H]mazindol binding to DA transporters (DAT) to verify the extent of the lesion, we then quantified the number of D1 binding sites using [3H]SCH23390 and D2 sites with [3H]spiroperidol. There were significant reductions in DAT sites at P0/1 (78 to 88%) and P7 (67 to 81%) but less significant changes at P15 (34 to 50% losses). The lesions were most effective for the dorsal caudate-putamen than more ventrally or in the nucleus accumbens. Our results demonstrate a significant reduction in D1 sites in all regions of the neostriatum following lesions at P0/1. The dorsal caudate-putamen was affected the most (51% loss, and the nucleus accumbens (41%) and ventral caudate-putamen less so (31%). No significant changes in D1 receptors were found at P7 or P15 and D2 receptors were unaffected with lesions in any of the age groups. The results indicate that there is a critical period for affecting expression of D1 receptors and this effect may, in addition, be related to the pattern of DA loss. Additionally, regulation of D2 receptors by this degree of loss of DA innervation does not occur during the first two weeks postnatally.

Sequential changes of dopaminergic receptors in the rat brain after 6-hydroxydopamine lesions of the medial forebrain bundle

We investigated the sequential patterns of changes in dopamine uptake sites, D1 and D2 receptors in the brain of animals lesioned with 6-hydroxydopamine using quantitative receptor autoradiography. The rats were unilaterally lesioned in the medial forebrain bundle and the brains were analyzed at 1, 2, 4 and 8 weeks postlesion. Degeneration of the nigrostriatal pathway caused a significant loss of dopamine uptake sites in the ipsilateral striatum, substantia nigra (SN) and ventral tegmental area (VTA) in the lesioned animals. Dopamine D1 receptors were significantly increased in the ventromedial part of striatum of the ipsilateral side from 2 to 4 weeks postlesion. In the ipsilateral SN, a transient increase in dopamine D1 receptors was observed only 1 week after lesioning. However, the frontal cortex, parietal cortex and dorsolateral part of the striatum showed no significant change in dopamine D1 receptors throughout the experiments. On the other hand, dopamine D2 receptors were decreased increased in the ipsilateral SN and VTA from 1 week to 8 weeks postlesion. In the ipsilateral striatum, dopamine D2 receptors were increased in the dorsolateral part from 2 weeks to 8 weeks and in the ventromedial part from 2 weeks to 4 weeks. However, the frontal cortex and parietal cortex showed no significant change in dopamine D2 receptors during postlesion. In the contralateral side, most of regions examined showed no significant change in dopamine uptake sites, dopamine D1 receptors and dopamine D2 receptors during postlesion except for a transient change in a few regions. These results demonstrate that 6-hydroxydopamine can cause a severe functional damage in dopamine uptake sites in the striatum, SN and VTA. Our findings also suggest that the up-regulation in dopamine D2 receptors is more pronounced than that in dopamine D1 receptors in the brain after 6-hydroxydopamine treatment. Furthermore, our results support the existence of dopamine D2 receptors on the neurons of SN and VTA. Thus, our findings provide insights into the pathogenesis of Parkinson's disease.

Effects of GM1 ganglioside treatment on dopamine innervation of the striatum of MPTP-treated mice

GM1 ganglioside has been shown to stimulate repair of the nigrostriatal dopamine system after injury. This has been particularly evident in the mouse MPTP model of Parkinsonism. Systemic administration of GM1 has been shown to increase striatal dopamine levels and lead to increased density of substantia nigra pars compacta neurons after MPTP administration versus mice treated with MPTP and saline. The purpose of the present study was to assess regional changes in dopaminergic innervation of the striatum of mice treated with MPTP then GM1. Studies consisted of [3H] mazindol binding of dopamine uptake sites, postmortem striatal tissue dopamine levels, and peak dopamine release in response to KCl stimulation measured in vivo. Results showed that measures of dopamine innervation were significantly increased in most striatal areas in MPTP+GM1-treated mice compared to MPTP+saline-treated controls. The results indicate that GM1 treatment increases measures of dopaminergic innervation after an MPTP lesion, possibly through sprouting of new terminals or increased dopamine production and release from remaining terminals.